Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02393016 2010-03-29
-1-
TRIPHASIC BIOREACTOR AND PROCESS FOR GAS EFFLUENT TREATMENT
FIELD OF THE INVENTION
This invention relates to the field of gas effluent treatment and air
purification. More
specifically, it concerns a triphasic bioreactor for the biological treatment
of gaseous
effluent. The invention also concerns a triphasic process for the biological
treatment
of gas effluent.
BACKGROUND
Contemporary industrial activities generate gaseous effluents containing a
multitude
of chemical compounds and contaminants which interfere with the equilibrium of
elements in nature and affect the environment at different levels. Acid rain,
the
green-house effect, smog and the deterioration of the ozone layer are examples
that
speak volumes about this problem. Reduction of noxious emissions is therefore
not
surprisingly the subject of more and more legislation and regulation.
Industrial
activities and applications which must contend with stricter environmental
regulatory
standards in order to expect any long term commercial viability, will turn
more and
more to biological and environmentally safe methods. Consequently, there is a
real
need for new apparatus and methods aimed at the biological treatment of
gaseous
waste or effluents.
There already exists a vast array of technologies aimed at the separation and
recovery of individual or mixed gases and a number of different biological
methods is
known to treat gaseous waste or effluents : bacterial degradation (JP 2000-
287679 ;
JP2000-236870), fermentation by anaerobic bacteria (WO 98/00558),
photosynthesis through either plants (CA 2,029,101 Al ; JP04-190782) or
microorganisms (JP 03-216180). Among the more popular are those gained through
the harnessing of biological processes such as peat biofilters sprinkled with
a flora of
CA 02393016 2010-03-29
-2-
microorganisms in an aqueous phase, or biofilter columns comprising
immobilized
resident microorganisms (Deshusses et al. (1996) Biotechnol. Bioeng. 49, 587-
598).
Although such biofilters have contributed to technological advances within the
field of
gaseous waste biopurification, the main drawbacks associated with their use
are
their difficult maintenance and upkeep, lack of versatility, as well as time
consuming
bacterial acclimation and response to perturbation periods (Deshusses et al.).
A number of biological sanitation/purification methods and products is known
to use
enzymatic processes, coupled or not to filtration membranes (S5250305 ;
US4033822; JP 63-129987). However, these are neither intended nor adequate for
the cleansing of gaseous waste or effluents. The main reason. for this is
that, in such
systems, contaminants are generally already in solution (US5,130,237 ;
US4,033,822; US4,758,417; US 5,250,305; W097/19196 ; JP 63-129987 ).
Efficient enzymatic conversion and treatability itself of gaseous waste or
effluents in
liquids therefore depend on adequate and sufficent dissolution of the gaseous
phase
in the liquid phase. However, the adequate dissolution of gaseous waste or
effluents
into liquids for enzymatic conversion poses a real problem which constitutes
the first
of a series of important limitations which compound the problem of further
technological advances in the field of gas biopurification.
Although triphasic Gas-Liquid-Solid (GLS) reactors are commonly used in a
large
variety of industrial applications, their utilization remains quite limited in
the area of
biochemical gas treatment (US6245304 ;US4743545). Also known in the prior art
are the GLS bioprocesses abundantly reported in the literature. A majority of
these
concerns wastewater treatment (JP09057289). These GLS processes are
characterized in that the gaseous intake serves the sole purpose of satisfying
the
specific metabolic requirements of the particular organism selected for the
wastewater treatment process. Such GLS treatment processes are therefore not
aimed at reducing gaseous emissions.
CA 02393016 2010-03-29
-3-
As previously mentionned, these systems are neither intended nor adequate for
the
treatment of gaseous waste or effluents. An additional problem associated with
the
use of these systems is the non retention of the solid phase within the
reactor.
Biocatalysts are in fact washed right out of the reactors along with the
liquid phase.
Different concepts are, nonetheless, based on this principle for the reduction
of
gaseous emissions, namely carbon dioxyde. Certain bioreactors allow the uptake
of
CO2 by photosynthetic organisms (CA229101 ;JP03-216180) and similar processes
bind CO2 through algae (CA2232707 ; JP08-116965 ; JP04-190782 ; JP04-075537).
However, the biocatalyst retention problem remains largely unaddressed and
io constitutes another serious limitation, along with gaseous effluent
dissolution, to
further technological advancements.
