Method for producing biogas from organic waste using dry bioelectrochemical anaerobic digestion process

Abstract

Provided is a bioelectrochemical leaching bed reactor combined with a microbial electrolysis device, the bioelectrochemical leaching bed reactor being characterized by comprising: a reactor upper part including a basket (130) for fixing the food waste; a reactor lower part for accommodating leachate generated from the reactor upper part; and the microbial electrolysis device provided in the reactor lower part, wherein the microbial electrolysis device comprises a membrane-type electrode and a voltage application unit for applying a voltage to the electrode, and the voltage application unit applies a voltage of more than 0.3 V and less than 1.2 V.

Description

Biogas production method using dry bioelectrochemical anaerobic digestion process from organic waste

[0001] The present invention relates to a method for producing biogas from organic waste, and more specifically, to a method for producing biogas from organic waste that can effectively induce the production of acetate and thereby accelerate the production of methane.

[0002] Anaerobic digestion of organic waste is categorized into dry and wet processes, depending on the condition of the organic waste. Anaerobic digestion (AD) refers to an anaerobic digestion technology with a total solids concentration (TS) typically exceeding 20% ​​(Rocamora et al., 2020).

[0003] Compared to conventional wet anaerobic digestion, dry anaerobic digestion is the preferred technology because it has the advantages of handling higher organic loading rates, requiring less water, and reducing energy input during internal mixing (see Kumar & Samader, 2020; Pera et al., 2021; Rocamora et al., 2020; Westerholm et al., 2020).

[0004] The operational stability of these dry ADs depends on feedstock characteristics, total solids content (TS), organic loading rate (OLR), hydraulic retention time (HRT), process temperature, pH, etc. (see Kothari et al., 2014; Kumar et al., 2021; Zhang et al., 2022).

[0005] In the dry AD process, which possesses these advantages, complex microbial metabolism occurs. First, solid organic matter in food waste (FW) is hydrolyzed and acidified to produce various volatile fatty acids (VFAs), such as acetic acid, propionic acid, and butyric acid. Except for acetic acid, which can be directly converted to methane, the remainder must be converted to acetic acid before methane can be produced (Tang et al., 2015; Zhang et al., 2022).

[0006] However, the Gibbs free energy during the conversion of propionic acid and butyric acid to acetic acid is positive (thermodynamically unfavorable), which limits the methane production rate of the entire system and causes problems in extending the anaerobic digestion time (Wang et al., 2022).

[0007] Additionally, large accumulation of short-chain fatty acids tends to cause acidification of the digestive system, which leads to unstable digestion and even system collapse, requiring the incorporation of other technologies such as microbial electrolysis cells (MEC) to improve this (Mu et al., 2020; Rocamora et al., 2020).

[0008] Microbial electrolysis devices (MECs) can produce hydrogen or methane by using organic matter, converting it, and transferring the generated electrons from the anode to the cathode through an external circuit by microorganisms under an applied voltage (Cheng & Logan, 2007; Escapa et al., 2013; Hamelers et al., 2010; Wang et al., 2021a).

[0009] Adding electrodes to anaerobic microbial systems with an applied voltage can increase the rate of organic matter decomposition, enhance methane production, and induce some reactions that would otherwise not proceed thermodynamically spontaneously (Cheng et al., 2009; Hamelers et al., 2010).

[0010] Previous studies have demonstrated a technology to produce methane by treating synthetic wastewater with MEC, where it was discovered that the methane generator could reduce CO2 for methane production using hydrogen produced at the cathode, indicating a new interspecies electron transfer pathway, making MEC-AD a promising technology for CO2 capture and methane production (Cheng et al., 2009; Clauwaert & Verstraete, 2009; Logan & Rabaey, 2012; Zhao et al., 2015).

[0011] However, research and methods for improving the efficiency of the applied voltage in AD combined with a microbial electrolysis device have not yet been disclosed.

