Processes for treating gases containing carbon dioxide

Abstract

The present invention is directed to a process for converting carbon dioxide to methane by contacting an aqueous solution containing dissolved carbon dioxide with an electronically charged packed bed comprising a support, preferably activated carbon granules, and a microbial biofilm under anaerobic conditions, wherein greater than 90 mole percent of the dissolved carbon dioxide in the aqueous solution is present as bicarbonate ions and / or carbonate ions.

Description

[Technical Field]

[0001] The present invention relates to a process for treating a gas containing carbon dioxide, in which carbon dioxide is converted to methane under anaerobic conditions in the presence of an electronically charged packed bed containing a carrier and microorganisms. [Background technology]

[0002] The article, titled "Granulr Carbon-Based Electrodes as Cathodes in Methane-Producing Bioelectrochemical Systems," published in Frontiers in Bioengineering and Biotechnology, Vol. 6, June 2018, paper 78, by Dandan Liu, Marta Roca-Puigros, Florian Geppert, Leire Caizan-Juanarena, Susakul P. Na Ayudthaya, Cees Buisman, and Annemiek ter Heijne, describes the process by which carbon dioxide is converted to methane under anaerobic conditions in the presence of an electrostatically charged bed containing activated carbon granules and a mixed culture of microorganisms. CO2 was supplied as a gas to an aqueous solution at pH 7.1. Biocathodes consisting of an electrostatically charged bed composed of activated carbon granules and a mixed culture of microorganisms were alternately charged for 2 minutes and left uncharged for 4 minutes. The reported "current to methane" efficiency was 55%. The reported overall energy efficiency was 25%. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Dandan Liu, Marta Roca-Puigros, Florian Geppert, Leire Caizan-Juanarena, Susakul P. Na Ayudthaya, Cees Buisman and Annemiek ter Heijne, “Granulr Carbon-Based Electrodes as Cathodes in Methane-Producing Bioelectrochemical Systems”, Frontiers in Bioengineering and Biotechnology, June 2018, Volume 6. [Overview of the project] [Problems that the invention aims to solve]

[0004] The objective of this invention is to improve the energy efficiency of methane production. [Means for solving the problem]

[0005] This objective is achieved through the following process.

[0006] A process for converting carbon dioxide to methane by contacting an aqueous solution containing dissolved carbon dioxide with an electronically charged packed bed composed of a carrier and a microbial biofilm under anaerobic conditions, wherein more than 90 mol% of the dissolved carbon dioxide in the aqueous solution exists as bicarbonate ions and / or carbonate ions.

[0007] The applicant found that, when dissolved carbon dioxide exists as bicarbonate and / or carbonate ions, a significantly more efficient energy conversion to methane can be achieved for the described process. [Brief explanation of the drawing]

[0008] [Figure 1] This document shows possible process schemes for the process of the present invention. [Figure 2]Circles represent Coulomb efficiency, white triangles represent voltage efficiency, and black squares represent energy efficiency. [Modes for carrying out the invention]

[0009] Dissolved carbon dioxide can exist as aqueous carbon dioxide, carbon ions, bicarbonate ions, and carbonate ions. The majority of dissolved carbon dioxide in aqueous solutions exists as bicarbonate ions and / or carbonate ions. More than 90 mol%, preferably more than 95 mol%, of dissolved carbon dioxide in aqueous solutions exists as bicarbonate ions and / or carbonate ions. The pH conditions in which these compounds exist in aqueous solutions are preferably greater than 7.5, preferably greater than 7.7, more preferably greater than 8, even more preferably in the range of 8 to 10, and even more preferably in the range of 8.5 to 9.5. These alkaline conditions can be achieved by basic salts formed between a weak acid and a strong base, such as sodium bicarbonate and potassium bicarbonate. Such basic salts can be formed by adding sodium cations or sodium and potassium cations. The concentration of sodium cations or the sum of sodium and potassium cations is suitable between 0.3 and 4 M, preferably between 0.4 and 2 M, and even more preferably between 0.5 and 1.5 M. The resulting aqueous solution is a buffer solution further containing sodium carbonate and sodium bicarbonate or potassium carbonate and potassium bicarbonate or a mixture thereof. The alkaline aqueous solution preferably further contains nutrients for microorganisms. Examples of suitable nutrients include ammonium, vitamins, and mineral elements. It may be desirable to add such nutrients to the alkaline aqueous solution to maintain active microorganisms.

