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.

Long-term open circuit microbial electrosynthesis system promotes methanogenesis

Microbial electrosynthesis(MES) can potentially provide a mean for storing renewable energy surpluses as chemical energy. However, the fluctuating nature of these energy sources may represent a threat to MES, as the microbial communities that develop on the biocathode rely on the continuous existence of a polarized electrode. This work assesses how MES performance, product generation and microbial community evolution are affected by a long-period(6 weeks) power off(open circuit). Acetogenic and H2-producing bacteria activity recovered after reconnection. However, few days later syntrophic acetate oxidation bacteria and H2-consuming methanogens became dominant, producing CH4 as the main product, via electromethanogenesis and the syntrophic interaction between eubacterial and archaeal communities which consume both the acetic acid and the hydrogen present in the cathode environment. Thus,the system proved to be resilient to a long-term power interruption in terms of electroactivity. At the same time, these results demonstrated that the system could be extensively affected in both end product generation and microbial communities.

A Comprehensive Review on Oxygen Reduction Reaction in Microbial Fuel Cells

The focus of microbial fuel cell research in recent years has been on the development of materials,microbes,and transfer of charges in the system,resulting in a substantial improvement in current density and improved power generation.The cathode is generally recognized as the limiting factor due to its high-distance proton transfer,slow oxygen reduction reaction(ORR),and expensive materials.The heterogeneous reaction determines power gen-eration in MFC.This comprehensive review describes-recent advancements in the development of cathode mate-rials and catalysts associated with ORR.The recent studies indicated the utilization of different metal oxides,the ferrite-based catalyst to overcome this bottleneck.These studies conclude that some cathode materials,in parti-cular,graphene-based conductive polymer composites with non-precious metal catalysts provide substantial ben-efits for sustainable development in the field of MFCs.Furthermore,it also highlights the potentiality to replace the conventional platinum air cathode for the large-scale production of the next generation of MFCs.It was evi-dent from the experiments that cathode catalyst needs to be blended with conductive carbon materials to make cathode conductive and efficient for ORR.This review discusses various antifouling strategies for cathode biofoul-ing and its effect on the MFC performance.Moreover,it also depicts cost estimations of various catalysts essential for further scale-up of MFC technology.

Selective butyric acid production from CO_(2)and its upgrade to butanol in microbial electrosynthesis cells

Microbial electrosynthesis(MES)is a promising carbon utilization technology,but the low-value products(i.e.,acetate or methane)and the high electric power demand hinder its industrial adoption.In this study,electrically efficient MES cells with a low ohmic resistance of 15.7 mU m^(2)were operated galvanostatically in fed-batch mode,alternating periods of high CO_(2)and H2 availability.This promoted acetic acid and ethanol production,ultimately triggering selective(78%on a carbon basis)butyric acid production via chain elongation.An average production rate of 14.5 g m^(-2)d^(-1)was obtained at an applied current of 1.0 or 1.5 mA cm^(-2),being Megasphaera sp.the key chain elongating player.Inoculating a second cell with the catholyte containing the enriched community resulted in butyric acid production at the same rate as the previous cell,but the lag phase was reduced by 82%.Furthermore,interrupting the CO_(2)feeding and setting a constant pH2 of 1.7e1.8 atm in the cathode compartment triggered solventogenic butanol production at a pH below 4.8.The efficient cell design resulted in average cell voltages of 2.6e2.8 V and a remarkably low electric energy requirement of 34.6 kWhel kg1 of butyric acid produced,despite coulombic efficiencies being restricted to 45%due to the cross-over of O_(2)and H2 through the membrane.In conclusion,this study revealed the optimal operating conditions to achieve energy-efficient butyric acid production from CO_(2)and suggested a strategy to further upgrade it to valuable butanol.

Effect of temperature switchover on the degradation of antibiotic chloramphenicol by biocathode bioelectrochemical system

Exposure to chloramphenicol（CAP）,a chlorinated nitroaromatic antibiotic,can induce CAP-resistant bacteria/genes in diverse environments. A biocathode bioelectrochemical system（BES） was applied to reduce CAP under switched operational temperatures.When switching from 25 to 10°C,the CAP reduction rate（kCAP） and the maximum amount of the dechlorinated reduced amine product（AMCl,with no antibacterial activity） by the biocathode communities were both markedly decreased. The acetate and ethanol yield from cathodophilic microbial glucose fermentation（with release of electrons） was also reduced. Formation of the product AMCl was enhanced by the biocathode dechloridation reaction compared with that produced from pure electrochemical or microbial dechloridation processes. The electrochemical and morphological analyses of cathode biofilms demonstrated that some cathodophilic microbes could adapt to low temperature and play a key role in CAP degradation. The resilient biocathode BES has a potential for the treatment of CAP-containing wastewater in temperature fluctuating environments.

