Apparatus and method for regulating microbial activity

Abstract

Apparatus and method for regulating microbial activity in organic waste streams for biogas production.

Description

[Technical Field]

[0001] The present invention broadly relates to apparatus and methods for regulating microbial activity in organic waste streams for biogas production. [Background technology]

[0002] Biogas is produced through the decomposition of organic matter in the absence of oxygen (known as anaerobic digestion). The resulting gas, composed mostly of methane (CH4) and carbon dioxide (CO2), can be used as fuel. Biogas is considered a low-emission fuel and can play a fundamental role in the decarburization of the energy matrix.

[0003] Anaerobic digesters generally comprise a chamber, an inlet for the raw materials, an outlet for the gas (which may be a vent or gas recovery outlet), and an outlet for the digested residue. They may also include means for mixing the reaction mixture to facilitate digestion. Anaerobic digesters can be quite large and may be constructed of concrete, including stainless steel, carbon steel, or concrete cast in site. Anaerobic digestion projects are typically large in scale due to high capital costs and long payback periods. Existing approaches to anaerobic digestion suffer from long hydraulic residence times and are vulnerable to operational variability.

[0004] Microbial electrolytic cells (MECs) typically operate under mild conditions and show promise in improving yields in biogas production starting from a wide range of organic feedstocks. However, existing MEC configurations are not suitable for use under large-scale, industrial conditions. [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] The object of the present invention is to provide a sustainable waste-energy process that recovers energy from waste by upgrading CO2 to biomethane, to make at least some progress in addressing one or more of the above drawbacks, and / or to provide at least a useful alternative to the public.

[0006] Other objects of the present invention will become apparent from the following description, which is given for illustrative purposes only. [Means for solving the problem]

[0007] Any consideration of documents, actions, materials, devices, articles, etc., contained herein is intended solely to provide context for the present invention. It should not be construed as acknowledging that any or all of these matters form part of the foundation of the prior art, or were common general knowledge in the art related to the present invention prior to the priority date.

[0008] (Summary of the invention) In a first aspect, the present invention provides a bioelectrode comprising a bacterial biofilm, the bioelectrode having a porous structure with a pore size within a certain range.

[0009] In a second aspect, the present invention provides a microbial electrolytic cell (MEC) comprising a solid cathode, a solid anode, and an electroactive biofilm.

[0010] In a third aspect, the present invention provides a process for colonizing a bioelectrode using microorganisms, comprising the steps of bringing a mixture comprising microorganisms into contact with an electrode, and applying a potential to the electrode during the contact step.

[0011] In a fourth aspect, the present invention provides a process for anaerobic digestion of a raw material in an anaerobic digester, the process comprising: supplying the raw material to a chamber of the anaerobic digester to form a reaction solution therein; contacting the reaction solution with a biocathode of a microbial electrolysis cell comprising a biocathode and a counter electrode; and applying a potential to the reaction solution.

[0012] In a fifth aspect, the present invention provides an external module comprising a chamber, the chamber being adapted to be in fluid communication with a chamber of an anaerobic digester.

[0013] In a sixth aspect, the present invention provides an anaerobic digester comprising a biocathode according to the first aspect.

[0014] The following embodiments and preferred forms may relate to any of the above aspects, either alone or in any combination of any two or more.

[0015] In some embodiments, the biocathode comprises primary pores in a first size range and secondary pores in a second size range.

[0016] In some embodiments, the biocathode comprises a biocompatible material and / or a carbon-based material, such as a felt, paper, carbon, metal or plastic-based sintered porous material.

[0017] In some embodiments, the electrode comprises fiber strands. In some embodiments, the fibers form a 3D open structure of primary pores. In some embodiments, the secondary pores are provided as recesses. In some embodiments, the recesses are formed by pretreatment of the fibers. Optionally, the pretreatment includes applying a potential to the electrode.

[0018] In some embodiments, the electrode surface is functionalized by an immobilized microorganism, enzyme, or catalyst material.

[0019] In some embodiments, the electrode is at least 1 m 2 / g, more preferably at least 2 m 2 and has a surface area of / g or more.

[0020] In some embodiments, the biofilm is a mature biofilm.

[0021] Preferably, the biofilm comprises at least one methanogenic microorganism and at least one electroactive microorganism.

[0022] In some embodiments, the MEC of the second aspect comprises a bioreactor electrode according to the first aspect.

[0023] In some embodiments, the MEC further comprises a dielectric material between the cathode and the anode.

[0024] In some embodiments, the potential applied during the step of contacting the electrode with the mixture comprising the microorganism is about +1.5 V / SCE.

[0025] In some embodiments, the potential is applied for a period of at least about 1 hour, preferably at least about 2 hours, more preferably about 2 hours during the contacting step. A shorter time can be used to promote the attachment of the microorganism, but the time can optionally be longer, for example, up to about 8 hours or more.

[0026] In some embodiments, the potential applied during the contacting step is the anode potential, and the microorganism forming colonies on the bioreactor electrode comprises a methanogenic microorganism.

[0027] In some embodiments, this process further comprises a pre-anodic oxidation step of applying an anode potential to the electrode before the contacting step. In some embodiments, the pre-anodic oxidation step comprises applying a potential of about +1.5 V / SCE.

[0028] In some embodiments, the potential is applied to the electrodes in cycles during the pre-anodic oxidation process. In some embodiments, the cycle is approximately 15 minutes on, 15 minutes off. Optionally, continuous cycles can be applied over a period of approximately 24 hours.

[0029] In some embodiments, the bioelectrode of the microbial electrolytic cell is located within the chamber of the anaerobic digester.

[0030] In a preferred embodiment, the bioelectrode comprises a biofilm.

[0031] In various embodiments of the second or further aspects, the bioelectrode is a bioelectrode according to the first aspect. In some embodiments, the bioelectrode is a cathode. The cathode may optionally be adapted to act favorably for direct methane production or to act favorably for direct interspecies electron transfer. In such embodiments, the cathode may optionally comprise a material such as graphite felt or stainless steel, as described herein.

[0032] In some embodiments, the bioelectrode is separated from the counter electrode by a dielectric material.

[0033] In some embodiments, the anaerobic digester comprises a microbial community with suspended microorganisms, and the bioelectrode of the microbial electrolytic cell comprises a microbial biofilm.

[0034] In some embodiments, the microbial electrolytic cell is located inside the chamber of the anaerobic digester. In other embodiments, the microbial electrolytic cell is located outside the chamber of the anaerobic digester and is in fluid communication with the chamber.

[0035] In some embodiments, the voltage applied between the bioelectrode and the counter electrode during the anaerobic digestion process is greater than 100mV, greater than 300mV, or greater than 600mV. Preferably, the voltage applied between the bioelectrode and the counter electrode is in the range of 600mV to 1200mV, more preferably in the range of 800mV to 1000mV.

[0036] In some embodiments, the temperature inside the anaerobic digester is in the range of about 30 to about 45°C, preferably about 39 to about 42°C, or about 35 to about 39°C, more preferably about 38°C.

[0037] Optionally, the raw materials / reaction solution may comprise municipal wastewater and / or fertilizer having a total solid content of preferably 1-10%, more preferably 1-5% or 5-7%.

[0038] In some embodiments, the chamber of the external module is adapted to receive a bioelectrode according to the first embodiment.

[0039] In some embodiments, the external module chamber further comprises a bioelectrode according to the first embodiment.

[0040] In some embodiments, the bioelectrode of the first embodiment is produced by the process of the third embodiment.

[0041] In some embodiments, the external module further comprises a pump for exchanging fluid between the external module's chamber and the anaerobic digester's chamber.

