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Anodic electro-fermentation (AEF), where an anode replaces the terminal electron acceptor, shows great promise. Recently a Lactococcus lactis strain blocked in NAD+ regeneration was demonstrated to use ferricyanide as an alternative electron acceptor to support fast growth, but the need for high concentrations of this non-regenerated electron acceptor limits practical applications. To address this, growth of this L. lactis strain, and an adaptively evolved (ALE) mutant with enhanced ferricyanide respiration capacity were investigated using an anode as electron acceptor in a bioelectrochemical system (BES) setup. Both strains grew well, however, the ALE mutant was significantly faster. The ALE mutant almost exclusively generated 2,3-butanediol, whereas its parent strain mainly produced acetoin. The ALE mutant interacted efficiently with the anode, achieving a record high current density of 0.81 ± 0.05 mA/cm2. It is surprising that a Lactic Acid Bacterium, with fermentative metabolism, interacts so well with an anode, which demonstrates the potential of AEF.

Microbial electrolysis systems (MES) facilitate the process of using waste for efficient production of hydrogen thus resulting in lower energy costs compared to conventional hydrogen production. However, the stability and robustness of anode-respiring biofilms often limit long-term MES application. In this study, a 10 L rotating disc bioelectrochemical reactor was used to analyze the anodic biofilm under rapidly changing processing conditions, including changes in anode potential and shear force. A low complexity biofilm formed by Shewanella oneidensis and Geobacter sulfurreducens was studied to determine the boundary conditions for achievable current density and species interaction in large-scale applications. Demonstrating its robustness to the applied changes, the biofilm produced a stable current density of 1.2 A m−2 over 1.5 months. Furthermore, a mathematical model was developed to predict the behavior of the system in terms of current output, which may allow automatic user-defined control of sub-processes in MES reactors in the future.

The electroenzymatic hydroxylation of 4-ethylbenzoic acid catalyzed by the recombinant unspecific peroxygenase from the fungus Agrocybe aegerita (rAaeUPO) was performed in a gas diffusion electrode (GDE)-based system. Enzyme stability and productivity are significantly affected by the way the co-substrate hydrogen peroxide (H2O2) is supplied. In this study, two in-situ electrogeneration modes of H2O2 were established and compared. Experiments under galvanostatic conditions (constant productivity of H2O2) were conducted at current densities spanning from 0.8 mA cm−2 to 6.4 mA cm−2. For comparison, experiments under H2O2-stat mode (constant H2O2 concentration) were performed. Here, four H2O2 concentrations between 0.06 mM and 0.28 mM were tested. A maximum H2O2 productivity of 5.5 µM min−1 cm−2 and productivity of 10.5 g L−1 d−1 were achieved under the galvanostatic condition at 6.4 mA cm−2. Meanwhile, the highest total turnover number (TTN) of 710,000 mol mol−1 and turnover frequency (TOF) of 87.5 s−1 were obtained under the H2O2-stat mode at concentration limits of 0.15 mM and 0.28 mM, respectively. The most favorable outcome in terms of maximum achievable TTN, TOF and productivity was found under the H2O2-stat mode at concentration limit of 0.2 mM. Here, a TTN of 655,000 mol mol−1, a TOF of 80.3 s−1 and a productivity of 6.1 g L−1 d−1 were achieved. The electrochemical H2O2-stat mode not only offers a promising alternative reaction concept to the well-established galvanostatic mode but also enhances the process performance of unspecific peroxygenases.

