U.S. patent application number 15/830772 was filed with the patent office on 2018-03-29 for system and process for recovering algal oil.
The applicant listed for this patent is H R D Corporation. Invention is credited to Rayford Gaines Anthony, Gregory G. Borsinger, Abbas Hassan, Aziz Hassan.
Application Number | 20180087003 15/830772 |
Document ID | / |
Family ID | 54072983 |
Filed Date | 2018-03-29 |
United States Patent
Application |
20180087003 |
Kind Code |
A1 |
Hassan; Abbas ; et
al. |
March 29, 2018 |
SYSTEM AND PROCESS FOR RECOVERING ALGAL OIL
Abstract
Herein disclosed is a method of processing a medium containing
algae microorganisms to produce algal oil and by-products,
comprising providing the medium containing algae microorganisms;
passing the medium through a rotor-stator high shear device;
disintegrating cell walls of and intracellular organelles in the
algae microorganisms to release algal oil and by-products; and
removing the algae medium from an outlet of the high shear device.
In an embodiment, disintegration is enhanced by a penetrating gas
capable of permeating the cell wall. In an embodiment, enhancement
is accomplished by super-saturation of the penetrating gas in the
medium or increased gas pressure in a vessel. In an embodiment, the
penetrating gas is different from the gas produced by the cell
during respiration. A suitable system is also discussed in this
disclosure.
Inventors: |
Hassan; Abbas; (Houston,
TX) ; Hassan; Aziz; (Houston, TX) ; Borsinger;
Gregory G.; (Chatham, NJ) ; Anthony; Rayford
Gaines; (College Station, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
H R D Corporation |
Houston |
TX |
US |
|
|
Family ID: |
54072983 |
Appl. No.: |
15/830772 |
Filed: |
December 4, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14831453 |
Aug 20, 2015 |
9862910 |
|
|
15830772 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
Y02P 20/142 20151101;
B01F 13/1016 20130101; Y02E 50/13 20130101; C12M 21/02 20130101;
A23D 9/00 20130101; C12P 7/6463 20130101; A23V 2002/00 20130101;
C10L 2290/54 20130101; C11B 1/02 20130101; C10L 2200/0476 20130101;
C12M 23/18 20130101; C12M 47/06 20130101; B01F 7/00766 20130101;
C10L 1/026 20130101; C11B 1/10 20130101; C11B 1/04 20130101; Y02P
20/141 20151101; Y02E 50/10 20130101; A23V 2002/00 20130101; A23V
2250/19 20130101; A23V 2250/202 20130101; A23V 2300/14 20130101;
A23V 2300/41 20130101 |
International
Class: |
C11B 1/10 20060101
C11B001/10; C12P 7/64 20060101 C12P007/64; A23D 9/00 20060101
A23D009/00; C11B 1/02 20060101 C11B001/02; C10L 1/02 20060101
C10L001/02; C12M 1/00 20060101 C12M001/00; C11B 1/04 20060101
C11B001/04; B01F 7/00 20060101 B01F007/00; B01F 13/10 20060101
B01F013/10 |
Claims
1. A system comprising a rotor-stator high shear device configured
to process a medium containing algae microorganisms to produce
algal oil and by-products, wherein said high shear device is
operated to disintegrate cell walls of and intracellular organelles
in the algae microorganisms to release algal oil and by-products,
wherein said high shear device comprises an inlet to take in said
medium containing algae microorganisms and an outlet for the algae
medium to be removed from the high shear device.
2. The system of claim 1 comprising at least two rotor-stator high
shear devices fluidly connected in series to process said medium
containing algae microorganisms and disintegrate cell walls of and
intracellular organelles in the algae microorganisms to release
algal oil and by-products.
3. The system of claim 1 further comprising a separation system
configured to separate algal oil and by-products from the
medium.
4. The system of claim 1 further comprising a conversion system
configured to convert algal oil to biodiesel.
5. The system of claim 1 comprising a pressurized vessel to enhance
said disintegration.
6. The system of claim 1 comprising a de-watering unit for the
medium upstream of the high shear device.
7. The system of claim 1 further comprising a tank or pond
configured to grow algae containing algae microorganisms and
optionally bacteria; a nutrient source consumable by said algae
microorganisms and optionally bacteria; another rotor-stator high
shear device configured to process carbon dioxide in a liquid
operating at a shear rate of greater than 1,000,000 s.sup.-1 to
form a carbon dioxide super-saturated liquid stream and feed said
stream into the tank/pond for algae growth; and a fluid line
configured to extract a medium containing algae from the tank or
pond and send the medium to the rotor-stator high shear device
configured to process said medium.
8. The system of claim 7, wherein said nutrient source comprises
municipal waste; sewage waste; paper pulp; chemical and
petrochemical; vegetable including grain, sugar; farm discharge;
animal farm discharge including beef, pork, poultry; canning
discharge, fishing discharge; farming discharge; food processing
discharge.
9. The system of claim 7 comprising a pretreating unit for said
nutrient source.
10. The system of claim 9, wherein said pretreating unit comprises
a high shear device and is configured to eliminate undesirable
pathogens via gas-assisted high shear lysing of pathogen cells.
11. The system of claim 9, wherein said pretreating unit is
configured to increase the bio-availability of nutrient in the
nutrient source.
12. The system of claim 7 being modular.
13. The system of claim 7 being integrated with an existing
facility.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional application of U.S. patent
application Ser. No. 14/831,453 filed Aug. 20, 2015, the disclosure
of which is hereby incorporated herein by reference.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not Applicable.
BACKGROUND OF THE INVENTION
Technical Field
[0003] The present invention relates generally to recovery of algal
oil. More particularly, the present invention relates to a system
and process for culture of algae and extraction of algal oil using
high shear.
Background of the Invention
[0004] In recent years, algal oil has been recognized as a valuable
agricultural land-saving alternative to plant feedstock, such as
soybean oil, canola and palm oil or animal, fish and bird fat and
tallow. Algae are the simplest plants that live in a water
environment. Many algae are unicellular that may or may not have a
cell wall. Similar to other plants, algae are photosynthetic. They
utilize carbon dioxide as a carbon source and store energy in the
form of lipids within the intracellular oil bodies, surrounded by
membranes. Algae multiply and grow at a very fast rate and,
depending on the genetic background and growth conditions, may have
very high oil content. In biodiesel production, the wild type
strains of algae or mutants and genetically modified
microorganisms, which are designed and selected to produce enhanced
levels of oil and/or high levels of oleic acid, are preferred. Such
strains can be obtained by Polymerase Chain Reaction (PCR)
mutagenesis or by exposure to ultraviolet or ionizing radiation and
chemical mutagens. Oil-overproducing strains can be engineered with
the help of the directed evolution and other biotechnological
techniques known to those skilled in the art.
[0005] In addition to methods and systems that stimulate and
increase production of oil in algae during culture, there is also
the need for methods and systems to extract algal oil. There are a
number of methods for disintegration of algae and recovering the
algal oil, such as pressing, extraction with organic solvents,
enzymatic degradation, lysis using osmosis and ultrasonic and
microwave-assisted disruption. Some of the new technologies for
algal oil extraction include enzymatic hydrolysis, pulsed electric
field (PEF) technology, and the use of amphyphillic solvents.
[0006] Clearly, there is a need and interest to continue to develop
systems and methods for algal oil extraction. Preferably such
systems and methods are economical and able to handle large volume
of algal culture.
SUMMARY
[0007] Herein disclosed is a method of processing a medium
containing algae microorganisms to produce algal oil and
by-products, comprising providing the medium containing algae
microorganisms; passing the medium through a rotor-stator high
shear device; disintegrating cell walls of and intracellular
organelles in the algae microorganisms to release algal oil and
by-products; and removing the algae medium from an outlet of the
high shear device. In an embodiment, disintegration is enhanced by
a penetrating gas capable of permeating the cell wall. In an
embodiment, enhancement is accomplished by super-saturation of the
penetrating gas in the medium or increased gas pressure in a
vessel. In an embodiment, the penetrating gas is different from the
gas produced by the cell during respiration.
[0008] In an embodiment, the medium containing algae microorganisms
is de-watered at least partially before the medium is passed
through the high shear device. In an embodiment, a solvent is added
to the at least partially de-watered medium before the medium is
passed through the high shear device. In an embodiment, the solvent
is a gas comprising carbon dioxide or air or oxygen or nitrogen; or
a liquid comprising an alcohol or hexane or vegetable oil and/or
animal fat or tallow.
[0009] In an embodiment, the method comprises separating algal oil
and byproducts from the algae medium removed from the high shear
device. In an embodiment, the method comprises converting the algal
oil to biodiesel.
[0010] In an embodiment, the method comprises producing the medium
containing algae microorganisms, comprising super-saturating a
liquid with carbon dioxide in a second rotor-stator high shear
device operating at a shear rate of greater than 1,000,000
s.sup.-1; feeding the carbon dioxide supersaturated liquid and a
nutrient source to algae microorganisms and optionally bacteria;
allowing the algae microorganisms to grow by consuming carbon
dioxide and the nutrient; and generating the medium containing
algae microorganisms.
[0011] In an embodiment, the nutrient source comprises municipal
waste; sewage waste; paper pulp; chemical and petrochemical;
vegetable including grain, sugar; farm discharge; animal farm
discharge including beef, pork, poultry; canning discharge, fishing
discharge; farming discharge; food processing discharge. In an
embodiment, the nutrient source is pretreated to eliminate
undesirable pathogens via gas-assisted high shear lysing of
pathogen cells or pretreated using high shear to increase the
bio-availability of nutrient in the nutrient source. In an
embodiment, the algae and/bacteria are genetically modified. In an
embodiment, the bacteria cause the breakdown of the nutrient source
to promote algae growth.
[0012] Herein also disclosed is a system comprising a rotor-stator
high shear device configured to process a medium containing algae
microorganisms to produce algal oil and by-products, wherein the
high shear device is operated to disintegrate cell walls of and
intracellular organelles in the algae microorganisms to release
algal oil and by-products, wherein the high shear device comprises
an inlet to take in the medium containing algae microorganisms and
an outlet for the algae medium to be removed from the high shear
device.
[0013] In an embodiment, the system comprises at least two
rotor-stator high shear devices fluidly connected in series to
process the medium containing algae microorganisms and disintegrate
cell walls of and intracellular organelles in the algae
microorganisms to release algal oil and by-products. In an
embodiment, the system comprises a separation system configured to
separate algal oil and by-products from the medium. In an
embodiment, the system comprises a conversion system configured to
convert algal oil to biodiesel.
[0014] In an embodiment, the system comprises a tank or pond
configured to grow algae containing algae microorganisms and
optionally bacteria; a nutrient source consumable by the algae
microorganisms and optionally bacteria; another rotor-stator high
shear device configured to process carbon dioxide in a liquid
operating at a shear rate of greater than 1,000,000 s-1 to form a
carbon dioxide super-saturated liquid stream and feed the stream
into the tank/pond for algae growth; and a fluid line configured to
extract a medium containing algae from the tank or pond and send
the medium to the rotor-stator high shear device configured to
process the medium.
[0015] In an embodiment, the system of this disclosure is modular
and is optionally integrated with an existing facility.
[0016] Certain embodiments of the above-described methods or
systems potentially provide overall cost reduction by providing
increased inhibition per unit of inhibitor consumed, permitting
increased fluid throughput, permitting operation at lower
temperature and/or pressure, and/or reducing capital and/or
operating costs. These and other embodiments and potential
advantages will be apparent in the following detailed description
and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] For a more detailed description of the preferred embodiment
of the present invention, reference will now be made to the
accompanying drawings, wherein:
[0018] FIG. 1 is a longitudinal cross-section view of a multi-stage
high shear device, as employed in an embodiment of the system.