[0012] Therefore, the problem to be solved by the present invention is to provide a method and system for effectively decomposing organic matter and producing biogas in an AD in the form of a leach bed reactor (LBR) combined with a microbial electrolysis device.

[0013] In order to solve the above problem, the present invention provides a bioelectrochemical leachate bed reactor combined with a microbial electrolysis device, comprising: an upper portion of the reactor including a basket (130) for fixing the food waste; a lower portion of the reactor for receiving leachate generated from the upper portion of the reactor; and a microbial electrolysis device provided in the reactor, wherein the microbial electrolysis device includes a membrane-shaped electrode and a voltage application unit for applying voltage to the electrode, and the voltage application unit is characterized in that a voltage of more than 0.3 V and less than 1.2 V is applied to a cathode of the electrode.

[0014] In one embodiment of the present invention, the voltage applying unit applies a voltage of 0.8 to 1.0 V, and the bioelectrochemical leach bed reactor includes a leach bed reactor (LBR).

[0015] In one embodiment of the present invention, the microbial electrolysis device is provided outside the reactor, the leachate flows into the microbial electrolysis device and is electrolyzed, and the microorganisms after being electrolyzed are reintroduced into the reactor.

[0016] In one embodiment of the present invention, the genus Methanosarcina in the biofilm of the cathode is 30% to 60%.

[0017] In one embodiment of the present invention, VFA, which is a substrate of one or more of acetate, ethanol and propionate, may be used at the anode to concentrate an anode-respiring bacteria biofilm such as Geobacter on the anode surface among the electrodes, while the anode potential is maintained at -0.4 to 0 V (vs. Ag / AgCl).

[0018] According to the present invention, in a bioelectrochemical leachate reactor combined with a microbial electrolysis device, the production of acetate can be effectively induced to accelerate methane production.

[0019] Figure 1 is a schematic diagram of a BLBR system according to one embodiment of the present invention.

[0020] Figure 2 is a graph showing the cumulative methane yield of BLBR with different applied voltages.

[0021] Figure 3 is a graph showing VS removal efficiency at different voltages.

[0022] Figures 4 to 7 show the results of measuring the production of SCOD (including VFA and other available organic substances), acetate, propionate, and butyrate, respectively.

[0023] Figures 8 to 10 are graphs of the relative abundance of microbial communities in the leachate, electrode, and food waste residue of the BLBR.

[0024] Figures 11 and 12 are graphs showing the relative abundance of (a) SPOB and (b) total bacterial genera that can participate in EET in leachate, electrode biofilm and FW residue samples under different conditions.

[0025] Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the attached drawings.

[0026] Before describing the present invention in detail, it should be noted that the terms or words used in this specification should not be interpreted as being unconditionally limited to their usual or dictionary meanings, and the inventor of the present invention may appropriately define and use the concepts of various terms in order to describe his or her invention in the best possible manner.

[0027] Furthermore, it should be noted that these terms and words should be interpreted with meanings and concepts that are consistent with the technical idea of ​​the present invention.

[0028] That is, the terms used in this specification are only used to describe preferred embodiments of the present invention, and are not intended to specifically limit the contents of the present invention.

[0029] It should be noted that these terms are defined taking into account the various possibilities of the present invention.

[0030] Additionally, in this specification, a singular expression may include a plural expression unless the context clearly indicates a different meaning.

[0031] Also, it should be noted that even if similarly expressed in plural, it can contain singular meaning.

[0032] Throughout this specification, whenever a component is described as "including" another component, it may mean that the component may further include any other component, rather than excluding any other component, unless specifically stated otherwise.

[0033] The present invention, in order to solve the above-described problem, can effectively induce acetate production and accelerate methane production by applying voltage in a microbial electrolysis-assisted anaerobic digestion process in a bioelectrochemical leach bed reactor (BLBR). The present invention will be described in more detail below through preferred embodiments.