[0010] Anaerobic conditions are preferably achieved by carrying out the process in the absence of molecular oxygen, and more preferably, in the absence of other oxidizing agents, such as nitrates. “Absence of molecular oxygen” means that the concentration of molecular oxygen in the packed aqueous solution in this process is at most 10 μM, preferably at most 1 μM, and more preferably at most 0.1 μM. Sulfates, which can be considered oxidizing agents, may be present at low concentrations, for example, 160 μM, as part of the mineral solution in so-called Wolfe's mineral solution. These low concentrations of sulfates have been found not to negatively affect the desired conversion of carbon dioxide.

[0011] This process is carried out by contacting the aqueous solution with an electronically charged bed consisting of activated carbon granules and microorganisms under anaerobic conditions in which carbon dioxide is converted to methane. The microorganisms may be a mixed culture or a single culture. Mixed cultures of microorganisms can be appropriately obtained from cultures grown anaerobically. Preferably, the mixed culture contains hydrogen-assimilating methanogenic bacteria such as Methanobacterium. Further microorganisms may be present, including anaerobic or facultative anaerobic bacteria such as proteobacteria such as Deltaproteobacteria and Betaproteobacteria.

[0012] Mixed cultures are preferably obtained from anaerobic systems, such as cultures grown anaerobically. Therefore, mixed cultures are obtained from sludge in anaerobic bioreactors, such as anaerobic fermenters, anaerobic digesters, or, for example, upward-flow anaerobic sludge blanket reactors (UASBs), which are used for anaerobic chain extension. Other suitable bioreactors for supplying sludge include expanded sludge beds (EGSBs), continuous batch reactors (SBRs), continuous stirred tank reactors (CSTRs), or anaerobic membrane bioreactors (AnMBRs). In this context, the term sludge refers to semi-solid cotton shavings or granules containing mixed cultures of microorganisms.

[0013] The carrier can be any carrier that provides a surface for the biofilm and has sufficient capacitance properties. Preferably, the carrier is biocompatible and has a 3D granular structure for attaching microorganisms and enhancing mass transfer between the bulk solution and the electrode. Preferably, the carrier is carbon-based. Examples of suitable carbon-based carriers are graphite and activated carbon granules.

[0014] The carrier bed preferably contains electrodes modified with activated carbon materials such as activated carbon granules or particles, activated carbon powder granules, or activated biocarbon granules. Preferably, the bed has an activated surface area of ​​500 to 1500 m². 2 The bed is packed with activated carbon granules between 1 / g, where microorganisms exist as biofilms on the surface with an activated surface area. A high surface area provides a surface on which microorganisms can reside. Therefore, a high surface area per unit volume provides a higher capacity to carry out the desired reaction of carbon dioxide to methane per unit volume of the reactor space.

[0015] Preferably, the granule dimensions are such that, on the one hand, the aqueous fraction can move through the space between the granules without causing a large pressure drop. This means that there is a practical lower limit to the granule dimensions. On the other hand, the granules should not be too large, because if they are too large, the distance they travel within the micropores of the activated carbon granules becomes long. The diameter based on the volume of the granules may be between 0.5 and 10 mm, and preferably between 1 and 4 mm.

[0016] The electronically charged packed bed composed of activated carbon particles is preferably part of the biocathode in a bioelectrochemical system that further includes an anode. The biocathode preferably includes a certain volume of activated carbon particles disposed in the packed bed. The packed bed may contact a current collector that is the surface of a carbon-containing material such as a graphite plate or felt, or a conductive electrode material such as a metal mesh, preferably a stainless steel mesh. The current collector is arranged such that the packed bed can be charged with electrons from the current collector.

[0017] The packed bed is further fluidly connected to the anode space of the bioelectrochemical system and is disposed in the cathode space of the bioelectrochemical system separated from the anode space by a cation exchange membrane. To compact the packed bed of activated carbon particles, it is preferable to add inert particles such as glass beads to the anode space to balance the pressure exerted by the packed bed on the cation exchange membrane.

