U.S. patent application number 12/943901 was filed with the patent office on 2011-05-26 for bioremediation system and methods.
This patent application is currently assigned to BIOVANTAGE RESOURCES. INC.. Invention is credited to Matthew Edward DONHAM, Ari MA'AYAN, Nicholas Arthur RANCIS, Michael Edward VERES.
Application Number | 20110120944 12/943901 |
Document ID | / |
Family ID | 43973096 |
Filed Date | 2011-05-26 |
United States Patent
Application |
20110120944 |
Kind Code |
A1 |
MA'AYAN; Ari ; et
al. |
May 26, 2011 |
Bioremediation System and Methods
Abstract
Algae-based bioremediation systems and methods in which algae is
grown in a photobioreactor with nutrients supplied from a nutrient
system. An effluent stream in need of remediation is ported to a
pond or lagoon and the lagoon is inoculated repetitively with algae
grown in the photobioreactor. In an embodiment, a first stage
comprises an anaerobic digester which generates combustible gas
that can be burned to generate at least a portion of the gas and
electricity needed to operate some or all of the nutrient system,
the photobioreactor and the lagoon or pond. In some embodiments,
the pond or lagoon is multiphasic, and comprises anaerobic and
aerobic remediation zones.
Inventors: |
MA'AYAN; Ari; (Lakewood,
CO) ; RANCIS; Nicholas Arthur; (Boulder, CO) ;
VERES; Michael Edward; (Highlands Ranch, CO) ;
DONHAM; Matthew Edward; (Colorado Springs, CO) |
Assignee: |
BIOVANTAGE RESOURCES. INC.
Golden
CO
|
Family ID: |
43973096 |
Appl. No.: |
12/943901 |
Filed: |
November 10, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61280847 |
Nov 10, 2009 |
|
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|
Current U.S.
Class: |
210/602 ;
210/170.09; 210/96.1 |
Current CPC
Class: |
Y02W 10/37 20150501;
A01G 33/00 20130101; C12M 27/06 20130101; Y02A 40/80 20180101; F21W
2131/40 20130101; C12M 29/08 20130101; F21Y 2115/10 20160801; C12M
23/18 20130101; G02B 6/001 20130101; C12M 27/24 20130101; G02B
6/0096 20130101; C12M 23/58 20130101; C12M 31/08 20130101; Y02A
40/88 20180101; F21V 33/0064 20130101; C12M 21/02 20130101; F21Y
2115/30 20160801; A01G 7/045 20130101; C12M 21/04 20130101 |
Class at
Publication: |
210/602 ;
210/170.09; 210/96.1 |
International
Class: |
C02F 3/32 20060101
C02F003/32 |
Claims
1. A bioremediation system comprising a photobioreactor for
supplying selected strains of algae, a nutrient system for
supplying sufficient growth medium to the photobioreactor to enable
continuous growth of the selected strains of algae, a multiphasic
remediation lagoon or pond adapted to receive organic waste for
remediation and also to receive, from the photobioreactor,
inoculations of the selected strains of algae.
2. The bioremediation system of claim 1 wherein the multiphasic
pond comprises at least an anaerobic zone and an aerobic zone, and
means for creating substantially consistent directional fluid flow
within the pond.
3. The bioremediation system of claim 1 wherein the substantially
consistent directional fluid flow is created by a paddlewheel.
4. The bioremediation system of claim 1 further comprising a
feedback loop for adjust the amounts of algae provided by a
subsequent inoculation.
5. The bioremediation system of claim 1 wherein the nutrient system
comprises a control system for metering the supply of selected
nutrients to facilitate algae growth in the photobioreactor.
6. A method for remediating waste streams comprising providing an
anaerobic digester region for performing a first remediation step,
the anaerobic digester generating combustible gas and an effluent
stream, combusting the gas to generate heat, electricity, and
CO.sub.2, supplying a portion of the heat, electricity and CO.sub.2
generated by the combusting step to a photobioreactor, supplying
another portion of the heat, electricity and CO.sub.2 generated by
the combusting step to a multiphasic pond, supplying to the
multiphasic pond the effluent stream and dense algae produced by
the photobioreactor.
7. The method of claim 6 wherein the photobioreactor comprises a
plurality of light pipes arranged within a tank for growing algae
throughout the volume of the tank.
Description
RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Patent Application Ser. No. 61/280,847, filed Nov. 10, 2009,
entitled Method for Algal Treatment of Effluent from an Anaerobic
Digester and Creation of Useful Algal Biomass, which is
incorporated herein for all purposes.
FIELD OF THE INVENTION
[0002] The present invention relates generally to wastewater
treatment systems and methods, and more particularly relates to
wastewater treatment systems utilizing anaerobic and aerobic
microorganisms for bioremediation.
BACKGROUND OF THE INVENTION
[0003] The vast majority of the world's wastewater does not undergo
treatment of any kind before being dumped into the nearest open
water source. This has resulted in an international health crisis,
where people die daily for lack of clean water. Unstable ecosystems
caused by nutrient rich waste runoff are creating high rates of
fish kill, ocean floor plant kill and large concentrations of
pathogenic bacteria. This is a direct effect of lack of treatment
or poor treatment and disposal of such waste streams. Effects such
as disastrous algae blooms in open water sources from eutrophic
conditions have drastically increased in the past decade and pose
unprecedented environmental problems.
[0004] Typical prior art wastewater treatment systems typically
employ mechanical aeration and chemical treatment. These systems
are expensive to build and to operate, not solely because of the
high energy costs incurred in the aeration process, but also
because of the manpower required to operate the expensive machinery
employed in such systems. Such mechanical/chemical treatment
facilities, even those that are considered "state of the art," have
a price tag in the millions and even up to hundreds of millions of
dollars, making them so expensive that many communities, in the US
and other parts of the developed world, have in the past been
unable to afford such sewage treatment systems. As a result, the
majority of the world's population lives with massive sewage
pollution.
[0005] Bioremediation of wastewater has been proposed in the past.
Such bioremediation systems typically employ a combination of
aerobic and anaerobic processes. In particular, such prior art
systems have generally proposed the use of anaerobic bacteria for
digestion of organic matter and the release of biogas, combined
with phototrophic organisms that produce oxygen to accelerate the
breakdown of organic matter by aerobic bacteria. (At the same time,
the aerobic bacteria produce carbon dioxide which is needed by the
phototrophic organisms.) Anaerobic digestion kills most of the
pathogenic bacteria found in raw sewage by depriving it of oxygen.
In addition, the anaerobic bacteria are able to digest most of the
biologically activating solids. Through this anaerobic digestion
process, levels of Biological Oxygen Demand (BOD) and Chemical
Oxygen Demand (COD) are greatly reduced, in addition to decreasing
the amount of solid content in the waste. In this manner, the
complementary nature of aerobic and anaerobic processes can be
harnessed to break down organic material into its elemental forms
without the use of `heat, beat and treat` systems currently used in
conventional, mechanical aeration/chemical treatment waste
remediation facilities.
