U.S. patent application number 13/651078 was filed with the patent office on 2013-08-29 for solar biofactory, photobioreactors, passive thermal regulation systems and methods for producing products.
This patent application is currently assigned to JOULE UNLIMITED TECHNOLOGIES, INC.. The applicant listed for this patent is Joule Unlimited Technologies, Inc.. Invention is credited to Stuart A. Jacobson, James R. McIntire, Scott A. Michonski, Frederick Morgan, Rainer Ponzel, Andrew H. Posner, Johan van Walsem.
Application Number | 20130224853 13/651078 |
Document ID | / |
Family ID | 42153977 |
Filed Date | 2013-08-29 |
United States Patent
Application |
20130224853 |
Kind Code |
A1 |
van Walsem; Johan ; et
al. |
August 29, 2013 |
Solar Biofactory, Photobioreactors, Passive Thermal Regulation
Systems And Methods for Producing Products
Abstract
The invention described herein relates to photobioreactors,
methods, assembly and use of such apparatus for culturing
light-capturing organisms in a cost-effective manner. Various
embodiments provide for a passive thermal regulation system
employing selected microorganisms in a photobioreactor apparatus
and methods for biological production of various fuel and chemical
products from these organisms. Additional embodiments provide a
solar biofactory system capable of culturing light capturing
organisms to an areal productivity of 3.3 g/m2/hr. Further
embodiments are directed to a photobioreactor capable of culturing
light capturing organisms to an OD.sub.730 of about 14 g/L DCW.
Such embodiments incorporate passive thermal regulation and
systems.
Inventors: |
van Walsem; Johan; (Acton,
MA) ; Morgan; Frederick; (Canton, MA) ;
Jacobson; Stuart A.; (Lexington, MA) ; Ponzel;
Rainer; (Hoevelhof, DE) ; McIntire; James R.;
(Castro Valley, CA) ; Michonski; Scott A.;
(Cambridge, MA) ; Posner; Andrew H.; (Cambridge,
MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Joule Unlimited Technologies, Inc.; |
|
|
US |
|
|
Assignee: |
JOULE UNLIMITED TECHNOLOGIES,
INC.
Bedford
MA
|
Family ID: |
42153977 |
Appl. No.: |
13/651078 |
Filed: |
October 12, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13061116 |
Feb 25, 2011 |
8304209 |
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PCT/US2009/006516 |
Dec 11, 2009 |
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13651078 |
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61216949 |
May 21, 2009 |
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61201548 |
Dec 11, 2008 |
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Current U.S.
Class: |
435/292.1 |
Current CPC
Class: |
Y02E 50/13 20130101;
C12N 1/12 20130101; Y02E 50/10 20130101; C12N 13/00 20130101; C12M
23/04 20130101; Y02E 50/17 20130101; C12P 5/02 20130101; C12P 7/02
20130101; C12M 41/20 20130101; C12M 21/02 20130101; C12N 1/20
20130101; C12P 7/065 20130101; C12P 7/40 20130101; C12M 21/12
20130101; C12P 7/16 20130101; C12P 7/649 20130101 |
Class at
Publication: |
435/292.1 |
International
Class: |
C12M 1/00 20060101
C12M001/00 |
Claims
1. A photobioreactor assembly comprising: a reactor structure; a
greenhouse structure configured to provide a greenhouse environment
for the reactor structure, the reactor structure and the greenhouse
structure spaced relative to each other to provide temperature
control of the photobioreactor; wherein the reactor structure
comprises a closed reactor and the greenhouse structure comprises
at least two side sheets spaced apart with the reactor disposed
therebetween.
2.-5. (canceled)
6. The photobioreactor assembly of claim 1, wherein at least a part
of a surface of the reactor is at least translucent.
7. The photobioreactor assembly of claim 1, wherein the sheets
diffuse light to illuminate the reactor.
8. The photobioreactor assembly of claim 1, wherein at least one
sheet includes a radiation shielding material.
9. The photobioreactor assembly of claim 1, wherein temperature
control is maintained within 10.degree. C. of ambient.
10. The photobioreactor assembly of claim 1, wherein temperature
control is maintained within 5.degree. C. of ambient.
11. The photobioreactor assembly of claim 1, further comprising
chimney means for allowing use of ambient air for temperature
control.
12. In a photobioreactor, the improvement of providing chimney
means for employing ambient air to provide temperature control of
the photobioreactor.
13.-45. (canceled)
46. The photobioreactor assembly of claim 1, wherein the reactor
structure is thermoformed.
Description
RELATED APPLICATION
[0001] This application is a continuation of U.S. application Ser.
No. 13/061,116, which is the U.S. National Stage of International
Application No. PCT/US2009/006516, filed Dec. 11, 2009, which
designates the U.S., published in English, and claims the benefit
of U.S. Provisional Application No. 61/201,548, filed on Dec. 11,
2008 and U.S. Provisional Application No. 61/216,949 filed on May
21, 2009. The entire teachings of the above applications are
incorporated herein by reference.
FIELD OF INVENTION
[0002] The disclosure herein generally relates to solar
biofactories, photobioreactor apparatus, photobioreactors, systems
and methods for culturing light capturing organisms using the same
for the biological production of carbon-based products of
interest.
BACKGROUND
[0003] Burning of fossil fuels is thought to have resulted in
elevated atmospheric carbon dioxide (CO.sub.2) concentrations. The
levels of carbon dioxide are expected to double in as little as 60
years based on changes in land use and continued burning of fossil
fuels. The increase in carbon dioxide concentrations as well as
other greenhouse gases is thought to keep heat within the
atmosphere, leading to higher global temperatures.
Sequestration--the long term capture and storage of carbon
dioxide--has been long thought of as a way to mitigate this
problem. Given however, that light and carbon dioxide make up most
of what is consumed, direct conversion of ambient carbon dioxide to
valuable products, such as fuels, chemicals, drugs, and their
precursors, represents an alternative and improved means to reduce
the effects of carbon dioxide while maintaining the core industrial
and commercial products our modern society demands.
[0004] Plants and other light capturing organisms are the main
method by which carbon dioxide is removed from the atmosphere.
Through photosynthesis, organisms use solar energy while capturing
carbon dioxide, important metabolic precursors can be made that can
be converted to biomass in amounts exceeding 90% (Sheehan John,
Dunahay Terri, Benemann John R., Roessler Paul, "A Look Back at the
U.S. Department of Energy's Aquatic Species Program: Biodiesel from
Algae," 1998, NERL/TP-580-24190). Previous approaches have sought
to increase production of algal biomass and potentially use that
biomass as a fuel. (Reed T. B. and Gaur S. "A Survey of Biomass
Gasification" NREL, 2001). It has been additionally demonstrated
that addition of a small subset of genes can enable light capturing
organisms to produce ethanol. Specifically, the expression of
alcohol dehydrogenase II and pyruvate decarboxylase from Z. mobilis
in a Cyanobacterium has been achieved resulting in low levels of
ethanol production (U.S. Pat. No. 6,699,696). Nonetheless, the
ability to produce algae as well as to produce products from light
capturing organisms has been well below the efficiency needed to
have a commercially viable and therefore meaningful impact on
ambient or waste carbon dioxide (U.S. Pat. No. 6,699,696; Sheehan
John, Dunahay Terri, Benemann John R., Roessler Paul, "A Look Back
at the U.S. Department of Energy's Aquatic Species Program:
Biodiesel from Algae," 1998, NERL/TP-580-24190)
[0005] One of the primary limitations of using algae as a method of
carbon dioxide sequestration or conversion to products has been the
development of efficient and cost-effective growth systems. Aquatic
organisms, such as algae, oysters, and lobsters, have been
primarily cultured in open systems. This approach allows for the
organisms to take advantage of the semi-natural environment while
keeping operational expenditures potentially lower. Open algal
ponds up to 4 km.sup.2 have been researched, which, while requiring
low capital expenditures, ultimately have low productivity as these
systems are also subject to a number of problems. Intrinsic to
being an open system, the cultured organisms are exposed to a
number of exogenous organisms which may be symbiotic, competitive,
or pathogenic. Symbiotic organisms can change the culture organisms
merely by exposing them to a different set of conditions.
Opportunistic species may compete with the desired organism for
space, nutrients, etc. Additionally, pathogenic invaders may feed
on or kill the desired organism. In addition to these complicating
factors, open systems are difficult to insulate from environmental
changes including temperature, turbidity, pH, salinity, and
exposure to the sun. These difficulties point to the need to
develop a closed, controllable system for the growth of algae and
similar organisms.
[0006] Not surprisingly, a number of closed photobioreactors have
been developed. Typically, these are cylindrical or tubular (i.e.,
U.S. Pat. No. 5,958,761, US Patent application No. 2007/0048859).
These bioreactors often require mixing devices, increasing cost,
and are prone to accumulating oxygen (O.sub.2), which inhibits
algal growth.
[0007] As discussed in WO 2007/011343, many conventional
photobioreactors comprise cylindrical algal photobioreactors that
can be categorized as either "bubble columns" or "air lift
reactors." Vertical photobioreactors, which operate as "bubble
columns" are large diameter columns with algal suspensions wherein
gas is bubbled in from the bottom. Using bubbling as a means of
mixing in large-diameter columns is thought to be inefficient,
providing for lower net productivity as certain elements of the
culture remain photo-poor and as large bubbles of gas do not
deliver necessary precursors. An alternative vertical reactor is
the air-lift bioreactor, where two concentric tubular containers
are used with air bubbled in the bottom of the inner tube, which is
opaque. The pressure causes upward flow in the inner tube and
downward in the outer portion, which is of translucent make. These
reactors have better mass transfer coefficients and algal
productivity than other reactors, though controlling the flow
remains a difficulty. Efficient mixing and gas distribution are key
issues in developing closed bioreactors and to date, such efficient
bioreactors do not exist.
[0008] Tubular bioreactors, when oriented horizontally, typically
require additional energy to provide mixing (e.g., pumps), thus
adding significant capital and operational expense. In this
orientation, the O.sub.2 produced by photosynthesis can readily
become trapped in the system, thus causing a significant reduction
in algal proliferation. Other known photobioreactors are oriented
vertically and agitated pneumatically. Many such photobioreactors
operate as "bubble columns"
[0009] All closed bioreactors also require light, either from the
sun or artificially derived (U.S. Pat. No. 6,083,740). Solar
penetration is typically enabled through translucent tubing, which,
with thinner diameter, enables more thorough saturation of the
algae. Some known photobioreactor designs rely on artificial
lighting, e.g. fluorescent lamps, (such as described by Kodo et al.
in U.S. Pat. No. 6,083,740), and can otherwise be provided by any
light source existing today. Photobioreactors that do not utilize
solar energy but instead rely solely on artificial light sources
can require enormous energy input, increasing cost, and rendering
these systems, as stand-alone approaches, impractical. Using
natural solar light requires a low cost means to allow for proper
penetration of the culture while maintaining the culture at a
temperature that is appropriate.
[0010] In addition, because of geometric design constraints, during
large-scale, outdoor algal production, both types of cylindrical
photobioreactors can suffer from low productivity, due to factors
related to light reflection and auto-shading effects (in which one
column is shading the other). Shading issues make for
inefficiencies on vertical bioreactor design, leading to low land
use.
[0011] Several flat-plate photobioreactor designs have been
disclosed for culturing microalgae: Samson R & Leduy A (1985)
Multistage continuous cultivation of blue-green alga Spirulina
maxima in the flat tank photobioreactors with recycle. Can. J.
Chem. Eng. 63: 105-112; Ramos de Ortega and Roux J. C. (1986)
Production of Chiorella biomass in different types of flat
bioreactors in temperate zones. Biomass 10: 141-156; Tredici M. R.
and Materassi R. (1992) From open ponds to vertical alveolar
panels: the Italian experience in the development of reactors for
the mass cultivation of photoautotrophic microorganisms. J. Appl.
Phycol. 4: 221-31. Tredici M. R., Carlozzi P., Zittelli G. C. and
Materassi R. (1991) A vertical alveolar panel (VAP) for outdoor
mass cultivation of microalgae and Cyanobacteria. Bioresource
Technol. 38: 153-159; Hu Q. and Richmond A. (1996) Productivity and
photosynthetic efficiency of Spirulina platensis as affected by
light intensity, algal density and rate of mixing in a flat plate
photobioreactor. J. Appl. Phycol. 8: 139-145; Hu Q, Yair Z. and
Richmond A. (1998) Combined effects of light intensity, light-path
and culture density on output rate of Spirulina platensis
(Cyanobacteria). European Journal of Phycology 33: 165-171; Flu et
al. WO 2007/098150, however, to date, no design or system has been
successfully scaled up for efficient growth of organisms in
commercial scale.
[0012] Many different photobioreactor configurations have been
described in the literature including flat panels, bubble columns,
tubular reactors and a variety of annular designs aimed at
improving the surface area to volume ratio to maximize conversion
of sunlight and CO.sub.2 to biomass or other products such as algal
oil. These reactors have distinct advantages compared to open
raceway with respect to controlling temperature, pH, nutrient and
limiting contamination (see Pulz, O. "Photobioreactors: Production
systems for phototrophic microorganisms", Appl. Microbiol
Biotechnol (2001) 57:287-293). Key limitations to their adoption
have been the cost vs. benefit as it relates to the product being
produced. Whereas valuable products such as carotenoids have been
produced in photobioreactors the production of biomass for fuels
could not be economically justified to date.
[0013] The art as it relates to enclosed photobioreactors achieve
temperature control in a variety of ways including external and
internal heat exchangers, spraying of cooling water directly on the
surface, use of cooled or heater sparge gas as well as submerging
the reactor directly in large pond of water that is separately
temperature controlled (see Molina Grima, E. et al
"Photobioreactors: light regime, mass transfer, and scale-up", J.
of Biotechnology (1999) 70:231-247; Hu, Q. et al "A flat inclined
photobioreactor for outdoor mass cultivation of photoautotrophs"
Biotechnology and Bioengineering (1996) 51:51-60 and Hu, Q. WO
2007/098150 A2 "Photobioreactor and uses therefor"). Currently, a
cost-effective thermal regulation system that can be implemented in
large scale does not exist.
[0014] What is needed, therefore, is an integrated photobioreactor
system that is scalable, low cost, and efficient for culturing
light-capturing organisms.
SUMMARY
[0015] In various embodiments, a solar biofactory is described
which can comprise photobioreactors that enable sufficient
productivity for organisms growing within to have commercial
viability. Disclosed are apparatuses, method of using the
apparatuses, methods for growing light capturing organisms with the
apparatuses and systems for growing light capturing organisms using
light, water and carbon dioxide. Such photobioreactor apparatus,
systems and methods are optimized for light capture while remaining
low in cost, scalable, and achieve efficient growth of organisms.
The methods also provide for employing and operating a solar
biofactory, light capturing organisms suitable for culturing in a
photobioreactor apparatus and methods for culturing the organisms.
In various embodiments, such organisms grown in the photobioreactor
apparatus of the solar biofactory are used in the production of
biomass and chemical intermediates as well as biologically produced
end products such as fuels, chemicals and pharmaceutical
agents.
[0016] Furthermore, the photobioreactor can be adapted to maximize
production of various desired end products in a defined area while
minimizing land use. Accordingly, in additional embodiments, the
invention provides a photobioreactor capable of culturing light
capturing organism to an areal productivity of at least about 3.3
g/m.sup.2/hr. In further embodiments, the invention provides a
photobioreactor capable of producing 0.45 g/m.sup.2/hr of EtOH or
various other fuels and chemicals. In more preferred embodiments,
the invention provides a photobioreactor capable of producing
various fuels and chemicals at a desired areal productivity that
minimizes land use and maximizes product output for commercial
scale, e.g., 20 g/m.sup.2/day or 1-1.5 g/m.sup.2/hr.
[0017] To address the need for thermal regulation, what is provided
are systems, methods and photobioreactor, photobioreactor
assemblies and apparatus designed to passively regulate heat
accumulation and dissipation in an economical and efficient manner.
In various aspects, provided herein is a photobioreactor
comprising: a reactor, wherein at least part of a surface of the
reactor is at least translucent; and a passive thermal regulation
system adapted to comprise a means to at least reduce requirements
of at least one of cooling, heating or a combination thereof for
the photobioreactor. In various embodiments, the passive thermal
regulation system regulates the temperature of the photobioreactor
between about 52 to about 65.degree. C. (preferably between 56 and
60.degree. C.) for a thermophile and about 37.degree. C. for a
mesophile.
[0018] Additional embodiments provide passive thermal regulation
systems that manage incident solar radiation. In certain aspects,
the photobioreactor comprises a surface coating means. In part, the
surface coating reflects heat. The photobioreactor further
comprises a ground surface coating or means to create diffuse
reflection of light. The coating or means selectively traps IR as
heat.
[0019] Still other embodiments include a rotatable mechanism to
allow heat preservation or minimize heat loss.
[0020] Alternative embodiments equip the photobioreactor with a
real time adaptive control system to adjust the inclination of a
photobioreactor assembly.
[0021] In another embodiment, the photobioreactor is designed such
that heat accumulation is minimized over time. Light not used to
drive biological processes will contribute to heating the
photobioreactor as can various inputs. The photobioreactor is
designed through one or more systems including blocking infrared
light, enablement of evaporative cooling, control of recycle rate,
and the use of heat exchanges, to mitigate accumulation of heat
over time.
[0022] In other embodiments is provided a photobioreactor assembly
comprising: a reactor structure; a greenhouse structure configured
to provide a greenhouse environment for the reactor structure, the
reactor structure and the greenhouse structure spaced relative to
each other to provide temperature control of the
photobioreactor.
[0023] During the production cycle, the photobioreactor further
comprises at least one microorganism selected from a thermophile, a
mesophile or a combination thereof. Optimized conditions can be
maintained to produce various products of interest during the
various times of the year. Depending on geographical location, a
thermophile can be employed in warmer temperatures (e.g., the
summer). Similarly, a mesophile can be employed in cooler climates
(e.g., the winter). Alternatively, thermophiles can be used in the
winter while the mesophiles can be used in the summer though not
optimal. The photobioreactor can provide optimal conditions for the
microorganisms to produce products such as fuels and chemicals. The
photobioreactor regulates temperature to optimize productivity. The
photobioreactor is capable of separating products continuously. The
photobioreactor is also capable of producing robust productivity
and yield of product. Various aspects of the photobioreactor allow
for at least reduced biomass concentration by direct production of
fuels and chemicals from light capturing organisms. Preferably,
separation of biomass from products of interest is obviated.
[0024] In certain aspects, the invention also provides a method for
producing fuels or chemicals comprising: [0025] (a) employing a
photobioreactor wherein at least part of a surface of the
photobioreactor is at least translucent; and a passive thermal
regulation system adapted to comprise a means to reduce
requirements of at least one of cooling, heating or a combination
thereof for the photobioreactor; [0026] (b) introducing into the
photobioreactor at least one organism selected from a mesophile, a
thermophile or a combination thereof; [0027] (c) culturing the
organism in the photobioreactor whereby the organisms utilize light
and CO.sub.2 to produce the fuels or chemicals; and [0028] (d)
removing the fuels or chemicals from the photobioreactor.
[0029] The method further includes employing an assembly comprising
a real time adaptive control system to optimize productivity, and
preferably, maintain optimum productivity.
[0030] Also provided is a method to produce carbon-based products
of interest comprising: [0031] (a) culturing light-harvesting
organism in media comprising increased N, P and/or Fe
concentration; [0032] (b) mixing and circulating the cultured media
in a photobioreactor comprising at least one panel having multiple
channels wherein the organism is cultured; whereby the organism is
cultured to a density of 6-10 g/L DCW to produce the products.
[0033] Disclosed herein are various organisms, e.g., engineered
organisms, phototrophs, autotrophs, heterotrophs and hyperlight
capturing organisms that can be employed in the photobioreactor. In
various embodiments, organisms are adapted to photosynthesize in
the liquid medium under conditions suitable for producing products
of interest, e.g., biomass and chemical intermediates as well as
biologically produced end products such as fuels, chemicals and
pharmaceutical agents.
BRIEF DESCRIPTION OF THE FIGURES
[0034] FIG. 1 depicts a thermoformed photobioreactor in a
flat-panel design.
[0035] FIG. 2 depicts an enlarged bottom portion of the
photobioreactor featuring a removable sparger.
[0036] FIG. 3 is a photographic representation of a reflective
shield on a photobioreactor.
[0037] FIG. 4 is a photographic representation of a reflective
shield on a photobioreactor.
[0038] FIG. 5 is a cross-section view along part of the width of
the photobioreactor illustrated in FIG. 1.
[0039] FIG. 6 illustrates the impact of mixing on light/dark cycle
time.
[0040] FIG. 7 is an illustration of a multiple photobioreactor
assemblies connected in fluid communication, each photobioreactor
featuring an internal downcomer providing circulation of media and
mixing of cultures.
[0041] FIG. 8 is a cross-section of multi-layered channels. A side
view of the same is shown in the bottom part of FIG. 8.
[0042] FIG. 9 is an expanded cross-sectional view of culture in
media in a photobioreactor as illustrated in FIG. 8.
