BIOELECTROCHEMICAL REACTOR WITH DOUBLE BIOANODE, METHOD FOR ANOFIC REGENERATION AND USE OF THE REACTOR FOR MICROBIAL ELECTROSYNTHESIS

Abstract

A bioelectrochemical reactor (1) has an anode chamber (11) having at least two bioanodes (12, 13), and an anodic electrolyte (14) with an anodic electroactive microorganisms,—a cathode chamber (21) with at least one biocathode (22), and a cathodic electrolyte (24) with a cathodic electroactive microorganisms. The anode chamber (11) is separated from the cathode chamber (21) by, running from the anode chamber to the cathode chamber, a cation exchange membrane (31) and an anion exchange membrane (32). The cation and anion exchange membranes are separated from each other by an inter-membrane chamber (30), and means for applying a potential difference between the interconnected bioanodes and the biocathode/biocathodes. The bioanodes and biocathode/biocathodes have active surfaces such that the total active surface of the biocathode/biocathodes (22) is greater than the total active surface of the two bioanodes (12, 13). The arrangement includes a method for regenerating the activity of the bioanodes of the reactor and to the use of said reactor for the electrosynthesis of organic acids and/or alcohols from organic waste.

Claims

1. A bioelectrochemical reactor comprising: an anode compartment comprising at least two anodes, called bioanodes, and an anode electrolyte comprising anodic electroactive microorganisms, a cathode compartment comprising at least one cathode, called a biocathode, and a cathode electrolyte comprising cathodic electroactive microorganisms, the anode compartment being separated from the cathode compartment by, running from the anode compartment to the cathode compartment, a cation exchange membrane and an anion exchange membrane, said cation and anion exchange membranes being separated from one another by an inter-membrane compartment, means for applying a potential difference between the bioanodes connected to one another and the one or more biocathodes, the bioanodes and one or more biocathodes having active areas such that the total active area of the one or more biocathodes is greater than the total active area of the two bioanodes.

2. The reactor as claimed in claim 1, wherein the bioanodes are removable.

3. The reactor as claimed in claim 1, wherein said reactor is a microbial electrosynthesis reactor, the anode compartment comprising one or more ports for injecting organic carbonaceous substrate, such as organic biowaste hydrolysates, the cathode compartment comprising one or more ports for injecting CO.sub.2 or for introducing an organic or inorganic carbon source and the inter-membrane compartment comprising a device for extracting the molecules synthesized within said reactor.

4. The reactor as claimed in claim 1, wherein the biocathode is a three-dimensional electrode.

5. The reactor as claimed in claim 4, wherein the biocathode comprises a granular material or takes the general form of a lattice.

6. The reactor as claimed in claim 4, wherein the biocathode comprises carbon grains arranged in a container made of stainless steel.

7. The reactor as claimed in claim 1, wherein the bioanodes take the general form of a panel, in particular a planar or rounded panel.

8. The reactor as claimed in claim 7, wherein the bioanodes are formed of a carbon fabric or felt, held in a metal frame, preferably a frame made of stainless steel.

9. The reactor as claimed in claim 1, wherein said reactor comprises means for regulating the pH, the temperature, and/or the electrolyte level.

10. A method for regenerating the activity of the bioanodes of the reactor as claimed in claim 2, comprising: a step of removing at least one of the bioanodes from the anode compartment, it being understood that at least one bioanode is left in the anode compartment, a step of cleaning, outside the reactor, said one or more removed bioanodes, then reintroducing them into the anode compartment, the reactor being kept in operation by applying a potential difference between the biocathode and the remaining bioanode in the anode compartment.

11. A method for regenerating the activity of the bioanodes of the reactor as claimed in claim 2, comprising: replacing at least one of the bioanodes of the anode compartment with an anode not colonized by electroactive microorganisms, it being understood that at least one bioanode is left in the anode compartment, the reactor being kept in operation by applying a potential difference between the biocathode and the remaining bioanode in the anode compartment.

12. The use of the reactor as claimed in claim 1 for the electrosynthesis of organic acids and/or alcohols from organic waste.

