WO2010056460A2

WO2010056460A2 - Reduction of carbon dioxide in a fermentation process

Info

Publication number: WO2010056460A2
Application number: PCT/US2009/060801
Authority: WO
Inventors: Jens Wiik Jensen; Eric Dickman
Original assignee: Uni-Control, Llc
Priority date: 2008-11-12
Filing date: 2009-10-15
Publication date: 2010-05-20
Also published as: WO2010056460A3

Abstract

The embodiments disclosed herein present a system and a method of reducing carbon dioxide emitted by a carbon dioxide producing process, for example, by converting carbon dioxide to bicarbonate and/or to carbon monoxide and oxygen. One embodiment of the invention discloses a fermentation system, comprising a fermentation bioreactor; a carbon dioxide absorption chamber configured to receive gaseous products from said fermentation bioreactor, wherein said gaseous products contain carbon dioxide; and a separation system in fluid communication with said bioreactor and said absorption chamber. In some cases, the fermentation bioreactor is a deep shaft reactor. In some cases, the carbon dioxide absorption chamber is a deep shaft reactor. A further embodiment of the invention discloses a fermentation system, comprising a pressurizable fermentation bioreactor; and a separation system in fluid communication with said pressurizable fermentation bioreactor. In some cases, the pressurizable fermentation bioreactor is a deep shaft reactor.

Description

REDUCTION OF CARBON DIOXIDE IN A FERMENTATION

PROCESS

FIELD OF THE INVENTION

[0001] This invention generally relates to fermentation processes, and more specifically to a system and a method of reducing carbon dioxide produced in a fermentation process.

BACKGROUND

[0002] The most familiar fermentation process is ethanol fermentation, in which yeasts are utilized in an anaerobic environment to convert sugars (e.g., glucose and fructose) to ethanol for wine, beer, or fuel with carbon dioxide as the by-product; and release some amount of energy. The chemical reaction taking place in this process is according to reaction (1):

C₆Hi₂O₆ → 2 CH₃CH₂OH + 2 CO₂ + (energy) (1)

[0003] Another anaerobic fermentation process is ABE fermentation - an anaerobic process that utilizes bacterial fermentation to produce acetone, butanol and ethanol from starch. A further example of fermentation process is the production of hydrogen by microorganisms via a carbon monoxide oxidation pathway, in which the microorganisms utilize carbon monoxide as the sole food source. The net production of hydrogen occurs according to the water-gas shift reaction, in which H₂ and CO₂ are produced in equimolar amounts, according to reaction

(2).

CO + H₂O → H₂ + CO₂ (2)

[0004] Fermentation in its general sense is a process of converting carbon-containing substrates into products and energy. It includes dark fermentation, photo-fermentation, aerobic and anaerobic fermentation processes. Most-commonly used substrates are carbon sources, such as, glucose, fructose, sucrose, lactose, starch, glycerol, fats, hydrocarbons, and carbon monoxide. Products produced via fermentation include ethanol, hydrogen, biogas, bio-diesel, acetone, and butanol. A universal by-product of fermentation processes is carbon dioxide, which is customarily vented into the atmosphere. Carbon dioxide is a greenhouse gas and there is continuing interest in developing ways to reduce the amount of carbon dioxide produced by fermentation processes. SUMMARY

[0005] The embodiments disclosed herein present a system and a method of reducing carbon dioxide emitted by a carbon dioxide producing process, for example, by converting carbon dioxide to bicarbonate and/or to carbon monoxide and oxygen.

[0006] One embodiment of the invention discloses a fermentation system, comprising a fermentation bioreactor; a carbon dioxide absorption chamber configured to receive gaseous products from the fermentation bioreactor, wherein the gaseous products contain carbon dioxide; and a separation system in fluid communication with the bioreactor and the absorption chamber. In some cases, the fermentation bioreactor is a deep shaft reactor. In some cases, the carbon dioxide absorption chamber is a deep shaft reactor. The separation system includes filtration devices, reverse osmosis, nano, ultra or micro filtration devices, centrifuges, floatation or gravitational sedimentation devices. The arrangement of these devices may be any as known to one skilled in the art to achieve desired separation needs. In some cases, the system further comprises a plasma furnace configured to receive gaseous effluent from the carbon dioxide absorption chamber, wherein the gaseous effluent contains carbon dioxide.