[0034]

[0035] Example

[0036] Materials and Methods

[0037] Food waste and inoculant collection

[0038] Food waste (FW) was collected from the cafeteria at the University of Waterloo (Waterloo, Ontario, Canada).

[0039] After collection, food waste was chopped, frozen at -20°C, and thawed at 4°C for 24 h before the experiment (Swakshar & Lee, 2020; Xiong et al., 2019).

[0040] Sludge was collected from the anaerobic digester at the Galt Wastewater Treatment Plant (Cambridge, Ontario, Canada). The sludge was then filtered through a mesh to remove large particles. The AD sludge was acclimated before being added as inoculum to the BLBR system. Acclimation was performed under anaerobic conditions with gradual mixing and a solid retention time (SRT) of at least 20 days. Operating conditions included an organic loading rate of at least 5 kg COD / m3-d, a mixing speed of 50–200 rpm, and a temperature of 20–35°C.

[0041]

[0042] Reactor configuration

[0043] Figure 1 is a schematic diagram of a BLBR system according to one embodiment of the present invention.

[0044] The anaerobic digestion system according to the present invention is a leach bed reactor (LBR), which is a batch-filled digestion system in which leachate is intermittently or continuously recycled to a waste bed, and the LBR effectively dissolves solid organic matter into liquid-phase volatile fatty acids (VFA) by hydrolyzing the solid organic matter through liquid recirculation.

[0045] Referring to Fig. 1, two cylindrical BLBRs were made of acrylic glass with an inner diameter of 14 cm and a height of 70 cm, and the total volume was 10 L.

[0046] A reactor according to one embodiment of the present invention comprises a reactor upper portion (100) including a removable upper cover (120) having a gas outlet and a sprinkler (110) for spraying leachate onto food waste, and a reactor lower portion (200) including a leachate holding bed.

[0047] In one embodiment of the present invention, the upper part (100) of the reactor includes a basket (130) in the middle for fixing food waste, and a mesh is provided at the lower part of the basket to prevent food waste larger than a certain size from flowing to the lower part (200) of the reactor.

[0048] That is, the basket according to one embodiment of the present invention is an acrylic glass FW basket with an inner diameter of 10 cm and a height of 25 cm, and is capable of preventing the entire bottom of the basket from being filled with leachate and falling into the leachate holding bed with a size of 5 mm.

[0049] A membrane-structured microbial electrolysis device having an anode and a cathode electrode and a component for applying voltage to the electrodes is provided at the bottom of the reactor according to the present invention. The electrodes are immersed in the leachate, and the electrodes are provided with a voltage applying unit (voltage variable device, potentiostat, 220) for applying voltage to the electrodes.

[0050] In particular, the voltage applied by the voltage applying unit of the present invention can be varied in consideration of the hydrogen production efficiency, which will be described in more detail below.

[0051] The leachate flowing downward from the holding bed was recycled by a digital peristaltic pump (210, Masterflex L / S Digital Drive, Model No. 07523-80, USA). Additionally, the leachate from the holding bed was internally mixed at 60 L / hr using a peristaltic pump (220, Masterflex L / S Economy Drive, Model No. 07554-90, USA).

[0052] The BLBR was operated at 35°C, maintained for mesophilic conditions, by recirculating heated water from a water heater controller (PolyScience 9702A11C 13-liter Advanced Digital Controller, PolyScience, USA) through PVC piping tied around the reactor body.

[0053] A pH controller (Milwich, MC-122 pH meter) was coupled to an on-site pH probe and a pump that injected sodium bicarbonate solution to maintain a neutral pH and provide alkalinity to the leachate. A gas counter (MilliGas counter, Ritter Apparatus, Bochum, Germany) was connected to the gas line at the top cover of the BLBR to measure biogas production. Leachate samples were taken from the mixing line, and biogas samples were taken from the gas line for routine analysis.