Sediment microbial fuel cell with floating biocathode for organic removal and energy recovery

A sediment microbial fuel cell （SMFC） with three dimensional floating biocathode （FBC） was developed for the electricity generation and biodegradation of sediment organic matter in order to avoid negative effect of dissolved oxygen （DO） depletion in aqueous environments on cathode performance and search cost-effective cathode materials. The biocathode was made from graphite granules with microbial attachment to replace platinum （Pt）-coated carbon paper cathode in a laboratory-scale SMFC （3 L in volume） filled with river sediment （organic content 49±4 g. kg^-1 dry weight）. After start-up of 10 days, the maximum power density of 1.00W.m^-3 （based on anode volume） was achieved. The biocathode was better than carbon paper cathode catalyzed by Pt. The attached biofilm on cathode enhanced power generation significantly. The FBC enhanced SMFC performance further in the presence aeration. The SMFC was continuously operated for an over 120-day period. Power generation peaked within 24 days, declined gradually and stabilized at a level of 1/6 peak power output. At the end, the sediment organic matter content near the anode was removed by 29% and the total electricity generated was equal to 0.251 g of chemical oxygen demand （COD） removed.

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.

Scaling up a novel denitrifying microbial fuel cell with an oxic-anoxic two stage biocathode

A scaled up microbial fuel cell （MFC） of a 50 L volume was set up with an oxic-anoxic two-stage biocathode and activated semicoke packed electrodes to achieve simultaneous power generation and nitrogen and organic matter removals. An average maximum power density of 43.1 W·m^-3 was obtained in batch operating mode. By adjusting the two extemal resistances, the denitrification in the A-MFC and power production in the O-MFC could be enhanced. In continuous mode, when the hydraulic retention times were set at 6 h, 8 h and 12 h, the removal efficiencies of COD, NHf-N and total nitrogen （TN） were higher than 95%, 97%, and 84%, respectively. Meanwhile the removal loads for COD, NH4^＋-N and TN were10, 0.37 and 0.4 kg·（m^3·d）^-1, respectively.

Hydrogen Production Using ‘‘Direct-Starting” Biocathode Microbial Electrolysis Cell and the Analysis of Microbial Communities

In this study, a ‘‘direct-starting'' procedure was used to activate a single-chamber biocathode microbial electrolysis cell(MEC) and the development of a biocathode was studied through output current curves and cyclic voltammograms. It only took 163 h for a successful start-up, and a current density of 14.75 A/m^2 was obtained. In the formal hydrogen-production stage, it was found that the biocathode MEC was comparable with the Pt/C cathode MEC in terms of current density and energy efficiency, and the hydrogen recovery, cathodic hydrogen recovery, and hydrogen production rate of the biocathode MEC were 71.22% ± 8.98%, 79.42% ± 5.94%, and 0.428 ± 0.054 m^3 H_2/m^3 days, respectively, which were slightly higher than those obtained with the Pt/C cathode MEC. Besides, under the effect of applied voltage, the microbial populations in the anodophilic biofilm of MEC(MECan) and the cathodophilic biofilm of MEC(MECca) were less diverse than those of the original aerobic activated sludge(AAS) and the anodophilic biofilm of MEC(MECan). Furthermore, the microbial community structures evidently differed between MECan/MECca and AAS/MFC.

