DEVICE AND METHOD FOR BIOLOGICAL METHANIZATION WITH A FOATING AND DEGATING COLUMN CONNECTED IN A CIRCUIT

Description

[0001] The present invention relates to a device for the biological methanation of carbon dioxide by means of methanogenic microorganisms having the features of patent claim 1. Furthermore, the present invention relates to a method for the biological methanation of carbon dioxide in a device by means of methanogenic microorganisms having the features of patent claim 9. Instead of carbon dioxide, carbon monoxide can also be used according to the invention, for example from the pyrolysis of plant residues or high-temperature co-electrolysis.

[0002] As an alternative to storing electrical energy in accumulators, the "power-to-gas" concept is becoming increasingly important due to the advantages of easier transport and longer-term storage of large amounts of energy. According to this concept, excess electrical power from renewable sources, for example, is used to electrolytically split water into hydrogen, which can then be chemically or biologically converted into storable methane by reacting with carbon monoxide and / or carbon dioxide. The chemical reaction is forced at temperatures exceeding 180 °C and high pressures and is only possible with relatively sophisticated catalysts. In contrast, the biological conversion of hydrogen and carbon dioxide into methane can occur using special microorganisms at ambient pressure and temperatures in the range of 25-70 °C.In natural, anaerobic, aqueous ecosystems such as swamps, water sediments, or flooded soils, consortia of several microorganisms produce methane from organic material such as plant and animal remains through a degradation chain. In an initial reaction, polymers are hydrolyzed to oligomers or monomers. In a second step, acidogenesis, carboxylic acids, ethanol, hydrogen sulfide, and ammonia are produced, as well as acetic acid, hydrogen, and carbon dioxide. In the third step, acetogenesis, lower fatty and carboxylic acids, as well as alcohols, are converted to acetic acid. In the fourth step, methanogenesis, acetic acid and / or carbon dioxide and hydrogen are converted to methane by methanogenic microorganisms, the archaea.

[0003] This fourth step can be specifically used to store energy in the form of methane if hydrogen is added to the corresponding medium containing methanogenic microorganisms. This converts the excess carbon dioxide to methane. Alternatively, the methanation step can also be carried out separately. In an aqueous medium containing only low concentrations of essential micro- and macroelements, externally supplied carbon dioxide or carbon monoxide is also converted to methane with H2 by the methanogenic archaea.

[0004] Such devices, in which the aforementioned fourth step is used to store energy in the form of methane, are already known. The solubility of hydrogen in the aqueous medium containing the methanogenic microorganisms has always proven problematic. Dissolving the hydrogen is very energy-intensive.

[0005] Furthermore, the pH of the aqueous medium depends on the amount of dissolved carbon dioxide in the system. An increase in the carbon dioxide content lowers the pH of the aqueous medium, while a decrease in the carbon dioxide content raises the pH. Both can adversely affect the pH range suitable for microorganisms.

[0006] The presence of carbon monoxide / carbon dioxide in the system is particularly important when hydrogen is also added to the biogas process, as this can then be immediately metabolized by the microorganisms. If the carbon monoxide / carbon dioxide content in the aqueous medium is too low, hydrogen accumulation occurs, which inhibits anaerobic degradation. It is therefore important to adjust the carbon monoxide / carbon dioxide concentration in the system to the ideal range.

[0007] A major challenge in biological methanation is – as described – the low solubility of hydrogen in aqueous media. When using conventional gasification techniques, the introduced hydrogen cannot be fully converted by the microbiology due to insufficient gas / liquid transfer and is largely converted into biogas unused. This is not only energetically unfavorable, but can also be problematic when fed into the natural gas grid, as a limit of a few vol.% hydrogen should not be exceeded.

[0008] To enable a homogeneous distribution of hydrogen and carbon monoxide / carbon dioxide in such aqueous media, the prior art generally proposes mechanical agitation of the substrate during gassing. However, mechanical agitation also consumes a considerable amount of energy. Furthermore, reactors with agitation devices are more difficult to clean due to their more complex design. Alternatively, reactors in which hydrogen or synthesis gas is introduced into the reactor via a plurality of finely distributed agitation units have also been proposed in the prior art.

