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Abstract Background 3-Hydroxypropionic acid (3-HP) is an important platform chemical which can be produced biologically from glycerol. Klebsiella pneumoniae is an ideal biocatalyst for 3-HP because it can grow well on glycerol and naturally synthesize the essential coenzyme B12. On the other hand, if higher yields and titers of 3-HP are to be achieved, the sustained regeneration of NAD+ under anaerobic conditions, where coenzyme B12 is synthesized sustainably, is required. Results In this study, recombinant K. pneumoniae L17 overexpressing aldehyde dehydrogenase (AldH) was developed and cultured in a bioelectrochemical system (BES) with the application of an electrical potential to the anode using a chronoamperometric method (+0.5 V vs. Ag/AgCl). The BES operation resulted in 1.7-fold enhancement of 3-HP production compared to the control without the applied potential. The intracellular NADH/NAD+ ratio was significantly lower when the L17 cells were grown under an electric potential. The interaction between the electrode and overexpressed AldH was enhanced by electron shuttling mediated by HNQ (2-hydroxy-1,4-naphthoquinone). Conclusions Enhanced 3-HP production by the BES was achieved using recombinant K. pneumoniae L17. The quinone-based electron transference between the electrode and L17 was investigated by respiratory uncoupler experiments. This study provides a novel strategy to control the intracellular redox states to enhance the yield and titer of 3-HP production as well as other bioconversion processes.

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/m2 and 4 A/m2. 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.

Bioelectrochemical systems are revolutionary new bioengineering technologies which integrate microorganisms or enzymes with the electrochemical method to improve the reducing or oxidizing metabolism. Generally, the bioelectrochemical systems show the processes referring to electrical power generation or achieving the reducing reaction with a certain potential poised by means of electron transfer between the electron acceptor and electron donor. Researchers have focused on the selection and optimization of the electrode materials, design of electrochemical device, and screening of electrochemically active or inactive model microorganisms. Notably, all these means and studies are related to electron transfer: efflux and consumption. Thus, here we introduce the basic concepts of bioelectrochemical systems, and elaborate on the extracellular and intracellular electron transfer, and the hypothetical electron transfer mechanism. Also, intracellular energy generation and coenzyme metabolism along with electron transfer are analyzed. Finally, the applications of bioelectrochemical systems and the prospect of microbial electrochemical technologies are discussed.

Bioelectrochemical systems (BESs) are capable of simultaneous wastewater treatment and resource recovery at low temperatures. However, the direct enrichment of psychrophilic and electroactive biofilms in BESs at 4°C is difficult due to the lack of understanding in the physioecology of psychrophilic exoelectrogens. Here, we report the start-up and operation of microbial fuel cells (MFCs) at 4°C with pre-acclimated inocula at different temperatures (4°C, 10°C, 25°C, and −20°C) for 7 days and 14 days. MFCs with 7-day-pretreated inocula reached higher peak voltages than did those with 14-day-pretreated inocula. The highest power densities were obtained by MFCs with 25°C – 7-day-, 25°C – 14-day-, and 4°C – 7-day-pretreated inocula (650–700 mW/m2). In contrast, the control MFCs with untreated inocula were stable at 450 mW/m2. The power densities of MFCs with 7-day-pretreated inocula were higher than those obtained by MFCs with 14-day-pretreated inocula. The MFCs with 10°C – 7-day-pretreated inocula and the control MFCs showed higher chemical oxygen demand (COD) removal (90–91%) than other MFCs. Illumina HiSeq sequencing based on 16S rRNA gene amplicons indicated that bacterial communities of the anode biofilms were shaped by pretreated inocula at different temperatures. Compared with the control MFCs with untreated inocula, MFCs with temperature-pretreated inocula demonstrated higher microbial diversity, but did not do so with −20°C-pretreated inocula. Principal components analysis (PCA) revealed an obvious separation between the inocula pretreated at 4°C and those pretreated at 10°C, implying that bacterial community structures could be shaped by pretreated inocula at low temperatures. The pretreatment period also had a diverse impact on the abundance of exoelectrogens and non-exoelectrogens in MFCs with inocula pretreated at different temperatures. The majority of the predominant population was affiliated with Geobacter with a relative abundance of 17–70% at different pre-acclimated temperatures, suggesting that the exoelectrogenic Geobacter could be effectively enriched at 4°C even with inocula pretreated at different temperatures. This study provides a strategy that was previously neglected for fast enrichment of psychrophilic exoelectrogens in BESs at low temperatures.

Biophotovoltaics is a relatively new discipline in microbial fuel cell research. The basic idea is the conversion of light energy into electrical energy using photosynthetic microorganisms. The microbes will use their photosynthetic apparatus and the incoming light to split the water molecule. The generated protons and electrons are harvested using a bioelectrochemical system. The key challenge is the extraction of electrons from the microbial electron transport chains into a solid-state anode. On the cathode, a corresponding electrochemical counter reaction will consume the protons and electrons, e.g., through the oxygen reduction to water, or hydrogen formation. In this review, we are aiming to summarize the current state of the art and point out some limitations. We put a specific emphasis on cyanobacteria, as these microbes are considered future workhorses for photobiotechnology and are currently the most widely applied microbes in biophotovoltaics research. Current progress in biophotovoltaics is limited by very low current outputs of the devices while a lack of comparability and standardization of the experimental set-up hinders a systematic optimization of the systems. Nevertheless, the fundamental questions of redox homeostasis in photoautotrophs and the potential to directly harvest light energy from a highly efficient photosystem, rather than through oxidation of inefficiently produced biomass are highly relevant aspects of biophotovoltaics.