[0043] FIG. 10 depicts a scaled, aerial view of a 1,000 acre solar
biofactory incorporating the flat-panel photobioreactor
apparatus.
[0044] FIG. 11 is a map of the U.S. solar insolation for projected
productivites.
[0045] FIG. 12 is a graphical representation of optimized heat
integration with variable temperature operation and external
heating/cooling reservoir.
[0046] FIG. 13 is a table of heat load on a photobioreactor using
fixed temperature mesophile or thermophile (net positive indicates
external cooling and net negative indicates external heating).
[0047] FIG. 14 is a diagram illustrating an arrangement of
photobioreactors with a diffuser roof.
[0048] FIG. 15 is an illustration of photobioreactor
greenhouses.
[0049] FIG. 16 is an illustration of a tilted photobioreactor
arrangement. In the bottom part, an aerial view of a
photobioreactor with increased surface area covered by side sheets
is shown.
[0050] FIG. 17 is a graphical representation showing fan power used
to cool an example reactor to a desired operating temperature for
two cases: mesophile (desired T.about.37.degree. C.) and
thermophile (desired T.about.58.degree. C.).
[0051] FIG. 18 shows graphically the effect of removing EDTA in the
media.
[0052] FIG. 19 shows the effect of various iron sources in the
media.
[0053] FIG. 20 contrasts the growth effect of an optimized media
compared to the A+ media.
[0054] FIG. 21 shows the change in growth of inoculants with
increased amount of N, P and Fe.
[0055] FIG. 22 is graphical representation of Synechococcus culture
growth to about 10 g/L after inoculation in the photobioreactor
apparatus.
[0056] FIG. 23 is a graph of a thermal management progression.
ABBREVIATIONS AND TERMS
[0057] The following explanations of terms and methods are provided
to better describe the present disclosure and to guide those of
ordinary skill in the art in the practice of the present
disclosure. As used herein, "comprising" means "including" and the
singular forms "a" or "an" or "the" include plural references
unless the context clearly dictates otherwise. For example,
reference to "comprising a cell" includes one or a plurality of
such cells. The term "or" refers to a single element of stated
alternative elements or a combination of two or more elements,
unless the context clearly indicates otherwise.
[0058] Unless explained otherwise, all technical and scientific
terms used herein have the same meaning as commonly understood to
one of ordinary skill in the art to which this disclosure belongs.
Although methods and materials similar or equivalent to those
described herein can be used in the practice or testing of the
present disclosure, suitable methods and materials are described
below. The materials, methods, and examples are illustrative only
and not intended to be limiting. Other features of the disclosure
are apparent from the following detailed description and the
claims.
[0059] A "biofuel" as used herein is any fuel that derives from a
biological source.
[0060] "Products", "products of interest" or "carbon-based products
of interest" refer to producing biological sugars, hydrocarbon
products, fuels, biofuels, solid forms of carbon, or pharmaceutical
agents as a result of culturing light harvesting organisms in the
presence of CO.sub.2 and light under conditions sufficient to
produce the carbon products. Biomass is also within the scope of
the term. Products can be further collected, processed or
separated. These products can be secreted. Within the scope of the
term includes alcohols such as ethanol, propanol, isopropanol,
butanol, fatty alcohols, fatty acid esters, ethyl esters, wax
esters; hydrocarbons and alkanes such as propane, octane, diesel,
Jet Propellant 8 (JP8); polymers such as terephthalate,
1,3-propanediol, 1,4-butanediol, polyols, Polyhydroxyalkanoates
(PHA), poly-beta-hydroxybutyrate (PHB), acrylate, adipic acid,
.epsilon.-caprolactone, isoprene, caprolactam, rubber; commodity
chemicals such as lactate, docosahexaenoic acid (DHA),
3-hydroxypropionate, .gamma.-valerolactone, lysine, serine,
aspartate, aspartic acid, sorbitol, ascorbate, ascorbic acid,
isopentenol, lanosterol, omega-3 DHA, lycopene, itaconate,
1,3-butadiene, ethylene, propylene, succinate, citrate, citric
acid, glutamate, malate, 3-hydroxypropionic acid (HPA), lactic
acid, THF, gamma butyrolactone, pyrrolidones, hydroxybutyrate,
glutamic acid, levulinic acid, acrylic acid, malonic acid;
specialty chemicals such as carotenoids, isoprenoids, itaconic
acid; pharmaceuticals and pharmaceutical intermediates such as
7-aminodeacetoxycephalosporanic acid (7-ADCA)/cephalosporin,
erythromycin, polyketides, statins, paclitaxel, docetaxel,
terpenes, peptides, steroids, omega fatty acids and other such
suitable products of interest. Such products are useful in the
context of biofuels, industrial and specialty chemicals, as
intermediates used to make additional products, such as nutritional
supplements, neutraceuticals, polymers, paraffin replacements,
personal care products and pharmaceuticals.
[0061] Autotroph: Autotrophs (or autotrophic organisms) are
organisms that produce complex organic compounds from simple
inorganic molecules and an external source of energy, such as light
(photoautotroph) or chemical reactions of inorganic compounds.
[0062] Phototroph: Phototrophs (photoautotrophs) are organisms that
carry out photosynthesis such as, eukaryotic plants, algae,
protists and prokaryotic cyanobacteria, green-sulfur bacteria,
green non-sulfur bacteria, purple sulfur bacteria, and purple
non-sulfur bacteria. Phototrophs also include engineered organisms
to carry out photosynthesis and hyperlight capturing organisms.
[0063] Heterotroph: Heterotrophs (or heterotrophic organisms) are
organisms that, unlike autotrophs, cannot derive energy directly
from light or from inorganic chemicals, and so must feed on organic
carbon substrates. They obtain chemical energy by breaking down the
organic molecules they consume. Heterotrophs include animals,
fungi, and numerous types of bacteria.
[0064] Light capturing organism: Light capturing organisms (or
light capturing organisms) are organisms that use light alone or in
combination with other energy sources, to drive the activities of a
cell. This includes photoautotrophs, phototrophs, heterotrophs
engineered to have the ability to use light to power some or all of
their activities, and engineered phototrophs/photoautotrophs.
[0065] Organism: The term is used here to encompass autotrophs,
phototrophs, heterotrophs, engineered light capturing organisms and
at the cellular level, e.g., unicellular and multicellular.
[0066] Hydrocarbon: generally refers to a chemical compound that
consists of the elements carbon (C), optionally oxygen (O), and
hydrogen (H). There are essentially three types of hydrocarbons,
e.g., aromatic hydrocarbons, saturated hydrocarbons and unsaturated
hydrocarbons. The term also includes fuels, biofuels, plastics,
waxes, solvents and oils.
[0067] Biosynthetic pathway: Also referred to as "metabolic
pathway," refers to a set of anabolic or catabolic biochemical
reactions for converting (transmuting) one chemical species into
another. For example, a hydrocarbon biosynthetic pathway refers to
the set of biochemical reactions that convert inputs and/or
metabolites to hydrocarbon product-like intermediates and then to
hydrocarbons or hydrocarbon products. Anabolic pathways involve
constructing a larger molecule from smaller molecules, a process
requiring energy. Catabolic pathways involve breaking down of
larger molecules, often releasing energy.
[0068] Cellulose: Cellulose [(C.sub.6H.sub.10O.sub.5).sub.n] is a
long-chain polymer polysaccharide carbohydrate, of beta-glucose. It
forms the primary structural component of plants and is not
digestible by humans. Cellulose is a common material in plant cell
wall. It occurs naturally in almost pure form only in cotton fiber;
in combination with lignin and any hemicellulose, it is found in
all plant material.
[0069] Surfactants: Surfactants are substances capable of reducing
the surface tension of a liquid in which they are dissolved. They
are typically composed of a water-soluble head and a hydrocarbon
chain or tail. The water soluble group is hydrophilic and can be
either ionic or nonionic, and the hydrocarbon chain is
hydrophobic.
[0070] Photobioreactor: A photobioreactor apparatus, bioreactor or
reactor is used interchangeably to describe an apparatus, device or
system that supports a biologically active environment. For
instance, a bioreactor can be a vessel wherein a chemical process
involving photosynthesis in organisms is carried out or
biochemically active substances are derived from such organisms.
Such bioreactors can support activities for either aerobic or
anaerobic organisms. These bioreactors are commonly cylindrical,
ranging in size from liters to cubic meters, and are often made of
stainless steel. Bioreactors that are adapted to allow use of light
energy in the cultivation or organisms are typically referred to as
photobioreactors and commonly employ transparent materials such as
glass or plastic to allow light to enter the interior of the
bioreactor. On the basis of mode of operation, a bioreactor may be
classified as batch, fed batch or continuous (e.g. continuous
stirred-tank reactor model). An example of a bioreactor is the
chemostat. Organisms growing in photobioreactors may be suspended
or immobilized. Various inventive embodiments are directed to
photobioreactor apparatus designs and to methods and systems
utilizing photobioreactor apparatus in a solar biofactory as is
described throughout. Certain photobioreactor apparatus for use
herein comprise an enclosed bioreactor system, as contrasted with
an open bioreactor, such as a pond or other open body of water,
open tanks, open channels, etc.
[0071] Light: The term "light" generally refers to sunlight but can
be solar or from artificial sources including incandescent lights,
LEDs, fiber optics, metal halide, neon, halogen and fluorescent
lights and solar light such as near-infrared and wavelength
generally between about 400-700 nm.
[0072] PAR: The term "PAR" is short for photosynthetically active
radiation and is measured in .mu.E/m.sup.2/s.
[0073] "Corrugated panel" "sheet", "reactor" or "chamber" refers to
the physical container where the culture is produced and circulated
and can be made using plastic materials such as polypropylene,
polyethylene, polyacrylate and polycarbonate sheets. The sheet can
be partitioned longitudinally and can form channels. The
corrugation can be in various geometric configurations such as
rectangular, trapezoidal, triangular, circular etc. The panel can
be transparent or at least translucent.
[0074] Channel: A channel generally refers to the area between each
partition of a corrugated-panel or a flat-sheet photobioreactor
where organisms circulate conducting photosynthesis. While channel
shape and size can vary an exemplary dimension of a channel is 10
mm.times.10 mm.times.1 m. A channel may also comprise an aperture
that allow air or CO.sub.2 to mix with the media.
[0075] Media: The term "liquid medium", "liquid media" or "media"
generally refers to the composition used for culturing organisms
contained within the photobioreactor apparatus typically comprising
for example in the case of algae and/or other light capturing
organisms, water or a saline solution (e.g. sea water or brackish
water) and sufficient nutrients to facilitate viability and growth
of such organisms. As discussed below, it is often advantageous to
utilize a liquid medium comprising brackish water, sea water, or
other non-potable water obtained from a locality in which the
photobioreactor apparatus will be operated and from which the
organism contained therein was derived or is adapted to. Media also
includes a nitrogen source, which can include, but is not limited
to nitrate salts, urea, ammonia and ammonium salts, uric acid, and
amino acids. Particular liquid medium compositions, nutrients, etc.
required or suitable for use in maintaining a growing light
capturing organism culture, e.g., fermentation media, are well
known in the art. Potentially, a wide variety of liquid media, any
medium in which an organism, when cultured, is capable of producing
can be utilized in various forms for various embodiments, as would
be understood by those of ordinary skill in the art. Such a medium
can also include appropriate salts, minerals, metals, and other
nutrients. It should be recognized, however, that a variety of
fermentation conditions are suitable and can be selected by those
skilled in the art. Potentially appropriate liquid medium
components and nutrients are, for example, discussed in detail in:
Rogers, L J. and Gallon J. R. "Biochemistry of the Algae and
Cyanobacteria," Clarendon Press Oxford, 1988; Burlew, John S.
"Algal Culture: From Laboratory to Pilot Plant." Carnegie
Institution of Washington Publication 600. Washington, D.C., 1961
(hereinafter "Burlew 1961"); and Round, F. E. The Biology of the
Algae. St Martin's Press, New York, 1965; each incorporated herein
by reference).
[0076] Sparger: A sparger or a gas sparger refers to any suitable
mechanism or device that can introduce for instance a plurality of
small air bubbles into a liquid or liquid medium.
[0077] "Light capturing organism" refers to all organisms, natural
or engineered, capable of photosynthesis such as photoautotrophic
organisms (i.e., plants, algae, and photosynthetic bacteria).
[0078] "Gas aperture" refers to the point on the where gas such as
CO.sub.2 and air introduced for example by sparging.
[0079] "Liquid manifold" refers to a part of the photobioreactor
where liquid is either introduced ("liquid introduction manifold")
or where the liquid is returned ("liquid return manifold").
[0080] "Passive" refers to temperature control achieved through the
use of no amount of, or a relatively small amount of, power input
using air such as ambient air. In some embodiments, power input may
be used for blowing air and operating a temperature control system.
In an embodiment, the power input may be obtained from a pV solar
panel or other power source preferably located near the
reactor.
[0081] Throughout this specification and claims, the word
"comprise" or variations such as "comprises" or "comprising", will
be understood to imply the inclusion of a stated integer or group
of integers but not the exclusion of any other integer or group of
integers.
DETAILED DESCRIPTION OF THE EMBODIMENTS
Photobioreactor Apparatus & Light Capture
[0082] In certain aspects, the invention provides an efficient,
low-cost, high surface area light capturing apparatus that is
scalable and easily implemented in open space such as the exemplary
photobioreactor apparatus as shown in FIG. 1. Such photobioreactor
apparatus is adapted to capture light through a panel 100. Since
different types of light capturing organisms can require different
light exposure conditions for optimal growth and proliferation,
additional modifications can be made to the construction of a
photobioreactor apparatus to capture light according to the various
embodiments.
[0083] In certain embodiments, the photobioreactor apparatus is
used with natural sunlight, however, in alternative embodiments, an
artificial light source providing light at wavelengths that is able
to drive photosynthesis may be utilized instead of or in addition
to natural sunlight. For example, a photobioreactor apparatus is
configured to utilize sunlight during the daylight hours and
artificial light in the nighttime, so as to increase the total
amount of time during the course of the day in which the
photobioreactor apparatus can convert light, CO.sub.2 and water to
products through use of photosynthetic organisms.
[0084] The effect of light on productivity is determined for each
photobioreactor design. In preferred embodiments, the
photobioreactor panel 100 is generally placed under a desired light
intensity for optimal growth conditions using selected light
capturing organisms. In various embodiments, the light intensity is
between 20 and 5000 .mu.E/m.sup.2/s. In other embodiments, light
intensities of less than 2000 .mu.E/m.sup.2/s are used, and in a
further embodiment, light intensities less than 500 .mu.E/m.sup.2/s
are used. Under certain conditions, light is penetrated through the
panel 100 or at least partially penetrated to control the depth of
light penetration in the panel 100. The photobioreactor panel 100
of the invention minimizes the time that the culture is exposed to
"dark zones" that are more apparent in the traditional tubular
columns. Preferably, the mixing and flow within the photobioreactor
panel is controlled such that optimized, and preferably, optimal
light/dark cycling is achieved to maximize the efficiency of the
bioreactor. Typically this requires cycling of the organisms
between the top and bottom layers of the channels 200 with cycle
times shorter than 1 sec. Preferably, dark zones where the culture
may be subjected to poor mixing and residence times approaching the
minute time scale are essentially eliminated. In various aspects,
at least one surface of the photobioreactor panel 100 captures
light allowing for maximum light capture for optimum
productivity.
[0085] The photobioreactor can be illustrated in various
dimensions, shape and designs. In preferred embodiments, the panel
100 is a corrugated sheet having a flat-plate design comprising
multiple parallel channels 200. The channels 200 allow for
continuous flow-through of culture while providing structural
support for the panel 100. Additional structural support (e.g.,
oval contact flats 105) can be implemented, for example through
thermoforming. The panel 100 may be in various shapes and sizes and
is generally designed to allow a desired amount of light to
penetrate the channel 200. A useful feature of the photobioreactor
panel 100 allows visible light spectra of wavelengths between
400-700 nm to enter the channel 200 for optimum PAR for the
organisms while filtering out the unwanted wavelengths in the
spectra.
[0086] Certain organisms used in the photobioreactor apparatus may
be sensitive to ultraviolet light or radiation, thus, certain
portions of the external surface of the panel 100, or
alternatively, the entire panel--outer and inner surface may be
covered with one or more light filters that can reduce or negate
transmission of the undesired radiation. Such filters are
integrated into the photobioreactor apparatus design to permit
wavelengths of the light spectrum that the organisms require for
growth while barring or reducing entry of the harmful portions of
the light spectrum. One such optical filter comprises a transparent
polymer film optical filter such as SOLUS.TM.. It is recognized
that a skilled artisan could employ a wide variety of other optical
filters and light blocking/filtering mechanisms for this
purpose.
[0087] In an alternative embodiment, reflective polymers or
materials such as foil, polyester film such as Mylar.RTM. can be
employed to reflect light to the panel 100 as shown in FIG. 2. In
such embodiments, polyester films are placed beneath or along the
sides of the panel 100 to reflect PAR back through the channels
200.
[0088] In other embodiments, materials may be employed to reflect
the spectrum, filter ultraviolet ray or re-emit at an alternate
wavelength. Polymers, such as those described in McDonald S A et al
Nat Mater 2005 4(2): 138-42 can be used to harvest light above 800
nm. Various polymers have been found that convert UV light to
visible spectra light. These polymers have a "whitening effect" by
harvesting light above 800 nm and re-emitting light at 400-450 nm,
which is peak absorbance of chlorophyll A. They have good thermal
stability (>300.degree. C.) and high fluorescent quantum yields
(>0.8). Polymers, such as those described herein can be used to
convert UV light into light that emits in the spectrum typically
absorbed by chlorophyll.
[0089] A number of other such UV-to-visible polymers with good
photostability exist. They include, for example,
4,4-bis(5-methyl-2-beazoxoazol)ethylene (Hostalux KS-N);
1,4-bis(benzoxazolyl-2-yl)naphthalene (Hostalux KCB);
2,5-biss-(5-tertbutylbenzoxazole-2-yl) thiophene (Uvitex OB);
2,2'-(4,4'-diphenolvinyl)dibenzoxazol; (Uvitex OB-1);
1,1'-biphenyl-4,4'-bis(2-(methoxyphenyl)ethenyl) (Uvitex 127). The
choice of a polymer is dependent on its photo-properties, thermal
properties, availability and cost.
[0090] Polymers can also be co-polymerized by techniques well known
to those skilled in the art. See Liu M O Mat Letters 2006 60(17-18)
2132-2137.
[0091] In certain aspects of the invention, the photobioreactor can
be constructed of any low cost stable building material such as
plastics (polycarbonate, polyethylene, polypropylene, chlorinated
PVC) that allows light through the panel to drive photosynthesis in
the organisms. For instance, such materials can be made of
polyethylenes, polypropylenes, polyethylene terephthalates,
polyacrylates, polyvinylchlorides, polystyrenes, polycarbonates,
thermoplastics, glass, resin-supported fiberglass or plexiglass,
etc. In certain embodiments, materials that reflect infrared
radiation including but not limited to quartz are used. These
materials can be interwoven or used instead of or in addition to
other materials used to enclose the panel 100.
[0092] Other examples of plastic material are LDPE, linear low
density polyethylene (LLDPE), fiber-reinforced LDPE, high-density
polyethylene (HDPE), poly vinyl chloride (PVC), polypropylene (PP),
single-layer nylon, polyester (PET), ethylene vinyl acetate (EVA),
polyvinyledine chloride (PVLC), ethylene vinyl alchohol (EVA),
polystyrene (PS) and any other transparent plastic known in the
art. Alternatively, since some plastic materials may have an
undesirable effect of reacting to certain desired output products,
materials such as those that do not react to products, e.g.,
translucent materials may be used to construct the photobioreactor
apparatus. Additionally, any combination of the above materials may
be used to create a multi-layer hybrid polymer. Thicknesses of
material may vary according to the structural integrity to reduce
the cost of the material in constructing the photobioreactor as
well as the selected photosynthetic organism grown in the
photobioreactor.
[0093] Various factors such scalability, flexibility and durability
should be considered when selecting for the photobioreactor
construction material. For example, the materials should be
subjected to variable heat, pressure and allow for turbulence
required for light cycling, shear-stress limitations. In some
embodiments, materials that prevent cell adhesion are used, for
example, biofilms, biocompatible materials, polymers, reduced
magnesium ion concentration of the medium (Walach, Marek R., Appl
Microbiol Biotechnol. Nov. 24, 2004)). Consideration should also be
given to ease of cleaning particulates and other undesirable
material build-up on the exterior of the photobioreactor.
[0094] The photobioreactor material can vary in thickness,
depending on the organisms' ability to receive PAR. A preferred
example is a corrugated polycarbonate panel 100 having about
1.0-2.0 mm thickness. More preferably, the thicknesses which may be
employed in the panel 100 is about 0.10 mm-100 mm, 0.25 mm-50 mm or
1.0 mm-5.0 mm. At such thicknesses, a moderate amount of turbulence
within the photobioreactor apparatus would have little effect on
its structural integrity while providing the desired level of flow
within the channels 200.