The main argument against the use of ultrafiltration membranes to solve this
biocatalyst retention problem is their propensity to clogging. Clogging
renders them
is unattractive and so their use is rather limited for the retention of
catalysts within
reactors. However, a photobioreactor for medical applications as an artificial
lung
(W09200380 ; US5614378) and an oxygen recovery system (US4602987 ;
US4761209) are notable exceptions making use of carbonic anydrase and an
ultrafiltration unit.
The patent applications held by the assignee, C02 Solution Inc., via Les
Systemes
Envirobio Inc.(EP0991462 ; W09855210; CA2291785) proposes a packed column
for the treatment of carbon dioxyde using immobilized carbonic anhydrase
without
the use of an ultrafiltration membrane. Carbonic anhydrase is a readily
availabe and
highly reactive enzyme that is used in other systems for the reduction of
carbon
dioxyde emissions (US4602987 ; US4743545 ; US5614378 ; US6257335). In the
system described by Trachtenberg for the carbonic anhydrase treatment of
gaseous
effluents (US6143556 ; CA2222030), biocatalyst retention occurs through a
porous
CA 02393016 2010-03-29
-4-
wall or through enzyme immobilization. However, important drawbacks are
associated with the use of enzyme immobilization, as will be discussed below.
Other major drawbacks are associated with the use of enzymatic systems. One of
these stems from systems where enzymatic activity is specifically and locally
concentrated. This is the case with systems where enzymes are immobilized at a
particular site or on a specific part of an apparatus. Examples in point of
such
systems are those where enzymes are immobilized on a filtration membrane
(JP60014900008A2 ; US4033822; US5130237; US5250305 ; JP54-132291 ; JP63-
io 129987 ; JP02-109986 ; DE3937892) or even, at a gas-liquid phase boundary
(WO
96/40414 ; US6,143,556). The limited surface contact area obtainable between
the
dissolved gas substrate, the liquid and the enzyme's active site poses an
important
problem. Hence, these systems generate significantly greater waste of input
material, such as expensive purified enzymes, because the contact surface with
the
gaseous phase is far from optimal and limits productive reaction rates.
Therefore, as
mentioned previously, overcoming the contact surface area difficulty should
yield
further technological advances.
Other examples of prior art apparatuses or methods for the treatment of gas or
liquid
effluent are given in the following documents : CA2160311; CA2238323;
CA2259492; CA2268641; JP2000-236870; JP2000-287679; JP2000-202239;
U34758417; US5593886; US5807722; US6136577; and US6245304.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an apparatus that is distinct
from and
overcomes several disadvantages of the prior art bioreactor for the treatment
of gas
effluent, as will be discussed in detail below.
CA 02393016 2010-03-29
-5-
In accordance with the present invention, that object is achieved with a
triphasic
bioreactor for treating a C02-containing gas, comprising:
a reaction chamber containing a liquid;
suspended enzymes provided within the liquid for catalyzing a reaction of C02
into bicarbonate and hydrogen ions to obtain a treated gas and an ion-rich
solution;
a liquid inlet in fluid communication with the reaction chamber for providing
the reaction chamber with the liquid;
gas bubbling means connected to the reaction chamber for bubbling the C02-
containing gas to be treated into the liquid thereby dissolving the gas into
the liquid;
a liquid outlet in fluid communication with the reaction chamber for releasing
the ion-rich solution; and
a gas outlet in fluid communication with the reaction chamber to release said
treated gas.
The bioreactor may also comprise a retention device for retaining the
biocatalysts
within the reaction chamber while the liquid outlet allows for the pressure
release of
the solution containing the reaction product.
The triphasic bioreactor of the present invention provides the advantages of
biologically treating gaseous waste and effluents while simultaneously
providing
biocatalysts in liquid suspension, optimizing gas phase dissolution into the
liquid
phase and thereby optimizing surface contact area between the gas, liquid and
solid
phases, as well as retaining the biocatalysts within the reactor while
allowing the
pressure release of liquid containing a reaction product exempt of
biocatalysts.
In accordance with a preferred aspect of the invention, the bioreactor
comprises a
pressure regulating valve to control a pressure created by the gas bubbled
within the
reaction chamber and a sampling means for sampling and analyzing liquid from
the
reaction chamber.