[0019] FIG. 2 is an overall process flow diagram for algae culture
and algal oil recovery, according to an embodiment of this
disclosure.
[0020] FIG. 3 illustrates the super saturation process of the
feedstock for algae, according to an embodiment of this
disclosure.
[0021] FIG. 4 illustrates a process for algae lysing and algal oil
recovery, according to an embodiment of this disclosure.
[0022] FIG. 5 illustrates another process for algae lysing and
algal oil recovery, according to an embodiment of this
disclosure.
[0023] FIG. 6 illustrates detail `A` for fluid connections as shown
in FIGS. 4, 5 and 11, according to an embodiment of this
disclosure.
[0024] FIGS. 7 and 8 show dissolved oxygen concentration of a 1:10
supersaturated oxygen solution in Example 1.
[0025] FIG. 9 shows dissolved carbon concentration of a
shear-induced, CO.sub.2 infused distilled water solution over time
in Example 1.
[0026] FIG. 10 shows the percentage of dissolved carbon remaining
in solution over time in Example 1, which is independent of SSCO2
concentration.
[0027] FIG. 11 illustrates a CO2-assisted high shear algae cell
disruption flow diagram, according to an embodiment of this
disclosure.
[0028] FIG. 12 shows the particulates observed within the rotor of
the high-shear unit in Example 2.
[0029] FIG. 13 shows time dependent effects of SSCO2-assisted high
shear lysis of algae cells observed by microscopy in Example 2.
[0030] FIG. 14 shows representative images of processed algae
slurry through the CO2-assisted high shear unit in Example 2.
[0031] FIG. 15 shows representative microscopic images of control
and processed (SSCO2-shear-colloid mill) algae slurry in Example
2.
[0032] FIG. 16 shows the oily surface observed on CO2-assisted high
shear processed algae slurry in Example 2.
[0033] FIG. 17 illustrates excess O2 leading to reactive oxygen
species (ROS) generation and cell death within yeast cells in
Example 3.
[0034] FIG. 18 shows representative microscopic images (40.times.)
of unprocessed control yeast (A), 1st pass samples exposed to 0 psi
back pressure (B), 20 psi back pressure (C), and 40 psi back
pressure (D) in Example 3.
[0035] FIG. 19 shows representative microscopic images (40.times.)
of unprocessed control yeast (A), 2nd pass samples exposed to 20
psi back pressure (B), and 40 psi back pressure (C) in Example
3.
[0036] FIG. 20 shows, in Example 3, representative microscopic
images (40.times.) of yeast continuously circulated through the
O2-assisted shear (HSPD+CM) system for 5 minutes. (A) unprocessed
(circulated, no O2, no high shear processing unit, no colloidal
mill) control yeast, (B) high shear processing unit+colloidal mill
(no O2), (C) high shear processing unit+colloidal mill, 20 psi back
pressure, (D) high shear processing unit+colloidal mill, 40 psi
back pressure.
[0037] FIG. 21 illustrates a process flow diagram of the cell lysis
method and system as discussed in Example 4.
[0038] FIG. 22 illustrates the effects of high shear speed on yeast
cell lysis assisted by O2 as discussed in Example 4.
DETAILED DESCRIPTION
[0039] It has been unexpectedly discovered that the use of a
rotor-stator high shear device is effective in the disintegration
of unicellular and/or multicellular algal (and/or bacterial)
microorganisms and their intracellular organelles to release oil
and other cell contents. After lysing the algal (and/or bacterial)
microorganisms and their intracellular organelles, the product is
separated and converted to modified, more valuable products, e.g.
algal oil. This finding is contrary to the general knowledge and
wisdom of the field of art. The method and system of this
application also bypass the cost for expensive apparatus and have
low operational cost. Examples of rotor-stator high shear device
include mechanical pulpers, refiners (e.g., Beloit Jones DD 3000
refiners, Voith Twin Flo TFE Refiner, Metso JC series refiners),
mills. Papermaking refiners can be either disc refiners or conical
refiners. The pulp enters through a feed port, travels between a
conical rotor and stator and then leaves through the discharge
port. The rotor and stator will have a bar and groove pattern. Only
one of the elements will rotate (the rotor). The gap between the
refiners can be controlled by pushing the rotor and stator
together. A disc refiner is very similar to the conical refiner.
The pulp travels between two discs with bars and grooves. There are
essentially three categories of disc refiner:
1. Single disc refiners, where the pulp goes between a rotating
rotor and a stationary stator. 2. Twin refiner where the rotor and
stator both rotate.
[0040] In papermaking the refiner serves to increase the
flexibility of the cell wall in order to promote increased contact
area, and also to fibrillate the external surface of the cell wall
to further promote the formation of hydrogen bonds as well as
increase the total surface area of fiber available for bonding.
[0041] The present invention can utilize any of the rotor stator
designs and configurations to create high shear for the purpose of
enhancing cell growth through gas super saturation and lysing
cells.
[0042] As used herein the term supersaturating of gas is used to
describe gas held within a liquid whose instantaneous quantity
exceeds that expected through Henry's Law. Although not wanting to
be limited by theory, supersaturation of gases is believed to occur
due to the extreme pressures under high shear conditions that
increases the solubility of the gas combined with micro dispersion
of the gases in the liquid.
[0043] Furthermore, it has been unexpectedly discovered that lysis
of cells is enhanced by using a high shear device coupled with
introduction of a gas capable of permeating the cell wall and thus
expanding the cell and reducing the cell wall integrity. Such
enhancement is achieved by high shear coupled with gas
super-saturation in the culture medium during lysing or high shear
coupled with a gas-pressurized vessel. The high shear device may be
of a rotor-stator design. Migration of gas is enhanced through
super saturation of gases by means of high shear or via increased
pressures such as in a vessel under elevated pressure. Various
techniques that utilize pressure to enhance cell lysing are known
to those experienced in the art including what is commonly referred
to as a French Press.
[0044] In an embodiment, enhancing cell lysing involves selection
of a suitable gas that preferentially penetrates cell walls. The
selection of a suitable gas is dependent on the nature of the cell
and the gas produced by the cell during respiration. As an example,
yeast that produce carbon dioxide did not exhibit enhanced lysing
when exposed to supersaturated carbon dioxide while yeast exposed
to supersaturated oxygen did exhibit enhanced lysing. The
enhancement of yeast lysing while exposed to supersaturated oxygen
was attributed to the differential gas pressure across the cell
wall and the observed expansion of the cell under exposure to
oxygen as opposed to carbon dioxide.
[0045] The disclosed method and system of enhanced cell lysing can
be applied to any gas producing algae. Selection of a suitable
supersaturated gas is dependent on the nature of the gas being
produced by the cell during respiration. Thus, a cell such as algae
producing oxygen and would be expected to have a higher
concentration of oxygen within the cell wall would not be expected
to experience enhanced lysing from exposure to supersaturated
oxygen. Gases such as carbon dioxide, nitrogen, sulfur oxides, and
other gases that would expect to migrate from the medium to within
the cell walls and reduce cell wall integrity would be expected to
enhance lysing. Similarly it has been shown that yeast producing
carbon dioxide did not experience enhanced lysing when exposed to
supersaturated carbon dioxide but did exhibit enhanced lysing when
exposed to supersaturated oxygen.
[0046] Although oxygen, nitrogen carbon dioxide and sulfur oxide
have been noted as gases to be used in enhancing cell lysing, other
suitable gases can be used to obtain the same effect of reducing
cell wall integrity, e.g., hydrogen, methane. In an embodiment,
hydrogen is super saturated into a medium and contributes to
enhanced lysing in cells that are not producing hydrogen during
respiration.
[0047] High Shear Device.
[0048] The high shear device of this application is shown in FIG. 1
and described herein. Although only one high shear device is shown
in FIG. 1, it should be understood that some embodiments of the
system may have two or more high shear devices arranged either in
series or parallel flow. HSD 200 is a mechanical device that
utilizes one or more generator comprising a rotor/stator
combination, each of which has a gap between the stator and rotor.
The gap between the rotor and the stator in each generator set may
be fixed or may be adjustable. HSD 200 is configured in such a way
that it is capable of producing submicron and micron-sized bubbles
or droplets of inhibitor in a continuous phase comprising the
carrier flowing through the high shear device. The high shear
device comprises an enclosure or housing so that the pressure and
temperature of the fluid therein may be controlled.
[0049] High shear devices are generally divided into three general
classes, based upon their ability to mix fluids. Mixing is the
process of reducing the size of particles or inhomogeneous species
within the fluid. One metric for the degree or thoroughness of
mixing is the energy density per unit volume that the mixing device
generates to disrupt the fluid particles. The classes are
distinguished based on delivered energy densities. Three classes of
industrial mixers having sufficient energy density to consistently
produce mixtures or emulsions with particle sizes in the range of
submicron to 50 microns include homogenization valve systems,
colloid mills and high speed mixers. In the first class of high
energy devices, referred to as homogenization valve systems, fluid
to be processed is pumped under very high pressure through a
narrow-gap valve into a lower pressure environment. The pressure
gradients across the valve and the resulting turbulence and
cavitation act to break-up any particles in the fluid. These valve
systems are most commonly used in milk homogenization and can yield
average particle sizes in the submicron to about 1 micron range.
The high shear device also includes attrition mills.
[0050] At the opposite end of the energy density spectrum is the
third class of devices referred to as low energy devices. These
systems usually have paddles or fluid rotors that turn at high
speed in a reservoir of fluid to be processed, which in many of the
more common applications is a food product. These low energy
systems are customarily used when average particle sizes of greater
than 20 microns are acceptable in the processed fluid.
[0051] Between the low energy devices and homogenization valve
systems, in terms of the mixing energy density delivered to the
fluid, are colloid mills and other high speed rotor-stator devices,
which are classified as intermediate energy devices. A typical
colloid mill configuration includes a conical or disk rotor that is
separated from a complementary, liquid-cooled stator by a
closely-controlled rotor-stator gap, which is commonly between
0.025 mm to 10 mm (0.001-0.40 inch). Rotors are usually driven by
an electric motor through a direct drive or belt mechanism. As the
rotor rotates at high rates, it pumps fluid between the outer
surface of the rotor and the inner surface of the stator, and shear
forces generated in the gap process the fluid. Many colloid mills
with proper adjustment achieve average particle sizes of 0.1-25
microns in the processed fluid. These capabilities render colloid
mills appropriate for a variety of applications including colloid
and oil/water-based emulsion processing such as that required for
cosmetics, mayonnaise, or silicone/silver amalgam formation, to
roofing-tar mixing.
[0052] Tip speed is the circumferential distance traveled by the
tip of the rotor per unit of time. Tip speed is thus a function of
the rotor diameter and the rotational frequency. Tip speed (in
meters per minute, for example) may be calculated by multiplying
the circumferential distance transcribed by the rotor tip, 2.pi.R,
where R is the radius of the rotor (meters, for example) times the
frequency of revolution (for example revolutions per minute, rpm).
A colloid mill, for example, may have a tip speed in excess of 22.9
m/s (4500 ft/min) and may exceed 40 m/s (7900 ft/min). For the
purpose of this disclosure, the term `high shear` refers to
mechanical rotor stator devices (e.g., colloid mills or
rotor-stator dispersers) that are capable of tip speeds in excess
of 5.1 m/s. (1000 ft/min) and require an external mechanically
driven power device to drive energy into the stream of products to
be reacted. For example, in HSD 200, a tip speed in excess of 22.9
m/s (4500 ft/min) is achievable, and may exceed 40 m/s (7900
ft/min). In some embodiments, HSD 200 is capable of delivering at
least 300 L/h at a tip speed of at least 22.9 m/s (4500 ft/min).
