The application and progress of bioelectrochemical systems (BESs) in soil remediation: A review

Soil pollution endangers human health and ecological balance,which is why finding a highly efficient way to deal with pollutants is necessary.Biological method is an environmentally friendly treatment method.Bioelectrochemical systems(BESs),which combine electrochemistry with biological methods,have been widely used to remediate polluted environments,including wastewater,sludge,sediment,and soil.In BESs,redox reactions occur on electrodes with electroactive bacteria,which convert pollutants into low-polluting or nonpolluting substances.With BESs being a promising technology in the remediation field,the decontamination mechanisms and applications in soil conducted by BESs have attracted much attention.Therefore,to better understand the research progress of BESs,this paper mainly summarizes the mechanism of different classified BESs.The applications of microbial fuel cells(MFCs)in four pollutants(petroleum,heavy metals,pesticides,antibiotics)and the possible applications of microbial electrolysis cells(MECs)in soil are discussed.The main problems in BESs and possible future development directions are also evaluated.

Influence evaluation of titania nanotube surface morphology on the performance of bioelectrochemical systems

In order to investigate the effect of the surface morphology and resistance of the TiO2 semiconductor on current output,TiO2 nanotube array bio-anodes(TNA)are synthesized at different electrolyte temperatures,thereby changing the length and surface roughness of the nanotubes.When the anodizing temperature is increased from 30 to 75℃,the length of the nanotubes increases from 1.459 to 4.183μm,which hinders the transfer of extracellular electrons to the electrodes.On the other hand,the surface roughness of TNA is significantly improved at higher temperatures,which is conducive to electron transfer.Therefore,samples processed at 45℃have the best current output performance.Compared with the treatment at 30℃under anodization,samples processed at 45℃can balance the resistance and roughness and have a higher electron transfer rate;the current output density of which is increased by 1.5 times,and the decolorization rate is increased by 0.8 times.Therefore,proper TNA surface morphology can improve the current output and the potential of wastewater treatment.

Enhanced depolluting capabilities of microbial bioelectrochemical systems by synthetic biology

Microbial bioelectrochemical system(BES)is a promising sustainable technology for the electrical energy recovery and the treatment of recalcitrant and toxic pollutants.In microbial BESs,the conversion of harmful pollutants into harmless products can be catalyzed by microorganisms at the anode(Type I BES),chemical catalysts at the cathode(Type II BES)or microorganisms at the cathode(Type III BES).The application of synthetic biology in microbial BES can improve its pollutant removing capability.Synthetic biology techniques can promote EET kinetics,which is helpful for microbial anodic electro-respiration,expediting pollutant removing not only at the anode but also at the cathode.They offer tools to promote biofilm development on the electrode,enabling more microorganisms residing on the electrode for subsequent catalytic reactions,and to overexpress the pollutant removing-related genes directly in microorganisms,contributing to the pollutant decomposition.In this work,based on the summarized aspects mentioned above,we describe the major synthetic biology strategies in designing and improving the pollutant removing capabilities of microbial BES.Lastly,we discuss challenges and perspectives for future studies in the area.

Selective recovery of Cu^2＋ and Ni^2＋ from wastewater using bioelectrochemical system

As the bioelectrochemical system, the microbial fuel cell （MFC） and the microbial electrolysis cell （MEC） were developed to selectively recover Cu^2＋ and Ni^2＋ ions from wastewater. The wastewater was treated in the cathode chambers of the system, in which Cu^2＋ and Ni^2＋ ions were removed by using the MFC and the MEC, respectively. At an initial Cu^2＋ concentration of 500 mg· L^-1, removal efficiencies of Cu^2＋ increased from 97.0%±1.8% to 99.0%±0.3% with the initial Ni^2＋ concentrations from 250 to 1000 mg· L^-1, and maximum power densities increased from 3.1±0.5 to 5.4±0.6W.m-3. The Ni^2＋ removal mass in the MEC increased from 6.84-0.2 to 20.54-1.5 mg with the increase of Ni^2＋ concentrations. At an initial Ni^2＋ concentration of 500 mg· L^-1, Cu^2＋ removal etticiencies decreased from 99.1%±0.3% to 74.2%±3.8% with the initial Cu^2＋ concentrations from 250 to 1000 mg -L1, and maximum power densities increased from 3.0±0.1 to 6.3±1.2W.m^-3. Subsequently, the Ni^2＋ removal efficiencies decreased from 96.9%-4-3.1% to 73.3%4-5.4%. The results clearly demonstrated the feasibility of selective recovery of Cu2~ and Ni2~ from the wastewater using the bioelectrochemical system.