[0054]

[0055] Reactor operation

[0056] The BLBR was fed with an acclimated inoculum containing 25% ISR, and the initial leachate volume was fixed at 2.5 L. The leachate in the holding bed was continuously mixed with a peristaltic pump (Masterflex L / S Digital Drive, 115 / 230 VAC, Model No. 07523-80, USA) at a rate of 60 L / hr.

[0057] The leachate recirculation pump was programmed to turn on for 15 seconds every 75 minutes, spraying leachate onto the top of the FW at a rate of 90 L / hr, corresponding to a leachate recirculation rate of 0.3 L / hr or 7.2 L / day. The initial VS of the FW was fixed at approximately 72 g for all experiments.

[0058] Before the start of each batch, all BLBRs were sparged with nitrogen gas to create anaerobic conditions at a flow rate of 0.5 L / min for 30 min. After each batch, centrifugation was performed at 9,500 rpm for 20 min, and the centrifuged solids were collected as inoculum for the next batch, allowing for the concentration of acclimated fermentative and methanogenic microorganisms in the reactor.

[0059] Two pairs of carbon fiber anodes and stainless steel cathodes, used to enrich Geobacter sp. prior to start-up, were placed in the leachate holding bed of each BLBR (Figure 4-1). The distance between the anodes and cathodes was 1.5 cm.

[0060] The tip of the electrode was connected to a potentiostat (Bio-logic, VSP, Gamble Technologies, Canada), a global voltage source. A reference electrode (Ag / AgCl, MF-2052, Bioanalytical System Inc., USA) was placed 5 mm from the anode and also connected to the potentiostat. One BLBR was run as a comparative example without applied voltage (open-circuit mode, OCM), and the other was operated at applied voltages between 0.3 and 1.2 V. The applied voltages were fixed at 0.3 V, 0.6 V, 0.9 V, and 1.2 V, respectively, with the potentiostat. The current, electrode potential, and other parameters were monitored and recorded every minute using the potentiostat and EC-Lab v10.23 software installed on a computer. To obtain reproducible results, the BLBR was operated for three consecutive batches for each applied voltage. Each batch of BLBR runs lasted 10 days.

[0061]

[0062] Experimental example

[0063] Methane production at various voltages

[0064] Figure 2 is a graph showing the cumulative methane yield of BLBR with different applied voltages.

[0065] Referring to Figure 2, the methane yield in the open-circuit mode set as the control was 199 mLCH4 / gVS. At this time, methane production gradually increased over the first 5 days and slowed down until the end of the operation.

[0066] The cumulative methane yield of the BLBR using an applied voltage of 0.3 V was 212 mLCH4 / gVS, which was similar to the control group. At an applied voltage of 0.6 V, the methane yield increased by 20.6% compared to the control group to 240 mLCH4 / gVS. When the applied voltage increased to 0.9 V, the cumulative methane yield was the highest at 293 mLCH4 / gVS, but decreased slightly to 236 mLCH4 / gVS at an applied voltage of 1.2 V. In this experiment, although the operation time in the BLBR was kept short at about 10 days, the methane yield was improved by 47.2% compared to the control group, indicating that the EET of the electrode can contribute to improving methane production in the anaerobic digestion of FW.

[0067] Furthermore, the BLBR tested at 0.6, 0.9, and 1.2 V exhibited a faster methane production rate than the control group during the first five days of operation. Furthermore, when the applied voltage was further increased to 1.2 V, the methane yield decreased. This may be because the lower cathode potential at higher applied voltages induces alkaline conditions, and the higher pH can inhibit some methanogens, reducing methane production. Furthermore, the final pH in the leachate of the BLBR tested at 2 V was 8.2, which was higher than that of the BLBR tested at 0.3.

[0068]

[0069] Organic matter removal and solubilization

[0070] Solid removal

[0071] In this experiment, the effect of applied voltage on solid removal related to BLBR for the control group was investigated and is shown in Fig. 3.

[0072]

[0073] *Figure 3 is a graph showing VS removal efficiency at different voltages.