[0042] In some embodiments, the external module is adapted to be stackable with other external modules.

[0043] The present invention may also be broadly said to consist of any or all combinations of two or more parts, elements, or features, individually or collectively, of the parts, elements, and features referred to or shown in the specification of this application, and where a particular integer having known equivalents in the art to which the present invention relates is referred herein, such known equivalents shall be deemed to be incorporated herein as if they were described separately.

[0044] References to the range of numbers disclosed herein (e.g., 1 to 10) also incorporate references to all rational numbers within that range (e.g., 1, 1.1, 2, 3, 3.9, 4, 5, 6, 6.5, 7, 8, 9, and 10), and also references to any range of rational numbers within that range (e.g., 2 to 8, 1.5 to 5.5, and 3.1 to 4.7). Therefore, all subranges of all ranges expressly disclosed herein are intended to be expressly disclosed by this specification. These are merely examples of what is specifically intended, and all possible combinations of numerical values ​​between the listed minimum and maximum values ​​should be considered to be expressly stated in this application in a similar manner.

[0045] Where references are made herein to patent specifications, other external documents, or other sources of information, these are generally for the purpose of providing a context for considering the features of the present invention. Unless otherwise specified, references to such external documents should not be construed as an acknowledgment that such documents or sources of information constitute prior art or form part of the common general knowledge in any jurisdiction.

[0046] Those skilled in the art will be able to see many modifications to the structure of the invention, as well as a wide range of different embodiments and applications, without departing from the scope of the invention as defined in the appended claims. The disclosures and descriptions herein are purely illustrative and are not intended to be limiting in any sense.

[0047] While the present invention is broadly defined above, those skilled in the art will understand that the present invention is not limited thereto and also includes embodiments illustrated in the following description. [Brief explanation of the drawing]

[0048] The present invention will be described with reference to the accompanying drawings. [Figure 1] This shows a reactor according to the first embodiment of the present invention, which has an internal MEC. [Figure 2] This shows a reactor according to a second embodiment of the present invention, which has an external MEC. [Figure 3] This graph shows the average biogas production (L / d; bar) and methane content (percentage; circle) over a 6-week period for anaerobic digester (AD) reactors, as well as reactors with internal and external MEC (ModIn) and external MEC (ModEx) systems. [Figure 4] This graph compares the methane production rates (mL CH4 / L(reactor) / d) for anaerobic digestion (AD) reactors, as well as reactors with internal and external MEC (ModIn) and reactors with external MEC (ModEx). [Figure 5] This graph compares the chemical oxygen demand removal efficiency (%COD removal) of anaerobic digestion (AD) reactors, as well as reactors with internal and external MEC (ModIn) and external MEC (ModEx) systems. [Figure 6] This graph compares the methane conversion rate (MCR) for anaerobic digester (AD) reactors, reactors with internal MEC (ModIn), and reactors with external MEC (ModEx). [Figure 7] This is a plot of the increment in surface area over time when a 15-minute on / off cycle of 1.5V is applied to the anode of a graphite felt. [Figure 8] This is a plot of the increment in surface area over time of two graphite felt electrodes in Fe2SO4 electrolyte at concentrations of 4.3 mg / L (low) and 430 mg / L (high), respectively. [Figure 9]This graph compares the methane production rate (MPR) of anaerobic digester (AD) reactors with graphite felt or stainless steel cathodes, as well as reactors with internal MEC (ModIn) and external MEC (ModEx), using a complete cell potential control strategy at open-circuit potential (OCP). [Figure 10] This graph compares the methane production rate (MPR) for reactors with internal MEC (ModIn) and external MEC (ModEx), equipped with graphite felt or stainless steel cathodes, and using a total cell potential control strategy at a potential of 0.8V; and [Figure 11] This graph compares the methane production rate (MPR) for reactors with internal MEC (ModIn) and external MEC (ModEx) using a full-cell potential control strategy at a potential of 1.5V, with either graphite felt or stainless steel cathodes. [Modes for carrying out the invention]

[0049] definition The following definitions are provided to better define the present invention and as guidance for those skilled in the art in carrying it out. Unless otherwise specified, all technical and scientific terms used herein should be understood as having the same meaning as those understood by those skilled in the art in the relevant field to which this disclosure belongs.

[0050] The general chemical and biological terms used herein have their usual meanings.

[0051] Examples of definitions of common terms in microbiology, molecular biology, and biochemistry can be found in Methods for General and Molecular Microbiology, 3 rdEdition,CAReddy,et al.(eds.),ASM Press,(2008);Encyclopedia of Microbiology,2nd ed.,Joshua Lederburg,(ed.).Academic Press,(2000);Microbiology By Cliffs Notes,I.Edward Alcamo,Wiley,(1996);Dictionary of Microbiology and Molecular Biology,Singleton et al.(2d ed.)(1994);Biology of Microorganisms 11t h ed.Brock et al.,Pearson Prentice Hall,(2006);Biodiversity of Fungi:Inventory and Monitoring Methods,Mueller et al.Academic Press,(2004);Genes IX,Benjamin Lewin,Jones&Bartlett Publishing,(2007);H.The Encyclopedia of Molecular Biology,Kendrew et al.(eds.),Blackwell Science This can be found in Ltd., (1994); and Molecular Biology and Biotechnology: a Comprehensive Desk Reference, Robert A. Meyers (ed.), VCH Publishers, Inc., (1995).

[0052] As used herein and in the claims, the term “comprising” means “consisting at least in part of.” In interpreting each statement containing the term “comprising” within this specification and in the claims, other characteristics may exist besides those preceded by the term. Related terms such as “comprise,” “comprised,” and “comprises” should be interpreted similarly.

[0053] As used herein, the term "and / or" means "and" or "or," or both.

[0054] As used herein, "(s)" following a noun signifies the plural and / or singular form of the noun.

[0055] In one embodiment, the term “statistically significant” as used herein refers to the possibility that the outcome or relationship is caused by something other than chance. The outcome is known in the art and can be found to be statistically significant using the statistical hypothesis tests used. Statistical hypothesis tests provide a “p-value” that represents the probability that the measured outcome is due to chance alone, as is known in the art. It is generally accepted in the art that a significance level of 5% (0.05) or less is considered statistically significant.

[0056] As used herein, the term “microbial community” refers to a group of two or more microorganisms. The microorganisms exist in a suspended state and are also attached to the bioelectrode. In some embodiments, the microorganisms form a biofilm on the bioelectrode. The microbial community is not homogeneous throughout the reactor and electrodes, with some microorganisms being more suited to colonizing at the cathode, some at the anode, and some remaining suspended.

[0057] Anaerobic digestion system As used herein, “anaerobic digester” refers to a vessel in which anaerobic digestion takes place. Industrial anaerobic digesters are very large, but smaller vessels that may be suitable for a home site are also included in the term “anaerobic digester” as used herein. The reaction vessels described in the following examples are referred to herein as “reactors,” but can also be considered as “anaerobic digesters” as used herein.

[0058] Industrial anaerobic digesters are approximately 10,000 m³ 3 It can have a working volume in the order of up to 1m, and by connecting several smaller reactors in parallel, a larger capacity can be reached. Anaerobic digesters suitable for residential sites are smaller, up to 1m 3 Although it can have a relatively small working volume, anaerobic digesters on farms or agricultural sites typically require 100-200 m³. 3 The range may be as described above. Commercial anaerobic digesters for producing biogas are, for example, 100-1000 m³. 3 It could be, and the typical size is about 600m 3 The invention described herein is suitable for use in reactors having a working volume of any of these size ranges.