Approximately four billion years ago, the first microorganisms to thrive on earth were anaerobic chemoautotrophic thermophiles, a specific group of extremophiles that survive and operate at temperatures ∼50 – 125°C and do not use molecular oxygen (O2) for respiration. Instead, these microorganisms performed respiration via dissimilatory metal reduction by transferring their electrons extracellularly to insoluble electron acceptors. Genetic evidence suggests that Gram-positive thermophilic bacteria capable of extracellular electron transfer (EET) are positioned close to the root of the Bacteria kingdom on the tree of life. On the contrary, EET in Gram-negative mesophilic bacteria is a relatively new phenomenon that is evolutionarily distinct from Gram-positive bacteria. This suggests that EET evolved separately in Gram-positive thermophiles and Gram-negative mesophiles, and that EET in these bacterial types is a result of a convergent evolutionary process leading to homoplasy. Thus, the study of dissimilatory metal reducing thermophiles provides a glimpse into some of Earth’s earliest forms of respiration. This will provide new insights for understanding biogeochemistry and the development of early Earth in addition to providing unique avenues for exploration and discovery in astrobiology. Lastly, the physiological composition of Gram-positive thermophiles, coupled with the kinetic and thermodynamic consequences of surviving at elevated temperatures, makes them ideal candidates for developing new mathematical models and designing innovative next-generation biotechnologies.KEY CONCEPTSAnaerobe: organism that does not require oxygen for growth.Chemoautotroph: organism that obtains energy by oxidizing inorganic electron donors.Convergent Evolution: process in which organisms which are not closely related independently evolve similar traits due to adapting to similar ecological niches and/or environments.Dissimilatory Metal Reduction: reduction of a metal or metalloid that uses electrons from oxidized organic or inorganic electron donors.Exoelectrogen: microorganism that performs dissimilatory metal reduction via extracellular electron transfer.Extremophiles: organisms that thrive in physical or geochemical conditions that are considered detrimental to most life on Earth.Homoplasy: a character shared by a set of species that is not shared by a common ancestorNon-synonymous Substitutions (Ka): a substitution of a nucleotide that changes a codon sequence resulting in a change in the amino acid sequence of a protein.Synonymous Substitutions (Ks): a substitution of a nucleotide that may change a codon sequence, but results in no change in the amino acid sequence of a protein.Thermophiles: a specific group of extremophiles that survive and operate at temperatures ∼50–125°C.

The corrosive issues are comprehensively caused in oilfield rejection system, in which sulfide is one of (bio-)chemical factors leading to high corrosive rate and blocking problem. Generally, aerobic treatment is a well-established and cost-effective unit for sulfide removal before oilfield wastewater reinjection. However, the residual dissolved oxygen (DO), which causes chemical, biological and electrochemical corrosion to water injection pipeline equipment, is still high after multi-stage filtration of DO removal. Here, a novel system to achieve quick and efficient DO removal through a three-electrode (cathode-anode-cathode)-upflow bioelectrochemical reactor (R CAC) was constructed before wastewater reinjection. Bioelectrodes were well established by utilizing organic matters of oilfield wastewater and conducted extracellular electron transport to achieve a steady DO removal from ∼5 mg/L to 0.01 mg/L (HRT 6 h), the DO removal efficiency reached approximately 100%, and the downside biocathode made the largest contribution for DO removal. In the treated wastewater, the corrosion rate of stainless steel N80 ultimately declined over 30 days testing. As a result of DO removal and ammonia conversion to nitrate by bioelectrodes, the corrosive microorganisms were substantially changed. Especially, sulfate-reducing bacteria (SRB) on the surface of N80 immersed in treated wastewater were decreased in abundance; while nitrate-reducing bacteria (NRB) enriched more, which can compete with SRB to prevent biological corrosion. Image 1 • A three-electrode bioelectrochemical reactor was constructed for dissolved oxygen removal. • Removal efficiency of dissolved oxygen can reach ca.100%. • The biocathodes made the most contribution of dissolved oxygen removal. • Corrosion rate of N80 stainless steel declined in the treated effluent during 30 days. • Sulfate-reducing bacteria on pipeline surface were decreased when immerged in treated effluent. [ABSTRACT FROM AUTHOR]

BACKGROUND: p‐Chloronitrobenzene (p‐CNB) is easily accumulated in the environment and subsequently is a threat to humans and the ecosystem. The anaerobic process as an important pathway for p‐CNB degradation has a relatively low degradation rate. This study illustrated that the strain Pseudomonas fluorescens was evaluated as the biocatalyst for bioaugmentation to enhance the p‐CNB removal in bioelectrochemical system (BES). RESULTS: When the initial p‐CNB concentration was 100 mg L−1, the p‐CNB removal efficiency reached 100% at 12 h in BES with P. fluorescens. All the p‐CNB removal efficiencies in BES were higher than that in anaerobic degradation and electrocatalysis. Meantime, the highest total organic carbon (TOC) removal efficiency was obtained at 89.8% after augmentation with P. fluorescens. During the bioaugmentation, microbial community analysis showed that the main abundance changes were in Pseudomonas, Romboutsia and Macellibacteroides. The cyclic voltammetry (CV) showed BES with bioaugmentation had the highest activity in reducing p‐CNB and hydrogen evolution. Combined with intermediates analysis, bioaugmentation possibly stimulated nitro reduction and hydrodechlorination rate in p‐CNB reduction. CONCLUSION: These results demonstrate that BES with P. fluorescens bioaugmentation could serve as a potential treatment process for p‐CNB removal. © 2019 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Azo dye presents severe pollution to water environment, which needs to be treated properly to minimize environmental impact. In this study, we developed a porous titanium suboxide electrode for electrochemical reduction of azo dye (Acid Red B) in dual-chamber bioelectrochemical system (BES). The decolorization efficiency could reach 91.9% on titanium suboxide, which followed the first-order reaction kinetics with apparent rate constant of kapp = 0.339 h−1, a value 89.4% higher than that (kapp = 0.179 h−1) for carbon cloth. The cyclic voltammogram and electrochemistry impedance spectroscopy (EIS) characterization indicated higher activity and lower charge-transfer resistance of titanium suboxide. The decolourization rate was positively related to cathode potential, reaching the maximum kinetic constant of 0.456 h−1 at − 1.15 V versus standard hydrogen electrode. Lower pH was favorable for decolorization because of requirement for excessive protons for the cleavage of azo bonds, indicated by 86.4% increase in kinetic constant when shifting pH from 9.0 (0.1643 h−1) to 5.0 (0.3064 h−1). The Tafel plot illustrated a higher corrosion resistance of titanium suboxide (the corrosion current of 1.28–1.84 mA/m2) than that of carbon cloth (6.19–11.43 mA/m2) in acidic condition, suggesting higher stability due to unique oxygen-deficiency crystalline structure. This study provides the first demonstration of titanium suboxide cathode to efficiently reduce azo dye via direct electron transfer in BES, which eliminates the need for time-consuming enrichment of electroactive biofilm and avoids the development of non-electroactive microorganisms. [ABSTRACT FROM AUTHOR]