[0074] Referring to Fig. 3, the VS removal efficiency in the control group was 74.3%, which was slightly improved to 75.6%, 77.6%, 74.7% and 75.2% in BLBR at applied voltages of 0.3 V, 0.6 V, 0.9 V and 1.2 V, respectively (p>0.05).

[0075] The above results demonstrate that there was little improvement in FW hydrolysis with applied voltage in the BLBR, indicating that the applied voltage did not improve the hydrolysis of FW during AD. Furthermore, while the hydrolysis of solid FW relies on the secretion and activity of other hydrolytic enzymes, the hydrolysis of FW in the BLBR occurred primarily in the FW basket, which was not submerged in the leachate containing the electrode. Therefore, the hydrolysis in the FW basket may not be directly affected by the applied voltage.

[0076] SCOD

[0077] Figures 4 to 7 show the results of measuring the production of SCOD (including VFA and other available organic substances), acetate, propionate, and butyrate, respectively.

[0078] Referring to Figure 4, SCOD (including VFA and other soluble organics) increased at the beginning of operation as a result of hydrolysis of solid organics and decreased due to methane production. While SCOD accumulated for the first 4 days in the control, SCOD accumulation time in the BLBR continued for 2 days. For the BLBR at an applied voltage of 0.3 V, the SCOD concentration reached a peak value of 16.8 gCOD / L after 2 days, which was almost twice the SCOD level in the control. The BLBR at other applied voltages consistently showed steeper increases and decreases in SCOD than the control. These results indicate that although VS removal was not significantly affected, the applied voltage stimulates fermentation (e.g., acid production) for SCOD in the BLBR.

[0079] Referring to Figures 5 to 7, acetate, propionate and butyrate were the major VFAs in the leachate in all runs of the BLBR and control, accounting for more than 70% of the SCOD within 2 days of operation.

[0080] Acetate, a favorable substrate for methanogens, showed a rapid increase consistent with the SCOD profile (Figure 5-4b). After 2 days of operation, acetate reached peak values ​​of 5.23 gCOD / L (0.3 V), 3.41 gCOD / L (0.6 V), 2.82 gCOD / L (0.9 V), and 2.60 gCOD / L (1.2 V). Thereafter, acetate was rapidly consumed, remaining below 0.1 gCOD / L (<1.56 mM acetate). In contrast, acetate gradually increased, reaching a plateau of 1.50 gCOD / L after 4 days of operation in the control group, which also coincided with the SCOD trend of the control group.

[0081] Acetate is a key intermediate in the AD process and can be produced through both acidogenesis and acetate production. The elevated acetate levels during the initial operation of the BLBR system indicate that both fermentation and acetate production will be improved under the applied voltage.

[0082] Acetate is a substrate for acetoclastic methanogenesis, through which methane is produced. Elevated acetate levels can also enhance acetoclastic methanogenesis and, therefore, methane production. Furthermore, increased acetate can stimulate ARBs, such as Geobacter, to use acetate as a substrate for EET and DIET, thereby enhancing concentrated synhydrotrophic methane production.

[0083] Although the propionate concentration in the BLBR was higher than that of the control, the propionate profile did not show a drastic change compared to acetate and butyrate. In the BLBR with an applied voltage of 0.3 V, the propionate level continued to increase until the end of the operation, reaching 4.3 gCOD / L (38.5 mM). The propionate level also increased with increasing applied voltage. The BLBR with 0.6 and 0.9 V showed a decrease in propionate concentration after 4 days of operation, whereas the propionate level in the BLBR with 1.2 V was very similar to that in the BLBR with 0.3 V. These results indicate that MEC-AD will improve acid production for propionate production in a specific voltage range of greater than 0.3 and less than 1.2 V, preferably greater than 0.4 and less than 1.1 V, and most preferably greater than 0.6 and less than 0.9 V.