[0006] Algae has long been proposed as a suitable phototrophic
organism for use in such bioremediation of wastes. One large
project using such an approach is the St. Helena Wastewater
Treatment plant in California, and other such plants have been put
into service elsewhere in the world.
[0007] These solutions have demonstrated a number of desirable
characteristics, but have had significant shortcomings. Because
these prior art systems do not have a mechanism for controlling the
algal specie(s) present, their algae cultures drift over time,
often with unwanted outcomes. These undesirable outcomes include
the growth of species that cannot be easily separated from the
water at the end of processing; the proliferation of species that
grow well during "normal" conditions, but are unable to grow in the
case of process excursions, e.g. an influx of an industrial
pollutant; or the proliferation of algaie species that grow well,
but do not perform all of the desired remediation.
[0008] Further, absent a mechanism for active replenishment of the
algae, wash-out events (e.g. from a rainstorm) can severely dilute
the algae culture density, such that the system is unacceptably
slow to return to an effective culture density.
[0009] Thus, there has been a long-felt, and growing, need for a
wastewater remediation system and method that is cost effective
while offering an efficient, stable remediation approach.
SUMMARY OF THE INVENTION
[0010] The present invention provides a system and method for
efficient, cost-effective bioremediation of wastewater and other
contaminated fluid streams. In one aspect, the invention includes a
photobioreactor (hereinafter sometimes "PBR" for simplicity) for
growing high concentrations of algae. The PBR comprises a tank
having specially configured light pipes distributed therein to
cause high density algae growth substantially throughout the tank.
Fluid flow in the tank is maintained at a level low enough to
prevent damage to the algae while at the same time allowing the
fluid to circulate throughout the tank.
[0011] Another aspect of the invention comprises a medium system
for supplying nutrients to the PBR or other growth system. The
nutrient system can comprise a plurality of separately selected
components which are then assembled into a nutrient stream through
a plurality of metering pumps, or, in some embodiments, can be
derived from a portion of the effluent of an anaerobic digester. In
some embodiments, the anaerobic digester forms a first stage of the
overall bioremediation system. The anaerobic digester stage, aside
from providing a stream rich in micro and macronutrients, also
provides significant amounts of CO.sub.2 to the PBR, which assists
in the growth of algae in the PBR. In addition, the anaerobic
digester generates significant quantities of biogas, which can be
utilized by a conventional biogas-powered generator to produce at
least a portion of the electricity required to operate the
bioremediation system of the present invention. Carbon dioxide from
the biogas can be used in the lagoon or pond to accelerate algae
growth before, after, or instead of burning of the biogas. In the
case where the biogas is burned, the resultant heat energy can be
used to warm the water in the lagoon, accelerating various of the
desirable biological processes ongoing there.
[0012] Yet another aspect of the invention comprises a remediation
lagoon or pond, typically although not necessarily using a raceway
design, where the remediation pond is fed high-density algal
inoculum from the photobioreactor system. A portion, in many cases
the majority, of the effluent from the anaerobic digester stage
provides the incoming fluid stream to be remediated in the
remediation pond. In some embodiments, the remediation pond can be
a multi-phasic pond utilizing multiple biological capabilities
enabling it to process the residual CO.sub.2, nitrogen and
phosphorus remaining in the effluent from the anaerobic digester
stage. In at least some embodiments, the multi-phasic ponds
comprise a plurality of horizontal strata, for example: aerobic at
the surface, aerobic/anaerobic, and anaerobic on the bottom. The
overall function is to remove residual nitrogen and phosphorus in
the system through the use of phototrophic microorganisms, while
simultaneously consuming CO.sub.2 and creating O.sub.2 to aid in
the breakdown of residual effluent from anaerobic digestion. These
ponds can be sized individually for each implementation or user
application.
THE FIGURES
[0013] FIG. 1 shows schematically an embodiment of a water
remediation in accordance with one aspect of the invention.
[0014] FIGS. 2A and 2B show, respectively, a cross-sectional side
view and an exploded view of an embodiment of a photobioreactor
having a single draft tube in accordance with one aspect of the
invention.
[0015] FIG. 2C shows an alternative embodiment of a photobioreactor
having a plurality of draft tubes.
[0016] FIG. 2D shows another embodiment of a photobioreactor
utilizing parallel plates with light rods in accordance with an
aspect of the invention.
[0017] FIG. 2E shows an alternative embodiment of a photobioreactor
utilizing parallel plates and external illumination.
[0018] FIG. 2F shows in flow diagram form the operation of the
photobioreactor in accordance with an aspect of the invention.
[0019] FIG. 3A shows an embodiment of a light rod as used in an
embodiment of the photobioreactor of FIGS. 2A and 2B.
[0020] FIG. 3B shows a first alternative embodiment of a light rod
in accordance with the invention.
[0021] FIG. 3C shows a second alternative embodiment of a light rod
in accordance with the invention.
[0022] FIG. 4A shows an embodiment of a nutrient system in
accordance with an aspect of the invention.
[0023] FIG. 4B shows in flow diagram form the operation of an
embodiment of the nutrient system in accordance with one aspect of
the invention.
[0024] FIGS. 5A-5B show an embodiment of a multiphasic pond in
accordance with an aspect of the invention.
[0025] FIG. 6 shows an embodiment of a bubbler in accordance with
an aspect of the invention.
[0026] FIG. 7 shows in schematic form an alternative embodiment of
a wastewater remediation system in accordance with an aspect of the
invention.
[0027] FIGS. 8A-8B show in system and flow diagram forms a
concentrator process in accordance with an aspect of the
invention.
[0028] FIG. 9 illustrates in generalized flow diagram form an
embodiment of a soft fail process in accordance with an aspect of
the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0029] Referring first to FIG. 1, a bioremediation system in
accordance with one aspect of the invention comprises a
photobioreactor or PBR 10, described in greater detail hereinafter,
which receives a nutrient stream from a nutrient system 15. The PBR
provides an optimized environment for the growth of highly
concentrated algae. The algae from the PBR 10 is supplied via a
conduit 20 to a wastewater pond or lagoon 25, which, in some but
not necessarily all embodiments, is a multiphasic pond as discussed
in connection with FIG. 5. The pond or lagoon 25 receives organic
waste 30, and, in many embodiments, can also receive atmospheric
CO.sub.2 as indicated at 35.