[0059] Anaerobic digestion has four stages: hydrolysis, acid production, acetic acid production, and methane production, each associated with a different microbial species. Anaerobic digestion processes include batch processes and continuous processes. In a batch process, the four stages proceed sequentially. Batch processes are typically slower and require larger volumes to achieve similar production to continuous processes. The present invention is suitable for either batch or continuous processes.

[0060] In one embodiment, the present invention relates to an anaerobic digester comprising a MEC as described herein. The MEC comprises at least a cathode and an anode. In the anaerobic digester of the present invention, the MEC can be provided in various ways. In some embodiments, the working electrode of the MEC is located within the chamber of the anaerobic digester, and the counter electrode of the MEC is located within the chamber of the anaerobic digester. In other embodiments, the working electrode of the MEC is located within the chamber of the anaerobic digester, and the counter electrode of the MEC forms part of the chamber wall. In other embodiments, the working electrode and counter electrode of the MEC are located outside the chamber of the anaerobic digester and are in fluid communication with the chamber of the anaerobic digester, for example, by the arrangement of an external module as described herein. This provides a simple means of retrofitting an existing anaerobic digester as an MEC anaerobic digestion system.

[0061] The reaction rate can be improved by mixing the raw materials to improve the transport of reactants between the bulk raw materials and the cathode and / or anode surfaces. For example, the means for mixing the reaction mixture may include pumps and circulation lines, impellers, baffles, deflectors, rotor / stator pairs, propellers, stirrers, screws, or other mixing means, or geometric features of a chamber or external module such as features related to an inlet or outlet.

[0062] In some embodiments, the cathode and / or anode may form part of or be associated with one or more blades of an impeller or other mixing means.

[0063] In some embodiments, the cathode and / or anode may form part of or be associated with one or more baffles inside the chamber.

[0064] In some embodiments, the cathode and / or anode may be positioned in close proximity to one or more blades of an impeller or other mixing means, or to the inlet or outlet of a pump circulation line, or to one or more baffles in the chamber of an anaerobic digester, or to one or more baffles in the chamber of an external module.

[0065] raw material The present invention may utilize organic waste as a raw material. The raw material may be organic waste or organic waste flow, for example, organic raw materials comprising urban wastewater, fertilizer, food waste, biosolids, food waste, spent grain, or yeast. Upon entering an anaerobic digester, the raw material begins to digest and its composition changes. During the digestion stage, the raw material is called the "reaction solution." When the reaction solution leaves the anaerobic digester, it is called the digested residue. The digested residue can be used as fertilizer.

[0066] In some embodiments, the raw materials undergo pretreatment or conditioning steps, typically including temperature control, particularly when legal requirements mandate heat treatment of the raw materials for hygienic reasons.

[0067] Depending on the circumstances, further pretreatment and adjustment steps may be carried out, such as adjusting the water content by diluting with water, or reducing the particle size distribution of the solid by using a hammer mill or grinding pump.

[0068] If the lignocellulose content of the waste is high, it is recommended to add co-inoculations to the raw materials, such as zebra fertilizer, horse manure fertilizer, or another organic fertilizer containing a high concentration of lignocellulose. The co-inoculations are preferably heterogeneous in composition, size, and structure, and can be easily decomposed by enzymes or bacteria.

[0069] Microbial electrolytic cell (MEC) The MEC comprises a solid cathode, a solid anode, and an electroactive biofilm. In some embodiments, the MEC further comprises a reference electrode. The cathode and anode are connected to one or more power sources or potentiostats. When in use, the MEC is immersed in a conductive electrolyte in the presence of microorganisms and a reaction solution.

[0070] Optionally, the MEC further comprises dielectric material. Connections between the anode, cathode, and, if present, the reference electrode can be appropriately made via electrical connectors made of corrosion-resistant material.

[0071] At least one of the cathode and / or anode of the MEC comprises an electroactive biofilm.

[0072] In some embodiments, the anode comprises an anode biofilm comprising a first group of microorganisms and a solid electrode. As discussed herein, the first group of microorganisms can be grown on the electrode. Optionally, the anode may further comprise a mechanical support on which the biofilm can be formed.

[0073] In some embodiments, the cathode comprises a cathode biofilm comprising a second group of microorganisms and a solid electrode. As discussed herein, the second group of microorganisms can be grown on the electrode. Optionally, the cathode may further comprise a mechanical support on which the biofilm can be formed.

[0074] The installation of the MEC as an internal unit within an anaerobic digester must accommodate the raw material inlet, waste and off-gas outlets, and any heating, monitoring, or sampling equipment already present in the anaerobic digester, while also providing the necessary electrical connections and maintenance access. The configuration of the MEC is also determined by the size of the electrodes, and the flow dynamics, mixing, and contact between the electrodes and the reaction fluid must be addressed, for example, by using an impeller or baffle arrangement as discussed herein.

[0075] Physical arrangement between cathode and anode In some embodiments, the cathode and anode can be appropriately positioned relative to each other to reduce ohmic overvoltage due to internal electrical resistance. For example, ohmic overvoltage can be reduced by decreasing the distance between the electrodes.

[0076] In some embodiments, the cathode and anode can be appropriately positioned relative to each other to facilitate the fermentation through the anaerobic digester or external module. In some embodiments, the cathode and anode can be appropriately positioned relative to each other to minimize the shear forces acting in the digested residue. This can be achieved, for example, by modeling the interior of the AD using computational fluid dynamics.

[0077] In some embodiments, the cathode and anode can be appropriately positioned relative to each other to provide adequate space for biofilm growth. For example, the biofilm can grow up to a thickness of 2 cm. The electrodes must be sufficiently spaced apart to avoid contact between biofilms growing on the electrodes. Preferably, the electrodes are spaced more than 2 mm apart. In some embodiments, the electrodes are spaced 2 to 50 mm apart, for example, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 45, or 50 mm apart.

[0078] Direct contact between the cathode and anode should be avoided because the digested residue does not act as an electrolyte. Therefore, in some embodiments, the cathode and anode are separated by a dielectric material.

[0079] Dielectric materials The dielectric material includes a non-conductive insulator to avoid direct contact between electrodes. It may be made from polyester, such as a stretched polyester film like biaxially oriented polyethylene terephthalate (BoPET) (e.g., Mylar™), or polypropylene. Alternatively, polytetrafluoroethylene (e.g., Teflon™), nonwoven materials, or other plastics may be used.

[0080] Electrode architecture / design For durability, electrodes are preferably solid rather than gel or electrolyte. Connectors may preferably be made of corrosion-resistant materials, such as titanium, stainless steel, graphite sheets, carbon felt, or coated metal. To reduce energy consumption, the electrode material is preferably selected to keep ohms and activation overpotentials to a minimum.

[0081] In some embodiments, the bioelectrode comprises a biocompatible material and / or carbon system material, such as felt, paper, carbon, metal, or plastic-based sintered or porous material.

[0082] The electrode surface can, advantageously, have a porous structure having a range of pore sizes. In some embodiments, the electrode surface comprises primary pores of a first size range and secondary pores of a second, smaller size range. The primary pores may be provided as a three-dimensional (3D) open structure. This provides attachment sites for electroactive microorganisms and improves mass transport. The smaller secondary pores increase the surface area and directly promote methane production.

[0083] Increasing the range of pore sizes in an open 3D structure provides an increase in surface area; smaller pores are useful for microbial colony formation, while larger pores reduce clogging.