[0084] Butyrate accumulation in the BLBR also showed a similar trend to acetate (Figure 4-4d). The butyrate concentration in the BLBR increased rapidly within two days of operation and then was abruptly consumed. The peak butyrate level increased to 4.2 g COD / L at 0.3 V, which was the maximum during all BLBR operations, and to 8.8 g COD / L at 0.9 V. When the applied voltage was further increased to 1.2 V, the peak butyrate level returned to 3.2 g COD / L.

[0085] In comparison, butyrate only reached 0.6 gCOD / L in the control group after 4 days of operation, which was 14.6 times lower than the maximum butyrate concentration of 0.9 V in the BLBR. The maximum butyrate concentration and rapid consumption in the BLBR may indicate that both acidogenesis and acetogenesis of butyrate were enhanced under the applied voltage. The acetogenesis of butyrate to acetate and hydrogen would also be thermodynamically favorable under extremely low hydrogen partial pressure, which could be achieved by enrichment of hydrogenotrophic methanogens in the MEC-AD system.

[0086]

[0087] Microbial community structure response to applied voltage

[0088] The microbial community structure of electrode biofilm samples as well as leachate and food waste residues under each applied voltage was analyzed by 16s rRNA sequencing.

[0089] The Shannon index for each condition showed a decrease in the electrode (anode and cathode) biofilm and food waste residue in the leachate samples, and Table 1 below shows the Shannon index for different samples under different conditions.

[0090] ConditionLeachateAnodeCathodeFood waste residueOCM4.423.773.763.920.3V4.423.833.564.050.6V4.473.873.984.070.9V4.383.813.644.131.2V4.573.984.074.28

[0091] Referring to Table 1 above, a greater decrease in the Shannon index was found in the anode and cathode biofilms under all conditions compared to the food waste residue sample. At an applied voltage of 0.9 V, the Shannon index of the cathode biofilm decreased from 4.38 (leachate sample) to 3.64, and at an applied voltage of 0.3 V, the Shannon index of the cathode biofilm decreased from 4.42 to 3.56. The Shannon index indicates the species diversity of the microbial community, and a decrease in the Shannon index suggests a decrease in the species diversity of the microbial species in these samples.

[0092]

[0093] Bacteria in BLBR

[0094] Figures 8 to 10 are graphs showing the relative abundance of microbial communities in the leachate, electrode, and food waste residue of the BLBR, i.e. (a) bacterial phylum level, (b) bacterial genus level, and (c) archaea genus level. Here, SS: leachate. AN: anode. CA: cathode. FWR: food waste residue.

[0095] Additionally, Figures 11 and 12 are graphs showing the relative abundance of (a) SPOB and (b) total bacterial genera that can participate in EET in leachate, electrode biofilm, and FW residue samples under different conditions. The graph inserted in Figure 11 is the relative abundance of Geobacter genus in anode biofilm samples under different conditions.

[0096] Referring to the above figures, the genera Clastomycetes, Bacteroides, and Actinomycetes were dominant in all samples. Specifically, they accounted for more than 80% of the bacterial phylum in the anode and cathode biofilms of the BLBR. Clastomycetes, Bacteroides, and Actinomycetes include a large number of fermentative bacterial genera capable of hydrolysis and acid production (e.g., Chlostridium, Trichococcus, Brooklawnia, Corynebacterium).

[0097] The abundance of these bacterial phyla increased to varying degrees in the electrode biofilm compared to the leachate sample, depending on the applied voltage. Furthermore, the phylum Proteobacteria, including various genera capable of electron production and EET (i.e., Geobacter), was more abundant in the anode biofilm (1.97%) than in the cathode biofilm (0.69%) at an applied voltage of 0.9 V, which may contribute to the enhanced methane production performance.

[0098] Referring to the above diagram showing the relative abundance of bacterial genera in leachate, electrode biofilm and food waste residue samples under various conditions, Clostridium genus capable of carbohydrate fermentation and VFA production including acetate and butyrate had a high abundance in BLBR.