Petroleum and petroleum product exploration, transportation, processing, and burning negatively impact soil ecosystems and cause severe damage. Hence, a study was conducted to evaluate the performance of microbial electrochemical treatment (MET) in terms of biodegradation and electricity generation with petroleum hydrocarbon-polluted soil by adding rice straw biochar pyrolyzed at 600 °C for different doses of 4%, 8%, and 12% w/w. This study confirmed for the first time that increasing the dose of biochar from 8% to 12% w/w in the anodic chamber of MET led to a decrease in its degradation of petroleum hydrocarbons from 87.8% to 49.2% and its current density from 3.5 A/m2 to 0.5 A/m2 in 20 days. Moreover, the relative abundance of Desulfuromonas and Geobacter, which have been reported to participate in inter-species electron transfer as electroactive bacteria, also decreased from 52.32% to 1.5% and 3.47–1.4%, respectively. This apparent change in primary genera further suggested that biochar content was the core factor reshaping the distribution of the bacterial community. The electrochemical investigation also shows that the redox-active quinone in biochar is responsible for extracellular electron transfer. The results of this study showed that the effectiveness of biochar for the degradation of petroleum hydrocarbons using microbial electrochemical treatment depends on the dose of biochar in the soil.

Sulphide oxidising bacteria (SOB) are known to spatially separate sulphide removal and current production, thereby acting as sulphide shuttles. The effect of anode potential, sulphide load and biomass concentration on discharge by sulphide shuttling SOB was investigated. SOB communities dominated by Thioalkalivibrio sulfidophilus were incubated with sulphide in batch experiments to produce sulphidic conditions. After sulphide had (partly) been removed the sulphidic SOB were exposed to potentials and current was measured. Discharge of sulphidic SOB were compared to discharge of aerated SOB and electrochemical oxidation of abiotic sulphide. The full methodology can be found in the related publication.

Syngas fermentation processes with acetogens represent a promising process for the reduction of CO₂ emissions alongside bulk chemical production. However, to fully realize this potential the thermodynamic limits of acetogens need to be considered when designing a fermentation process. An adjustable supply of H₂ as electron donor plays a key role in autotrophic product formation. In this study an anaerobic laboratory scale continuously stirred tank reactor was equipped with an All-in-One electrode allowing for in-situ H₂ generation via electrolysis. Furthermore, this system was coupled to online lactate measurements to control the co-culture of a recombinant lactate-producing Acetobacterium woodii strain and a lactate-consuming Clostridium drakei strain to produce caproate. When C. drakei was grown in batch cultivations with lactate as substrate, 1.6 g·L⁻¹ caproate were produced. Furthermore, lactate production of the A. woodii mutant strain could manually be stopped and reinitiated by controlling the electrolysis. Applying this automated process control, lactate production of the A. woodii mutant strain could be halted to achieve a steady lactate concentration. In a co-culture experiment with the A. woodii mutant strain and the C. drakei strain, the automated process control was able to dynamically react to changing lactate concentrations and adjust H₂ formation respectively. This study confirms the potential of C. drakei as medium chain fatty acid producer in a lactate-mediated, autotrophic co-cultivation with an engineered A. woodii strain. Moreover, the monitoring and control strategy presented in this study reinforces the case for autotrophically produced lactate as a transfer metabolite in defined co-cultivations for value-added chemical production.

Bioelectrochemical systems (BES) are increasingly being explored as an auxiliary unit process to enhance conventional waste treatment processes. This study proposed and validated the application of a dual-chamber bioelectrochemical cell as an add-on unit for an aerobic bioreactor to facilitate reagent-free pH-correction, organics removal and caustic recovery from an alkaline and saline wastewater. The process was continuously fed (hydraulic retention time (HRT) of 6 h) with a saline (25 g NaCl/L) and alkaline (pH 13) influent containing oxalate (25 mM) and acetate (25 mM) as the target organic impurities present in alumina refinery wastewater. Results suggested that the BES concurrently removed the majority of the influent organics and reduced the pH to a suitable range (9-9.5) for the aerobic bioreactor to further remove the residual organics. Compared to the aerobic bioreactor, the BES enabled a faster removal of oxalate (242 ± 27 vs. 100 ± 9.5 mg/L.h), whereas similar removal rates (93 ± 16 vs. 114 ± 23 mg/L.h, respectively) were recorded for acetate. Increasing catholyte HRT from 6 to 24 h increased the caustic strength from 0.22% to 0.86%. The BES enabled caustic production at an electrical energy demand of 0.47 kWh/kg-caustic, which is a fraction (22%) of the electrical energy requirement for caustic production using conventional chlor-alkali processes. The proposed application of BES holds promise to improve environmental sustainability of industries in managing organic impurities in alkaline and saline waste streams.