The power consumption may be about 1.5 kW. HSD 200 combines high
tip speed with a very small shear gap to produce significant shear
on the material being processed. The amount of shear will also be
dependent on the viscosity of the fluid in HSD 200. Accordingly, a
local region of elevated pressure and temperature is created at the
tip of the rotor during operation of the high shear device. In some
cases the locally elevated pressure is about 1034.2 MPa (150,000
psi). In some cases the locally elevated temperature is about
500.degree. C. In some cases, these local pressure and temperature
elevations may persist for nano or pico seconds.
[0053] An approximation of energy input into the fluid (kW/L/min)
can be estimated by measuring the motor energy (kW) and fluid
output (L/min). As mentioned above, tip speed is the velocity
(ft/min or m/s) associated with the end of the one or more
revolving elements that is creating the mechanical force applied to
the fluid. In embodiments, the energy expenditure of HSD 200 is
greater than 1000 watts per cubic meter of fluid therein. In
embodiments, the energy expenditure of HSD 200 is in the range of
from about 3000 W/m.sup.3 to about 7500 W/m.sup.3.
[0054] The shear rate is the tip speed divided by the shear gap
width (minimal clearance between the rotor and stator). The shear
rate generated in HSD 200 may be in the greater than 20,000
s.sup.-1. As used herein the term s.sup.-1 defined as inverse
seconds, a term known to those experienced in the art to be used in
defining shear rate for a fluid flowing between two parallel plates
In some embodiments the shear rate is at least 40,000 s.sup.-1. In
some embodiments the shear rate is at least 100,000 s.sup.-1. In
some embodiments the shear rate is at least 500,000 s.sup.-1. In
some embodiments the shear rate is at least 1,000,000 s.sup.-1. In
some embodiments the shear rate is at least 1,600,000 s.sup.-1. In
some embodiments the shear rate is at least 2,000,000 s.sup.-1. At
high shear rates (e.g., above 1,000,000 s.sup.-1 or 1,600,000
s.sup.-1 or 2,000,000 s.sup.-1), the HSD is able to super-saturate
the liquid/medium with a gas (or gases), which is advantageous for
algal culture wherein it is necessary and desirable to deliver high
concentrations of CO.sub.2 to algae. So far, such delivery has been
a bottleneck for algal culture and thus for deriving algal oil.
Algae are diverse group of photosynthetic organisms that typically
grow in bodies of water as unicellular or multicellular forms. As
aquatic or marine organisms, algae acquire the carbon dioxide
necessary for photosynthesis by Brownian motion and diffusion.
Further, certain species of algae fix carbon derived from carbon
dioxide to produce and store fatty oils, carbohydrates, proteins,
polysaccharides, and other compounds, hereinafter hydrocarbons. The
acquisition of carbon dioxide, hereinafter CO.sub.2, from water
represents a limiting step in growth rate and storage of these
compounds. As certain algae are potentially useable in liquid fuel
production, the uptake and fixation of carbon is a limiting step in
preparing alga-derived biofuels. The method and system of this
application are capable to reducing this hindrance and
significantly improve efficiency for algal culture and algal oil
recovery.
[0055] In embodiments, the shear rate generated by HSD 200 is in
the range of from 20,000 s.sup.-1 to 100,000 s.sup.-1. For example,
in one application the rotor tip speed is about 40 m/s (7900
ft/min) and the shear gap width is 0.0254 mm (0.001 inch),
producing a shear rate of 1,600,000 s.sup.-1. In another
application the rotor tip speed is about 22.9 m/s (4500 ft/min) and
the shear gap width is 0.0254 mm (0.001 inch), producing a shear
rate of about 901,600 s.sup.-1. HSD 200 is capable of highly
dispersing the inhibitor into a continuous phase comprising the
carrier, with which it would normally be immiscible. In some
embodiments, HSD 200 comprises a colloid mill. Suitable colloidal
mills are manufactured by IKA.RTM. Works, Inc. Wilmington, N.C. and
APV North America, Inc. Wilmington, Mass., for example. In some
instances, HSD 200 comprises the Dispax Reactor.RTM. of IKA.RTM.
Works, Inc.
[0056] The high shear device comprises at least one revolving
element that creates the mechanical force applied to the fluid
therein. The high shear device comprises at least one stator and at
least one rotor separated by a clearance. For example, the rotors
may be conical or disk shaped and may be separated from a
complementarily-shaped stator. In embodiments, both the rotor and
stator comprise a plurality of circumferentially-spaced teeth. In
some embodiments, the stator(s) are adjustable to obtain the
desired shear gap between the rotor and the stator of each
generator (rotor/stator set). Grooves between the teeth of the
rotor and/or stator may alternate direction in alternate stages for
increased turbulence. Each generator may be driven by any suitable
drive system configured for providing the necessary rotation.
[0057] In some embodiments, the minimum clearance (shear gap width)
between the stator and the rotor is in the range of from about
0.025 mm (0.001 inch) to about 3 mm (0.125 inch). In certain
embodiments, the minimum clearance (shear gap width) between the
stator and rotor is about 1.5 mm (0.06 inch). In certain
configurations, the minimum clearance (shear gap) between the rotor
and stator is at least 1.7 mm (0.07 inch). The shear rate produced
by the high shear device may vary with longitudinal position along
the flow pathway. In some embodiments, the rotor is set to rotate
at a speed commensurate with the diameter of the rotor and the
desired tip speed. In some embodiments, the high shear device has a
fixed clearance (shear gap width) between the stator and rotor.
Alternatively, the high shear device has adjustable clearance
(shear gap width).
[0058] In some embodiments, HSD comprises a single stage dispersing
chamber (i.e., a single rotor/stator combination, a single
generator). In some embodiments, high shear device 200 is a
multiple stage inline disperser and comprises a plurality of
generators. In certain embodiments, HSD 200 comprises at least two
generators. In other embodiments, high shear device 200 comprises
at least 3 high shear generators. In some embodiments, high shear
device 200 is a multistage mixer whereby the shear rate (which, as
mentioned above, varies proportionately with tip speed and
inversely with rotor/stator gap width) varies with longitudinal
position along the flow pathway, as further described herein
below.
[0059] In some embodiments, each stage of the external high shear
device has interchangeable mixing tools, offering flexibility. For
example, the DR 2000/4 Dispax Reactor.RTM. of IKA.RTM. Works, Inc.
Wilmington, N.C. and APV North America, Inc. Wilmington, Mass.,
comprises a three stage dispersing module. This module may comprise
up to three rotor/stator combinations (generators), with choice of
fine, medium, coarse, and super-fine for each stage. This allows
for creation of dispersions having a narrow distribution of the
desired bubble or droplet size (e.g., gas bubbles or liquid
droplets of inhibitor). In some embodiments, each of the stages is
operated with super-fine generator. In some embodiments, at least
one of the generator sets has a rotor/stator minimum clearance
(shear gap width) of greater than about 5 mm (0.2 inch). In
alternative embodiments, at least one of the generator sets has a
minimum rotor/stator clearance of greater than about 1.7 mm (0.07
inch).
[0060] Referring now to FIG. 1, there is presented a longitudinal
cross-section of a suitable high shear device 200. High shear
device 200 of FIG. 1 is a dispersing device comprising three stages
or rotor-stator combinations. High shear device 200 is a dispersing
device comprising three stages or rotor-stator combinations, 220,
230, and 240. The rotor-stator combinations may be known as
generators 220, 230, 240 or stages without limitation. Three
rotor/stator sets or generators 220, 230, and 240 are aligned in
series along drive shaft 250.
[0061] First generator 220 comprises rotor 222 and stator 227.
Second generator 230 comprises rotor 223, and stator 228. Third
generator 240 comprises rotor 224 and stator 229. For each
generator the rotor is rotatably driven by input 250 and rotates
about axis 260 as indicated by arrow 265. The direction of rotation
may be opposite that shown by arrow 265 (e.g., clockwise or
counterclockwise about axis of rotation 260). Stators 227, 228, and
229 may be fixably coupled to the wall 255 of high shear device
200.
[0062] As mentioned hereinabove, each generator has a shear gap
width which is the minimum distance between the rotor and the
stator. In the embodiment of FIG. 1, first generator 220 comprises
a first shear gap 225; second generator 230 comprises a second
shear gap 235; and third generator 240 comprises a third shear gap
245. In embodiments, shear gaps 225, 235, 245 have widths in the
range of from about 0.025 mm to about 10 mm. Alternatively, the
process comprises utilization of a high shear device 200 wherein
the gaps 225, 235, 245 have a width in the range of from about 0.5
mm to about 2.5 mm. In certain instances the shear gap width is
maintained at about 1.5 mm. Alternatively, the width of shear gaps
225, 235, 245 are different for generators 220, 230, 240. In
certain instances, the width of shear gap 225 of first generator
220 is greater than the width of shear gap 235 of second generator
230, which is in turn greater than the width of shear gap 245 of
third generator 240. As mentioned above, the generators of each
stage may be interchangeable, offering flexibility. High shear
device 200 may be configured so that the shear rate will increase
stepwise longitudinally along the direction of the flow 260.
[0063] Generators 220, 230, and 240 may comprise a coarse, medium,
fine, and super-fine characterization. Rotors 222, 223, and 224 and
stators 227, 228, and 229 may be toothed designs. Each generator
may comprise two or more sets of rotor-stator teeth. In
embodiments, rotors 222, 223, and 224 comprise more than 10 rotor
teeth circumferentially spaced about the circumference of each
rotor. In embodiments, stators 227, 228, and 229 comprise more than
ten stator teeth circumferentially spaced about the circumference
of each stator In embodiments, the inner diameter of the rotor is
about 12 cm. In embodiments, the diameter of the rotor is about 6
cm. In embodiments, the outer diameter of the stator is about 15
cm. In embodiments, the diameter of the stator is about 6.4 cm. In
some embodiments the rotors are 60 mm and the stators are 64 mm in
diameter, providing a clearance of about 4 mm. In certain
embodiments, each of three stages is operated with a super-fine
generator, comprising a shear gap of between about 0.025 mm and
about 4 mm.
[0064] High shear device 200 is configured for receiving at inlet
205 a fluid mixture from line 13. The mixture comprises inhibitor
as the dispersible phase and carrier fluid as the continuous phase.
Feed stream entering inlet 205 is pumped serially through
generators 220, 230, and then 240, such that product dispersion is
formed. Product dispersion exits high shear device 200 via outlet
210 (and line 18 of FIG. 1). The rotors 222, 223, 224 of each
generator rotate at high speed relative to the fixed stators 227,
228, 229, providing a high shear rate. The rotation of the rotors
pumps fluid, such as the feed stream entering inlet 205, outwardly
through the shear gaps (and, if present, through the spaces between
the rotor teeth and the spaces between the stator teeth), creating
a localized high shear condition. High shear forces exerted on
fluid in shear gaps 225, 235, and 245 (and, when present, in the
gaps between the rotor teeth and the stator teeth) through which
fluid flows process the fluid and create product dispersion.
Product dispersion exits high shear device 200 via high shear
outlet 210.
[0065] The product dispersion has an average droplet or gas bubble
size less than about 5 .mu.m. In embodiments, HSD 200 produces a
dispersion having a mean droplet or bubble size of less than about
1.5 .mu.m. In embodiments, HSD 200 produces a dispersion having a
mean droplet or bubble size of less than 1 .mu.m; preferably the
droplets or bubbles are sub-micron in diameter. In certain
instances, the average droplet or bubble size is from about 0.1
.mu.m to about 1.0 .mu.m. In embodiments, HSD 200 produces a
dispersion having a mean droplet or bubble size of less than 400
nm. In embodiments, HSD 200 produces a dispersion having a mean
droplet or bubble size of less than 100 nm. The dispersion may be
capable of remaining dispersed at atmospheric pressure for at least
about 15 minutes.
