Patent Application
20230123627
The present invention relates to the field of the biological treatment of effluents such as wastewater or sludge. It finds a particularly advantageous application in the field of hydrogen production by the biological treatment of these effluents.
The collection and treatment of effluents, and more specifically of wastewater, involve a significant consumption of energy. In addition, their energy potential is currently largely under-valued. The share of energy consumption in the United States is now estimated at 3% for the treatment of wastewater purification station effluents. In particular, the processes of aeration of basins, for the degradation by oxidation of biomass, involve a significant energy cost without making use of the energy potential of the biomass.
A typical energy recovery route for biomass from wastewater is anaerobic digestion. However, anaerobic digestion is limited to the anaerobic digestion of sludge and anaerobic treatment of industrial effluents with high organic load rates, otherwise the investment associated with the anaerobic digestion units is no longer profitable. In addition, anaerobic digestion requires a long residence time of the effluents in the anaerobic digestion units, for example more than two weeks, and requires coupling with an aerobic treatment to finalise the water purification.
Electrochemical systems coupled to microorganisms have emerged for the energy recovery of wastewater. These systems generally include electroactive biofilms. It is known on the one hand microbial fuel cells comprising an air cathode for the production of electricity. On the other hand, it is known microbial electrolysers for the production of hydrogen. However, these systems are limited by the low current densities that can pass through the electroactive biofilms. Their performance and their prospects for industrialisation therefore remain limited.
It is known from the document P. Belleville, et al., Low voltage water electrolysis: Decoupling hydrogen production using bioelectrochemical system, International Journal of Hydrogen Energy, 43 (32), 2018, p. 14867-14875, a system comprising a bioelectrochemical reactor comprising an assembly of microbial fuel cells, configured to oxidise biomass from wastewater and produce a mediator in its reduced form. The system further includes an electrolyser configured to oxidise the reduced mediator and thereby induce production of the hydrogen. However, the conversion of biomass by this system can still be optimised.
An object of the present invention is therefore to provide a device making it possible to optimise the conversion of biomass into a reduced mediator.
The other objects, features and advantages of the present invention will become apparent on examination of the following description and the accompanying drawings. It is understood that other advantages can be incorporated.
To achieve this objective, according to one embodiment there is provided a device for converting biomass into a redox mediator agent in reduced form, comprising an assembly of several microbial fuel cells connected in series by a fluidic flow line, each microbial fuel cell comprising:
Advantageously, the value of the external resistance of at least one of said two microbial fuel cells is distinct from the value of the external resistance of the other of said two microbial fuel cells, so as to favour, in at least one of said two microbial fuel cells, the fermentative microorganisms relative to the electroactive microorganisms and, in the other of said at least two microbial fuel cells, the electroactive microorganisms relative to the fermentative microorganisms.
Thus, the assembly of microbial fuel cells forms a bioelectrochemical reactor allowing the conversion of biomass, for example from wastewater, into the mediator in its reduced form. This conversion involves successive metabolic reactions by syntrophy between fermentative microorganisms and electroactive microorganisms. The assembly of microbial cells in series and an associated variation in external resistance along the assembly induces segregation of fermentative microorganisms and electroactive microorganisms along the assembly. Spatial segregation of the metabolic reactions involved in the conversion of biomass is therefore obtained along the assembly. This segregation of metabolic reactions maximises their yield and improves syntrophy between fermentative microorganisms and electroactive microorganisms.
Compared to existing solutions, the conversion device maximises the treatment of effluent biomass, and its energy recovery in the form of a reduced redox mediator. The device enables the energy recovery of effluents with an organic load that is too low for anaerobic digestion units. The device can also be associated with anaerobic digestion units to complete them. In addition, because the external resistance is spatially varied along the assembly, the conversion device maximises the processing of the biomass while being able to operate continuously.
A second aspect relates to a system for converting biomass into dihydrogen comprising:
The electrolyser is therefore designed ad hoc to the chosen mediator.