[0007] Another embodiment of the invention presents a system to reduce the amount of carbon dioxide emitted by a carbon dioxide producing process, comprising a carbon dioxide absorption chamber configured to receive gaseous products that contain carbon dioxide produced in the carbon dioxide producing process; and a separation system in fluid communication with the carbon dioxide absorption chamber. In some cases, the carbon dioxide absorption chamber is a deep shaft reactor. In some cases, the system further comprises a plasma furnace configured to receive gaseous effluent from the carbon dioxide absorption chamber, wherein the gaseous effluent contains carbon dioxide. The separation system includes filtration devices, reverse osmosis, nano, ultra or micro filtration devices, centrifuges, floatation or gravitational sedimentation devices. The arrangement of these devices may be any as known to one skilled in the art to achieve desired separation needs. [0008] A further embodiment of the invention discloses a fermentation system, comprising a pressurizable fermentation bioreactor; and a separation system in fluid communication with the pressurizable fermentation bioreactor. In some cases, the pressurizable fermentation bioreactor is a deep shaft reactor. In some cases, the system further comprises a plasma furnace configured to receive gaseous effluent from the pressurizable fermentation bioreactor, wherein the gaseous effluent contains carbon dioxide. The separation system includes filtration devices, reverse osmosis, nano, ultra or micro filtration devices, centrifuges, floatation or gravitational sedimentation devices. The arrangement of these devices may be any as known to one skilled in the art to achieve desired separation needs. [0009] Yet another embodiment of the invention discloses a method to reduce the amount of carbon dioxide emitted by a carbon dioxide producing process, comprising: (1) introducing an aqueous solution into a carbon dioxide absorption chamber; (2) regulating the pH of the aqueous solution to be alkaline with an alkaline substance; (3) passing a first quantity of carbon dioxide gas through the aqueous solution, whereby at least a portion of the carbon dioxide is dissolved and converted to bicarbonate; (4) withdrawing a stream of bicarbonate- containing liquid from the absorption chamber; and (5) withdrawing a second quantity of carbon dioxide gas from the absorption chamber, wherein the second quantity is less than the first quantity. The alkaline substance used to regulate the pH of the aqueous solution includes sodium hydroxide, potassium hydroxide, calcium hydroxide, barium hydroxide, caesium hydroxide, strontium hydroxide, lithium hydroxide, rubidium hydroxide, and ammonium hydroxide. In some cases, the pH of the aqueous solution in the absorption chamber is > 8. In some embodiments, the stream of bicarbonate-containing liquid is further passed through a separation system to regenerate fresh water and/or to precipitate bicarbonate and separate bicarbonate from the liquid as bicarbonate sludge. In some cases, the method further comprises introducing the second quantity of carbon dioxide gas from the absorption chamber into a plasma furnace, wherein carbon dioxide is split into carbon monoxide and oxygen. In certain embodiments, super-atmospheric pressure is applied to the aqueous solution in the absorption chamber, which increases carbon dioxide solubility. The application of super-atmospheric pressure includes establishing a hydrostatic pressure head on the aqueous solution in the absorption chamber.

[0010] A further embodiment of the invention presents a method of reducing the amount of carbon dioxide emitted by a fermentation process, comprising: (1) introducing an aqueous nutrient medium into a fermentation bioreactor; (2) introducing fermentative microorganisms into the nutrient medium in the bioreactor, wherein the microorganisms are capable of growing at alkaline pH to produce products comprising carbon dioxide; (3) regulating the pH of the nutrient medium to be alkaline with an alkaline substance; (4) introducing a carbon- containing food source into the nutrient medium in the bioreactor, wherein the carbon- containing food source is biologically fermented to produce products comprising carbon dioxide, a portion of which is dissolved and converted to bicarbonate; (5) withdrawing a stream of bicarbonate-containing MLSS from the fermentation bioreactor; and (6) withdrawing a quantity of carbon dioxide gas from the fermentation bioreactor, wherein the quantity is less than the quantity of carbon dioxide produced by the microorganisms originally.

[0011] The strain of the fermentative microorganisms includes Carboxydothermus hydrogenoformans Z-2701, Rubrivivax gelatinosus, Rhodospirillum rubrum, Bdellovibrio sp., Rhodopseudomonas palustris, Rhodobacter sphaeroides, Citrobacter sp. Y19, Methanosarcina acetivorans c2A, and Bacillus smithii. The alkaline substance used to regulate the pH of the nutrient medium includes sodium hydroxide, potassium hydroxide, calcium hydroxide, barium hydroxide, caesium hydroxide, strontium hydroxide, lithium hydroxide, rubidium hydroxide, and ammonium hydroxide. In some cases, the pH of the nutrient medium is > 8. In some embodiments, the stream of bicarbonate-containing MLSS is passed through a separation system to achieve at least one of the following effects: (1) to regenerate fresh water; (2) to produce biomass sludge; and (3) to precipitate bicarbonate and separate bicarbonate as bicarbonate sludge. In certain embodiments, super-atmospheric pressure is applied to the nutrient medium in the fermentation bioreactor, which increases carbon dioxide solubility. The application of super-atmospheric pressure includes establishing a hydrostatic pressure head on nutrient medium in the fermentation bioreactor. In some cases, the method further comprises introducing the quantity of carbon dioxide gas from the fermentation bioreactor into a plasma furnace, wherein carbon dioxide is split into carbon monoxide and oxygen.

[0012] These and other embodiments of the present invention, and various features and potential advantages will be apparent with reference to the following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 is a schematic process flow diagram illustrating a system for carbon dioxide reduction in a fermentation process, according to an embodiment of the invention.

[0014] Figure 2 is a schematic process flow diagram illustrating another system for carbon dioxide reduction in a fermentation process, according to another embodiment of the invention. NOTATION AND NOMENCLATURE

[0015] Certain terms are used throughout the following description and claims to refer to particular system components. This document does not intend to distinguish between components that differ in name but not function.

[0016] For the purposes of this disclosure, the term "carbon dioxide" is used interchangeably with formula "CO₂". The term "carbon monoxide" is used interchangeably with formula "CO". The term "mixed liquor suspended solids", hereinafter used as "MLSS", is used in a generalized sense to refer to the solid-liquid mixture that is generated in a fermentation bioreactor. The term "regulate" includes adjusting and maintaining of a parameter via necessary steps and with suitable means. For example, to "regulate" a pH, acidic or alkaline substances are added in suitable amounts at necessary time points to adjust the pH to a preset range and maintain the pH in said range.