[0066] Without wishing to be limited to a particular theory, it is
believed that the level or degree of high shear may be sufficient
to increase rates of mass transfer and also produce localized
non-ideal conditions that enable reactions to occur that would not
otherwise be expected to occur based on Gibbs free energy
predictions. Localized non ideal conditions are believed to occur
within the high shear device resulting in increased temperatures
and pressures with the most significant increase believed to be in
localized pressures. The increase in pressures and temperatures
within the high shear device are instantaneous and localized and
quickly revert back to bulk or average system conditions once
exiting the high shear device. In some cases, the high shear device
induces cavitation of sufficient intensity to dissociate one or
more of the reactants into free radicals, which may intensify a
chemical reaction or allow a reaction to take place at less
stringent conditions than might otherwise be required. Cavitation
may also increase rates of transport processes by producing local
turbulence and liquid micro-circulation (acoustic streaming). An
overview of the application of cavitation phenomenon in
chemical/physical processing applications is provided by Gogate et
al., "Cavitation: A technology on the horizon," Current Science 91
(No. 1): 35-46 (2006). The high shear device of certain embodiments
of the present system and methods induces cavitation whereby
inhibitor and/or carrier fluid are dissociated into free radicals.
The cavitation effects cause and promote the disintegration of
algal cells, allowing fast and efficient release of all
intracellular oil.
[0067] Algal Oil Recovery Process.
[0068] In an embodiment, the method of this disclosure comprises
processing a medium containing algae microorganisms to produce
algal oil and by-products, comprising providing the medium
containing algae microorganisms; passing said medium through a
rotor-stator high shear device; disintegrating cell walls of and
intracellular organelles in the algae microorganisms to release
algal oil and by-products; and removing the algae medium from an
outlet of the high shear device. The processed medium contains
algal oil, extracted from the broken cells, the cell debris and
other components. In some cases, the high shear device for cell
lysing is operated at a shear rate of 20,000 to 10,000,000, or
alternatively 100,000 to 2,000,000, or alternatively 200,000 to
500,000 (in inverse seconds, s.sup.-1). In some cases, the high
shear device for cell lysing is operated at a shear rate of 200,000
s.sup.-1 or above. In some cases, the high shear device for cell
lysing is operated at a shear rate of 200,000 s.sup.-1 or above. In
some cases, the high shear device for cell lysing is operated at a
shear rate of 300,000 s.sup.-1 or above. In some cases, the high
shear device for cell lysing is operated at a shear rate of 400,000
s.sup.-1 or above. In some cases, the high shear device for cell
lysing is operated at a shear rate of 500,000 s.sup.-1 or above. In
some cases, the high shear device for cell lysing is operated at a
shear rate of 600,000 s.sup.-1 or above. In some cases, the high
shear device for cell lysing is operated at a shear rate of 700,000
s.sup.-1 or above. In some cases, the high shear device for cell
lysing is operated at a shear rate of 800,000 s.sup.-1 or above. In
some cases, the high shear device for cell lysing is operated at a
shear rate of 900,000 s.sup.-1 or above. In some cases, the high
shear device for cell lysing is operated at a shear rate of
1,000,000 s.sup.-1 or above. In some cases, the high shear device
for cell lysing is operated at a shear rate of 2,000,000 s.sup.-1
or above. It should be noted that as the shear rate is calculated
by measuring the shear gap and rotor speed, in the case where the
configuration of the rotor stator is a disc or conical the shear
rate (inverse seconds) will vary across the disc or cone as the
apparent rotational speed will vary across the radius of the disc.
In such cases, the ranges mentioned above apply to the average
shear rates of such rotor-stator devices.
[0069] In some cases, the medium containing algae microorganisms is
de-watered at least partially before the medium is passed through
said high shear device. In some cases, the medium is de-watered to
obtain dry algae for further processing. In some embodiments, a
solvent is added to the at least partially de-watered medium before
the medium is passed through said high shear device. In some cases,
the solvent is a gas comprising carbon dioxide or air or oxygen or
nitrogen. In some cases, the solvent is a liquid comprising an
alcohol or hexane or vegetable oil and/or animal fat or tallow. In
an embodiment, 30% or more of algal oil is released for
recovery.
[0070] After lysing the algae, the algal oil and byproducts are
separated from the medium. The separation process is known in the
art and comprises a process selected from the group consisting of
washing, sedimentation, centrifugation, filtration, vaporization,
distillation, freezing, extraction, or combinations thereof. Any
suitable separation process is contemplated to be within the scope
of this disclosure. In embodiments, the separated algal oil is then
converted to valuable products, e.g., fuel including biodiesel, by
any means known in the art. In embodiments, the separated
byproducts are used for producing pharmaceuticals or fertilizers or
animal feeds.
[0071] In an embodiment, 30% or more of algal oil is released and
recovered. In an embodiment, 40% or more of algal oil is released
and recovered. In an embodiment, 40% or more of algal oil is
released and recovered. In an embodiment, 50% or more of algal oil
is released and recovered. In an embodiment, 60% or more of algal
oil is released and recovered. In an embodiment, 70% or more of
algal oil is released and recovered. In an embodiment, 80% or more
of algal oil is released and recovered. In an embodiment, 90% or
more of algal oil is released and recovered.
[0072] Algae Culture Process.
[0073] In a further embodiment, an improved algae culture/growth
process comprises super-saturating a liquid with carbon dioxide in
a second rotor-stator high shear device operating at a shear rate
of greater than 1,000,000 s.sup.-1; feeding said carbon dioxide
supersaturated liquid and a nutrient source to algae microorganisms
and optionally bacteria; allowing the algae microorganisms to grow
by consuming carbon dioxide and the nutrient; and generating said
medium containing algae microorganisms. In various embodiments, the
nutrient source is any source that enables microorganism growth,
including but not limited to municipal waste, sewage waste, paper
pulp, chemical and petrochemical, vegetable (grain, sugar), farm
discharge, animal farm discharge (beef, pork, poultry), canning
discharge, or fishing discharge as well as other nutrient
containing discharge from other farming and farm product processing
operations. Carbon dioxide may be obtained from any source, such as
power plants, refineries, paper mills.
[0074] In various embodiments, the nutrient source may contain
undesirable microorganisms, e.g., sewage waste. These undesirable
microorganisms are herein called pathogens in this disclosure. As
such, the nutrient is pretreated before fed to the microorganisms.
The pretreatment comprises lysing the cells of the undesirable
pathogens using a high shear device assisted by a penetrating gas
(e.g., in super-saturation state) as discussed herein. Preferably,
the penetrating gas is different from the gas produced by the cells
of the pathogens during respiration. For example, the nutrient
source is super saturated with a blend of oxygen (air or
oxygen-enriched air or oxygen) and carbon dioxide using a high
shear device and then passed through another high shear device. Or
the nutrient source is pretreated in a high shear device while a
suitable penetrating gas or gas combination is simultaneously fed
into the high shear device. Alternatively, the nutrient source is
held in a French Press containing a pressurized penetrating gas for
a period of time and then processed in a high shear device. By such
pretreatment, the pathogens are eliminated and the nutrient source
is suitable for algae culture.
[0075] In other embodiments, the pretreatment of the nutrient
source using high shear (with or without gas assistance) is able to
break down the nutrient (e.g., sugar, carbohydrate) in the nutrient
source to miniscule size so that it is easily digested/consumed by
the microorganisms. As such, the bio-availability of the dispersed
nutrient is significantly increased to promote microorganism
growth.
[0076] In embodiments, the algae and/or bacteria used in this
process are genetically modified. Such genetic modification is
performed based on the type of the nutrient source to maximize
algae growth. The bacteria that are co-cultured with algae cause
the breakdown of said nutrient source to promote algae growth.
[0077] System for Algal Oil Recovery.
[0078] In an embodiment, a system that is capable of recovering
algal oil comprise a rotor-stator high shear device configured to
process a medium containing algae microorganisms to produce algal
oil and by-products, wherein said high shear device is operated to
disintegrate cell walls of and intracellular organelles in the
algae microorganisms to release algal oil and by-products, wherein
said high shear device comprises an inlet to take in said medium
containing algae microorganisms and an outlet for the algae medium
to be removed from the high shear device. In some cases, the system
comprises at least two rotor-stator high shear devices fluidly
connected in series to process said medium containing algae
microorganisms and disintegrate cell walls of and intracellular
organelles in the algae microorganisms to release algal oil and
by-products. In various embodiments, the system further comprises a
separation system configured to separate algal oil and by-products
from the medium. In embodiments, the system further comprises a
conversion system configured to convert algal oil to biodiesel.
Such separation and conversion systems are known in the art and all
such suitable systems are considered to be within the scope of this
disclosure.
[0079] System for Algae Culture.
[0080] In another embodiment, an algae culture system upstream of
the algal oil recovery system comprises a tank or pond configured
to grow algae containing algae microorganisms and optionally
bacteria; a nutrient source consumable by said algae microorganisms
and optionally bacteria; another rotor-stator high shear device
configured to process carbon dioxide in a liquid operating at a
shear rate of greater than 1,000,000 s.sup.-1 to form a carbon
dioxide super-saturated liquid stream and feed said stream into the
tank/pond for algae growth; and a fluid line configured to extract
a medium containing algae from the tank or pond and send the medium
to the rotor-stator high shear device configured to process said
medium. The combination of the algae culture system and algal oil
recovery system are modular, versatile, and movable. As such, it is
easy to integrate such systems with an existing facility for carbon
dioxide sequestration, waste management, and bio-fuel production.
As is clear to one skilled in the art, such integration has
numerous benefits and fulfills a multitude of purposes.
[0081] Algae Culture and Algal Oil Recovery.
[0082] In an embodiment, as illustrated schematically in FIG. 2, an
overall process flow of algae culture and algal oil recovery is
shown. A waste stream or water source (i.e., nutrient source) is
super saturated with gas (CO.sub.2 and optionally O.sub.2/air) in a
high shear device. Oxygen or air is added in some cases, e.g., the
use of sewage waste as the nutrient source so that the BOD and COD
contents would meet standards. The supersaturated stream is
introduced to algae/bacteria growth chamber. After the desired
growth of algae is achieved, a medium containing algae is processed
in another rotor-stator high shear device as described herein above
for cell lysing. Algal oil and byproducts are released and
subsequently recovered.
[0083] In an embodiment, as shown in FIG. 3, a feedstock (e.g.,
feedstock from water source and/or recycle stream from a chemical
plant, power plant, waste treatment, paper mill or other process
operation producing waste stream) is fed through a pump to one or
more high shear units. Gas injection of CO.sub.2 (and optionally
O.sub.2/air) may take place before or after the pump before the
high shear units. A supersaturated stream is obtained and fed to
the growth vessel (or raceway/pond) of algae. In some cases, a
portion of the supersaturated stream is recycled through the high
shear units. In some cases, a portion of the medium in the growth
vessel is recycled through the high shear units. When desired
growth of algae is reached, a medium containing algae is taken from
the growth vessel to the lysing and recovery processes
downstream.
[0084] In an embodiment, as illustrated by FIG. 4, a medium
containing algae (grown/mature algae) and optionally diatomaceous
earth is sent through a pump (e.g., Cole Palmer pump) to one or
more high shear devices for cell lysing. Optionally a solvent is
added (e.g., CO.sub.2 or hexane) either before the pump or after
the pump to be processed in the high shear device. In some cases,
one of the high shear devices is a MK2000/4 colloid mill by IKA.
After cell lysing, the medium containing the released algal oil,
byproducts, and cell debris is sent to a separation and recovery
process.
