Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Vertical Pond Photo Bioreactor with Low-cost Thermal Control System
FIELD OF INVENTION
The disclosure herein generally relates to vertical photobioreactor apparatus
for
culturing microalgae and other light capturing organisms' using a
photosynthetic
process. More particularly, the invention relates to a vertical pond
photobioreactor able to farm large volumes of culture on a small surface area
and integrate into the reactor a conditioning system, a fast maintenance
system,
a light penetrating system at daytime and an LED lighting system at night
time.
The growth of phototropic organisms in a photobioreactor present multiple
design
challenges; a first challenge is to provide a photobioreactor that presents
sufficient light intensity to the organisms for maximum growth and as
uniformly as
possible throughout the support media (usually nutrient rich water), and this
both
at daytime and at night time; a second challenge is to reduce maintenance and
cleaning costs of the system; a third challenge is to control the temperature
of the
culture in a cost-effective manner; and finally but not the least, to provide
a
reactor that can be produced using a low-cost manufacturing method.
BACKGROUND
Burning of fossil fuels is thought to have resulted in elevated atmospheric
carbon
dioxide (CO<sub>2</sub>) concentrations. The levels of carbon dioxide are expected
to
double in as little as 60 years based on changes in land use and continued
burning of fossil fuels. The increase in carbon dioxide concentrations as well
as
other greenhouse gases is thought to keep heat within the atmosphere, leading
to higher global temperatures. Sequestration--the long term capture and
storage
of carbon dioxide-has been long thought of as a way to mitigate this problem.
Given however, that light and carbon dioxide make up most of what is consumed,
direct conversion of ambient carbon dioxide to valuable products, such as
fuels,
chemicals, drugs, and their precursors, represents an alternative and improved
means to reduce the effects of carbon dioxide while maintaining the core
industrial and commercial products our modern society demands.
.One of the primary limitations of using algae as a method of carbon dioxide
sequestration or conversion to products has been the development of efficient
and cost-effective growth systems. Open algal ponds up to 4 km<sup>2</sup> have
been researched, which, while requiring low capital expenditures, ultimately
have
low productivity as these systems are also subject to a number of problems.
Intrinsic to being an open system, the cultured organisms are exposed to a
number of exogenous organisms which may be symbiotic, competitive, or
pathogenic. Symbiotic organisms can change the culture organisms merely by
exposing them to a different set of conditions. Opportunistic species may
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compete with the desired organism for space, nutrients, etc. Additionally,
pathogenic invaders may feed on or kill the desired organism. In addition to
these
complicating factors, open systems are difficult to insulate from
environmental
changes including temperature, turbidity, pH, salinity, and exposure to the
sun.
These difficulties point to the need to develop a closed, controllable system
for
the growth of algae and similar organisms.
Not surprisingly, a number of closed photobioreactors have been developed.
Typically, these are cylindrical or tubular (i.e., U.S. Pat. No. 5,958,761, US
Patent application No. 2007/0048859). These bioreactors often require
mixing devices, increasing cost, and are prone to accumulating oxygen
(O<sub>2</sub>), which inhibits algal growth.
As disclosed in WO 2007/011343, many conventional photobioreactors
comprise cylindrical algal photobioreactors that can be categorized as
either "bubble columns" or "air lift reactors." Vertical photobioreactors,
which operate as "bubble columns" are large diameter columns with algal
suspensions wherein gas is bubbled in from the bottom. Using bubbling as
a means of mixing in large-diameter columns is thought to be inefficient,
providing for lower net productivity as certain elements of the culture remain
photo-poor and as large bubbles of gas do not deliver necessary
precursors. An alternative vertical reactor is the air-lift bioreactor, where
two
concentric tubular containers are used with air bubbled in the bottom of the
inner tube, which is opaque. The pressure causes upward flow in the inner
tube and downward in the outer portion, which is of translucent make.
These reactors have better mass transfer coefficients and algal productivity
than other reactors, though controlling the flow remains a difficulty.
Efficient
mixing and gas distribution are key issues in developing closed bioreactors
and to date, such efficient bioreactors do not exist.