[0018] The aqueous solution present in the anode is called the anolyte, and the aqueous solution present in the cathode is called the catholyte. Preferably, a recirculation is performed in which a part of the catholyte is supplied to the anode to become part of the anolyte, and a part of the anolyte is supplied to the cathode to become part of the catholyte. It can be seen that such recirculation results in a more efficient process in which most of the dissolved carbon dioxide in the aqueous solution exists as bicarbonate ions and / or carbonate ions.

[0019] Preferably, the oxygen content that may be present in the anolyte should be low if it is supplied to the cathode to become part of the catholyte. The oxygen content can be reduced by removing oxygen from this anolyte stream by gas-liquid separation. Alternatively, a physical or chemical oxygen scavenger such as a sulfite or an organic scavenger may be used to reduce the oxygen content. Also, the anolyte can be purged with an O2-free gas such as N2 and / or CO2. Oxygen can also be removed from the anolyte by electrochemical removal techniques.

[0020] Preferably, the methane content that may be present in the catholyte should be low when supplying this to the anode to form part of the anolyte. The methane content can be reduced by removing methane from this anolyte stream by gas-liquid separation.

[0021] The packed bed of activated carbon particles can be charged in such a system by applying a potential to the bioelectrochemical system, resulting in a current flowing between the biocathode and the anode, electrons being donated at the anode, and electrons being supplied to the packed bed at the cathode. At the anode, an oxidation reaction such as the oxidation of water occurs and the necessary electrons are supplied. The potential can be achieved by an external power source that generates electricity, such as power generated by wind and / or sunlight. Alternatively, the electrons, and thus the power source, may be partially supplied by a chemical reaction at the anode. An example of such a chemical reaction is the oxidation of biologically organic matter (i.e., COD) described in Cerrillo, M., Vinas, M. and Bonmati, A (2017) Unravelling the active microbial community in a thermophilic anaerobic digester-microbial electrolysis cell coupled system under different conditions. Water Research 110, 192 - 201.

[0022] The anode is placed in the anode space and is made of a material suitable for oxidizing the selected electron donor. Suitable materials for water as the electron donor are platinum, ruthenium, iridium, iridium-coated titanium, and mixtures thereof. An example of a suitable anode material is a platinum-iridium-coated titanium plate. Preferably, the anode is an iridium-coated titanium mesh, such as a ruthenium-iridium-coated titanium mesh. The electrochemical catalytic properties of iridium-tantalum-coated titanium mesh for the oxidation of water have been found to be higher than those of platinum-iridium-coated titanium anodes. Experimental results showed that the anode potential required for water separation was much lower than in previous experiments, i.e., a current density of 5 A / m². 2 In this experiment, the anode potential was 1.14V for Ag / AgCl (3M KCl), while in a previous experiment, the anode potential was 1.9V for Ag / AgCl (3M KCl) at the same current density. The anode potential was 10 A / m 2 It was expected that the anode potential would increase at high current densities. However, the actual increase in anode potential was negligible.

[0023] The charged packed bed is appropriately charged to a capacitance between 10 and 100 F / g. Preferably, charging is carried out in a bioelectrochemical system including a biocathode, anode, and cation exchange membrane. The electron-charged packed bed is part of the biocathode. The packed bed is charged by applying a voltage / current to the bioelectrochemical system, generating a current between the biocathode and anode for a certain period of time, as a result of the packed bed being filled with electrons. Preferably, the packed bed is charged by applying a cathode potential between -0.50 and -0.60 V relative to Ag / AgCl to the current collector of the biocathode, or by applying 2 to 200 A / m 2 Preferably 5-120 A / m 2 It is charged by applying the current density between the two points to the cathode electrode.

[0024] The electronically charged bed does not necessarily need to be connected to an external power source so that it is not powered when carrying out this process. When the bed is sufficiently charged with electrons, this process can be carried out over a long period of time. For example, in a situation where the electronically charged bed is not powered, this process can be carried out for a period of 0.03 to 12 hours, preferably 0.05 to 10 hours. This is advantageous because it preferably allows the use of a discontinuous power source that generates electricity, such as solar and / or wind power, which are sustainable and renewable external power sources. The ability of this process to operate when such a discontinuous power supply is temporarily unavailable is advantageous.