[0009] EP 3 013 937 B1 relates, in a first aspect, to a device for producing methane by means of methanogenic microorganisms by reacting H 2 and CO 2 , comprising: at least one reactor; an aqueous medium provided in the at least one reactor, wherein the methanogenic microorganisms are located in the aqueous medium; a feed device configured to introduce H 2 and CO 2 into the at least one reactor, wherein the H 2 and CO 2 form a gaseous mixture therein; a reaction enhancement device configured to increase the contact surface between the aqueous medium with the methanogenic microorganisms and the gaseous mixture; and a recirculation device configured to recirculate at least a portion of the gas accumulating in the reactor,wherein the recirculation rate of the gas accumulating in the reactor is greater than the feed rate of the substrate gas into the reactor. In a second aspect, EP 3 013 937 B1 relates to the use of an apparatus according to the invention for producing methane by means of methanogenic microorganisms by reacting H 2 and CO 2 . In a third aspect, EP 3 013 937 B1 relates to a process for producing methane in an inventive reactor apparatus by means of methanogenic microorganisms located in the reactor apparatus in an aqueous medium by reacting H 2 and CO 2 as a reaction gas mixture, wherein during the reaction, the contact surface between the aqueous medium containing the methanogenic microorganisms and the gaseous mixture is increased by means of a reaction-enhancing device, and wherein at least a portion of the gas accumulating in the reactor is returned to the reactor apparatus by means of a recirculation device.where the recirculation rate of the gas accumulating in the reactor is greater than the feed rate of the reaction mixture into the reactor.,

[0010] DE 102018 117281 A1 relates to a device for the biological methanation of carbon dioxide by means of methanogenic microorganisms by reacting hydrogen and carbon dioxide, comprising the following: (a) a reactor; (b) a medium provided in the reactor with methanogenic microorganisms; (c) a supply device for supplying an H-containing gas into the medium; wherein the supply device comprises a plurality of gas guide units, each of the gas guide units having a plurality of gassing units, each of which has a plurality of outlet openings for supplying the H-containing gas into the medium, wherein the supply device is designed such that the supply of the H-containing gas can be effected by successive application of the gas guide units.Furthermore, the invention also relates to a process for the biological methanation of carbon dioxide in a reactor device using methanogenic microorganisms as part of a medium provided in a reactor, characterized in that an H-containing gas is supplied to the medium via a plurality of gas supply units, each of the gas supply units having a plurality of gassing units, each of which has a plurality of outlet openings, wherein the H-containing gas is supplied by successively pressurizing the gas supply units. Carbon dioxide can be added to the H-containing medium as required.

[0011] EP 0 154 334 A2 relates to a method for conducting reactions and mass transfer processes in heterogeneous fluid systems. These often present the problem of separating a reaction component or even an auxiliary material from the reaction solution after the reaction or exchange stage and returning it to the process. This is associated with considerable effort, particularly when pressure and high temperatures are applied, in the form of additional, complex upstream equipment. To overcome this disadvantage, the invention provides for connecting a reactor with stirred-tank characteristics as the first stage to a reactor with tubular characteristics as the second stage by means of pipelines in the region of their upper and lower ends, in the manner of a communicating hydraulic system.

[0012] It was therefore the object of the present invention to provide a device and a method for the biological methanation of carbon monoxide / carbon dioxide in which methane is present in high concentrations. In addition, less energy should be required during the conversion of hydrogen and carbon monoxide / carbon dioxide to methane in an aqueous medium than with conventional systems, and a simplification should be achieved with regard to known devices and methods. Nevertheless, the hydrogen must be supplied in such a way that it is sufficiently dissolved in the medium. Furthermore, the carbon dioxide content should be adjustable so that it lies in the optimal range for the microorganisms and that hydrogen accumulation does not occur. Furthermore, it is still crucial for a continuous and high methane formation rate that high-performance microorganisms are present in the system at an optimal concentration at all times.However, various chemical and biological factors lead to varying degrees of deviation from this ideal situation during operation. The reaction water formed also dilutes the microorganisms. Among other things, excessively high or low pH values ​​or temperatures, the lack of essential trace elements that are not yet precisely known, or the addition of inhibiting substances when using complex substrates can also damage the biology. If methanation occurs directly in the biogas process, excessive loading rates or an excessive hydrogen supply can also damage the acetogenic microorganisms in particular. If genetically optimized high-performance strains are used, mutations and / or contamination will occur over time. In this case, new batches of the high-performance strains must be introduced.To achieve high productivity rates, a controlled adjustment of the microorganism concentration is therefore necessary.