CA 02393016 2010-03-29
-6-
The gas bubbling means preferably comprises a gas inlet of the reaction
chamber to
receive the gas to be treated and a bubbler located in a bottom portion of the
reaction chamber. The bubbler has a gas inlet connected to the gas inlet of
the
reaction chamber and a plurality of gas outlets to diffuse the gas in the
reaction
chamber. The gas bubbling means further comprises a pipe to connect the gas
inlet
of the reaction chamber to the gas inlet of the bubbler.
The biocatalysts used in the bioreactor are preferably selected from the group
consisting of enzymes, liposomes, microoganisms, animal cells, plant cells and
a
io combination thereof. Most preferably, the biocatalysts are entrapped in
porous
substrates pervading the reaction chamber. Alternatively, the biocatalysts may
be
carried by the liquid that feeds the reaction chamber.
The retention device preferably comprises a filter having pores with a smaller
diameter than the diameter of the biocatalysts. More preferably, the filter is
a
membrane filter.
In accordance with a first preferred embodiment, the membrane filter is
located
inside the reaction chamber upstream from the liquid outlet.
In accordance with a second preferred embodiment, the membrane filter is
located
outside the reaction chamber. In such a case, the retention device further
comprises
a first piping means and a second piping means. The first piping means is for
piping
liquid, which contains biocatalysts and reaction products, from the liquid
outlet of the
reaction chamber to the membrane filter where a permeate liquid containing the
reaction products is separated from a retentate liquid containing the
biocatalysts.
The second piping means is for piping the retentate liquid to the liquid inlet
of the
bioreactor.
CA 02393016 2010-03-29
-7-
In accordance with a preferred aspect of the invention, the triphasic
bioreactor is
used for reducing carbon dioxide contained in a gas effluent. In such a case,
the gas
effluent to be treated contains carbon dioxide, the liquid filling the
bioreactor is an
aqueous liquid and the biocatalysts are enzymes capable of catalyzing the
chemical
conversion of the dissolved carbon dioxide into an aqueous solution containing
hydrogen ions and bicarbonate ions. More preferably, the enzymes are carbonic
anhydrase.
In accordance with a still further preferred aspect of the invention, the
bioreactor
1o comprises an additional reaction chamber, as defined hereinabove, in series
with the
reaction chamber, hereinafter referred to as the first reaction chamber, to
further
treat the previously treated gas. In such a case, the biocatalysts filling the
first
reaction chamber are preferably different from the biocatalysts filling the
additional
reaction chamber.
The present invention also provides a method for the biocatalytic treatment of
gas
effluent which is basically a three-step process.
First, a reaction chamber filled with biocatalysts is filled with a liquid
thereby
suspending the biocatalysts in the liquid. Second, a gas to be treated is
bubbled into
the liquid thereby dissolving it into the liquid and creating a pressure
inside the
reaction chamber. The bubbling thereby promotes the biocatalytic reaction
between
the liquid and the gas to be treated in order to obtain a treated gas and a
solution
containing a reaction product. Third, the solution containing the reaction
product is
released by pressure from the reaction chamber whilst retaining the
biocatalysts
within the reaction chamber. During the second and third steps, the pressure
is
controlled within the reaction chamber and treated gas is released from the
reaction
chamber.
CA 02393016 2010-03-29
-8-
In accordance with the present invention, there is also provided a triphasic
process
for treating a C02-containing gas, comprising:
a) suspending enzymes in a liquid within a reaction chamber;
b) injecting the C02-containing gas to be treated into the liquid of the
reaction chamber to promote dissolution of, the gas into the liquid, and
allowing the
enzymes to promote the chemical conversion of the dissolved CO2 into an
aqueous
solution containing hydrogen ions and bicarbonate ions and obtaining a treated
gas;
c) releasing the solution obtained in step b) from the reaction chamber;
and
d) releasing the treated gas obtained in step b).
BRIEF DESCRIPTION OF THE DRAWINGS
Other objects and advantages of the invention will become apparent upon
reading
the detailed description and upon referring to the drawings in which:
Figure 1 is a cross-sectional side view of a triphasic bioreactor according to
a first
preferred embodiment of the invention.
Figure 2 is a schematic side view of a triphasic bioreactor according to a
second
preferred embodiment of the invention having an external tangential flow
filter.
Figure 3 is a schematic side view of a triphasic bioreactor according to
another
embodiment of the invention, having an integrated filter.
Figure 4 is a schematic side view of a triphasic bioreactor according to a
further
embodiment, having an integrated tangential flow filter.