Thus, the production of dihydrogen is decoupled from the conversion of biomass, the mediator acting as an energy carrier for the production of dihydrogen. The energy efficiency of dihydrogen production is increased while reducing its production cost.
A third aspect relates to a biomass conversion method comprising:
Thus, the method achieves spatial variation of the external resistance in the microbial fuel cell assembly of the converter device, and thus induces segregation of fermentative microorganisms and electroactive microorganisms along the assembly.
Compared to existing solutions, the conversion method optimises the treatment of biomass and its energy recovery. The method makes it possible to reduce the cost of treating biomass, compared to solutions using turbines or by injecting air.
In addition, the method can be carried out on a continuous basis, by converting the biomass along the assembly.
The aims, objects, as well as the features and advantages of the invention will become more apparent from the detailed description of an embodiment thereof which is illustrated by the following accompanying drawings in which:
The drawings are given by way of example and are not limiting of the invention. They constitute schematic representations of principle intended to facilitate understanding of the invention and are not necessarily on the scale of practical applications. In particular, the relative dimensions of the components of the conversion device and/or of the conversion system are not representative of reality.
Before starting a detailed review of embodiments of the invention, the following are optional features of the first aspect of the invention which can optionally be used in combination or alternatively:
Optional features of the second aspect of the invention are set out below, which can optionally be used in combination or alternatively:
Optional features of the third aspect of the invention are set out below, which can optionally be used in combination or alternatively:
It is specified that in the context of the present invention, the term biomass generally designates organic material of human, plant, animal, bacterial or fungal origin.
The term “chemical oxygen demand”, abbreviated COD, of the biomass is understood to mean the concentration of oxidizable compounds present in the biomass, such as, for example, fermentable sugars.
The term “load” of the biomass is understood to mean the daily volume load, i.e. a quantity corresponding to the COD per volume passing through the device, over a day. The load can be determined by Q×[COD]/V, with Q the flow rate of the biomass and V its volume, or by τ×[COD], with τ the hydraulic retention time in the device, and more specifically in I assembly of microbial fuel cells.
In general and in the scope of the present invention, the term “redox mediator” is understood to mean a compound receiving at least one electron from another chemical compound, for example an electrode, during a reduction reaction, to go from an oxidised form to a reduced form, and giving up at least one electron to another chemical compound, for example an electrode, during an oxidation reaction, to go from a reduced form to an oxidised form.
The term “semi-permeable” describes a membrane which allows certain compounds in solution to pass through both sides of this membrane and which opposes the passage of other compounds in the same solution. For example, a semi-permeable membrane can be configured to let pass on either side of this membrane, molecules of a size less than a threshold size, while the passage of molecules of a size greater than this size is blocked. As an alternative or in addition, a semi-permeable membrane can be configured to allow only certain loaded species to pass. For example, a cationic semipermeable membrane only allows cations to pass by blocking anions.
By “active surface of an electrode”, this means the portion of the contact surface of at least one electrolyte and an electrode on which an electrode reaction occurs.
By a parameter “substantially equal/greater/less than” a given value is meant that this parameter is equal/greater/less than the given value, to within plus or minus 10%, or even to within plus or minus 5%, of this value.
In the detailed description which follows, use may be made of terms such as “previous”, “next”, “before”, “rear”, “upstream”, “downstream”. These terms are to be interpreted relatively in relation to the normal direction of flow of a fluid in the converter device and/or the converter system. For example, when a first element is located “upstream” of a second element, the first element is disposed closer to a point of origin of the flow of a fluid than the second element. On the contrary, when a first element is located “downstream” of a second element, the first element is disposed further from the point of origin of the fluid flow than the second element.