[0030] The wastewater pond or lagoon 25, which can cover less than
an acre to tens or hundreds of acres and could even be an open
water area such as a lake or bay given sufficiently large algae
supplies, comprises in some embodiments a relatively shallow pond
having at least one remediation strata and, in the case of
multiphasic ponds, a plurality of strata. As explained in greater
detail hereinafter, the algae from the PBR are provided to the
lagoon in doses sufficient to inoculate the lagoon; that is, to
provide enough algae to the lagoon that the natural conditions in
the lagoon will permit the algae to thrive for a reasonable period
of time, propagating naturally. The algae typically, although not
necessarily, operate symbiotically with bacteria with which they
comingle in the lagoon. In the embodiment in which both algae and
bacteria are present, bacterial action reduces BOD and TSS (Total
Suspended Solids) and reduces nitrogen while producing CO.sub.2.
Compared to the bacteria, algae reduce BOD, TSS, and nitrogen to a
lesser extent, and substantially reduce phosphorus, all while
producing oxygen. This symbiotic relationship, in which the
bacteria produce CO.sub.2 consumed by the algae as the algae
produce O.sub.2 consumed by the bacteria, significantly accelerates
the activity of both organisms. (In addition, some CO.sub.2 and
O.sub.2 come in from the atmosphere.)
[0031] By moving the wastewater through the pond or lagoon at a
suitable rate, to ensure sufficient mixing, to maintain homogeneity
of the water chemistry & temperature, as well as maintain
suspension of the algae and bacteria, the outflow from the pond 25
is substantially remediated. Optionally, a final treatment 40 can
be provided, in the form of an algae separation step and/or a
maturation or clarification stage. An algae separation step permits
collection of the algae biomass for value-added applications (e.g.
fertilizer). A maturation pond, constructed wetland, or similar
solution would promote settling of the algae and further reduction
of nitrates and phosphates. In addition, in some embodiments
automated feedback, indicated at 45, can be provided which
determines the water quality of the outflow and accordingly adjusts
the level of inoculation to ensure that proper levels of water
quality are achieved and maintained. In systems where no final
treatment step is performed, the water quality of the output of the
pond 25 is used to provide feedback.
[0032] Referring next to FIGS. 2A and 2B, an embodiment of the
photobioreactor of the present invention can be better understood,
shown in cross-sectional and exploded perspective views,
respectively. A draft tube 200 is centrally disposed within a
housing or tank 205. In an embodiment, the tank has a useful
capacity of about 50 gallons with a diameter of approximately 22
inches, while the draft tube has a capacity of approximately 4.5
gallons and a diameter of approximately seven inches. The relative
volumes and diameters of the tank 200 and draft tube 205 can vary
substantially, although in at least some embodiments a draft tube
diameter of five to twenty-five percent of the tank diameter has
been found useful. In some embodiments, the tank is sized to have a
height/diameter ratio approximately 1.5:1, although this ratio is
not limiting and the relative dimensions of the tank can vary
significantly.
[0033] Arranged within the draft tube are one or more light rods or
pipes 210, as described in greater detail in connection with FIG.
3A. A plurality of light pipes 210 are also arranged within the
housing 205 and around the outside of the tube 200, The exact
number of light pipes 210 both within the diffusion tube and
arranged outside of the diffusion tube can vary depending upon the
size of the tank and the particular implementation of the
invention. In general, it is desirable to space the light pipes
apart by approximately twice the absorption distance of the light
emitted from the light pipes. In an embodiment, for example, the
light pipes are spaced approximately 10-15 centimeters apart,
although the exact dimensions can vary depending on numerous
factors, including the type of algae, the level of algae
concentration desired for a particular PBR, and the wavelength and
power of the LED's providing light to the light pipes.
[0034] The housing 205 contains growth media 215, as described in
greater detail in connection with FIG. 4, together with algae
selected to be appropriate for the particular remediation system.
Light of one or more preselected wavelengths, appropriate to
facilitate growth of the selected algae, is supplied by one or more
LED's 220 or similar light sources associated with each of the
light pipes 210. While LED's are the preferred light source for
many embodiments, other light sources are acceptable for some
embodiments, including lasers, diode lasers, diode pumped solid
state lasers, diode pumped fiber lasers, high intensity discharge
lamps and other lamps, infrared sources converted to wavelengths
appropriate for the particular strains of algae, or even sunlight
coupled to the light pipes using heliostats or similar devices. For
convenience, the light source will be described herein as "LED",
but is to be understood as meaning any light source appropriate for
the particular implementation of the invention. The LED's 220 are
disposed at the top thereof, typically above the top of the media,
where light emitted from the LED's is transmitted down the light
pipe through a coupling 225. In some embodiments, multiple LED's
can be used to emit light of different wavelengths along a single
rod, a single LED can emit multiple wavelengths along a single rod,
or some rods can have LED's emitting a first wavelength while other
rods have LED's emitting other wavelengths. In addition, in some
embodiments various dyes can be used in the rods to convert light
of one wavelength to another more appropriate for the strains of
algae being grown in the tank.
[0035] Each of the light pipes can also include a homogenizer or
mixer, as shown in FIG. 3A, to improve spatial uniformity in the
light pipes, although the homogenizer is not required for all
implementations. Each of the LED's can have associated therewith a
heat sink or heat exchanger 230, to keep the LED's at an
appropriate operating temperature. In at least some
implementations, it is desirable to cool the LED's sufficiently
that heat from the LED's does not adversely affect the growth of
the algae within the tank. To facilitate cooling of the LED's, one
or more fans 235 can be positioned at an orifice in an air dome
240, with a ventilation gap 245 disposed between the air dome 240
and a tank lid 250 to allow air to exit. In general, the purpose of
the light pipes 210 is to transit light from the LED's as uniformly
as possible throughout the tank, to encourage algae growth at all
levels within the tank, while not transmitting the heat from the
LED's into the tank and not impeding fluid flow within the
tank.
[0036] In an embodiment, the light rods are supported by a tank lid
250, which has orifices 255 therethrough. Each of the light pipes
210 slides through an orifice 255 so that the majority of the light
pipe fits into the tank 205. The lid can also provide a connection
point for one or more supports 260 for the draft tube 200, so that
the top of the draft tube is maintained somewhat below the surface
of the liquid in the tank, and the open bottom of the draft tube is
maintained above the bottom of the tank.
[0037] To maximize the concentration of algae within the growth
medium in the tank, the algae are typically moved or stirred gently
within the tank. One technique for facilitating such slow movement
is to blend CO.sub.2 or other gas (depending on what algae is being
cultured and for what purpose) with compressed air via a computer
controlled valve 265 and blender 270. In some embodiments, no
compressed air is used. Depending upon the particular
implementation, the bubbled gas can be inert with respect to the
growth medium and the culture being grown, or it can promote the
growth of the culture such as by providing a nutrient, or it can
otherwise regulate conditions in the tank such as by changing pH.