[0025] This process can be carried out using an electronically charged packed bed as part of the bioelectrochemical system, where no power is supplied to the electronically charged packed bed of the bioelectrochemical system. In such embodiments, the packed bed is charged before carrying out the above process by applying a potential to the bioelectrochemical system to generate a current between the biocathode and anode. This process can also be carried out even if the packed bed is charged as described above. Furthermore, because there is no external power source, it is also possible to carry out a process in which the packed bed is charged alternately and not charged. In this embodiment, some net charging occurs when carrying out the process. Subsequently, the system is connected to an external power source and power is supplied.

[0026] Furthermore, this process may be carried out in multiple bioelectrochemical systems, where each system consists of a biocathode and an anode, with one bioelectrochemical system performing the process and another bioelectrochemical system being charged. The system performing this process can be carried out while the electron-charged bed is not being powered. The charged bioelectrochemical system is powered so that the bed is electron-charged. Optionally, further bioelectrochemical systems in the multiple bioelectrochemical systems perform the process while charging the bed by applying potential / current to the bioelectrochemical systems.

[0027] Preferably, a packed bed consisting of a carrier and a microbial biofilm is obtained in the activation step. The activation step is carried out by supplying a current to a packed bed consisting of a carrier and a microbial biofilm derived from sludge of an anaerobic wastewater treatment facility, at a pH higher than 8 and under anaerobic conditions, in an amount that results in a cathode potential lower than the theoretical hydrogen evolution potential of -0.61V vs. Ag / AgCl (3M KCl). The resulting packed bed, particularly a packed bed consisting of activated carbon granules and mixed cultured microorganisms, was found to be more stable and to avoid hydrogen evolution at the cathode compared to cases where such activation does not occur. It is preferable to carry out the activation after turning on the current supply until a stable and optimal potential is obtained.

[0028] Furthermore, the present invention relates to a method for activating or reactivating a bioelectrochemical system comprising an anode and a biocathode consisting of a packed bed composed of a carrier and mixed cultured microorganisms from sludge of an anaerobic wastewater treatment plant, by supplying a certain amount of current such that the cathode potential is lower than -0.61V relative to Ag / AgCl (3M KCl) under anaerobic conditions and at a pH higher than 8. To avoid confusion, the above method for activating or reactivating a bioelectrochemical system is carried out by supplying a current at a cathode potential higher than the theoretical hydrogen evolution potential at -0.61V relative to Ag / AgCl (3M KCl) at pH 7. The theoretical hydrogen evolution potential is pH-dependent. For example, at pH 8.5, the theoretical hydrogen evolution potential is -0.71V relative to Ag / AgCl (3M KCl).

[0029] The aqueous solution containing dissolved carbon dioxide may be a deliberately created solution or a naturally occurring solution such as seawater. A deliberately created aqueous solution can be obtained by contacting a gas containing carbon dioxide with an aqueous solution having a pH greater than 8 to obtain an aqueous solution in which the majority of the dissolved carbon dioxide exists as bicarbonate ions and / or carbonate ions. The aqueous solution having a pH greater than 8 in such an absorption process preferably contains sodium ions or sodium ions and potassium ions as described above. The gas containing carbon dioxide may be any gas containing carbon dioxide. Examples of such gases include flue gas obtained in a combustion process, exhaust gas from a water-gas shift process, synthesis gas, biogas from anaerobic digestion for wastewater treatment, air, amine gas, natural gas, related gases, (bio)purified gas, biomass, coal, or gas streams derived from the gasification of other organic residues.

[0030] The absorption process is typically carried out in an absorption or contact column where gas and liquid flows are in opposition. Preferably, the absorption process is carried out in a vertical column, where a carbon dioxide-containing gas is continuously supplied to the column at a lower position, and an alkaline aqueous solution is continuously supplied at a higher position, such that the substantially upward-flowing gas flow comes into contact with the substantially downward-flowing liquid flow. The column further comprises an outlet at its lower end for the packed aqueous solution and an outlet at its upper end for the gas having a lower carbon dioxide content.

[0031] The pH of the aqueous solution during the absorption process decreases as a result of the dissolved carbon dioxide. Therefore, it is preferable that the pH and composition of the starting aqueous solution are such that the majority of the dissolved carbon dioxide in the resulting aqueous solution exists as bicarbonate and / or carbonate ions. Optionally, an alkaline compound may be added after the absorption step to achieve these conditions.