The system 2 for converting biomass 10 is now described with reference to
The system 2 comprises a device 1 for converting the biomass 10 into a redox mediator 11 in its reduced form 110. The device 1 is configured to degrade the biomass 10 and thus treat the effluent. In order to degrade the biomass 10, the device is more specifically configured to reduce the organic load of the biomass 10, hereinafter referred to as the biomass load, during the flow of the effluent in the device 1. The device 1 is further configured to create a reserve of chemical energy by the reduction of the mediator 11. This energy reserve can then be utilized by an electrolyser 21 configured to generate dihydrogen from the mediator 11 in its reduced form 110. The device 1 and the system 2 make it possible to enhance the energy power of the biomass of an effluent.
The general operation of the system 2 can be as follows, described with reference to
The system 2 comprises an electrolyser 21 configured to oxidise the mediator 11 from its reduced form 110 to its oxidised form 111. This oxidation reaction can be coupled with the reduction of hydrogen ions, or equally protons, of formula H+, to induce production of dihydrogen 20.
To produce dihydrogen 20 from the mediator 11 in its reduced form 110, the electrolyser 21 can comprise a first compartment 210 comprising an anode 2100 and a solution configured to enable oxidation of the mediator 11. The electrolyser can comprise a second compartment 211 comprising a cathode 2110 and a solution configured to enable the reduction of hydrogen ions. The first compartment 210 and the second compartment 211 can be separated so as to avoid the mixture of their respective solutions, while ensuring an ionic conductivity between the compartments 210, 211. For example, the first compartment 210 and the second compartment 211 can be separated by a semi-permeable membrane 212. The semi-permeable membrane 212 can more specifically be a cationic membrane, allowing cations to pass, and blocking anions.
Alternatively, to produce dihydrogen 20 from the mediator 11 in its reduced form 110, the electrolyser 21 can comprise a first compartment 210 comprising an anode 2100 and a solution configured to enable the oxidation of the mediator 11 and a second compartment 211 comprising a cathode 2110 and a solution configured to enable the reduction of hydrogen ions, the anode 2100 exhibiting an active surface at least twice, even three times, greater than an active surface of the cathode 2110. In this case, the electrolyser 21 can advantageously have no semi-permeable membrane 212 between the first and second compartments 210 and 211. Thus, the solution enabling the oxidation of the mediator 11 is the same as that enabling the reduction of hydrogen ions. If the electrolyser 21 has no semi-permeable membrane 212 between the first and second compartments 210 and 211, it is preferable that:
The electrolyser 21 can further comprise a generator 213 enabling to impose the circulation of an electric current between the anode 2100 and the cathode 2110. Preferably, the generator 213 imposes a voltage between the anode 2100 and the cathode 2110. This voltage is preferably greater than or equal to the absolute value of the difference between the redox potential of the mediator 11 between its oxidised form 111 and its reduced form 110 and the redox potential of the H+/H2 pair. This voltage is, for example, substantially equal to 1.5 V.
The following table shows the coulombic efficiency according to the presence or not of a phosphate buffer and of the surface ratio between the anode and the cathode (measurements taken at 1.5 V of voltage difference between the anode and the cathode of the electrolyser):
Thanks to the voltage imposed between the anode 2100 and the cathode 2110, the oxidation of the mediator 11 in the first compartment 210 can be induced according to the following reaction.
Medred→Medox+n e−
With Medred meaning the mediator 11 in its reduced form 110, Medox, meaning the mediator 11 in its oxidised form 111 and n, an integer greater than or equal to 1.
Thanks to the voltage imposed between the anode 2100 and the cathode 2110, the reduction of protons in the second compartment 211 can be induced according to the following reaction.
2H++2e−→H2(g)
The overall redox reaction can thus occur in the electrolyser according to the following reaction, according to an example where the oxidation of the mediator 11 brings an electron into play.
2Medred+2H+→2Medox+H2(g)
The use of a mediator 11 can enable to avoid a dioxygen production occurring during an electrolysis of the water. Thus, the risk of explosion linked to a reaction between dioxygen and dihydrogen is minimised, even avoided. The addition of a module configured to separate these gases prior to their reaction is not necessary.