The combined stream is supplied to the bottom of the draft tube 200
via a flowmeter 275 and a diffuser 277, where the diffuser operates
to convert the gas stream into gas bubbles sized to be suitable for
providing movement of the algae. The bubbles of gas mixture entrain
the growth media and move algae in the draft tube upward as
indicated by the upward flow arrows. In an embodiment, typical
bubble size is on the order of 1 mm, but can vary significantly, in
a range of 0.2 mm to 3 mm, or more.
[0038] Because the top of the draft tube is below the surface of
the liquid, and also suspended above the bottom of the tank 200
preferably at a distance that facilitates a vacuum effect in at
least some embodiments, the algae and growth media flow over the
top of the draft tube and move downward within the portion of the
tank outside the draft tube, as indicated by the downward flow
arrow. In an embodiment using a single draft tube, a gas flow rate
of 0.1-0.2 cubic feet per minute provides sufficient movement of
the algae, although this flow rate is not intended to be limiting.
This movement promotes homogenaeity of the growth medium within the
tank, prevents settling, and also facilitates the algae moving
along the length of the light rods, so that the algae are
relatively uniformly illuminated by the light emitted from the
light rods throughout the volume of the tank 205, thus yielding
relatively uniform growth throughout the tank, rather than merely
at the surface as found in prior art systems. Additional growth
medium can be supplied as necessary from a medium tank, as
discussed in connection with FIG. 4, via tube 280A, while seed
amounts of algae are supplied via tube 280B or through an orifice
in lid 250. The junction of the walls and bottom of the tank can be
rounded to facilitate smooth movement of the algae and to prevent
algae from clogging at what would otherwise be a sharp corner,
although such rounding is not necessary in all embodiments.
[0039] To promote good algae growth, the temperature of the growth
media is controlled by means of a thermal control jacket 285, the
temperature of which can be regulated by thermal control unit 290.
The thermal control jacket can, for example, be formed with tubes
therethough for heating or cooling fluid flow, or can be comprised
of polymer heating/cooling material. In addition, pH, level, and
temperature, indicated by sensors 295A-C, are monitored by control
system 295D, typically a computer (not shown.) Once the algae
concentration in the tank has reached the desired level, a
computer-controlled drain valve 297 permits the algae to be
transferred to a lagoon or pond seen in FIG. 1 to facilitate the
remediation process. In some embodiments, algae concentrations of
less than 50 mg/L up to 5000 mg/L or more can be achieved, with
concentrations from 50 mg/L to 1000 mg/L being easily
obtainable.
[0040] It will be appreciated that, while a single draft tube has
been shown in FIGS. 2A-2B, multiple draft tubes can be used and may
be desirable in tanks having a larger diameter, as shown in FIG.
2C. In general, having a plurality of smaller diameter draft tubes
distributed around a larger tank will provide better fluid flow,
especially near the edge of the tank, than a single tube of
equivalent flow in the middle of a tank. In an embodiment, a gas
flow of approximately 0.1 to 0.2 cubic feet per minute per draft
tube provides sufficient stirring and movement of the algae and
growth medium within the tank, where the combined diameters of the
draft tubes comprises approximately five to twenty-five percent of
the total surface area of fluid within the tank.
[0041] In the alternative embodiment of FIG. 2C, which is a
cross-sectional view of a photobioreactor in which like numerals
refer to like elements from FIG. 2A, a plurality of draft tubes 200
are disposed within the tank 205. Although only two such draft
tubes 200 are shown, the design illustrated can accommodate a large
range of draft tubes. Thus, for example, between one and four draft
tubes are desirable for some embodiments where the tank is
approximately 150 gallons, while an embodiment using a 300 gallon
tank uses five draft tubes. The foregoing numbers are exemplary
only and are not limiting. In general the number and placement of
the draft tubes is intended to facilitate appropriate upward and
downward flow of the algae-laden medium as described before in
connection with FIGS. 2A-2B, where the algae is permitted to grow
throughout the volume of the tank, rather than just at the surface
as in prior art designs.
[0042] Referring next to FIG. 2D, which shows in perspective view
with a transparent front wall a still further alternative
embodiment of the PBR shown in FIG. 2A, it will be appreciated that
the shape of the tank need not be round, and in fact can be any
shape that permits sufficient light to reach the volume of algae
growing in the medium. For clarity, elements with like
functionality are again shown with the same reference numerals used
in FIG. 2A, and, for clarity, many elements with identical
functionality to those discussed in connection with FIG. 2A are
omitted. Thus, the perimeter of the tank 205 shown in the
embodiment of FIG. 2D is rectangular, with one or more baffles 2100
arrayed within the tank and extending from below the surface of the
fluid to a distance above the bottom of the tank. The baffles thus
create spaces having the same functionality as draft tubes 200. By
placing diffusers 2110 with appropriate gas flow at the bottom of
alternating baffled spaces, the desired upward and downward flows
are created within alternating baffled spaces in the tank, as shown
by the flow arrows. As with the PBR of FIG. 2A, a plurality of
light pipes are disposed within the tank through a lid 2115.
Although a linear array of light pipes 210 is shown in FIG. 2D, it
will be apparent that the number and placement of the light pipes
will vary with the dimensions of the tank 200, and need not be
linear.
[0043] It will also be understood, from the description of FIGS.
2A-2C, that the wall-to-wall baffles shown in FIG. 2D are not
required in all embodiments, and instead can be replaced with draft
tubes as shown in FIGS. 2A-2C. In addition, the width of the tank
can be varied as desired, with multiple draft tubes and multiple
light pipes arrayed in accordance with the teachings given in
connection with FIGS. 2A-2C. It will also be appreciated that, in
some embodiments, light pipes can be placed in the corners of the
tank, to prevent a fall-off in illumination at the corners,
although such positioning could in some instances result in a less
efficient use of the light from the corner light pipes. Adding a
reflector behind the light pipe can reduce the loss. In addition,
with light pipes positioned in the corners, the fluid flow in the
corners is decreased and dead spots may occur.
[0044] Turning next to FIG. 2E, which shows a still further
alternative embodiment of a PBR in accordance with an aspect of the
invention, in some embodiments the light pipes 210 can be replaced
with externally positioned LED's or equivalent light sources 2105.
A thermal jacket 2110 is still provided, with orifices therethrough
to accommodate the placement of the LED's 2105. Heat sinks 2115 are
provided in at least some arrangements, and a cover [not shown] can
be provided to control the air flow through the heat sinks,
effectively creating a plenum. As with the design of FIG. 2D,
baffles or draft tubes are disposed within the tank to create the
appropriate flow of the algae and growth medium. The remaining
elements of FIG. 2A (such as light pipes, controls, etc.) are not
repeated in FIG. 2E for clarity, but would be included as
appropriate in implementations of the embodiment shown in FIG. 2E.