[0095] To introduce liquid and return the same to the
photobioreactor apparatus, in certain aspects of the invention,
manifolds (130, 140) are connected to the panel 100. A preferred
embodiment for joining the manifolds together with the
photobioreactor are thermal plastic welding, adhesives or epoxy set
for an appropriate time, pressure and temperature for the materials
used. Alternatively, the panel and the manifolds are extruded
together or thermoformed.
[0096] The surface of the panel 100 and the manifolds (130, 140)
can be flat or contoured optimally to control PAR. In one
embodiment, the entirety of the photobioreactor apparatus can
employ the same material including the various manifolds enclosing
the panel 100.
[0097] In preferred embodiments, the reactor structure has a
cross-section as shown, in part, in FIG. 5. The cross-section is
positioned as indicated in FIG. 1 (see line with arrow, the arrow
indicating the viewing direction). The reactor is preferably formed
through a thermoform twin-sheeting process. In this implementation,
the reactor is not segmented into distinct channels, but rather has
a broad upflow (upcomer 510) and downflow region (internal
downcomer 520) allowing for enhanced cross mixing. There is a
bonded strip 530 that separates the upflow region from the downflow
region. This division between the upflow and downflow sections of
the reactor typically extends up the length of the active region of
the reactor. It also typically serves to bond the top and bottom
sheet together. In this view, the left side is the downflow side.
In addition, oval contact flats 105 can be included throughout the
reactor to locally stiffen the reactor from ballooning under
hydrostatic pressure from the culture. The top and bottom walls are
wavy, unlike a flat panel bioreactor. The waviness provides several
benefits: it further stiffens the walls allowing for thinner
plastic sheets, it provides increased surface area on the outside
of the reactor that improves heat transfer out of the reactor, for
example, when cooling air is blowing along it, and it provides
increased exposed surface area of the culture which in conjunction
with an overhead light diffuser can decrease the light intensity
that the culture is exposed to. As the reactor flow is typically
driven with air-lift and the reactor can be operated at an angle
less than vertical, air bubbles introduced in the bottom header
tend to rise in the peaks of the waves on the top surface. Thus,
better mixing and light-dark cycling can be expected in the peak
regions relative to the valley regions. The reactor walls are
preferably spaced vertically so that for the desired operating OD,
most of the PAR light is absorbed in the culture and little PAR is
transmitted and lost through the reactor bottom. Spacing the walls
more than this can create unproductive dark volume. Since the
mixing in the valley regions of the reactor is less optimal than in
the peak regions, the vertical reactor gap (i.e., vertical distance
between the top surface of a bottom sheet and bottom surface of the
top sheet of a reactor structure) is typically smaller in the
valley regions to reduce the reactor volume associated with regions
of reduced mixing. But the minimum vertical reactor gap in the
valley regions is still designed to be sufficient for capturing
most of the PAR radiation. From the thermoforming process, all
transitions within the reactor can be performed smoothly, enhancing
the cleanability of the reactor, reducing contamination issues.
[0098] Another embodiment of the present invention shares the
advantages described in the previous paragraph is a photobioreactor
comprising a reactor structure for containing a culture medium. The
reactor structure includes a top sheet and a bottom sheet which are
bonded together to form a reactor volume for containing a culture
medium. The vertical reactor gap along at least part of the width
(i.e., cross-sectional width as shown, e.g., in FIG. 3) of the
reactor structure increases and descreases repeatedly. Preferably,
the vertical reactor gap along at least part of the width of the
reactor structure minimizes and maximizes repeatedly. More
preferably, the vertical reactor gap along at least part of the
width of the reactor structure minimizes and maximizes repeatedly
while being not smaller than a minimum vertical reactor gap
selected such that for an operating OD substantially all
(typically, at least 50 percent, more typically, at least 75
percent, even more typically, at least 90 percent, yet even more
typically, at least 95 percent) of PAR light transmitted through
the top sheet is absorbed in the culture. Even more preferably, the
vertical reactor gap along at least part of the width of the
reactor structure minimizes and maximizes periodically while being
not smaller than a minimum vertical reactor gap selected such that
for an operating OD substantially all (typically, at least 50
percent, more typically, at least 75 percent, even more typically,
at least 90 percent, yet even more typically, at least 95 percent)
of PAR light transmitted through the top sheet is absorbed in the
culture. Yet even more preferably, the vertical reactor gap along
at least part of the width of the reactor structure varies
periodically between a minimum vertical reactor gap and a maximum
vertical reactor gap, wherein the minimum vertical reactor gap is
provided in troughs of the bottom sheet (i.e., troughs of the
internal surface of the bottom sheet) and the minimum vertical
reactor gap is selected such that for an operating OD substantially
all (typically, at least 50 percent, more typically, at least 75
percent, even more typically, at least 90 percent, yet even more
typically, at least 95 percent) of PAR light transmitted through
the top sheet is absorbed in the culture. Yet even more preferably,
the vertical reactor gap along at least part of the width of the
reactor structure varies periodically between a minimum vertical
reactor gap and a maximum vertical reactor gap, wherein the minimum
vertical reactor gap is provided in the troughs of the bottom
sheet, the maximum vertical reactor gap is provided at the peaks of
the bottom sheet and the minimum vertical reactor gap is selected
such that for an operating OD substantially all (typically, at
least 50 percent, more typically, at least 75 percent, even more
typically, at least 90 percent, yet even more typically, at least
95 percent) of PAR light transmitted through the top sheet is
absorbed in the culture. Most preferably, the vertical reactor gap
along at least part of the width of the reactor structure varies
periodically between a minimum vertical reactor gap and a maximum
vertical reactor gap, wherein the minimum vertical reactor gap is
provided in the troughs of the bottom sheet, the maximum vertical
reactor gap is provided at the peaks of the bottom sheet, the
minimum vertical reactor gap is selected such that for an operating
OD substantially all (typically, at least 50 percent, more
typically, at least 75 percent, even more typically, at least 90
percent, yet even more typically, at least 95 percent) of PAR light
transmitted through the top sheet is absorbed in the culture, the
troughs of the bottom sheet are positioned vertically below troughs
of the top sheet and peaks of the bottom sheet are positioned
vertically below peaks of the top sheet. Further, preferably, the
surface of the bottom sheet and/or top sheet changes smoothly.
Typically, the maximum vertical reactor gap is between 1 and 10
times the minimum vertical reactor gap. More typically, the maximum
vertical reactor gap is between 1 and 5 times the minimum vertical
reactor gap. Also, typically, the distance between consecutive
peaks of the bottom sheet is between 1 and 10 times the minimum
vertical reactor gap. More typically, the distance between
consecutive peaks of the bottom sheet is between 1 and 5 times the
minimum vertical reactor gap. Also, typically, the vertical reactor
gap increases and decreases at least three times, more typically,
at least 5 times, even more typically, between 5 and 100 times, and
yet even more typically, between 5 and 50 times. Further, the top
sheet and the bottom sheet can be bonded along the length of sheets
to divide the reactor volume into an upflow volume (upcomer) and
downflow volume (internal downcomer).
[0099] In further embodiments of the present invention the reactor
structure as described in the previous paragraph can be a part of a
photobioreactor assembly as described herein and/or include a
passive thermal regulation system as described herein. For example,
one of these further embodiments is a photobioreactor assembly
comprising a reactor structure as described in the previous
paragraph, and a greenhouse structure configured to provide a
greenhouse environment for the reactor structure, the reactor
structure and the greenhouse structure spaced relative to each
other to provide temperature control of the photobioreactor.
Another example of these further embodiments is a photobioreactor
assembly comprising a reactor structure, and a greenhouse structure
configured to provide a greenhouse environment for the reactor
structure, the reactor structure and the greenhouse structure
spaced relative to each other to provide temperature control of the
photobioreactor, wherein the reactor structure comprises two spaced
apart reactors as described in the previous paragraph and the
greenhouse structure comprises a diffuser roof element arranged
between the reactors.
[0100] In further designs, the photobioreactor has a flexible
fitting design conducive to adhesive bonding, ultrasonic welding or
insert/functional twinsheet thermoforming as shown in FIG. 1. The
photobioreactors are amenable to various dimensions such as lab
size (.about.1.6.times.4)' .about.8 L capacity or pilot/commercial
(.about.4.times.6)' .about.25 L capacity.
[0101] Further, finite element analysis is conducted to optimize
structural staking pattern, reduce material thickness and
consumption and verify thermal expansion & photobioreactor
attachment. Additionally, fluid flow and mass transfer analysis,
e.g., computational fluid dynamics create visual internal flow
pattern and verify volumetric flow rate through baffle &
reactor-to-reactor connecter.
[0102] In various embodiments, the photobioreactor apparatus is
raised at an angle to most optimally capture light in accordance
with various factors depending on for instance light intensity and
geographic location. Preferably, the angle is about 10 to 30
degrees relative to the ground. In preferred embodiments, one end
of the panel 100 is fixed or pivoted at the base to be freely
rotatable, for example to follow the light source during the course
of the day. The effect is to create an effective PAR, optimal
exposure to light, track the source of the solar energy during the
day and throughout the year for maximum biomass yield. A
photobioreactor design at a 30-degree tilt can provide fairly
uniform yearly insolation in the southwest U.S. for example.
Gas Bubbles for Air-Lift
[0103] Various designs can be employed to optimally capture light
and efficiently transfer gas to the light-harvesting organisms that
are aimed at maximizing cell growth and/or productivity through the
use of a photobioreactor apparatus and proper mixing with
CO.sub.2.
[0104] A low-cost efficient mixing system is integrated into the
photobioreactor apparatus. In various aspects, bubbles allow for
more efficient gas exchange of carbon dioxide uptake and oxygen
removal. Use of air and gas bubbles achieves mass diffusion, mixing
and pumping with the added benefit of being cost-effective. In
certain embodiments, carbon source such as CO.sub.2 containing flue
gas is sparged into the photobioreactor and exhaust air such as
O.sub.2 is removed from the system via an exhaust vent 115. In a
preferred photobioreactor design with a corrugated panel 100, air
bubbles and gas e.g., CO.sub.2 are suitable in providing optimal
mixing and circulation of culture and media with minimum
hydrodynamic force. Furthermore, such aeration exerts little harm
to the culture. The bubbles act as a mechanism, e.g., as an
air-lift pump, circulating the culture without the need for
ancillary pumping. Bubbles are generated by sparging air and
CO.sub.2 through a sparger 110, which rise to the top manifold 140
relatively quickly. Preferably, bubble characteristics are improved
by initiating them at an optimal size.
[0105] In various embodiments, the air-lift used for mixing
effectively eliminates large circulation pumps resulting in
significant capital and operating costs savings. As shown in FIG. 6
air bubbles are much more effective in promoting radial mixing than
simple liquid pumping. Light/Dark (L/D) cycling time of less than
200 ms can be accomplished with very low power input. In certain
embodiments, a preferred air-lift design provides sufficient liquid
velocity to obtain a pure bubble flow regime. In Example 2, data
shown to obtain a light/dark cycle time of order 100-150
milliseconds while using reasonable levels of mixing power shows
that the mixing caused by air bubbles in the air bubble lift driven
flow is more favorable than mixing associated with turbulent mixing
resulting from pumping the liquid. In various embodiments, the
conversion of order 80 W/m.sup.2 of insolation into product is
preferred and therefore it is preferred to use a relatively small
fraction of the converted energy for mixing of the culture.
Accordingly, the air bubbles provide much more efficient mixing
than pumps at the same power while allowing use of a modest amount
of total mixing energy relative to the energy conversion to
product. The motive force can be provided by other means and
various suitable pumps and are known to those of ordinary skill in
the art.
[0106] Depending on the relative velocities of the liquid medium
flow and gas bubble flow within the photobioreactor apparatus, and
governing the flow rate, photomodulation frequency of greater or
less cycles per second may be achieved. In one instance, a high
frequency "flashing light" effect during photosynthetic activity
has been found to be very beneficial for growth and productivity of
many species of algae (Burlew 1961). Configuring the
photobioreactor apparatus with photomodulation, therefore, may
provide additional or more extended exposure of the organism to
dark, rest periods and may increase productivity.
[0107] In certain other embodiments, the photobioreactor apparatus
is equipped with controls to adjust the liquid flow direction. For
instance, gas is fed to the liquid medium via the apertures 120
using gas spargers 110, which is configured to create a plurality
of bubbles rising up to the top manifold 140, thereby inducing
liquid flow. In more preferred embodiments, gas spargers 110 are
configured and positioned at the bottom of the channel 200 to
introduce carbon dioxide so as to create circulation and mixing
from various sized gas bubbles that rise up to the surface of the
liquid medium contained within the channel 200. The velocity of
bubbles is likely to affect the air-liquid interface. In certain
instances, the bubbles may collect and as a consequence provide the
liquid flow an increased surface area for increased light capture
(FIG. 8). Additionally, since bubbles are inherently unstable,
stabilizing means such as adding surfactants is contemplated.
[0108] In certain embodiments, air is sparged into an aperture 120
at a desired pressure e.g., 5 L/m where the bubbles rise upwards
through the medium and burst at the air-liquid interface. After the
sparged gas creates an upward pressure or lift and forces the
culture upwards towards the liquid return manifold 140, the culture
is circulated back via a downcomer 520 to the liquid introduction
manifold 130. In certain instances, a pump may be included for
sufficient liquid velocity and to maintain desired two-phase flow
regime. In certain instances, the sizing and flow in the downcomer
520 can be arranged to minimize the residence time of the culture
in order to maximize overall productivity and minimize wasteful
side-reactions such as respiration under conditions of non-optimal
light exposure. Additionally, the downcomer 520 may be either an
internal or external feature of the photobioreactor. A downcomer
provides internal circulation within the photobioreactor. FIG. 7
shows multiple integrated photobioreactors in fluid communication,
each with an internal downcomer 520. One notable advantage of an
internal downcomer is the ability to culture the light capturing
organisms and transfer to the next photobioreactor unit while
maintaining exposure to the light source thereby increasing
productivity. Additional advantage includes a setup where the
downcomer is fully integrated in a single unit reducing complexity,
parts and costs.
[0109] A desired amount of light is exposed to the photobioreactor
and gas is sparged at a specific interval, which is a function of
cell productivity. Residence time is governed by the height of the
channel, the initial speed, and pressure of gas injected into the
channel. The pumping rate is defined by the flow rate of the gas
per the residence time of the bubble to travel the distance of the
channel to keep the reactor in steady-state. Bubbles achieve the
desired result of mixing and mass diffusion but generally, the
bubbles will rise to the surface of the channel fairly quickly.
Studying of the fraction of channel residence time of air bubbles
of various diameters that rise to the top of the channel indicates
the optimal bubble size to be about 0.5 mm to about 2 mm. In
various embodiments, bubbles are generated at a desired initial
diameter, for instance, to about 1 mm, however, bubble sizes can
vary dramatically. Alternatively, the desired initial bubble size
may be larger to create a greater surface area of the culture in
the channels for better light capture.
[0110] In certain instances, media may run countercurrent to the
sparged air in the channel 200 but such downward movement media
flow can be minimized. As such, the culture may experience
co-current and counter-current gas exchange during circulation.
[0111] In various embodiments, the photobioreactor is at a
particular angle. For instance, the photobioreactor tilt optimum
may be at 30.degree. (FIG. 8). This has shown to provide fairly
uniform yearly insolation in the southwest U.S. Modifying or
adjusting the angle of the photobioreactor apparatus may improve
performance. Changing the angle may be performed manually or
automatically according to a set of instructions and/or
calculations and/or in response to values from various sensors
(e.g., temperature sensors or light intensity sensors). Realtime
control of the positioning of the photobioreactor apparatus may be
facilitated as part of the computer-implemented control
strategy.
[0112] In certain embodiments supplemental pumping may be required
as a result of the incline while in other embodiments, the air-lift
pump is sufficient to provide the needed pumping for circulation.
Additional riser height may not be effective in increasing pumping
due to increased pressure loss associated with riser piping.
Increasing riser piping diameter to reduce pressure loss may result
in substantial dead volume for the cells.
Photobioreactor Operation
[0113] The bioreactor assembly is connected to a gas introduction
manifold 110 to sparge air and gas about 1-3% CO.sub.2 to each
channel 200. The panel 100 is also connected to a liquid
introduction manifold 130 where the culture and media are
introduced through an inlet 160 optionally via a peristaltic pump
to the panel 100. The air bubbles and CO.sub.2 culture mix the
culture and is passed through the channels 200 to a liquid return
manifold 140. The return manifold 140 may comprise a gas exhaust
115 to vent O.sub.2. Alternatively, the culture may be optionally
circulated via a pump, through a heat exchanger and through a probe
block to measure OD, pH and temperature. The culture can be
diverted via drain valve. Products can be released through an
extraction valve for separation or collection. The return manifold
may also connect to a separator, collector or a condenser. Removal
or extraction of desired products of interest can be from either
the liquid or gas phase. Any such product can be collected by this
mechanism or by a separate mechanism.
[0114] In various embodiments, multiple units of the
photobioreactor apparatus can be assembled together in modular
fashion with relative ease. An example of a multiple
photobioreactor apparatus assembly is shown in FIG. 10. After the
initial sparge of air and gas, using the air-lift created by the
sparged air and gas bubbles, the high pressure of the liquid return
manifold 140 (top) of a first panel 100 moves the culture to the
low pressure liquid introduction manifold 130 (bottom) of a second
panel 100. A series of panels can be assembled to take advantage of
this cost-effective and efficient pressure gradient.
[0115] Various control points regulate operation of the
photobioreactor assembly. For instance, temperature is controlled
by thermal management system of the invention. Additionally, pH can
be controlled by CO.sub.2 concentration. The optical density can be
controlled to maintain optimal cell concentration and nutrient
profile can be based on feed-forward control. Minimal overpressure
to maintain sanitary operation and air flow can be controlled to
achieve mass transfer and stripping.
[0116] As for control instrumentation, degree of localization of
instrumentation and overall automation structure for large solar
field is optimized and instruments are minimized or consolidated to
achieve low cost but reliable automation at lowest level possible
with data aggregation to central computer systems.
Circulating and Media Recycle
[0117] In various embodiments, culture is moved from the bottom of
the channels 200 up to the height of the top of the channel
200--the liquid return manifold 140 by the gas bubbles as described
earlier and then dispersed down through a downcomer 520 connecting
the liquid introduction manifold 130 the channels 200 and
subsequently returned to the channels 200. In other preferred
embodiments, culture collected at the liquid return manifold 140 is
recycled and recirculated via a separate panel 100.
[0118] In certain embodiments, various conduits are integrated to
the photobioreactor apparatus. For instance, media may be passed
through various conduits to regulate temperature through a heat
exchanger or a water basin. Conduits may block light to employ
organisms to undergo light-dark cycle. Gas can be pumped through
tubing such as condensation resistant tubing to various inlets. A
conduit may be constructed with a variety of suitable materials
such as chlorinated PVC, copper, stainless steel or brass. As light
is used by reactor placement, the materials can be opaque, and as
such, any conduit or fluid piping material known in the art can be
used. Tubing that resists biofouling, photoinhibition or those
commonly used in fermentations is used.
[0119] The internal diameter or minimum internal cross-sectional
dimension of conduit will depend on a wide variety of desired
operating conditions and parameters and should be selected based
upon the needs of a particular application. In general, an
appropriate inner diameter of conduit can depend upon, for example,
desired volumetric or production capacity, impact of turbulence on
cells (although certain cells are known to be sheer tolerant), and
the resistance of materials to biofilms.
[0120] Furthermore, while the culture is in the photobioreactor, a
certain volume of water or other liquid are added in order to
compensate for evaporative losses or media/water not otherwise
recycled through the system. Water and other liquids can be added
via the inlet 160 on the liquid introduction manifold 130. By
contrast, effluent can be removed after being filtered and the
desired materials can be siphoned off to a separate collector.
[0121] Fouling can harm the overall sterility and efficiency of the
photobioreactor apparatus and its components. To reduce or avoid
it, in some embodiments the photobioreactor apparatus is easily
cleanable and be as smooth as possible.
[0122] Accordingly, in various embodiments, the materials and
devices selected are resistant to biofouling to achieve a
self-cleaning effect.
Input Sources--CO.sub.2 and Water Recycle & Removal
[0123] The photobioreactor system is designed to produce desired
carbon-based products including biomass and chemical intermediates
as well as biologically produced end products such as fuels,
chemicals and pharmaceutical agents and other compounds from
minimal inputs: light, water and carbon dioxide (FIG. 9). Input gas
can be used from a number of sources including ambient air,
concentrated sources, and industrial sources. Carbon dioxide can be
supplied from a source where the carbon dioxide would otherwise be
emitted into the atmosphere. In certain embodiments, the gas used
comes from a source wherein the carbon dioxide concentration is
significantly higher than that found in the atmosphere (0.03%). In
particular, such concentrations of carbon dioxide can be found in
the effluent, flue gas or offgas streams of coal plants,
refineries, cement factories, distillaries, breweries, natural gas
facilities, breweries, pharmaceutical plants, chemical processing
plants, any plants that produce greater than ambient carbon dioxide
and the like. Offgas from an example coal plant is at 50-55.degree.