According to an example, the electrolyser 21 has no microorganisms. Thus, the electrolyser does not bring any metabolic reaction into play, enabling the production of dihydrogen 20. The density of current circulating in the electrolyser is thus not limited by microorganisms. The production of dihydrogen at the electrolyser is thus optimised, which offers a viable way of enhancing an effluent for the production of hydrogen at a low cost.
The device 1 can be uncoupled from the electrolyser 21. The device 1 can more specifically be electrically independent from the electrolyser 21. Thus, the electric operating parameters applied to the electrolyser 21 can be distinct from the electric parameters applied to the device 1. These electric parameters can, for example, be the voltage and the current density. Contrary to the solutions, wherein an electrolyser is electrically coupled to a PCM, the conversion system 2 enables to independently adjust the electric parameters of the device 1 and the electric parameters of the electrolyser 21. The electric parameters of one from among the device 1 and the electrolyser 21 can thus not limit the operation of the other. The conversion of the biomass 10 to the mediator 11 in its reduced form 110, and the production of dihydrogen 20 from the mediator 11 in its reduced form 110, can thus be independently optimised.
The device 1 can be connected to the electrolyser 21 by a fluidic connecting line 22, configured to drive the mediator 11 in its reduced form 110 at least the device 1 to the electrolyser 21. Preferably, and as illustrated by
The device 1 for converting biomass 10 to the mediator 11 in its reduced form 110 is now described with reference to
As illustrated by
It is understood that the conversion of the biomass 10 to the mediator 11 in its reduced form 110 makes successive metabolic reactions occur by syntrophy between fermentative microorganisms 1200b and electroactive microorganisms 1200b. In order to optimise this conversion, the device 1 is configured to induce a segregation of the fermentative microorganisms 1200b and electroactive microorganisms 1200b along the assembly 12. The PCM assembly 12 can in particular comprise fermentative microorganisms and electroactive microorganisms, their relative proportions varying between at least two distinct PCMs of the assembly 12, even between each PCM of the assembly 12.
To induce this segregation along the assembly 12, the value of the external resistance 1203 of a PCM 120 is distinct from the value of the external resistance 1203 of at least one other PCM 120 of the assembly 12. More specifically, these resistance values are distinct at a given time t. The value of an external resistance 1203 of a PCM can in particular be distinct from the value of the external resistance 1203 of another consecutive PCM 120 of the assembly 12. For this, at least one PCM 120 can be electrically independent from one or other PCMs of the assembly 12. Preferably, each PCM is electrically independent from other PCMs of the assembly 12. Thus, the external resistance 1203 varies spatially along the assembly 12, in the flow direction of the effluent in the flow line 13. This direction is illustrated in
A low external resistance 1203 favours the load transfer in the PCM, and therefore favours the development of electroactive microorganisms 1200b, at the expense of that of the fermentative microorganisms 1200b. More specifically, when the external resistance 1203 is less than the internal resistance of a PCM, the load transfer is maximised between the anode 1200a and the electroactive microorganisms 1200b, which favours their development. Thus, the conversion of organic acids 10′ to the mediator 11 in its reduced form 110 is optimised.
According to the value of the external resistance 1203 of a PCM, it is understood that one from among the fermentative microorganisms 1200b and the electroactive microorganisms 1200b can be favoured in a PCM. With the value of the external resistance 1203 being spatially variable along the assembly 12, a segregation between fermentative microorganisms 1200b and electroactive microorganisms 1200b is obtained along the assembly 12. Furthermore, the spatial variation of the external resistance 1203 along the assembly 12 enables a treatment of the biomass 10 continuously, relative to a solution wherein the resistance would be varied only temporarily for a PCM, even a PCM assembly.
