Study on Biological Pathway of Carbon Dioxide Methanation Based on Microbial Electrolysis Cell

Realization of CO_(2) resource utilization is the main development direction of CO_(2) reduction.The CO_(2) methana-tion technology based on microbial electrolysis cell(MEC)has the characteristics of ambient temperature and pressure,green and low-carbon,which meets the need of low-carbon energy transition.However,the lack of the system such as the change of applied voltage and the reactor amplification will affect the methane production efficiency.In this research,the efficiency of methane production with different applied voltages and different types of reactors was carried out.The results were concluded that the maximum methane production rate of the H-type two-chamber microbial electrolysis cells(MECs)at an applied voltage of 0.8 V was obtained to be 1.15 times higher than that of 0.5 V;under the same conditions of inoculated sludge,the reactor was amplified 2.5 times and the cumulative amount of methane production was 1.04 times higher than the original.This research can provide a theoretical basis and technical reference for the early industrial application of CO_(2) methanation tech-nology based on MEC.

Enhanced straw fermentation process based on microbial electrolysis cell coupled anaerobic digestion

The low quality and yield of methane severely hinder the industrial application of straw biogas fermentation, and no effective solution has been found so far. In this study, a novel method was developed when a microbial electrolysis cell(MEC) was coupled with normal anaerobic fermentation to enhance methane yield and purity. The fermentation process achieved a methane purity of more than 85%, which is considerably higher than that of previously published reports. With microbial stimulation and an electric current, the degradation of fibers has been greatly enhanced. The MEC system substantially improved the yield and purity of biogas, bringing a new path to the synthesis of methane by carbon dioxide and hydrogen ions in solution under electron irradiation. Electrochemical index analysis showed extra methane synthesis, due to the external circuit electron transfer. The results of the gas chromatography and solid degradation rate showed that the carbon source of extra methane was CO_(2) produced during normal fermentation and additional volatile solid degradation. These results show that the MEC considerably enhanced the quality and yield of methane in the straw fermentation process, providing insights into normal anaerobic fermentation.

Degradation Pathway of Benzothiazole and Microbial Community Structure in Microbial Electrolysis Cells

In this study, benzothiazole was entirely mineralized by an up-flow internal circulation microbial electrolysis reactor. The bioelectrochemical system was operated at ambient temperature under continuous-flow mode. The analysis of metabolite which was extracted by HPLC-MS from the bioreactor indicated that benzothiazole derivative ( BTH ) was firstly converted into 2-hydroxybenzothiazole in the microbial electrolysis cell (MEC) and then mineralized within three steps, i.e., the fracture of thiazole-ring through a series of oxidation and hydrolysis, the deamination and hydroxylation of 2-aminobenzenesulfonic acid, and the mineralization of various carboxylic acids to CO2 and H2O. Bacterial community analysis indicated that the applied electric field could selectively enrich certain species and the dominate bacteria on the electrodes belonged to Proteobacteria, Bacteroidetes, and Firmicutes. Results show that MEC can improve the degradation efficiency of BTH in wastewater, enable the microbiological reactor to satisfy the requirements of high loading rate, thereby fulfilling the scale-up of whole process in the future.

Fuzzy logic controller implementation on a microbial electrolysis cell for biohydrogen production and storage

This work presents the implementation of fuzzy logic control(FLC) on a microbial electrolysis cell(MEC).Hydrogen has been touted as a potential alternative source of energy to the depleting fossil fuels. MEC is one of the most extensively studied method of hydrogen production. The utilization of biowaste as its substrate by MEC promotes the waste to energy initiative. The hydrogen production within the MEC system, which involves microbial interaction contributes to the system's nonlinearity. Taking into account of the high complexity of MEC system, a precise process control system is required to ensure a wellcontrolled biohydrogen production flow rate and storage application inside a tank. Proportionalderivative-integral(PID) controller has been one of the pioneer control loop mechanism. However, it lacks the capability to adapt properly in the presence of disturbance. An advanced process control mechanism such as the FLC has proven to be a better solution to be implemented on a nonlinear system due to its similarity in human-natured thinking. The performance of the FLC has been evaluated based on its implementation on the MEC system through various control schemes progressively. Similar evaluations include the performance of Proportional-Integral(PI) and PID controller for comparison purposes. The tracking capability of FLC is also accessed against another advanced controller that is the model predictive controller(MPC). One of the key findings in this work is that the FLC resulted in a desirable hydrogen output via MEC over the PI and PID controller in terms of shorter settling time and lesser overshoot.