Since the light sources 2105 are external for the embodiment of
FIG. 2E, the width of the tank is preferably constrained to ensure
good illumination throughout the volume of the algae and medium
flowing within the tank, and thus the width of the tank is
typically at most a few inches. In at least some embodiments, LED's
2105 are disposed on both sides of the tank.
[0045] Referring next to FIG. 2F, the process flow for growing
algae within the PBR's shown in FIG. 2A-2D can be better
appreciated. Growth medium is supplied to the growing tank 2200 via
tube 2205 from the medium preparation system (FIG. 4), either
manually or under computer control 2207, as indicated by a level
sensor 2210. Seed amounts of the selected species, one or more, of
algae are added via tube 2215, again either manually or under
computer control, or through one of the orifices in the tank lid
prior to inserting the associated light pipe. Illumination 2220 is
enabled from the control system, and the climate control sleeve
2225, or thermal jacket, brings the growth medium in the tank to a
temperature appropriate for growing the algae within the tank, as
monitored by temperature sensor 2230. The control system blends
gases such as CO2, air, nitrogen, or other gases, via solenoid
valve 2235 and blender 2240, and throttles the volume of gas
supplied to the tank via flowmeter 2245. The volume of gas is
controlled by the control system both for purposes of setting the
pH, as monitored by pH sensor 2250, and for the purpose of ensuring
proper flow within the tank. Depending upon the constituents in the
growth medium, the species of algae, and the bioproducts desired to
be produced by the algae, various other sensors are monitored by
the control system, for example phosphate levels 2255, nitrate
levels 2260, dissolved O.sub.2 2265, and turbidity 2270. In
addition to turbidity as a method for monitoring culture density, a
colorimeter and/or a chlorophyll fluorescence probe can be used.
When it is desirable to remove the algae and associated bioproducts
from the tank, either manually or via the control system a valve
2275 is opened and the algae-laden fluid is removed from the tank
via outlet 2280, either to be supplied to bioremediation lagoons or
ponds, or otherwise used or disposed of.
[0046] Referring next to FIGS. 3A-3C, various embodiments of the
light pipe of the present invention can be appreciated in greater
detail. Referring first to FIG. 3A, an exploded view of an
embodiment of a light pipe is shown. A clear rod 300, sized of a
length to permit the rod to reach substantially to the bottom of a
tank of a photobioreactor, comprises a series of alternating
frosted and unfrosted sections 305 and 310. The rod 300 is
typically comprised of acrylic or other polymer, or any other
suitable material which is optically clear at the wavelength of the
light emitted by one or more LED's 315 and capable of having a
surface texture created on portions thereof to create the frosted
and unfrosted sections 305 and 310. As noted before, the LED's can
be of multiple wavelengths, with different wavelengths emitted from
each rod, or all rods emitting multiple wavelengths, or all rods
emitting the same wavelength. It is noted that, while the foregoing
describes a single wavelength, those skilled in the art will
recognize that, in this context, "wavelength" is more accurately a
wavelength band, as LED's emit a spectral spread, where the center
wavelength is described as the "wavelength" of the LED. Also, as
noted previously, dyes can be used in or on the rods to convert
light of a wavelength generated by the LED's to light of a
different wavelength suited to the algae.
[0047] The LED's 315 are mounted in a mounting block 320, which is
thermally coupled to a heatsink 325 depending on the heat generated
by the LED's 315. In some embodiments, it is desirable to provide
spatially uniform light from the LED's to the rods 300, in which
case a homogenizer 330 can be disposed in the optical path between
the output of the LED's 315 and the input 335 of the rod 300. The
homogenizer 330 typically has a non-circular cross-section
throughout most or all of its length and utilizes internal
reflection, including total internal reflection depending upon the
material used, to create spatial uniformity of the light at the
output of the homogenizer. The input face 335 of the homogenizer
330 is typically sized so that its input dimensions are
substantially matched to the output of the LED's, thereby allowing
the homogenizer to capture all or nearly all of the light output of
the LED's. Similarly, the dimensions of the output face of the
homogenizer are sized to substantially match the input of the rod
300, so that the loss of light at the transition from the
homogenizer to the rod is minimized. It is not necessary that the
output of the homogenizer be congruent with either the output of
the LED's or the input of the light rod. In the case of the output
of the LED's, the input face of the homogenizer can be larger. In
the case of the input to the light rod, the output face of the
homogenizer can, for example, be a square with its corners
intersecting or contained within the circular face of the rod 300,
or can be any other shape reasonably contained within but
substantially covering the input face of the rod 300, although
homogenizers with an odd number of sides offer improved performance
in some instances.
[0048] In an important aspect of the light rods 300, the
arrangement of frosted and unfrosted sections 305 and 310 control
the location along its length and amount of light emitted from the
rod. Light entering the input to the rod is transmitted along the
unfrosted sections by total internal reflection. However, at each
frosted section, at least some of the light striking the sidewall
of the rod is emitted, or coupled, from the rod. The rod, which may
have any cross-section that permits total internal reflection, can
have a uniform cross-section along its length, or can monotonically
decrease in size. In addition, the distal end 340 of the rod 300
can either be rounded and frosted to prevent light loss, or can be
mirrored to cause the light to be retroreflected back up the rod,
allowing transmission through the sidewall of the rod as described
above. Because the end segment of the rod is a special case, where
real coupling can be significantly less than theoretical coupling
due to the exponential decay of the light, such mirroring or
rounding and frosting can increase actual coupling to a reasonable
approximation of theoretical coupling.
[0049] In at least some embodiments, the length of the frosted
section increases relative to the length of the adjacent unfrosted
section for each successive portion of the rod. In some
arrangements, the combination of an unfrosted section and the
adjacent frosted section can be thought of as a single segment 345,
and the segment length remains the same along the length of the rod
while the relative length of the frosted section within each
segment increases for each successive segment. The amount of light
transmitted by each frosted section is proportional to its length,
and so the relative lengths of the various frosted sections can be
expressed mathematically. Where z represents the location along the
rod of length L, and P(z) represents the intensity of the light in
the rod as a function of z, and the strength of the coupling due to
the frosting can be continuously varied along the length of the rod
in a controlled manner by varying the depth, shape and/or
periodicity of the grooves in the frosting, then .alpha.(z) can be
a coupling coefficient that describes the strength of the
fractional coupling of the light per unit length from the rod by
the frosting as a function of z. In addition, let Q(z) be the light
power coupled out of the rod per unit length at a particular
distance z along the rod. Thus Q(z)=.alpha.(z) P(z), and the
objective is to determine the function .alpha.(z) that will produce
the desired uniform distribution of light Q(z) coupled out of the
rod at the various frosted sections
[0050] For incoherent light and assuming conservation of energy, we
have
dP(z)/dz=-Q(z)=-.alpha.(z)P(z) [Eq. (1)]
with the boundary condition P(0)=P.sub.o. Solving for the
.alpha.(z) that will produce a uniform Q(z) in Eq. (1), Q(z) is set
equal to Q.sub.o as is the boundary condition P(L)=0. The solutions
are:
Q(z)=Q.sub.o=P.sub.o/L
P(z)=P.sub.o(1-z/L)
.alpha.(z)=L.sup.-1(1-z/L).sup.-1 [Eqs. (2)]
[0051] It will be appreciated that the dynamic range that can be
achieved for .alpha.(z) is limited in real systems, and there will
be some maximum value .alpha..sub.max that cannot be exceeded. Thus
the high values of .alpha.(z) as z/L approaches 1 prescribed by Eqs
(2) cannot be obtained and there will be some deviation from ideal
behavior. This will manifest itself as a dip in the value of Q(z),
the light power coupled out per unit length near the very end of
the rod.