Bioelectrochemical systems (BESs) are known to enhance the remediation of hydrocarbon-contaminated soil and sediments compared with natural attenuation, and the primary mechanism has been assumed as anaerobic degradation facilitated by electroactive bacteria (EAB) using the electrode as electron acceptor. However, known EAB were rarely found on the anodes of reported BESs, which challenged the fundamental mechanism of BESs although significant current generation was always observed during degradation of these recalcitrant substrates. This study however found the abundant EAB Geobacter (∼27.3%) in the anodic biofilms, which confirmed the role of electroactive bio-anode on the conversion of hydrocarbons into the current for the enhancement of remediation. Widespread occurrence of aerobic hydrocarbon-degrading bacteria (HDB) (e.g. ∼24.0% Parvibaculum and ∼30.6% Pseudomonas) was observed in soils with limited dissolved oxygen (∼0.4 mg/L). The higher abundance of dehydrogenase genes was found in the anode biofilms than that in soils, indicating anodic microorganisms may be mainly responsible for the removal of intermediates of aerobic hydrocarbons degradation in soils. High water saturation level and sandy soil texture showed positive impacts on bioelectrochemical remediation, while clay soil and unsaturation condition pose challenges in mass transfers in the matrix. The reactor performance was consistent with the phylogenetic molecular ecological network (pMENs) analysis, which showed that sandy soil BESs had tighter microbial network interactions than clay soil reactors. Image 1 • High abundance of Geobacter was found in the anodic communities of soil BESs. • Widespread occurrence of aerobic hydrocarbon-degrading bacteria in anoxic soils. • High water content and sandy soil texture positively impact remediation. • Tighter ecological network interaction means high remediation efficiency. [ABSTRACT FROM AUTHOR]

Purpose: An osmotic microbial fuel cell (OsMFC) is derived from the integration of a forward osmosis (FO) membrane into a conventional microbial fuel cell (MFC), with enhanced performance in bioelectricity generation from organic matter and recovery of high-quality water. The environmental impacts of this newly developed technology, however, have not been studied. To understand and potentially reduce the environmental impacts of the OsMFC technology, the environmental impacts have been assessed. Methods: An attributional life cycle assessment (LCA) model has been developed to evaluate the cradle-to-grave environmental impacts of the OsMFC based on a lab-scale prototype. The International Life Cycle Data System (ILCD) method has been applied to calculate and characterize the environmental impacts of treating 1 L of water by using the OsMFC technology in GaBi 8.7. Sensitivity and scenario analyses have been employed to assess the environmental impact variations based on changing power densities and different disposal methods, respectively. Results and discussion: The results indicate that several factors including raw material extraction, system operation, and end-of-life (EoL) stages have relatively large impacts in certain categories. The raw material extraction and system operation take up 50.04% and 32.06% of global warming potential (GWP), respectively. The EoL expends 98.02% of ecotoxicity potential (ETP), 54.31% of eutrophication potential (EP), and 52.24% of human toxicity potential (HTP). A comparison of the OsMFC with other bioelectrochemical systems (BESs) reveals that it has higher GWP due to the polymethylmethacrylate (PMMA) sheeting used to construct the cell and the stainless steel used to build the cathode electrode, but comparable acidification potential (AP), eutrophication potential (EP), ozone depletion potential (ODP), and respiratory inorganics (RI). The greenhouse gas (GHG) emissions of the OsMFC are also benchmarked with those of the conventional wastewater treatment methods, and it shows that the OsMFC has higher GHG emissions than the conventional wastewater treatment methods at the current power density. However, the results may change dramatically with the change of materials and cell configurations. Conclusions: According to the analysis, cell materials, cell configuration, electricity usage during the operation stage, and disposal methods are major problems to solve in the development of the OsMFC technology. Enhancement of power density and alternation of cell materials and configuration may turn out to be effective methods to alleviate the environmental impacts and increase market competitiveness of the OsMFC technology in the future. [ABSTRACT FROM AUTHOR]

Anode potential is a critical factor in the biodegradation of organics in bioelectrochemical systems (BESs), but research on these systems with complex recalcitrant co-substrates at set anode potentials is scarce. In this study, carbamazepine (CBZ) biodegradation in a BES was examined over a wide range of set anode potentials (−200 to +600 mV vs Ag/AgCl). Current generation and current densities were improved with the increase in positive anode potentials. However, at a negative potential (−200 mV), current generation was higher as compared to that for +000 and +200 mV. The highest CBZ degradation (84%) and TOC removal efficiency (70%) were achieved at +400 mV. At +600 mV, a decrease in CBZ degradation was observed, which can be attributed to a low number of active bacteria and a poor ability to adapt to high voltage. This study signified that BESs operated at optimum anode potentials could be used for enhancing the biodegradation of complex and recalcitrant contaminants in the environment. Unlabelled Image • LSV analysis showed anode potential enhanced the microbial colonization in BES. • High potential favored BES, but after +400 mV, BES performance declined. • CBZ biodegradation and TOC removal were enhanced in BES aided by anodic potential. • Microbes with high tendency to degrade CBZ were enriched by a controlled potential. [ABSTRACT FROM AUTHOR]

Bioelectrochemical systems (BES) encompass a group of bio-based technologies capable of directly converting organic matter into electricity. In these systems, which are derived from conventional electrochemical technologies, the ion exchange membrane is a key element because of its influence on the economic feasibility and performance of BES. This study examined the impact of the long-term operation of BES on the mechanical, chemical, and electrochemical properties of five different kinds of cation exchange membranes (Nafion-117, CMI-7000, Zirfon UTP 500, FKE, and FKB) through several techniques: (i) scanning electron microscopy and atomic force microscopy to assess the changes on the membrane surface, (ii) thermogravimetric analysis to evaluate the structural stability of the membranes, and (iii) ion exchange capacity to monitor any change in their electrochemical properties. Results confirmed that there is not an ideal membrane for BES. While Nafion and CMI exhibited the strongest chemical structure, they also underwent the highest fouling, as revealed by a fast increase in surface roughness. • No significant fouling and breakings in membrane surfaces were observed. • Nafion and CMI show the most robust chemical structures and increases in roughness. • The ion exchange capacity showed a moderate decay in all membranes. • After the four-month-long membrane operation, the current density was constant. [ABSTRACT FROM AUTHOR]