Efficient degradation of aqueous dichloromethane by an enhanced microbial electrolysis cell:Degradation kinetics,microbial community and metabolic mechanisms

Dichloromethane(DCM)has been listed as a toxic and harmful water pollutant,and its re moval needs attention.Microbial electrolysis cells(MECs)are viewed as a promising alterna tive for pollutant removal,which can be strengthened from two aspects:microbial inocula tion and acclimation.In this study,the MEC for DCM degradation was inoculated with the ac tive sludge enhanced by Methylobacterium rhodesianum H13(strain H13)and then acclimated in the form of a microbial fuel cell(MFC).Both the introduction of strain H13 and the initi ation in MFC form significantly promoted DCM degradation.The degradation kinetics were fitted by the Haldane model,with V_(max),K_(h),K_(i)and v_(max)values of 103.2 mg/L/hr,97.8 mg/L268.3 mg/L and 44.7 mg/L/hr/cm^(2),respectively.The cyclic voltammogram implies that DCM redox reactions became easier with the setup of MEC,and the electrochemical impedance spectrogram shows that the acclimated and enriched microbes reduced the charge transfe resistance from the electrode to the electrolyte.In the biofilm,the dominant genera shifted from Geobacter to Hyphomicrobium in acclimation stages.Moreover,Methylobacterium played an increasingly important role.DCM metabolism mainly occurred through the hydrolytic glutathione S-transferase pathway,given that the gene dcmA was identified rather than the dhlA and P450/MO.The exogenous electrons facilitated the reduction of GSSG,directly o indirectly accelerating the GSH-catalyzed dehalogenation.This study provides support fo the construction of an efficient and stable MEC for DCM removal in water environment.

初始pH调控对MEC脱硫性能的影响及其微生物作用机制

采用微生物电解池(MEC)工艺,在阳极电活性微生物的协同作用下实现硫化物的脱除,是沼气脱硫新工艺和研究热点。针对长期运行的脱硫MEC工艺,由于非特异性阳离子竞争使阳极产生的质子向阴极转移受阻,造成MEC脱硫效率低、稳定运行难,本研究采用不同初始pH调控脱硫MEC的质子平衡,通过脱硫性能、电化学性能和微生物动力学解析,阐明pH调控对MEC脱硫性能的影响和微生物作用机制。结果表明,初始pH在7~9时均可形成稳定且具有高效脱硫功能的阳极生物膜,最大电流密度相近,脱硫效率均达95%以上,COD去除率80%以上。与初始pH为8、9相比,初始pH为7时,脱硫过程pH波动最小,MEC运行稳定,S^(2-)去除最高达100%;阳极生物膜的氧化还原峰最显著,质子与电子转移速率加快;优势微生物Thiomonas与Desulfovibrio丰度更高,主要参与硫化物的氧化脱除。可见,通过脱硫MEC阳极室初始pH的调控,可有效提高MEC脱硫工艺性能和运行稳定性,为沼气微生物电化学脱硫的应用提供技术支撑。

Approximate Analytical Expressions for the Concentrations of Acetate and Methane in the Microbial Electrochemical Cell

Mathematical modeling of microbial electrochemical cells (MXCs) for both microbial fuel cell and microbial electrolysis cell is discussed. The model is based on the system of reaction diffusion of reaction-diffusion equation containing a non-linear term related to substrate consumption rates by electrogeneic and methanogenic microorganism in the bioflim. This paper presents the approximate analytical method to solve the non-linear differential equation that describes the diffusion coupled with acetate (substrate) consumption rates. Simple analytical expressions for the concentrations of acetate and methane have been derived for all experimental values of bulk concentration, distributions of microbial volume fraction, local potential in the biofilm and biofilm thickness. In addition, sensitivity of the parameters on concentrations is also discussed. Our analytical results are also validated with the numerical results and limiting cases results. Further, a graphical procedure for estimating the kinetic parameters is also suggested.