Figure 5 is a schematic side view of a triphasic bioreactor according to a
still further
embodiment, having a filter cartridge.
CA 02393016 2010-03-29
-9
Figure 6 is a schematic side view of a series of linked triphasic bioreactors
for the
treatment of gas effluent.
While the invention will be described in conjunction with example embodiments,
it
will be understood that it is not intended to limit the scope of the invention
to such
embodiments. On the contrary, it is intended to cover all alternatives,
modifications
and equivalents as may be included as defined by the appended claims.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE
io INVENTION
Referring to Figures 1 or 2, the triphasic bioreactor (1) is an apparatus for
physico-
chemically treating a gas (10). Minimally, it features a reaction chamber (2)
filled with
biocatalysts (4) in suspension in a liquid (3), a liquid inlet (5) and liquid
(6) and gas
(7) outlets in fluid communication with the reaction chamber (2). It is worth
noting
that the use of the article "a" means "at least one" and hence a triphasic
bioreactor
according to the invention may advantageously comprise more than one reaction
chamber, and/or more than one liquid and gas outlet and inlets. The liquid
inlet (5) is
for receiving the liquid (3) and filling the reaction chamber (2). The
reaction chamber
(2) is made of an appropriate material that could be glass, plastic, stainless
steel, a
synthetic polymer or other suitable material.
A gas bubbling means (8) and a retention device (9) are also provided. The gas
bubbling means (8) is for receiving the gas (10), or gases, to be treated
inside the
reaction chamber (2) and for bubbling it into the liquid (3) thereby both
dissolving the
gas to be treated (10) into the liquid (3) and creating a pressure within the
reaction
chamber (2). The biocatalysts (4) are chosen so as to be able to biocatalyze a
reaction between the gas (10) to be treated and the liquid (3) in order to
obtain a
treated gas (11) and a solution (12) containing a reaction product. The liquid
outlet
CA 02393016 2010-03-29
-10-
(6) is for releasing by pressure the solution (12) containing the reaction
product while
the retention device (9) retains the biocatalysts (4) within the reaction
chamber (2).
The gas outlet (7) is for releasing the treated gas (11) from the reaction
chamber (2).
The triphasic bioreactor (1) preferably includes a pressure regulating valve
(13) to
control the pressure created by the gas (10) bubbled into the reaction chamber
(2).
The pressure regulating valve (13) may be located in the gas outlet (7). The
triphasic
bioreactor (1) may also include a valve (14) at the liquid outlet (6) and/or
at the liquid
inlet (5) for regulating the flow of liquid (3) into and out of the reaction
chamber (2).
io As will become more apparent further along in the description, these
features are
used for both regulating the pressure inside the reaction chamber (2) so as
not to
exceed the pressure limits the apparatus may withstand, but also to better
control
the pressure release of the solution (12) containing the reaction product.
As shown in Figure 2, the triphasic bioreactor (1) may include a mixer (15)
within the
reaction chamber (2) to mix the liquid (3), the biocatalysts (4) and the gas
(10). Any
type of mixer known in the art could be used. For example, as shown in Figure
2, the
mixer (15) might include an axial propeller (16) operatively connected to a
top cover
(18) of the reaction chamber (2) by means of a driving shaft (17). In such a
case, the
bioreactor also comprises a suitable driving means for driving the shaft into
rotation.
In order to drive forward the reaction between the gas to be treated (10) and
the
liquid (3), the biocatalysts (4) must comprise a molecule capable of reacting
with the
substrates, namely the dissolved gas (10) and the liquid (3), so as to yield a
treated
gas (11) and a solution (12) containing a reaction product. Biocatalysts
comprising
such a molecule may be selected from a wide variety of biological materials
including enzymes, liposomes, microoganisms, animal cells and/or plant cells
and
the like. Fractions, complexes or combinations thereof may also be used
simultaneously. Fractions of enzymes may comprise, for example, specific sub-
units
CA 02393016 2010-03-29
-11-
of an enzyme, such as its catalytic sub-units. Fractions of a microorganism,
animal
or plant cell may comprise, for example, specific sub-cellular organelles or
compartments such as cellular membranes, ribosomes, mitochondria, chloroplasts
or fractions such as cytoplasmic or nuclear extracts. For the purpose of the
invention, the biocatalysts may also be entrapped in a porous substrate, for
example, an insoluble gel particle such as silica, alginate,
alginate/chitosane,
alginate/carboxymethylcelIu lose, etc. For the purpose of the invention,
biocatalysts
may also be immobilized on solid packing in suspension in the liquid, such as
enzymes covalently bound to plastic packing. Alternatively, enzymes might be
in a
io free state, or chemically linked in an albumin or PEG network. All of these
biological
materials, which may be obtained through routine methods that are well
documented
in the scientific literature and known to the person skilled in the art, may
be made of
use with the present invention which is quite versatile.