The assembly 12 can comprise a first PCM 120 group 120a and a second PCM 120 group 120b, following, for example consecutively, in the flow direction of the effluent in the flow line 13. According to this flow direction, the first group 120a is located before the second group 120b. Equally, the first group 120a is located upstream from the second group 120b. The two groups can both be halved from the PCMs 120 of the assembly 12. According to the example illustrated in
The external resistance 1203 of a PCM upstream from the assembly 12, for example of a PCM of the first group 120a, can be chosen so as to favour the fermentative microorganisms 1200b. The external resistance 1203 of a PCM downstream from the assembly 12, for example of the second group 120b, can be chosen so as to favour the electroactive microorganisms 1200b. Thus, the fermentative microorganisms 1200b can degrade the biomass 10 mainly in a first portion upstream from the assembly 12 in the flow direction, to supply organic acids to the electroactive microorganisms 1200b mainly in a second downstream portion of the assembly 12 in this direction. The PCMs 120 downstream from the assembly 12 can be more populated in electroactive microorganisms, using organic acids to reduce the mediator 11. According to an example, the value of the external resistance 1203 of a first PCM 120 of the assembly 12 is less than or equal to the value of the external resistance 1203 of a second PCM 120 of the same assembly 12. In particular, the first PCM 120 can be located before the second PCM 120 in the flow direction. The assembly 12 can exhibit a decreasing gradient of the external resistance 1203 on at least some of the PCMs 120 along the assembly. Thus, the relative proportions between the fermentative microorganisms 1200b and the electroactive microorganisms 1200b develop progressively along the assembly. By progressively, it is understood that the difference between the percentage of fermentative microorganisms 1200b or electroactive microorganisms 1200b relative to the total number of microorganisms, between two consecutive PCMs, is substantially less than 50%, even less than 30%, even less than 20%. The relative proportions between the fermentative microorganisms 1200b and the electroactive microorganisms 1200b in the biofilm can, for example, be deduced from the measurement of the concentrations of fermentation subproducts.
The internal resistance of a PCM corresponds to the sum of the resistances to the load transfers in the reactor, comprising the resistances of the connecting wires, the resistance of the anodic biofilm, the resistance of each of the electrolytes in the anodic compartment and in the cathodic compartment, the resistance of the membrane and the resistance of load transfer to the cathode. For a PCM, when the external resistance is equal to the internal resistance, it is known that the PCM produces the maximum electric power. Each external resistance 1203 can be between Rint-50 ohm and Rint+1000 ohm.
According to an example, the value of the external resistance 1203 of a PCM of the first group 120a is between 0.8 Rint<Rext<1.5 Rint. The value of the external resistance 1203 of at least one PCM 120 of the first group 120a can be greater than the value of the internal resistance of this PCM 120. For example, this PCM is the first PCM of the assembly 12 in the flow direction.
The value of the external resistance 1203 Rext of a PCM 120 of the second group 120e, even the last PCM of the assembly 12 in the flow direction, can be between Rint/10<Rext<4 Rint/5, with Rint the value of the internal resistance of this PCM 120. In the current solutions, the value of the external resistance 1203 is generally fixed to that of the internal resistance to maximise the electric current circulating in an electric circuit between the anode 1200a and the cathode 1201a. Contrary to these solutions, one objective is to favour the load transfer in a PCM downstream from the assembly 12, by imposing an external resistance 1203 less than the internal resistance of the PCM to optimise the reduction of the mediator 11. This load transfer can be more specifically favoured between the anode 1200a and the cathode 1201a, from the organic material (the biomass and/under the fermentation subproducts) to the mediator. The mediator can exhibit a redox potential greater than that of the organic material. The mediator can exhibit a redox potential of substantially 250 mV relative to the NHE. The difference of the external resistances 1203 between two consecutive PCMs can, for example, be less than 0.1 Rint. It is noted that this factor can vary, this factor depending in particular on the architecture of the assembly, on the number of PCMs and on the type of effluent.