Microbial electron uptake (EU) is the biological capacity of microbes to accept electrons from electroconductive solid materials. EU has been leveraged for sustainable bioproduction strategies via microbial electrosynthesis (MES). MES often involves the reduction of carbon dioxide to multi-carbon molecules, with electrons derived from electrodes in a bioelectrochemical system. EU can be indirect or direct. Indirect EU-based MES uses electron mediators to transfer electrons to microbes. Although an excellent initial strategy, indirect EU requires higher electrical energy. In contrast, the direct supply of cathodic electrons to microbes (direct EU) is more sustainable and energy efficient. Nonetheless, low product formation due to low electron transfer rates during direct EU remains a major challenge. Compared to indirect EU, direct EU is less well-studied perhaps due to the more recent discovery of this microbial capability. This mini-review focuses on the recent advances and challenges of direct EU in relation to MES. [ABSTRACT FROM AUTHOR]

Periplasmic c -type cytochromes are essential for the electron transport between the cytoplasmic membrane bound menquinol oxidase CymA and the terminal ferric iron reductase MtrABC in the outer membrane of Shewanella oneidensis cells. Either STC or FccA are necessary for periplasmic electron transfer. We followed the hypothesis that the elimination of potential competing reactions in the periplasm and the simultaneous overexpression of STC (cctA) could lead to an accelerated electron transfer to the cell surface. The genes nrfA , ccpA , napB and napA were replaced by cctA. This led to a 1.7-fold increased ferric iron reduction rate and a 23% higher current generation in a bioelectrochemical system. Moreover, the quadruple mutant had a higher periplasmic flavin content. Further deletion of fccA and its replacement by cctA resulted in a strain with ferric iron reduction rates similar to the wild type and a lower concentration of periplasmic flavin compared to the quadruple mutant. A transcriptomic analysis revealed that the quadruple mutant had a 3.7-fold higher cctA expression which could not be further increased by the replacement of fccA. This work indicates that a synthetic adaptation of Shewanella towards extracellular respiration holds potential for increased respiratory rates and consequently higher current densities. • Periplasmic electron transfer is tailored and competing pathways deleted STC overproduction leads to 1.7-fold increase in ferric iron reduction rates. • STC overexpression also leads to 23% higher current densities. • c-type cytochrome gene replacement by cctA leads to 3.7-fold higher cctA expression. [ABSTRACT FROM AUTHOR]

Polyferric sulfate (PFS) is a coagulant widely used for removing contaminants from the aqueous phase; however, PFS destabilizes and recrystallizes in the solid phase in the presence of dissimilatory iron reducing bacteria (DIRB), which has a profound influence on the cycle of Fe and the fate of the associated pollutants. Our objective is to investigate the combined effects of medium composition and electric field stimulation on the biomineralization of PFS. Batch experiments were conducted with PFS and the DIRB Shewanella oneidensis MR-1 under anoxic conditions to examine the microbial reduction of PFS to Fe(II) and its subsequent biotransformation. The high concentration of phosphorous in phosphate buffer solution (PBS) is responsible for slower and less extensive Fe(II) generation compared to the lower concentration of phosphorous in a medium of 1,4-piperazinediethanesulfonic acid (PIPES). The PBS system induces the formation of green rust (SO 4 2−) and vivianite as the major minerals; in contrast, magnetite is the predominant end product in the PIPES system. The application of an anodic potential of 0.2 V significantly stimulates Fe(II) release from PFS, leading to precipitation and transformation of more crystalline minerals in increased quantities. The results demonstrate that Fe(II) catalyzes biomineralization of PFS to a variety of secondary products; this electron transfer process is highly dependent on the rate and magnitude of PFS reduction and the surface reaction with the host compound and adsorbed ions. Unlabelled Image • Fe(II) is produced from bioreduction of PFS in the presence of DIRB. • Biogenic Fe(II) catalyzes biomineralization of PFS to various secondary products. • Green rust and vivianite are the major minerals in the phosphate-buffered medium. • Magnetite is the primary product in the PIPES system. • Electric field stimulates Fe(II) production and induces more crystalline minerals. [ABSTRACT FROM AUTHOR]

Azo dye wastewater treatment is urgent necessary nowadays. Electrochemical technologies commonly enable more efficient degradation of recalcitrant organic contaminants than biological methods, but those rely greatly on the energy consumption. A novel process of biofilm coupled with electrolysis, i.e., bioelectrochemical system (BES), for methyl orange (MO) dye wastewater treatment was proposed and optimization of main influence factors was performed in this study. The results showed that BES had a positive effect on enhancement of color removal of MO wastewater and 81.9% of color removal efficiency was achieved at the optimum process parameters: applied voltage of 2.0 V, initial MO concentration of 20 mg/L, glucose loads of 0.5 g/L and pH of 8.0 when the hydraulic retention time (HRT) was maintained at 3 d, displaying an excellent color removal performance. Importantly, a wide range of effective pH, ranging from 6 to 9, was found, thus greatly favoring the practical application of BES described here. The absence of a peak at 463 nm showed that the azo bond of MO was almost completely cleaved after degradation in BES. From these results, the proposed method of biodegradation combined with electrochemical technique can be an effective technology for dye wastewater treatment and may hopefully be also applied for treatment of other recalcitrant compounds in water and wastewater. [ABSTRACT FROM AUTHOR]

The extracellular electron transfer (EET) efficiency in bioelectrochemical systems has been proven to be dependent on anode potentials. To explore the underlying mechanism, previous studies have mainly focused on EET conduit and bacterial biomass but rarely concerned with the role of extracellular polymeric substances (EPS) surrounding electroactive cells. In this study, the response of Geobacter biofilms to anode potentials was investigated with a special emphasis on the mechanistic role of EPS. The electrochemical activities and cell viabilities of Geobacter soli biofilms were simultaneously attenuated at 0.4 and 0.6 V compared to −0.2 and 0 V. It was found that the biofilms (especially the biofilm region closer to electrode surface) grown at −0.2 and 0 V produced relatively more extracellular redox-active proteins and less extracellular polysaccharides, which conferred higher electron accepting/donating capacities to EPS and consequently facilitated EET. Meanwhile, electrically nonconductive extracellular polysaccharide-dominated interior layers were formed in the biofilms grown at 0.4 and 0.6 V, which limited direct EET but might serve as physical barriers for protecting cells in these biofilms from the increasing stress by poised electrodes. These results demonstrated that the production of EPS under different anode potentials might be finely regulated by cells to keep balance between EET efficiency and cell-protection. This study provides a new insight to investigate the Geobacter biofilms coping with various environments, and is useful for optimizing electrochemical activity of anode biofilms. Image 1 • Highest EET and cell viability observed in biofilms grown at −0.2 and 0 V. • Heterogeneity is elucidated in spatial distribution of both viable cells and EPS. • Electrochemical activity of biofilm is positively related to redox activity of EPS. • Polysaccharide-dominated interior layers of EPS in 0.4 and 0.6 V biofilms hinder EET. [ABSTRACT FROM AUTHOR]