[0032] The temperature during the absorption process can be between 5 and 45°C, preferably between 30 and 40°C. The pressure can be in the range of 0 bara to 100 bara, preferably between atmospheric pressure and 80 bara.

[0033] The absorption process is preferably carried out in such a way that oxygen does not dissolve in the filled aqueous solution. This can be achieved by starting with carbon dioxide gas with a low oxygen content. However, if the gas contains oxygen, some pretreatment may be necessary. Trace amounts of oxygen are also acceptable, as in one preferred embodiment, oxygen will also enter the cathode compartment through the membrane from the anode where oxygen is formed.

[0034] Preferably, a gas containing carbon dioxide has a pH greater than 8 and is brought into countercurrent contact with an aqueous solution containing dissolved methane obtained by the process according to the present invention, and the gas removes methane from the aqueous solution to obtain a gas containing methane. In this way, methane is effectively isolated from the aqueous reaction mixture, while carbon dioxide is absorbed using the same unit operation.

[0035] Figure 1 shows a possible process scheme for the process of the present invention. A gas containing carbon dioxide (1) has a pH greater than 8 in an absorption column (3) and is in countercurrent contact with an aqueous solution (2) containing dissolved methane obtained in a reactor (4). In column (3), gas (1) removes methane from the aqueous solution (2) to obtain a gas containing methane. In this way, methane is effectively isolated from the aqueous reaction mixture (2, 2a), while carbon dioxide is absorbed in the same column (3). The methane-rich gas is obtained as a gas stream (5). In the resulting aqueous solution (6) containing dissolved carbon dioxide, most of the dissolved carbon dioxide exists as bicarbonate ions and / or carbonate ions. This aqueous solution (6) is cooled in a heat exchanger (7) and supplied under anaerobic conditions to an electron-charged packed bed (8) consisting of a carrier and a microbial biofilm. In the electron-charged packed bed (8), carbon dioxide as bicarbonate ions and / or carbonate ions reacts to methane. This is thought to be achieved without the production of hydrogen as an intermediate reaction product. The electron-charged packed bed (8) is part of the biocathode (8a) in a bioelectrochemical reactor (4) which also includes an anode (9) and an ion exchange membrane (10) to avoid oxygen that may be formed at the anode (9) flowing to the biocathode (8a). The membrane is optional. The membrane is not necessary if the reactor (4) is designed so that methane produced at the biocathode (8a) does not reach the anode (9) and oxygen produced at the anode (9) does not reach the biocathode (8a).

[0036] The aqueous reaction mixture (2, 2a) obtained from the biocathode (8a) is supplied to the column (3) via the mixing vessel (13). Makeup water (14), makeup corrosive substances (15), and makeup nutrients and vitamins (16) may be added to the mixing vessel (13). A cathodic bleed stream (17) removes a portion of the cathodic liquor from the process.

[0037] At the anode, water is oxidized, and the resulting oxygen is discharged to the anolyte buffer tank (19) via (18). Fresh anolyte is supplied to the anolyte compartment of reactor (9) via (20). In this container, molecular oxygen is separated as (21). Makeup water (22) and makeup corrosive substances (23) are added, and an anolyte bleed stream (24) discharges a portion of the aqueous solution from the process.

[0038] A portion of the anolyte (12) is supplied to the mixing vessel (13) to become part of the cathodelime, and a portion of the cathodelime (11) is supplied to the anolyte buffer tank (19) to become part of the anolyte. These flows (11, 12) may be treated to reduce the oxygen and methane content as described above. [Examples]

[0039] The present invention is illustrated by the following non-limiting examples, which demonstrate the energy efficiency of a process. This energy efficiency is defined as follows. Generally, the energy efficiency of an electron-driven process as a process according to the present invention is described as the external electrical energy that leads to the desired final product, methane. The energy efficiency is calculated as equation (1).

[0040]

number

[0041] Regarding the CH4 manufacturing process of the present invention,

[0042]

number

[0043]

number

[0044] In the formula, N CH4 is the amount (mol) of methane generated during a certain time (t), 8 is the amount of electrons required to generate one molecule of CH4, F is the Faraday constant (96485 C / mol e - ), and I is the current (A).

[0045] Voltage efficiency (

[0046] [Number] ) is explained as the portion of the energy input reaching CH4 (i.e., the cell voltage required to operate the system) and is calculated as shown in Equation 3.