[0017] For the purposes of this disclosure, the term "coupled to" and "coupled with" includes fluid communication between the coupled components, either directly or indirectly, unless otherwise specified. The concept of fluid communication includes the passage or flow of gas, gas mixture, liquid, liquid mixture, gas-liquid mixture, gas-solid mixture, liquid-solid mixture, and gas-liquid-solid mixture. Indirect fluid communication means that there may be one or more intervening components between the coupled components. Embodiments and related figures used herein are only exemplary and are not to limit the scope of the invention as set forth in the appended claims.

[0018] Deep shaft reactors disclosed herein include all such reactors for all purposes and applications, not limited by their size, shape, function, method of use, or material of make. Underground, above-ground, or partially underground deep shaft reactors are also included in this disclosure. Embodiments and related figures used herein are only exemplary and are not to limit the scope of the invention as set forth in the appended claims.

DETAILED DESCRIPTION

A System to Reduce CO₂ (I)

[0019] As illustrated in Figure 1, an exemplary fermentation assembly comprises a carbon source supply vessel 20, a fermentation bioreactor 100, a carbon dioxide absorption chamber 200, a centrifuge system 70, and a filtration system 90. [0020] The carbon source supply vessel 20 is any suitable open or closed vessel that is used to contain, store, or process a carbon source needed for a fermentation process. For example, if sugars are the carbon source used for a fermentation process, vessel 20 may be a sterilized vessel wherein sugars are mixed or dissolved before being transferred to the fermentation bioreactor 100. If a gaseous carbon source is used (e.g., CO), vessel 20 may be a saturation chamber wherein the gaseous carbon source is dissolved in a suitable liquid before being sent to the fermentation bioreactor 100 to increase mass transfer efficiency and reaction rate. [0021] The fermentation bioreactor 100 may be any as known to one skilled in the art for a fermentation process. For example, a deep shaft reactor is used for the producing of hydrogen via biological fermentation of carbon monoxide as the food source for selected microorganisms. Another example is a batch tank reactor for sugar fermentation to produce ethanol. The carbon dioxide absorption chamber 200 may be any closed chamber or vessel to contain suitable absorbing agents for CO₂. In some embodiments, carbon dioxide absorption chamber 200 is a deep shaft reactor.

[0022] In embodiments, centrifuge system 70 includes one or more centrifuge units that are able to separate solids from liquids. The centrifuge units may be any as known to one skilled in the art, chosen according to the separation needs (e.g., loading capacity, rate of disposal). In some cases, filtration system 90 includes reverse osmosis, nano or ultra filtration membranes, the use of which produces fresh and sterile water after an aqueous solution is passed through. The filtration system and centrifuge system constitute a separation system, which may further include liquid centrifuges, ultra filtration devices, and any other suitable separation apparatus. Figure 1 is only an illustration of a possible arrangement for such a separation system; in practice, the arrangement of said separation system may be direct fluid connection to reactor 100 or any other connection as known to one skilled in the art to meet desired separation needs.

System Assembly (I)

[0023] Fermentation bioreactor 100 is configured to receive carbon-containing substrates from carbon source supply vessel 20 via stream 38. Fermentation bioreactor 100 and CO₂ absorption chamber 200 are coupled to one another via stream 45, wherein the gas mixture produced in fermentation bioreactor 100 is sent into CO₂ absorption chamber 200. MLSS generated in fermentation bioreactor 100 is extracted as stream 42 and sent to centrifuge system 70. After gas stream 45 passes through CO₂ absorption chamber 200, the resulting gas mixture is extracted as gas stream 55; the resulting solution in CO₂ absorption chamber 200 is extracted as liquid stream 65 and sent to centrifuge system 70.

[0024] Centrifuge system 70 is coupled with fermentation bioreactor 100 via stream 42, with CO₂ absorption chamber 200 via stream 65, and with filtration system 90 via stream 85. It also has multiple outlets for sludge output, such as streams 75 and 78 shown in Figure 1; and additional inlets for introduction of necessary agents, such as stream 72 shown in Figure 1. The supernatant from centrifuge system 70 is extracted as stream 85 and sent to filtration system 90. Filtration system 90 has at least one outlet for filtrate stream 92 and at least one outlet for filtrand (i.e., residue) stream 95. In some cases, filtrate stream 92 is recycled to bioreactor 100, e.g., combined with stream 15 as fresh water makeup for further use. For example, when nano filtration system is utilized, filtered water is fresh and sterile, which is suitable to be reused as feed water for bioreactors.