[0099] In particular, the highest abundance of this genus was observed in the anode biofilm at applied voltages of 0.6 V and 0.9 V, which were 5.3 times higher than those in the leachate sample, respectively.

[0100] The genus Corynebacterium is also capable of fermentation and, although low in abundance in the control samples, showed higher abundance in the electrode biofilms than in the leachate samples from the BLBR.

[0101] The abundances of other fermentative bacteria, including Christensenellaceae, Tricoccus, Brooklawnia, and Syntrophomonas, remained stable or exhibited minor changes between the leachate and electrode biofilms. In contrast, the genus Jeotgalibaca significantly decreased in all BLBR samples compared to the control. The relatively high abundance of Jeotgalibaca in LBRs operated without electrodes suggests that this bacterial genus may not be adapted to the environment of the bioelectrochemical system.

[0102] Under all conditions, the bacterial community structures between the food waste residue and leachate samples were very similar, suggesting that metabolic reactions in the FW basket and suspension of the BLBR would not significantly vary between the BLBR and the control. Furthermore, the total abundance of fermentative bacterial genera (mainly Clostridium, Christensenellaceae, Tricococcus, and Brooklawnia) was reduced in the cathode biofilm compared to the anode biofilm of the BLBR.

[0103]

[0104] Archaea of ​​BLBR

[0105] Referring to Fig. 10 above, Methanobacterium, a hydrogenotrophic methanogen, showed a significant increase in all cathode biofilm samples in the BLBR compared to the control group (12.5% ​​of archaea in the biofilm). The highest abundance of Methanobacterium was observed in the cathode biofilm at an applied voltage of 0.6 V, at 61.0%, and other conditions also had abundances ranging from 39.4% to 40.9% in the cathode biofilm compared to 12.5% ​​in the control group's cathode biofilm.

[0106] This genus is known to participate in direct and indirect interspecies electron transfer in syntrophic methanogenesis. Meanwhile, the genus Methanosarcina, which can perform both acetate substitution and CO2 reduction for methane production and can accept electrons from abiotic extracellular surfaces, also accounted for a relatively high abundance (31.8–51.2%) of the archaeal community in the cathode biofilms within the BLBR. Therefore, the predominant abundance of Methanobacterium and Methanosarcina (accounting for 82.2–93.6% of the total) in the cathode biofilms indicates that the cathode biofilms can more effectively accept electrons from the cathode for methane production and promote methane production.

[0107] Additionally, the anode biofilms also showed a predominant abundance of Methanobacterium and Methanosarcina, which accounted for 91.1–95.8% of the total archaea in the anode biofilms under different applied voltages, which was quite similar to the total abundance of 94.3% in the control anode biofilm (Fig. 10). The high abundance of Methanobacterium and Methanosarcina, although small, may suggest that these anode biofilms may serve as another potential site for synthetic methane production between ARB and methanogens via DIET, as they increase the number of EET-capable bacteria.

[0108] The above experimental results indicate that the voltage-applied BLBR enhanced methane production. Therefore, the theoretical methane production from this type of EET in the BLBR could be estimated and further used to identify the contributors to the enhanced methane production, which are summarized in Table 2 below.

[0109] Group0.3 V0.6 V0.9 V1.2 VV EET (L)0.0250.471.201.47V Total (L)14.517.421.217.1% of V EET in total methane production0.182.695.648.62CE (%)0.101.514.966.08