Subitec GmbH, a German company (as disclosed on their website
(http://en.subitec.com/microalgae-technology/patents.html ) developed Flat
Panel Airlift photobioreactors with multiple advantages as disclosed in two
families of patents EP 1169 428 131 - photobioreactors with improved light
input and EP 1 326959 131 - Bioreactor for the cultivation of
microorganisms, and processes for manufacturing the same. However,
these flat panel reactors contain limited volumes of algal solutions, have no
integrated heating or cooling system and are difficult to clean.
Tubular bioreactors, when oriented horizontally, typically require additional
energy to provide mixing (e.g., pumps), thus adding significant capital and
operational expense. In this orientation, the O<sub>2</sub> produced by
photosynthesis
can readily become trapped in the system, thus causing a significant reduction
in
algal proliferation. Other known photobioreactors are oriented vertically and
agitated pneumatically. Many such photobioreactors operate as "bubble
columns."
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All closed bioreactors require light, either from the sun or artificially
derived (U.S.
Pat. No. 6,083,740). Solar penetration is typically enabled through
translucent
tubing, which, with thinner diameter, enables more thorough saturation of the
algae. Some known photobioreactor designs rely on artificial lighting, e.g.
fluorescent lamps, (such as described by Kodo et al. in U.S. Pat. No.
6,083,740),
and can otherwise be provided by any light source existing today.
Photobioreactors that do not utilize solar energy but instead rely solely on
artificial light sources can require enormous energy input, increasing cost,
and
rendering these systems, as stand-alone approaches, impractical. Using natural
solar light requires a low cost means to allow for proper penetration of the
culture
while maintaining the culture at a temperature that is appropriate.
Many different photobioreactor configurations have been described in the
literature including flat panels, bubble columns, tubular reactors and a
variety of
annular designs aimed at improving the surface area to volume ratio to
maximize
conversion of sunlight and CO<sub>2</sub> to biomass or other products such as algal
oil. These reactors have distinct advantages compared to open raceway with
respect to controlling temperature, pH, nutrient and limiting contamination
(see
Pulz, O. "Photobioreactors: Production systems for phototrophic
microorganisms", Appl. Microbiol. Biotechnol (2001) 57:287-293). Key
limitations
to their adoption have been the cost vs. benefit as it relates to the product
being
produced. Whereas valuable products such as carotenoids have been produced
in photobioreactors the production of biomass for fuels could not be
economically
justified to date.
The art as it relates to enclosed photobioreactors achieve temperature control
in
a variety of ways including external and internal heat exchangers, spraying of
cooling water directly on the surface, use of cooled or heater sparge gas as
well
as submerging the reactor directly in large pond of water that is separately
temperature controlled (see Molina Grima, E. et al "Photobioreactors: light
regime, mass transfer, and scale-up", J. of Biotechnology (1999) 70:231-247;
Hu,
Q. et al "A flat inclined photobioreactor for outdoor mass cultivation of
photoautotrophs" Biotechnology and Bioengineering (1996) 51:51-60 and Hu, Q.
WO 2007/098150 A2 "Photobioreactor and uses therefor"). Currently, a cost-
effective thermal regulation system that can be implemented in large scale
does
not exist.
What is needed, therefore, is a low-cost efficient integrated photobioreactor
system that is scalable, is virtually maintenance-free, presents good light
exposure to microorganism, integrates its own temperature control and may be
produced using a low-cost manufacturing method such as extrusion.
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SUMMARY
In various embodiments, a vertical serpentine-shape pond photobioreactor is
described which can provide sufficient productivity for growing micro-
organisms
for commercial application. The disclosed apparatus works in combination with
a
translucent disposable sleeve inserted into the apparatus chamber which
contains the microalgae culture. The method of temperature control for any
photobioreactor using the principle taught by this invention is provided by
incorporating on the interior surface of the bioreactor fins that create a
space
over which is resting the plastic sleeve. By displacing a fluid in-between
these
fins such as air or water, an air or water jacket is created for conditioning
the
content of the sleeve. Such photobioreactor apparatus and methods are
optimized for light capture and require virtually no maintenance. Using a low-
cost
extrusion process keeps costs down. The serpentine-shape of the bioreactor is
provided by bending a rectangular-shape extruded profile to form the chamber
of
the bioreactor. This bending method, also called BendTrusionTM (BendTrusion is
a Trade Mark of Soheyl Mottahedeh) was developed and disclosed in another
invention of the same inventor. Said method ensures that costs remain low so
that replication of the apparatus is scalable and that the system achieves
efficient growth of the culture. In various embodiments, such organisms grown
in
the disposable sleeve positioned in the vertical pond chamber are used in the
production of biomass and chemical intermediates as well as a means to
biologically produce end products such as fuels, chemicals and pharmaceutical
agents.