C., and is composed of 10.9% CO.sub.2 0.01% CO, 9% H.sub.2, 3.01%
CH.sub.4, 3.0% O.sub.2, 0.106% SO.sub.2, 74% N.sub.2.
Concentrations of the various elements can change based on
operating parameters as well as from facility to facility.
[0124] The integrated solar biofactory can be adapted to treat such
emitted gas and provide air pollution control and renewable energy
solution to fossil fuel burning facilities, such as power
generating facilities. The solar biofactory also comprise emissions
control devices and regeneration systems that can remove undesired
gases and other pollutants from the environment.
[0125] Carbon capture and sequestration (CCS) from power plants and
various other sources at present is a costly and energy intensive
endeavor, however, the integrated solar biofactory provides an
alternative to CCS and provides a means for converting carbon
dioxide into fuels and chemicals in scale. Accordingly, the method
provides for accounting for or more preferably receiving carbon
credits comprising: culturing light capturing organisms in a
photobioreactor or photobioreactor assembly using carbon dioxide,
light and water; measuring the input, use or reduction of carbon
dioxide that is captured by the photobioreactor; and determining an
amount of carbon credits based on the input, use or reduction of
carbon dioxide.
[0126] The gas at an inlet can be at the same, greater, or less
pressure than as released as it would for the offgas streams.
Higher than ambient pressures can be used for fluid movement within
the photobioreactor apparatus as appropriate.
[0127] In certain embodiments, the gas sparged into the
photobioreactor channels 200 moves cocurrently with the media.
After passing through channels 200, the gas exits the chamber
through gas exhaust vent 115. These outlets may release directly
into the atmosphere, or connect to gas conduits. In some
embodiments, the gas conduits reconnect to the gas inlet allowing
for gas recycle. In some embodiments the recycling gas conduits
also have a system allowing for separation of elements in the gas
phase. The outlets and conduits may also be regulated as to
maintain desired pressures and concentrations in the
photobioreactor.
[0128] In those cases where no conduit, recycle, or collection
system exists, the gas is released directly into the surroundings.
In various aspects, oxygen is primarily exhausted from the
photobioreactor and therefore does not accumulate.
[0129] In those cases where the gas is recycled, anywhere between 0
and 100% of the gas removed from the photobioreactor can be
returned with the balance released directly into the surroundings.
The amount released can be controlled to reach desired reactor
conditions. The amount not released defines the recycle rate. In
some embodiments, not all of the gas is recycled such that various
elements harmful to achieving maximal productivity, such as oxygen,
can be removed. The recycle can be before or after separation of
gas elements into one or more components. As such recycle does not
necessarily refer to the gas as a bulk but as a relative amount to
the gas removed from the photobioreactor. Recycled gas is then
blended in some proportion with gas at the gas inlet of the
appropriate reactor system to achieve the desired reactor
conditions.
[0130] Water useful in the solar biofactory can be no-salt,
low-salt, brackish, marine, or high salt. The water can derive from
natural stores (e.g., lakes, rivers, ponds, etc) or from processed
streams.
[0131] There are numerous recognized advantages in the solar
biofactory as for example it optimizes land use, excellent
(preferably maximum) light capture and distribution, efficiently
controls heat, low cost, within a closed culture, has flexible
design, scalable and ease of construction, good volume, optimal
mixing, cost-effective means of pumping, requires minimal inputs
and it obviates the need for added steps to convert biomass to
their component sugars. The focus from feedstock has shifted to
renewable and lower cost sources of biomass, for example, the use
of non-starch, non-food-related biomass such as trees, grasses, and
waste materials. The largest components of these biomass sources
are cellulose, hemicellulose, and lignin. The focus on these
sources still falls short in comparison to the solar biofactory
system as they employ steps for hydrolyzing biomass, mechanical
milling, dilute-acid thermochemical pretreatment and other such
methods to convert biomass into their component sugars. The solar
biofactory can achieve highly efficient productivity with light
capturing organisms using light, carbon dioxide, and water as
inputs.
Photobioreactor Scale Up
[0132] FIG. 10 represents a schematic aerial diagram of a novel
solar biofactory composed in part of multiple photobioreactor
apparatuses. A scalable design for cost-competitive production of
biofuel should be low cost, easy to construct, assemble and require
considerably less capital and maintenance costs. In various
embodiments, the photobioreactor apparatus is scalable to about any
volume, e.g., 1 to 90,000 L, easily connected in fluid
communication to a separate vessel or reactor allowing easy
assembly of a multiple photobioreactor design. In various
embodiments, the photobioreactor is about 10 to about 1,000 L.
[0133] In certain aspects of the invention, the photobioreactor is
configured to a particular dimension, e.g., 4 ft.times.8 ft
("cell"). Such individual cells are in fluid communication and
configured to cover 200 m.sup.2 as a Circulation Unit. More
preferably, the Circulation Units are assembled modularly to 1000
acres yielding 27.5 MM Gal as shown in FIG. 10.
[0134] A single photobioreactor unit can be employed as the same
basic building block for full-scale eliminating scale-up risk. For
instance, multiple photobioreactor units approximately 4 ft.times.8
ft are connected together into a 40' module for simplified
logistics and installation. Approximately 60 photobioreactors can
cover about 2000 sq ft (200 m.sup.2). An industrial unit of 0.4
acre includes full process functionality and is simply multiplied
to increase capacity. A Commercial Production Unit can comprise
2500 industrial units, covering approximately 1,000 acres (2
km.times.2 km). At scale, it is capable of producing 27.5 MM
gallons of EtOH for example. Industrial unit can be multiplied to
any desired size based on land and CO.sub.2 availability.
[0135] A distillation plant can be located nearby to collect,
process or refine the final product.
[0136] The solar biofactory can be placed in a number of locations,
preferably near a flue gas source, where light is ubiquitous as
intensity varies by location and land area, preferably next to a
water source. In various embodiments, the photobioreactor apparatus
is above ground or in the ground or even in the ocean.
[0137] In various aspects of the invention, the solar biofactory
can be either open or closed.
[0138] In certain embodiments, the solar biofactory is a closed
system. In various embodiments, can be aseptic and overcomes the
common light penetration limitations. In alternative embodiments, a
water basin is placed adjacent to the photobioreactor apparatus to
regulate temperature. For instance, the culture can be circulated
through a water basin.
Photobioreactor Biomass Productivity
[0139] The solar biofactory also provides methods to achieve
organism productivity as measured by production of desired
products, which includes cells themselves.
[0140] The desired level of products produced from the engineered
light capturing organisms in the solar biofactory system can be of
commercially utility. For example, the engineered light capturing
organisms in the solar biofactory system convert light, water and
carbon dioxide to produce biofuels, biomass or biochemicals at
about 1 g/L per 12 hr day or in certain embodiments, about 2.5 g/L
per 12 hr day or greater. Similarly, the engineered light capturing
organisms in the solar biofactory system convert light, water and
carbon dioxide to produce chemicals, carbon-based products of
interest or pharmaceutical agents at about 5 g/L per 12 hr day or
greater.
[0141] In certain preferred embodiments, the photobioreactor
produces about 10 g/L DCW biomass, or about 13.7 g/L DCW biomass.
In one instance, an areal productivity of 79 g/m.sup.2 per 24 hours
has been demonstrated in 5 L lab prototype corrugated flat-plate
photobioreactor.
[0142] The photobioreactor system affords high areal productivities
that offset associated capital cost. Superior areal productivities
are achieved by: optimizing cell culture density through control of
growth environment, optimizing CO.sub.2 infusion rate and mass
transfer, optimizing mixing to achieve highest photosynthetic
efficiency/organisms, achieving maximum extinction of insolating
light via organism absorption, achieving maximum extinction of
CO.sub.2 and initial product separation.
[0143] In particular, southwestern US has sufficient solar
insolation to drive maximum areal productivities to achieve about
>25,000 gal/acre/year ethanol or about >15,000 gal/acre/year
diesel although majority of the US has insolation rates amenable to
cost effective production of commodity fuels or high value
chemicals (FIG. 11).
[0144] Furthermore, CO.sub.2 is also readily available in the
southwestern US region, which is calculated to support large scale
commercial deployment of the invention to produce 120 Bn gal/year
ethanol, or 70 Bn gal/year diesel.
Temperature Control & Heat Balance
[0145] In various embodiments, it is important to control the
temperature within the photobioreactor apparatus for culturing
organisms during operation. Generally, the temperature of the
liquid medium within the photobioreactor apparatus should be
maintained between about 5.degree. C. and about 60.degree. C.,
between about 30.degree. C. and about 60.degree. C., and in some
embodiments, between about 37.degree. C. and about 60.degree. C.
Temperature can be easily regulated and maintained depending on the
organism used in the photobioreactor apparatus for optimal growth,
circulation and productivity.
[0146] When using solar inputs, infrared light, which is not
usable, if not otherwise reflected or converted, will produce heat.
Other light inputs that are not used or reflected may also
contribute to heat, but not with the same magnitude. A number of
means can be used to enable temperature regulation. The input gases
represent another potential heat source. If carbon dioxide is being
used from the offgas of plants, its temperature is typically about
50.degree. C. to 60.degree. C., and therefore represents a second
heat source. Mechanical devices necessary for the fermentation or
culturing can also be another source of heat. The cellular
processes are contemplated to be net endothermic and should
therefore not significantly contribute. As the cells require
specific temperature ranges for optimal function, temperature
control is important to the reactors. A number of means can be used
to control the temperature of the photobioreactor based on the
total heat needs of the reactor and the various other means being
employed. For example, if the infrared contribution is eliminated,
the reactor system no longer requires active cooling through heat
exchangers or other means, but can be maintained with fluid control
and evaporation alone.
[0147] Other means of cooling include evaporative cooling, reducing
the gas recycle (e.g., requiring more external fluid to be added at
a lower (ambient) temperature, or heat exchanger. A heat exchanger
may be employed to maintain the bioprocess at a constant
temperature. Heat exchangers as well as fluids can be used to
compensate for evaporation losses as the temperature is likely to
be lower than around 40 to around 60.degree. C.
[0148] Evaporative cooling techniques can be employed, as the need
for a separate operating equipment is obviated. In some embodiments
this can include distributing cooling water over the top surface of
photobioreactor using a distribution pipe or sprays and optionally
collecting the water in a tray at the bottom of the
photobioreactor. Reduced recycle may be used, but has a higher cost
given the need for potentially large supplies of water. As a
further alternative, carbon dioxide can be stored as dry ice and
used for cooling purposes.
[0149] A drawback of various closed photobioreactor systems is the
significant amount of water consumption and the potential use of
evaporative cooling towers, fans, circulation pumps and the
associated electrical costs. In certain aspects, the solar
biofactory is advantageous in reducing the cooling load and the
electrical load. For instance, the photobioreactor panel 100 can be
layered on top to create a multi-layered panel as shown in the
bottom part of FIG. 8. In various embodiments, water is circulated
through a select few channels 350 while other channels 300 remain
empty. In such embodiments, the culture is circulated through only
the channels 200 of one panel 100. Variations of such embodiments
are possible, for instance, to alternate channels (e.g., one out of
every four channels) that circulate water as well as varying the
layers of panels to regulate temperature.
[0150] In various embodiments, thermophiles are used in the
photobioreactor running at 60.degree. C., which will allow 100% of
heat to be rejected under hottest summer conditions with passive
radiation and natural convection without any assistance. In
preferred embodiments, low grade heat at 60.degree. C. is also
usable to drive EtOH distillation without external source of heat.
In other embodiments, water in pond or the like is used to absorb
heat during the day and cooling at night passively or actively.
Other options are use of material to reduce or reject heat or other
suitable means of insulation required at night. In preferred
embodiments, a culture comprising a single organism is run for the
entire year. Alternative embodiments allow use of mesophile during
winter and thermophile during summer to optimize process.
[0151] Thermophiles can be cultured in the photobioreactor
apparatus at 60.degree. C. during operation and 35.degree. C.
during nighttime "cooling" operation. An alternative could be to
run the photobioreactor at 50.degree. C. Mesophiles can be cultured
at 37.degree. C. during operation and at 15.degree. C. during
nighttime "cooling" operation. Another approach is to culture
thermophiles in the photobioreactor in the spring, summer and fall
and the mesophiles in the winter.
[0152] In certain embodiments, thermal storage system is employed
to store heat during the day and cold at night. Preferably, the
required amount of external heat/cooling is minimized but the
photobioreactor apparatus can be designed to require only external
heat.
[0153] In certain embodiments, the solar energy absorbed and
rejected by the photobioreactor varies over the course of a given
day and at different times of the year.
[0154] In other embodiments, the photobioreactor system may include
a heat source, a cooling source or a combination of both. Under
conditions, for example during nighttime where the temperature
drops, heat is preferable.
[0155] In certain aspects, heat is added to the photobioreactor
system taking into consideration various factors such as solar
irradiance inputs such as latitude/longitude, day, time, plate tilt
angle, earth's orbit and atmosphere and adjusting for reflective
losses. In other aspects, the output heat is natural convection or
radiation.
[0156] In other aspects, alternative for heat rejection and non-PAR
photon utilization include light scattering pigments with
concentrating pV (MIT), thermal electrical couples, piezo
electrical couples (thermal expansion etc.), selective coatings
etc., pumps, sensors and control systems were integrated into the
system. Various components in systems integration include for
example, the use of a water basin for thermal regulation.
Photobioreactor & Passive Thermal Regulation
[0157] Various embodiments of the invention concern a process for
converting CO.sub.2 to various products of interest. A novel
feature is the integration of a passive thermal regulation system
to obviate the costly implementation of heat exchange used in
photobioreactors.
[0158] The use of the passive thermal regulation system in an
enclosed photobioreactor has distinct advantages for the production
of fuels and chemicals using various host cells of interest. It has
the further advantage of enabling growth of engineered phototrophic
strains.
[0159] The ability to produce a chemical or fuel product directly
from sunlight and CO.sub.2 dramatically improves the economics of
the process by eliminating costly and inefficient separation,
chemical conversion of the biomass and also obviates the need to
develop new markets for significant quantities of biomass
co-product. A photobioreactor that optimizes the expression of the
end-product at the same time as allowing separation of the product
directly from the broth (i.e. continuous product removal)
dramatically improves the economics such that the increased capital
cost of the enclosed photobioreactor is fully justified.
[0160] Certain embodiments of the proposed solar biofactory
overcomes all of these limitations: photon conversion efficiency,
overheating, radiative and convective losses, excessive cooling,
low productivity or even an extensive lag at the start of the next
daylight cycle and in extreme conditions results in freezing with
extensive damage to the culture and the photobioreactor itself and
for the first time allows for cost competitive production of fuels
and chemicals using only sunlight and CO.sub.2 (and minor
quantities of additional nutrients) to produce end products (fuels
and chemicals) using engineered phototrophs using passive heating
and cooling exclusively or essentially exclusively whilst
eliminating external sources of cooling and heating. In certain
embodiments, the invention further separates the end-product
continuously with the production culture being effectively
immobilized in the photobioreactor eliminating costly separation
and handling of relatively low concentration of biomass (e.g. less
than 20 g/L, less than 10 g/L and especially less than 5 g/L).
Rather than exchanging the heat that is absorbed by the culture
with external utilities natural heating and cooling is used to
manage the heat load dynamically through an optimized
photobioreactor assembly that combines a real time adaptive control
system to continuously adjust the inclination of photobioreactor
units based on multi-wall plastic panels that can absorb sunlight
and heat in a controlled manner throughout the day and night to
regulate temperature to maintain optimum productivity. To
accomplish this, the photobioreactor units have engineered surface
coatings including but not limited to a reflective heat shield on
one side. Additional features include a ground surface coating or
material (e.g. sand) that creates diffuse reflection of visible
light while selectively trapping IR as heat to limit heat gain of
the photobioreactor during the day while allowing heat preservation
of the photobioreactor at night by rotating the photobioreactor
panels to face the ground with the reflective shield facing upwards
minimizing radiative losses. These features and additional
embodiments are described in more detail below. It should be
realized that several variations are possible that will become
obvious to these skilled in the art when considering the general
concept of a photobioreactor that manages incident solar radiation
in a passive manner. Non-limiting examples include: pigments
dispersed in plastic to reject UV, fluorescent pigments dispersed
in plastic to up-shift non-usable wavelengths to visible light
(e.g. UV to PAR shift), pigments such as organic solar
concentrators integrated with photovoltaics to generate electricity
with part of the spectrum, IR reflective coatings to reject heat,
and IR absorptive materials as groundcover to serve as passive heat
sink during the day that can be used at night to release heat.
[0161] Selective thin film pV coating to convert portions of the
spectrum that are not efficiently or less efficiently converted by
the phototroph to create a hybrid fuel and electricity
photobioreactor.
[0162] In various aspects, materials such as acrylic used to
assemble the photobioreactor are adapted to have certain
characteristics, which can be exhibited depending on changes
relative to the light intensity. For instance, the material may
turn more translucent or even opaque at a higher light intensity
and reject excess light thereby rejecting excess heat. By contrast,
the material may turn more transparent or even clear at a lower
light intensity. In preferred embodiments, pigments, dyes or thin
films are incorporated into the acrylic. In various embodiments,
pigmented acrylic panels are extruded during the photobioreactor
manufacturing process. Similarly, materials that are adapted to be
sensitive to various other parameters such as temperature
fluctuations, weather patterns, pH changes are within the scope of
this invention.
Photosynthetically Active Radiation
[0163] At maximum photon conversion efficiency approximately 20-25%
of PAR (photosynthetically active radiation) or 10% of the total
sunlight spectrum can be converted to useful chemical energy
depending on the exact composition of the biomass or chemical or
fuel product targeted (Pirt, J. "The thermodynamic efficiency
(quantum demand) and dynamics of photosynthetic growth", New
Phytol. (1986) 102:3-37). Certain phototrophic cultures selectively
reflect some portion of the IR wavelengths (approximately 40% of IR
above 750 nm) (Gitelson, A. et al "Photic volume in
photobioreactors supporting ultrahigh population densities of the
photoautotroph Spirulina platensis" Applied and Environmental
Microbiology (1996) 62:1570-1573). Therefore, the bulk of the
incident sunlight to a photobioreactor is ultimately converted to
heat that has to be removed to maintain optimum culturing
conditions and even avoid total loss of the culture due to
overheating. The opposite effect occurs at night when radiative and
convective losses results in cooling of the culture volume.
Excessive cooling could damage the culture, result in low
productivity or even an extensive lag at the start of the next
daylight cycle and in extreme conditions results in freezing with
extensive damage to the culture and the photobioreactor itself. To
protect against both conditions both heating and cooling is
typically required to control the photobioreactor temperature. The
implications of these heat gains and losses are further detailed in
FIG. 13 which shows net heat absorbed and FIG. 12 which shows heat
flux integration. The magnitude of the heat flows involved
essentially limits the application of current enclosed
photobioreactor technology to very temperate climate zones or small
units that can make effective use of inexpensive waste heat that
may be locally available (e.g. from the power plant or factory
supplying the CO.sub.2). During warmer days the cooling
requirements of a 1000 acre facility would be of similar order to
that of a 600 MW power plant. Clearly, this represents a
significant challenge for large-scale applications in areas that
receive good sunlight but without very significant cooling water
resources. The cost of countering these heat flows using heat
exchange fluids with associated storage, pumps, cooling towers,
heat exchange surfaces and supplemental heat energy is a
significant impediment to the adoption of enclosed photobioreactor
technology for production of large volume fuel and chemical
products.
Photobioreactor Passive Thermal Management
[0164] The passive thermal regulation system can be implemented in
various photobioreactors including flat panels, bubble columns,
tubular reactors and a variety of annular designs aimed at managing
cooling and heating. Many design variations of the photobioreactor
are contemplated within the scope of the invention. Preferably, by
maximizing the surface area of the photobioreactor to capture
light, maximum amount of light is exposed and captured by the
microorganisms to produce products of interest. Provided below is
one such photobioreactor design.
[0165] In various embodiments, the photobioreactor may be
fabricated with inexpensive materials such as acrylic or
polycarbonate. For instance, such materials may be extruded into
multiple parallel channels and welded to a header assembly to form
a single panel. Alternatively, the series of channels and the
header assembly may be co-extruded to form a panel. The walls that
form the channels within the panel provide structural integrity and
support capable of being impact resistant and weather resistant. In
an embodiment, the reactor volume may be about 5 liters. In other
embodiments, the volume of the reactor may be about 15 to about 25
liters or greater.
[0166] In various embodiments, many photobioreactors can be aligned
in fluid communication to make up a solar biofactory. The
photobioreactors may be set at an angle, anywhere from 0 to
90.degree. depending on various conditions. For example during
daytime operations, the photobioreactors are at a 90.degree. angle
primarily for diffuse light capture to reduce excess light and
photoinhibition while reducing the likelihood of subsequent
increase in temperature. For nighttime operations, the
photobioreactors are at a 0.degree. angle to maintain temperature
in the absence of light.