[0084] In some embodiments, the electrode comprises fiber strands, which form a 3D open structure of primary pores. For example, the spaces between the fiber strands may be on the order of size of about 10 μm or more, allowing for the movement of microorganisms through the electrode. Secondary pores can be formed by processing the fibers. In some embodiments, secondary pores are formed by applying an anodic potential to the electrode (pre-anodic oxidation step). As described herein, “secondary pores” may also refer to surface depressions. Surface depressions of fibers, approximately 1 μm in size, are comparable in size to microbial cells. They can provide an increase in surface area and improve the roughness necessary for microbial adhesion.

[0085] Optionally, the fiber or electrode surface can be treated to promote microbial attachment, for example, by heat treatment, or using plasma or etching techniques.

[0086] Optionally, the electrode surface is functionalized with immobilized microorganisms, enzymes, or other catalytic materials, such as titanium having catalytic properties for hydrogen production.

[0087] Preferably, the electrode has a surface area of at least 1 m 2 / g, more preferably at least 2 m 2 / g, for example at least 3 m 2 / g or at least 4 m 2 / g.

[0088] The pretreatment of the electrode for forming the biofilm will be further described below.

[0089] In some embodiments, the electrode comprises a material that favors direct methane production, such as stainless steel or a graphite plate. In other embodiments, the electrode comprises a material that favors direct interspecies electron transfer (DIET), such as a carbon felt.

[0090] In some preferred embodiments, the electrodes can be selected with reference to the raw material to be digested. Depending on their composition, different raw materials reach bottlenecks at different stages of the anaerobic digestion process. For example, manure contains a high content of lignocellulosic biomass, and the bottleneck stage is the hydrolysis stage, and thus the selection of GF electrodes to promote hydrolytic microorganisms can be considered. Municipal wastewater or food waste is more easily hydrolyzed, and the bottleneck is in the final methane production stage, in which case, despite being more expensive than a stainless steel cathode, a GF cathode can be selected to promote methanogenic bacteria. Furthermore, raw materials containing solid materials are more likely to contaminate porous electrodes, so non-porous electrodes can be considered.

[0091] Microorganisms The present invention uses a microbial community comprising one or more microorganisms selected from the operational classification units (OTUs): hydrolyzable microorganisms, acid-producing microorganisms, acetate-producing microorganisms, and methane-producing microorganisms, preferably comprising both acetolactate-type microorganisms and hydrogen-assimilating microorganisms.

[0092] While a hybrid consortium implies the coexistence of both biofilms and suspension cells, OTUs are not evenly distributed between biofilms and suspension cells, but rather are associated with environments more favorable to their metabolism. Microbial species active in the oxidation stage of anaerobic digestion (hydrolysis, acetic acid production) tend to prefer the anode, while methane-producing microorganisms are active in the methane-producing stage associated with the cathode.

[0093] The cathode is the source of electrons for methane production, but methane-producing microorganisms are negatively charged and do not interact with the cathode due to electrostatic repulsion. Other microbial species can transfer electrons from the cathode to methane-producing microorganisms via direct interspecific electron transfer (DIET).

[0094] The microbial community may include methanogenic microorganisms, such as archaea that can be obtained from animal manure; electroactive microorganisms that can electrically interact with solid electrodes; microorganisms that can directly perform interspecies electron transfer, such as electron transfer between electroactive microorganisms and methanogenic microorganisms; and microorganisms that produce extracellular polymeric substances (EPS), such as exopolysaccharides, which can act as anchors for forming biofilms. Optionally, the microbial community may comprise microorganisms that perform two or more of these roles. In some embodiments, the various species of the microbial community can be obtained from animal manure.

[0095] Colony-forming units (CFUs) are units used to estimate the number of viable cells in a sample. Determining colony-forming units requires culturing microorganisms and counting only viable cells, i.e., cells capable of growing and forming visible colonies.

[0096] Precolony formation of electrodes Before or during the operation of an anaerobic digester, a biofilm forms on the cathode and anode, thereby forming bioelectrodes. This process can be enhanced by applying an electrical potential to the electrodes, which attracts electroactive microorganisms toward the electrodes through electrostatic attraction.

[0097] In some embodiments, a biofilm, preferably a mature biofilm, is formed on the electrode as a pretreatment before use in an anaerobic digestion system. Preferably, the biofilm comprises at least one methane-producing microorganism and at least one electroactive microorganism.

[0098] Mature biofilms act as a natural defense mechanism against environmental changes, including pH fluctuations and the presence of toxins, thereby increasing the overall resilience of the system.

[0099] By controlling the polarity of solid electrodes, it is possible to control their function as electron donors / acceptors and promote the maturation of biofilms on specific electrodes.

[0100] Accordingly, in one embodiment, the present invention provides a process for colonizing a bioelectrode using microorganisms, comprising the steps of bringing a mixture comprising microorganisms into contact with an electrode, and applying a potential to the electrode during the contact step.

[0101] The applied potential is preferably greater than 300mV and less than 2000mV, more preferably in the range of 600mV to 1200mV, and even more preferably in the range of 800 to 1000mV.

[0102] In some embodiments, the bioelectrode is intended to be used as a biocathode, and the applied potential is the anode potential. That is, the bioelectrode acts as an anode during the colonization process. The anode potential attracts electroactive microorganisms that are not attracted to the cathode. Optionally, prior to the colonization process, the process includes a step of applying the anode potential to the electrode to form secondary pores (the pre-anodic oxidation step described above).

[0103] Biofilms generally take some time to form on electrodes, typically on the order of several days.

[0104] In some embodiments, the presence of a biofilm on an electrode can be detected by a change in current.

[0105] Pre-colonization of biofilms on electrodes offers advantages when the intended raw material does not have a suitable microbiome for anaerobic digestion. For example, methane-producing bacteria are anaerobic, oxygen-sensitive, and not present in sufficient quantities in urban wastewater to effectively colonize electrodes. Conventional anaerobic digestion processes typically use high proportions of co-inoculated material, such as up to 10 kg of fertilizer:90 kg of food waste. Pre-seeding of biofilms on electrodes avoids the need for large amounts of co-inoculation.

[0106] Anaerobic digestion process In one embodiment, the present invention relates to a process for the anaerobic digestion of raw materials in an anaerobic digester, wherein this process - The raw materials are supplied to the chamber of the anaerobic digester, and a reaction solution is formed within the anaerobic digester. - The raw material is brought into contact with the bioelectrode of a microbial electrolytic cell (MEC) equipped with a bioelectrode and a counter electrode. - This includes applying an electrical potential between a bioelectrode and a counter electrode.

[0107] Steady-state operation of an anaerobic digestion process can usually be achieved after approximately three hydrological residence time (HRT) periods. For example, if the HRT is 20 days, steady-state operation can be reached after approximately 60 days.

[0108] The process of the present invention increases the overall methane production rate by using a low voltage. This reduces the hydraulic residence time (HRT) required to complete the reaction, and therefore reduces the size of the system required to handle a given raw material, thereby reducing the cost of operating the system.

[0109] The process of the present invention increases resilience to operational fluctuations caused by the formation of mature electrobiofilms, which is a natural formation that separates cell residence time from hydrological residence time, thereby increasing the microbial population in the system.

[0110] Lower operating temperatures require less energy consumption for heating but reduce the reaction rate. In some embodiments, the operating temperature range is about 30 to about 45°C, for example, about 35 to about 45°C, about 35 to about 42°C, about 38 to about 42°C, or about 35 to about 40°C. Preferably, the operating temperature range is about 39 to about 42°C, or about 35 to about 39°C.

[0111] External module In one embodiment, the present invention relates to an external module comprising a chamber, wherein the chamber is adapted to be in fluid communication with the chamber of an anaerobic digester.