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BRIEF DESCRIPTION OF THE FIGURES
FIG. 1 is a perspective cross-section view of a part of the panel that will be
extruded and bent to form a serpentine-shape or a helical -shape vertical pond
photobioreactor.
FIG. 2 depicts the view of the panel of FIG. 1 containing a first outer
translucent
plastic sleeve and a second inner also translucent plastic sleeve that
incorporates strips of membrane.
FIG. 3 depicts a perspective view of a part of a tubular shape photobioreactor
having some shorter and some longer inner fins with four LED cord sections.
FIG. 4 depicts a cross-section view of FIG. 4 with a plastic sleeve inside for
containing an algal solution
FIG. 5 depicts a perspective view of the panel of FIG. 1 with a translucent
plastic sleeve substantially inserted in it but for a small portion hanging
outside a
the panel side opening.
FIG. 6 depicts a perspective view of the multi-layered sleeve of FIG. 2
FIG. 7 is an illustration of a multiple photobioreactor assemblies connected
in
fluid communication, each photobioreactor featuring a removable lower
connector provided with two removable spargers for providing circulation of
media and mixing of cultures.
FIG. 8 depicts a tubular extruded profile bended in a pyramidal shape.
FIG. 9 depicts another tubular extruded profile bended in a conical shape.
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DETAILED DESCRIPTION OF THE EMBODIMENTS
Photobioreactor Apparatus & Light Capture
The invention provides an efficient, low-cost, high surface area light
capturing
apparatus that is scalable and easily implemented in open space such as the
exemplary photobioreactor apparatus as shown in FIG. 7. Such photobioreactor
apparatus is adapted to capture light through a generally horizontally-
oriented
elongate panel 100 shown in FIG. 1. The elongate panel 100 may take on the
shape of a vertical rising serpentine as shown in FIG. 7, a helically-shaped
cylinder (not shown), a helically shaped cone (FIG. 9) or pyramid (FIG. 8), or
any
combination of these shapes . Since different types of light capturing
organisms
can require different light exposure conditions for optimal growth and
proliferation, additional modifications can be made to the construction of a
photobioreactor apparatus to capture light according to the various
embodiments.
In certain embodiments, the photobioreactor apparatus is used with natural
sunlight, however, in alternative embodiments, an artificial light source such
as
Light Emitting Diodes (LED) 380 shown in FIGS. 3 and 4 providing light at
wavelengths that is able to drive photosynthesis may be utilized instead of or
in
addition to natural sunlight. For example, a photobioreactor apparatus is
configured to utilize sunlight during the daylight hours and artificial light
in the
nighttime, so as to increase the total amount of time during the course of the
day
in which the photobioreactor apparatus can convert light, CO<sub>2</sub> and water
to
products through use of photosynthetic organisms.
The photobioreactor of the invention can be illustrated in various dimensions,
shape and designs. In preferred embodiments, the photobioreactor is made of an
extruded panel 100 with a generally rectangular cross-sectional profile. Panel
100 takes on the shape of a horizontally-oriented flat-panel design that is
bent in
various shapes. Shapes may vary from serpentine 110 to a range of helically-
shaped profiles including cylindrical (not shown), conical 130 or pyramidal
140
configurations, or a combination thereof. Panel 100 is comparable to a
vertical
raceway or a vertical pond. The top 112 and bottom 114 ends of panel 100 are
configured so as to face respectively the top 112 and bottom 114 of other
panel
100 ends. A connector 212 connects two panel ends 112 and a connector 214
connects two panel ends 114. Connectors 212 and 214 allow for continuous
flow-through of culture while providing input of air, of co<sub>2</sub> and of
nutrients.