Soil contamination by petroleum hydrocarbons (PHCs) causes various acute problems such as crop growth, yield, and grain quality. Many Physico-chemical and biological approaches are employed to remove the PHCs from polluted soil. However, some of these approaches are too slow, or ineffective, and/or environmentally unfriendly. Indeed, bioelectrochemical systems (BES) combine biological methods and electrochemistry in the context of a redox reaction. BES is gaining attention from scientists and policymakers as a promising technology for the remediation of soil contaminated with PHCs. This review discusses BES working principles, mechanisms, design configuration, operational parameters, and advances in BES applications to remediate PHCs from contaminated soil efficiently. The role of biosurfactants and biochar in enhancing PHC degradation in soil using BES mediating extracellular electron transfer (EET) and biofilm formation is highlighted. Furthermore, recent innovations in this field, technical and economic challenges and limitations in scaling-up BES, and future perspectives are discussed. This review suggests that biochar-based single-chamber air-cathode reactors are preferred because of their lower cost compared to the other classic configurations. Additional efforts are needed in the design of BES reactors, soil characteristics, and seasonal variations in BES performance over a long period of operation to improve the efficiency of soil remediation and power production as well as to apply it on a large scale.

Microbial electrosynthesis (MES) has been highlighted as a means to valorize inorganic gaseous carbon, such as CO2, into value-added chemicals using electricity as the reducing power. Electrode-based electron transfer delivers respiratory electrons to a live-cell biocatalyst through a biofilm matrix or via electron shuttle molecules. The addition of artificial mediators, such as neutral red (NR) and 2-hydroxy-1,4-naphthoquinone (HNQ), increased acetate synthesis significantly, suggesting that these mediators improve the electron transport capability between the suspended cells and electrode. Regular media replacement also improves MES by adapting mediator-utilizing species in the reactor. MES without a mediator initially produced acetate at a reasonable rate (5.1 ± 0.2 mmol/l/day), but the rate became negligible in the later stage. In contrast, MES with NR or HNQ showed a higher acetate production rate (4.6 ± 0.4 vs. 7.4 ± 0.4 mmol/l/day, respectively) as the media replacement progressed. Confocal laser scanning microscopy and 3D imaging showed that the biofilm matrix consisted of live and dead cells, while the composition was different in the MES with and without a mediator. Microbial community analysis by next-generation sequencing (NGS) showed that acetogenic Acetobacterium (in suspension) and Sporomusa (in both suspension and biofilm) were dominant during the 96 days of operation. The biofilm and planktonic community interacted dynamically under MES conditions. This result provides a realistic model of biofilms and planktonic cells in the MES. The interaction of the suspended cells with the biofilm-forming electrode via electron shuttles could improve volumetric acetate production and stabilize the MES performance.

Electroactive bacteria have a wide range of applications, including electricity production, bioremediation, and the sensing of toxic compounds. Bacterial biofilm formation is often mediated by the second messenger cyclic guanosine monophosphate (c-di-GMP) synthesized by a diguanylate cyclase (DGC). The role of c-di-GMP in the expression of c-type cytochromes has been previously reported. The aim of this study was to determine the bioelectrogenic activity of Cupriavidus metallidurans strain CH34 pJBpleD*, which possesses a constitutively active DGC that increases c-di-GMP levels. Notably, the heterologous expression of the constitutively active DGC in C. metallidurans strain CH34 pJBpleD* showed a higher biofilm formation and increased the electrical current production up to 560%. In addition, C. metallidurans CH34 pJBpleD* showed increased levels of c-type cytochromeassociated transcripts compared with the wild-type strain CH34. Scanning electron microscopies revealed a denser extracellular matrix with an increased exopolymeric substance content in the CH34 pJBpleD* biofilm on the electrode surface. The results of this study suggest that higher levels of c-di-GMP synthesized by a constitutively active diguanylate cyclase in C. metallidurans strain CH34 pJBpleD* activated the formation of an electroactive biofilm on the electrode, enhancing its exoelectrogenic activity.