[0085] In an embodiment, as illustrated by FIG. 4, a medium
containing algae (grown/mature algae) and inorganics (e.g.,
diatomaceous earth) is sent through a pump (e.g., Ross pump) to one
or more high shear devices for cell lysing. Optionally a solvent is
added (e.g., CO.sub.2 or hexane) either before the pump or after
the pump to be processed in the high shear device. In some cases,
one of the high shear devices is a MK2000/4 colloid mill by IKA. In
some cases, recycle streams are extracted and sent through one or
more high shear units for multiple-pass operation. After cell
lysing, the medium containing the released algal oil, byproducts,
and cell debris is sent to a sludge separation tank (optional). A
bottom stream from the separation tank is taken to recycle for
biomass, sludge, water feed, and/or sugar recovery. The top layer
from the separation tank is extracted and separated (under optional
vacuum) into oil, water, and biomass. The water and biomass are
recycled for desired use and the oil is further processed and
converted to biodiesel.
[0086] Detail `A` in FIGS. 4 and 5 for fluid connection is shown in
FIG. 6. As is known to one skilled in the art, any comparable
arrangement may be made to serve the same function and is
contemplated to be within the scope of this disclosure.
[0087] Features.
[0088] The disclosed method and system are versatile, low in
capital cost and operational cost. Furthermore, the system is
modular, making it easy to be integrated into any existing facility
or infrastructure, e.g., power plants, sewage treatment plants,
canning factories, food processing units, etc.
[0089] The separated solids may be recycled and used for many other
purposes, such as producing pharmaceuticals, fertilizers, animal
feeds, etc.
Example 1
[0090] Effects of Super-Saturation Using High Shear.
[0091] Carbon dioxide (CO.sub.2) is readily soluble in water in the
form of a dissolved gas. Surface waters normally contain less than
10 ppm free carbon dioxide, while some ground waters may easily
exceed that concentration. Over the typical temperature range
(0-30.degree. C.), the solubility is about 200 times that of
oxygen. When CO2 reacts with water, it immediately forms carbonic
acid (H.sub.2CO.sub.3), which is relatively unstable. This further
dissociates to form bicarbonate (HCO.sub.3.sup.-) and carbonate
(CO.sub.3.sup.2-) ions.
[0092] Compared with oxygen, the estimation of carbon dioxide in
water presents much greater difficulties. Although pH is widely
used to measure the presence of carbonic acids and carbonates in
solution, the presence of carbonate forming ions, including
calcium, magnesium, and sodium may interfere with total dissolved
carbon measurements.
[0093] The total inorganic carbon (TIC) or dissolved inorganic
carbon (DIC) is the sum of inorganic carbon species (including
carbon dioxide, carbonic acid, bicarbonate anion, and carbonate) in
a solution. It is customary to express carbon dioxide and carbonic
acid simultaneously as CO2*. TIC is a key parameter when making
measurements related to the pH of natural aqueous systems, and
carbon dioxide flux estimates:
TIC=[CO.sub.2*]+[HCO.sub.3.sup.-]+[CO.sub.3.sup.2-]
[0094] where, TIC is the total inorganic carbon; [CO.sub.2*] is the
sum of carbon dioxide and carbonic acid concentrations
([CO.sub.2*]=[CO.sub.2]+[H.sub.2CO.sub.3]); [HCO.sub.3.sup.-] is
the bicarbonate concentration; [CO.sub.3.sup.2-] is the carbonate
concentration.
[0095] Each of these species are related by the following pH-driven
chemical equilibrium equation:
CO.sub.2+H.sub.2OH.sub.2CO.sub.3H.sup.++HCO.sub.3.sup.-2H.sup.++CO.sub.3-
.sup.2-
[0096] The concentrations of the different species of DIC (and
which species is dominant) depend on the pH of the solution, as
shown by a Bjerrum plot. Total inorganic carbon is typically
measured by the acidification of the sample which drives the
equilibria to CO.sub.2. This gas is then sparged from solution and
trapped, and the quantity trapped is then measured, usually by
infrared spectroscopy using a Total Organic Carbon (TOC)
analyzer.
[0097] Total Organic Carbon (TOC) is a sum measure of the
concentration of all organic carbon atoms covalently bonded in the
organic molecules of a given sample of water. TOC is typically
measured in Parts Per Million (ppm or mg/L). As a sum measurement,
Total Organic Carbon does not identify specific organic
contaminants. It will, however, detect the presence of all
carbon-bearing molecules, thus identifying the presence of any
organic contaminants, regardless of molecular make-up.
[0098] A typical analysis for TOC measures both the Total Carbon
(TC) as well as Inorganic Carbon (IC, or carbonate). Subtracting
the Inorganic Carbon from the Total Carbon yields TOC.
(TC-IC=TOC).
[0099] Dissolved oxygen can easily be measured and reported as mg/L
using a dissolved oxygen probe (Milwaukee Instruments) submerged in
solution.
[0100] Initially, 3 L of distilled water were sheared using a high
shear device to monitor the concentration of dissolved oxygen in
solution over time. However, the concentration of dissolved oxygen
exceeded the measurement capability of the dissolved oxygen probe
(MW600, Milwaukee Instruments). Therefore, the test was repeated
and the supersaturated oxygen solution was immediately diluted 1:10
prior to measurements. In this case, three liters of distilled
water were sheared in the presence of oxygen gas and quickly
diluted to a 1:10 concentration in 3 one liter flasks. The
concentration of the 1:10 supersaturated oxygen solution was
initially measured to be an average of 17.6 mg/L. Within 5 minutes,
the concentration of the dissolved oxygen dropped to an average of
6.7 mg/L, a 62% loss of dissolved oxygen in the 1:10 solution
(FIGS. 7 and 8). To establish the dissolved oxygen equilibrium
point, the dissolved oxygen concentration was monitored daily for a
total of 4 days. The data show that a dissolved oxygen equilibrium
point was reached between 2 and 3 days following supersaturation,
and that the dissolved oxygen concentration maintained a final
concentration of 4.3 mg/L. As a control, the dissolved oxygen
concentration of distilled water was concurrently monitored at 4.3
mg/L throughout the test. These results indicate that the tested
shear technology effectively supersaturates distilled water with
oxygen; however, this effect is of very short duration.
[0101] Similar to the supersaturated oxygen tests, 3 liters of
distilled water were sheared in the presence of carbon dioxide and
evaluated for total dissolved carbon using a TOC analyzer. Also
like the dissolved oxygen tests, the concentration of dissolved
carbon in the neat solution exceeded the instrument's measurement
capability. Therefore, the neat solution was diluted to 1:10,
1:100, and 1:1000 in triplicate to quantify dissolved carbon over
time. Potassium hydrogen phthalate (KHP) is commonly used as a
standard for dissolved carbon measurements by TOC. A freshly
prepared 10 g/L KHP solution of was diluted into a concentration
range between 1 mg/L-1000 mg/L and used to establish the dissolved
carbon standard curve. This range of standards was prepared daily,
while the original diluted supersaturated CO2 solutions were
maintained in septum-sealed glass vials and measured daily to
quantify dissolved carbon over time and establish the SSCO2
equilibrium point. The pH of each solution was concurrently
monitored.
[0102] The average initial concentration of the 1:10 dissolved
carbon solution was measured to be 5675 ppm, or 5675 mg/L. The
initial pH of each solution averaged 3.4. This unusually high
concentration of dissolved carbon was confirmed by preparing fresh
SSCO2 distilled water solutions and repeating the TOC measurement.
The concentration of dissolved carbon dropped by about 47% within 2
days, then reached equilibrium within the following 2 days (FIG.
9). The final dissolved carbon concentration of the 1:10 SSCO2 was
measured to be an average of 2655 mg/L and a pH of 3.4. As a
control, distilled water was likewise measured. The TOC measurement
of dissolved carbon in distilled water was 0 mg/L and the pH was
measured to be 7.
[0103] The concentration of dissolved carbon in the 1:100 and
1:1000 SSCO2 solutions likewise diminished in the first 2-3 days,
then reached equilibrium within 4 days (FIG. 9). The pH of each of
these solutions also remained consistent throughout the tests at pH
3.4 and 3.5 respectively. These data indicate that even a small
amount of dissolved CO2 in distilled water causes a drop in pH from
an initial value of 7 to 3.4-3.5 and that pH alone cannot be used
to calculate the concentration of dissolved carbon in distilled
water when excess carbon is present. Interestingly, when the loss
of dissolved carbon is expressed as a percentage of the total
measured carbon, all three dilutions showed a similar pattern (FIG.
10). These data indicate that the rate of loss of dissolved carbon
from a shear-induced supersaturated solution is independent of
initial concentration and that the dilution of a SSCO2 solution
with additional distilled water may provide an accommodating
environment for excess CO2. It should also be noted these data were
collected from diluted solutions which may or may not be easily
extrapolated to reflect a neat SSCO2 solution.
[0104] Results Summary.
[0105] Shearing of distilled water in the presence of oxygen gas
produces a supersaturated oxygen solution. Shearing of distilled
water in the presence of carbon dioxide gas produces a
supersaturated carbon dioxide solution that is maintained over
time. The initial concentration of dissolved carbon in a SSCO2
solution diluted to 1:10 was 5675 mg/L, which then equilibrated to
maintain a concentration of 2655 mg/L. The percentage loss of
dissolved carbon from diluted SSCO2 solutions was consistent over
the range of dilutions. Addition of dissolved carbon to distilled
water causes a drop in pH from 7 to .about.3.4, but does not
reflect the concentration of dissolved carbon when excess carbon is
present.
[0106] As demonstrated by Example 1, the significant
super-saturation level of carbon dioxide in solution caused by high
shear processing is able to promote algae growth and reduce/resolve
the bottleneck of insufficient CO.sub.2 delivery to algae
microorganisms, which is critical in algae culture and recovery of
algal oil.
Example 2
[0107] Effects of Cell Lysing Using High Shear.
[0108] Cost-effective methods of disruption of the algal cell wall
are fundamental to obtain higher lipid extraction efficiencies,
meaning greater net energy output from the process. For this
example, the effects of a method of algae cell disruption,
CO2-assisted high shear, was assessed using cultured Chlorella sp.
The combination of the actions of supersaturated micro-sized
CO.sub.2 bubbles and physical shearing offer a unique hybrid
approach to algae cell lysing and lipid recovery. It has been
unexpectedly discovered that supersaturated micro-sized CO.sub.2
bubbles work in synergy with mechanical high shear action to
improve cell disintegration efficiency.
[0109] Although the energy required vs. energy recovery (energy
return on investment) of this system was not assessed during the
current testing, the system is expected to improve upon the EROI of
other algae disruption technologies because it does not require
pre-drying, high pressures, nor increased heat. Rather, it relies
on cost-effective technologies. The efficiency and damage
characteristics induced with these treatments were quantified and
evaluated using direct optical microscopy and cell counting
techniques. Release and recovery of intracellular lipids were also
quantified.
[0110] Materials and Methods.
[0111] Algae Biomass and Lipid Production. Chlorella sp. (UTEX
2714) were cultivated in Bold 3N growth media and scaled to 500 L
within 8'' diameter vertical airlift photobioreactors exposed to a
daily 18/6 cycle of artificial illumination. Cell culture density
was measured daily by dry cell weight. Nitrogen was limited once
the culture reached 1.8 g/L to stimulate lipid accumulation within
the cells. Once the culture density reached 2 g/L, 10% of each
culture was tested as "dilute" culture while the remaining 90% of
the culture was concentrated by centrifugation to a final
"concentrate" of 12-15 g/L pumpable slurry. Algae lipids were
extracted using a modified Folch method, quantified
gravimetrically, and expressed as % total lipid/dry cell
weight.