System Operation (I)

[0025] The anaerobic fermentation for hydrogen production is used herein as an exemplary process to illustrate the process flow diagram shown in Figure 1. Carbon monoxide (CO) is the food source for certain microorganisms that produce hydrogen (H₂) via a CO oxidation pathway that includes a net reaction (2). Examples of potentially suitable microorganisms for hydrogen production are represented by a group of bacteria that consume carbon monoxide under aqueous anaerobic conditions and release H₂, including thermophilic Carboxydothermus hydrogenoformans Z-2701, Rubrivivax gelatinosus and Rhodospirillum rubrum. Some additional examples of bacteria that are potentially suitable for production of hydrogen include Bdellovibrio sp., Rhodopseudomonas palustris, Rhodobacter sphaeroides, Citrobacter sp. Yl 9, Methanosarcina acetivorans c2A, and Bacillus smithii. Any suitable photosynthetic or fermentative microorganism may be used, provided that it contains a viable H₂ generation pathway and does not destroy the H₂ product significantly. Alternatively, any other microbes capable of producing hydrogen, ethanol, bio-diesel (e.g., algae), butanol, and renewable bio-fuels may be used.

[0026] Carbon monoxide is provided as stream 15 into the carbon source supply vessel 20, which in this case is a CO saturation chamber. The source of CO may be any as known to one skilled in the art, including filtered gasification products from combustion/incineration, syngas from gasification or plasma gasification, and purchased CO tanks. Any suitable carbon monoxide-containing gas may serve as the feed for the incubation mixture, provided that the concentrations of other gaseous components of the feed are not prohibitively toxic to the selected microorganisms. Accordingly, in some embodiments it is desirable to include a feed gas pre-cleaning step to remove any components that are potentially detrimental to the selected microorganisms. For example, known synthesis gas cleanup techniques may be employed for this purpose.

[0027] Sterile water and/or product water from filtration unit 90 is used in the CO saturation chamber 20 to dissolve CO with pH regulated utilizing stream 25 and additional nutrients added utilizing stream 35. The pH adjusting substances in stream 25 include acidic and alkaline agents. In certain embodiments, alkaline agents used to regulate pH include sodium hydroxide (NaOH), potassium hydroxide (KOH), calcium hydroxide (Ca(OH)₂), barium hydroxide (Ba(OH)₂), caesium hydroxide (CsOH), strontium hydroxide (Sr(OH)₂), lithium hydroxide (LiOH), rubidium hydroxide (RbOH), and ammonium hydroxide. The pH of feed stream 38 and the pH of the liquid in bioreactor 100 are determined according to the microorganisms utilized for each specific fermentation process so that the microorganisms are healthy to maximize production efficiency.

[0028] The nutrients and the amounts added as stream 35 are according to the microorganisms utilized for each specific fermentation process. For example, according to American Type Culture Collection (ATCC), Van Niel's yeast agar is used as the culture medium for Rubrivivax gelatinosus, which contains K₂HPO₄, MgSO₄, yeast extract, agar, and water. Streams 25 and 35 are shown to be added to stream 38 in Figure 1. Alternatively, streams 25 and 35 may be added directly into bioreactor 100. Feed stream 38 is injected at proper positions via an injection means (e.g., injection nozzles) to provide the carbon source and other necessary substances. In some cases, feed stream 38 is injected so as to act as a lifting pump for the internal flow of bioreactor 100, because the dissolved gas causes feed stream 38 to have a lower density than the mixture in bioreactor 100. The liquid containing MLSS in bioreactor 100 is represented by the shaded area in Figure 1. Bioreactor 100 may further include a mixing means to provide sufficient circulation of liquid and MLSS. [0029] Due to the growth of the microorganisms used in fermentation processes, it is necessary to extract a portion or all of the biomass from bioreactor 100 to maintain its operation. In practice, what is extracted from bioreactor 100 is MLSS. Stream 42 denotes the extraction of MLSS to centrifuge system 70 for solid-liquid separation. Sludge extracted from MLSS is taken out as stream 75 and may be recycled as a carbon source to generate energy or used as feedstocks for animals. Separated liquid (the supernatant) is extracted as stream 85 and sent to filtration system 90 to regenerate fresh water (stream 92). If nano filtration system is used, regenerated fresh water is sterile and may be reused as water feed for the bioreactor (e.g., combined with stream 15).

[0030] In certain embodiments, when the bioreactor is operated at high pH (e.g., greater than 8, 8.5, or 10) regulated by the addition of a hydroxide, the extraction of MLSS will also take out bicarbonate in solution. In such scenarios, after MLSS is centrifuged and the sludge is extracted, the supernatant is sent to another centrifuge unit and lime is added (for example, through stream 72) to precipitate bicarbonate extracted as stream 78 and obtain a secondary supernatant. Bicarbonate sludge in stream 78 may be used as a construction material or sent to a plasma gasification process to assist vitrification process. The secondary supernatant is then sent to filtration system 90 through stream 85. In order to avoid scaling of bicarbonate salts on the membranes for filtration system 90, Flocon® 100 is added to stream 85 (not shown). After filtration, fresh water (extracted as stream 92) is obtained from filtration system 90 and a minimum amount of residue exits the system as stream 95. If nano filtration system is used, regenerated fresh water is sterile and may be reused as water feed for the bioreactor (illustrated by the arrow with a dashed line in Figure 1).