[0013] To achieve the stated objective(s), the present invention provides a device having the features of claim 1. The device according to the invention is suitable for the biological methanation of carbon dioxide using methanogenic microorganisms by converting hydrogen and carbon monoxide and / or carbon dioxide. The device according to the invention comprises the following: (a) a gassing column and a degassing column, each having a bottom side and an upper side opposite the bottom side; (b) a medium containing methanogenic microorganisms provided in the gassing column and the degassing column; (c) a feed device for feeding a hydrogen-containing gas into the medium of the gassing column, the feed device being arranged in the region of the bottom side of the gassing column; (d) a discharge device for discharging a methane-containing gas from the degassing column; (e) a connecting line between the gassing column and the degassing column in the region of the bottom sides; (f) a pump for transferring medium via the connecting line from the gassing column to the degassing column; and (g) a return line between the gassing column and the degassing column in the region of the upper sides for returning medium from the degassing column to the gassing column.

[0014] The gassing column and degassing column are connected by the connecting line at the bottom and by the return line at the top. The medium contained in both columns can thus be circulated between the gassing column and the degassing column. The pump is designed to transfer the medium from the gassing column to the degassing column via the connecting line. The medium pumped from the gassing column to the degassing column can be returned from the degassing column to the gassing column via the return line. Since the pressure in the medium in the gassing column is higher at the bottom than at the top, the medium in this area can absorb more hydrogen-containing gas.For the same reason, more methane may be dissolved in the medium near the bottom of the gassing column than near the top. Since the connecting line is located near the bottom of the two columns, the higher pressure here means that medium with a higher dissolved methane content is transferred from the gassing column to the degassing column. Since the pressure in the degassing column decreases due to the medium rising within it, the solubility of the methane in the medium also decreases. In this way, the methane evaporating from the medium can be removed via the removal device in the degassing column. Hydrogen not already utilized in the gassing column is converted in the degassing column. Therefore, there is relatively little hydrogen in the product gas.In other words, the pressure difference in the two columns is used to obtain as little hydrogen and as much methane as possible in the product gas.

[0015] According to the invention, the feed device is arranged in the region of the bottom of the gassing column. In this way, the hydrogen-containing gas introduced into the gassing column flows upwards in the gassing column, counter to the medium flowing downwards therein. The methanogenic microorganisms in the medium convert the carbon monoxide and / or carbon dioxide contained therein into methane, consuming the supplied hydrogen. Since methane is more soluble in the medium than hydrogen, and the higher pressure in the region of the bottom of the gassing column also makes the methane more soluble there than in the region of the top of the gassing column, predominantly the dissolved methane is transferred with the medium transferred to the degassing column.

[0016] Furthermore, the preferably parallel arrangement of the gassing column and degassing column has the advantage that the pump can create a circulating movement of the medium with relatively low energy expenditure, whereby the height of the liquid column in the degassing column is only slightly higher than in the gassing column. Due to this difference in the height of the liquid (so-called fill level difference) between the degassing column and the gassing column, the medium in the area of ​​the upper sides of the columns can be recirculated from the degassing column to the gassing column via the return line. The pump between the gassing column and degassing column only has to overcome the fill level difference between the two columns as well as minor flow pressure losses and pressure differences in the gas region of the columns. The energy requirement of the pump can thus be kept relatively low, and the energy expenditure for biological methanation is thus kept extremely low.