MDC和MEC及其耦合系统在水处理应用的研究进展

为了处理废水,介绍了微生物脱盐燃料电池和微生物电解电池的起源、原理并结合国内外研究对其各自在废水处理方面的应用。提出了一种无需外加电源辅助的新工艺—MDC-MEC耦合系统,结合以上二者的原理为此耦合系统运行提供一定理论基础,此系统能够结合微生物脱盐电池特性,利用MDC进行产电、脱氨及氨回收,并将MDC作为微生物电解电池的外加电源辅助制氢,也对其在国内外在废水处理方面的应用进行综述,最后对MDC-MEC耦合系统的性能优化进行了展望。

阴极材料对MEC-AD体系产甲烷性能的影响评估

为了研究阴极材料对微生物电解池(MEC)耦合厌氧消化(AD)体系产甲烷性能的影响,分别将不锈钢、钛、泡沫铜、泡沫镍作为阴极,分析不同阴极材料所处体系在不同电压条件下的产气性能、阴极材料的电化学特性以及阳极微生物群落结构。结果表明:在4种阴极材料中,泡沫铜和泡沫镍所处的体系产甲烷、析氢性能最强,电子传递效率及电化学活性较不锈钢和钛强,所处体系中阳极产甲烷功能菌含量明显高于不锈钢和钛,故直接电子传递效率较强。由于泡沫铜易被氧化,故泡沫镍作为阴极材料具有一定的优越性。

Hydrogen production performance of the non⁃platinum⁃based MoS_(2)/CuS cathode in microbial electrolytic cells

MoS_(2)/CuS composite catalysts were successfully synthesized using a one-step hydrothermal method with sodium molybdate dihydrate,thiourea,oxalic acid,and copper nitrate trihydrate as raw materials.The hydrogen pro-duction performance of MoS_(2)/CuS prepared with different molar ratios of Mo to Cu precursors(n_(Mo)∶n_(Cu))as cathodic catalysts was investigated in the two-chamber microbial electrolytic cell(MEC).X-ray diffraction(XRD),X-ray pho-toelectron spectroscopy(XPS),scanning electron microscopy(SEM),transmission electron microscope(TEM),linear scanning voltammetry(LSV),electrochemical impedance analysis(EIS),and cyclic voltammetry(CV)were used to characterize the synthesized catalysts for testing and analyzing the hydrogen-producing performance.The results showed that the hydrogen evolution performance of MoS_(2)/CuS-20%(nMo∶nCu=5∶1)was better than that of platinum(Pt)mesh,and the hydrogen production rate of MoS_(2)/CuS-20%as a cathode in MEC was(0.2031±0.0237)m^(3)_(H_(2))·m^(-3)·d^(-1) for 72 h at an applied voltage of 0.8 V,which was slightly higher than that of Pt mesh of(0.1886±0.0134)m^(3)_(H_(2))·m^(-3)·d^(-1).The addition of a certain amount of CuS not only regulates the electron transfer ability of MoS_(2) but also increases the density of active sites.