[0047] [Number]

[0048] In this equation, ΔG CH4 is the change in Gibbs free energy of the oxidation from CO2 to CH4 (890×10 3 J / mol CH4), and

[0049] [Number] is the applied cell voltage (V), 8 is the amount of electrons required to generate one molecule of CH4, and F is the Faraday constant (96485 C / mol e - ).

[0050] [Example 1] A bioelectrochemical system (BES) was operated, and a long-term experiment was conducted for 60 days. The BES configuration was similar to that described by Liu, Dandan, Marta Roca-Puigros, Florian Geppert, Leire Caizan-Juanarena, Na Ayudthaya, P. Susakul, Cees Buisman, and Annemiek Ter Heijne, "Granular carbon-based electrodes as cathodes in methane-producing bioelectrochemical systems," Frontiers in bioengineering and biotechnology 6(2018):78. The cathode electrode consisted of 10.3 g of granular activated carbon, which was completely packed into the cathode chamber. A flat graphite plate was used as a current collector. Each electrode was 33 cm². 3 Anode chamber and cathode chamber with a flow path of (11cm × 2cm × 1.5cm). The anode chamber and cathode chamber are 22cm 2 The cations were separated by a cation exchange membrane with a projected surface area of ​​(11 cm × 2 cm). The total volumes of the anolyte and cathode liquid were 500 mL and 330 mL, respectively. The cathode liquid circulation bottle was designed to increase the H / D (height / diameter) ratio to enable better absorption of CO2. A high anolyte flow rate of 94 mL / min was used to remove the O2 generated at the anode electrode. N2 was continuously bubbled in the anolyte recirculation bottle at a rate of 80 mL / min. The cathode liquid recirculation rate was 11 mL / min.

[0051] 30 mL of anaerobic sludge from the Eerbeek upstream anaerobic sludge blanket (UASB) digestion was inoculated into the cathode chamber. The volatile suspended solids content of the inoculated anaerobic sludge was 30.6 g / L. Methane generation BES was controlled by a constant current (fixed current) using a potentiostat. Furthermore, the cell voltage was manually monitored via a multimeter. Liquid samples for pH and conductivity measurements were taken twice a week from both the anode and cathode liquids. The following results were obtained.

[0052] Initially, the cathode solution consisted of a 50 mM phosphate buffer (1.36 g / L KH2PO4 and 5.67 g / L Na2HPO4) containing 0.2 g / L NH4Cl, 1 mL / L Wolfe's vitamin solution, and 1 mL / L Wolfe's modified mineral solution. The anode solution consisted of only a 50 mM phosphate buffer. Because the same phosphate buffer was used for both the cathode and anode solutions, the initial pH and conductivity of both solutions were the same (i.e., pH 6.7 and conductivity 7.68 mS / cm). After an initial period (not shown), the current density was 5 A / m². 2 When electrons were supplied using the biocathode, stable performance was obtained (from day 0 to day 30). During this period, the obtained voltage efficiency was approximately 50%, and the Coulomb efficiency of 83-85% led to an energy efficiency of 40-42%.

[0053] After 30 days, the cathode and anode solutions were changed to a high-concentration saline medium containing 1.0 M carbonate / bicarbonate buffer with a conductivity of approximately 40 mS / cm (Na:K ratio of 4:1). The medium contained 0.2 g / L NH4Cl, 1 mL / L Wolfe's vitamin solution, and 1 mL / L Wolfe's modified mineral solution. The resulting cathode solution had a pH of 7.7–7.8. After the change in medium, the voltage efficiency immediately increased to approximately 83%. The Coulomb efficiency initially decreased to 65%. This decrease can be explained by osmotic pressure shock to the biocathode. However, after several days of operation, the biofilm adapted, and the Coulomb efficiency recovered to approximately 85%. As a result, the energy efficiency of methane-producing BES was improved by changing the medium.

[0054]

number

Claims

1. A process for converting carbon dioxide to methane by contacting an aqueous solution containing dissolved carbon dioxide with an electronically charged packed bed containing a carrier and a microbial biofilm under anaerobic conditions, The aqueous solution contains sodium cations between 0.3 and 4 M or sodium and potassium cations between 0.3 and 4 M. A process in which more than 90 moles of dissolved carbon dioxide in an aqueous solution exist as bicarbonate ions and / or carbonate ions.