[0167] In certain embodiments, the inclination of the
photobioreactors is adjusted quickly in anticipation of advancing
weather patterns using a real-time local weather tracking control
system. The system can utilize National Weather Service local
forecasts and recent local weather patterns to manage the thermal
loads and photosynthetic requirements of the photobioreactor field,
such as solar irradiation exposure, shading, radiative and
convective losses, and ground reflection. The software control
system responds to local weather changes, for example cloud cover
and rainfall, wind speeds and solar intensity, controlling
photobioreactor inclination accordingly. The Passive Thermal
Management System can shift a solar biofactory plant into
preservation mode when undesirable weather conditions approach,
thereby protecting the culture and reducing internal energy losses.
In preferred embodiments the photobioreactor inclination can have
the ability to move into a horizontal, or close-to-horizontal
position, thus reducing radiative losses and maintaining heat of
the internal thermal mass during cold weather and especially at
night. Heat absorbed and stored in the ground will be contained in
the horizontal, or close-to-horizontal position, and will provide
additional passive energy.
[0168] The controller communicates with a centralized data center
to exchange weather observations and to receive thermal management
instructions. Controller instructions are driven by real-time local
weather. Historic thermal management records will be used to
optimize future calculations.
[0169] Importantly, the intelligent, centralized thermal management
system can reduce or more preferably, eliminate the need for
supplemental heating and/or cooling, thereby significantly reducing
energy consumption. The system combines weather stations and
advanced stepper motor and controls technology in a network-centric
design. It can also communicate with the thermal management data
center where a sophisticated inclination scheme is applied to
tailor heat load and optimize photosynthetic efficiency to the
local weather.
[0170] Additionally, flue gas injection can provide adequate freeze
protection, as well as supplemental heating if required. It is
anticipated that additional supplemental heating provided by the
flue gas will be greater than about 1 W m.sup.-2 but less than
about W m.sup.-2. In any event to maximize the efficiency of the
system and make maximum use of passive thermal management it is
desirable to limit any supplemental heating and cooling to less
than about 10 W m.sup.-2 more preferably less than about 5 W
m.sup.-2 and most preferably less than about 3 W m.sup.-2.
[0171] FIG. 14 is a side view of multiple photobioreactors oriented
North-South. In various embodiments, the photobioreactor comprises
a roof 400 connected to at least a second photobioreactor. In
certain embodiments, the roof diffuses light, illuminating east and
west-facing photobioreactor throughout the day. Additionally, the
roof also creates a greenhouse environment around the reactors to
achieve desired temperatures. In preferred embodiments, a desired
distance between two photobioreactors provides a space or chimneys
350 between photobioreactor with adjustable closures on top and
bottom 500 for passive temperature control. There is an optional
fan 300 configuration to draw air through the chimney for
additional temperature control.
[0172] FIG. 15 is a side view of another embodiment of a
photobioreactor assembly. In this embodiment, at least two side
sheets 700 enclose each photobioreactor in a greenhouse
environment. A gap between each photobioreactor and the side sheets
700 creates a chimney 350 that cools the photobioreactor when the
top/bottom closures are open. Cooling through the chimney can be
passive or driven by fans 300. The photobioreactor sidewalls may be
shaped to increase area to reduce light intensity and increase heat
transfer area. The side sheets can be diffusing to spread
light.
[0173] FIG. 16 (upper part) is a side view of another embodiment of
a photobioreactor assembly. In this embodiment, at least two side
sheets 700 enclose each photobioreactor in a greenhouse
environment. A gap between each photobioreactor and the side sheets
700 creates a chimney 350 that cools the photobioreactor when the
top/bottom closures 500 are open. Cooling through the chimney 350
can be passive or driven by fans 300. The photobioreactor sidewalls
100 can be shaped to increase area to reduce light intensity and
increase heat transfer area FIG. 16 (bottom part). The side sheets
700 can be diffusing to spread light for intensity control. The
side sheets 700 and reactor walls 100 may have surface treatment to
preferably pass/reflect specific wavelengths for intensity and
thermal control. The side sheets 700 and reactor walls 100 can be
manufactured with wavelength specific absorbing dyes. The side
sheets and reactor walls can be shaped to modify surface area to
enhance heat transfer and modify light intensity to the media.
[0174] In the embodiment of FIG. 16, the reactor tilt angle can be
changed for specific seasons, or throughout the day, to improve
control of passive thermal management. A radiation shield can be
applied to the back of the reactor (side sheet or reactor walls)
for thermal management control. Thermal insulation can be applied
to the back of the reactor (side sheet or reactor walls) for
thermal management control. The panel can be rotated to face the
ground at night to minimize radiation losses to the sky. Individual
rows can be rotated to different angles to optimize light intensity
and thermal control. Depending on the season, not all rows need to
be used.
[0175] In certain embodiments, the side sheets and reactor walls
may be made from materials such as acrylic or polycarbonate, with
high optical clarity. In one embodiment, an anti-reflective coating
may be applied to the side sheets and/or reactor walls. Dyes that
are absorptive in IR may also be included in the materials. In
other embodiments, thermochromic dyes may be added that are tuned
to darken once the sheet reaches a certain temperature.
[0176] The diffuser roof may be constructed of acrylic or
polycarbonate with surface treatment or a thin film added to make
it diffusive. In some embodiments, dyes that are absorptive in IR
may be used in constructing the diffuser roof. Some embodiments may
include thermochromic dyes that are tuned to darken once the
diffuser roof element reaches a certain temperature.
[0177] Chimney and Spacing: In some embodiments, the side sheets
are spaced about 1 inch from the reactor walls, but the spacing may
range from about 0.5 to about 2 inches.
[0178] Regarding the adjustable closures (top and bottom), in some
embodiments these may be electrically driven. In other embodiments
these can be driven hydraulically by thermal actuators, and thus be
fully passive.
[0179] Regarding fans, in some embodiments they can be individual
small fans at each reactor, or a larger fan supplying a small group
of reactors. In some embodiments the fans can be powered by
photovoltaic panels.
[0180] Several advantages of the passive thermal regulation include
illumination of the photobioreactor under a novel passive cooling
regime with low capital costs allowing organisms to maintain
maximum productivity in a wide range of environments; use of
multiple photobioreactors in a modular array that can be expanded
without significant modification over land areas from about
100-about 10,000 acres; use of key inputs such as concentrated
CO.sub.2 emanating from critical sectors, e.g., fossil fuel energy
production and cement manufacturing, to directly convert CO.sub.2
emissions to desired output products; ability to located solar
biofactories, e.g., near CO.sub.2 sources or pipelines so that
CO.sub.2 distribution is minimized within the facility with minimal
parasitic loads. Preferred photobioreactor designs will be
optimized to ensure optimum or maximum light capture, mixing,
CO.sub.2 injection and fuel separation while minimizing energy
needs.
[0181] In some embodiments, the photobioreactors are able to
achieve passive thermal control within about 5.degree. C. to about
10.degree. C. of ambient.
[0182] In some embodiments, the photobioreactor comprises at least
two different organisms. A thermotolerant cyanobacteria, plant or
algae or another thermophilic strain can accommodate the
temperature spectrum envisioned for year-round heat integration in
the solar conversion process. Alternatively, a mix of thermophilic
strains and mesophilic strains may also be used.
[0183] In other embodiments, the methods are disclosed to use of
photobioreactors to enable the production of carbon-based products
on non-arable land. The photobioreactor and process design are
optimized to ensure efficient conversion of sunlight to fuel.
Advanced bioprocessing and optics design principles are deployed to
optimize light distribution, mass and heat transfer and mixing to
maximize productivity.
[0184] Preferably, photobioreactor design, prototyping and
manufacturing design meet process requirements with a cost target
of less than about $20/m.sup.2 of land area to allow for a scalable
solution that can be deployed over a large area. Design for
Manufacturability (DFM) concepts are a particular focus to enable
low cost, reliable mass production. Fermentation nutrient control
strategies are developed that are tightly integrated with organism
engineering to ensure maximum yield of end-product on fixed
carbon.
[0185] In various embodiments, the combination of strain
optimization via carbon flux control and the photobioreactor of the
invention has increased ethanol output to daily areal productivity
levels surpassing those projected for mature cellulosic-based
processes (>3.5 g/m.sup.2/day).
[0186] An example pilot plant for the production of diesel fuel may
occupy approximately 1 acre of non-arable land and may produce
about 25 gallons of diesel per day. A diesel process prototype
pilot plant may function in an operational environment as
follows:
[0187] Continuous, controlled chain-length diesel production at an
areal productivity of .about.20 g/m.sup.2/day from a concentrated
industrial CO.sub.2 source with net water use less than about 5
gal/gal fuel;
[0188] >30 days continuous production at >5% photon energy
capture efficiency;
[0189] An integrated production platform that can scale to energy
independence at a cost that is competitive with current fossil
resources without subsidies; and
[0190] Such process offsets the impacts of conventional power
generation by converting waste CO.sub.2 to valuable liquid fuels
through use of flue gas or other concentrated CO.sub.2 sources.
[0191] The highly efficient, integrated process reduces or
eliminates costly and wasteful intermediates and processes
resulting in a very high net positive energy ratio. The passive
thermal management reduces or eliminates the need for external
cooling sources, resulting in little, if any, evaporative water
loss.
[0192] In certain aspects, contamination by competing organisms is
problematic for efficient carbon conversion. At laboratory scale,
the photobioreactor can be sterilized and run in monoculture mode.
Organism engineering strategies or scaled process methods developed
would help to minimize contamination issues at full-scale.
Accordingly, the photobioreactors are sterilizable individually or
in multiple arrays.
[0193] Passive thermal designs that allow tight temperature control
in the largest range of locations, and minimize water and parasitic
power consumption, are important to the success of the technology.
Further refinement of the current passive thermal design concepts
are contemplated by performing stress and life cycle tests under
simulated and real outdoors conditions.
[0194] Preferably, photobioreactors may be located in environments
that experience significant solar radiation and large temperature
transitions.
Nighttime Operations
[0195] Operating at night can significantly increase to potentially
double total productivity. Accordingly, operating a solar
biofactory with artificial light is also contemplated. It is
contemplated that various artificial lighting sources adapted to
the solar biofactory, e.g., fluorescent lamps can be used. Such
solar biofactory can harness power from the grid to drive
biological processes at night.
[0196] In another embodiment, inputs that would not otherwise be
used at night in the absence of artificial light can be used.
Carbon dioxide from a concentrated source can be concentrated and
stored, preferentially as dry ice to allow for cooling as well as
condensation free gas distribution. Power for this can be
preferentially used from the same concentrated source (e.g., a coal
plant) but at non-peak times of night (e.g., 12-4 AM).
[0197] In another embodiment, the cell system can have two
biological elements to it (either in the same cell or in multiple
cells) wherein it is light driven during the day and driven by
stored or otherwise derived inputs at night. For example a cell can
harvest light and covert to an intermediate during the day and the
same or different cell can convert that intermediate to a desirable
end product at night.
Operations During Different Seasons
[0198] FIG. 13 indicates the net heat load of the photobioreactor
as a function of different seasons for both a thermophile operating
at 65.degree. C. and a mesophile operating at 37.degree. C. In the
event of a net negative load supplemental heating must be supplied.
Approximately 10-20 W m.sup.-2 of solar energy can be captured as
chemical energy (fuel) and therefore waste heat at essentially zero
cost would be required to ensure a positive overall energy balance.
Given the amount of waste heat available at a power plant this
would limit the potential size of a facility to less than 1 acre
per MW of operating capacity. In the event that cooling is required
(positive net heat absorbed) this would require significant cooling
water. A 1000 acre facility with a cooling requirement of 100 W
m.sup.-2 requires 400 MW of cooling (similar order as a 600 MW
power plant unit). Such a significant cooling water requirement
would limit the potential application of the photobioreactor
technology at large scale.
[0199] Accordingly, the passive thermal regulation would obviate
the need or at least reduce the dependency on water and minimize
energy input required to circulate or pump water.
[0200] FIG. 12 shows the net heat absorbed into a photobioreactor
over the course of a day. Data is shown for operation during
different times of the year. Average local temperatures for day and
night are shown, indicating the large variation in ambient
conditions in which the reactor is operating. Integrated heat
fluxes are indicated. The size of buffer storage required to absorb
heat during the day that is then used to heat the reactor during
the night is shown for a 1000 acre plant. The excess daily heat
values are negative indicating that even after using the buffer
storage, external heating of about 5 to about 35 W m.sup.-2 is
required depending on the time of year and the operating
temperature. Given typical waste heat available form a power plant
this would limit the size of a facility to approximately 1 acre per
MW power plant capacity, whereas at least 10 acres can be supported
by the typical CO.sub.2 emission the same power plant rating of 1
MW. Optimization of the heat integration significantly minimize
external heating and cooling but requires production strains that
can operate over a wide range of temperatures and a large buffer
storage.
[0201] A modular and mass-manufactured photobioreactor is the
building block of this invention. Preferably, the photobioreactor
is designed for deployment in pre-fabricated assemblies that can be
installed easily with minimal skilled labor. Muli-wall
(multi-skinned) extruded Polycarbonate or Acrylic (PMMA) sheet
provides the substrate for the radiant and insulative barrier or
shield, and reflective thin film technology, as well as the conduit
for the growth of the photosynthetic organisms. More preferably,
the photobioreactor is bonded (multi-stage molding, vibration or
laser welding) to a proprietary header and sparger mechanism. The
entire assembly snaps into a light weight, structural substrate
(e.g. carbon fiber-reinforced or aluminum) and mounts to a
single-axis incliner that houses the stepper motor and controls
mechanism. The single-axis incliner serves as a mechanical
underpinning for multiple photobioreactor assemblies and is adapted
to adjust in real-time to optimize photosynthetic efficiency and
regulate shading to manage heat loads.
[0202] Systematically spaced photobioreactor assemblies combine to
form a geometrically optimized modular field. The sub-field design
geometrically optimizes the layout to maximize the harvested solar
energy and to minimize undesired thermal effects.
Photobioreactor Passive Thermal Management & Weather Tracking
Technology
[0203] The inclination of the photobioreactors is adjusted quickly
in anticipation of advancing weather patterns using a real-time
local weather tracking control system. The system will utilize
National Weather Service local forecasts and recent local weather
patterns to manage the thermal loads and photosynthetic
requirements of the photobioreactor field, such as solar
irradiation exposure, shading, radiative and convective losses, and
ground reflection. The software control system responds to local
weather changes, for example cloud cover and rainfall, wind speeds
and solar intensity, controlling photobioreactor inclination
accordingly. The Passive Thermal Management System can shift the
plant into preservation mode when undesirable weather conditions
approach, thereby protecting the culture and reducing internal
energy losses. Photobioreactor inclination can have the ability to
move into a horizontal, or close-to-horizontal position, thus
reducing radiative losses and maintaining heat of the internal
thermal mass during cold weather and especially at night. Heat
absorbed and stored in the ground can be contained in the
horizontal, or close-to-horizontal position, and can provide
additional passive energy.
[0204] The controller communicates with a centralized data center
to exchange weather observations and to receive thermal management
instructions. Controller instructions are driven by real-time local
weather. Historic thermal management records will be used to
optimize future calculations.
[0205] The intelligent, centralized thermal management system will
reduce or eliminate the need for supplemental heating and/or
cooling, thereby reducing energy consumption. The system combines
weather stations and advanced stepper motor and controls technology
in a network-centric design. It communicates with a thermal
management data center where an inclination scheme is applied to
tailor heat load and optimize photosynthetic efficiency to the
local weather.
[0206] Flue gas injection can provide adequate freeze protection,
as well as supplemental heating if required. It is anticipated that
additional supplemental heating provided by the flue gas will be
greater than about 1 W m.sup.-2 but less than about 10 W m.sup.-2.
In any event to maximize the efficiency of the system and make
maximum use of passive thermal management it is desirable to limit
any supplemental heating and cooling to less than about 10 W
m.sup.-2 more preferably less than about 5 W m.sup.-2 and most
preferably less than about 3 W m.sup.-2.
[0207] FIG. 17 is a graphical representation showing fan power used
to cool an example reactor to a desired operating temperature for
two cases: mesophile (desired T.about.37.degree. C.) and
thermophile (desired T.about.58.degree. C.). The graph shows a
solution for an example tilted greenhouse, tilted at 30 degrees,
south-facing. The computation is for a summer day (.about.mid-July)
at solar noon, assuming average solar insolation. In particular,
the graph shows how much fan power is used in the example
configuration to cool the reactor to a desired operating
temperature for two cases: mesophile (desired T.about.37.degree.
C.) and thermophile (desired T.about.58.degree. C.). The x-axis
shows the difference between desired operating temperature and the
ambient temperature. Note that the mesophile and thermophile cases
essentially collapse in this way of displaying the results. As the
ambient gets cooler, the "difference" gets larger and the amount of
fan power decreases. In this example, the plot indicates that so
long as the ambient temperature is more than 10 degrees C. less
than operating temperature, the system can be run passively.
[0208] Temperature control of the photobioreactors may be obtained
using air, preferably ambient air. In example systems, less than
about 10 W/m2 of power input is used to obtain the cooling (e.g.,
for blowing the air and operating the temperature control system),
and preferably less than about 5 W/m.sup.2. For example, in a
system for which one may need to reject on the order of about 500
W/m.sup.2 of heat at mid-day, the input power is about 1% of the
heat load to be rejected. In one implementation, the power may be
obtained from a pV solar panel located near the reactor. pV panels
typically produce about 130 W/m.sup.2. For instance, if 5 W/m.sup.2
power is provided by the pV panel, the area of the PV panel can be
less than 4% of the ground area. In this implementation, cooling
may be obtained from sources local to the reactor, minimizing
infrastructure. An air-based cooling system provides the advantage
of being more location independent.
Culture Media
[0209] The liquid medium contained within the chamber of the
photobioreactor apparatus during operation may comprise water or a
saline solution (e.g. sea water or brackish water) mixed with
sufficient nutrients to facilitate viability and growth of light
capturing organisms contained therein. Depending on the organism,
it may be advantageous to use liquid medium comprising brackish
water, sea water, or other non-potable water obtained from a
locality in which the photobioreactor apparatus will be operated
and from which the organism contained therein was derived from or
is adapted to.
[0210] Organisms are, in particular, supplemented with one or
nitrogen sources. In one embodiment, the nitrogen source is one or
more of urea, uric acid, ammonia, ammonium salts, nitrate, or one
or more amino acids. In certain embodiments, the nitrogen source is
ammonia. In an alternative embodiment, the nitrogen source is
provided through the gas inlet, which can take the form of one or
more of N.sub.2, NO, NO.sub.x, among others.
[0211] Particular liquid medium compositions, nutrients, etc.
required or suitable for use in maintaining a growing algae or
other light capturing organism culture (e.g., liquid BG-11 medium,
A+) are generally well known in the art. Potentially, a wide
variety of liquid media can be utilized in various forms for
various embodiments of the solar biofactory, as would be understood
by those of ordinary skill in the art. Appropriate liquid medium
components and nutrients are, for example, discussed in detail in:
Rogers, L J. and Gallon J. R. "Biochemistry of the Algae and
Cyanobacteria," Clarendon Press Oxford, 1988; Burlew, John S.
"Algal Culture: From Laboratory to Pilot Plant." Carnegie
Institution of Washington Publication 600. Washington, D.C., 1961
(hereinafter "Burlew 1961"); and Round, F. E. The Biology of the
Algae. St Martin's Press, New York, 1965; Golden S S et al. (1987)
"Genetic engineering of the Cyanobacteria chromosome" Methods
Enzymol 153:215-231 and in S. S. Golden and L. A. Sherman, J.
Bacteriology 158:36 (1984), incorporated herein by reference).
[0212] Enhanced media composition is described in Examples 3, 4 and
5. In various embodiments, the invention provides a media
composition as set forth in Example 4. Additional embodiments
include increased amount N, P and/or Fe in the media for enhanced
growth of light capturing organisms.
[0213] During operation of the photobioreactor apparatus, the panel
100 is filled with enough liquid medium so as to permit circulation
of the liquid medium (e.g., in one direction) during operation. In
some embodiments, at least some portion of the volume of the panel
is left unfilled with liquid medium.
[0214] It is contemplated that certain conditions, such as low pH,
high EtOH or organic acids in medium, are likely to render the
photobioreactor environment harsh for culturing organisms
pH of Media
[0215] The pH of the liquid medium can be monitored with a pH
probe. pH of the medium can be controlled at desirable levels for a
particular organism by adjusting CO.sub.2 or chemicals, such as,
ammonia, tris, urea, HEPES, hydrochloric acid and sodium hydroxide.
Preferably, the addition of acidic CO.sub.2 to the photobioreactor
is controlled to match the production of products to maintain a
stable pH under balanced growth or production conditions. The
choice of nitrogen source in the media is important as a means to
provide for pH control. Additionally, the amount of evaporation and
appropriate new fluid addition provides for another means to
provide pH control.
[0216] In general, chemicals for nutrient level maintenance and pH
control and other factors may be added automatically directly into
the liquid phase within the photobioreactor apparatus, if desired.
The computer control system can also be configured to control the
liquid phase temperature in the photobioreactor apparatus by either
or both of controlling a heat exchange system or other temperature
control system within or connected with the photobioreactor
apparatus, or, in alternative embodiments removing liquid medium
from the photobioreactor apparatus and passing through a heat
exchanger in, for example, a temperature controlled water bath or a
water basin.