In order to achieve a carbon-efficient circular economy, a paradigm shift is required to valorize carbon dioxide (CO2) and organic wastes to value-added products. Among others, microbial electrosynthesis (MES) and electrofermentation (EF) technologies have shown the potential to contribute to the circular carbon economy. Besides carbon conversion, both technologies can be applied to store excess green energy in the form of valuable transportable chemicals. This article sheds light on the current status of MES and EF technologies by covering the most important literature from the last two years. Recent progress on reactor design and process optimization, scale-up attempts, and a summary of ongoing or completed technology-oriented research projects over the recent years are presented. Furthermore, the key challenges and future research perspectives desired to enable the rapid implementation of the technology are also discussed.

Acetobacterium woodii is known to produce mainly acetate from CO₂ and H₂, but the production of higher value chemicals is desired for the bioeconomy. Using chain-elongating bacteria, synthetic co-cultures have the potential to produce longer-chained products such as caproic acid. In this study, we present first results for a successful autotrophic co-cultivation of A. woodii mutants and a Clostridium drakei wild-type strain in a stirred-tank bioreactor for the production of caproic acid from CO₂ and H₂ via the intermediate lactic acid. For autotrophic lactate production, a recombinant A. woodii strain with a deleted Lct-dehydrogenase complex, which is encoded by the lctBCD genes, and an inserted D-lactate dehydrogenase (LdhD) originating from Leuconostoc mesenteroides, was used. Hydrogen for the process was supplied using an All-in-One electrode for in situ water electrolysis. Lactate concentrations as high as 0.5 g L–1 were achieved with the AiO-electrode, whereas 8.1 g L–1 lactate were produced with direct H₂ sparging in a stirred-tank bioreactor. Hydrogen limitation was identified in the AiO process. However, with cathode surface area enlargement or numbering-up of the electrode and on-demand hydrogen generation, this process has great potential for a true carbon-negative production of value chemicals from CO₂.

Bioelectrochemical anaerobic digestion (BEAD) is an attractive way to enhance biogas production in the anaerobic digestion process. Exploring cost-effective biocatalysts with remarkable catalytic ability is a pivotal issue for the industrial application of BEAD systems. In this study, intact anaerobic granular sludge (AGS) was employed as a biocatalyst in an attempt to achieve high-efficiency CH4 production via interactions between exoelectrogens and methanogens. The biogas production in the BEAD system was optimized by controlling the applied voltage (0, 0.6, 0.8, and 1 V) and acetate load (1000, 5000, and 10000 mg/L). The CH4 production rate increased with applied voltage and acetate loading, while the overall energy efficiency was the highest at an applied voltage of 0.8 V and an acetate load of 5000 mg/L. The BEAD system with AGS as the biocatalyst was also efficient for the degradation of highly concentrated organic waste, with an average methane production rate of 86.23 ± 7.12 L/m2/d and CH4 content as high as 88.87%. Microbial communities including organic-degrading bacteria and exoelectrogens (e.g., Syntrophomonas, Geobacter) and hydrogenotrophic methanogenic archaea (r.g., Methanobacterium) were enriched at the anode and the cathode, respectively. The AGS-based BEAD system represents a promising industrial application in biogas production.