[0112] CO2-Assisted High Shear Algae Cell Disruption Set Up and
Test Matrix.
[0113] The process flow for CO2-assisted high shear algae cell
disruption is shown in FIG. 11. Biomass slurry sample flow and
processing was initiated as follows: the fluid flow pressure of
dilute or concentrated algal slurry through the system was
initiated at .about.80 psi and subsequently increased to 85-105
psi. The high shear unit was then turned on and maintained at a
rotational speed of 15,000 or 26,000 rpm as indicated in the
results section. Diffused CO2 was introduced into the system at the
shear unit an initial pressure of 80 psi, then adjusted to 85-105
psi to reduce sample sputtering from the collection nozzle. When
applicable, the colloid mill was turned on. In some test cases, the
back pressure to the shear unit was increased in increments of 20
psi from 0 psi to 80 psi. Once the target test parameters were met,
processed samples were collected in Erlenmeyer flasks for
subsequent cell disruption and lipid release analyses.
[0114] A matrix of test conditions were applied to the algae
samples. Matrix variables included fluid flow pressure entering the
high shear unit (0, 80-150 psi), back pressure to the high shear
unit (0-80 psi), CO2 pressure entering the high shear unit (0,
80-105 psi), and dilute (2 g/L DCW) vs. concentrated (12-13 g/L)
Chlorella algae.
[0115] Quantification of Cell Disruption.
[0116] The effectiveness of each treatment was qualitatively
visualized by brightfield microscopy (10.times.-40.times.), and
quantified by measuring the fraction of physically disrupted cells
(Spiden, 2013). ImageJ, a public-domain image processing and
analysis software, was used to ensure consistency in cell counting
by minimizing variability in analysis between samples. Measurements
of the total area occupied by cells were used to verify the intact
cell counts. This was particularly useful for samples with cell
clumping, typically observed in samples that had been homogenized
at higher pressures. All imaging was performed using an AmScope
B120C-E1 Siedentopf Binocular Compound Microscope with a 1.3 MP
digital camera. Cell counts were compared to unprocessed (flowed
through the system but no shear, mill, or CO2) algae from the same
batch. Cell viability was assessed using a standard XTT viability
assay, which measures mitochondrial enzymatic activity.
[0117] Quantification of Recovered Extracellular Lipids Following
Shear Processing.
[0118] Lipids released as a result of cell rupture were quantified
by sweeping the extracellular medium by inversion with 10% hexane
for 30 seconds. The hexane layer containing released lipids was
phase partitioned and recovered following centrifugation of the
sample. Following hexane distillation, the recovered dry lipids
were quantified gravimetrically and expressed as the % of released
lipids/dry cell weight of biomass.
[0119] System Operation and Cleaning.
[0120] Prior to activating the system for each set of tests, warm
tap water was cycled through the system. Once flow was established,
each component (high shear unit, CO2 gas flow, colloid mill) of the
system was turned on. The system was deemed fully operational if:
1) the fluid flow through the system was unrestricted, 2) the shear
and colloid mill units reached full rotational speed, 3) all gas
and fluid flow pressures were achieved, and 4) the pH of the final
water solution dropped to expected levels, typically from .about.pH
8-9 to .about.pH 5-6. The system was then turned off, the remaining
water in the system was replaced with algae slurry, and the process
was repeated prior to adjusting test parameters and data
collection. Following each set of tests, any remaining algae slurry
in the system was replaced with warm tap water, which was
circulated through the system for 30 minutes prior to shutting the
system down. In some cases, a thin opaque film lining the clear
tubing in the system was observed in the following days, suggesting
that a biofilm may have developed within the system. This
observation was further supported when it was also noted that the
fluid flow through the system appeared to be slightly restricted
upon start-up. In these cases, isopropyl alcohol was circulated
through the system, followed by a citrate solution, until the fluid
flow was restored.
[0121] Following system operation using diatomaceous earth, the
restriction in fluid flow was even more pronounced and in some
cases, the high shear unit became non-operational and displayed an
Error F50 message (rotor shaft blocked). Cleaning the flow path
with the isopropyl alcohol-citrate method was insufficient to
restore fluid flow or shear unit operation. Instead, the system
required disassembly, direct soft brush cleaning, and reassembly
before the system could be restored to and operational condition.
The disassembly included the plumbing emanating from the mag lev
pump to the shear unit and the rotor shaft of the high shear unit
(FIG. 12). Once the system was manually cleaned and reassembled,
operation was restored and testing was resumed. The issues with
restricted fluid flow caused by the addition of diatomaceous earth
may become less relevant as the system is scaled up to a commercial
scale, although biofilm formation may still occur.
[0122] Results and Discussion.
[0123] In order to identify the operating conditions that maximized
algae cell disruption, a test matrix in which individual parameters
were varied one at a time was created. Testing started with the
basic CO2-assisted high shear system alone, followed by the
addition of diatomaceous earth (silica remnants of algae diatoms)
to enhance local shearing, and finally by the downstream addition
of a colloid mill.
[0124] CO2-Assisted High Shear Algae Cell Disruption.
[0125] Initially, dilute and concentrated Chlorella sp. cells were
processed through the CO2-assisted high shear unit at 15,000 rpm
without additional exposure to the downstream colloid mill. In our
previous work, we had shown that the infusion of excess CO2 into
the process stream supersaturates the effluent solution with CO2
and causes a significant drop in slurry pH. Since the infusion of
excess CO2 into the shear unit was integral to the current cell
disruption process flow, we again monitored pH throughout these
tests. Along with changes in pH, the fluid flow pressures at
various points throughout the process flow path were systematically
changed one at a time in order to identify the operating parameters
that maximized algae cell rupture, which was qualitatively
evaluated microscopically following each sample run. To quantify
the percentage of cells disrupted (lysed) following some test runs,
cell counts were also performed on equal volumes of processed
unprocessed control cells from the same batch. The pH of the
processed slurry dropped by .about.35%, indicating that the infused
CO2 was supersaturated into the buffered algae slurry. However,
none of the initial operating test conditions, 80-150 psi (shear
influent), 80-105 psi (CO2), 0 psi back pressure to the shear unit
caused any significant cell disruption. Others have reported robust
mechanical (blender) shear-induced algae lysis for algae exposed to
the shearing forces for 20 minutes. For the current tests, the
shearing mechanism differs in three important ways: algae slurry
flows through an inline dual-stage particle distribution rotor, CO2
is directly fed into the process flow stream, and exposure to shear
forces in this system is 1-2 seconds. Given the short exposure time
and microscopic size of the individual cells (3-5 .mu.m), Following
an initial evaluation, the culture was re-processed through the
unit a second time (2.sup.nd pass) and samples were again imaged
immediately. Although not significant, some cell disruption was
visualized by the presence of additional cell debris and a 4%
decline in cell number compared to controls. A 3.sup.rd pass of the
slurry through the system did not cause additional cell disruption,
suggesting that additional processing beyond a single pass may not
be useful (for Chlorella).
[0126] Because the slurry is supersaturated with CO2 as it is
processed through the system, and excess CO2 is lethal to many
species of algae, the effects of prolonged exposure to excess CO2
were likewise evaluated. An additional 60-minute incubation
following processing revealed striking differences between these
samples and freshly processed or control samples. Significantly
more cellular debris was visualized microscopically and on a
macroscopic scale, the color of the 1st pass culture changed from a
bright kelly green to a greenish-gray. These data indicate not only
cellular compromise, but that the phytol tails of chlorophyll
molecules within the slurry had been cleaved, changing the overall
optical character of the slurry. This effect was further
exaggerated after a 120 minute waiting period (FIG. 13).
[0127] These tests were repeated with thawed (non-viable) algae
concentrate (14% w/v) with very different results. There was no
increased cellular debris visualized following either the 1st and
2nd pass, nor was there any increased cell disruption following an
additional 60 m or 120 m incubation period. Together, these data
suggest that the increased cell disruption following additional
incubation in the supersaturated CO2 slurry was caused by the
chemical actions of excess CO2 rather than mechanical shearing.
Although CO2-induced cell disruption appears to be a somewhat
effective method to compromise a small population of viable
Chlorella, the optical changes that occurred with this process also
suggest that unwanted chemical degradation to targeted co-products
may also be occurring.
[0128] As a means to increase the CO2 cavitation effects within the
shear unit, the back pressure to the shear unit was incrementally
increased from 0-80 psi. The shear unit influent pressure was held
at 100 psi and the CO2 gas pressure to the shear unit was likewise
held at 100 psi. At 0 psi back pressure to the shear unit, the
slurry exiting the process flow collection nozzle could be
described as "sputtering and spitting" and minimal lysis was
observed. Applying back pressure to the unit (20, 40, 60 and 80
psi) caused both decreased sputtering and increased cell
disruption, with the greatest effects at 20 psi and 40 psi (FIG.
14). At these back pressures, fluid flow exiting the collection
nozzle was restored to a consistent stream. Cellular debris was
estimated to be the result of .about.30% cell lysis, and was
quantified by cell counts to be 27%. Following an additional 2 h
incubation period, total cell lysis increased to 73%.
[0129] Summary of CO2-Assisted High Shear Algae Cell
Disruption.
[0130] The effects of all fluid and gas flow variables tested
through the mechanical shearing (15,000 rpm) unit on viable dilute
Chlorella cells were negligible. Although immediate cell disruption
was not apparent, viable Chlorella cells that were further
incubated in the processed supersaturated CO2 slurry were disrupted
in a time-dependent manner. Cell disruption caused by an extended
exposure to excess CO2 caused additional chemical reactions that
negatively impact chlorophyll. Applying a back pressure of 20-40
psi to the shear unit enhanced the immediate effects of the
CO2-assisted high shear process.
[0131] Diatomaceous Earth+CO2-Assisted High Shear Algae Cell
Disruption.
[0132] Diatomaceous earth consists of fossilized remains of
diatoms, a type of hard-shelled (silica) algae, and is used
commercially as a mild abrasive. Abrasive materials that are
similar in size to the individual algae cells (.about.5 .mu.m) can
enhance cell shearing. As part of the testing matrix, 0.01-1% w/v
of diatomaceous earth (7-10 .mu.m) was homogenized into to the
algae slurry prior to entering the process stream. The rotational
speed of the shear unit was also increased from 15,000 rpm to
26,000 rpm. A matrix of tests was conducted, with 100 psi influent,
100 psi gas pressure, and 40 psi back pressure to the shear unit
yielding the best results. Initially, a 1% (w/v) solution was added
to the algae slurry and processed through the system. This caused
the system, including the plumbing and the shear unit rotor shaft
to clog. Following manual cleaning, the concentration of
diatomaceous earth was reduced to 0.01% (w/v). The addition of
0.01% DE to the algae slurry processed under the matrix test
conditions yielded similar cell lysing results as controls with no
DE. However, the Chlorella cells that were originally present in
clusters were separated into single cells following a first pass
through the shear unit. A second pass of the 0.01% DE SSCO2 algae
slurry through the system did not improve immediate cell rupturing.
When the concentration of DE was increased to 0.1%, the lysing
efficiency from a single pass improved significantly. Like the
result using a 0.01% DE supplement, clusters of algae cells were
separated into single cells and the percentage of lysed cells
following a single pass was 54%. Further, an oily sheen was
detected on the surface of the processed slurry, indicating the
release of intracellular lipids from the algae cells within the
process slurry. This result could not be repeated, however, as the
system clogged repeatedly using a DE concentration of 0.1%. This
54% increase in lysing may have been a single result of the
accumulated DE in the system, and when the system was cleaned, this
effect was lost.
[0133] Summary of Diatomaceous Earth+CO2-Assisted High Shear Algae
Cell Disruption.