A strategy for enhancing anaerobic digestion of waste activated sludge: Driving anodic oxidation by adding nitrate into microbial electrolysis cell

Cathodic reduction of CO_2 and anodic oxidation of organic matters are crucial to methaneproducing microbial electrolysis cell(MEC) applied in anaerobic digestion of waste activated sludge. However, cathodic CO_2 reduction is usually restrained by slow metabolism rates of H_2-utilizing methanogens and low electron-capturing capacity of CO_2, which consequently slows down the anodic oxidation that participates to sludge disintegration. Herein, a strategy with adding nitrate as electron acceptor to foster electronic transfer between the anode and cathode was proposed to improve anodic oxidation. Results showed that the average efficiency of anodic oxidation in the nitrate-added MEC increased by 55.9%. Accordingly,volatile suspended solid removal efficiency in the nitrate-added MEC was 21.9% higher than that of control MEC. Although the initial cumulative methane production in the nitrateadded MEC was lower than that of control MEC, the cumulative methane production in 24 days was 8.9% higher. Fourier transform infrared spectroscopy analysis indicated that anodic oxidation of MEC with nitrate accelerated the disintegration of sludge flocs and cell walls. Calculation on current signal further revealed that anodic oxidation driven by cathodic nitrate reduction was the main mechanism responsible for the improved sludge digestion.

Treatment of recalcitrant wastewater and hydrogen production via microbial electrolysis cells

A large amount of real complex wastewaters are generated every year,which leads to a great environmental burden.Various treatment technologies were deployed to remove the contaminants in the wastewaters.However,these actual wastewaters have not been sufficiently treated due to their complex properties,high-concentration organics,incomplete utilization of hard-biodegradable substrates,the high energy input required,etc.Recently,microbial electrolysis cells(MECs),a great potential technology,has emerged for various wastewater treatment,because not only do they demonstrate satisfactory performance during wastewater treatment,but they also generate renewable H2 as a clean energy carrier.Unlike previous reviews,this review introduced the characteristics of every complicated wastewater,and focused on analyzing and summarizing MEC development for wastewater treatment.The performances of MECs were systematically reviewed in terms of organics removal,H2 production,Columbic efficiency,and energy efficiency.MEC performances for treating actual complex wastewaters and producing H2 can be optimized through operation parameters,electrode materials,catalyst materials,etc.In addition,the challenges and opportunities including complexity of wastewaters,instability of H2 production,robust microorganisms,effect of membrane on two-chamber MEC,and integration of MEC with other treatment processes were deeply discussed.Except for the technical feasibility,both environmental feasibility and economic feasibility also need to meet social requirements.This review can indeed provide a basis for high-efficiency treatment and practical commercial applications of recalcitrant wastewaters via MECs in the future.

Effects of organic strength on performance of microbial electrolysis cell fed with hydrothermal liquefied wastewater

Microbial electrochemical technology has drawn increasing attention for the treatment of recalcitrant wastewater as well as production of energy or value-added chemicals recently.However,the study on the treatment of hydrothermal liquefied wastewater(HTL-WW)using microbial electrolysis cell(MEC)is still in its infancy.This study focused on the effects of organic loading rates(OLRs)on the treatment efficiency of recalcitrant HTL-WW and hydrogen production via the MEC.In general,the chemical oxygen demand(COD)removal rate was more than 71.74%at different initial OLRs.Specially,up to 83.84%of COD removal rate was achieved and the volatile fatty acids were almost degraded at the initial OLR of 2 g COD/L·d in the anode of MEC.The maximum hydrogen production rate was 3.92 mL/L·d in MEC cathode,corresponding to a hydrogen content of 7.10%at the initial OLR of 2 g COD/L·d.And in the anode,the maximum methane production rate of 826.87 mL/L·d was reached with its content of 54.75%at the initial OLR of 10 g COD/L·d.Analysis of electrochemical properties showed that the highest open circuit voltage of 0.48 V was obtained at the initial OLR of 10 g COD/L·d,and the maximum power density(1546.22 mW/m3)as well as the maximum coulombic efficiency(6.01%)were obtained at the initial OLR of 8 g COD/L·d.GC-MS analysis revealed the existence of phenols and heterocyclic matters in the HTL-WW,such as 1-acetoxynonadecane and 2,4-bis(1-phenylethyl)-phenol.These recalcitrant compounds in HTL-WW were efficiently removed via MEC,which was probably due to the combination effect of microbial community and electrochemistry in MEC anode.