[0112] Advantageously, the external module can be retrofitted to existing anaerobic digesters. It also offers ease of MEC replacement, ease of MEC maintenance, and ease of combining multiple MECs into a single anaerobic digester. Therefore, the external module provides a "plug-and-play" solution for improving the performance and operation of anaerobic digesters.

[0113] The external module may include inlets and outlets for the reaction fluid to pass through, the necessary electrical connections, and optionally include ports or openings for maintenance access and sensors for monitoring the digestion process. The external module may also be configured to accommodate the entire surface area of ​​the electrodes.

[0114] Applied potential The voltage or potential applied by a power source, multiple power sources, or potentiostat should overcome ohms, diffusion, and activation overpotentials to ensure that nutrients and reagents effectively reach the reaction site and that the electroactive biofilm can capture the electron donor / receptor capacity of the relevant electrodes.

[0115] The voltage can be applied as the full cell potential or as a half-cell potential pair with a reference electrode. Using a full-cell potential control strategy, only two electrodes (working electrode and counter electrode) function both for potential difference control and as an electrical circuit for conducting the resulting current, i.e., the potential between the two half-cells. Using a half-cell potential control strategy, the anode or cathode is connected to a reference or pseudo-reference electrode, and a controller is used to maintain the voltage between the working electrode and the reference or pseudo-reference electrode, allowing a minimum current to flow through it and direct it towards the counter electrode.

[0116] The applied voltage is preferably greater than 300mV and less than 2000mV, more preferably in the range of 600mV to 1200mV, and even more preferably 800mV to 1000mV.

[0117] Optionally, the voltage can be applied intermittently, and a variable renewable energy source, such as a photovoltaic panel or wind power, can be used. [Examples]

[0118] Example 1 - Anaerobic digester with internal MEC Figure 1 shows a schematic diagram of an anaerobic digester 100 comprising a reactor having a body 10 surrounding a reaction chamber 12. The reactor is provided with a source for supplying raw materials 14 to the reaction chamber 12 via a pump 16. The raw materials are organic raw materials as described herein. The pump 16 may be a softening pump, a peristaltic pump, a progressive cavitation pump, a centrifugal pump, or other pump suitable for supplying raw materials to the reaction chamber 12.

[0119] Once inside the reaction chamber 12, the raw materials (referred to as the reaction solution) remain in the reaction chamber for a sufficient time for anaerobic digestion to occur (the hydraulic residence time of the raw materials as discussed herein). In the example shown, the raw materials may be circulated within the reaction chamber 12 via the circulation line 18 and the pump 20. Valves 22 and 24 control the use of the circulation line 18.

[0120] In embodiments of the present invention having electrodes inside the reaction chamber 12, the circulation line 18 improves the circulation of the raw materials, but the circulation line 18 is not required. Optionally, alternative means for circulating the reaction mixture within the reaction chamber can be provided, such as an impeller chamber or baffle as discussed herein.

[0121] The MEC is provided in the form of an anode 26 and a cathode 28 connected by a power supply 30. The temperature is maintained by a heater 32 and controlled by a temperature control TC.

[0122] The gases generated within the reaction chamber 12 collect in the headspace of the reaction chamber and exit through a gas line 34 controlled by a valve 36. They are then collected in a container 38, which may be, for example, a gas bag. A valve 40 provides gas control. The reaction liquid exits the reaction chamber through an outlet line 42 controlled by a pump 44 and is then called digested residue, which is received in a digested residue storage unit 46. It will be understood that the exchange of raw materials within the reaction chamber can be achieved using only one of the pumps 16 and 44. In this embodiment, the raw materials are exchanged at a rate of 1 L / day, which corresponds to an exchange rate of approximately 5% of the working volume of the reaction chamber per day.

[0123] Example 2 - Anaerobic digester with external MEC module Figure 2 shows a schematic diagram of an anaerobic digester 200 comprising a reactor having a body 110 surrounding a reaction chamber 112. The reactor is provided with a raw material source 114 supplied to the reaction chamber 112 via a pump 116. The raw material is an organic raw material as described herein. The pump 116 may be a softening pump, a peristaltic pump, a progressive cavitation pump, a centrifugal pump, or another pump suitable for supplying the raw material to the reaction chamber 112. The temperature inside the reaction chamber 112 is maintained by a heater 132 and controlled by a temperature control TC.

[0124] Once inside the reaction chamber 112, the reaction liquid remains within the chamber for a sufficient time for anaerobic digestion to occur (the hydraulic residence time of the reaction liquid as described herein). The reaction liquid is circulated within the reaction chamber 112 via a circulation line 118 and pumps 120, 131 controlled by valves 122, 124, and 131. As shown in the figure, after passing through the circulation line 118 and pump 120, the reaction liquid enters the external module 127. The MEC is located within the external module 127 and includes an anode 126 and a cathode 128 connected by a power supply 130.

[0125] The gases generated in the reaction chamber 112 collect in the headspace of the reaction chamber and exit through a gas line 134 controlled by a valve 136. They are then collected in a container 138, which may be a gas bag, for example. A valve 140 provides gas control. The reaction liquid exits the reaction chamber through an outlet line 142 controlled by a pump 144 and is then called digested residue, which is received in a digested residue storage unit 146. It will be understood that the exchange of raw materials in the reaction chamber can be achieved using only one of the pumps 116 and 144. In this embodiment, the raw materials are exchanged at a rate of 1 L / day, which corresponds to an exchange rate of raw materials of approximately 5% of the working volume of the reaction chamber per day.

[0126] Example 3 - Anaerobic digestion using internal and external MEC modules Materials and methods The series of reactors operated either with two graphite felt electrodes located within the internal volume of the reactor, as outlined below, or as external modules. The electrodes were prepared in the same manner as described in Example 5 below. The reactor was a stainless steel vessel with a total volume of 30 L, providing a working volume of 20 L.

[0127] The reactor operated by continuously circulating the contents at a flow rate of 2 L / min using a peristaltic pump and a circulation line controlled by a timer configured to provide a 15-minute on, 15-minute off cycle.

[0128] Conditions and repetition, raw materials The raw material used in the following examples was liquid cow manure fertilizer that had been pre-treated to remove solid particles. The treatment involved mixing solid cow manure fertilizer with an equivalent amount of fresh water, stirring with a hand drill and a Rushton impeller to de-agglomerate, and letting it stand overnight. The mixture was then further stirred to de-agglomerate, and the solid particles were removed by filtering through a nylon sleeve with pores of approximately 0.5 mm. An equivalent amount of water was then added. This process was repeated until a ratio of 1:5 kg of initial fertilizer:water was added to produce liquid fertilizer.

[0129] The pretreatment for producing liquid fertilizer avoids the scaling-down issues in the relatively small working volume of the reactor used in this embodiment. The solid material removed from the fertilizer has a high lignocellulose content and does not contribute significantly to biogas production. The lignocellulose content contributes to the chemical oxygen demand (COD) of the material containing all organic matter, but not to the biological oxygen demand (BOD). These solids also represent operational challenges in existing anaerobic digestion processes.

[0130] Table 1 lists the variables monitored for each batch of liquid fertilizer. The fertilizer-to-water ratio can be adjusted as needed to standardize across batches.

[0131] In this example, the ratio of fertilizer to water used is 1:1, an estimated dilution ratio found in a typical New Zealand dairy farm, where the fertilizer is collected with water and then pumped to a paddy field, pond, or corresponding treatment. The test conditions are not designed to be particularly favorable to the process of the present invention, but rather to be representative conditions that may be found in a "typical" anaerobic digestion plant.