[0134] Increasing the rotational speed of the shear unit from
15,000 rpm to 26,000 rpm (maximum) did not cause additional cell
disruption over controls (15,000 rpm, 100 psi influent, 100 psi
CO2, 40 psi back pressure). Addition of 0.01% diatomaceous earth to
the process slurry caused algae clusters to separate, but did not
increase cell disruption under any condition over controls
following two passes through the system. Addition of 0.1%
diatomaceous earth to the process slurry caused a 24% increase in
cell disruption (54%) over controls processed without DE (30%),
likely due to excess DE in the system.
[0135] 0.01% Diatomaceous Earth (DE)+CO2-Assisted High Shear
(SSCO2)+Colloid Mill (CM) Algae Cell Disruption.
[0136] A colloid mill is a machine that is used to reduce the
particle size of a solid in suspension in a liquid, or to reduce
the droplet size of a liquid suspended in another liquid. Colloid
mills work on the rotor-stator principle: a rotor turns at high
speeds (2000-18000 RPM). The resulting high levels of hydraulic
shear applied to the process liquid disrupt structures in the
fluid. Colloid mills are frequently used to increase the stability
of suspensions and emulsions, but can also be used to reduce the
particle size of solids in suspensions. Higher shear rates lead to
smaller droplets (.about.1 .mu.m) that are more resistant to
emulsion separation. For the current application, the goal was to
break .about.3-10 .mu.m-sized algae into fragments and release
commercial co-products (oil) into the surrounding medium.
Therefore, an MK/2004 Colloid Mill was introduced as an additional
shearing mechanism downstream of the CO2-assisted high shear unit.
Primary factors that influence cell shearing include the gap
distance between rotors and the rotation speed. Initially, the
rotational speed was set to 3160 rpm and the gap was set to 0.208
mm. The pressure of the slurry entering the shear unit was set to
100 psi, CO2 gas pressure was set to 95 psi, and the back pressure
to the shear unit was set to 40 psi. These conditions produced a
smooth fluid flow exiting the sample collection nozzle and the
lowest pH of the processed slurry. Process controls included algae
slurries without DE, and slurries with 0.01% DE but processed
through the colloid mill in the "off" mode. In this case, clusters
of Chlorella cells were again reduced to single cells and the
reduction in cell count was .about.35%. When the colloid mill gap
was decreased to 0.104 mm and no DE was added to the process
slurry, lysing improved by 5%. However, when 0.01% DE was added to
the process stream with a colloid mill gap width at 0.104 mm,
widespread debris was visualized and the total number of cells
decreased by 81% compared to unprocessed controls from the same
batch slurry (FIG. 15). The total intracellular oil available
within this batch of algae slurry was calculated to be 16.7%. A
small amount of oil can often be detected in the extracellular
medium as a result of the solvent sweep method to recover lipids in
the process medium. In this case, the percentage of oil in the
extracellular medium was calculated to be 1.8%.
[0137] Following the first pass of the slurry plus 0.01% DE through
the high-shear unit and colloid mill with the gap adjusted to 0.104
mm, the percentage of extracellular oil increased to 12.2%. In
other words, this process (0.01% Diatomaceous Earth
(DE)+CO2-assisted High Shear (SSCO2)+Colloid Mill (CM), i.e.,
DESSCO2CM process) caused the release of 62% of the intracellular
oil into the extracellular medium, some of which could be observed
at the surface of the processed slurry (FIG. 16). The difference
between cell lysis (81%) and lipid release (62%) may be explained
in part by noting the species of lipids that were made readily
available by the current processing parameters. Non-GMO Chlorella
triglycerides (.about.2-20%) are typically packaged within cells as
easily accessible lipid bodies whereas phospholipids (30-85%) are
embedded within membranes and can be resistant to recovery by sweep
solvents. The release of 62% of total lipids indicates that the
current process method significantly disrupts cellular membranes
containing phospholipids allowing their recovery from a single
solvent sweep.
[0138] These tests were conducted at a bench scale. Although up to
81% of algae cells were disrupted, some operational challenges were
noted. Under all of the combinations of parameters tested, the
addition of diatomaceous earth appeared to be necessary to increase
lysing efficiency.
[0139] Summary of Diatomaceous Earth+CO2-Assisted High
Shear+Colloid Mill Algae Cell Disruption.
[0140] The addition of the downstream colloid mill with the gap set
to 0.104 mm improved algae cell lysis by .about.50%, for a total of
81% of cells ruptured. The following parameters yielded 81% cell
lysis and 62% lipid release: 0.01% DE; IKA Magic high shear unit,
26,000 rpm; colloid mill, 3160 rpm, 0.104 mm gap; 100 psi influent
pressure (to the shear unit); 95 psi CO2 gas pressure (to the shear
unit); 40 psi back pressure (to the shear unit). DE accumulates
within the small diameter tubing in the system over time and
decreases fluid flow and lysing efficiency, and eventually leads to
severe blockage that requires manual cleaning. Larger scale systems
may be less susceptible to DE accumulation. Given the low energy
requirements for this system, this process could significantly
improve the energy balance for production of algal biofuels,
especially if it can be synergistically combined with a vacuum to
efficiently harvest released algal cell lipids.
Example 3
[0141] Gas-Assisted High Shear Cell Lysing.
[0142] Flow-through algae cell disruption testing was demonstrated
in Example 2 using a CO2-infused high-speed, high-pressure
rotor-stator homogenizer (HSPH) and colloid mill homogenizer (CMH).
The testing showed that the infusion of pressurized CO2 into the
HSPH and immediate exposure to the CMH are unique and important
drivers of the cellular disruption efficiency. A proposed mechanism
states that the rapid infusion of CO2 into the algal cells causes
intracellular disruption and cellular swelling, and the immediate
subsequent exposure to shear forces significantly enhances cellular
disruption and product recovery. Although energy balance was not
examined, the algae were compromised in a single pass, and
therefore, the required energy input into the system is expected to
be far less than current non-CO2 shearing technologies that require
multiple passes.
[0143] The CO2-assisted shearing system was likewise tested using
yeast as the bio-feedstock. After replacing CO2 with O2,
significant yeast lysis was observed.
[0144] Materials and Methods.
[0145] Yeast Biomass Production.
[0146] A genetically engineered strain of yeast, Yarrowia
lipolytica, provided by Dr. Hal Alper, University of Texas. Baker's
yeast, Saccharomyces cerevisiae were fermented in 37.degree. C.
dH2O supplemented with 20% D-glucose and 2% bacto yeast extract
within 2 L sterilized glass bioreactors. Culture density was
recorded by absorbance at 600 nm. Cultures near the end of the
exponential phase of growth were used for testing.
[0147] CO2-Assisted High Shear Algae Cell Disruption Set Up and
Test Matrix.
[0148] The process flow for CO2-assisted high shear yeast cell
disruption is shown in. Biomass slurry sample flow was initiated as
follows: the fluid flow pressure of dilute or concentrated yeast
slurry through the system was initiated at 100 psi. The high shear
unit was then turned on and maintained at a rotational speed of
26,000 rpm. Diffused CO2 was introduced into the system at the
shear unit an initial pressure of 80 psi, then adjusted to 95 psi
to reduce sample sputtering from the collection nozzle. The colloid
mill was then activated. In some test cases, the back pressure to
the shear unit was increased in increments of 20 psi from 0 psi to
40 psi. Once the target test parameters were met, processed samples
were collected in Erlenmeyer flasks for subsequent cell disruption
analyses.
[0149] O2-Assisted High Shear Yeast Cell Disruption Set Up.
[0150] The process flow for O2-assisted high shear yeast cell
disruption was identical to the CO2-assisted high shear system
except that the CO2 was replaced with O2 gas infusion.
[0151] Quantification of Cell Disruption.
[0152] The effectiveness of each treatment was qualitatively
visualized by brightfield microscopy (10.times.-40.times.), and
quantified by measuring the fraction of physically disrupted cells.
ImageJ, a public-domain image processing and analysis software, was
used to ensure consistency in cell counting by minimizing
variability in analysis between samples. Measurements of the total
area occupied by cells were used to verify the intact cell counts.
This was particularly useful for samples with cell clumping,
typically observed in samples that had been homogenized at higher
pressures. All imaging was performed using an AmScope B120C-E1
Siedentopf Binocular Compound Microscope with a 1.3 MP digital
camera. Cell counts were compared to unprocessed (flowed through
the system but no shear, mill, +/-CO2 or O2) yeast from the same
batch.
[0153] Results and Discussion.
[0154] CO2-Assisted High Shear Yeast Cell Disruption.
[0155] In order to identify the operating conditions that maximized
yeast cell disruption, a test matrix in which individual parameters
were varied one at a time was created. Yeast was initially
processed through the CO2-assisted high shear, high-pressure
homogenization (HSPH) system using the parameters that were
previously observed to maximize algae cell disruption (shear unit
speed, 26,000 rpm; colloid mill, 3160 rpm, gap 0.14 mm; 100 psi
shear unit influent; 95 psi CO2 to the shear unit; 40 psi back
pressure to the shear unit). No diatomaceous earth was used in the
yeast process testing.
[0156] Despite using the same conditions that caused .about.80% of
processed Chlorella cells to lyse, no significant cell lysis was
observed for processed yeast cells after one, two, or three
processing passes. Increasing the back pressure to the shear unit
likewise had no significant effect on yeast cell lysis. The
differences between algae and yeast cellular respiration
requirements (CO2 vs O2) may explain this result. Algae readily
take up CO2 in the form of CO2 gas or dissolved carbonate and
release O2 as a byproduct of cellular respiration. In contrast,
yeast preferentially take up O2 by gradient diffusion across its
membrane and releases CO2 as a byproduct of cellular metabolism.
When there are two gases separated by a permeable membrane (like
the cell/plasma membrane), the gas will move across the membrane
from the high concentration environment, in this case the
gas-infused shear unit, to the low concentration of that gas (the
intracellular compartment) until the concentrations on each side
equalize. As long as there is always a lower concentration of
oxygen inside the cell than outside the cell, oxygen will
continuously diffuse into the cell. Isenschmid et al. (1995)
reported that yeast exposed to 60 bar (870 psi) CO2 for 15 minutes
were not lysed; rather the yeast cells appeared intact but were
rendered non-viable likely due to CO2 toxicity. For the current
tests, the goal was cellular destruction that facilitated lipid
extraction and recovery, and therefore additional testing using CO2
as the infusion gas was discontinued, and replaced with O2 gas.
[0157] Substituting O2 as the gas infused into the shear mechanism
was predicted to have advantages over CO2-assisted shearing.
Firstly, yeast cells preferentially take up O2 gas. Because yeast
efficiently metabolize O2, the concentration of O2 within the
intracellular compartment remains low and the concentration
gradient for O2 diffusion into yeast cells is comparatively large.
Second, the supersaturating concentration of O2 within the shear
unit forces excess O2 into the cells. Excess O2 intake within yeast
leads to the generation of reactive oxygen species within the
intracellular compartment, which in turn leads to cell expansion
and eventually cell death (FIG. 17). The expanded membranes of
O2-supersaturated yeast cells were predicted to have less localized
tensile strength and therefore more susceptible to shearing
forces.
[0158] O2-Assisted High Shear Yeast Cell Disruption.
[0159] Yeast were processed through the O2-HSPH-CM system, with
minor modifications to the operating parameters (90 psi (from 100
psi) to the shear unit and 85 psi (from 95 psi) O2) to accommodate
differences in slurry viscosity and smooth process flow, then
visualized at 40.times. and quantified for changes in cell density
(FIGS. 18-19). Clusters of yeast cells observed in unprocessed
control samples appeared to be broken up in processed samples,
especially those that were exposed to supersaturating O2. Cell
density was reduced in the samples where 20 psi or 40 psi back
pressure to the shear unit was applied, -12% and -9% respectively.