[0017] It is further preferred according to the invention that atmospheric pressure prevails at the upper end of the medium in the degassing column.

[0018] In the device according to the invention, the discharge device is preferably arranged in the region of the upper side of the degassing column. The reason for this is that the methane has a lower solubility in the medium due to the lower hydraulic pressure in the region of the upper side of the degassing column, so that it can outgas from the medium and be discharged through the discharge device. For this purpose, the degassing column can have a pipe with a serrated weir or serrated weir cascade in the region of the upper side, in addition to the discharge device, which is preferably designed as a pipeline.

[0019] The medium is preferably a (complex) aqueous medium and contains, in addition to water and substrate and optionally genetically optimized methanogenic microorganisms, in particular hydrogenotrophic methanogenic microorganisms in pure or mixed culture. The substrate preferably comprises carbon monoxide and / or carbon dioxide and hydrogen as the main components for energy production by the methanogenic microorganisms and can also contain trace elements and / or other complex additives, such as liquid manure. Methanogenic microorganisms within the meaning of the present invention are those microorganisms that can produce methane from carbon dioxide and hydrogen or from acetic acid, i.e. are methane producers or methane-forming microorganisms. Hydrogenotrophic methanogenic microorganisms within the meaning of the present invention are those methanogenic microorganisms that produce methane from carbon dioxide and hydrogen.Methanogenic microorganisms belong to the domain Archaea and, within it, to the phylum Euryarchaeota. Methanogenic microorganisms include, among others, the orders Methanobacteriales, Methanococcales, Methanomicrobiales, Methanocellales, Methanosarcinales, and Methanopyrales. Within the scope of the present invention, it is envisaged that methanogenic microorganisms can originate from all orders, but do not have to. It is therefore preferred that the methanogenic microorganisms be a mixed or pure culture of various microorganisms of the phylum Euryarchaeota. In addition to the aforementioned microorganisms, the medium can also contain all microorganisms present in a reactor of a biogas plant.

[0020] In a further embodiment, the device according to the invention preferably comprises a feed device for feeding a gas containing carbon dioxide or carbon monoxide (e.g., from the pyrolysis of plant residues or co-electrolysis) or an organic precursor compound thereof, which is converted into carbon monoxide and / or carbon dioxide by microorganisms contained in the medium, into the medium of the gassing column, wherein the feed device is arranged in the region of the bottom side of the gassing column. According to the invention, the following are preferably considered as precursor compounds: e.g., sugar-, starch-, or cellulose-containing industrial residues and wastewater such as whey, molasses, waste from yeast and soy product production, the corn or potato starch industry, the paper industry, etc., as well as other biomass-containing waste.In addition to the microorganisms mentioned above, the medium may contain the following microorganisms for the transfer of precursor compounds: representatives of Bacteria (especially Firmicutes, Bacteroidetes, Actinobacteria, Fibrobacteres / Acidobacteria and Crenarchaeota).

[0021] Furthermore, the device according to the invention preferably comprises a device for discharging liquid with retention of microorganisms. This enables the removal of reaction water produced during biological methanation. This has the advantage that the amount of substance within the device can be kept within a constant range. Otherwise, the reaction water produced during biological methanation would constantly increase the amount of substance within the device. In order to separate the reaction water from the medium containing microorganisms, the device mentioned can be a filtration module, for example a membrane module, which is designed such that the reaction water, but not microorganisms, is discharged. According to the invention, the reaction water is discharged as soon as the fill level difference between the degassing column and the gassing column exceeds a predetermined maximum value.Together with a supply line for microorganisms and a discharge line without retention of the microorganisms, the controlled adjustment of an optimal microorganism concentration is possible.

[0022] In a further embodiment, the device according to the invention preferably has a gas extraction line in the region of the upper side of the gassing column, by means of which gas extraction line unreacted hydrogen, undissolved methane and carbon monoxide and / or carbon dioxide are conducted from the region of the upper side of the gassing column to the region of the bottom side of the gassing column. The amount of gas removed in this way serves to simplify the control: in principle, enough hydrogen is supplied that it can be converted almost completely. However, the control of the device according to the invention is more stable if a small portion of the resulting gas is always withdrawn in the region of the upper side of the gassing column and fed back in to the region of the bottom side of the gassing column.