Effect of air-exposed biocathode on the performance of a Thauera-dominated membraneless single-chamber microbial fuel cell (SCMFC)

To investigate the effect of air-exposed biocathode（AEB） on the performance of singlechamber microbial fuel cell（SCMFC）, wastewater quality, bioelectrochemical characteristics and the electrode biofilms were researched. It was demonstrated that exposing the biocathode to air was beneficial to nitrogen removal and current generation. In Test 1 of 95%AEB, removal rates of ammonia, total nitrogen（TN） and chemical oxygen demand（COD）reached 99.34% ± 0.11%, 99.34% ± 0.10% and 90.79% ± 0.12%, respectively. The nitrogen removal loading rates were 36.38 g N/m3/day. Meanwhile, current density and power density obtained at 0.7 A/m3 and 104 m W/m3 respectively. Further experiments on opencircuit（Test 2） and carbon source（Test 3） indicated that this high performance could be attributed to simultaneous biological nitrification/denitrification and aerobic denitrification, as well as bioelectrochemical denitrification. Results of community analysis demonstrated that both microbial community structures on the surface of the cathode and in the liquid of the chamber were different. The percentage of Thauera, identified as denitrifying bacteria, maintained at a high level of over 50% in water, but decreased gradually in the AEB. Moreover, the genus Nitrosomonas, Alishewanella, Arcobacter and Rheinheimera were significantly enriched in the AEB, which might contribute to both enhancement of nitrogen removal and electricity generation.

Trickling filter in a biocathode microbial fuel cell for efficient wastewater treatment and energy production

Aiming to reduce the energy input, oxygen supply by trickling filter was employed in a biocathode microbial fuel cell(MFC) to examine its performance of electricity production and sewage treatment. During batch operation, trickling MFC(TMFC) could start and aerate effectively(DO>3.60 mg/L). During continuous operation, TMFC produced a maximum current density of 71.8 A/m^3 and maximum power density of 26.2 W/m^3 under the hydraulic retention time(HRT) of 10 h. By increasing the HRT to 15 h, 90.6% of COD and 99.0% of ammonia in simulated domestic sewage were efficiently removed and the maximum power density was 19.4 W/m^3. Continuous purification of real municipal wastewater achieved 85.9% of COD removal rate and 91.6%of ammonia removal rate. Sequencing result of biocathodic microorganisms indicated that it consisted of four major classes and the dominant class was γ-proteobacteria, which accounted for up to 84.38%. The dominant genus was Acinetobacter, which accounted for 57.81%. The phylogenetic tree showed different relationships among the 19 species of biocathode microorganisms and the predominant species was Acinetobacter calcoaceticus.

Electricity-driven ammonia oxidation and acetate production in microbial electrosynthesis systems

Microbial electrosynthesis(MES)is an emerging technology for producing chemicals,and coupling MES to anodic waste oxidation can simultaneously increase the competitiveness and allow additional functions to be explored.In this study,MES was used for the simultaneous removal of ammonia from synthetic urine and production of acetate from CO_(2).Using graphite anode,83.2%±5.3%ammonia removal and 28.4%±9.9%total nitrogen removal was achieved,with an energy consumption of 1.32 kWh/g N for total nitrogen removal,0.45 kWh/g N for ammonia nitrogen removal,and 0.044 kWh/g for acetate production.Using boron-doped diamond(BDD)anode,70.9%±12.1%ammonia removal and 51.5%±11.8%total nitrogen removal was obtained,with an energy consumption of 0.84 kWh/g N for total nitrogen removal,0.61 kWh/g N for ammonia nitrogen removal,and 0.043 kWh/g for acetate production.A difference in nitrate accumulation explained the difference of total nitrogen removal efficiencies.Transport of ammonia and acetate across the membrane deteriorated the performance of MES.These results are important for the development of novel elcctricity-driven technologies for chemical production and pollution removal.

Sustainable green technology on wastewater treatment:The evaluation of enhanced single chambered up-flow membrane-less microbial fuel cell

This study demonstrated the potential of single chamber up-flow membrane-less microbial fuel cell（UFML-MFC） in wastewater treatment and power generation. The purpose of this study was to evaluate and enhance the performance under different operational conditions which affect the chemical oxygen demand（COD） reduction and power generation,including the increase of KCl concentration（MFC1） and COD concentration（MFC2）. The results showed that the increase of KCl concentration is an important factor in up-flow membrane-less MFC to enhance the ease of electron transfer from anode to cathode. The increase of COD concentration in MFC2 could led to the drop of voltage output due to the prompt of biofilm growth in MFC2 cathode which could increase the internal resistance. It also showed that the COD concentration is a vital issue in up-flow membrane-less MFC.Despite the COD reduction was up to 96%, the power output remained constrained.