[0052] In those cases where the span of values that can be achieved
for .alpha.(z) needs to be adjusted higher or lower, it is possible
to do such by selecting a different diameter for the light rod.
This will alter the number of reflections each light ray will
undergo per unit length of the rod and thus, assuming that the
properties of the frosting do not change, .alpha.(z) will scale
inversely proportionally to the rod diameter. For rods having N
segments of uniform length, where F.sub.i represents the fractional
light power coupled out of the i.sup.th segment and index i=1 at
the first segment and equals N at the last segment, the above
equations simplify to
Q.sub.i=Q.sub.o=P.sub.o/N
P.sub.i=P.sub.o(N+1-i)/N
F.sub.i=(N+1-i).sup.-1 [Eqs. (3)]
Following are tables that present the entire solutions of Eqs. 3
for N=2, N=5, N [0053] =10, and N=20, where
TABLE-US-00001 [0053] i P.sub.i Q.sub.i P.sub.i+1 F.sub.i For N =
2: 1 1.0000 0.5000 0.5000 50.00% 2 0.5000 0.5000 0.0000 100.00% For
N = 5: 1 1.0000 0.2000 0.8000 20.00% 2 0.8000 0.2000 0.6000 25.00%
3 0.6000 0.2000 0.4000 33.33% 4 0.4000 0.2000 0.2000 50.00% 5
0.2000 0.2000 0.0000 100.00% For N = 10: 1 1.0000 0.1000 0.9000
10.00% 2 0.9000 0.1000 0.8000 11.11% 3 0.8000 0.1000 0.7000 12.50%
4 0.7000 0.1000 0.6000 14.29% 5 0.6000 0.1000 0.5000 16.67% 6
0.5000 0.1000 0.4000 20.00% 7 0.4000 0.1000 0.3000 25.00% 8 0.3000
0.1000 0.2000 33.33% 9 0.2000 0.1000 0.1000 50.00% 10 0.1000 0.1000
0.0000 100.00% For N = 20 1 1.0000 0.0500 0.9500 5.00% 2 0.9500
0.0500 0.9000 5.26% 3 0.9000 0.0500 0.8500 5.56% 4 0.8500 0.0500
0.8000 5.88% 5 0.8000 0.0500 0.7500 6.25% 6 0.7500 0.0500 0.7000
6.67% 7 0.7000 0.0500 0.6500 7.14% 8 0.6500 0.0500 0.6000 7.69% 9
0.6000 0.0500 0.5500 8.33% 10 0.5500 0.0500 0.5000 9.09% 11 0.5000
0.0500 0.4500 10.00% 12 0.4500 0.0500 0.4000 11.11% 13 0.4000
0.0500 0.3500 12.50% 14 0.3500 0.0500 0.3000 14.29% 15 0.3000
0.0500 0.2500 16.67% 16 0.2500 0.0500 0.2000 20.00% 17 0.2000
0.0500 0.1500 25.00% 18 0.1500 0.0500 0.1000 33.33% 19 0.1000
0.0500 0.0500 50.00% 20 0.0500 0.0500 0.0000 100.00% i = segment
index; P.sub.i = incident light power Q.sub.i = coupled out light
power; P.sub.i+1 = transmitted light power; and F.sub.i =
fractional light power coupled out
[0054] As noted previously, the distal end (the last segment) is a
special case, where beveling, rounding or other shaping can be used
to achieve nearly 100% coupling as well as coupling out any light
propagating ballistically down the rod 300.
[0055] For segments of uneven length, the outcome is substantially
the same, where the light output of any segment is determined by
comparing the length of a given segment to the average segment
length. Stated mathematically, let L.sub.i be the physical length
of the ith segment. Since the overall length of the rod is L,
L = i = 1 N L i [ Eq . ( 4 ) ] ##EQU00001##
where .SIGMA. denotes the sum over all segments, that is all values
of i from 1 thru N. In order to produce a distribution of coupled
out power that is uniform over the physical length of the rod, it
is necessary to scale the values of Q.sub.i, the light power that
is coupled out of the i.sup.th segment, by L.sub.i/L.sub.av where
L.sub.av is the average segment length given by L.sub.av=L/N. The
solutions of Eq. (3) then become:
Q i = ( L i / L av ) ( P o / N ) = ( L i / L ) P o P i = P o - k =
1 i - 1 Q k F i = Q i / P i , [ Eq . ( 5 ) ] ##EQU00002##
where .SIGMA. denotes the sum of all of the values of Q.sub.k
coupled out previously in segments k=1 thru k=i-1. The numerical
evaluations of Eqs. (5) are easily obtained using a spreadsheet
that starts with the known values for i=1 of
Q.sub.1=(L.sub.1/L)P.sub.o, P.sub.1.dbd.P.sub.o, and
F.sub.1=L.sub.1/L and then fills in each line for higher values of
i based on the values from the proceeding line. As a specific
example, consider the case of a rod with 10 segments, nine of which
have length 1 and one of which (the 3rd segment) has length 3. The
results are shown in the table below. Examination of the results
shows that the coupled out light power Q.sub.3 for the 3rd segment
is three times as high as the power coupled out by the other
segments, as expected.