[0110] V here EETis the theoretical methane production amount assuming that all electrons transferred from the anode are used for methane production. Referring to the above results, the highest theoretical methane yield of EET through a closed circuit at an applied voltage of 1.2 V was 1.47 L, which was only 8.6% of the total methane yield during operation. Under these circumstances, the CE of BLBR was only about 6%. In the BLBR system, the theoretical methane yield through EET was much smaller than the total methane production, indicating that methane production through EET in a closed circuit cannot contribute to the methane yield, and the enhanced methane production may be more due to improved acidogenesis and acetogenesis under an applied voltage that increases the substrate (VFA) for methane production. As discussed above, it is desirable to apply a voltage to the BLBR in the range of 0.8 to 1.0 V, preferably 0.4 to 1.2 V, most preferably 0.6 to 1.1 V, and most suitably 0.9 V. In particular, the optimal applied voltage for methane production was 46% higher than the control group when it was 0.9 V. Further increasing the voltage to 1.2 V actually decreased the methane yield. In addition, no significant difference in VS removal was observed between these operations with different applied voltages. Furthermore, the contribution of direct electron transfer to the enhanced methane yield was less than 10%. The microbial community structure of the cathode biofilm indicated that the enrichment of hydrogenotrophic methane production through syn-methanogenesis could be attributed to enhanced acidogenesis and acetogenesis induced by the applied voltage.

[0111] Anode voltage conditions

[0112] In one embodiment of the present invention, a substrate such as acetate, ethanol, or propionate may be separately used to concentrate an anode-respiring bacterial biofilm such as Geobacter on the anode surface of the electrode.

[0113] In this experimental example, 10 mL of returned sludge collected from a sewage treatment plant was inoculated into the anode chamber of a dual-chamber microbial electrochemical device. As described above, 25 mM acetate culture medium was used as a substrate to enrich anode-respiring bacterial biofilms, such as geojectors. To maintain anaerobic conditions, the anode chamber was purged with N2 gas for more than 30 minutes and the culture medium was pumped into the anode chamber.

[0114] In one embodiment of the present invention, the anode and cathode used electrodes of the same material as above, and the two chambers were separated using an anion exchange membrane. The pH of the anode chamber was maintained at neutral, the temperature was maintained at 25 degrees, and the anode potential was fixed at -0.4 V (vs Ag / AgCl) using a potentiostat. The anode chamber was mixed using a magnetic stirrer, the hydraulic retention time was maintained at 5 hours (based on the anode chamber), and the current density and voltage were measured once every 2 minutes. As a result of the experiment, the average current density was 6±0.2 A / m2 based on the anode surface area, and Geobacter was the dominant species among the bacteria.

[0115]

[0116] The present invention relates to a method for producing biogas using a dry bioelectrochemical anaerobic digestion process from organic waste, and has industrial applicability.

Claims

1. A bioelectrochemical leaching bed reactor combined with a microbial electrolysis device, The upper part of the reactor including a basket (130) in which the food waste is fixed; A lower part of the reactor that receives leachate generated from the upper part of the reactor; and Includes a microbial electrolysis device equipped in the above reactor, The above microbial electrolysis device includes a membrane-shaped electrode and a voltage applying unit for applying voltage to the electrode, A bioelectrochemical leaching bed reactor combined with a microbial electrolysis device, characterized in that the voltage applying unit applies a voltage of more than 0.3 V and less than 1.2 V to the cathode of the electrode.

2. In paragraph 1, A bioelectrochemical leaching bed reactor combined with a microbial electrolysis device, characterized in that the voltage applying unit applies a voltage of 0.8 to 1.0 V.

3. In paragraph 1, The above bioelectrochemical leach bed reactor is characterized by including a leach bed reactor (LBR).

4. In paragraph 1, A bioelectrochemical leachate reactor characterized in that the microbial electrolysis device is provided outside the reactor, the leachate flows into the microbial electrolysis device and is electrolyzed, and the microorganisms after electrolysis are re-introduced into the reactor.

5. In paragraph 1, A bioelectrochemical leaching bed reactor characterized in that the biofilm of the cathode comprises 30% to 60% of the genus Methanosarcina.

6. In paragraph 1, A bioelectrochemical leachate reactor characterized in that VFA, which is a substrate of one or more of acetate, ethanol and propionate, can be used on the anode to concentrate an anode-respiring bacteria biofilm such as Geobacter on the anode surface among the above electrodes, and at this time, the anode potential is maintained at -0.4 to 0 V (vs. Ag / AgCl).

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