Optical Density
[0217] The optical density of the liquid medium can be measured at
certain wavelengths appropriate for the given organism. These
wavelengths, which are assumed to be linearly related to biomass
concentration, are generally well known in the art. Cell density
can be calculated using spectrophotometer measurements (see,
Hiroyasu et al., 1998). Such readings can be used to monitor
organism concentration to ensure proper cell activity as well as
potential signs of challenges to the desired cell population, such
as non-optimal media conditions, altered pH, high concentrations of
toxic substances, as well as the presence of exogenous
organisms.
Operating Conditions and Cell Population Control
[0218] In various embodiments, engineered organisms are cultured in
the solar biofactory, systems and methods. In such embodiments, in
order to keep the concentration of organisms within the
photobioreactor apparatus within a range suitable for long term
operation and productivity, a portion of the organism may be
harvested and the photobioreactor apparatus may be supplemented
with fresh, organism-free medium (or previously harvested medium
having a low concentration) to adjust concentration of organism
within the photobioreactor apparatus. Concentration can increase
exponentially with time (the log growth phase) up to a certain
point, after which the concentration will tend to level off and
proliferation and growth will decrease. In certain embodiments, the
concentration within the photobioreactor apparatus is maintained
within an operating range that is near the upper end of the
concentration in which the organism is still in the log growth
regime. As would be understood by those by those skilled in the
art, the particular growth curve characterizing a given species of
organism will be different from species to species and, even within
a given species of organism, may be different depending on
differences in operating and environmental factors, as well as with
any genetic modifications that may have been made through the
insertion of exogenous nucleic acids or through an evolutionary
process (e.g., liquid medium composition, growth temperature, gas
feed composition, etc.).
[0219] Harvesting the organism, adjusting concentration, and
introducing additional liquid medium can be facilitated via inlet
means and outlet means as described earlier. Control of the
concentration of organism is important both from the standpoint of
maintaining a desirable level of growth and proliferation as well
as providing desirable levels of photomodulation within the
conduits. The organism can be harvested periodically or
continuously to maintain the desired concentration range during
operation.
[0220] According to one method, harvesting takes place in a
semi-continuous fashion, meaning that only a portion of the
organism is removed from the photobioreactor apparatus at a given
time. To harvest the organism, media containing the organism is
removed from the photobioreactor and allowed to settle such that
the density of the organism will allow it to settle at the bottom
of the chamber, wherein the organism can be readily removed.
Additionally, flocculants, chemicals that cause the organism to
clump and settle, may be used, in certain embodiments, to assist in
the harvest. Some useful flocculants include clay (e.g. with
particle size <2 .mu.m), aluminum sulfate or polyacrylamide.
After settling, organism may be withdrawn through the bottom of the
channels or through various outlets. The water and nutrients
contained in the harvested cells can be extracted and recycled to
the liquid medium supply of the photobioreactor apparatus. This
step may reduce waste and water use of the photobioreactor
apparatus and the overall system, thereby lowering environmental
impact and operational cost. In certain cases cells can be
separated from the medium using filtration (e.g. micro- or
ultrafiltration using polymeric, ceramic or metal membranes),
centrifugation (e.g. decanter or high speed disc centrifuge) or
flotation before harvesting. Removed cells may then be processed by
any means known in the art, such as extraction of the cell membrane
for the production of biodiesel, saccharification of polymeric
moieties for the production of ethanol, and burning of the biomass
for the generation of energy, among others.
[0221] In some embodiments, cell concentration is kept constant by
maintaining the photobioreactor apparatus as a chemostat wherein
the fluid is constantly flowed and retaining within a closed loop.
Through this method, which is well known to those skilled in the
art, dead or dying cells can be readily removed as processed by any
means known in the art.
[0222] In certain embodiments, a solar biofactory is adapted to be
used with sensors, controllers, programmable logic controllers and
a control system, networked together for the photobioreactor
apparatus. Such control systems are well-known in the art and can
be modified or adapted to accordingly by a skilled artisan.
[0223] The solar biofactory systems and methods can be configured
with various probes and monitors for measuring the pressure of the
feed gas fed into the spargers (e.g., one or more pressure
monitors), as well as one or more flow meters for measuring gas
flow rates, and one or more flow meters for measuring bulk liquid
flow rate within the photobioreactor apparatus. Gas and liquid flow
rates can be controlled, at least in part, to facilitate desired or
optimal levels of photomodulation by inducing desirable liquid flow
patterns within the photobioreactor apparatus. Another control
factor dictating the overall flow of gas fed to photobioreactor
apparatus can be the desired level of removal of pollutants such as
CO.sub.2 and/or NO.sub.x by the photobioreactor apparatus. For
example, the system includes appropriate gas composition monitoring
devices for monitoring the concentration of various gases, such as
CO.sub.2, NO.sub.x, O.sub.2, etc. in the feed gas and treated gas.
Gas inlet flow rate and/or distribution to the spargers can be
adjusted and controlled to yield a desirable level of pollutant
removal by the solar biofactory system.
Organisms
[0224] Various embodiments of solar biofactory systems and methods
described herein enable conversion of light, water and carbon
dioxide into biomass, biofuels, chemical intermediates, chemicals,
pharmaceutical agents and biologically produced chemicals in any
light capturing organisms. Light capturing organisms include
autotrophs, phototrophs, heterotrophs, and organisms engineered to
downregulate or knock out expression of an endogenous gene, express
one or more heterologous genes, overexpress one or more endogenous
genes related to photosynthesis or its central metabolism.
[0225] Plants include but are not limited to the following genera:
Arabidopsis, Beta, Glycine, Jatropha, Miscanthus, Panicum,
Phalaris, Populus, Saccharum, Salix Simmondsia, and Zea. Algae and
cyanobacteria include but are not limited to the following genera:
Acanthoceras, Acanthococcus, Achnanthes, Achnanthidium,
Actinastrum, Actinochloris, Actinocyclus, Actinotaenium,
Amphichrysis, Amphidinium, Amphikrikos, Amphipleura, Amphiprora,
Amphithrix, Amphora, Anabaena, Anabaenopsis, Aneumastus,
Ankistrodesmus, Ankyra, Anomoeoneis, Apatococcus, Aphanizomenon,
Aphanocapsa, Aphanochaete, Aphanothece, Apiocystis, Apistonema,
Arthrodesmus, Artherospira, Ascochloris, Asterionella,
Asterococcus, Audouinella, Aulacoseira, Bacillaria, Balbiania,
Bambusina, Bangia, Basichlamys, Batrachospermum, Binuclearia,
Bitrichia, Blidingia, Botrdiopsis, Botrydium, Botryococcus,
Botryosphaerella, Brachiomonas, Brachysira, Brachytrichia,
Brebissonia, Bulbochaete, Bumilleria, Bumilleriopsis, Caloneis,
Calothrix, Campylodiscus, Capsosiphon, Carteria, Catena, Cavinula,
Centritractus, Centronella, Ceratium, Chaetoceros, Chaetochloris,
Chaetomorpha, Chaetonella, Chaetonema, Chaetopeltis, Chaetophora,
Chaetosphaeridium, Chamaesiphon, Chara, Characiochloris,
Characiopsis, Characium, Charales, Chilomonas, Chlainomonas,
Chlamydoblepharis, Chlamydocapsa, Chlamydomonas, Chlamydomonopsis,
Chlamydomyxa, Chlamydonephris, Chlorangiella, Chlorangiopsis,
Chlorella, Chlorobotrys, Chlorobrachis, Chlorochytrium,
Chlorococcum, Chlorogloea, Chlorogonium, Chlorolobion, Chloromonas,
Chlorophysema, Chlorophyta, Chlorosaccus, Chlorosarcina,
Choricystis, Chromophyton, Chromulina, Chroococcidiopsis,
Chroococcus, Chroodactylon, Chroomonas, Chroothece, Chrysamoeba,
Chrysapsis, Chrysidiastrum, Chrysocapsa, Chrysocapsella,
Chrysochaete, Chrysochromulina, Chrysococcus, Chrysocrinus,
Chrysolepidomonas, Chrysolykos, Chrysonebula, Chrysophyta,
Chrysopyxis, Chrysosaccus, Chrysophaerella, Chrysostephanosphaera,
Clodophora, Clastidium, Closteriopsis, Closterium, Coccomyxa,
Cocconeis, Coelastrella, Coelastrum, Coelosphaerium, Coenochloris,
Coenococcus, Coenocystis, Colacium, Coleochaete, Collodictyon,
Compsogonopsis, Compsopogon, Conjugatophyta, Conochaete,
Coronastrum, Cosmarium, Cosmioneis, Cosmocladium, Crateriportula,
Craticula, Crinalium, Crucigenia, Crucigeniella, Cryptoaulax,
Cryptomonas, Cryptophyta, Ctenophora, Cyanodictyon, Cyanonephron,
Cyanophora, Cyanophyta, Cyanothece, Cyanothomonas, Cyclonexis,
Cyclostephanos, Cyclotella, Cylindrocapsa, Cylindrocystis,
Cylindrospermum, Cylindrotheca, Cymatopleura, Cymbella,
Cymbellonitzschia, Cystodinium Dactylococcopsis, Debarya,
Denticula, Dermatochrysis, Dermocarpa, Dermocarpella, Desmatractum,
Desmidium, Desmococcus, Desmonema, Desmosiphon, Diacanthos,
Diacronema, Diadesmis, Diatoma, Diatomella, Dicellula, Dichothrix,
Dichotomococcus, Dicranochaete, Dictyochloris, Dictyococcus,
Dictyosphaerium, Didymocystis, Didymogenes, Didymosphenia,
Dilabifilum, Dimorphococcus, Dinobryon, Dinococcus, Diplochloris,
Diploneis, Diplostauron, Distrionella, Docidium, Draparnaldia,
Dunaliella, Dysmorphococcus, Ecballocystis, Elakatothrix,
Ellerbeckia, Encyonema, Enteromorpha, Entocladia, Entomoneis,
Entophysalis, Epichrysis, Epipyxis, Epithemia, Eremosphaera,
Euastropsis, Euastrum, Eucapsis, Eucocconeis, Eudorina, Euglena,
Euglenophyta, Eunotia, Eustigmatophyta, Eutreptia, Fallacia,
Fischerella, Fragilaria, Fragilariforma, Franceia, Frustulia,
Curcilla, Geminella, Genicularia, Glaucocystis, Glaucophyta,
Glenodiniopsis, Glenodinium, Gloeocapsa, Gloeochaete, Gloeochrysis,
Gloeococcus, Gloeocystis, Gloeodendron, Gloeomonas, Gloeoplax,
Gloeothece, Gloeotila, Gloeotrichia, Gloiodictyon, Golenkinia,
Golenkiniopsis, Gomontia, Gomphocymbella, Gomphonema,
Gomphosphaeria, Gonatozygon, Gongrosia, Gongrosira, Goniochloris,
Gonium, Gonyostomum, Granulochloris, Granulocystopsis, Groenbladia,
Gymnodinium, Gymnozyga, Gyrosigma, Haematococcus, Hafniomonas,
Hallassia, Hammatoidea, Hannaea, Hantzschia, Hapalosiphon,
Haplotaenium, Haptophyta, Haslea, Hemidinium, Hemitoma,
Heribaudiella, Heteromastix, Heterothrix, Hibberdia, Hildenbrandia,
Hillea, Holopedium, Homoeothrix, Hormanthonema, Hormotila,
Hyalobrachion, Hyalocardium, Hyalodiscus, Hyalogonium, Hyalotheca,
Hydrianum, Hydrococcus, Hydrocoleum, Hydrocoryne, Hydrodictyon,
Hydrosera, Hydrurus, Hyella, Hymenomonas, Isthmochloron,
Johannesbaptistia, Juranyiella, Karayevia, Kathablepharis,
Katodinium, Kephyrion, Keratococcus, Kirchneriella, Klebsormidium,
Kolbesia, Koliella, Komarekia, Korshikoviella, Kraskella,
Lagerheimia, Lagynion, Lamprothamnium, Lemanea, Lepocinclis,
Leptosira, Lobococcus, Lobocystis, Lobomonas, Luticola, Lyngbya,
Malleochloris, Mallomonas, Mantoniella, Marssoniella, Martyana,
Mastigocoleus, Gastogloia, Melosira, Merismopedia, Mesostigma,
Mesotaenium, Micractinium, Micrasterias, Microchaete, Microcoleus,
Microcystis, Microglena, Micromonas, Microspora, Microthamnion,
Mischococcus, Monochrysis, Monodus, Monomastix, Monoraphidium,
Monostroma, Mougeotia, Mougeotiopsis, Myochloris, Myromecia,
Myxosarcina, Naegeliella, Nannochloris, Nautococcus, Navicula,
Neglectella, Neidium, Nephroclamys, Nephrocytium, Nephrodiella,
Nephroselmis, Netrium, Nitella, Nitellopsis, Nitzschia, Nodularia,
Nostoc, Ochromonas, Oedogonium, Oligochaetophora, Onychonema,
Oocardium, Oocystis, Opephora, Ophiocytium, Orthoseira,
Oscillatoria, Oxyneis, Pachycladella, Palmella, Palmodictyon,
Pnadorina, Pannus, Paralia, Pascherina, Paulschulzia, Pediastrum,
Pedinella, Pedinomonas, Pedinopera, Pelagodictyon, Penium,
Peranema, Peridiniopsis, Peridinium, Peronia, Petroneis, Phacotus,
Phacus, Phaeaster, Phaeodermatium, Phaeophyta, Phaeosphaera,
Phaeothamnion, Phormidium, Phycopeltis, Phyllariochloris,
Phyllocardium, Phyllomitas, Pinnularia, Pitophora, Placoneis,
Planctonema, Planktosphaeria, Planothidium, Plectonema, Pleodorina,
Pleurastrum, Pleurocapsa, Pleurocladia, Pleurodiscus, Pleurosigma,
Pleurosira, Pleurotaenium, Pocillomonas, Podohedra,
Polyblepharides, Polychaetophora, Polyedriella, Polyedriopsis,
Polygoniochloris, Polyepidomonas, Polytaenia, Polytoma,
Polytomella, Porphyridium, Posteriochromonas, Prasinochloris,
Prasinocladus, Prasinophyta, Prasiola, Prochlorphyta,
Prochlorothrix, Protoderma, Protosiphon, Provasoliella, Prymnesium,
Psammodictyon, Psammothidium, Pseudanabaena, Pseudenoclonium,
Psuedocarteria, Pseudochate, Pseudocharacium, Pseudococcomyxa,
Pseudodictyosphaerium, Pseudokephyrion, Pseudoncobyrsa,
Pseudoquadrigula, Pseudosphaerocystis, Pseudostaurastrum,
Pseudostaurosira, Pseudotetrastrum, Pteromonas, Punctastruata,
Pyramichlamys, Pyramimonas, Pyrrophyta, Quadrichloris,
Quadricoccus, Quadrigula, Radiococcus, Radiofilum, Raphidiopsis,
Raphidocelis, Raphidonema, Raphidophyta, Peimeria, Rhabdoderma,
Rhabdomonas, Rhizoclonium, Rhodomonas, Rhodophyta, Rhoicosphenia,
Rhopalodia, Rivularia, Rosenvingiella, Rossithidium, Roya,
Scenedesmus, Scherffelia, Schizochlamydella, Schizochlamys,
Schizomeris, Schizothrix, Schroederia, Scolioneis, Scotiella,
Scotiellopsis, Scourfieldia, Scytonema, Selenastrum, Selenochloris,
Sellaphora, Semiorbis, Siderocelis, Diderocystopsis, Dimonsenia,
Siphononema, Sirocladium, Sirogonium, Skeletonema, Sorastrum,
Spermatozopsis, Sphaerellocystis, Sphaerellopsis, Sphaerodinium,
Sphaeroplea, Sphaerozosma, Spiniferomonas, Spirogyra, Spirotaenia,
Spirulina, Spondylomorum, Spondylosium, Sporotetras, Spumella,
Staurastrum, Stauerodesmus, Stauroneis, Staurosira, Staurosirella,
Stenopterobia, Stephanocostis, Stephanodiscus, Stephanoporos,
Stephanosphaera, Stichococcus, Stichogloea, Stigeoclonium,
Stigonema, Stipitococcus, Stokesiella, Strombomonas,
Stylochrysalis, Stylodinium, Styloyxis, Stylosphaeridium,
Surirella, Sykidion, Symploca, Synechococcus, Synechocystis,
Synedra, Synochromonas, Synura, Tabellaria, Tabularia, Teilingia,
Temnogametum, Tetmemorus, Tetrachlorella, Tetracyclus, Tetradesmus,
Tetraedriella, Tetraedron, Tetraselmis, Tetraspora, Tetrastrum,
Thalassiosira, Thamniochaete, Thorakochloris, Thorea, Tolypella,
Tolypothrix, Trachelomonas, Trachydiscus, Trebouxia, Trentepholia,
Treubaria, Tribonema, Trichodesmium, Trichodiscus, Trochiscia,
Tryblionella, Ulothrix, Uroglena, Uronema, Urosolenia, Urospora,
Uva, Vacuolaria, Vaucheria, Volvox, Volvulina, Westella,
Woloszynskia, Xanthidium, Xanthophyta, Xenococcus, Zygnema,
Zygnemopsis, and Zygonium.
[0226] Green non-sulfur bacteria include but are not limited to the
following genera:
[0227] Chloroflexus, Chloronema, Oscillochloris, Heliothrix,
Herpetosiphon, Roseiflexus, and Thermomicrobium.
[0228] Green sulfur bacteria include but are not limited to the
following genera: Chlorobium, Clathrochloris, and
Prosthecochloris,
[0229] Purple sulfur bacteria include but are not limited to the
following genera: Allochromatium, Chromatium, Halochromatium,
Isochromatium, Marichromatium, Rhodovulum, Thermochromatium,
Thiocapsa, Thiorhodococcus, and Thiocystis,
[0230] Purple non-sulfur bacteria include but are not limited to
the following genera: Phaeospirillum, Rhodobaca, Rhodobacter,
Rhodomicrobium, Rhodopila, Rhodopseudomonas, Rhodothalassium,
Rhodospirillum, Rodovibrio, and Roseospira.
[0231] In various embodiments, engineered organism are modified to
comprise an engineered nucleic acid that encodes a heterologous
protein that is expressed by the engineered cell, causes
overexpression of an endogenous protein within the engineered cell,
causes downregulation of an endogenous protein in the engineered
cell, or causes a gene knock-out in the engineered cell. Selection,
modification and use of such organisms in the photobioreactor
apparatus and systems that can be optimized for growth at
particular operating conditions expected within the photobioreactor
apparatus are described in more detail in commonly-owned U.S.
Provisional Patent Application Ser. Nos. 60/971,224; 60/987,046;
60/987,058; 60/987,056; 60/987,055; 60/987,054; 60/987,053;
60/987,052; 60/987,051; 60/987,050; 60/987,049, which are
incorporated herein by reference.
[0232] In certain embodiments, the photoautotrophic organism can be
transformed with exogenous DNA, engineered nucleic acids, organisms
engineered to down-regulate or knock out expression of an
endogenous gene, express heterologous gene, overexpress an
endogenous gene related to photosynthesis. In various embodiments,
engineered light capturing organisms include: Arabidopsis thaliana,
Panicum virgatum, Miscanthus giganteus, and Zea mays (plants),
Botryococcus braunii, Chlamydomonas reinhardtii and Dunaliela
salina (algae), Synechococcus sp PCC 7002, Synechococcus sp. PCC
7942, Synechocystis sp. PCC 6803, and Thermosynechococcus elongatus
BP-1 (cyanobacteria), Chlorobium tepidum (green sulfur bacteria),
Chloroflexus auranticus (green non-sulfur bacteria), Chromatium
tepidum and Chromatium vinosum (purple sulfur bacteria),
Rhodospirillum rubrum, Rhodobacter capsulatus, and Rhodopseudomonas
palusris (purple non-sulfur bacteria).
[0233] Still other organisms, e.g., heterotrophs can be engineered
to confer photoautotrophic properties. The resultant engineered
organism will convert light, water and carbon dioxide into biomass
and carbon-based products of interest. Such organisms include,
without limitation, Acetobacter aceti, Acetobacter sp., Bacillus
subtilis, Bacillus sp., Clostridium ljungdahlii, Clostridium
thermocellum, Clostridium sp., Escherichia coli, Escherichia sp.,
Penicillium chrysogenum, Penicillium sp., Pichia pastoris, Pichia
sp., Saccharomyces cerevisiae, Saccharomyces sp.,
Schizosaccharomyces pombe, Schizosaccharomyces sp., Pseudomonas
fluorescens, Pseudomonas sp., Salmonella typhimurium, Salmonella
sp., Thermus thermophilus, Thermus sp., Zymomonas mobilis and
Zymomonas sp.
Separation of Products and Removal of Products from the Gas
Phase
[0234] The solar biofactory is aimed at enabling highly productive
organisms to be maximally productive. A critical element of this is
the ability to capture what is being made. In addition to biomass,
numerous biofuels, biochemicals, drugs, and other products can be
produced. Several of these products, including but not limited to
ethanol, butanol, butyric acid, propane, propanol, and methanol,
have sufficiently low boiling points that they will likely be
present in the gas stream given operations at .about.50.degree. C.