The external resistance 1203 of at least one PCM 120 of the assembly 12 can be chosen according to the load of the biomass 10. For example, the external resistance 1203 of at least one PCM is chosen according to the COD of the biomass 10 supplied to the conversion device 1. The external resistance 1203 of the other PCMs can further be adapted according to an experimental or theoretical model connecting the load of the biomass 10 supplied and the planned development of this load along the assembly 12. The external resistance 1203 of each PCM of the assembly 12 can be chosen according to the load of the biomass 10 measured in each PCM. Thus, the segregation of the microorganisms 1200b can be adapted to the composition of the biomass 10, even adapted to the development of this composition along the assembly. The treatment of the biomass 10 and its conversion to the mediator 11 in its reduced form 110 are therefore also maximised.
According to an example, the external resistance 1203 of at least one PCM 120 of the assembly 12 can be chosen according to the concentration of acetate measured, for example, at the input of a PCM 120 of the assembly 12. For example, the resistance 1203 can be between Rint//10<Rext<4 Rint/5, when the concentration of acetate measured is greater than 5 mM. The electroactive microorganisms 1200b mainly use fermentation subproducts, and in particular subproducts of low molar mass such as acetate. The external resistance 1203 can therefore be adapted along the assembly 12 so as to favour the electroactive microorganisms 1200b when the concentration of acetate is sufficient. Thus, the segregation of microorganisms 1200b along the assembly 12 can be adapted to the conversion state of the biomass 10 during its transit in the device 1.
For this, the device 1 can comprise a module for characterising the biomass 10, for example prior to its supply the assembly 12. The module for characterising the biomass 10 can alternatively or complementarily be configured to measure the COD, even the concentration of acetate, the biomass 10 in at least one, even more, even each PCM 120 of the assembly 12.
The load of the biomass 10 can be evaluated from the chemical oxygen demand, abbreviated COD below. The COD is an indicative measurement of the quantity of oxygen which can be consumed by chemical reactions in a solution, and in particular in an aqueous solution, such as an effluent. The chemical reactions can more specifically be reactions of oxidations of oxidable compounds. The COD is generally expressed as mass of oxygen consumed relative to the volume of the solution. The measurement can, for example, be taken according to the standard test method for determining the chemical oxygen demand of water (ASTM D1252-06(2020)). In units of the international system, the COD can be expressed in milligrams per litre (mg/L). Typically, the COD makes it possible to quantify the quantity of oxidable organic material in water. For example, the COD makes it possible to quantify the quantity of oxidable pollutants present in effluents.
The load of the biomass 10 can be characterised by the concentration of volatile organic compounds which can be measured by high performance liquid chromatography (HPLC).
Any other indicator of the load of the biomass 10 can be provided. The online measuring modules of this indicator are known to a person skilled in the art. For example, the total organic carbon can be cited, corresponding to the carbon content linked to the organic substances dissolved and undissolved in a fluid. Moreover, the biochemical oxygen demand can be cited, corresponding to the quantity of biodegradable organic materials, by biochemical oxidation by microorganisms over a given time, typically 5 days. The biochemical oxygen demand only represents the most biodegradable organic compounds, while the COD relates to substantially the whole oxidable organic material.
The arrangement of the cascading PCMs makes it possible to improve the selectivity of the biological functions of each PCM and to maximise the production of the mediator in its reduced form 110 in the cathodic behaviour of the PCMs 120 of the second group 120b, for example in the last PCM 120 of the assembly 12. By cascade, this means that PCMs 120 are fluidically connected at least in series, even further in parallel, even by a combination of fluidic connections in series and in parallel, for example by the fluidic flow line 13. On all of these PCMs 20, the device 1 can comprise, in total, at least ten, even at least twenty PCMs 120. The greater the number of PCMs 120 connected together, the higher the volume of biomass 10 treated by the device 1, in a given time.
The assembly 12 comprises at least three PCMs 120 connected in series, even at least five, even at least ten PCMs in series. Synergically with the feature according to which the PCM assembly exhibits a decreasing gradient of the value of the external resistances 1203 along at least some of the assembly, the greater the number of PCMs connected in series, the more the external resistance 1203 can be adjusted spatially along this part of the assembly 12.