Conversion of nitrogen and carbon in enriched paddy soil by denitrification coupled with anammox in a bioelectrochemical system

The aim of this study is to investigate conversion of nitrogen and COD in enriched paddy soil by nitrification coupled with anammox process in a dual chamber bioelectrochemical system.The paddy soil was enriched for denitrification coupled with anammox by microbial consortia and was acclimatized in the cathodic chamber of microbial fuel cells(MFCs).The bioelectrochemical systems were treated with different ammonium concentrations in the cathodic chamber:the MFC with low concentration ammonium(LA-MFC,50 mg/L ammonium),the MFC with medium concentration ammonium(MA-MFC,500 mg/L ammonium),and MFC with high concentration ammonium(HA-MFC,1000 mg/L ammonium),and the initial COD in the anodic chamber was 1200 mg/L.The CK treatments were conducted with1000 mg/L ammonium under the same conditions,except without inoculum in the cathode chamber.The consumption rate of ammonium in the cathodic chambers of CK,LA-MFC,MA-MFC,and HA-MFC were 9%,64%,84%,and 84%,respectively.The degradation rate for COD achieved in the anode chambers of CK,LA-MFC,MA-MFC,and HA-MFC were 70%,86%,93%,and 93%,respectively.The analysis of the microbial community of three treated MFCs in the cathode chamber indicated that the nitrification-denitrification process occurs in the cathode chamber.The dominant species for nitrification was Nitrospira,and the dominant species for denitrification were Denitratisoma,Dechloromonas,and Candidatus_Competibacter.Moreover,anammox process also observed in the cathode chamber.The functional genes nir S/K,hzs B,and 16S rDNA were assessed by qPCR analysis,and the results confirmed the presence of denitrification-coupled anammox in the cathodic chamber.

Effects of cathode potentials and nitrate concentrations on dissimilatory nitrate reductions by Pseudomonas alcaliphila in bioelectrochemical systems

The effects of cathode potentials and initial nitrate concentrations on nitrate reduction in bio- electrochemical systems （BESs） were reported. These factors could partition nitrate reduction between denitrification and dissimilatory nitrate reduction to ammonium （DNRA）. Pseudomonas alcaliphilastrain MBR utilized an electrode as the sole electron donor and nitrate as the sole electron acceptor. When the cathode potential was set from -0.3 to -I.1 V （vs. Ag/AgC1） at an initial nitrate concentration of 100 mg NO^-N/L, the DNRA electron recovery increased from （10.76 ± 1.6）% to （35.06 ± 0.99）%; the denitrification electron recovery decreased from （63.42 ± 1,32）% to （44.33 ± 1.92）%. When the initial nitrate concentration increased from （29.09 ± 0.24） to （490.97 ± 3.49） mg NO3-N/L at the same potential （-0.9 V）, denitrification electron recovery increased from （5.88 ± 1.08）% to （50.19 ±2.59）%; the DNRA electron recovery declined from （48.79 ±1.32）% to （16.02 ± 1.41）%. The prevalence of DNRA occurred at high ratios of electron donors to acceptors in the BESs and denitrification prevailed against DNRA under a lower ratio of electron donors to acceptors. These results had a potential application value of regulating the transformation of nitrate to N2 or ammonium in BESs for nitrate removal.

Microbial reduction of organosulfur compounds at cathodes in bioelectrochemical systems

Organosulfur compounds,present in e.g.the pulp and paper industry,biogas and natural gas,need to be removed as they potentially affect human health and harm the environment.The treatment of organosulfur compounds is a challenge,as an economically feasible technology is lacking.In this study,we demonstrate that organosulfur compounds can be degraded to sulfide in bioelectrochemical systems(BESs).Methanethiol,ethanethiol,propanethiol and dimethyl disulfide were supplied separately to the biocathodes of BESs,which were controlled at a constant current density of 2 A/m^(2) and 4 A/m^(2).The decrease of methanethiol in the gas phase was correlated to the increase of dissolved sulfide in the liquid phase.A sulfur recovery,as sulfide,of 64% was found over 5 days with an addition of 0.1 mM methanethiol.Sulfur recoveries over 22 days with a total organosulfur compound addition of 1.85 mM were 18% for methanethiol and ethanethiol,17% for propanethiol and 22% for dimethyl disulfide.No sulfide was formed in electrochemical nor biological control experiments,demonstrating that both current and microorganisms are required for the conversion of organosulfur compounds.This new application of BES for degradation of organosulfur components may unlock alternative strategies for the abatement of anthropogenic organosulfur emissions.