As such, the gas stream represents a simplified way for these
products to be collected. Independent of the presence or absence of
a recycle, the gas stream will contain processes effluent gas from
its source, waste gas from the organisms (e.g., oxygen), and
potentially gaseous product. These components can be separated out
by methods well known in the art.
[0235] Compounds such as ethanol can be captured by cooling the gas
and collecting at the appropriate point for ethanol, similar to as
in fractional distillation. Gases such as oxygen can be captured
with metals and through pressure swing adsorption operations.
[0236] The removal of such compounds can occur independent of which
apparatus is used. Any recycle that would occur would be after the
removal of desired compounds. The removed compounds can either be
sufficiently pure or be subject to additional purification prior to
commercial use.
[0237] Solar heat results in EtOH enrichment into purge air, which
is suited for capture in the photobioreactor, for example in the
liquid return manifold 140. Purification of ethanol based on
distillation and/or condensation scheme developed in ASPEN and
laboratory measurements.
[0238] Recovery energy consumption is expected to be comparable to
best in class conventional EtOH recovery.
[0239] Of particular note, separation of biofuels from their
production vectors as in traditional plants represents a very
significant source of capital expenditure. By incorporating it
fundamentally into the process, the solar biofactory can
significantly reduce operating expenditures.
Removal of Product from the Liquid Phase
[0240] Products not found in the gas phase will be found intermixed
in the liquid phase. The product itself may be a solid (e.g., heavy
hydrocarbons) or liquid (e.g., mid range hydrocarbons), but can be
separated from the liquid media. Since strain development would
result in a secreted product, a simple gravity decanting at
photobioreactor is contemplated. Crude decant stream is pumped to
central plant for solids polishing and dewatering to final product
specifications.
[0241] In removing the product of interest from the liquid phase, a
certain volume of cell and media mixture is removed, which is then
put through a separation process to isolate the desired product.
This is performed independent of the product. Different products
with different properties are then separated by means well known in
the art. Solids can be separated by settling, centrifugation and
filtration. Hydrophilic or otherwise water soluble substances are
collected through techniques including but not limited to
distillation. Hydrophobic substances including but not limited to
alkanes, alkenes, alkynes, fatty alcohols, fatty aldehydes, fatty
acids, fatty esters, ethyl esters and other hydrophobic or organic
materials can be separated through a biphasic system. Vapor-phase
extraction of water soluble substances for recovery of organic
substances from an aqueous medium is also contemplated.
[0242] In certain embodiments, light capturing organisms are grown
in a photobioreactor apparatus with a continuous supply of inputs
via inlet means and continuous removal of product via an outlet
means. Batch, fed-batch, and continuous fermentations are common
and well known in the art and examples can be found in Thomas D.
Brock in Biotechnology: A Textbook of Industrial Microbiology,
Second Edition (1989) Sinauer Associates, Inc., Sunderland, Mass.,
or Deshpande, Mukund V., Appl. Biochem. Biotechnol (1992),
36:227.
[0243] Using embodiments of the solar biofactory, system and
methods, the product of interest can be secreted, released, removed
or extracted from the cells in the solar biofactory. In one
embodiment, the product is excreted, secreted or released from the
organism into the media for extraction as described above. In
embodiments where the final product is released from an organism, a
continuous process can be employed, e.g., fed-batch, and continuous
fermentations. In this approach, a photobioreactor apparatus with
organisms producing desirable products can be assembled in multiple
ways.
[0244] In one embodiment, the reactor is operated in bulk
continuously, with a portion of media removed and held in a less
agitated environment such that an aqueous product will
self-separate out with the product removed and the remainder
returned to the fermentation chamber. In another embodiment, the
reactor is operated in fed-batch.
[0245] In embodiments where the product does not separate into an
aqueous phase, media is removed and appropriate separation
techniques (e.g., chromatography, distillation, etc.) are employed.
Separation by distillation may be advantageous in low ambient
temperatures.
[0246] To process biomass, the optimal biomass density is measured
at an optical density (OD.sub.730) and subjected to process streams
resulting from, for example, the primary fractionation or
saccharification of lignocellulosic biomass, which can be typically
highly complex slurries that are difficult to process and separate.
Such slurries often contain substantial levels (10-20% w/w) of
insoluble lignocellulosic solids as well as high concentrations of
soluble biomass sugars (>10-20%) along with a variety of other
soluble components (organic and inorganic acids, aldehydes,
phenolics, etc.) that are typically present at lower levels. Known
separation process technologies such as solid/liquid (S/L)
separations of such slurries, are used for bulk or primary S/L
separations, as well as for secondary/polishing S/L separations.
Other separation techniques are used to recover products and
facilitate bio/catalysis, e.g., reactive separations schemes that
will enable in situ combination with bio/catalysis steps,
techniques to remove smaller suspended particles or high molecular
weight compounds from partially clarified liquors and use of
membrane separation systems for separation and recovery of specific
components (e.g., specific sugars or organic acids) or classes of
components (e.g., mixed sugars or mixed phenolics) from clarified
biomass hydrolyzate liquors.
[0247] Alternatively, the product is not secreted by the organism.
In this embodiment, fed-batch or batch fermentation approach is
employed. In such cases, cells are grown under continued exposure
to inputs (light, water, and carbon dioxide) as specified above
until the reaction chamber is saturated with cells and product. A
significant portion to the entirety of the culture is removed, the
cells are lysed, and the products are isolated by appropriate
separation techniques (e.g., chromatography, distillation,
filtration, centrifugation, ultrafiltration, microfiltration, etc.
or combinations thereof). The obtained biomass might be subjected
to a washing step, the liquid being added to the separated
fermentation supernatant.
[0248] Desired products such as small molecules drugs and
biological can be separated using known separation techniques.
Exemplary separation techniques include gel electrophoresis,
including but not limited to isoelectric focusing and capillary
electrophoresis; dielectrophoresis; sorting, including but not
limited to fluorescence-activated sorting techniques;
chromatography, including but not limited to HPLC, FPLC, size
exclusion (gel filtration) chromatography, affinity chromatography,
ion exchange chromatography, hydrophobic interaction
chromatography, immunoaffinity chromatography, and reverse phase
chromatography; ligand-receptor binding, such as biotin-avidin,
biotin-streptavidin, maltose-maltose binding protein (MBP),
calcium-calcium binding peptide; aptamer-target binding; zip code
hybridization; and the like. Detailed discussion of separation
techniques can be found in, among other places, Rapley; Sambrook et
al.; Sambrook and Russell; Ausbel et al.; Molecular Probes
Handbook; Pierce Applications Handbook; Capillary Electrophoresis:
Theory and Practice, P. Grossman and J. Colburn, eds., Academic
Press (1992); Wenz and Schroth, PCT International Publication No.
WO 01/92579; M. Ladisch, Bioseparations Engineering: Principles,
Practice, and Economics, John Wiley & Sons (2001); and Liebler,
Introduction to Proteomics, Humana Press (2002).
[0249] One exemplary separation process provided for water
insoluble products herein is a two phase (bi-phasic) separation
process. This process involves fermenting the genetically
engineered production hosts under conditions sufficient to produce
a fatty acid derivative or other hydrophobic compound, allowing the
derivative to collect in an organic phase and separating the
organic phase from the aqueous fermentation broth. This method can
be practiced in both a batch and continuous fermentation
setting.
[0250] Bi-phasic separation uses the relative immisciblity of fatty
acid derivatives to facilitate separation. Immiscible refers to the
relative inability of a compound to dissolve in water and is
defined by the compounds partition coefficient. The partition
coefficient, P, is defined as the equilibrium concentration of
compound in an organic phase (in a bi-phasic system the organic
phase is usually the phase formed by the fatty acid derivative
during the production process, however, in some examples an organic
phase can be provided (such as a layer of octane to facilitate
product separation) divided by the concentration at equilibrium in
an aqueous phase (i.e. fermentation broth). When describing a two
phase system the P is usually discussed in terms of log P. A
compound with a log P of 10 would partition 10:1 to the organic
phase, while a compound of log P of 0.1 would partition 10:1 to the
aqueous phase. One or ordinary skill in the art will appreciate
that by choosing a fermentation broth and the organic phase such
that the fatty acid derivative being produced has a high log P
value, the fatty acid derivative will separate into the organic
phase, even at very low concentrations in the fermentation
vessel.
[0251] There are essentially three types of hydrocarbon products:
(1) aromatic hydrocarbon products, which have at least one aromatic
ring; (2) saturated hydrocarbon products, which lack double, triple
or aromatic bonds; and (3) unsaturated hydrocarbon products, which
have one or more double or triple bonds between carbon atoms. A
"hydrocarbon product" may be further defined as a chemical compound
that consists of C, H, and optionally O, with a carbon backbone and
atoms of hydrogen and oxygen, attached to it. Oxygen may be singly
or double bonded to the backbone and may be bound by hydrogen. In
the case of ethers and esters, oxygen may be incorporated into the
backbone, and linked by two single bonds, to carbon chains. A
single carbon atom may be attached to one or more oxygen atoms.
Hydrocarbon products may also include the above compounds attached
to biological agents including proteins, coenzyme A and acetyl
coenzyme A. Hydrocarbon products include, but are not limited to,
hydrocarbons, alcohols, aldehydes, carboxylic acids, ethers,
esters, carotenoids, and ketones.
[0252] Hydrocarbon products also include alkanes, alkenes, alkynes,
dienes, isoprenes, alcohols, aldehydes, carboxylic acids,
surfactants, wax esters, polymeric chemicals [polyphthalate
carbonate (PPC), polyester carbonate (PEC), polyethylene,
polypropylene, polystyrene, polyhydroxyalkanoates (PHAs),
poly-beta-hydroxybutryate (PHB), polylactide (PLA), and
polycaprolactone (PCL)], monomeric chemicals [propylene glycol,
ethylene glycol, and 1,3-propanediol, ethylene, acetic acid,
butyric acid, 3-hydroxypropanoic acid (3-HPA), acrylic acid, and
malonic acid], and combinations thereof. In some embodiments, the
hydrocarbon products are alkanes, alcohols, surfactants, wax esters
and combinations thereof. Other hydrocarbon products include fatty
acids, acetyl-CoA bound hydrocarbons, acetyl-CoA bound
carbohydrates, and polyketide intermediates.
[0253] Using the solar biofactory system and methods, light
harvesting organisms can be grown to produce hydrocarbon products
and intermediates over a large range of sizes. Specific alkanes
that can be produced include, for example, ethane, propane, butane,
pentane, hexane, heptane, octane, nonane, decane, undecane,
dodecane, tridecane, tetradecane, pentadecane, hexadecane,
heptadecane, and octadecane. In various embodiments, the
hydrocarbon products are octane, decane, dodecane, tetradecane, and
hexadecane. Hydrocarbon precursors such as alcohols that can be
produced include, for example, ethanol, propanol, butanol,
pentanol, hexanol, heptanol, octanol, nonanol, decanol, undecanol,
dodecanol, tridecanol, tetradecanol, pentadecanol, hexadecanol,
heptadecanol, and octadecanol. In additional embodiments, the
alcohol is selected from ethanol, propanol, butanol, pentanol,
hexanol, heptanol, octanol, nonanol, and decanol.
[0254] Hydrocarbons can additionally be produced as biofuels. A
biofuel is any fuel that derives from a biological source--recently
living organisms or their metabolic byproducts. A biofuel may be
further defined as a fuel derived from a metabolic product of a
living organism. In various embodiments, produced biofuels include,
but are not limited to, biodiesel, biocrude, ethanol, petroleum,
butanol, and propane.
[0255] Surfactants are used in a variety of products, including
detergents and cleaners, and are also used as auxiliaries for
textiles, leather and paper, in chemical processes, in cosmetics
and pharmaceuticals, in the food industry and in agriculture. In
addition, they may be used to aid in the extraction and isolation
of crude oils which are found hard to access environments or as
water emulsions. There are four types of surfactants characterized
by varying uses. Anionic surfactants have detergent-like activity
and are generally used for cleaning applications. Cationic
surfactants contain long chain hydrocarbons and are often used to
treat proteins and synthetic polymers or are components of fabric
softeners and hair conditioners. Amphoteric surfactants also
contain long chain hydrocarbons and are typically used in shampoos.
Non-ionic surfactants are generally used in cleaning products.
[0256] Solid forms of carbon including, for example, coal,
graphite, graphene, cement, carbon nanotubes, carbon black,
diamonds, and pearls. Pure carbon solids can comprise such
materials as coal and diamond.
[0257] Pharmaceuticals can be produced including, for example,
isoprenoid-based taxol and artemisinin, or oseltamivir.
Detection and Analysis
[0258] Generally, the products of interest produced from the solar
biofactory can be analyzed by any of the standard analytical
methods, such as gas chromatography (GC), mass spectrometry (MS)
gas chromatography-mass spectrometry (GCMS), and liquid
chromatography-mass spectrometry (LCMS), high performance liquid
chromatography (HPLC), capillary electrophoresis, Matrix-Assisted
Laser Desorption Ionization time of flight-mass spectrometry
(MALDI-TOF MS), nuclear magnetic resonance (NMR), near-infrared
(NIR) spectroscopy, viscometry (Knothe, G., R. O. Dunn, and M. O.
Bagby. 1997. Biodiesel: The use of vegetable oils and their
derivatives as alternative diesel fuels. Am. Chem. Soc. Symp.
Series 666: 172-208), titration for determining free fatty acids
(Komers, K., F. Skopal, and R. Stloukal. 1997. Determination of the
neutralization number for biodiesel fuel production. Fett/Lipid
99(2): 52-54), enzymatic methods (Bailer, J., and K. de Hueber.
1991. Determination of saponifiable glycerol in "bio-diesel."
Fresenius J. Anal. Chem. 340(3): 186), physical property-based
methods, wet chemical methods etc. can be used to analyze the
levels and the identity of the product produced by the organisms
used in a solar biofactory.
[0259] Production of Fuels & Chemicals
[0260] This invention, or a subsequent related version, will be
used to produce commercial product (such as ethanol, alkanes,
glucose, etc.) from various microbiological production strains. The
invention will also generate valuable control code and software
that can be used more broadly in other phototrophic production
systems targeting a variety of value-added products that can be
produced by algae, microalgae and cyanobacteria. The invention is
therefore of wide ranging value to any production system that has
the objective to utilize sunlight in a process that requires
management of the thermal load while limiting the requirement of
external heating and cooling utilities to maintain temperature
control for viability and optimum performance.
[0261] In various aspects, the invention sets forth a
photobioreactor capable of culturing light capturing organisms to
an OD.sub.730 of about 14 g/L DCW. Preferably, the PBR is capable
of culturing light capturing organisms to an OD.sub.730 of about at
least 2-5 g/L, 5-10 g/L or 10-20 g/L DCW.
[0262] In other aspects, the invention sets forth a photobioreactor
capable of culturing light capturing organisms to a DCW
productivity of 3.5 g/m.sup.2/hr.
[0263] Preferred embodiments include a photobioreactor comprising a
passive thermal regulation system.
[0264] References cited herein discuss the general concepts of
photobioreactors and associated temperature control using water
baths, ponds, water sprays, flue gas based temperature control or
internal and external heat exchangers. None suggests passive
thermal control as a strategy to regulate the growth conditions of
the phototroph such that both daytime and night time conditions are
optimized. Passive heating and cooling is used in largely
stationary situations such as building using a variety of adaptive
features (see for instance "Passive Solar Heating and Cooling" at
the website of the Arizona Solar Center
http://www.azsolarcenter.com/technology/pas-3.html).
[0265] Adjustable solar tracking is also used in the concentrating
solar thermal industry to track and focus sunlight to a central
point to capture heat energy at a suitably high temperature to
generate power or split water thermally for hydrogen generation
(see for instance website of eSolar at http://www.esolar.com). None
of the systems used in the art suggest that it would be possible to
regulate the culturing conditions within a reactor using
microorganisms by adjusting the orientation on a real-time basis.
One reference suggests that adjusting the tilt angle of a
flat-plate reactor twice or four times a year can improve
productivity by optimizing the light regime in the reactor when
compared to utilizing a fixed tilt angle. Compared to a fixed tilt
angle throughout the year the productivity was improved by
approximately 7% adjusting the tilt angle twice and by almost 15%
when adjusting the tilt angle four times (Hu, Q., Faiman, D. and
Richmond, A. "Optimal tilt angles of enclosed reactors for growing
photoautotrophic microorganisms outdoors" Journal of Fermentation
and Bioengineering (1997) 85:230-236). The same reference provides
a design drawing that uses a thermostat and cooling water supply
pipe and sprinklers to control temperature. The reference actually
teaches against the use of passive control. It is a novel feature
to integrate a passive thermal control system to control the growth
conditions to at least reduce but more preferably eliminate
essentially all external cooling and heating utility thus
overcoming one of the greatest impediments to effective culturing
of photoautotrophs in enclosed reactors.
[0266] The following examples are illustrative and are non-limiting
to the present teachings.
Example 1
[0267] The following illustrates an exemplary photobioreactor, a
prototype developed to study fluid and gas mechanics, mass transfer
and cell growth characteristics. A Sunlite.RTM. SLT multiwall
polycarbonate sheet (FarmTek) was cut to a particular dimension.
Each partition measured about 10 mm.times.10 mm. The sheet was
capped horizontally at the top and the bottom using acrylic tubes
(McMaster). A separate sparge tube was assembled near the bottom
cap. At the center of each vertical partition, a hole was
punctured. The sparge tube also punctured, was then glued together
at the interface between the tube and the photobioreactor chamber
until it was sealed.
[0268] A heat exchanger was connected to the photobioreactor
assembly and a 1/10 hp centrifugal pump was used to circulate the
fluid within the photobioreactor. The flowrate was controlled by a
half-inch globe valve. The heat exchanger was connected to a
circulating heater/chiller unit to keep the temperature constant at
37.degree. C. A peristaltic pump (Cole Palmer) with a 0.2.mu.
filter was used to pump media into the photobioreactor. A pH and D.
O. probe (Neponset Controls) were installed on the reactor assembly
to monitor OD, pH and temperature. pH was controlled with CO.sub.2
and its to the photobioreactor was controlled by use of a solenoid
valve and LabVIEW software. Air was supplied from an air
compressor. A condenser was also installed on the gas outlet to
control evaporation loss from the bioreactor.
[0269] The bioreactor configuration also included super high output
florescent lighting installed anywhere from 2-8 inches above the
bioreactor assembly. The light bank held eight T-5 54 watt bulbs,
48'' in length. Six of the bulbs installed were 6500 k cool white
and the other two bulbs were 300 k warm white; each with a lumen
output of 5,000 per bulb. Mylar.RTM. sheet was placed under the
assembly. The bioreactor assembly was tilted at a 30 degree
angle.
[0270] The photobioreactor assembly proposed above has been
constructed and tested in actual field conditions. It is proposed
to construct a "sand box" that can use different ground covers
(optimizing heat absorption, diffuse reflection and heat storage
for passive heating at night or during cold periods) and install
sufficient photobioreactors within this space such that edge
effects will be eliminated. These photobioreactors can then be
equipped with simple manually adjustable inclination to confirm
that the intended surface coatings and treatments combined with
inclination control can indeed be used to effectively control
temperature with minimal external heating and cooling.
[0271] 4'.times.8' multi-wall PALRAM polycarbonate sheet was
purchased online from FarmTek (www.farmtek.com; 1440 Field of
Dreams Way, Dyersville, Iowa 52040)
[0272] DEGLAS IMPACT 8 mm double-skinned sheet, color clear 0119:
47.25'' wide.times.8' long and DEGLAS IMPACT 16 mm double-skinned
sheet, color clear 0119: 47.25'' wide.times.8' long acrylic sheet
was purchased from Evonik Cyro Canada, Inc. (www.evonik.com; 180
Attwell Drive, Suite 101, Toronto, ON, M9W 6A9)
[0273] Makrolon multi UV 2/10-10.5, Makrolon multi UV 3/16-16,
Makrolon multi UV 3X/16-25 sheet samples were received from
Sheffield Plastics Inc., a Bayer MaterialScience Company
(www.sheffieldplastics.com; www.bayerimsa.com;
www.bayersheeteurope.com; 119 Salisbury Road, Sheffield, Mass.
01257)
[0274] Assorted sizes of Acrylic tubing was purchased online from
McMaster-Carr (www.mcmaster.com; 200 New Canton Way Robbinsville,
N.J. 08691-2343)
[0275] Pumps, heat exchanger and probes purchased from standard
equipment suppliers (i.e. VWR, Cole Parmer, Fisher)
[0276] Mylar reflective sheet from International Plastics Inc.,
3052 NE Harrison St., Issaquah, Wash. 98029.
Example 2
Impact of Mixing
Air Bubbles v. Liquid Pump
[0277] The photobioreactor was kept at a constant temperature of
37.degree. C.