2. The process according to claim 1, wherein the carrier is activated carbon granules or activated biocarbon granules.

3. The process according to any one of claims 1 to 2, wherein no power is supplied to the electronically charged bed.

4. The process according to claim 3, wherein the electronically charged packed bed is part of a biocathode in a bioelectrochemical system further comprising an anode, an ion exchange membrane, and a cathode, and the packed bed is charged by applying a potential to the bioelectrochemical system, thereby generating an electric current between the biocathode and the anode for a certain period of time.

5. The process according to claim 4, wherein the aqueous solution present in the anode is called the anodic solution, the aqueous solution present in the cathode is called the cathode solution, and a recirculation occurs in which a portion of the cathode solution is supplied to the anode to become part of the anodic solution, and a portion of the anodic solution is supplied to the cathode to become part of the cathode solution.

6. The process according to any one of claims 1 to 2, wherein the electronically charged packed bed is part of a biocathode in a bioelectrochemical system further comprising an anode, and at some point the process is carried out when the packed bed is charged by applying a potential to the bioelectrochemical system, thereby generating an electric current between the biocathode and the anode, and at another point the process is carried out when no power is supplied to the electronically charged packed bed.

7. The process according to any one of claims 4 to 6, wherein the process is carried out in a plurality of bioelectrochemical systems, each system comprising a biocathode and an anode, and in one or more bioelectrochemical systems, the process is carried out while power is not supplied to the electronically charged packed beds of the one or more bioelectrochemical systems, and while the process is not carried out, power is supplied to the packed beds of one or more other bioelectrochemical systems among the plurality of bioelectrochemical systems so that these packed beds are charged electronically.

8. The process according to any one of claims 5 to 7, wherein the process is carried out for a period of 0.03 to 12 hours when no power is supplied to the electronically charged filler.

9. The process according to any one of claims 3 to 7, wherein the power source is electricity generated by solar and / or wind power.

10. The aforementioned packed bed can be heated by applying a cathode potential of -0.50 to -0.60 V relative to Ag / AgCl (3M KCl) to the cathode electrode, or by applying 5 to 200 A / m ２ The process according to any one of claims 4 to 9, wherein the cathode electrode is charged by the application of a current density between the two states.

11. The process according to any one of claims 4 to 10, wherein the anode is a titanium mesh coated with iridium and / or tantalum.

12. The process according to any one of claims 4 to 7, wherein the power supply is generated by a chemical reaction at the anode.

13. The aforementioned filled bed is 500 to 1500 m ２ The process according to any one of claims 1 to 12, wherein the bed is filled with activated carbon granules having an activated surface area between / g, and microorganisms are present as a biofilm on the surface of the activated surface area.

14. The process according to any one of claims 1 to 13, wherein the pH of the aqueous solution exceeds 7.

7.

15. The process according to claim 14, wherein the pH of the aqueous solution is greater than 8.

16. The process according to any one of claims 1 to 15, wherein the aqueous solution contains sodium cations or sodium and potassium cations in a concentration between 0.5 and 1.5 M.

17. The process according to any one of claims 4 to 16, wherein the carrier and the biofilm of the microorganisms are obtained in an activation step carried out by supplying a certain amount of current to a packed bed composed of the carrier and the biofilm of the microorganisms at a pH greater than 8 and anaerobic conditions, with a cathode potential greater than the theoretical hydrogen evolution potential of -0.61 V for Ag / AgCl (3M KCl) at a pH of 7, and the microorganisms are mixed culture microorganisms from sludge of an anaerobic wastewater treatment facility.

18. The process according to any one of claims 1 to 17, wherein an aqueous solution containing dissolved carbon dioxide is obtained by contacting a gas containing carbon dioxide with an aqueous solution having a pH greater than 8 to obtain an aqueous solution in which the majority of the dissolved carbon dioxide exists as bicarbonate ions and / or carbonate ions.

19. The process according to claim 18, wherein a gas containing carbon dioxide is brought into countercurrent contact with an aqueous solution containing dissolved methane obtained by the process according to any one of claims 1 to 17, having a pH greater than 8, and the gas removes methane from the aqueous solution to obtain a gas containing methane.

Images