Progress in plant-based bioelectrochemical systems and their connection with sustainable development goals

Living organisms’energy conversion is considered as an essential and sustainable green energy source and future bio-hybrid technologies.Recently,plants were used after harvesting as biomass in bio-fermentation as an energy source.In bio-electrochemical systems,microorganisms work with plants to generate electricity,hydrogen,or methane.This work discusses the simultaneous pollutant removal and electricity generation in plant-based bio-electrochemical systems(P-BES).Factors affecting the P-BES performance and the removal efficiencies of the different organic and inorganic pollutants were illustrated.Furthermore,the plant-based bioelectrochemical systems’role in achieving the sustainable development goals(SDGs)was discussed.The SDGs contribution of plant-based bioelectrochemical systems were presented and discussed to evaluate such systems’ability to achieve the three pillars of sustainable development,i.e.,economic,environmental,and social.

＂NEW＂ resource recovery from wastewater using bioelectrochemical systems： Moving forward with functions

Bioelectrochemical systems （BES） have been extensively studied ｜br resource recovery from wastewater. By taking advantage of interactions between microorganisms and electrodes, BES can accomplish wastewater treatment while simultaneously recovering various resources including nutrients, energy and water （＂NEW＂）. Despite much progress in laboratory sit, dies, BES have not been advanced to practical applications. This paper aims to provide some subjective opinions and a concise discussion of several key challenges in BES-based resource recovery and help identil- the potential application niches that may guide further technological development. In addition to further increasing recovery efficiency, it is also important to have more lbcus on the applications of the recovered resources such as how to use the harvested electricity and gaseous energy and how to separate the recovered nutrients in an energy-efficient way. A changc in mindset fur energy performance of BES is necessary to understand overall energy production and consumption. Scaling up BES can go through laboratory scale, transitional scale, and then pilot scale. Using functions as driving forces lbr BES research and development will better guide the investment of efforts.

Multienzyme co-immobilization-based bioelectrode:Design of principles and bioelectrochemical applications

Enzyme cascade reactions play significant roles in bioelectrochemical processes because they permit more complex reactions. Co-immobilization of multienzyme on the electrode could help to facilitate substrate/intermediate transfer among different enzymes and electron transfer from enzyme active sites to the electrode with high stability and retrievability. Different co-immobilization strategies to construct multienzyme bioelectrodes have been widely reported, however, up to now, they have barely been reviewed. In this review, we focus on recent state-of-the-art techniques for constructing co-immobilized multienzyme electrodes including random and positional co-immobilization. Particular attention is given to strategies such as multienzyme complex and surface display. Cofactor co-immobilization on the electrode is also crucial for the enhancement of catalytic reaction and electron transfer, yet, few studies have been reported. The up-to-date advances in bioelectrochemical applications of multienzyme bioelectrodes are also presented. Finally, key challenges and future perspectives are discussed.

A tartrate-EDTA-Fe complex mediates electron transfer and enhances ammonia recovery in a bioelectrochemical-stripping system

Traditional bioelectrochemical systems(BESs)coupled with stripping units for ammonia recovery suffer from an insufficient supply of electron acceptors due to the low solubility of oxygen.In this study,we proposed a novel strategy to efficiently transport the oxidizing equivalent provided at the stripping unit to the cathode by introducing a highly soluble electron mediator(EM)into the catholyte.To validate this strategy,we developed a new kind of iron complex system(tartrate-EDTA-Fe)as the EM.EDTA-Fe contributed to the redox property with a midpoint potential of
0.075 V(vs.standard hydrogen electrode,SHE)at pH 10,whereas tartrate acted as a stabilizer to avoid iron precipitation under alkaline conditions.At a ratio of the catholyte recirculation rate to the anolyte flow rate(RC-A)of 12,the NH4 t-N recovery rate in the system with 50mM tartrate-EDTA-Fe complex reached 6.9±0.2 g Nm^(-2) d^(-1),approximately 3.8 times higher than that in the non-EM control.With the help of the complex,our system showed an NH4 t-N recovery performance comparable to that previously reported but with an extremely low RC-A(0.5 vs.288).The strategy proposed here may guide the future of ammonia recovery BES scale-up because the introduction of an EM allows aeration to be performed only at the stripping unit instead of at every cathode,which is beneficial for the system design due to its simplicity and reliability.