[0132] [Table 1]

[0133] The reactor operated under the same constant conditions and was supplied with standardized liquid fertilizer. A peristaltic pump was used for sampling and supply to achieve a throughput of 1 L / day, and a constant volume of approximately 20 L was maintained in the reactor over a hydrological residence time (HRT) of 20 days. An automatic temperature controller in the reactor was set to 38.5°C and switched on when the reaction mixture temperature dropped below 38°C, collecting the off-gas in a gas bag. pH was actively controlled to be maintained within a specific range (7.5–8, by adding NaOH as needed).

[0134] In some reactors, the electrodes were integrated into the main reaction vessel (ModIn 1, 2, 3, 4). To address the technical challenges of implementing this process on an industrial scale, as described herein, some tests utilized external modules (ModEx 1, 2, 3, 4). In this example, eight reactors were operated, with four replica reactors for each of the ModIn and ModEx configurations. Furthermore, a ninth reactor was operated without electrodes to model the performance of a typical anaerobic digester (AD). In the ModIn configuration, the electrochemical cell is immersed within the main reaction vessel, while the ModEx configuration has an external module whose contents are continuously exchanged through the main reaction vessel.

[0135] result Gas generation performance As the organic matter load (OLR) increased, the system went through a transition period in which the methane production rate (MPR) increased before day 30. The AD control had the lowest MPR, mostly due to lower biogas production, but its methane content was also at the lower end of the group, despite being higher than expected from the references.

[0136] Figure 3 shows the average biogas volume generated and methane content over the entire 6-week period.

[0137] Industrial applications are more generally concerned with biogas production because methane content is typically determined by the waste used as raw material, and the specific quality of the raw material and gas is ensured by including necessary pre / post-treatment, accepting the inherent costs of performing them. However, as MEC integration increases reaction rates, different KPIs focused purely on methane production seem more appropriate.

[0138] Therefore, for comparison between the ModIn and ModEx configurations relative to the AD control, the methane production rate (MPR, mL) was used. CH4 The volume of methane produced per unit volume of the reactor and the volume of methane per hour are preferred as KPIs to demonstrate methane production capacity, which have a direct interpretation to industrial scale. To avoid the effects of transient periods that increase the methane production rate in comparison, the last month of operation is selected to represent the stable performance of the bioreactor after the initial start-up phase.

[0139] Figure 4 shows mL CH4 This shows the average methane production rate per L-day. This data, along with the standard deviation and coefficient of variation, is also shown in Table 3.

[0140] [Table 2]

[0141] Clearly, the MEC reactor, either with internal or external modules, delivers approximately a 20% improvement compared to the AD control. Importantly, although the majority of the reaction fluid resides within the reactor chamber and away from the MEC electrodes, the ModEx configuration reflects the performance of ModIn. This validates a ModEx integration strategy for retrofitting the technology to existing anaerobic digesters.

[0142] The coefficient of variation indicates the relative weight of the standard deviation compared to the mean; >1 suggests a high standard deviation, and <1 suggests a low standard deviation. A single-factor ANOVA was performed to evaluate whether the overall performance improvement for ModIn and ModEx configurations was statistically significant. This established that both ModIn and ModEx showed significantly different performance for AD, but there was no significant difference in performance between the ModIn and ModEx configurations (Figure 4).

[0143] COD removal performance The COD removal efficiency was calculated from the raw data according to the following formula.

[0144]

number

[0145] Using this parameter, and considering all available data (see Appendix C), excluding reactors that malfunctioned at some point in time, the average over the same period used for MPR comparison is calculated as shown in Table 4 and Figure 5. COD removal was slightly improved in the ModEx and ModIn configurations compared to the AD control.

[0146] [Table 3]

[0147] Anaerobic digestion links the energy matrix with the organic waste network. Therefore, it can be applied as either an energy generation or waste treatment technology. The latter is a more common application of anaerobic digestion due to its traditionally low reaction rates. In the case of waste treatment, COD removal is the most relevant performance parameter.

[0148] Since this invention relates to energy generation rather than waste treatment, the improvement in COD removal is noteworthy. This is an indirect result of carbon leaching towards off-gas rather than cell proliferation, and is an additional benefit provided by this invention. This effect corresponds to an increase in the methane conversion rate (MCR, mL) in proportion to the methane yield per unit of supplied COD. CH4 / g COD The units (of measurement) are also noteworthy. Table 5 and Figure 6 summarize the performance of ModIn and ModEx configurations compared to the AD control.

[0149] [Table 4]

[0150] Example 4 - Pre-anodization Materials and methods The analysis was performed using a three-electrode, 100 mL single-chamber electrochemical cell. The cell had a working electrode (anode) of 3 × 1 cm carbon graphite felt; a titanium wire as a dummy reference electrode; and a counter electrode which was a 6 mm stainless steel (SS) tube located 2 cm away from the working electrode. The electrolyte used was 100 mL of 10 g / L FeSO4 solution.

[0151] Pre-anodization of the working electrode was performed by applying a voltage of 1.5V to the graphite felt anode in 15-minute on / off cycles. This was repeated for 24 hours.

[0152] Overview of the Methodology In porous electrode materials, estimating the actual surface area available for electrochemical reactions is extremely difficult. However, by using graphite electrodes with different total surface areas as a source of comparison, we can construct curves in which peak current and charge correlate with the corresponding surface area, and then use a regression equation to estimate the "sample" material surface area from the obtained peak current / charge ratio.

[0153] This analysis allows for the estimation of the actual surface area of ​​the electrode and enables the comparison of the effects of several pretreatment parameters, such as the number of anodizing cycles and the electrolyte strength used. The evaluation procedure consists of three steps. --Construct a reference graph of peak current for known surface electrode areas. --Ideally, linear regression should be performed at various scan speeds to select the best fit (avoiding diffusion limitations). -- Determine the peak current of an unknown sample and estimate its surface area.

[0154] Peak current method This method allows for the measurement of the electroactive surface area of ​​a porous electrode based on a linear relationship between peak current and electroactive surface area. The electroactive surface area measured by this method may be affected by the electrode particle size, sintering temperature, and / or chemical etching (if any), in addition to the pore size and porosity. It is particularly sensitive to the thickness of the diffusion layer, which is a function of the CV scanning speed. The procedure is as follows: - For flat, plate-shaped electrodes with known (different) surface areas, construct surface area versus peak current plots to obtain a linear relationship between them. -By performing a series of voltammograms, we identify whether more than one reaction is occurring and select those that are controlled solely by ion diffusion. -By repeating the process at various scanning speeds, a plot of peak current versus surface area can be constructed, and various straight lines can be drawn at different scanning speeds. -If the line is a straight line, the system responds to the Landres-Sebic equation.

[0155] result When a 15-minute on / off cycle of 1.5V is applied to the graphite felt anode over a 24-hour period, the voltage increases over time (Figure 7), indicating an increase in the electrode surface area.

[0156] As can be seen from the figure, there is a clear positive correlation between the duration of the voltage cycle and the measured surface area. Here, the m of the treated electrode piece 2 The actual surface area of ​​the unit was reported; the electrode was 1 × 3 cm and had a thickness of 3 mm. The surface area was 0.23–0.41 m² within 24 hours of processing. 2 It can be seen that this increases by approximately 64%.