[0031] Gas mixture (e.g., H₂, CO₂, N₂) produced in bioreactor 100 is extracted as stream 45 and sent into CO₂ absorption chamber 200, wherein the pH is alkaline, regulated with an alkaline substance, including sodium hydroxide (NaOH), potassium hydroxide (KOH), calcium hydroxide (Ca(OH)₂), barium hydroxide (Ba(OH)₂), caesium hydroxide (CsOH), strontium hydroxide (Sr(OH)₂), lithium hydroxide (LiOH), rubidium hydroxide (RbOH), and ammonium hydroxide. In some embodiments, the pH in CO₂ absorption chamber 200 is regulated to be greater than 8. In some embodiments, the pH in CO₂ absorption chamber 200 is regulated to be greater than 8.5. In some embodiments, the pH in CO₂ absorption chamber 200 is regulated to be greater than 10. The volume of water in the CO₂ absorption chamber 200 and the flow rate of gas in stream 45 are selected so that a desired amount of the generated CO₂ is absorbed in chamber 200. The liquid in CO₂ absorption chamber 200 is represented by the shaded area in Figure 1. In certain embodiments, super-atmospheric pressure is applied to the liquid in the CO₂ absorption chamber because elevated pressure increases carbon dioxide solubility. The application of super-atmospheric pressure includes establishing a hydrostatic pressure head on nutrient medium in said fermentation bioreactor. CO₂ absorption chamber 200 may further include a mixing means to maximize CO₂ absorption rate. The resulting gas mixture after CO₂ absorption (e.g., H₂ and N₂) is extracted as stream 55. If necessary, stream 55 may go through further separation processes to obtain desired end products. For example, stream 55 may pass through an additional CO₂ absorption chamber to further eliminate any residue CO₂. In the case that a hydroxide is used to regulate the pH in chamber 200, CO₂ is converted to bicarbonate and bicarbonate solution is extracted as stream 65 and sent to centrifuge system 70.

[0032] In some embodiments, the system further comprises a plasma furnace or plasma torch (not shown in Figure 1). Stream 55 comprising CO₂ is recycled to the plasma furnace where CO₂ is split into carbon monoxide (CO) and oxygen (O₂). The produced oxygen may be used as an oxygen source for other reactions, such as plasma gasification. The produced CO may be used in applications such as biological water gas shift reaction. In some cases, the system comprising the plasma furnace may omit the CO₂ absorption chamber 200. CO₂ contained in gas stream 45 may be separated (e.g., using pressure swing absorption) and sent to the plasma furnace to produce CO and O₂.

[0033] In centrifuge system 70, lime is added through stream 72 to bicarbonate solution (stream 65) to precipitate bicarbonate. Bicarbonate sludge is extracted as stream 78 and may be used as a construction material or used as a stabilizer in the plasma furnace vitrification process by gasifying it. The supernatant of bicarbonate solution is then sent to filtration system 90 through stream 85. In order to avoid scaling of bicarbonate salts on the membranes for filtration system 90, Flocon® 100 is added to stream 85 (not shown). After filtration, fresh water (extracted as stream 92) is obtained from filtration system 90 and a minimum amount of residue exits the system as stream 95. If nano filtration system is used, regenerated fresh water is sterile and may be reused as water feed for the bioreactor (illustrated by the arrow with a dashed line in Figure 1).

A System to Reduce CO₂ (II)

[0034] As illustrated in Figure 2, another exemplary embodiment to reduce carbon dioxide produced in a fermentation process comprises a carbon source supply vessel 20', a fermentation bioreactor 100', a centrifuge system 70', and a filtration system 90'. [0035] The carbon source supply vessel 20' is any suitable open or closed vessel that is used to contain, store, or process a carbon source needed for a fermentation process. For example, if sugars are the carbon source used for a fermentation process, vessel 20 may be a sterilized vessel wherein sugars are mixed or dissolved before being transferred to the fermentation bioreactor 100'. If a gaseous carbon source is used (e.g., CO), vessel 20' may be a saturation chamber wherein the gaseous carbon source is dissolved in a suitable liquid before being sent to the fermentation bioreactor 100' to increase mass transfer efficiency and reaction rate. [0036] The fermentation bioreactor 100' in this case is a pressurizable vessel, such as a deep shaft reactor. This embodiment takes advantage of the phenomenon of elevated CO₂ solubility under elevated pressure. When the pressure of the liquid in bioreactor 100' is sufficiently high (e.g., the depth of the volume of liquid in bioreactor 100' is greater than 20 meters), it will cause generated CO₂ to be dissolved more readily. The level of elevated pressure is limited by the microorganisms utilized in the fermentation process, i.e., such pressures should not jeopardize the health and function of the microorganisms significantly. Furthermore, certain microorganisms are able to tolerate more alkaline growth environment (pH > 7). For example, Rubrivivax gelatinosus utilized for hydrogen production, which takes CO as the food source, is able to grow and produce hydrogen in an environment with pH > 8.5. If a hydroxide is utilized to regulate the pH in bioreactor 100', a portion of generated CO₂ is converted to bicarbonate, taking advantage of increased CO₂ solubility under elevated pressure and high pH environment.

[0037] In embodiments, centrifuge system 70' includes one or more centrifuge units that are able to separate solids from liquids. The centrifuge units may be any as known to one skilled in the art, chosen according to the separation needs (e.g., loading capacity, rate of disposal). In some cases, filtration system 90' includes nano filtration membranes, the use of which produces fresh and sterile water after an aqueous solution is passed through. The filtration system and centrifuge system constitute a separation system, which may further include centrifuges, ultra and micro filtration devices, and any other suitable separation apparatus. Figure 2 is only an illustration of a possible arrangement for such a separation system; in practice, the arrangement of said separation system may be any as known to one skilled in the art to meet desired separation needs.