Microbial electrolysis cells with biocathodes and driven by microbial fuel cells for simultaneous enhanced Co（Ⅱ） and Cu（Ⅱ） removal

Cobalt and copper recovery from aqueous Co （II） and Cu（II） is one critical step for cobalt and copper wastewaters treatment. Previous tests have primarily examined Cu（II） and Co（II） removal in microbial electro- lysis cells （MECs） with abiotic cathodes and driven by microbial fuel cell （MFCs）. However, Cu（II） and Co（II） removal rates were still slow. Here we report MECs with biocathodes and driven by MFCs where enhanced removal rates of 6.0＋0.2mg·L^-1·h^-1 for Cu（II） at an initial concentration of 50 mg·L^-1 and 5.3~0.4mg·L^-1·h^-1 for Co（II） at an initial 40 mg· L^-1 were achieved, 1.7 times and 3.3 times as high as those in MECs with abiotic cathodes and driven by MFCs. Species of Cu（II） was reduced to pure copper on the cathodes of MFCs whereas Co（II） was removed associated with microorganisms on the cathodes of the connected MECs. Higher Cu（II） concentrations and smaller working volumes in the cathode chambers of MFCs further improved removal rates of Cu（II） （115.7 mg·L^-1·h^-1） and Co（II） （6.4 mg·L^-1·h^-1） with concomi- tantly achieving hydrogen generation （0.054-0.00 mol·mol^-1 COD）. Phylogenetic analysis on the bio- cathodes indicates Proteobacteria dominantly accounted for 67.9% of the total reads, followed by Firmicutes （14.0%）, Bacteroidetes （6.1%）, Tenericutes （2.5%）, Lentisphaerae （1.4%）, and Synergistetes （1.0%）. This study provides a beneficial attempt to achieve simultaneous enhanced Cu（II） and Co（II） removal, and efficient Cu（II） and Co（II） wastewaters treatment without any external energy consumption.

Pesticide wastewater treatment using the combination of the microbial electrolysis desalination and chemical-production cell and Fenton process

The combination of the microbial electrolysis desalination and chemical-production cell(MEDCC)and Fenton process for the pesticide wastewater treatment was investigate in this study.Real wastewater with several toxic pesticides,1633 mg/L COD,and 200 in chromaticity was used for the investigation.Results showed that desalination in the desalination chamber of MEDCC reached 78%.Organics with low molecular weights in the desalination chamber could be removed from the desalination chamber,resulting in 28%and 23%of the total COD in the acid-production and cathode chambers,respectively.The desalination in the desalination chamber and organic transfer contributed to removal of pesticides(e.g.,triadimefon),which could not be removed with other methods,and of the organics with low molecular weights.The COD in the effluent of the MEDCC combined the Fenton process was much lower than that in the perixo-coagulaiton process(<150 vs.555 mg/L).The combined method consumed much less energy and acid for the pH adjustment than that the Fenton.

Identification of potential electrotrophic microbial community in paddy soils by enrichment of microbial electrolysis cell biocathodes

Electrotrophs are microbes that can receive electrons directly from cathode in a microbial electrolysis cell(MEC).They not only participate in organic biosynthesis,but also be crucial in cathode-based bioremediation.However,little is known about the electrotrophic community in paddy soils.Here,the putative electrotrophs were enriched by cathodes of MECs constructed from five paddy soils with various properties using bicarbonate as an electron acceptor,and identified by 16S rRNA-gene based Illumina sequencing.The electrons were gradually consumed on the cathodes,and 25%–45% of which were recovered to reduce bicarbonate to acetic acid during MEC operation.Firmicutes was the dominant bacterial phylum on the cathodes,and Bacillus genus within this phylum was greatly enriched and was the most abundant population among the detected putative electrotrophs for almost all soils.Furthermore,several other members of Firmicutes and Proteobacteria may also participate in electrotrophic process in different soils.Soil pH,amorphous iron and electrical conductivity significantly influenced the putative electrotrophic bacterial community,which explained about 33.5% of the community structural variation.This study provides a basis for understanding the microbial diversity of putative electrotrophs in paddy soils,and highlights the importance of soil properties in shaping the community of putative electrotrophs.