Structural support between layers of panels 100 is provided to reduce pressure
on curved portions of photobioreactors.
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The inside surface of panel 100 is covered with multiple fins 116
perpendicularly
oriented in relation to the surface. Fins 116 play collectively the function
of an air
or water jacket for heating or cooling sleeve 300 and 360.
The panel 100 may be in various shapes and sizes and is generally designed to
allow a desired amount of light to penetrate the channel 200. A useful feature
of
the photobioreactor panel 100 allows visible light spectra of wavelengths
between 400-700 nm to enter sleeve 300 for optimum LED lighting of the
organisms at night time while filtering out the unwanted wavelengths in the
spectra.
An elongate flexible thin sleeve 300 similar to a plastic film is positioned
inside
panel 100 to contain an algal solution; sleeve 300 is at least partially
translucent;
In another embodiment of the invention, sleeve 300 is provided with strips 310
of
a translucent film being bonded side-by-side to strips of membrane 320.
Membrane 320 may be of an osmosis membrane type or of a reverse osmosis
membrane type or of a micro-filter type.
Translucent strips 310 may be bonded to membrane strips 320 side-by-side
lengthwise as shown in FIGS. 2 and 6 or helically (not shown).
Membrane strips 320 are configured to gradually dewater the algal solution
reducing the amount of energy needed before lipid extraction is initiated.
In another embodiment of the invention, a sleeve 360 is provided by containing
inside a fully translucent outer sleeve 300 a combined membrane-plastic sleeve
320.
A fluid inserted in-between the outer sleeve 300 and the combined membrane-
plastic sleeve 320 is provided to affect the algal fluid. Fluidic effects on
the algal
fluid are intended to cause an intended reaction on or to stimulate algal
growth,
to condition the algal fluid by heating or cooling it, to improve extraction
of lipids,
to create enzymatic reactions or engender reactions of the like.
As mentioned before, temperature control of the algal solution inside sleeve
300
may be achieved by displacing a fluid in the space between fins 116, around
sleeve 300.
The disposable flexible sleeve 300, 320 and 360 may be selected from
biodegradable materials. To guarantee a bacteria-free environment to the algal
solution, sleeves 300, 320 and 360 may be sterilized by both UV and Gamma
light before use.
Providing photobioreactor panel 100 with a disposable low-cost sleeve 300
enables to maintain and clean the system in a cost-effective manner,
eliminating
the need to waste excessive amount of water or of chemicals to clean the
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photobioreactor panel 100. Furthermore, a quick replacement of a disposable
sleeve 300 and 360 extending partially or extending along the full length of
an
assembly of multiple photobioreactor panels 100 reduces effectively operation
downtime for maintenance.
The fluid displaced or circulated in-between finsl 16 is selected from the
group
consisting of a gas, a liquid, a slurry containing solid particles or a
combination
thereof. Displacing a fluid in-between fins 116 for conditioning the algal
solution
may not be limited to only heating or cooling. Other types of conditioning may
also be provided such as:
- Illuminating the algal solution with a fluorescent gas or a bio-luminescent
or
chemo luminescent liquid or gas;
- reflecting light by circulating in between fins 116 a reflective liquid such
as an
aluminized liquid. This may save energy by reflecting back an artificial light
intended to illuminate the algal solution and reduce losses of light to the
external environment.
- Shielding the algal solution against darkness or excess light may be another
advantage
- Filling with water space between fins 116 acts as a water lens to magnify
light
to provide maximum light input to the algal solution
- knowing that a magnetic field promotes growth of a culture by manifolds,
circulating a liquid with magnetic particles may be very beneficial
- when de-magnetizing is required, circulating a liquid with the right
property
may be beneficial to the culture
- controlling light density by circulating a colored liquid may reduce the
negative
effects of excess light
- circulating a liquid that filters some light colors such as UV light known
to
inhibit organisms growth is beneficial to the culture
- insulating the algal solution against cold or excess heat with for example
soap
bubbles has proven to be very efficient in greenhouses used in the Northern
Hemisphere
- shielding the algal solution against darkness against radiation is another
features of the water jacket of the invention
- using a solution containing some light-emitting organisms that generate
light
at night may reduce the amount of artificial light.