[0278] Air Bubbles
TABLE-US-00001 Air bubble Flow Air bubble Flow Tilt Angle (deg) 10
Tilt Angle (deg) 30 Mixing Light-Dark Mixing Power Light-Dark Power
Input Cycle Time Input Cycle Time (W/m2) (ms) (W/m2) (ms) 1.6 220
2.7 200 2.4 200 4.0 180 3.1 180 5.3 160 3.9 160 6.6 140 4.7 150 7.9
130 5.4 140 9.1 120 6.2 140 10.4 110
[0279] Liquid Pump
TABLE-US-00002 Liquid Pump Liquid Pump Tilt Angle (deg) 10 Tilt
Angle (deg) 30 Mixing Light-Dark Mixing Power Light-Dark Power
Input Cycle Time Input Cycle Time (W/m2) (ms) (W/m2) (ms) 12 1290
15 1300 31 940 36 960 56 780 63 800 86 680 96 700 120 610 133 630
158 560 175 580 200 520 220 540
Example 3
Media Study & Optimization
[0280] A series of studies were conducted to determine the types
and amounts of nutrients required in a medium to allow
Synechococcus sp. PCC 7002 to reach a concentration of at least 10
g/L dry cell weight (DCW). The A+ media previously published had
not been extensively studied and the amount of cell growth that it
could support was unknown. The A+ media contents are provided in
the following Table:
TABLE-US-00003 Amount Ingredient per liter Units Comments NaCl 18 g
1.8% NaCl; compare to seawater at 2.8% NaCl KCl 0.6 g NaNO.sub.3 1
g Nitrogen source 500 g/l 10 mL Final [Mg2+] = 0.049%; compare
MgSO.sub.4.cndot.7H.sub.2O to seawater at 0.128%; store nonsterile
at 4.degree. C. 50 g/l KH.sub.2PO.sub.4 1 mL Store nonsterile at
4.degree. C. 17.76 g/l CaCl.sub.2 15 mL Store nonsterile at
4.degree. C. 3 g/l 10 mL Alternative liquid stocks; store
NaEDTA.sub.tetra nonsterile at 4.degree. C. 3.89 g/l 1 mL Store
nonsterile at 4.degree. C. FeCl.sub.3.cndot.6H.sub.2O (in 0.1N HCl)
1M Tris 8.25 mL Provides buffering activity; replaces (pH 8.2) 100
g/l stock; store nonsterile at 4.degree. C. P1 Metals 1 mL Trace
metals; store nonsterile at Solution room temperature MilliQ
H.sub.2O 950 mL 4 mg/l 1 mL Vitamin B.sub.12
[0281] Studies were conducted by making modifications to A+ media,
inoculating it with Synechococcus sp. PCC 7002 and then tracking
the optical density against culture age in flasks. The growth
caused by the changes in any variable was then compared. DCW was
also determined in some cases. This data was used to then build an
optimized media that could support growth up to at least 15 g/L
DCW.
[0282] A+ was used as the initial starting point for the media
studies. After an improvement was discovered studies would be
conducted on the improved media. Improvements in media were
measured by the growth that was supported. Freshly prepared media
was used in each study. This helped to avoid a precipitate often
seen in the media during storage. The inoculum used for each
experiment was made by inoculating a single Synechococcus sp. PCC
7002 colony into a bubble tube and growing up for several days.
Samples from the bubble tube were then inoculated in 125 mL flasks
with 10 mL of each type of media. The starting optical density of
each flask and the weight of the flask with the culture in it was
then measured. All flasks were placed in Infors shakers at 150 RPM,
37.degree. C. and 2.0% CO.sub.2.
[0283] Evaporation losses were corrected daily by adding filter
sterilized MilliQ water. The amount of water added was determined
by the change in weight that occurred each day. After correcting
for evaporation and thoroughly mixing by shaking each flask, a 100
.mu.l of the culture was removed. The sample was then diluted and
optical density (OD) measurements were taken on a SpectraMax at a
wavelength of 730 nm. Dilutions were made to achieve an OD between
the range of 0.04-0.40, as this is the range thought to have the
best accuracy in measurement. Provided the dilutions are made to
the desired range and approximate conversion to Dry Cell Weight
(DCW in g/L) can be obtained by dividing the OD by 3.0. Growth in
the form of OD was then plotted over time and compared to see how
each change in variable effected the growth.
[0284] Antifoam Selection Study
[0285] Four types of Antifoam were added to flasks at a
concentration of 200 .mu.l/L. These samples were then grown
overnight and growth rates were compared. Microscope pictures were
then taken to determine what effect if any the various antifoams
had upon a cyanobacterium. The results for the Antifoam Selection
Study can be seen in Table 1.
TABLE-US-00004 TABLE 1 Effect of Various Antifoams: Optical Density
vs. Age OD after Growth Rate Doubling Sample Initial OD 13.5 hours
hr{circumflex over ( )}-1 Time A+ 0.339 1.535 0.11 6.20 Antifoam B
Emulsion 0.338 1.355 0.10 6.74 Antifoam 204 0.342 1.545 0.11 6.21
Suppressor 3965 0.333 1.695 0.12 5.75 MCA 222 0.337 1.735 0.12
5.71
[0286] Suppressor 3965 was selected as the optimal antifoam. This
was due to its decreased doubling time and that MCA 222 may have
looked slightly less healthy under the microscope when compared to
A+ and Suppressor 3965.
[0287] Table 2 shows the results for the PO.sub.4/EDTA test. This
study varied the concentration of KH.sub.2PO.sub.4 in the media and
it also investigated the effect of removing EDTA. Optical density
vs. culture age was recorded and compared.
TABLE-US-00005 TABLE 2 Effect of Varied Concentrations of
KH.sub.2PO.sub.4 and EDTA: Optical Density vs. Age Culture Age 1A
50 mG 1B 50 mg 2A 100 mg 2B 100 mg 3A 250 mg 3B 250 mg 4A no 4B no
(hrs) PO.sub.4 PO.sub.4 PO.sub.4 PO.sub.4 PO.sub.4 PO.sub.4 EDTA
EDTA 0 0.158 0.158 0.152 0.175 0.176 0.168 0.162 0.177 21.5 2.65
2.55 2.5 2.75 2.52 2.94 1.15 1.2 44.75 6.44 6.8 6.2 6.92 6.2 7.44
1.74 1.72 71 10.96 10.44 10.96 11.2 10.28 11.28 1.88 1.84 94.75
12.8 12.6 12.84 13.04 11.6 13.88 1.72 2.04 117.25 13.52 13.36 13.48
13.72 12.6 13.76 -- --
[0288] The data shown in table and Table 2 suggest that EDTA may be
an essential component of the media and that it should not be
removed. Increasing the levels of phosphate did not have a
noticeable effect on cell growth. The growth curve shows a nutrient
limitation at a culture age of 100 hours. This implied that the
cells were running out of another essential nutrient before they
were running out of phosphate. See FIG. 18.
[0289] Iron Source Test
[0290] Cultures were grown with different sources of iron. The
sources used were: ferric chloride (A+ iron source), ferric citrate
and ferrous sulfate. Table 3 shows the data for the various iron
sources.
TABLE-US-00006 TABLE 3 Effect of Varied Iron Sources on Cell
Growth: Optical Density Vs. Age Time Ferric Ferric (hrs) FeCl.sub.3
FeCl.sub.3 Citrate Citrate FeSO.sub.4 FeSO.sub.4 0 0.127 0.124
0.114 0.12 0.128 0.121 21.3 2 1.83 2.08 2.39 2.36 2.32 73.3 7.12
7.08 12.56 12.64 12.8 12.2 94.05 7.92 7.8 13.28 13.68 13.88 13.8
115.55 9.08 9.04 15.56 15.24 15.68 14.96 135.8 8.84 9.96 14.88
14.84 14.88 15.88
[0291] A graph of this data can be seen in FIG. 19.
[0292] The iron sources ferric citrate and ferrous sulfate both
showed a similar positive impact on growth when compared to
FeCl.sub.3. The decision was made to switch to ferric citrate as an
iron source because it outperformed FeCl.sub.3 and unlike
FeSO.sub.4 it contained a chelating agent. This study and the EDTA
study clearly shows the benefit of chelators in media.
[0293] The media with 2.times. nitrogen, iron and phosphate (JB
2.0) showed a significant improvement in growth when compared to
A+. Comparing just the average of JB 2.0 to A+ average resulted in
the data shown in Table 4. (The media protocol for JB 2.0 is shown
in Example 4)
TABLE-US-00007 TABLE 4 JB2.0 Compared to A+: Optical Density Vs.
Age Culture A+ JB 2.0 Age A+ A+ Avg. JB 2.0 JB 2.0 Avg. 0 0.127
0.126 0.1265 0.133 0.125 0.129 21.5 2.36 1.96 2.16 2.24 2.22 2.23
70 10.28 10.6 10.44 11.56 10.56 11.06 92.5 12.24 12.12 12.18 15.72
13.64 14.68 118.5 13.44 13.12 13.28 19.68 17.76 18.72 139 13.76
13.44 13.6 21.68 19.84 20.76 166 13.68 13.44 13.56 24.16 22.24 23.2
188 13.6 13.84 13.72 24.64 23.68 24.16
[0294] A+ had a significant decline in growth rate around hour 100
whereas JB 2.0 continued to grow unhindered until hour 139. This
can be attributed to a nutrient limitation that eventually
developed in the A+ media that did not occur in the 2.times.
nitrogen, phosphate and iron JB 2.0 media (FIG. 20).
[0295] The three variables of nitrogen, phosphate and iron where
identified as the key nutrient sources that run out first in the
media.
[0296] NPFe Dry Cell Weights
TABLE-US-00008 Dry Cell Weight Test (g/L) 1A 2X NPFe 7.83 1B 2X
NPFe 7.61 2A 4X NPFe 11.83 2B 4X NPFe 12 3A 6X NPFe 11.39 3B 6X
NPFe 12.39
[0297] The media with 2.times. nitrogen, phosphate, and iron grew
to about an OD of 25 before it hit nutrient limitation. It became
chlorotic at that point and stopped growing. The 4.times. and the
6.times. amounts continued on to an OD of 40. This was the basis
for the media protocol JB 2.1 which has the concentrations of
nitrogen, phosphate and iron at 4.times. (FIG. 21).
Example 4
Enhanced Media Composition
[0298] The following table lists the procedure for creating 1 Liter
of culture media.
TABLE-US-00009 Chemical mg/L added FW Molarity Units Source NaCl
18000 58.44 308 mM Fisher KCl 600 74.55 8.05 mM Fisher NaNO.sub.3
4000 84.99 47.06 mM Sigma Aldrich MgSO.sub.4--7H.sub.2O 5000 246.47
20.29 mM Sigma Aldrich KH.sub.2PO.sub.4 200 136.09 1.47 mM Fisher
CaCl.sub.2 266 110.99 2.40 mM Sigma NaEDTA.sub.tetra 30 372.24
80.59 uM Fisher Ferric Citrate 14.1 244.95 57.48 uM Acros Or-
ganics Tris 1000 121.14 8.25 mM Fisher Vitamin B.sub.12 0.004
1355.37 2.95E-03 uM Sigma (Cyanocobalamin) Aldrich H.sub.3BO.sub.3
34 61.83 554 uM Acros Or- ganics MnCl.sub.2--4H.sub.2O 4.3 197.91
21.83 uM Sigma ZnCl 0.32 136.28 2.31 uM Sigma MoO.sub.3 0.030
143.94 0.21 uM Sigma Aldrich CuSO.sub.4--5H.sub.2O 0.0030 249.69
0.012 uM Sigma Aldrich CoCl.sub.2--6H.sub.2O 0.012 237.93 0.051 uM
Sigma
[0299] Vitamin B.sub.12 should be stored in the dark at 4.degree.
C. All other liquid stocks may be stored unsterile at room
temperature. Weigh out 18.0 grams of NaCl in a plastic weigh boat
and pour it into a 2 Liter graduated cylinder. Using a separate
plastic weigh boat, weigh out 600 mg of KCl and add it into the 2 L
cylinder. Add 4 grams of NaNO.sub.3 into the cylinder. Add half of
the desired final volume of MilliQ H.sub.2O, 500 mL for a 1 Liter
batch. Place the cylinder on a stir plate, add a magnetic stirrer
and mix well. Let the media mix during the addition of the
components below. From a previously made stock solution of 500 g/L
MgSO.sub.4 7H.sub.2O add 10 mL to the media. From a previously made
stock solution of 50 g/L KH.sub.2PO.sub.4 add 4 mL to the media.
From a filtered stock solution of 17.76 g/L CaCl.sub.2 add 15 mL to
the media. The need for the filtered CaCl.sub.2 is to help prevent
precipitation in storage. From a stock solution of 3 g/l
NaEDTA.sub.tetra add 10 mL to the media. From a stock solution of
3.52 g/l Ferric Citrate (in 0.1 N HCl) add 4 mL to the media. From
a stock of 1 M Tris (pH 8.2) add 8.25 mL. Add 1 mL of P1 metals to
the media. The components of the P1 metal solution can be seen
below. Add 1 mL of 4 mg/L Vitamin B.sub.12 to the media. After all
of the above components have been added and mixed bring the volume
with MilliQ H.sub.2O in the cylinder up to the 1 Liter mark. After
the addition let the media mix for one minute. Filter sterilize the
media using a 0.22 .mu.M pore size filter, into an autoclaved 1
Liter bottle. Sterile technique should be used. Keep the pH of the
media within 7.9-8.0. Higher than 8.0 can cause precipitation.
Example 5
Culturing Synechococcus sp. PCC 7002 in Enhanced Media
Composition
[0300] Synechococcus sp. PCC 7002 (ATCC) was inoculated in JB 2.1
plus 1 g/L citric acid media in a photobioreactor apparatus under
continuous illumination and bubbled with air containing 1% CO.sub.2
in the photobioreactor apparatus and monitored for growth.
[0301] Reactor details: Airflow .about.1 VVM ("40" on rotometer),
Air @ 25 psig, CO2 @ 30 psig
[0302] CFP #3
TABLE-US-00010 Culture age DCW .DELTA. growth dbl (hr) OD pH g/L
time rate time 0.00 1.75 0.271 8.0 1.7 5.50 0.433 7.8 3.8 0.125 6
19.50 3.95 7.8 14.0 0.158 4 23.50 5.66 7.8 4.0 0.090 8 42.50 13.30
7.8 19.0 0.045 15 73.00 21.84 7.9 30.5 0.016 43 91.50 27.30 7.9
10.9 18.5 0.012 57 116.50 32.30 7.8 12.3 25.0 0.007 139.50 33.20
7.8 11.70
[0303] CFP #2
TABLE-US-00011 Culture age DCW (hr) OD g/L 0.00 0.20 19.75 3.58 1.2
42.50 13.70 4.6 66.50 27.40 8.0 91.50 30.00 10.3 115.50 34.20 10.2
139.50 35.00 9.7
[0304] The result of the experiment produced about 10 g/L (DCW) of
Synechococcus.
Example 6
Culturing Genetically Modified Synechococcus sp. PCC 7002
[0305] Construction of pJB5
[0306] A pJB5 base plasmid was designed as an empty expression
vector for recombination into Synechococcus sp. PCC 7002. Two
regions of homology, the Upstream Homology Region (UHR) and the
Downstream Homology Region (DHR) were designed to flank the
construct. These 500 bp regions of homology correspond to positions
3301-3800 and 3801-4300 (Genbank Accession NC.sub.--005025) for the
UHR and DHR, respectively. The aadA promoter, gene sequence, and
terminator were designed to confer spectinomycin and streptomycin
resistance to the integrated construct. For expression, pJB5 was
designed with the aph2 kanamycin resistance cassette promoter and
ribosome binding site (RBS). Downstream of this promoter and RBS,
restriction endonuclease recognition sites are designed and
inserted for NdeI and EcoRI, as well as the sites for XhoI, BamHI,
SpeI and Pad. Following the EcoRI site, the terminator from the
pyruvate decarboxylase gene of Zymomonas mobilis (pdc) is included.
Convenient XbaI restriction sites flank the UHR and DHR, allowing
cleavage of the DNA intended for recombination from the rest of the
vector. pJB5 was constructed by DNA2.0 (Menlo Park, Calif.).
[0307] The pJB5-gene of interest construct is cloned into
Synechococcus sp. PCC 7002 using the following protocol.
Synechococcus 7002 is grown for 48 hours from colonies in an
incubated shaker flask at 30.degree. C. at 1% CO.sub.2 to an
OD.sub.730 of 1 in optimized medium described in Frigaard N U et
al. (2004) "Gene inactivation in the cyanobacterium Synechococcus
sp. PCC 7002 and the green sulfur bacterium Chlorobium tepidum
using in vitro-made DNA constructs and natural transformation"
Methods Mol Biol 274:325-340. 500 .mu.L of culture is added to a
test-tube with 30 .mu.L of 1-5 .mu.g of DNA prepped from a Qiagen
Qiaprep Spin Miniprep Kit (Valencia, Calif.) for each construct.
Cells are incubated with sparging of 1% CO.sub.2 at approximately 1
vvm (volume gas per volume liquid per minute) for 4 hours. 200
.mu.L of cells are plated on optimized medium plates with 1.5%
agarose and grown at 30.degree. C. for two days in low light. 10
.mu.g/mL of spectinomycin based on total plate agar volume is added
as a concentrated solution underneath the agar on each plate.
Resistant colonies are visible in 7-10 days. See WO2009/111513 for
further details of microorganism engineering and culturing.
[0308] The genetically Modified Synechococcus sp. PCC 7002 is
inoculated in the enhanced media under continuous illumination and
bubbled with air containing 1% CO.sub.2 in the photobioreactor
apparatus of the invention and monitored for growth.
[0309] Below is a table of Synechococcus sp. PCC 7002 cultured in a
photobioreactor of the invention.
TABLE-US-00012 daily productivity age OD DCW g/m.sup.2/hr 0 0.199
0.333689 19.75 3.58 6.0030488 0.57 25 5.86 9.8262195 1.46 42.5 13.7
22.972561 1.50 66.6 22.4 37.560976 1.21 91 30 50.304878 1.04 115
34.2 57.347561 0.59
Example 7
Ethanol Productivity Model
[0310] To calculate the productivity the following assumptions were
made:
[0311] Radiation: photosynthetically active radiation (PAR)
fraction of total solar radiation.apprxeq.47%, historical average
PAR at ground based on NREL 1991-2005 datasets, assumes future
radiation characteristics will be consistent with historic
values;
[0312] Production: production rate is linear with radiation
intensity, well-documented photon utilization is 8 photons/CO.sub.2
fixed into biomass (Pirt, S J 1983, Biotechnol Bioeng, 25:
1915-1922), 85% of PAR striking the photobioreactor system enters
the culture, 85% of PAR photons entering the photobioreactor are
available for conversion, 15% lost to photoinhibition &
radiation when culture not at operating temperature, Estimate 3
days of culture growth followed by 8 weeks of production; 95%
online production, Estimate 5% of photosynthetic energy dedicated
to cell maintenance (Pirt S J 1965 Proc Roy Soc 163: 224-231).
[0313] Method of calculating ethanol productivity based on ethanol
concentration in the culture and the stripping rate:
[0314] The ethanol concentration in the bioreactor culture is a
function of two quantities: [0315] (a) The production rate
(k.sub.p): The production rate is the rate of increase of ethanol
concentration in the liquid with time i.e.:
[0315] [ Ethanol ] t = k p ##EQU00001## [0316] (b) The stripping
rate (s): Due to the volatility of ethanol, it will be continuously
leaving the liquid in the form of vapor. The rate at which it
leaves the reactor is a function of the concentration of ethanol in
the liquid and a variety of other factors such as temperature,
airflow, etc. For our purposes, all other factors are held fixed
hence we can think of the rate of ethanol loss being solely
dependent on the liquid concentration, i.e:
[0316] [ Ethanol ] t = - s [ Ethanol ] ##EQU00002##
Combining the two equations, we can write:
[ Ethanol ] t = k p - s [ Ethanol ] ##EQU00003##
Note that in the above equation, the production rate k.sub.p is
time independent which is clearly false. In reality, it would
depend on time via the density of the culture and the light regime.
However, as long as we treat the production rate k.sub.p as an
average production rate between measurements, the relation is
valid.
[0317] The equation is a basic first order equation and can be
easily solved to obtain:
k p = s [ Ethanol ( t ) ] ts - s [ Ethanol ( t = 0 ) ] ts - 1
##EQU00004##
Note that this gives a production rate that is in terms of
concentration of ethanol per unit time for the incident light
intensity at which the experiment was conducted. This has to be
multiplied by the reactor volume to obtain the production rate in
terms of grams of ethanol per unit time. Units can then be
converted to suitable time units such as day instead of hour. For
example, in our case, we define the stripping rate in units of h
(-1) and our reactor of volume V covers and area of 0.5 m 2.
Therefore our production rate (in grams per square meter per day)
is given by 2 k.sub.p V*24 at the incident light intensity at which
the experiment was conducted.
[0318] While this invention has been particularly shown and
described with references to example embodiments thereof, it will
be understood by those skilled in the art that various changes in
form and details may be made therein without departing from the
scope of the invention encompassed by the appended claims.
* * * * *
References