Retention of the biocatalysts (4) inside the reaction chamber (2) is an
important
feature of the invention as biological materials are often quite expensive. In
order to
allow the pressure release of solution (12) containing the reaction product
whilst
retaining the biocatalysts (4) within the reaction chamber (2), the retention
device (9)
must be adapted according to the relative and respective sizes of the reaction
products and the biocatalysts (4), as well as co-factors when appropriate.
Pressure release of the solution (11) containing the reaction product may be
likened
to pressure filtration such as ultrafiltration or microfiltration, which are
defined as the
action of filtering a solution through a fine membrane by pressure.
"Ultrafiltration" is a
term which is, in the strict sense, reserved for the physical separation of
particles of
0,005 to 0,1 m in size.
Although, in a variety of its embodiments the present invention may make use
of
ultrafiltration or microfiltration membranes (19) (20), as shown in Figures 2-
6, it is by
CA 02393016 2010-03-29
-12-
no means restricted to their use. For instance, depending upon the size of the
biocatalysts and reaction product, an appropriate retention device (9) may
comprise
a simple grid and/or perforated base, at the bottom of the reaction chamber
(2), as
shown in Figure 1, for slowing the flow of' solution (11) containing the
reaction
product from the reaction chamber (2) whilst retaining the biocatalysts (4)
inside the
reaction chamber (2).
In the present invention, pressure is generated within the reaction chamber
(2) by
bubbling the gas to be treated (10) into the liquid (3). This pressure
contributes to the
io dissolution of the gas to be treated (10) inside the liquid (3) containing
the
biocatalysts (4) and therefore to its further physico-chemical transformation.
The
partial pressure inside the reaction chamber (2) is greater on one side of the
retention device (9). There is consequently greater dissolution of gas to be
treated
according to the law of dissolution of gases, known as the law of Henry, which
states
that the concentration of a given dissolved gas is proportional to its partial
pressure
in the atmosphere at the surface of the liquid. As stated above, the retention
device
(9) preferably comprises a filter (19). If the biocatalyst materials are sub-
microns
particles, for example in the range of 0,005 to 0,1 m in size, a membrane
filter is
preferably used. Such a membrane filter may be made of cellulose, nylon,
polymethyl methacrylate, PVDF or the like, with pores having a smaller
diameter
than the diameter of the biocatalysts, and co-factors when appropriate.
As shown in Figures 1, and 3 to 5, the membrane filter (19) may be integrated
inside
the reaction chamber (2) upstream from the liquid outlet (6). In such an
embodiment,
the liquid flows perpendicularly to the filter (19) as in classic frontal
filtration.
Appropriate pore size allows permeate liquid (12) to exit through the filter
(19)
exempt of biocatalysts (4). The solution (12) containing the reaction product
must
therefore pass through the filter (19) first in order to be able to exit the
reaction
chamber (2) via the liquid outlet (6). The permeate liquid (12) or filtrate
released may
CA 02393016 2010-03-29
-13-
therefore pass through the filter (19) first in order to be able to exit the
reaction
chamber (2) via the liquid outlet (6). The permeate liquid (12) or filtrate
released may
then be discarded or conveyed/piped to other treatment units for further
treatment
such as decantation, ion exchange, etc.
Alternatively, the bioreactor (1) may include an integrated filter cartridge
(20) fixed
inside the reaction chamber (2) and positioned at the desired height within
the
reaction chamber (2), as shown in Figure 5. The filter cartridge (20) is
linked directly
to the non-pressurized liquid outlet (6) and allows for filtration of the
solution (11)
io containing the reaction product, but not the biocatalysts (4), directly
into the liquid
outlet (6). As mentioned above, the pore size of the membrane (19) inside the
cartridge (20) is dependent upon both the size of the biocatalysts (4) and the
reaction product, as well as co-factors when appropriate.
is Optionally, the bioreactor (1) may also incorporate a closed loop circuit
(21) including
a pump (22) to circulate liquid tangentially to the membrane (19), as shown in
Figures 2 and 4. This particular embodiment of the invention is different
because
instead of being perpendicular to the filter, the flow of liquid is
"tangential" relatively
to the filter membrane (19). Liquid therefore "sweeps" the filter membrane
(19)
20 tangentially thereby promoting recirculation of the liquid (3) and the
biocatalysts (4).