An overview of bioelectrokinetic and bioelectrochemical remediation of petroleum-contaminated soils

The global problem of petroleum contamination in soils seriously threatens environmental safety and human health.Current studies have successfully demonstrated the feasibility of bioelectrokinetic and bioelectrochemical remediation of petroleum-contaminated soils due to their easy implementation,environmental benignity,and enhanced removal efficiency compared to bioremediation.This paper reviewed recent progress and development associated with bioelectrokinetic and bioelectrochemical remediation of petroleum-contaminated soils.The working principles,removal efficiencies,affecting factors,and constraints of the two technologies were thoroughly summarized and discussed.The potentials,challenges,and future perspectives were also deliberated to shed light on how to overcome the barriers and realize widespread implementation on large scales of these two technologies.

Bioelectrochemical Response and Kinetics of Choline Oxidase Entrapped in Polyaniline-Polyacrylonitrile Composite Film

A novel choline oxidase electrode was constructed by entrapping choline oxidase into polyaniline polyacrylonitrile composite film. The enzyme film was prepared by in situ electropolyme rization of aniline into porous polyacrylonitrile coated platinum electrode in the presence of choline oxidase. The enzyme electrode exhibited sensitive and stable electrochemical response to choline. The kinetics analysis showed that the mass transport is partially rate limiting. The influences of pH, applied potential and temperature on the response of the enzyme electrode were also described.

Decoupling hydrogen production from water oxidation by integrating a triphase interfacial bioelectrochemical cascade reaction

Water electrolysis to produce H2 is a promising strategy for generating a renewable fuel.However,the sluggish-kinetics and low value-added anodic oxygen evolution reaction(OER)restricts the overall energy conversion efficiency.Herein we report a strategy of boosting H_(2)production at low voltages by replacing OER with a bioelectrochemical cascade reaction at a triphase bioanode.In the presence of oxygen,oxidase enzymes can convert biomass into valuable products,and concurrently generate H_(2)O_(2) that can be further electrooxidized at the bioanode.Benefiting from the efficient oxidase kinetics at an oxygen-rich triphase bioanode and the more favorable thermodynamics of H_(2)O_(2)oxidation than that of OER,the cell voltage and energy consumption are reduced by~0.70 V and~36%,respectively,relative to regular water electrolysis.This leads to an efficient H_(2)production at the cathode and valuable product generation at the bioanode.Integration of a bioelectrochemical cascade into the water splitting process provides an energy-efficient and promising pathway for achieving a renewable fuel.

Direct ammonium oxidation to nitrogen gas (Dirammox) in Alcaligenes strain HO-1: The electrode role

It has been recently suggested that Alcaligenes use a previously unknown pathway to convert ammonium into dinitrogen gas(Dirammox)via hydroxylamine(NH2OH).This fact alone already implies a significant decrease in the aeration requirements for the process,but the process would still be dependent on external aeration.This work studied the potential use of a polarised electrode as an electron acceptor for ammonium oxidation using the recently described Alcaligenes strain HO-1 as a model heterotrophic nitrifier.Results indicated that Alcaligenes strain HO-1 requires aeration for metabolism,a requirement that cannot be replaced for a polarised electrode alone.However,concomitant elimination of succinate and ammonium was observed when operating a previously grown Alcaligenes strain HO-1 culture in the presence of a polarised electrode and without aeration.The usage of a polarised electrode together with aeration did not increase the succinate nor the nitrogen removal rates observed with aeration alone.However,current density generation was observed along a feeding batch test representing an electron share of 3%of the ammonium removed in the presence of aeration and 16%without aeration.Additional tests suggested that hydroxylamine oxidation to dinitrogen gas could have a relevant role in the electron discharge onto the anode.Therefore,the presence of a polarised electrode supported the metabolic functions of Alcaligenes strain HO-1 on the simultaneous oxidation of succinate and ammonium.

Microbial electrosynthesis of acetate from CO_(2)in three-chamber cells with gas diffusion biocathode under moderate saline conditions