[0023] In principle, several operating modes of the device according to the invention are possible, of which the following two are preferred: (a) methanation of a gas mixture of methane and carbon dioxide, and (b) methanation of pure carbon dioxide, carbon monoxide or a mixture of both.

[0024] According to the invention, operating mode (a) is suitable when the gas stream of the reactants comes from organic waste treatment plants, from digestion towers of sewage treatment plants, landfill gases, etc. Here, the control is more demanding, since the added carbon dioxide cannot initially be controlled independently of the methane.

[0025] In operating mode (b), the flow rate of carbon dioxide or carbon monoxide to be methanized can be freely selected within certain limits. Carbon dioxide can then come from other sources, for example, exhaust air from beer and wine production, exhaust air from cement plants, or from plants for carbon dioxide capture from the atmosphere. Mixtures of carbon dioxide and carbon monoxide can originate, for example, from pyrolysis.

[0026] Furthermore, according to the invention, it is preferred that the pumping capacity of the pump used (for transporting the medium from the gassing column to the degassing column) be at least large enough that the resulting volume flow multiplied by the solubility difference of the methane (top / bottom of the gassing column) in the medium is greater than the amount of methane produced. If carbon dioxide is to be methanized, which is produced in a supplied mixture of carbon dioxide and methane, the pumping capacity should be increased due to the methane already present in the reactant stream.

[0027] According to the invention, the addition of carbon dioxide can also be controlled by the pH value: During methanation, the pH value generally rises. To prevent the pH value from exceeding a predetermined value of, for example, pH = 8.0, the amount of added carbon dioxide is increased as the pH value rises. If the pH value is too low, for example, less than pH = 7.5, the methanation rate decreases. In this case, the amount of carbon dioxide must be reduced or a cation-containing solution must be added. In addition, the optimal pH range can also be adjusted using buffering and acidic or, if necessary, alkaline substances, preferably residues and waste materials. When operating the plant as an anaerobic digestion plant, these can also be the substrates.

[0028] The height of the columns is preferably selected so that the fill level of the medium in the gassing column is more than 10 m, more preferably more than 20 m, and even more preferably more than 30 m. The advantage of a greater height is that the hydrostatic pressure in the bottom area is greater, and thus more hydrogen and methane can be dissolved.

[0029] The gassing column and / or the degassing column can also be equipped with liquid-permeable packings such as Rasching rings or coarse-fibered fleece. This can improve mass transfer and immobilize microorganisms.

[0030] In addition to the aforementioned device for discharging liquid with retention of microorganisms, the device according to the invention can also comprise a device for discharging liquid without retention of microorganisms. In addition, the device according to the invention can also comprise a supply device for a liquid containing microorganisms, which preferably contains microorganisms in a highly concentrated form. These supply and discharge devices enable a controlled adjustment of the microorganism concentration in the medium.

[0031] The present invention also relates to a process for the biological methanation of carbon monoxide and / or carbon dioxide in a device using methanogenic microorganisms as part of a medium provided in the device. The process is characterized in that the medium is circulated via a gassing column and a degassing column, the columns being connected to one another via a connecting line in the region of their bottom sides and via a return line in the region of the upper sides opposite the bottom sides, wherein the medium moves downwards in the gassing column and upwards in the degassing column, wherein a hydrogen-containing gas is supplied to the medium in the region of the bottom side of the gassing column.

[0032] Since the solubility is proportional to the pressure, by adding the hydrogen-containing gas in the area of ​​the bottom side of the gassing column, more hydrogen can dissolve in the medium.