Excess sludge contains a large amount of organic matter, most of which is present in the form of bacteria and extracellular polymeric substances. In this study, a photosynthetic bioelectrochemical system (BES) combined with ultrasonic treatment (UT) was investigated to mineralize sludge. The sludge was disintegrated by the UT, and the supernatant separated from the treated sludge was further degraded through a bioelectrochemical system containing photosynthetic bacteria (PSB‐BES). The UT efficiency was enhanced by supernatant separation. The PSB‐BES method effectively improved the degradation of the soluble chemical oxygen demand (SCOD) from the supernatant. The SCOD and protein removal were increased 1.4 and 1.5 times, respectively, compared to BES without PSB. In addition, the effects of several key operating factors including illumination, voltage, and temperature were systematically investigated. This study provides a basis for further development of sludge mineralization processes. Practitioner points: The sludge was disintegrated by the ultrasound treatment.The supernatant separated from treated sludge was further degraded by a bioelectrochemical system combined with photosynthetic bacteria.The ultrasonic treatment efficiency was enhanced by supernatant separation.The PSB‐BES method effectively improved the soluble chemical oxygen demand (SCOD) degradation from the supernatant.The effects of several key operating factors including light (dark–photo), voltage, and temperature were systematically investigated. [ABSTRACT FROM AUTHOR]

The early formation of electroactive biofilms was investigated with gold electrodes inoculated with Geobacter sulfurreducens. Biofilms were formed under an applied potential of 0.1 V/SCE, with a single batch of acetate 10 mM, on flat gold electrodes with different random surface roughness. Roughness with arithmetical mean height (S a) ranging from 0.5 to 6.7 μm decreased the initial latency time, and increased the current density by a factor of 2.7 to 6.7 with respect to nano-rough electrodes (S a = 4.5 nm). The current density increased linearly with S a up to 14.0 A·m−2 for S a of 6.7 μm. This linear relationship remained valid for porous gold. In this case, the biofilm rapidly formed a uniform layer over the pores, so porosity impacted the current only by modifying the roughness of the upper surface. The current density thus reached 14.8 ± 1.1 A·m−2 with S a of 7.6 μm (7 times higher than the nano-rough electrodes). Arrays of 500-μm-high micro-pillars were roughened following the same protocol. In this case, roughening resulted in a modest gain around 1.3-fold. A numerical model showed that the modest enhancement was due to ion transport not being sufficient to mitigate the local acidification of the structure bottom. • Surface roughness of gold electrodes was studied in the 0.5 to 6.7 μm range. • Current density was increased by a factor of 2.7 to 6.8 vs nano-rough electrodes. • Current density increased proportionally to arithmetical mean height (S a). • Porosity impacted current density by modifying the surface roughness. • Roughening a micro-structured surface exacerbated local acidification. [ABSTRACT FROM AUTHOR]

BACKGROUND: Scaling up bioelectrochemical systems for the treatment of wastewater faces challenges. Material costs, low conductivity of wastewater and clogging are issues that need a novel approach. The granular capacitive moving bed reactor can potentially solve these challenges. In this reactor, capacitive activated carbon granules are used as bioanode material. The charge storage capabilities of these capacitive granules allow for the physical separation of the charging and the discharging process and therefore a separation of the wastewater treatment and energy recovery process. RESULTS: This study investigates the performance of the granular capacitive moving bed reactor. In this reactor, activated granules were transported from the bottom to the top of the reactor using a gas lift and settled on top of the granular bed, which moved downwards through the internal discharge cell. This moving granular bed was applied to increase the contact time with the discharge anode to increase the current density. The capacitive moving bed reactor (total volume 7.7 L) produced a maximum current of 23 A m−2 normalized to membrane area (257 A m−3granules). Without granules, the current was only 1.4 A m−2membrane. The activity of the biofilm on the granules increased over time, from 436 up to 1259 A m−3granules. A second experiment produced similar areal current density and increase in activity over time. CONCLUSION: Whereas the produced current density is promising for further scaling up of bioanodes, the main challenges are to improve the discharge of the charged granules and growth of biofilm on the granules under shear stress. © 2019 The Authors. Journal of Chemical Technology & Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Anaerobic fermentation liquid of waste organic matters (WOMs) is rich in volatile fatty acids (VFAs), which can be treated with bioelectrochemical systems for both electrical energy recovery and organics removal. In this work, four major VFAs in the fermented WOMs supernatant were selected to examine their electron donation characteristics for power output and their complicated interplays in microbial fuel cells (MFCs). Results indicated a priority sequence of acetate, propionate, n-butyrate and i-valerate when served as the sole electron donor for electricity generation. The MFC solely fed with acetate showed the highest coulombic efficiency and power density, and the longest period for electricity production. When two of the VFAs were added with equal proportion, both acids contributed positively to electricity generation, while the selective or competitive use of substrates by diverse microorganisms behaved as an antagonism effect to prolong the degradation time of each VFA. When acetate and propionate, the preferable substrates for electricity generation, were mixed in various proportions, their large concentration difference led to improved electrical performance but decreased organic removal rate. [ABSTRACT FROM AUTHOR]