13. The use as claimed in claim 12, wherein the organic waste is chosen from: biowaste hydrolysates, hydrolyzed sludge from wastewater treatment plants, various organic liquid fractions from wastewater treatment plants, municipal wastewater after primary settling, organic industrial waste, agro-food waste, digestates from wastewater treatment plants, or a mixture of a plurality thereof.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0049] Other features and advantages of the invention will become apparent from the description below of non-limiting exemplary embodiments, with reference to the appended diagrams, in which:

[0050] FIG. 1 is a diagram of a bioelectrochemical reactor, according to the invention, showing the various compartments and the location of the bioelectrodes;

[0051] FIG. 2 is a diagram showing the possible regulation systems present in a reactor according to the invention (the electrodes not being shown for greater clarity);

[0052] FIG. 3 is a front view of the biocathode, FIG. 3A being a profile diagram of the biocathode of FIG. 3;

[0053] FIG. 4 is a front view of a bioanode, FIG. 4A being a profile diagram of said bioanode of FIG. 4;

[0054] FIG. 5 is a perspective view from above of a reactor according to the invention;

[0055] FIG. 6 shows the interior of the compartments of the reactor of FIG. 5;

[0056] FIG. 7 presents a graph showing the anodic current density of the reactor of FIG. 5, as a function of time, before and after regeneration of one of the bioanodes of the anode compartment.

EXAMPLES

[0057] With reference to the figures, the reactor according to the invention generally consists of three compartments separated by ion exchange membranes, namely: an anode compartment 11 containing two bioanodes 12 and 13 that are electrically connected to the outside the reactor, and a cathode compartment 21 comprising the biocathode 22, an anode compartment 11 being separated from the cathode compartment 21 by an inter-membrane compartment 30.

[0058] A cation exchange membrane 31 separates the anode compartment 11 from the inter-membrane compartment 30 and an anion exchange membrane 32 separates the cathode compartment 21 from the inter-membrane compartment 30.

[0059] The anode compartment 11 contains an anode electrolyte 14 comprising anodic electroactive microorganisms. The cathode compartment 21 contains a cathode electrolyte 24 comprising cathodic electroactive microorganisms.

[0060] A potential difference 2 is applied between the biocathode 22 and the two bioanodes 12 and 13. The anode compartment comprises in particular a port 3 for injecting organic carbonaceous substrate.

[0061] Various regulation systems, in said reactor according to the invention, may be incorporated into said reactor and are shown diagrammatically in FIG. 2. It is possible to have, in particular, a system for regulating the level of the anode liquid 4a and/or cathode liquid 4c, a system for regulating the anode pH 5a and/or cathode pH 5c, a system for regulating the temperature of the anode compartment 6a and/or of the cathode compartment 6c by means, for example, of a heating resistor 7a and/or 7c. Finally, a system for regulating the pressure of the gas phase 9a or 9c may be provided in each of the electrode, i.e. anode 8a or cathode 8c, compartments. Indeed, the reactor is closed by a cover 10.

[0062] One example of the structure of the cathode is shown in FIGS. 3 and 3A.

[0063] The biocathode 21 consists of a frame 27 with a size of 30×30 cm defining four housings in the example presented here. These housings incorporate metal baskets 23 with a thickness of between 4 and 5 cm in which carbon granules 25 are placed. The metal frame 27 is connected to a current collector 26 surmounting said frame.

[0064] One example of the structure of a bioanode is shown in FIGS. 4 and 4A (exploded view).

[0065] For example, the bioanode 12 consists of a metal frame 17 formed of two parallel walls which between them enclose two parallel stainless steel grids 18 housing a carbon fabric 15 between them. This carbon fabric 15 may take the form of a single element or the form of strips of fabric arranged in parallel as shown schematically in FIG. 4. The assembly is held together, for example, by means of bolts 19.

[0066] A more precise description of the bioelectrochemical reactor 1 according to the invention is shown schematically in FIGS. 6 and 7.

Example 1

[0067] The bioelectrochemical reactor 1 according to the invention, shown schematically in FIGS. 5 and 6, has been designed to replicate industrial conditions. This reactor comprises three compartments separated by two ion exchange membranes: an anode compartment 11 that contains two bioanodes 12 and 13 (which are electrically connected to the outside of the reactor). This compartment is separated by a cation exchange membrane 31 from an inter-membrane compartment 30 which is itself separated by an anion exchange membrane 32 from the cathode compartment 21 that contains the biocathode 22. The volumes of these three compartments are 5.25 L, 2 L and 5.25 L, respectively.