[0033] The methane that forms is at least partially dissolved in the medium and transported via the connecting line into the degassing column. The ascending movement of the medium in the degassing column transports the methane towards the top of the degassing column. The pressure reduction of the medium towards the top of the degassing column allows the methane to outgas from the medium and be discharged at the top of the degassing column. The descending movement of the medium in the gassing column and the ascending movement of the medium in the degassing column is preferably brought about by a pump. This results in a difference in the fill level of the medium contained between the degassing column and the gassing column, i.e. the fill level in the degassing column is higher than in the gassing column. The medium from the degassing column can be returned to the gassing column via the return line.

[0034] In the process according to the invention, it is also preferred that reaction water formed during the methanation reaction is removed from the circuit.

[0035] The temperature of the medium in the gassing column during the process according to the invention is preferably in a range from 30 °C to 70 °C.

[0036] The inventive method preferably uses the inventive device described above. All method steps described herein in connection with the inventive device should also be considered as possible features of the inventive method, and vice versa.

[0037] The present invention will now be described with reference to the following Figure 1 and the embodiment, but is not limited to this specific embodiment. Figure 1 schematically shows a device according to the invention which can be used, for example, in the method according to the invention.

[0038] Figure 1shows a device 1 according to the invention. The device 1 has, on one side, a gassing column 2 and, on the other side, a degassing column 3, which are connected in the region of their bottom sides by a connecting line 7 and in the region of the upper sides by a return line 9 such that a medium 4 can move in a circuit between the gassing column 2 and the degassing column 3. The medium 4 moves downwards in the gassing column 2, is transferred via the connecting line 7 into the degassing column 3, in which it moves upwards. A return of medium 4 from the degassing column 3 to the gassing column 2 takes place via the return line 9. A hydrogen-containing gas can be introduced into the medium 4 in the gassing column 2 via a feed device 5a. The feed device 5a is - as in Figure 1shown - arranged in the region of the bottom of the gassing column 2. The hydrogen-containing gas supplied thereby moves upwards against the downwardly moving medium 4. Due to the higher pressure of the liquid column of the medium 4 in the region of the bottom of the gassing column 2, the hydrogen-containing gas is more soluble in this region than in the region of the upper side of the gassing column 2. Furthermore, a gas containing carbon dioxide or carbon monoxide or a precursor compound thereof can also be supplied to the medium 4 of the gassing column 2 via a supply device 5b. The supply of this gas also preferably takes place in the region of the bottom of the gassing column 2. Furthermore, the device 1 preferably has a supply device 5c for a liquid containing microorganisms. The supply devices 5a, 5b and 5c preferably have valves via which the inflow of the corresponding gases can be controlled.The presence of methanogenic microorganisms in the medium can convert carbon dioxide and / or carbon monoxide into methane, forming water. Since methane is more soluble than hydrogen in the preferably aqueous medium 4, the methane-enriched medium 4 is passed through the connecting line 7, where it then moves upwards in the degassing column 3. The decreasing liquid column pressure in the degassing column 3 reduces the solubility of the methane in the medium 4. This allows the methane to outgas from the medium 4 in the upper region of the degassing column 3 and be removed from the circuit via a discharge device 6. As shown in the . Figure 1As shown, in the area of ​​the upper side of the degassing column, the discharge device 6 can have a pipe with a serrated weir or serrated weir cascade through which the medium 4 can pass together with methane-containing gas. The medium 4 located above the serrated weir pipe can be transferred back to the area of ​​the upper side of the gassing column 2 through the preferably slightly sloping return line 9. The methane-containing gas degassed from the medium 4 is removed from the circuit via the discharge device 6. A pump 8 ensures the circulating movement of the medium between the gassing column 2 and the degassing column 3. The pump 8 only has to generate the energy for the fill level difference between the degassing column 3 and the gassing column 2. In order to discharge reaction water formed from the device 1, a device 10a for discharging liquid with retention of microorganisms can be provided in the connecting line 7.To ensure that only liquid and no other microorganisms 4 are removed from the circuit, a membrane (not shown), for example, can be provided in the device 10a. To remove medium from the circuit, a device 10b for removing liquid (without retaining microorganisms) can also be provided. To control the removal of liquid, the devices 10a and 10b can have valves. The pump 8 can—as shown in . Figure 1 shown - be integrated into the connecting line 7. A gas extraction line 11 can be installed above the liquid column of the medium 4 in the gassing column 2, with which the gas located there can be returned to the medium 4, for example, via the feed device 5a. To control this return, the gas extraction line 11 must have a gas recirculation pump 12. List of reference symbols:

[0039] 1Device 2Gasing column 3Degassing column 4Medium 5aFeed device for the hydrogen-containing gas 5bFeed device for the carbon dioxide or carbon monoxide-containing gas or an organic precursor compound thereof 5cFeed device for a liquid containing microorganisms 6Discharge device 7Connecting line 8Pump 9Return line 10aDevice for discharging liquid with retention of microorganisms 10bDevice for discharging liquid (without retention of microorganisms) 11Gas sampling line 12Gas recirculation pump

Claims

1. Apparatus (1) for the biological methanation of carbon monoxide and / or carbon dioxide by means of methanogenic microorganisms by reacting hydrogen and carbon monoxide and / or carbon dioxide, the apparatus comprising the following: (a) a gassing column (2) and a degassing column (3), each having a bottom side and an upper side which is opposite the bottom side; (b) a medium (4) containing methanogenic microorganisms which is provided in the gassing column (2) and the degassing column (3); (c) a feed device (5a) for feeding a hydrogen-containing gas into the medium (4) of the gassing column (2), wherein the feed device (5a) is arranged in the region of the bottom side of the gassing column (2); (d) a discharge device (6) for discharging a methane-containing gas from the degassing column (3); (e) a connecting line (7) in the region of the bottom sides, between the gassing column (2) and the degassing column (3); (f) a pump (8) for transferring the medium (4) from the gassing column (2) into the degassing column (3) via the connecting line (7); and (g) a return line (9) in the region of the upper sides, between the gassing column (2) and the degassing column (3), for returning the medium (4) from the degassing column (3) into the gassing column (2).

2. Apparatus (1) according to claim 1, wherein the discharge device (6) is arranged in the region of the upper side of the degassing column (3).

3. Apparatus (1) according to either claim 1 or claim 2, which comprises a feed device (5b) for feeding a carbon-dioxide-containing or carbon-monoxide-containing gas or an organic precursor compound thereof into the medium (4) of the gassing column (2), which gas is converted into carbon monoxide and / or carbon dioxide by microorganisms contained in the medium (4), wherein the feed device (5) is arranged in the region of the bottom side of the gassing column (2).

4. Apparatus (1) according to any of claims 1 to 3, which comprises a device (10a, 10b) for discharging liquid.

5. Apparatus (1) according to claim 4, in which the device is a device (10a) for discharging liquid with retention of microorganisms.

6. Apparatus (1) according to any of claims 1 to 5, which comprises a feed device (5c) for a liquid containing microorganisms.

7. Apparatus (1) according to any of claims 1 to 6, which comprises a gas extraction line (11) in the region of the upper side of the gassing column (2), by means of which line unreacted hydrogen, undissolved methane and carbon monoxide and / or carbon dioxide are guided from the region of the upper side of the gassing column (2) into the region of the bottom side of the gassing column (2).

8. Apparatus (1) according to any of claims 1 to 7, in which the gassing column (2) and / or the degassing column (3) comprise liquid-permeable packing materials.

9. Process for the biological methanation of carbon monoxide and / or carbon dioxide in an apparatus (1) by means of methanogenic microorganisms as part of a medium (4) provided in the apparatus (1), characterized in that the medium (4) is guided in a circuit via a gassing column (2) and a degassing column (3), the columns (2, 3) being connected to one another via a connecting line (7) in the region of their bottom sides and via a return line (9) in the region of the upper sides opposite the bottom sides, in which the medium (4) moves downward in the gassing column (2) and upward in the degassing column (3), in which a hydrogen-containing gas is fed to the medium (4) in the region of the bottom side of the gassing column (2).

10. Method according to claim 9, in which the apparatus (1) used is an apparatus (1) according to any of claims 1 to 8.