TABLE-US-00002 N = 10 F.sub.i i L.sub.i P.sub.i Q.sub.i P.sub.i+1
(Fractional (Segment (Segment (Incident (Coupled Out (Transmitted
Light Power Index) Length) L.sub.i/L.sub.av Light Power) Light
Power) Light Power) Coupled Out) 1 1 0.08333 1.0000 0.0833 0.9167
8.33% 2 1 0.08333 0.9167 0.0833 0.8333 9.09% 3 3 0.25000 0.8333
0.2500 0.5833 30.00% 4 1 0.08333 0.5833 0.0833 0.5000 14.29% 5 1
0.08333 0.5000 0.0833 0.4167 16.67% 6 1 0.08333 0.4167 0.0833
0.3333 20.00% 7 1 0.08333 0.3333 0.0833 0.2500 25.00% 8 1 0.08333
0.2500 0.0833 0.1667 33.33% 9 1 0.08333 0.1667 0.0833 0.0833 50.00%
10 1 0.08333 0.0833 0.0833 0.0000 100.00%
[0056] The practical effects of the mathematical descriptions given
above can be appreciated from FIGS. 3B and 3C, which show,
respectively, where FIG. 3B shows segments of uniform length while
FIG. 3C shows segments of uneven length, in which segment N.sub.3
is twice as long as the other segments. The hatched portions
represent the frosted sections of each segment, where light is
coupled out. Thus, for FIG. 3B and equal length segments, the
coupling is as shown in the table for N=5. But, for the design of
FIG. 3C, where N.sub.3 is twice as long as the other segments, the
equivalent number of segments is six, and N.sub.3 couples out
1/3+1/4 of the light, or a total of 48.3% across the longer
segment.
[0057] It will be appreciated by those skilled in the art that,
while the rod 300 is shown as a consistent diameter down its
length, other shapes and cross-sections of light rods are also
acceptable. Thus, for example, tapered light rods can also be used
in at least some embodiments. Likewise, the light rod 300 need not
be straight in some embodiments, and instead can be curved in any
suitable arrangement. Non-circular cross-sections, while harder to
manufacture in some cases, may offer more uniform light
distribution characteristics along the length of the rod in some
embodiments. Further, while the frosting is assumed to be identical
for each segment in the foregoing calculations and examples, in
some embodiments it is desirable to vary the optical properties of
the frosting at each segment. Such variations in the frosting
provides a means to extend the dynamic range over which the
coupling can be varied. Likewise, the variation in the frosting
does not need to be continuous. Having a few discrete values, such
as "weak", "medium" and "strong", offers benefit in some
embodiments, while continuously variable frosting allows fine
tuning of the fractional power coupled out by each segment.
[0058] Referring next to FIGS. 4A-4B, the nutrient system for
supplying a regulated nutrient stream to the algae growing in the
PBR can be better appreciated. A plurality of carboys 400A-n, each
containing a component of a predetermined nutrient mix appropriate
for a specific strain of algae, are associated with a plurality of
metering pumps 410A-n, each of which is computer controlled. The
metering pumps thus supply a desired mix of nutrients into a mixing
tank 420, which receives water 425 via a computer controlled valve
430. A number of filters 435 and 440 can also be installed between
the inlet water and the mixing tank; for example, five micron and
carbon filters, respectively.
[0059] The outlet of the mixing tank is supplied to a computer
controlled pump 445, which supplies the mixed nutrient stream to a
computer controlled valve 450. The valve 450 directs the nutrient
mix either to be recirculated in the tank via recirculation line
460 or to be supplied to an associated PBR or group of PBR's as
indicated at 470. Filters 455 and 465, which can, for example, be
two micron filters, can be provided on the recirculate and PBR tank
lines, respectively.
[0060] With particular reference to FIG. 4B, the process for
preparing the growth medium using the system of FIG. 4A can be
better appreciated. The process starts at step 4000, and at step
4005 the tank 420 is filled with water to a predetermined level as
determined by level sensor 475, after which the pump 445 is turned
on and configured to recirculate the tank contents by valve 450 as
shown at step 4010. At step 4015, the water in the tank is heated
by heater 485 to a predetermined temperature as measured by
temperature sensor 480. The nutrient constituents appropriate for
the particular growth medium being developed are the supplied to
the tank from carboys 400A-n via their associated metering pumps
410A-n at step 4020. The constituents of the growth medium can vary
with the particular algae strain for which the growth medium is
intended. The mix of water and nutrients is then circulated, as
shown at step 4025, until the nutrients are uniformly distributed,
after which the growth medium is supplied to an associated PBR at
step 4030. The process either completes, as shown at step 4030, or
loops back to step 4005 to begin again.
[0061] Referring next to FIGS. 5A-5B, a multi-phasic pond in
accordance with an aspect of the invention can be better
appreciated. FIG. 5A shows a pond 500 with a paddlewheel 505 in top
plan view, and also shows the location across which the
cross-sectional view of FIG. 5B is taken. FIG. 5B shows the various
strata of the pond. In particular, an anaerobic zone 510 is located
at the bottom of the pond. An anaerobic/aerobic transition zone 515
is located above the anaerobic zone, at the top of which are
disposed one or more CO.sub.2 supply tubes 520. The CO.sub.2 supply
tubes are typically porous tubing for distributing CO.sub.2
substantially uniformly across at least a substantial portion of
the pond 500. The CO2 is utilized by aerobic bacteria in an aerobic
zone 525. The paddlewheel 505 creates a flow, shown from left to
right in exemplary FIG. 5B, such that mixing of the effluent being
remediated across the various zones is facilitated. In ponds or
lagoons having only an aerobic zone, the tubes 520 can be arrayed
on the bottom of the pond or lagoon.
[0062] Referring next to FIG. 6, a bubble column with internal
lighting in accordance with an aspect of the invention can be
better appreciated. In some instances, it is desirable to study the
growth of algae or other flora in a carefully controlled
environment, such as for research. In such instances, it is
sometimes desirable to ensure appropriately controlled illumination
and nutrient supplies, while not circulating the growth medium or
growing species in a larger tank. For such implementations, the
bubble column of FIG. 6 is appropriate. A tank 600 has a sealed
bottom and has disposed therein at least one light rod 605 of the
type described in connection with FIGS. 3A-3C. Although a round
tank 600 is shown, the tank need not be round in all instances, and
instead can be any convenient shape. The light rod can be centrally
disposed or disposed asymmetrically, and can be configured together
with the shape of the tank to provide whatever uniformity of
illumination or lack thereof is desired. In an embodiment, the
position of the light rod can be varied within the tank to
facilitate different illumination patterns. Compressed air or other
gases, utilized in the manner described in connection with FIGS.
2A-2B et seq., are supplied to a diffuser 610 located at the bottom
of the tank via a tube 615, which can either enter the tank from
the bottom or down an inside wall as shown. The diffuser can be
configured to supply gas uniformly across the bottom of the tank or
in any desired pattern, but the sole agitation and mixing is
through the upward movement of the bubbles through the algae-laden
medium, since there is no larger tank for creating the upward and
downward flows of the systems shown in FIGS. 2A-2F. In at least
some embodiments, a supply tube 620 is provided by which algae can
be introduced to the column. The supply tube 620 can be located at
any convenient position on the tank, including a lid 625, or an
orifice in the lid through which the light rod 605 passes, a
sidewall, or the bottom of the tank.
[0063] In operation, the bubble column is filled with a growth
medium, and algae strains are introduced. A gas mixture appropriate
for the particular study being conducted is introduced via the
diffuser, and the resulting bubbles entrain the algae as described
above. However, because the bubble column is not contained within
an outer housing or tank, the fluid levels are typically maintained
at levels below overflowing in most embodiments.