The captive biocatalysts (4) therefore remain in liquid suspension. Clogging
of the
pores of the membrane filter is consequently considerably reduced.
In accordance with a second preferred embodiment of the invention, the
membrane
25 filter (19) may be located outside of the reaction chamber (2), as shown in
Figures 2
and 6. According to this particular embodiment, the retention device (9) will
further
include a first pipe, or any other means adapted to convey a liquid, for
piping the
solution (12) containing biocatalysts (4) and reaction products from the
liquid outlet
(6) of the reaction chamber (2) to the membrane filter (19) where a permeate
liquid
CA 02393016 2010-03-29
-14-
retention device (9) further comprises a second pipe for piping the retentate
liquid
(26) back to the liquid inlet (5) and into the bioreactor's reaction chamber
(2). The
permeate liquid (12) may be discarded, or conveyed/piped to other treatment
units
for further treatment such as decantation, ion exchange etc.
An important feature of the invention is the gas bubbling means (8). In one
embodiment of the triphasic bioreactor, the gas bubbling means (8) preferably
comprises a bubbler (24) or a number of these, as shown in Figure 1, located
in the
bottom portion of the reaction chamber (2). The bubbler (24) has a gas inlet
(29)
io connected to a gas inlet (23) of the reaction chamber (2) by means of a
suitable pipe
(27), to receive the gas effluent (10) to be treated The bubbler (24) also
comprises a
plurality of gas outlets (28) to diffuse the gas in the reaction chamber (2).
As shown in Figure 1, the gas bubbling means may include a bubbler (24) in the
form of a removable cap, made of a foam-like material, covering a gas outlet
nozzle,
at the bottom portion of the triphasic bioreactor (2). Foam-like material is
advantageous as it.provides the plurality of gas outlets (28) needed to
diffuse very
fine bubbles and contributes to their uniform distribution within the liquid
(3)
containing the biocatalysts (4). The reduction in size of the gas bubbles
enhances
both gas dissolution and contact surface between gas (10) and liquid (3) phase
reactants and the biocatalysts (4). As stated above, the invention may include
a
mixer (15) in order to enhance the uniform distribution of gas (10) bubbles
and
biocatalysts (4) within the liquid (3).
The relative size and dimensions of the reaction chamber (2), as well as the
relative
porosity of the filter membranes used, if any, is dependent upon particular
usage
requirements and directly proportional to the liquid flow rates required. As
expected,
liquid flow rates may vary greatly between different applications. Appropriate
CA 02393016 2010-03-29
-15-
dimension adjustments and allowances should therefore be made when passing
from one type of application to the other.
In accordance with a preferred aspect of the invention, the triphasic
bioreactor is
used for removing carbon dioxide from a gas effluent (10) containing carbon
dioxide.
In such a case, the liquid (3) filling the reaction chamber (2) is an aqueous
solution,
preferably water, and the biocatalysts (4) are enzymes capable of catalyzing
the
chemical conversion of the dissolved carbon dioxide into an aqueous solution
(12)
containing hydrogen ions and bicarbonate ions. The enzymes are, preferably,
io carbonic anhydrase.
The transformation of CO2 into bicarbonate ions, usually a slow naturally
occurring
process, is catalyzed by the enzyme in suspension in the reaction chamber (2).
Without catalysis, the equilibrium reaction must undergo an intermediate
hydration
1s that slows the transformation of C02 into bicarbonate ions. The following
equations
describe the relevant processes:
without enzyme : dissolved CO2 - H2CO3 H + + HC03 (I)
with enzyme : dissolved C02 - H+ + HC03" (II)
The enzyme carbonic anhydrase, which is of relatively low molecular weight
(30,000
daltons), may be made to form part of a complex in order to increase its size.