[0157] Two different electrolyte intensities were compared using Fe2SO4 at 4.3 mg / L and 430 mg / L. While the lower-intensity electrolyte appears to achieve a larger surface area, the increment achieved is not significant at 33%, compared to 32% achieved by the higher-intensity electrolyte. Both electrolytes also show a similar trend with respect to the slope of the increment in surface area over time with voltage cycling (Figure 8). This indicates that similar increments in surface area can be achieved using either the lower-intensity or higher-intensity electrolyte. Those skilled in the art will recognize that many salts are suitable for use as electrolytes to increment the surface area of ​​electrodes.

[0158] This difference in surface estimates of the two electrolyte strengths is likely due to the thickness of the bilayer formed during the process, which can cause the system to act as a capacitor storing more or less energy, potentially affecting peak current measurements.

[0159] Example 5 - Microbial adhesion Materials and methods A three-electrode cell, including a working electrode (WE), counter electrode (CE), and reference electrode (RE), was used to control the potential of one specific electrode, in this case the cathode, which was connected as the anode for the microbial attachment / colony formation phase. During the microbial attachment phase, the anode potential attracted electroactive microorganisms such as methanogenic bacteria that are not attracted to the cathode.

[0160] Several samples were prepared using a four-electrode cell instead of a three-electrode cell. The four-electrode cell houses a second WE, and the distances between each WE and the CE and RE are arranged to be as similar as possible. This makes it possible to test different materials from the WE, in this case GF and pre-anodized GF, under the same conditions.

[0161] The counter electrode (CE) used was a 6mm x 2cm stainless steel tube (316L) with a thickness of approximately 0.1mm, which provided good electrical conditions and was not expected to allow microorganisms to colonize. Due to the complexity of fertilizer waste as an electrolyte and the complexity of bacterial growth in the presence of solids, typical electrode references such as Ag / AgCl can be subject to significant variability due to potential clogging of the electrode frit. Therefore, in this example, a pseudo-reference electrode (RE) of coiled titanium wire was used. The working electrode (WE) tested measured 1 x 3cm and contained graphite felt (GF) and pre-anodized GF (3mm thick).

[0162] After setting up the cell, a potential of approximately +1.5V / SCE was applied to the WE for a period of 8 hours to promote the attachment of methane-producing bacteria.

[0163] Biofilm growth on electrodes can be monitored by collecting information such as cyclic voltammograms indicating how much charge is being transferred, peak currents, and other information described below. Changes in the WE voltammogram over time may indicate surface modification that may be due to microbial adhesion, given the test conditions.

[0164] The described tests used both microbial communities and nutrient media. The nutrient medium was yeast extract medium (2 g / L yeast extract + 20 mL / L salt), and the microbial community was introduced using fertilizer diluted 1:7. Weotern microbial activity (WE) was periodically monitored through cyclic voltammetry at 0.15 V / sec between -4 and 4 volts, starting at 0.1 V and progressing to 0.02 V. Voltammograms were performed first for the nutrient medium; after adding the fertilizer as an inoculum; then every 1-2 hours over a total experimental period of 8 hours; the upper time limit was chosen to avoid duplication of any archaea or bacteria involved in the methane production process.

[0165] Monitor the voltammogram and the peak current and ratio I an / I cat , and I cat The comparison was made according to the potential.

[0166] To evaluate whether the materials and pretreatments have a measurable effect on electrode colony formation, WE-CE electrode pairs were individually tested according to the following steps. - Arrange the electrodes in a three-electrode electrochemical cell; - Use 50 mL (approximately 50% of the cell volume) of electrolyte (nutrient medium without another COD source); - Perform the first cyclic voltammetry analysis; - Add the COD source until it reaches approximately 50% of the cell volume and the desired final COD; - Perform a new cyclic voltammetry analysis under the same CV parameters as the first cyclic voltammetry analysis; - Add the inoculant; Two further CV analyses are performed every 1-2 hours under the same CV parameters as the first cyclic voltammetry analysis.

[0167] Microscopic examination UV fluorescence microscopy was performed on multiple fresh samples of GF and pre-anodic GF electrodes, prepared by applying a 1V anode potential to the working electrode for 3 hours in the presence of 50% v / v raw material fertilizer + 50% synthetic urban wastewater. After air-drying each sample, fluorescent DAPI staining was applied. Multiple fields of view were imaged to assess uniformity and determine the number of fields of view necessary to evaluate future samples.

[0168] result Microscopic examination Estimates of the percentage of electrode area coated by bacteria were obtained using DAPI staining and fluorescence microscopy (Axio Imager M2, Zeiss) at 400× magnification. Some methodological problems in estimating the area included the presence of heavily stained areas in the center of the anodized sample and some autofluorescent fibers. For this reason, values ​​for the anodized sample were obtained from the edges of the sample. The strongly stained fluorescent areas may be patches of organic debris present in the fertilizer that adhered to the material during the process, such as fats, which have been reported to produce nonspecific DAPI staining, and may have adhered when the electrode was removed from the fertilizer, and are clearly visible as a thin upper layer in the fertilizer.

[0169] Based on microscopic examination results, the estimated percentage of the surface area covered by bacteria was 4.34% for GF samples and 3.38% for anodic oxidation samples.

[0170] Cyclic voltammetry For the anodized GF sample, the anodic current peak decreased over time, and it was observed that the change in the anodic current peak was greater during the first 30 minutes compared to the value at 0 minutes.

[0171] For the GF sample, the voltammogram shape was slightly different because no anodic current peak was observed, and the obtained current was also lower than that obtained for the anodized GF sample (3500 vs. 5500 μA).

[0172] The observed decrease in peak current corresponds to approximately 4-5%, which, according to microscopic analysis, is very close to the approximate covered surface area of ​​3.38-4.34%.

[0173] Due to the similarity of the voltammograms in terms of peak position and changes in current values ​​over time, the inventors conclude that the fluctuations in the voltammograms for either the GF sample or the anodic-oxidized GF sample can be understood as being due to surface modification, which is a result of surface colony formation observed in microscopic analysis.

[0174] Example 6 - Effect of voltage, electrode material Materials and methods The effect of voltage on the reactor used in Example 3 was investigated as follows. Using a full-cell potential control strategy, three different conditions were used for each of the AD, ModEx, and ModIn configurations: open-circuit potential (OCP), 0.8V, and 1.5V. Steady-state operation was performed with an organic load of 1.3 gCOD / L. * D, a 20-day HRT, and a temperature setpoint of 38°C were used. Two different materials were investigated for the cathode: graphite felt (GF) and stainless steel mesh (SS). GF electrodes were used for all anodes.

[0175] The reactor operated at 0.8V until it reached a steady state, and then the voltage was changed to OCP or 1.5V until the steady state was maintained for approximately two months. A series of 24 parameters were monitored as indicators of system health. The most relevant performance indicator was LCH4 / m 3 *It was found to be MPR at d. This KPI was selected due to its importance to the volumetric methane production capacity of the bioreactor.

[0176] result The results are shown in Table 6.

[0177] [Table 5]

[0178] Since there was no mechanism to apply different voltages to the AD reactor, the AD reactor is shown only in the OCP control unit (Figure 9).

[0179] At first glance, it is noteworthy that the OCP performance of the ModIn and ModEx reactors is very close to that of the control AD, with only 3% or 4% in terms of MPR, despite achieving 11% or 16% in terms of biogas volumetric production (Table 6, Figure 9). This suggests a decrease in the methane content of the biogas produced. However, when comparing reactors with SS cathodes to those with GF cathodes, the GF cathode clearly results in a significant improvement in MPR. This suggests that GF (still present in the anodes of all prototypes) effectively assists the hydrolysis step (which is considered the bottleneck in the AD process of cow manure fertilizer). Also, surprisingly, applying a voltage of 1.5V did not yield higher performance than 0.8V (compare Figures 10 and 11), and therefore, the preferred voltage for these reactors is between these two values. When 0.8V is applied, biogas production increases by 23-30%, but when using 1.5V, it is only 2-13%. It's worth noting that while there's virtually no difference between configurations when 0.8V is used, at 1.5V, ModEx only generates an additional 2-5% biogas.