The industrial adoption of microbial electrosynthesis(MES)is hindered by high overpotentials deriving from low electrolyte conductivity and inefficient cell designs.In this study,a mixed microbial consortium originating from an anaerobic digester operated under saline conditions(∼13 g L^(−1)NaCl)was adapted for acetate production from bicarbonate in galvanostatic(0.25 mA cm^(−2))H-type cells at 5,10,15,or 20 g L^(−1)NaCl concentration.The acetogenic communities were successfully enriched only at 5 and 10 g L^(−1)NaCl,revealing an inhibitory threshold of about 6 g L^(−1)Na^(+).The enriched planktonic communities were then used as inoculum for 3D printed,three-chamber cells equipped with a gas diffusion biocathode.The cells were fed with CO_(2)gas and operated galvanostatically(0.25 or 1.00 mA cm^(−2)).The highest production rate of 55.4 g m^(−2) d^(−1)(0.89 g L^(−1)d^(−1)),with 82.4%Coulombic efficiency,was obtained at 5 g L^(−1)NaCl concentration and 1 mA cm^(−2)applied current,achieving an average acetate production of 44.7 kg MWh−1.Scanning electron microscopy and 16S rRNA sequencing analysis confirmed the formation of a cathodic biofilm dominated by Acetobacterium sp.Finally,three 3D printed cells were hydraulically connected in series to simulate an MES stack,achieving three-fold production rates than with the single cell at 0.25 mA cm^(−2).This confirms that three-chamber MES cells are an efficient and scalable technology for CO_(2)bio-electro recycling to acetate and that moderate saline conditions(5 g L^(−1)NaCl)can help reduce their power demand while preserving the activity of acetogens.

Immobilisation of electrochemically active bacteria on screen-printed electrodes for rapid in situ toxicity biosensing

are time-consuming and not sensitive enough.However,bacteria typically connect to electrodes through biofilm formation,leading to problems due to lack of uniformity or long device production times.A suitable immobilisation technique can overcome these challenges.Still,they may respond more slowly than biofilm-based electrodes because bacteria gradually adapt to electron transfer during biofilm formation.In this study,we propose a controlled and reproducible way to fabricate bacteria-modified electrodes.The method consists of an immobilisation step using a cellulose matrix,followed by an electrode polarization in the presence of ferricyanide and glucose.Our process is short,reproducible and led us to obtain ready-to-use electrodes featuring a high-current response.An excellent shelf-life of the immobilised electrochemically active bacteria was demonstrated for up to one year.After an initial 50% activity loss in the first month,no further declines have been observed over the following 11 months.We implemented our bacteria-modified electrodes to fabricate a lateral flow platform for toxicity monitoring using formaldehyde(3%).Its addition led to a 59% current decrease approximately 20 min after the toxic input.The methods presented here offer the ability to develop a high sensitivity,easy to produce,and long shelf life bacteria-based toxicity detectors.

Ecological responses to substrates in electroactive biofilm:A review

Substrate as the electron donor of bioelectrochemical system(BES) has fateful impacts on the microbial community composition of electroactive biofilm(EAB), via the selection upon functional microorganisms such as exoelectrogens, fermenters and methanogens, as well as their interactions. Electrochemical performance as the terminal reflects of electroactivity and the correspondence between community members have been summarized. Exoelectrogens responsible to the conversion towards electricity from their respective preferred substrates such as acetate, propionate, glucose and cellulose has been found to be finite in a small range, e.g., Geobacter, Shewanella and Pseudomonas. Their demands of micromolecular electron donors and the selective pressure of primary substrates facilitate the existence of competitive or cooperative biological processes to exoelectrogenesis. The inherent mechanisms of the dynamics of such interactions have been explored with electrochemical methods,defined co-culture experiments and community analysis. Complete view of the metabolic network in electroactive microbial communities has been shed light on, and appeals further investigation.

Performance of low temperature Microbial Fuel Cells(MFCs)catalyzed by mixed bacterial consortia

Microbial Fuel Cells（MFCs） are a promising technology for treating wastewater in a sustainable manner. In potential applications, low temperatures substantially reduce MFC performance. To better understand the effect of temperature and particularly how bioanodes respond to changes in temperature, we investigated the current generation of mixed-culture and pure-culture MFCs at two low temperatures, 10°C and 5°C. The results implied that the mixed-culture MFC sustainably performed better than the pure-culture（Shewanella） MFC at 10°C, but the electrogenic activity of anodic bacteria was substantially reduced at the lower temperature of 5°C. At 10°C, the maximum output voltage generated with the mixed-culture was 540–560 m V, which was 10%–15% higher than that of Shewanella MFCs. The maximum power density reached 465.3 ± 5.8 m W/m^2 for the mixed-culture at10°C, while only 68.7 ± 3.7 m W/m^2 was achieved with the pure-culture. It was shown that the anodic biofilm of the mixed-culture MFC had a lower overpotential and resistance than the pure-culture MFC. Phylogenetic analysis disclosed the prevalence of Geobacter and Pseudomonas rather than Shewanella in the mixed-culture anodic biofilm, which mitigated the increase of resistance or overpotential at low temperatures.

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.