System Assembly (H)

[0038] Fermentation bioreactor 100' is configured to receive carbon-containing substrates from carbon source supply vessel 20' via stream 38'. Fermentation bioreactor 100' and centrifuge system 70' are coupled to one another via stream 42', wherein the MLSS produced in fermentation bioreactor 100' is sent to centrifuge system 70'. Centrifuge system 70' is coupled with fermentation bioreactor 100' via stream 42' and filtration system 90' via stream 85'. It also has multiple outlets for sludge output, such as streams 75' and 78' shown in Figure 2; and additional inlets for introduction of necessary agents, such as stream 72' shown in Figure 2. The supernatant from centrifuge system 70' is extracted as stream 85' and sent to filtration system 90'. Filtration system 90' has at least one outlet for filtrate stream 92' and at least one outlet for fϊltrand (i.e., residue) stream 95'. In some cases, filtrate stream 92' is recycled to bioreactor 100' for further use. For example, when nano filtration system is utilized, filtered water is fresh and sterile, which is suitable to be reused as feed water (e.g., fresh water make up) for bioreactors.

System Operation (II)

[0039] The anaerobic fermentation for hydrogen production is used herein as an exemplary process to illustrate the process flow diagram shown in Figure 2. Carbon monoxide (CO) is the food source for certain microorganisms that produce hydrogen (H₂) via a CO oxidation pathway that includes a net reaction (2). Examples of potentially suitable microorganisms for hydrogen production are represented by a group of bacteria that consume carbon monoxide under aqueous anaerobic conditions and release H₂, including thermophilic Carboxydothermus hydrogenoformans Z-2701, Rubrivivax gelatinosus and Rhodospirillum rubrum. Some additional examples of bacteria that are potentially suitable for production of hydrogen include Bdellovibrio sp., Rhodopseudomonas palustris, Rhodobacter sphaeroides, Citrobacter sp. Yl 9, Methanosarcina acetivorans c2A, and Bacillus smithii. Any suitable photosynthetic or fermentative microorganism may be used, provided that it contains a viable H₂ generation pathway and does not destroy the H₂ product significantly. Alternatively, any other microbes capable of producing hydrogen, ethanol, bio-diesel (e.g., algae), butanol, and renewable bio-fuels may be used.

[0040] Carbon monoxide is provided as stream 15' into the carbon source supply vessel 20', which in this case is a CO saturation chamber. The source of CO may be any as known to one skilled in the art, including filtered combustion/incineration products, syngas, and purchased CO tanks. Any suitable carbon monoxide-containing gas may serve as the feed for the incubation mixture, provided that the concentrations of other gaseous components of the feed are not prohibitively toxic to the selected microorganisms. Accordingly, in some embodiments it is desirable to include a feed gas pre-cleaning step to remove any components that are potentially detrimental to the selected microorganisms. For example, known synthesis gas cleanup techniques may be employed for this purpose.

[0041] Sterile water is used in the CO saturation chamber 20' to dissolve CO with pH regulated utilizing stream 25' and additional nutrients added utilizing stream 35'. The pH adjusting substances in stream 25' include acidic and alkaline agents. In certain embodiments, alkaline agents used to regulate pH include sodium hydroxide (NaOH), potassium hydroxide (KOH), calcium hydroxide (Ca(OH)₂), barium hydroxide (Ba(OH)₂), caesium hydroxide (CsOH), strontium hydroxide (Sr(OH)₂), lithium hydroxide (LiOH), rubidium hydroxide (RbOH), and ammonium hydroxide. The pH of feed stream 38' and the pH of the liquid in bioreactor 100' are determined according to the microorganisms utilized for each specific fermentation process so that the microorganisms are healthy to maximize production efficiency.

[0042] The nutrients and the amounts added as stream 35' are according to the microorganisms utilized for each specific fermentation process. For example, according to American Type Culture Collection (ATCC), Van Niel's yeast agar is used as the culture medium for Rubrivivax gelatinosus, which contains K₂HPO₄, MgSO₄, yeast extract, agar, and water. Streams 25' and 35' are shown to be added to stream 38' in Figure 2. Alternatively, streams 25' and 35' may be added directly into bioreactor 100'. Feed stream 38' is injected at proper positions via an injection means (e.g., injection nozzles) to provide the carbon source and other necessary substances. In some cases, feed stream 38' is injected so as to act as a lifting pump for the internal flow of bioreactor 100', because the dissolved gas causes feed stream 38' to have a lower density than the mixture in bioreactor 100'. The liquid containing MLSS in bioreactor 100' is represented by the shaded area in Figure 2. Bioreactor 100' may further include a mixing means to provide sufficient circulation of liquid and MLSS.

[0043] Due to the growth of the microorganisms used in fermentation processes, it is necessary to extract a portion or all of the biomass from bioreactor 100' to maintain its operation. In practice, what is extracted from bioreactor 100' is MLSS. Stream 42' denotes the extraction of MLSS to centrifuge system 70' for solid-liquid separation. Sludge extracted from MLSS is taken out as stream 75' and may be recycled as a carbon source to generate energy or used as feedstocks for animals. Separated liquid (the supernatant) is extracted as stream 85' and sent to filtration system 90' to regenerate fresh water (stream 92'). If nano filtration system is used, regenerated fresh water is sterile and may be reused as water feed for the bioreactor.