According to the example illustrated in
The device 1 can comprise several assemblies 12 connected in parallel by the fluidic flow line 13. Thus, the volume of biomass treated by the device, in a given time, can be increased. According to the example illustrated in
The fluidic flow line 13 can comprise one or more flow conduit(s) making it possible to connect the PCMs 120 of the assembly(ies) 12. For example, as illustrated in
As illustrated in
The fermentative microorganisms 1200b and/or the electroactive microorganisms 1200b can be chosen from among bacteria and fungi. More specifically, the fermentative microorganisms 1200b and/or the electroactive microorganisms 1200b are bacteria. The fermentative microorganisms 1200b and/or the electroactive microorganisms 1200b collected in the purification station can be inoculated to the device 1 prior to its use.
The mediator 11 can exhibit a redox potential barely dependent on variations in concentration of the mediator 11 between its oxidised form 111 and its reduced form 110. The mediator 11 can be buffered by an acid/base pair, and in particular a phosphate buffer comprising, for example, sodium hydrogen phosphate, of chemical formula Na2HPO4 and sodium dihydrogen phosphate, of formula NaH2PO4. Thus, the pH of the solution comprising the mediator is controlled, which makes it possible to avoid the degradation of the mediator. The mediator 11 can be comprised in a solution of controlled pH at least at the electrolyser 21, and preferably at the electrolyser 21 and of the conversion device 1. By at least one of these features, even synergically between these two features, the redox potential of the mediator is stabilised. The mediator 11 thus exhibits a great reversibility and a great stability for its conversion between its reduced form 110 and its oxidised form 111. The mediator thus stabilised can exhibit a redox potential relatively independent from the variations in concentration of the mediator between its oxidised form and its reduced form. The redox potential can in particular vary by less than +/−20%, even +/−10% of its standard value. The redox potential of the mediator is between 410 mV and 450 mV relative to the NHE, under standard conditions at pH=7 and at a temperature of T=25° C.
According to an example, the mediator 11 can exhibit a redox potential less than that of the O2/H2O pair. According to an example, the mediator 11 is a hexacyanoferrate complex. The iron atom of the hexacyanoferrate complex can exhibit an oxidation degree of (III) in its oxidised form 111, and an oxidation degree of (II) in its reduced form 110. The chemical formula of the mediator can be [Fe(CN)6]3− in its oxidised form 111 and [Fe(CN)6]4− in its reduced form 110. According to this example, the voltage between the cathode 2110 and the anode 2100 of the electrolyser 21 can be greater than or equal to 0.36 V to be greater than or equal to the absolute value of the difference between the redox potential of the H+/H2 pair and the redox potential of the mediator 11. Preferably, the voltage between the cathode 2110 and the anode 2100 of the electrolyser 21 can be substantially equal to 1 V. According to this example, the hexacyanoferrate complex can be comprised in a phosphate buffer solution of pH substantially equal to 7.
Examples of materials which could be used in the system 1 are now given.
For each PCM 120, the anode 1200a and the cathode 1201a can be graphite electrodes. The cationic semi-permeable membrane 1202 separating the first compartment 1200 and the second compartment 1201 of each PCM can be a perfluorinated Naflon®-type membrane.
In case of the presence of a semi-permeable membrane 212 of the electrolyser 21, the anode 2100 can be a nickel foam and the cathode 2110 can be graphite felt containing platinum. The semi-permeable membrane 212 separating the first compartment 210 and the second compartment 211 of the electrolyser 21 can be a cationic semi-permeable membrane.