No cell reduction was observed in samples that were not exposed to
supersaturating O2. Higher magnification microscopy revealed that
the cell membranes of yeast exposed to excess O2 visually appeared
thinner and the intracellular compartment somewhat more opaque.
Despite these morphological changes, the cells largely remained
intact. After 30 minutes, the yeast slurry was processed through
the O2-HSPH-CM a second time. Microscopic inspection and cell
counting revealed no significant changes in either morphology or
cell density, indicating that a delayed second pass had no
significant effects on the process slurry.
[0160] Once yeast cells were exposed to supersaturating O2, it was
predicted that the cells would swell and cellular membranes would
be susceptible to shear forces. In addition, SSO2 causes the
generation of ROS and subsequent cell death. The 30 minute delay
between process passes was not long enough to cause cell death
(typically occurs in 4-6 hours), but may have provided enough time
for cells to initiate defense mechanisms that restore cellular
integrity, albeit futile in the end. To test this hypothesis, yeast
slurry was processed through the O2-HSPH-CM using the same
operating parameters as the previous test, then immediately
processed a second time through the system. An immediate second
process pass caused significant cellular disruption, visualized as
widespread debris and quantified by cell counts. The cell density
of the slurry was reduced by 36% (20 psi BP) and 34% (40 psi BP)
compared to controls that were circulated through the system but
not exposed to O2 or shear forces.
[0161] To characterize the effects of multiple passes through the
O2-HSPH-CM system, a follow-up test whereby the slurry was
continually circulated through the system for 5 minutes was
conducted. Each process pass was calculated to require 1.2 minutes.
Therefore, an average yeast cell circulating through the system for
5 minutes was exposed to .about.4 passes through the system.
Widespread debris was again visualized in samples that were exposed
to O2-HSPH-CM (FIGS. 20C and 20D), and a further reduction in cell
density was likewise documented, -47% (20 psi BP) and -53% (40 psi
BP) compared to unprocessed controls (FIG. 20A). Interestingly, O2
appears to be a critical feature for significant yeast disruption
through this system. Like the previous tests using shear forces,
yeast cells clusters were reduced to single cells, however, the
reduction in slurry density was minimal (-15%) (FIG. 20B).
Together, these data indicate that shear forces are effective in
separating clusters of cells and disrupting O2 saturated cells, and
that effective cell lysis occurs immediately following cellular
compromise by excess intracellular O2. Additional testing is
required to optimize the lysing performance of the O2-high shear
processing unit-colloidal mill system and determine whether the
effects are species specific.
[0162] Summary.
[0163] Despite substantial progress in the development of cell
factories for the production of advanced biofuels, there is still
need for further improvement in the production capacity of these
cell factories and in technologies that extract and recover the
synthesized fuel products. Engineered yeast cells are an attractive
platform for renewable fuel production, but due to the high tensile
strength of yeast membranes, cost-effective lysis of these cells
for recovery their fuel products has limited the scalability of
this platform. The method as discussed herein whereby O2 is
supersaturated into the process stream within a rotational shear
device coupled with a colloid mill was shown to rupture >50% of
yeast cells within 5 minutes with no added heat or chemical agents.
Additional circulation through the system and minor changes to
operating procedures will likely increase lysing efficiency
further. Unlike simple external shearing forces created by
commercial homogenizers, the cellular disruption caused by the
O2-high shear processing unit-colloidal mill system is thought to
be the result of a different mechanism, namely by creating
intracellular disarray, membrane swelling and loss of structural
integrity that increases the cell's susceptibility to subsequent
shear forces.
Example 4
[0164] Demonstration of High Shear Cell Lysing.
[0165] As shown previously, the gas-assisted high shear process
validated that the system is capable of 1) supersaturating algae
growth media with CO2 which leads to enhanced CO2 consumption and
bioremediation, 2) rupturing a significant fraction of Chlorella
vulgaris algae or Saccharomyces sp. yeast following a single
process pass. The process flow path includes a gas-assisted 3-stage
high shear unit followed by a colloid mill. Previous cell lysis
tests suggested that the first exposure to gas-assisted high shear
causes cells within the slurry to take up excess gas and swell, a
condition that compromises cell integrity. A second exposure to
shear while the cells remain compromised is sufficient to rupture
up to 92% of algal cells and 52% of yeast cells.
[0166] The primary focus of the last set of tests was to identify
process flow pressures that optimized cell lysis. Previous tests
indicated that a high shear unit rotational speed greater than
15,000 rpm was required to maximize algae cell lysis. Therefore,
the rotational speed was increased to 26,000 rpm, a condition that
resulted in enhanced algae cell lysis. The rotational speed of the
high shear unit was likewise held constant at 26,000 rpm for
subsequent yeast lysis testing. For the current tests, we
investigated the effect of O2-assisted high shear speed vs. cell
lysis.
[0167] Materials and Methods.
[0168] Yeast Biomass Production.
[0169] Baker's yeast, Saccharomyces cerevisiae, were inoculated
into 37.degree. C. dH2O supplemented with 20% D-glucose and 2%
bacto yeast extract within 2 L sterilized glass bioreactors
supplemented with constant ambient aeration. Culture density was
recorded by absorbance at 600 nm. The cultures were scaled up
within 20 L glass carboys followed by transfer to 90 L vertical
airlift photobioreactors. Cultures near the end of the exponential
phase of growth were used for testing.
[0170] O2-Assisted High Shear Algae Cell Disruption Set Up and Test
Matrix.
[0171] The process flow for O2-assisted high shear yeast cell
disruption is shown in FIG. 21. Yeast slurry sample flow was
established in rapid succession as follows: the fluid flow pressure
of dilute yeast slurry through the system was initiated at 100 psi
then adjusted to 90 psi. The high shear unit was then turned on and
maintained at a rotational speed of 3,000-26,000 rpm as indicated.
Concurrently, diffused O2 was introduced into the system at the
shear unit an initial pressure of 100 psi, then adjusted to 85 psi
to reduce sample sputtering from the collection nozzle. Control
runs were evaluated by running the slurry flowed through the system
The back pressure to the shear unit was adjusted to 40 psi. Once
the target test parameters were met, a timer was started. Processed
samples were collected 2 minutes later, or after approximately 2
passes through the system, in Erlenmeyer flasks for subsequent cell
disruption analyses.
[0172] Quantification of Cell Disruption.
[0173] The effectiveness of each treatment was qualitatively
visualized by bright field microscopy (40.times.), and quantified
by measuring the fraction of physically disrupted cells (Spiden,
2013). ImageJ, a public-domain image processing and analysis
software, was used to ensure consistency in cell counting by
minimizing variability in analysis between samples. Measurements of
the total area occupied by cells were used to verify the intact
cell counts. This was particularly useful for samples with cell
clumping, typically observed in samples that had been homogenized
at higher pressures. All imaging was performed using an AmScope
B120C-E1 Siedentopf Binocular Compound Microscope with a 1.3 MP
digital camera. Cell counts were compared to unprocessed (flowed
through the system but no shear, mill) yeast from the same
batch.
[0174] Results and Discussion. Effect of Shear Speed on O2-Assisted
High Shear Yeast Cell Disruption.
[0175] A test matrix in which the operational shear speed of the
IKA multi-stage high shear unit was adjusted from 0 rpm (negative
control) to 26,000 rpm (see Table 1).
TABLE-US-00001 TABLE 1 Test matrix of O2-assisted high shear speed
vs. yeast cell lysis. Colloid % reduction Back mill Colloid in cell
Circulation Pump pressure Shear rotor mill number time (min)
pressure O.sub.2 to shear unit speed clearance (compared 1 pass =
60 s (psi) pressure unit (psi) speed (Hz) gap (mm) to control)
Generate sufficient (100 L) yeast culture Start-up procedure 2 90
85 20 26000 3160 0.104 55.2 2 90 85 20 22000 3160 0.104 56.8 2 90
85 20 18000 3160 0.104 15.1 2 90 85 20 14000 3160 0.104 6.2 2 90 85
20 10000 3160 0.104 6.6 2 90 85 20 6000 3160 0.104 0 2 90 85 20
3000 3160 0.104 1.5 2 90 85 20 0 3160 0.104 0 Shut down procedure
Start-up procedure 2 90 85 20 26000 0 0.104 49.1 2 90 85 20 22000 0
0.104 47.9 2 90 85 20 18000 0 0.104 17.8 2 90 85 20 14000 0 0.104
16 2 90 85 20 10000 0 0.104 9.2 2 90 85 20 6000 0 0.104 5.4 2 90 85
20 3000 0 0.104 4.3 2 90 85 20 0 0 0.104 0 Shut down procedure
Report Total lab time (min)
[0176] Initially, yeast slurry was circulated through the system
while both the high shear unit and colloid mill were not activated.
Samples were collected following a 2 minute circulation and the
cell density was evaluated and established as 100%. For the first
set of shear speed vs. cell disruption tests, the colloid mill
operational speed was held at 3160 rpm and the mill gap was held at
0.104 mm, reflecting the optimized speed and gap distance
identified in previous tests while the operational speed of the
high shear unit was incrementally varied with each process run.
[0177] FIG. 22 shows a linear relationship between lower shear
speeds (3000 rpm-18,000 rpm) and cell disruption. The effect of the
downstream colloid mill was minimal. Cell disruption was
significantly improved with high shear speeds from 18,000 rpm
through 26,000 rpm. Again, the effect of the colloid mill was
minimal under this scenario. This result differs from previous
testing where the colloid mill increased cell disruption after a
single pass. Previous testing showed that after a single pass
through the high shear unit at 26,000 rpm, .about.70% of yeast
cells appeared swollen and stressed, but intact. A subsequent
exposure to a shearing mechanism (colloid mill, 3160 rpm, 0.104 mm
gap) caused a significant fraction of these compromised cells to
lyse. For the current tests, the slurry was circulated for 2
minutes and the slurry was exposed to O2-assisted high shear at
least twice, or both the high shear unit plus the colloid mill for
2 minutes for a total of .about.4 passes through a shearing
mechanism. These data indicate that multiple exposures to
O2-assisted high shear at rotational speeds greater than 18,000 rpm
is sufficient to rupture .about.50-56% of yeast cells within the
process stream and that the addition of another downstream shear
mechanism may not be necessary.
[0178] While preferred embodiments of the invention have been shown
and described, modifications thereof can be made by one skilled in
the art without departing from the spirit and teachings of the
invention. The embodiments described herein are exemplary only, and
are not intended to be limiting. Many variations and modifications
of the invention disclosed herein are possible and are within the
scope of the invention. Where numerical ranges or limitations are
expressly stated, such express ranges or limitations should be
understood to include iterative ranges or limitations of like
magnitude falling within the expressly stated ranges or limitations
(e.g., from about 1 to about 10 includes, 2, 3, 4, etc.; greater
than 0.10 includes 0.11, 0.12, 0.13, and so forth). Use of the term
"optionally" with respect to any element of a claim is intended to
mean that the subject element is required, or alternatively, is not
required. Both alternatives are intended to be within the scope of
the claim. Use of broader terms such as comprises, includes,
having, etc. should be understood to provide support for narrower
terms such as consisting of, consisting essentially of, comprised
substantially of, and the like.
[0179] Accordingly, the scope of protection is not limited by the
description set out above but is only limited by the claims which
follow, that scope including all equivalents of the subject matter
of the claims. Each and every claim is incorporated into the
specification as an embodiment of the present invention. Thus, the
claims are a further description and are an addition to the
preferred embodiments of the present invention. The disclosures of
all patents, patent applications, and publications cited herein are
hereby incorporated by reference, to the extent they provide
exemplary, procedural or other details supplementary to those set
forth herein.
* * * * *