Biodegradation was regarded an environmentally benign and cost‐effective technology for formaldehyde (CH2O) removal. However, the biotoxicity of CH2O inhibited microbial activity and decreased removal performance. We developed a novel heterotopic CH2O biodegradation process that combined bioelectrochemical system (BES) and UV/H2O2. Instead of exogenous addition, H2O2 was biosynthesized with electron transferred from electrochemically active bacteria. Heterotopic biodegradation of CH2O was more efficient and faster than in situ biodegradation, as confirmed by 69%–308% higher removal efficiency and 98% shorter degradation time. Operated under optimal conditions for 30 min, which are optical distance of 2 cm, initial H2O2 concentration of 102 mg/L, and pH 3, heterotopic biodegradation removed 78%, 73%, 49%, and 30% of CH2O with 6, 8, 10, and 20 mg/L initial concentration. Mild formation of hydroxyl radicals from UV/H2O2 is beneficial to sustainable CH2O degradation and efficient H2O2 utilization. Heterotopic biodegradation is a promising technology for efficient degradation of other organic compounds with biological toxicity. Practitioner points: H2O2 biosynthesis through electrochemically active bacteria (EAB) served as source of ·OH for CH2O removal in UV/H2O2.Heterotopic CH2O biodegradation avoided the biotoxicity of CH2O.Heterotopic biodegradation of CH2O saved 98% time than in‐situ biodegradation.Heterotopic CH2O biodegradation improved 69%–308% efficiency than in‐situ. [ABSTRACT FROM AUTHOR]

Leachate generated in landfills is considered as a hazardous waste stream due to its composition and needs adequate treatment for environmental protection purposes. Nonetheless, a contemporary technology should not only be able to deal with its degradation, but at the same time, recover energy in various forms. Such valorization approaches with priority on these dual-aims are potentially those that rely on anaerobic biosystems. In the literature, processes considered on that matter include fermentative, digestive and bioelectrochemical set-ups to deliver energy-carriers such as biohydrogen (DF), biogas (AD) and electricity (BES), respectively. Moreover, to enhance the global efficiency of leachate utilization, it has been recently trending to develop integrated options by combining these systems (DF, AD, BES) into a cascade scheme. In this review, it is intended to give an insight to the research activities realized in these fields and show possible directions towards the better exploitation of leachate feedstock under anaerobic conditions. • Options for leachate valorization in anaerobic biosystems are overviewed. • Treatment approaches with simultaneous energy recovery are outlined. • Potential of biohydrogen, biogas and bioelectrochemical systems are discussed. • Integrated applications are proposed for better process efficiency. [ABSTRACT FROM AUTHOR]

First large-scale experiences of bioelectrochemical systems (BES) are underway. However, there is still little knowledge on how the different elements that integrate a BES behave in near real-life conditions. This paper aims at assessing the impact of long-term operation on the cation exchange membrane and on the anodic biofilm of two 16 L Microbial Electrolysis Cells (MEC) designed for hydrogen production and ammonia recovery from pig slurry. Membrane deterioration was examined by physical, chemical and microscopy techniques at different locations, revealing a strong attachment of microorganisms and a significant decay in membrane properties such as ion exchange capacity and thermal stability. Anode microbial communities did not show a dramatic shift in the eubacteria composition at different sampling areas, although the relative abundance of some bacterial groups showed a clear vertical stratification. After 100 days of continuous operation, MEC performance did not declined significantly maintaining ammonium transport rates and H 2 production rates of 15.3 gN d−1 m−2 and 0.2 LH 2 ·L−1 reactor ·d−1 respectively. • Large-scale BES can lead to a vertical stratification of anode microbial communities. • Shear stress is hampering the development of an anodic biofilm. • Ion exchange capacity of the membrane is reduced as consequence of the biofouling. • Membrane matrix is specially deteriorated at the top of the reactor. • Hydrogen production is feasible in a MEC treating a complex substrate. [ABSTRACT FROM AUTHOR]

Highlights • Increase of intracellular FAD concentration resulting in electroactive E. coli. • Neutral red-mediated electrosynthesis is applied to the MES reaction. • More reductive products are achieved by E. coli 8739(pRibAB-YbjI-YigB, pRibECF). • The succinate yield is improved by E. coli T110(pRibAB-YbjI-YigB, pRibECF). Abstract In this study, the FAD synthesis pathway was manipulated to increase its cellular concentration and thereby improve the electroactivity of E. coli. In a microbial electrosynthesis (MES) system with neutral red as electron carrier and fumarate as the sole electron acceptor, the engineered strains derived from three E. coli lines displayed increased electric current in the reaction system, indicating improved electroactivity. Furthermore, the production of succinate from fumarate increased by around 60% compared with that of the parent strains, confirming the improvement of E. coli electroactivity by manipulating the FAD synthesis pathway. An MES reaction was performed with engineered E. coli 8739, and an altered metabolic profile with more reductive fermentation products was obtained. When the electroactive succinate-producing strain E. coli T110 was used in the MES, a yield of 0.97 ± 0.02 mol/mol glucose was achieved, which corresponds to an approximately 1.4-fold increase compared with the fermentation with no electricity supply or non-electroactive T110. In addition, a carbon concentration mechanism (CCM) was employed to further improve succinate production and yield in the MES, which produced a succinate yield of 1.16 mol/mol glucose, a 1.7-fold increase compared with that of the parent strain T110, indicating that the electroactive E. coli could be used in MES to produce specific fermentation products with improved yield. [ABSTRACT FROM AUTHOR]

In this work, a dynamic computational model is developed for a single chamber microbial fuel cell (MFC), consisting of a bio-catalyzed anode and an air-cathode. Electron transfer from the biomass to the anode is assumed to take place via intracellular mediators as they undergo transformation between reduced and oxidized forms. A two-population model is used to describe the biofilm at the anode and the MFC current is calculated based on charge transfer and Ohm's law, while assuming a non-limiting cathode reaction rate. The open circuit voltage and the internal resistance of the cell are expressed as a function of substrate concentration. The effect of operating parameters such as the initial substrate (COD) concentration and external resistance, on the Coulombic efficiency, COD removal rate and power density of the MFC system is studied. Even with the simple formulation, model predictions were found to be in agreement with observed trends in experimental studies. This model can be used as a convenient tool for performing detailed parametric analysis of a range of parameters and assist in process optimization. • A fast converging mathematical model is developed to describe a microbial fuel cell. • Model based on bioanode kinetics assuming a non-limiting cathode. • Effect of operating parameters on system performance is studied. • Proposed model can serve as a good starting point for MFC system optimization studies. [ABSTRACT FROM AUTHOR]