In the case of the electrolyser 21 without a semi-permeable membrane 212, the 904L, 314 and 316L-type nickel or pure nickel alloys and the stainless steels of austenitic phases of 8% to 26% nickel, but also 0% to 7% molybdenum, are potentially constitutive materials of the cathode 2110. More specifically, as is illustrated in
Indicative compositions of solutions in the different compartments of the reactors are now given. In the anodic compartment 1200 of the PCM 120, the effluent can come from wastewater containing the biomass 10 and the composition of which depends on the activity sector (for example, urban, agribusiness or agricultural). In the cathodic compartment 1201 of the PCM 120 and in the compartment 210 of the electrolyser 21, the mediator 11 can be at a concentration of between 0.1 M and 10 M and stabilised at pH 7 with a phosphate buffer (for example, of composition 0.5 M of Na2HPO4 and 0.5 M of NaH2PO4). The compartment 211 of the electrolyser 21 can comprise a K2SO4 or Na2SO4 solution at a concentration of between 0.1 and 1 M and stabilised at pH 7 with a phosphate buffer (for example, of composition 0.5 M of Na2HPO4 and 0.5 M of NaH2PO4).
The method for converting biomass 10 implementing the conversion device 1, even the conversion system 2, described above, is now detailed. The method comprises a supply of biomass 10, for example of an effluent comprising the biomass 10, to the device 1. The method further comprises an adjustment of the value of the external resistance 1203 of at least one PCM 120, even of each PCM 120, according to the features described above. The method comprises a conversion of the biomass 10 to organic acids 10′ by the fermentative microorganisms 1200b, and a reduction of the mediator 11 of an oxidised form 111 to a reduced form 110.
The adjustment of the value of the external resistance 1203 of at least one PCM 120, even of each PCM 120, can be done according to the load of the biomass 10, or from an indicator of this load. For this, the method can comprise a step of measuring the load of the biomass 10, or from an indicator of this load, prior to its supply to the device 1 and/or during its flow in the device 1. As an example, a low COD value to activate the anodic transfer is substantially equal to 5 mg/L. Alternatively or complementarily, the hydraulic retention time of the effluent in the device 1 can be adapted according to the load of the biomass 10. In particular, the retention time of the effluent can be extended, the lower the load of the biomass 10 is. For this, the conversion device can comprise a pump 14, for example, disposed on the fluidic flow line 14 as illustrated in
The adjustment of the value of the external resistance 1203 can be done at regular intervals, for example, weekly, even daily. The regular adjustment of the external resistance makes it possible to improve the segregation of the microorganisms 1200b and therefore the production of the mediator 11 in its reduced form 110 when using the device 1. The adjustment of the value of the external resistance 1203 can be synchronised between the PCMs 120 or done independently between the PCMs 120.
The method can further comprise a supply of the mediator 11 in reduced form 110 to the electrolyser 21 and a production of dihydrogen 20 by the electrolyser 21 from the mediator 11 in reduced form 110.
The method can be implemented continuously. The method could be implemented continuously, it is understood that its steps are not necessarily successive. According to an example, the biomass 10 can be supplied continuously to the conversion device 1. According to an alternative or complementary example, the mediator 11 can circulate continuously from the device 1 to the electrolyser 21 and conversely. Synergically, with the feature according to which the mediator 11 exhibits a stabilised potential, the method thus enables a stable and continuous production of dihydrogen.
The method can further comprise an inoculation of the fermentative and/or electroactive microorganisms 1200b to the device 1. For example, a collection of the fermentative and/or electroactive microorganisms 1200b in the purification station can be done. The fermentative and/or electroactive microorganisms 1200b can then be inoculated to the device 1 prior to, or during, its use. When the fermentative and/or electroactive microorganisms 1200b are inoculated to the device 1 prior to its use, the method can comprise a stabilisation step configured such that the device 1 reaches stable performances for the treatment of the effluent and of the reduction of the mediator 11.
The conversion method can further comprise any step making it possible to obtain and/or implement a feature described above of the device 1 and/or of the conversion system 2.
In view of the description above, it clearly appears that the invention proposes a device making it possible to optimise the conversion of the biomass, for example from wastewater, to a reduced mediator. In particular, the invention makes it possible to maximise the conversion of fermentable sugars to the reduced mediator, which can be used for the production of hydrogen at a low cost by an electrolyser.
| Number | Date | Country | Kind |
|---|---|---|---|
| FR2003204 | Mar 2020 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/058282 | 3/30/2021 | WO |