[0064] Referring next to FIG. 7, an alternative embodiment of a
wastewater remediation system in accordance with an aspect of the
invention is shown in schematic form. Organic waste 700 is supplied
to an anaerobic digester 705, which begins the breakdown process
and generates methane 710 and an effluent stream 715, comprised in
part of CO.sub.2, nitrogen, phosphorus and other constituents. The
effluent is supplied to a multiphasic pond 720, together with water
725 as needed. The methane provides fuel for a generator/boiler
730, which generates heat 735 that is supplied back to the
anaerobic digester 705. The generator 730 also provides CO.sub.2
740 to a photobioreactor 745, typically constructed in accordance
with the aforementioned teachings, as well as the multiphasic pond
720. The generator 730 also supplies electricity and heat 750 to
both the PBR 745 and the multiphasic pond 720, and may in some
implementations supply additional electricity at 775. The pond 720
receives additional atmospheric CO2 at 760, if needed, and outputs
remediated wastewater. The remediated wastewater can then be given
an optional final treatment, as shown at 765, such as an
ultraviolet polish, carbon filtration, or other remediation step.
In some embodiments, the pond 720 can also generate usable biomass
as shown at 770.
[0065] Referring next to FIGS. 8A-8B, a concentrator system and
process can be better appreciated. Some species of algae grow best
under one set of conditions, but produce desired products more
rapidly under different conditions. One example is algae that grows
best when supplied with nitrogenous nutrients, but produces higher
concentrations of lipids when deprived of nitrogenous nutrients. To
maximize the productivity of a system, it is desirable to create
different growing conditions to achieve the different goals, and
also to achieve the transition as quickly as possible. As shown in
FIGS. 8A-8B, algae of a desired species is grown to a desired
density at step 800 in a PBR 850 using a first growth medium
designed to achieve high algae density as promptly as possible.
Once the density level has been achieved, at least a portion of the
algae is transferred to a concentrator tank 855, as shown at step
810, typically although not necessarily through a
computer-controlled valve 860. The transfer process requires that a
substantial amount of the first growth medium be transferred with
the algae, to prevent damage to the algae.
[0066] After transfer to the concentrator tank 855, the combination
of algae and the first growth medium are allowed to settle as shown
at step 815, causing the growth medium, which is largely water, to
clarify. Then, at step 820, the clarified growth medium is removed,
either from the top of the concentrator or any other suitable
location that will not remove and/or damage the algae within the
concentrator 855. It will be appreciated that not all of the first
growth medium can be removed, but a significant percentage, in the
range of 75%, can be removed without damaging the algae. Then, at
step 825, the remaining growth medium and the algae are transferred
to a blooming tank 870 through a valve 875, also typically but not
necessarily computer-controlled. A second growth medium is used in
the blooming tank 870, formulated to stimulate development of the
desired products, as shown at step 830. It will be appreciated
that, in at least some embodiments, the second growth medium is
added to the blooming tank in advance of the transfer of the algae
into the blooming tank, to minimize physical damage to the algae
during transfer, although these steps can be reversed depending
upon the particular algae, the amount of first growth medium
remaining after step 820, and the trauma likely to be suffered by
the algae during the transfer process. To facilitate a smooth
transfer with minimal trauma to the algae, a concentrator tank 855
having a funnel-shaped lower portion can be used, where the algae
settles in the funnel-shaped portion both to permit easy removal of
the first growth medium and to permit easy transfer to the blooming
tank. Once the algae and second growth medium are combined in the
blooming tank 870, the process waits until adequate amounts of the
desired products are produced by the algae, at which point those
products are removed for further use, and shown at step 835. The
blooming tank can be configured in substantially the same way as
the PBR 850, and in some implementations the PBR 850 can be re-used
as the blooming tank.
[0067] In use, the first growth medium can, for example, be
nitrogen-rich and thus encourage rapid growth of selected algae.
The transfer to the concentrator and removal of the first growth
medium rapidly reduces the levels of nitrogen and other nutrients,
including trace elements, in the algae. Then, the second growth
medium can be, for example, pure water, or nitrogen-depleted. At
this point the selected algae begin to produce lipids or other
products which can be used, for example, as biofuels. The result,
and benefit, of the concentration process is that it rapidly
accelerates the depletion of nutrients in the growth medium which,
in turn, accelerates the generation of the desired products. For
example, if the concentration process were not used, the desired
depletion of nitrogen in the first growth medium could take in the
range of ten days, during which time the rate of algae growth would
be substantially sub-optimal, while at the same time the algae
would not be producing the desired levels of usable products. By
comparison, the concentration process of the present invention can
be accomplished within minutes or, at most, hours, such that the
beginning of production occurs much more rapidly, resulting in
increased efficiency and lower operating costs.
[0068] Inevitably, power failures will occur regardless of the
quality of backup systems. Algae is somewhat fragile, and loss of
power for extended periods will kill the algae being grown in the
PBR's and blooming tanks. To prevent unnecessary loss of algae in
the event of a power failure, it is desirable to provide a
soft-fail sequence by which the life of the algae is prolonged for
as long as possible. A soft-fail process is described in FIG. 9,
where a check is made at step 905 to determine whether power is at
proper levels. If yes, the process loops so that checking for power
failures is essentially continuous. If power is not at proper
levels, the process advances to step 910 and any preparation of
growth medium is halted, as is any algae transfer or discharge. In
addition, as shown at step 915, the LED's are turned off. Further,
at step 920, the temperature tolerances set into the control system
are automatically expanded. Still further, the pH target in the
tank is adjusted for the particular species being grown to maximize
culture viability, as shown at step 925. Finally, the gas stream is
switched from continuous operation to intermittent, so that mixing
in the tank continues although not at the same levels. It will be
appreciated that steps 910 to 930 can be performed either
essentially concurrently, or in stages where the time increment
between each step can be adjusted depending upon the particular
operating conditions, the strain(s) of algae, and the projected
time before power is restored. Finally, as shown at step 935, the
state of the power is tested again. If power has been restored, the
operations of steps 910-930 are restored to normal conditions as
shown at step 940. If power has not been restored, the check
continues until power is restored or reserve power is lost.
[0069] From the foregoing, it can be appreciated that new and novel
bioremediation systems and methods have been described, with novel
aspects regarding illumination, nutrient supply and mixing, algae
growth processes, generation of biomass and other products, and
soft failure processes. Having fully described a preferred
embodiment of the invention and numerous alternatives of the
various aspects of the invention, those skilled in the art will
recognize, given the teachings herein, that numerous alternatives
and equivalents exist which do not depart from the invention. It is
therefore intended that the invention not be limited by the
foregoing description, but only by the appended claims.
* * * * *