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.

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.

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.

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.

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.

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.

Enhanced hydrogen production in microbial electrolysis through strategies of carbon recovery from alkaline/thermal treated sludge

The aim of this study was to investigate the biohydrogen production from thermal(T),alkaline(A)or thermal-alkaline(TA)pretreated sludge fermentation liquid(SFL)in a microbial electrolysis cells(MECs)without buffer addition.Highest hydrogen yield of 36.87±4.36 mgH_(2)/gVSS(0.026 m^(3)/kg COD)was achieved in TA pretreated SFL separated by centrifugation,which was 5.12,2.35 and 43.25 times higher than that of individual alkaline,thermal pretreatment and raw sludge,respectively.Separating SFL from sludge by centrifugation eliminated the negative effects of particulate matters,was more conducive for hydrogen production than filtration.The accumulated short chain fatty acid(SCFAs)after pretreatments were the main substrates for MEC hydrogen production.The maximum utilization ratio of acetic acid,propionic acid and n-butyric acid was 93.69%,90.72%and 91.85%,respectively.These results revealed that pretreated WAS was highly efficient to stimulate the accumulation of SCFAs.And the characteristics and cascade bioconversion of complex substrates were the main factor that determined the energy efficiency and hydrogen conversion rate of MECs.

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.

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.

Effects of bicarbonate and cathode potential on hydrogen production in a biocathode electrolysis cell

A biocathode with microbial catalyst in place of a noble metal was successfully developed for hydrogen evolution in a microbial electrolysis cell （MEC）. The strategy for fast biocathode cultivation was demonstrated. An exoelectrogenic reaction was initially extended with an H2-full atmosphere to enrich Ha-utilizing bacteria in a MEC bioanode. This bioanode was then inversely polarized with an applied voltage in a half-cell to enrich the hydrogen-evolving biocathode. The electrocatalytic hydrogen evolution reaction （HER） kinetics of the biocathode MEC could be enhanced by increasing the bicarbonate buffer concentration from 0.05 mol·L-1 to 0.5 mol· L-1 and/or by decreasing the cathode potential from -0.9 V to - 1.3 V vs. a saturated calomel electrode （SCE）. Within the tested potential region in this study, the HER rate of the biocathode MEC was primarily influenced by the microbial catalytic capability. In addition, increasing bicarbonate concentration enhances the electric migration rate of proton carriers. As a consequence, more mass H＋ can be released to accelerate the biocathode-catalyzed HER rate. A hydrogen production rate of 8.44 m3. m 3. d1 with a current density of 951.6 A. m-3 was obtained using the biocathode MEC under a cathode potential of - 1.3 V vs. SCE and 0.4 mol· L-1 bicarbonate. This study provided information on the optimization of hydrogen production in biocathode MEC and expanded the practical applications thereof.

Carbon Fibers for Bioelectrochemical:Precursors,Bioelectrochemical System,and Biosensors

Carbon fibers(CFs)demonstrate a range of excellent properties including(but not limited to)microscale diameter,high hardness,high strength,light weight,high chemical resistance,and high temperature resistance.Therefore,it is necessary to summarize the application market of CFs.CFs with good physical and chemical properties stand out among many materials.It is believed that highly fibrotic CFs will play a crucial role.This review first introduces the precursors of CFs,such as polyacrylonitrile,bitumen,and lignin.Then this review introduces CFs used in BESs,such as electrode materials and modification strategies of MFC,MEC,MDC,and other cells in a large space.Then,CFs in biosensors including enzyme sensor,DNA sensor,immune sensor and implantable sensor are summarized.Finally,we discuss briefly the challenges and research directions of CFs application in BESs,biosensors and more fields.

Enhancement of hydrogen production and energy recovery through electro-fermentation from the dark fermentation effluent of food waste

To enhance hydrogen production efficiency and energy recovery,a sequential dark fermentation and microbial electrochemical cell(MEC)process was evaluated for hydrogen production from food waste.The hydrogen production,electrochemical performance and microbial community dynamics were investigated during startup of the MEC that was inoculated with different sludges.Results suggest that biogas production rates and hydrogen proportions were 0.83 L/L d and 92.58%,respectively,using anaerobic digested sludge,which is higher than that of the anaerobic granular sludge(0.55 L/L d and 86.21%).The microbial community were predominated by bacterial genus Acetobacterium,Geobacter,Desulfovibrio,and archaeal genus Methanobrevibacter in electrode biofilms and the community structure was relatively stable both in anode and cathode.The sequential system obtained a 53.8% energy recovery rate and enhanced soluble chemical oxygen demand(sCOD)removal rate of 44.3%.This research demonstrated an important approach to utilize dark fermentation effluent to maximize the conversion of fermentation byproducts into hydrogen.

Response of indigenous Cd-tolerant electrochemically active bacteria in MECs toward exotic Cr（VI） based on the sensing of fluorescence probes

Electrochemically active bacteria （EAB） on the cathodes of microbial electrolysis cells （MECs） can remove metals from the catholyte, but the response of these indigenous EAB toward exotic metals has not been examined, particularly from the perspective of the co-presence of Cd（II） and Cr（VI） in a wastewater. Four known indigenous Cd-tolerant EAB of Ochrobactrum sp X l, Pseudomonas sp X3, Pseudomonas delhiensis X5, and Ochrobactrum anthropi X7 removed more Cd（II） and less Cr（VI） in the simultaneous presence of Cd（II） and Cr（VI）, compared to the controls with individual Cd（II） or single Cr（VI）. Response of these EAB toward exotic Cr（VI） was related to the associated subcellular metal distribution based on the sensing of fluorescence probes. EAB cell membrane harbored more cadmium than chromium and cytoplasm located more chromium than cadmium, among which the imaging ofintracelluler Cr（III） ions increased over time, contrary to the decreased trend for Cd（II） ions. Compared to the controls with single Cd（II）, exotic Cr（VI） decreased the imaging of Cd（II） ions in the EAB at an initial 2 h and negligibly affected therealier. However, Cd（II） diminished the imaging of Cr （III） ions in the EAB over time, compared to the controls with individual Cr（VI）. Current accelerated the harboring of cadmium at an initial 2 h and directed the accumulation of chromium in EAB over time. This study provides a viable approach for simultaneously quantitatively imaging Cd（II） and Cr （III） ions in EAB and thus gives valuable insights into the response of indigenous Cd-tolerant EAB toward exotic Cr（VI） in MECs.

Bioelectrochemical system-mediated waste valorization

Bioelectrochemical systems(BESs)are a new and emerging technology in the field of fermentation technology.Electrical energy was provided externally to the microbial electrolysis cells(MECs)to generate hydrogen or value-added chemicals,including caustic,formic acid,acetic acid,and peroxide.Also,BES was designed to recover nutrients,metals or remove recalcitrant compounds.The variety of naturally existing microorganisms and enzymes act as a biocatalyst to induce poten-tial differences amid the electrodes.BESs can be performed with non-catalyzed electrodes(both anode and cathode)under favorable circumstances,unlike conventional fuel cells.In recent years,value-added chemical producing microbial electrosyn-thesis(MES)technology has intensely broadened the prospect for BES.An additional strategy includes the introduction of innovative technologies that help with the manufacturing of alternative materials for electrode preparation,ion-exchange membranes,and pioneering designs.Because of this,BES is emerging as a promising technology.This article deliberates recent signs of progress in BESs so far,focusing on their diverse applications beyond electricity generation and resulting performance.