微波联合MEC处理市政污泥运行性能研究

以微波预处理污泥为底物,厌氧消化污泥为接种物,构建单室无膜微生物电解池(MEC)进行批式实验,考察外加电压对系统运行性能的影响。结果表明:在外加电压为0~1.2 V的范围内,系统甲烷产量、溶解性有机物(SCOD)去除率及挥发性悬浮物(VSS)去除率均随电压的升高而升高,最大值分别为286 mL、85.1%和59.6%,比0 V电压组分别提高了89.4%、56.9%和39.9%。更高的外加电压(1.6 V)则对微生物代谢活性产生抑制作用,导致系统运行性能下降。

双区式MEC处理低C/N比轻度污染废水研究

以异养硝化-好氧反硝化菌为主体,构建了微氧-缺氧双区式微生物电解池MEC(R1),并以缺氧单区MEC(R2)作为对照组,采用连续进水方式,研究其对低C/N比轻度污染废水的脱氮处理效果及微生物强化机制。结果表明,在进水COD 70~80 mg/L、TN质量浓度35~40 mg/L、电流3m A、溶解氧(DO)质量浓度0. 5~1. 0 mg/L的条件下,连续运行约1个月后,R1出水COD、TN质量浓度即可达到一级A排放标准;当C/N比为2~5时,R1出水TN质量浓度为(4. 90±1. 08)^(14. 50±0. 133) mg/L,COD为(8. 20±2. 36)^(12. 53±5. 03) mg/L,均达到了一级A标准,硝化-好氧反硝化及弱电强化作用是脱氮和COD去除的主要途径。高通量测序分析结果表明,R1中细菌多样性虽与R2相当,但细菌丰富度明显大于R2;而且,R1中的贫营养硝化反硝化菌属Zoogloea丰度明显大于R2,且含有自养型反硝化菌属Moheibacterm、好氧反硝化菌属Ferruginibacter和Denitratisoma及可为反硝化提供聚β-羟丁酸的Plasticicumulans菌属。研究表明双区式MEC可有效处理低COD、低TN、低C/N比的废水,且具有启动快的特点,具有良好的应用潜力。

MEC产氢过程中抑制产甲烷作用的研究进展

生物电化学系统中,对抑制产甲烷作用的研究是在微生物电解池(MEC)厌氧消化产氢中非常重要的一环。依据目前的研究结果,主要采用定期曝气、缩短HRT、加入甲烷抑制剂、控制温度、调节SRT、控制氧化还原电位等方法来抑制产甲烷菌的活性。其中,低温,调节SRT和氧化还原电位对于需要长时间运行的MEC反应器而言,是相对较好的方法。

微生物电解池催化CO_(2)电转化为甲烷:影响因素、电子传递和展望

化石燃料作为能源供应的主要来源,燃烧导致大量CO_(2)的释放和温室效应,CO_(2)的捕获和再利用越来越受到人们的关注.微生物电解池(MEC)作为一种新的CO_(2)再利用技术,可通过将电活性微生物与电化学刺激相结合,将CO_(2)通过生物电化学作用回收为低碳燃料(如CH_(4)),从而实现CO_(2)固定和能量回收.尽管近年来MEC领域有较多研究,但仍然存在许多问题阻碍了该技术的规模化和产业化.本文梳理了CO_(2)电化学产甲烷的工作原理、性能影响的关键因素、生物阴极电活性功能微生物及其胞外电子传递机制、电催化耦合技术的最新研究进展,提出了MEC辅助CO_(2)电甲烷化技术的未来研究需求和挑战.