[0044] Because a portion of generated CO₂ is converted to bicarbonate due to elevated pressure and high pH in bioreactor 100', bicarbonate solution is extracted together with MLSS in stream 42'. After MLSS is centrifuged and the sludge is extracted, the supernatant is sent to another centrifuge unit and lime is added (for example, through stream 72') to precipitate bicarbonate extracted as stream 78' and obtain a secondary supernatant. Bicarbonate sludge in stream 78' may be used as a construction material or sent to the plasma gasification reactor to aid the vitrification process. The secondary supernatant is then sent to filtration system 90' through stream 85'. In order to avoid scaling of bicarbonate salts on the membranes for filtration system 90', Flocon® 100 is added to stream 85' (not shown). After filtration, fresh water (extracted as stream 92') is obtained from filtration system 90' and a minimum amount of residue exits the system as stream 95'. If nano filtration system is used, regenerated fresh water is sterile and may be reused as water feed for the bioreactor (illustrated by the arrow with a dashed line in Figure 2).

[0045] Gas mixture (e.g., H₂, CO₂, N₂) produced in bioreactor 100' is extracted via stream 45' and processed via suitable separation methods. For example, CO₂ is removed from H₂ by using a diffusion membrane that is H₂ permeable and excludes larger size molecules like CO₂. Alternatively, stream 45' may pass through a CO₂ absorption chamber to reduce CO₂ as previously described. In some embodiments, stream 45 ' comprising CO₂ is recycled to the plasma furnace (not shown in Figure 2) where CO₂ is split into carbon monoxide (CO) and oxygen (O₂). The produced oxygen may be used as an oxygen source for other reactions, such as plasma gasification. The produced CO may be used in applications such as biological water gas shift reaction.

[0046] The operation of a CO₂ reduction system is periodic, continuous or semi-continuous, depending on the requirements of a particular application. As illustrated in Figure 1 , carbon source supply stream 15, pH adjustment stream 25, and nutrient stream 35 may be carried out simultaneously or separately with the operation of each being periodic, continuous or semi- continuous, depending on the reaction progression in bioreactor 100. MLSS extraction via stream 42 may be periodic, continuous or semi-continuous, depending on the capacity of the bioreactor and the growth rate of the microorganisms utilized. The extraction of gas mixture via stream 45 may also be periodic, continuous or semi-continuous. For example, if a constant operating pressure is to be maintained in bioreactor 100, gas extraction should be continuous. In some applications, it is desirable to increase the pressure of bioreactor 100, for example to increase CO₂ solubility, then it is best to extract the gases periodically or semi-continuously. Based on the same principle, in some applications, extraction of gas stream 55 and extraction of solution stream 65 from CO₂ absorption chamber 200 should also be periodic, continuous or semi-continuous, depending on the needs of the system and the goals of the operation. The operation of centrifuge system 70 and filtration system 90 should be synchronized and coordinated with the extraction operation of stream 65 and stream 42. [0047] With reference to the embodiment illustrated in Figure 2, carbon source supply stream 15', pH adjustment stream 25', and nutrient stream 35' may be carried out simultaneously or separately with the operation of each being periodic, continuous or semi-continuous, depending on the reaction progression in bioreactor 100'. MLSS extraction stream 42' may be periodic, continuous or semi-continuous, depending on the capacity of the bioreactor and the growth rate of the microorganisms utilized. The extraction of gas stream 45 ' may also be periodic, continuous or semi-continuous. In some applications, if a constant operating pressure is to be maintained in bioreactor 100', gas extraction should be continuous. In some applications, it is desirable to increase the pressure of bioreactor 100', for example to increase CO₂ solubility, gases are extracted periodically or semi-continuously. The operation of centrifuge system 70' and filtration system 90' should be synchronized and coordinated with the extraction operation of stream 42'.

[0048] Without further elaboration, it is believed that one skilled in the art can, using the description herein, utilize the present invention to its fullest extent. The embodiments described herein are to be construed as illustrative and not as constraining the remainder of the disclosure in any way whatsoever. While the preferred embodiments of the invention have been shown and described, many variations and modifications thereof can be made by one skilled in the art without departing from the spirit and teachings of the invention. Accordingly, the scope of protection is not limited by the description set out above, but is only limited by the claims, including all equivalents of the subject matter of the claims.

Claims

CLAIMSWhat is claimed is:

1. A fermentation system, comprising: a. a fermentation bioreactor; b. a carbon dioxide absorption chamber configured to receive gaseous products from said fermentation bioreactor, wherein said gaseous products contain carbon dioxide; and c. a separation system in fluid communication with said bioreactor and said absorption chamber.

2. The system of claim 1 wherein said fermentation bioreactor is a deep shaft reactor.

3. The system of claim 1 wherein said carbon dioxide absorption chamber is a deep shaft reactor.

4. The system of claim 1 wherein said separation system includes at least one device selected from the group consisting of filtration devices, reverse osmosis, nano, ultra or micro filtration devices, centrifuges, floatation and gravitational sedimentation devices.

5. The system of claim 1 further comprising a plasma furnace configured to receive gaseous effluent from said carbon dioxide absorption chamber, wherein said gaseous effluent contains carbon dioxide.