[0068] The size of each bioanode 12, 13 is 30×30 cm and it is less than 1 cm thick. The active areas of these two bioanodes is thus 0.36 m.sup.2, if the four faces of the two bioanodes are considered. The biocathode 22 comprises a volume of 1.2 L of carbon grains, which have an active area of approximately 3 m.sup.2, i.e. of the order of 10 times the total active area of the bioanodes.

[0069] These bioelectrodes are connected to a potentiostat (BioLogic®, France, VMP3 not shown, controlled by EC-Lab software), a potential difference of 1.1 V being imposed between the bioanodes and the biocathode.

[0070] Reference electrodes 33, 34 may be present in the anode 11 and/or cathode 12 compartments, respectively. In an industrial-scale reactor, these reference electrodes may be absent.

[0071] The cathode electrolyte 24 is BMP medium modified with 30 g/L of NaHCO.sub.3. The basic anode electrolyte 14 is composed of 12.5 g/L of Na.sub.2HPO.sub.4.7H.sub.2O, 3 g/L of KH.sub.2PO.sub.4, 0.5 g/L of NaCl, 1 g/L of NH.sub.4Cl and 30 g/L of NaHCO.sub.3. The electrolyte of the inter-membrane compartment 30 is composed of 35 g/L of KCI and 32.6 g/L of KH.sub.2PO.sub.4.

[0072] The pH of the anode electrolyte is kept at 7 by automatically injecting a K.sub.2CO.sub.3 solution into the anode compartment. The biowaste used is hydrolysates, highly loaded with organic matter, for example the COD value of which is between 100 and 150 g/L. These hydrolysates are introduced into the anode electrolyte by injecting a volume of 10 to 20 mL, either daily or when the anode current drops below approximately 0.5 A/m.sup.2.

[0073] A device (not shown) for collecting the molecules synthesized may be connected to the inter-membrane compartment.

[0074] A slight overpressure (for example 20-30 mbar) may be maintained in the gas space of the anode and cathode compartments, preventing air from entering these compartments.

Preparation of Inoculum for the Biocathode

[0075] In the case of application of the method of the invention to the electrosynthesis of organic acids or alcohols, the inoculum for the biocathode 22 may be prepared from an anaerobic digester sludge. The preparation consists in applying treatments to, on the one hand, inactivate methanogenic microorganisms which compete with the desired reaction and, on the other hand, to enrich the sludge with microorganisms of interest.

[0076] The first step consists in heat-treating the inoculum (at 90° C. for 20 minutes) which results in the methanogens being inactivated.

[0077] The second step consists in enriching the sludge with microorganisms of interest by adding hydrogen and carbon dioxide in a closed flask in batch mode. This operation may be repeated twice. The microorganisms of interest here comprise bacteria capable of using the electrons or hydrogen generated at the cathode to synthesize the desired compounds (organic acids or alcohols).

[0078] The culture resulting from this enrichment may be used directly and introduced into the cathode compartment 21 upon starting the reactor.

Example 2—Regeneration of a Bioanode

[0079] The reactor, such as described in example 1, was put into operation for a period of 140 days. A potential difference of 0.9 V was applied between, on the one hand, the bioanodes that are electrically connected to each other (arranged in parallel) and, on the other hand, the biocathode.

[0080] In order to quantify the activity of a bioanode, the most commonly used method is to measure the maximum current density that it is capable of producing in the presence of an organic substrate. The current density at the bioanodes was thus tracked as a function of time (see the curve in FIG. 7 showing the current density as a solid line).

[0081] After approximately 18 days, a decrease in this current density was observed, a sign of aging of the bioanodes (range A-A in FIG. 7). One of its bioanodes was then regenerated (arrow R) according to the following method:

[0082] The frame 17 and the current collector 16 of one of the removable bioanodes were removed from the anode compartment 11 by sliding within one of the slots 20 (see FIG. 6) cleaned using a detergent and then dried, the grid 18 made of stainless steel and the carbon fabrics 15 were replaced with new materials.

[0083] The new, renewed bioanode was then put back in the position closest to the membrane 31, the other bioanode having been moved into the other slot, closer to the outer wall of the reactor.

[0084] It can clearly be seen that after this replacement of one of the bioanodes, activity returns for at least forty days. Aging is then observed again from the peak B-B in FIG. 7. The second bioanode may then be replaced as presented above for the first bioanode.