• Novel control strategy was used for bio electrochemical recovery of copper from distillery waste. • 6.8 L tubular BES was constructed and tested with MPPT and applied voltage as control strategies. • MPPT performs better at high Cu2+ concentration with double metal removal efficiency. • The form of copper recovered can be manipulated at low Cu2+ with MPPT and constant applied voltage. Copper recovery from distillery effluent was studied in a scalable bioelectro-chemical system with approx. 6.8 L total volume. Two control strategies based on the control of power with maximum power point tracking (MPPT) and the application of 0.5 V using an external power supply were used to investigate the resultant modified electroplating characteristics. The reactor system was constructed from two electrically separated, but hydraulically connected cells, to which the MPPT and 0.5 V control strategies were applied. Three experiments were carried out using a relatively high copper concentration i.e. 1000 mg/L followed by a lower concentration i.e. 50 mg/L, with operational run times defined to meet the treatment requirements for distillery effluents considered. Real distillery waste was introduced into the cathode to reduce ionic copper concentrations. This waste was then recirculated to the anode as a feed stock after the copper depletion step, in order to test the bioenergy self-sustainability of the system. Approx. 60–95% copper was recovered in the form of deposits depending on starting concentration. However, the recovery was low when the anode was supplied with copper depleted distillery waste. Through process control (MPPT or 0.5 V applied voltage) the amount and form of the copper recovered could be manipulated. [ABSTRACT FROM AUTHOR]

• Many microorganisms can reduce soluble U(VI) to insoluble U(IV). • This ability can be used to remediate uranium contaminated environments. • In situ stimulation of microbial activity for U containment has been widely studied. • Alternative approaches are bioreactors and electrochemically catalyzed bioreduction. • Bioreduction rates are greatly affected by uranium speciation and bioavailability. Biological reduction of soluble uranium from U(VI) to insoluble U(IV) coupled to the oxidation of an electron donor (hydrogen or organic compounds) is a potentially cost-efficient way to reduce the U concentrations in contaminated waters to below regulatory limits. A variety of microorganisms originating from both U contaminated and non-contaminated environments have demonstrated U(VI) reduction capacity under anaerobic conditions. Bioreduction of U(VI) is considered especially promising for in situ remediation, where the activity of indigenous microorganisms is stimulated by supplying a suitable electron donor to the subsurface to contain U contamination to a specific location in a sparingly soluble form. Less studied microbial biofilm-based bioreactors and bioelectrochemical systems have also shown potential for efficient U(VI) reduction to remove U from contaminated water streams. This review compares the advantages and challenges of U(VI)-reducing in situ remediation processes, bioreactors and bioelectrochemical systems. In addition, the current knowledge of U(VI) bioreduction mechanisms and factors affecting U(VI) reduction kinetics (e.g. pH, temperature, and the chemical composition of the contaminated water) are discussed, as both of these aspects are important in designing efficient remediation processes. [ABSTRACT FROM AUTHOR]

Denitrifying bioelectrochemical system provided an alternative technology for nitrogen removal, even power recovery from wastewater, and its nitrogen removal performance and intermediate accumulation were affected by the extracellular electron transfer modes and rate-limiting steps in denitrifying biocathodes. In the current study, the extracellular electron transfer modes and rate-limiting steps for nitrate reduction and nitrite reduction of denitrifying biocathode were investigated through cyclic voltammetry. When the cathode potential swept from 0.003 to − 0.897 V (vs. Ag/AgCl), denitrifiers were indispensable for electrochemical denitrification. Three peak potentials were found in the cyclic voltammogram of denitrifying biocathode, where E1 (− 0.471 to − 0.465 V) and E2 (− 0.412 to − 0.428 V) represented respectively nitrate reduction and nitrite oxidation while E3 (− 0.822 to − 0.826 V) represented nitrite reduction. Nitrate reduction involved the direct electron transfer mode while nitrite reduction involved the mediated electron transfer mode. Intracellular catalytic reaction was the rate-limiting step for nitrate reduction, independent on the electrochemical activity of denitrifying biocathode and the nitrate supply. The nitrate supply posed an effect on the rate-limiting step for nitrite reduction. The mediator transfer was the rate-limiting step for nitrite reduction in the absence of nitrate. But both mediator transfer and intracellular catalytic reaction became the rate-limiting steps for nitrite reduction in the presence of sufficient nitrate. [ABSTRACT FROM AUTHOR]

Abstract The effect of extremely low-frequency electromagnetic fields (ELF-EMFs) on human health has become a worldwide concern, and no molecule/factor has been established as a measurable indicator of this effect. Diseases related to ELF-EMF are generally accompanied with energy metabolic dysfunction, and the energy in metabolism often flows in terms of electrons in all living cells. Hence, this study specifically investigated the relationship between metabolic current and ELF-EMF. By applying 0–128 Gauss ELF-EMFs to Geobacter sulfurreducens -inoculated bioelectrochemical systems, we found that metabolic current was increased and oscillated in ELF-EMF-exposed G. sulfurreducens. All effects were exposure dose dependent. Moreover, the oscillation amplitude varied linearly with the ELF-EMF strength. These results reveal that metabolic current can be used as a dosimetric indicator of the effect of ELF-EMF on living organisms, including human beings. Highlights • Metabolic current was increased and oscillated under ELF-EMF treatment. • The two effects were exposure dose dependent. • The increased metabolic current serves ATP production. • Metabolic current can be used as a dosimetric indicator of ELF-EMF effect. • A new method for monitoring ATP production in living cells. [ABSTRACT FROM AUTHOR]