6. A system to reduce the amount of carbon dioxide emitted by a carbon dioxide producing process, comprising: a. a carbon dioxide absorption chamber configured to receive gaseous products that contain carbon dioxide produced in said carbon dioxide producing process; and b. a separation system in fluid communication with said carbon dioxide absorption chamber.

7. The system of claim 6 wherein said carbon dioxide absorption chamber is a deep shaft reactor.

8. The system of claim 6 further comprising a plasma furnace configured to receive gaseous effluent from said carbon dioxide absorption chamber, wherein said gaseous effluent contains carbon dioxide.

9. A fermentation system, comprising: a pressurizable fermentation bioreactor; and a separation system in fluid communication with said pressurizable fermentation bioreactor.

10. The system of claim 9 wherein said pressurizable fermentation bioreactor is a deep shaft reactor.

11. The system of claim 9 further comprising a plasma furnace configured to receive gaseous effluent from said pressurizable fermentation bioreactor, wherein said gaseous effluent contains carbon dioxide.

12. A method of reducing the amount of carbon dioxide emitted by a carbon dioxide producing process, comprising: introducing an aqueous solution into a carbon dioxide absorption chamber; regulating the pH of said aqueous solution to be alkaline with an alkaline substance; passing a first quantity of carbon dioxide gas through said aqueous solution, whereby at least a portion of said carbon dioxide is dissolved and converted to bicarbonate; withdrawing a stream of bicarbonate-containing liquid from said absorption chamber; and withdrawing a second quantity of carbon dioxide gas from said absorption chamber, wherein said second quantity is less than said first quantity.

13. The method of claim 12 wherein said alkaline substance to regulate the pH of said aqueous solution is selected from the group consisting of sodium hydroxide, potassium hydroxide, calcium hydroxide, barium hydroxide, caesium hydroxide, strontium hydroxide, lithium hydroxide, rubidium hydroxide, and ammonium hydroxide.

14. The method of claim 12 wherein the pH of said aqueous solution is regulated to be > 8.

15. The method of claim 12 further comprising passing said stream of bicarbonate- containing liquid through a separation system to achieve at least one of the following effects: to regenerate fresh water; and to precipitate bicarbonate and extract bicarbonate as bicarbonate sludge.

16. The method of claim 15 wherein lime is utilized to precipitate bicarbonate.

17. The method of claim 12 further comprising introducing said second quantity of carbon dioxide gas from said absorption chamber into a plasma furnace, wherein carbon dioxide is split into carbon monoxide and oxygen.

18. The method of claim 12 further comprising applying super-atmospheric pressure to said aqueous solution in said absorption chamber, which increases carbon dioxide solubility.

19. The method of claim 18, wherein applying super-atmospheric pressure comprises establishing a hydrostatic pressure head on said aqueous solution in said absorption chamber.

20. A method of reducing the amount of carbon dioxide emitted by a fermentation process, comprising: a. introducing an aqueous nutrient medium into a fermentation bioreactor; b. introducing fermentative microorganisms into the nutrient medium in the bioreactor, wherein said microorganisms are capable of growing at alkaline pH to produce products comprising carbon dioxide; c. regulating the pH of said nutrient medium to be alkaline with an alkaline substance; d. introducing a carbon-containing food source into said nutrient medium in the bioreactor, wherein said carbon-containing food source is biologically fermented to produce products comprising carbon dioxide, a portion of which is dissolved and converted to bicarbonate; e. withdrawing a stream of bicarbonate-containing MLSS from said fermentation bioreactor; and f. withdrawing a quantity of carbon dioxide gas from said fermentation bioreactor, wherein said quantity is less than the quantity of carbon dioxide produced by the microorganisms originally.

21. The method of claim 20 wherein the strain of said fermentative microorganisms is selected from the group consisting of Carboxydothertnus hydrogenofortnans Z-2701, Rubrivivax gelatinosus, Rhodospirillum rubrum, Bdellovibrio sp., Rhodopseudomonas palustris, Rhodobacter sphaeroides, Citrobacter sp. Y20, Methanosarcina acetivorans c2A, and Bacillus smithii.

22. The method of claim 20 wherein said alkaline substance to regulate the pH of said nutrient medium is selected from the group consisting of sodium hydroxide, potassium hydroxide, calcium hydroxide, barium hydroxide, caesium hydroxide, strontium hydroxide, lithium hydroxide, rubidium hydroxide, and ammonium hydroxide.

23. The method of claim 20 wherein the pH of said nutrient medium is regulated to be > 8.

24. The method of claim 20 further comprising passing said stream of bicarbonate- containing MLSS through a separation system to achieve at least one of the following effects: to regenerate fresh water; to produce biomass sludge; and to precipitate bicarbonate and extract bicarbonate as bicarbonate sludge.

25. The method of claim 24 wherein lime is utilized to precipitate bicarbonate.

26. The method of claim 20, comprising applying super-atmospheric pressure to said nutrient medium in said fermentation bioreactor, which increases carbon dioxide solubility.

27. The method of claim 26, wherein applying super-atmospheric pressure comprises establishing a hydrostatic pressure head on nutrient medium in said fermentation bioreactor.

28. The method of claim 20 further comprising introducing said quantity of carbon dioxide gas from said fermentation bioreactor into a plasma furnace, wherein carbon dioxide is split into carbon monoxide and oxygen.