- A combination of the above features may be also be provided by circulating
the right fluid in the air or water jacket of the invention.
The distance between fins 116 may be configured so that when sleeve 300 is
filled with an algal solution, sleeve 300 and 360 may rest over tips of fins
116
without having the thin plastic sleeve 300, 320 and 360 to creep into the
space
between fins 116. This may be achieved by selecting the right sleeve
thickness,
the right distancing between fins 116 and the right perimeter of the sleeve of
slightly smaller dimension than the panel interior perimeter when distances
between all fins 116 tips are added.
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To speed up insertion and exit of sleeve 300, 320 and 360, phobioreactor panel
100 chamber of generally rectangular-shape is provided with a narrow side
opening 150 positioned along the full length of the photo bioreactor panel
100. In
practice, this narrow opening 150 assists in the fabrication of the extrusion
die
used for the extrusion of panel 100.
In an embodiment of sleeve 300, 320 and 360 wherein a photo bioreactor panel
100 is provided with a side opening 150, the width of sleeve 300, 320 and 360
may be extended so that a portion of sleeve 300, 320 and 360 may be gripped in
between the upper and lower lips of side opening 150. Such an arrangement
may be useful when extra sleeve material helps when sealing the space around
which a perfusion needle (connected to a tube) such as for oxygen (O<sub>2</sub>)
removal is inserted into sleeve 300, 320 and 360. In another instance, when
inserting a right-hand and a left-hand sparger tubes (not shown) or nutrient
delivery tubes into the algal culture, puncturing of the sleeve 300, 320 and
360 is
required to access algal culture. Connectors 212 and 214 are configured to
seal
all tubes and deliver conditioning fluids without fluid leakage.
When sleeve 320 is used in the photo bioreactor 1000 as a means to dewater the
algal solution, fins 116 serve as water collection channels with gravity
bringing
liquids down into bottom collector 212 which is provided with means to channel
such restored water for recycling purposes.
A photo bioreactor bottom end 114 may be connected via a bottom connector
214 to a bottom end of another bioreactor 114; similarly two top ends 112 of
two
bioreactor panels 100 may be connected together via a top connector 212.
The bottom connector 212 is provided with tubes for sparging a mix of air and
COsub2 and for delivery of nutrients into the algal solution. Also, this
bottom
connector is provided with a channel for displacing a conditioning fluid
around the
sleeve 300, 320 or 360 inside the photobioreator panel 100 chamber.
To minimize leaking, length of sleeve 300, 320 and 360 may extend to cover the
entire length of multiple photo bioreactor pnels 100 when connected together.
However, for convenience or for quick inter-changeability of disposable
sleeves
300, 320 and 360 the sleeve 300, 320 and 360 length may extend to line the
inner space of one or two photo bioreactor panels 100 at a time. Also, the
length
necessary to line some photo bioreactor panels 100 with one type of membrane
320 and a length to line other photo bioreactor panels 100 with another
membrane type may vary depending on algal solutions and algal growth level or
other desired factors intended to reduce production costs of end products.
In yet another embodiment of the invention as shown in FIGS. 3 and 4, selected
fins 118 are more elevated than other fins 116. This additional length for
longer
fins 118 causes sleeve 300, 320 or 360 to adopt the body shape of these longer
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fins 118 along the full length of the photo bioreactor panel-type or tubular-
type
200. These longer fins 118 act as light guides that bring extra light deeper
into
the algal culture.
In preferred embodiments, the reactor structure has a rectangular cross-
sectional profile as shown in FIGS. 1, 2, 5, 6 and 7. The reactor is
preferably
formed through an extrusion process inline with a thermoplastic bending
machine. This bending machine, also called BendTrusionTM (BendTrusion is a
Trade Mark of Soheyl Mottahedeh) has been disclosed by the same present
inventor Mottahedeh in US Patent 7,841,850.
The reactor flow is typically driven with air-lift; bubbles introduced in the
bottom
connector 214 tend to rise on the top surface in the bell portion of upper
connector 212.