Bioelectrochemical systems (BESs) are capable of simultaneous wastewater treatment and resource recovery at low temperatures. However, the direct enrichment of psychrophilic and electroactive biofilms in BESs at 4°C is difficult due to the lack of understanding in the physioecology of psychrophilic exoelectrogens. Here, we report the start-up and operation of microbial fuel cells (MFCs) at 4°C with pre-acclimated inocula at different temperatures (4°C, 10°C, 25°C, and −20°C) for 7 days and 14 days. MFCs with 7-day-pretreated inocula reached higher peak voltages than did those with 14-day-pretreated inocula. The highest power densities were obtained by MFCs with 25°C – 7-day-, 25°C – 14-day-, and 4°C – 7-day-pretreated inocula (650–700 mW/m2). In contrast, the control MFCs with untreated inocula were stable at 450 mW/m2. The power densities of MFCs with 7-day-pretreated inocula were higher than those obtained by MFCs with 14-day-pretreated inocula. The MFCs with 10°C – 7-day-pretreated inocula and the control MFCs showed higher chemical oxygen demand (COD) removal (90–91%) than other MFCs. Illumina HiSeq sequencing based on 16S rRNA gene amplicons indicated that bacterial communities of the anode biofilms were shaped by pretreated inocula at different temperatures. Compared with the control MFCs with untreated inocula, MFCs with temperature-pretreated inocula demonstrated higher microbial diversity, but did not do so with −20°C-pretreated inocula. Principal components analysis (PCA) revealed an obvious separation between the inocula pretreated at 4°C and those pretreated at 10°C, implying that bacterial community structures could be shaped by pretreated inocula at low temperatures. The pretreatment period also had a diverse impact on the abundance of exoelectrogens and non-exoelectrogens in MFCs with inocula pretreated at different temperatures. The majority of the predominant population was affiliated with Geobacter with a relative abundance of 17–70% at different pre-acclimated temperatures, suggesting that the exoelectrogenic Geobacter could be effectively enriched at 4°C even with inocula pretreated at different temperatures. This study provides a strategy that was previously neglected for fast enrichment of psychrophilic exoelectrogens in BESs at low temperatures. [ABSTRACT FROM AUTHOR]

Biophotovoltaics is a relatively new discipline in microbial fuel cell research. The basic idea is the conversion of light energy into electrical energy using photosynthetic microorganisms. The microbes will use their photosynthetic apparatus and the incoming light to split the water molecule. The generated protons and electrons are harvested using a bioelectrochemical system. The key challenge is the extraction of electrons from the microbial electron transport chains into a solid-state anode. On the cathode, a corresponding electrochemical counter reaction will consume the protons and electrons, e.g., through the oxygen reduction to water, or hydrogen formation. In this review, we are aiming to summarize the current state of the art and point out some limitations. We put a specific emphasis on cyanobacteria, as these microbes are considered future workhorses for photobiotechnology and are currently the most widely applied microbes in biophotovoltaics research. Current progress in biophotovoltaics is limited by very low current outputs of the devices while a lack of comparability and standardization of the experimental set-up hinders a systematic optimization of the systems. Nevertheless, the fundamental questions of redox homeostasis in photoautotrophs and the potential to directly harvest light energy from a highly efficient photosystem, rather than through oxidation of inefficiently produced biomass are highly relevant aspects of biophotovoltaics. [ABSTRACT FROM AUTHOR]

Highlights • The use of certain anion/cation exchange membranes in MFC is first presented. • The type of membrane separator affected the efficiency of MFC start-up. • MFC with anion exchange membrane showed outstanding performance. • Geobacter was dominantly selected on anodes independently of membrane type. • Voltammograms indicated various anode surface coverage of redox components. Abstract In this study, microbial fuel cells (MFCs) – operated with novel cation- and anion-exchange membranes, in particular AN-VPA 60 (CEM) and PSEBS DABCO (AEM) – were assessed comparatively with Nafion proton exchange membrane (PEM). The process characterization involved versatile electrochemical (polarization, electrochemical impedance spectroscopy – EIS, cyclic voltammetry – CV) and biological (microbial structure analysis) methods in order to reveal the influence of membrane-type during start-up. In fact, the use of AEM led to 2–5 times higher energy yields than CEM and PEM and the lowest MFC internal resistance (148 ± 17 Ω) by the end of start-up. Regardless of the membrane-type, Geobacter was dominantly enriched on all anodes. Besides, CV and EIS measurements implied higher anode surface coverage of redox compounds for MFCs and lower membrane resistance with AEM, respectively. As a result, AEM based on PSEBS DABCO could be found as a promising material to substitute Nafion. [ABSTRACT FROM AUTHOR]

Graphical abstract Representation of targets of bioelectrochemical system to enhance the performance and methanogenesis control. Highlights • Extensive competition between methanogens & electrogens reduces Coulombic yield. • Methanogens can be suppressed by physical, chemical & biological pretreatment means. • Selective anodic biofilm enrichment by bioaugmentation & applied potential methods. • Physical pretreatment & intermittent chemical dosing suitable for field application. Abstract Suppression of methanogens is considered as one of the main challenges in achieving the practical application of several types of bioelectrochemical system (BES). Feasibility of mixed culture as an inoculum in BES is mainly restricted by methanogenic population. Methanogens compete with electrogens (in bioanodes) or acetogens (in biocathodes) for substrate which results in diminishing Coulombic efficiency. Selection of particular inoculum pretreatment method affects the microbial diversity in anodic/cathodic microenvironments and hence the performance of BES. This review discusses various physical, chemical and biological pretreatment methods for suppressing the growth of methanogens. Selective microbial enrichment in anodic/cathodic biofilm can be promoted with bioaugmentation and/or applied external potential approach to harvest maximum Coulombs from the substrate. For field application of BES, physical pretreatment methods can be proposed with intermittent addition of chemical inhibitors and conversion of methane to electricity in order to make the process inexpensive along with recovering the maximum energy. [ABSTRACT FROM AUTHOR]

Abstract In this paper, the typical organic component of humic acid (HA) was studied to explore its effect on the co-metabolic biodegradation of Tetrabromobisphenol A (TBBPA) in bioelectrochemical systems (BES). The degradation efficiency, intermediate metabolites and microbial diversity were investigated to demonstrate the impact of HA on the biodegradation of TBBPA in BES-HA-T (Bioelectrochemical system with TBBPA as substrate and HA as a stimulating factor). The highest biodegradation rate (93.2%) for TBBPA were obtained, which illustrated that HA played a positive role in the biodegradation of TBBPA. According to the analysis of the intermediate metabolites, it can be concluded that HA has changed the biodegradation pathway of TBBPA. The analysis of microbial diversity showed that the interaction of microorganisms had great effects on the anaerobic biodegradation of TBBPA, especially Trichococcus and Anaerolineaceae. Meanwhile, the abundance of Desulfobulbus in the BES-HA (Bioelectrochemical system with HA as a stimulating factor) had a positive effect on the improvement of electrochemical system performance. Graphical abstract Image 106 Highlights • HA was used to improve the performance of BES for TBBPA biodegradation. • The pathway of TBBPA biodegradation in BES with HA was deduced. • The different characteristic species were found in anode biofilm. [ABSTRACT FROM AUTHOR]