[0180] The improved performance is more pronounced with respect to MPR, with an applied voltage of 1.5V resulting in a 9-15% increase in MPR, and an applied voltage of 0.8V resulting in a 21-34% increase in MPR. While ModEx-SS is less than 30% at 0.8V, in practice, both ModIn reactors achieve a 34% improvement in MPR regardless of electrode material, which again suggests that the main effect of the cow manure fertilizer lies in the anode rather than the cathode.

[0181] The scope of the present invention is not intended to be limited to the examples described above. As those skilled in the art will understand, many modifications are possible without departing from the scope of the invention as described in the appended claims.

Claims

1. A bioelectrode comprising a bacterial biofilm, having a porous structure with a pore size within a certain range.

2. The bioelectrode according to claim 1, comprising a primary pore of a first size range and a secondary pore of a second size range.

3. The bioelectrode according to claim 1 or 2, wherein the bioelectrode comprises a biocompatible material and / or a carbon-based material, such as felt, paper, carbon, metal, or plastic-based sintered porous material.

4. The bioelectrode according to any one of claims 1 to 3, wherein the electrode comprises a fiber strand.

5. The bioelectrode according to claim 4, wherein the fibers form a 3D open structure of primary pores.

6. The bioelectrode according to claim 4 or 5, wherein the secondary pores are provided as recesses.

7. The bioelectrode according to claim 6, wherein the recess is formed by the pretreatment of the fiber.

8. The bioelectrode according to claim 7, wherein the pretreatment includes applying an electric potential to the electrode.

9. The bioelectrode according to any one of claims 1 to 8, wherein the electrode surface is functionalized with immobilized microorganisms, enzymes, or catalytic materials.

10. The electrode is at least 1 m ２ / g, more preferably at least 2m ２ A bioelectrode according to any one of claims 1 to 9, having a surface area of ​​ / g.

11. The bioelectrode according to any one of claims 1 to 10, wherein the biofilm is a mature biofilm.

12. The bioelectrode according to any one of claims 1 to 11, wherein the biofilm comprises at least one methane-producing microorganism and at least one electroactive microorganism.

13. A microbial electrolytic cell (MEC) comprising a solid cathode, a solid anode, and an electroactive biofilm.

14. The MEC according to claim 13, comprising the bioelectrode according to any one of claims 1 to 12.

15. The MEC according to claim 13 or 14, further comprising a dielectric material between the cathode and the anode.

16. A process for colonizing bioelectrodes using microorganisms, - A step of bringing an electrode into contact with a mixture containing microorganisms, and - A process comprising the step of applying a potential to the electrodes during the step of bringing them into contact.

17. The process according to claim 16, wherein the potential applied during the contact step is approximately +1.5 V / SCE.

18. The process according to claim 16 or 17, wherein the potential is applied during the contact step for a period of at least about 1 hour, preferably at least about 2 hours, and more preferably about 2 hours.

19. The process according to any one of claims 16 to 18, wherein the potential applied during the contact step is the anode potential, and the microorganisms that form colonies on the bioelectrode are methane-producing microorganisms.

20. The process according to any one of claims 16 to 19, further comprising a pre-anodic oxidation step of applying an anode potential to the electrodes before the contact step.

21. The process according to claim 20, wherein the pre-anodic oxidation step includes applying a potential of approximately +1.5 V / SCE.

22. The process according to claim 20 or 21, wherein the potential is applied to the electrode in cycles during the pre-anodic oxidation step.

23. The process according to claim 22, wherein the cycle is a period of approximately 15 minutes on and 15 minutes off.

24. The process according to claim 22 or 23, wherein a continuous cycle is applied over a period of approximately 24 hours.

25. A process for the anaerobic digestion of raw materials in an anaerobic digester, wherein the process is: - The raw materials are supplied to the chamber of the anaerobic digester, and a reaction solution is formed within the anaerobic digester. - The reaction solution is brought into contact with the bioelectrode of a microbial electrolytic cell equipped with a bioelectrode and a counter electrode, - A process comprising applying an electric potential to the reaction solution.

26. The process according to claim 25, wherein the bioelectrode of the microbial electrolytic cell is positioned within the chamber of the anaerobic digester.

27. The process according to claim 25 or 26, wherein the bioelectrode comprises a biofilm.

28. The process according to any one of claims 25 to 27, wherein the bioelectrode is the bioelectrode according to any one of claims 1 to 12.

29. The process according to any one of claims 25 to 28, wherein the bioelectrode is a cathode.

30. The process according to claim 29, wherein the cathode is adapted to be advantageous for direct methane production.

31. The process according to claim 29, wherein the cathode is adapted to facilitate direct interspecies electron transfer between species.

32. The process according to any one of claims 29 to 31, wherein the cathode comprises graphite felt.

33. The process according to any one of claims 29 to 31, wherein the cathode comprises stainless steel.

34. The process according to any one of claims 25 to 33, wherein the bioelectrode is separated from the counter electrode by a dielectric material.

35. The process according to any one of claims 25 to 34, wherein the anaerobic digester comprises a microbial community comprising suspended microorganisms, and the bioelectrode of the microbial electrolytic cell comprises a microbial biofilm.

36. The process according to any one of claims 25 to 35, wherein the microbial electrolytic cell is located inside the chamber of the anaerobic digester.

37. The process according to any one of claims 25 to 35, wherein the microbial electrolytic cell is located outside the chamber of the anaerobic digester and is in fluid communication with the chamber of the anaerobic digester.

38. The process according to any one of claims 25 to 37, wherein the voltage applied between the bioelectrode and the counter electrode is greater than 100 mV, greater than 300 mV, or greater than 600 mV.

39. The process according to any one of claims 25 to 38, wherein the voltage applied between the bioelectrode and the counter electrode is in the range of 600 mV to 1200 mV, preferably in the range of 800 mV to 1000 mV.

40. The process according to any one of claims 25 to 39, wherein the temperature inside the anaerobic digester is in the range of about 30 to about 45°C, preferably about 39 to about 42°C, or about 35 to about 39°C, more preferably about 38°C.

41. The process according to any one of claims 25 to 40, wherein the raw materials / reaction solution preferably comprises urban wastewater and / or fertilizer having a total solid content of 1 to 10%, more preferably 1 to 5% or 5 to 7%.

42. The chamber is an external module comprising a chamber, which is adapted to be in fluid communication with the chamber of an anaerobic digester.

43. The external module according to claim 42, wherein the chamber is adapted to receive a bioelectrode according to any one of claims 1 to 12.

44. The external module according to claim 42 or 43, wherein the chamber further comprises a bioelectrode according to any one of claims 1 to 12.

45. The external module according to claim 44, wherein the bioelectrode is produced by the process described in any one of claims 16 to 24.

46. The external module according to any one of claims 42 to 45, further comprising a pump for exchanging fluid between the chamber of the external module and the chamber of the anaerobic digester.

47. The external module according to any one of claims 42 to 46, wherein the external module is adapted to be stackable with another external module.

48. An anaerobic digestion apparatus comprising a bioelectrode according to any one of claims 1 to 12.

49. The anaerobic digester according to claim 48, wherein the bioelectrode is produced by the process described in any one of claims 16 to 24.

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