This, in
turn, allows the use of membranes with greater porosity and enhances liquid
flow
rates. Different types of enzyme complexes may be formed. Among these are
those
using whole cells such as red blood cells. However, with red blood cells, the
enzymes rapidly leak out and are lost. Encapsulation techniques may therefore
overcome this problem. Enzymes may be immobilized on solid packing. Packing
made of polymers such as nylon, polystyrene, polyurethane, polymethyl
methacrylate, functionnalized silica gel, etc. may be used. Enzymes may also
be
CA 02393016 2010-03-29
-16-
entrapped in insoluble gel particles such as silica, alginate,
alginate/chitosane or
alginate/carboxymethylcellulose, etc. or covalently linked or non covalently
linked in
a network of albumin, PEG or other molecule. Such a network constitutes a
loose
type network. It may appear as a cloudy suspension, "filaments" of which are
often
visible to the naked eye. For the purpose of the invention, alginate particles
should
preferably possess a diameter comprised in a range from 1 to 9 mm, and
preferably,
a diameter inferior to 3 mm.
Thanks to the different features of the triphasic bioreactor, such as the
bubbling
io means and the enclosed reactor filled with the aqueous liquid, the pressure
obtained
inside the reaction chamber (2) permits the gas effluent containing carbon
dioxide to
rapidly dissolve into the liquid (3) which contains the carbonic anhydrase
biocatalysts
(4), thereby optimizing the reaction conditions of reaction (II). A tangential
flow
filtration system, such as shown in Figures 2, 4 and 6, allows the solution
(12)
containing the bicarbonate ions to be released from the reaction chamber (2)
while
part of the liquid containing the carbonic anhydrase biocatalysts (4) is
returned to the
reaction chamber (2).
In order to better monitor the parameters of the reaction process such as pH,
temperature, reaction by-product concentration, etc., the triphasic bioreactor
(1) may
incorporate a sampling means (25) for sampling and analyzing liquid from
inside the
reaction chamber, as shown in Figure 2. As well, thermoregulation circuits may
be
added onto the reaction chamber in order to optimize temperature conditions.
Gas
composition analyzers may also be provided at the gas inlet (5) and/or outlet
(7).
Additional valves may also be added onto the liquid and gas inlets and outlets
in
order to better regulate the flow rates of the different phases, the level of
liquid inside
the reaction chamber, the pressure inside the reaction chamber, etc.
CA 02393016 2010-03-29
ti
-17-
In yet another embodiment, the invention may consist in a series of reaction
chambers (2), with one or more additional reaction chambers, as shown in
Figure 6.
These may be linked so as to treat gas simultaneously or sequentially. In
reaction
chambers linked in succession, as shown in Figure 6, the gas outlet (7) which
releases the treated gas from one reaction chamber (2) may be linked in fluid
communication to the next reaction chamber (2) through its gas inlet (23).
This
allows for further or extensive treatment of the gas. The number of reaction
chambers therefore depends on the extent of gas treatment required. Extensive
or
further treatment might entail treating the gas repeatedly in successive
reaction
io chambers, all of which contain the same biocatalysts. However, extensive or
further
treatment might also entail different treatments in succession, the particular
biocatalysts varying from one reaction chamber to the next. Therefore
biocatalysts
in one reaction chamber may be different from the biocatalysts in the other
reaction
chamber(s) in such a series.
Another object of the invention is to provide a triphasic process for physico-
chemically treating a gas effluent. The process of the invention is basically
a three-
step process. First, a reaction chamber, filled with the biocatalysts (4) in
suspension
in the liquid (3), is provided. Second, the gas to be treated (10) is bubbled
into the
liquid (3) in the reaction chamber (2) in order to dissolve the gas to be
treated (10)
into the liquid (3) and to increase a pressure within the reaction chamber
(2).
Bubbling thereby promotes the biocatalytic reaction between the liquid (3) and
the
gas (10) in order to obtain a treated gas (11) and a solution (12) containing
a
reaction product. Third, the solution (12) containing a reaction product is
pressure
released from the reaction chamber (2) whilst retaining the biocatalysts (4)
within the
reaction chamber (2). All the while during the second and third steps, the
pressure is
controlled within the reaction chamber (2) and a treated gas (11) is released
from the
reaction chamber (2).
CA 02393016 2010-03-29
-18-
In yet another embodiment of the invention, the last step of the process may
occur
through ultrafiltration. The ultrafiltration may be conducted either inside or
outside of
the reaction chamber.
Although preferred embodiments of the present invention have been described in
detail herein and illustrated in the accompanying drawings, it is to be
understood that
the invention is not limited to these precise embodiments and that various
changes
and modifications may be effected therein without departing from the scope or
spirit
of the present invention.