Environmental pollution by hydrophobic hydrocarbons is increasing, notably nowadays due to a large amount of industrial activity. Microbial electrochemical technologies (MET) are promising bio-based systems which can oxidize hydrophobic hydrocarbon pollutants and produce bioelectricity simultaneously. However, MET faces some issues in terms of soil remediation, including low mass transfer, limited electro-activity of anodes as electron acceptors, low bioavailability of hydrocarbons, and the limited activity of beneficial bacteria and inefficient electron transport. This study aims to investigate the role of the addition of rhamnolipid as an analyte solution to the MET to enhance the efficacy and concurrently solve the abovementioned issues. In this regard, a novel long chain of RL was produced by using low-cost carbon winery waste through non-pathogenic Burkholderia thailandensis E264 strains. Different doses of RL were tested, including 10, 50, and 100 mg/L. A maximum enhancement in the oxidation of hydrophobic hydrocarbons was found to be up to 72.5%, while the current density reached 9.5 Am-2 for the MET reactor having a dose of 100 mg/L. The biosurfactants induced a unique microbial enrichment associated with Geobacter, Desulfovibrio, Klebsiella, and Comamona on the anode surface, as well as Pseudomonas, Acinetobacter, and Franconibacter in soil MET, indicating the occurrence of a metabolic pathway in microbes working with the anode and soil bioelectrochemical remediation system. According to cyclic voltammetry analysis, redox peaks appeared, showing a minor shift in redox MET-biosurfactant compared to the bare MET system. Furthermore, the phytotoxicity of polluted soil to L. sativum seeds after and before MET remediation shows a decrease in phytotoxicity of 77.5% and 5% for MET-biosurfactant system and MET only, respectively. With MET as a tool, this study confirmed for the first time that novel long-chain RL produced from non-Pseudomonas bacteria could remarka

Methane emissions from the sewer system are considered to be a non-negligible source of aggravating the greenhouse effect. Meanwhile, the sewer system has long been plagued by sulfide-induced corrosion problems. This study explored the possibility of using a bioelectrochemical system to intensify the competition between electroactive bacteria, methanogens and sulfate-reducing bacteria, thereby reducing the production of methane and sulfide. Dual-chamber bioelectrochemical reactors were constructed and operated in fed-batch mode with the coexistence of Electroactive bacteria, Methanogenic archaea and Sulfate-reducing bacteria. Acetate was supplied as the sole carbon source. The results indicated that electrogenesis induced by the anode potentials of -0.42 V and -0.2 V (vs. Ag/AgCl) had advantages over methanogenesis and sulfidogenesis in consuming acetate. The stimulated electrogenesis by anode potentials resulted in a decrease in pH. Methane production was suppressed in the reactors with anode potentials of -0.42 and -0.2 V compared to open circuit controls. In contrast to methane, the capacity for sulfide production was facilitated in the reactors with the anode potentials of -0.42 V and -0.2 V compared to open circuit controls. 16s rRNA gene analysis showed that Geobacter was the most abundant genus on the anode biofilm in the anode potential-controlled reactor, while acetoclastic methanogens dominated in open circuit controls. Methanosaeta and Methanosarcina were the most abundant methanogens in open circuit controls. Collectively, our study demonstrates that the use of electrodes with anode potential control can help to control methane emissions, but could not yet prevent sulfide production, which requires further research.

Microbial electrochemical approach is an emerging technology for biogas upgrading through carbon dioxide (CO2) reduction and biomethane (or value-added products) production. There are limited literature critically reviewing the latest scientific development on the Bioelectrochemical (BES) based biogas upgrading technology, including CO2 reduction efficiency, methane (CH4) yields, reactor operating conditions, and electrode material tested in BES reactor. This review analyzes the reported performance and identifies the crucial parameters to be considered for future optimization, which is currently missing. In this review, the performances of BES approach of biogas upgrading under various operating settings in particular fed-batch, continuous mode in connection to the microbial dynamics and cathode materials have been thoroughly scrutinized and discussed. Additionally, other versatile application options associated with BES based biogas upgrading, such as resource recovery, are presented. The three-dimensional electrode materials have shown superior performance in supplying the electrons for the reduction of CO2 to CH4. Most of the studies on the biogas upgrading process conclude hydrogen (H2) mediated electron transfer mechanism in BES biogas upgrading.

Low organic carbon-to-nitrogen ratio and existing sulfate (SO42−) in industrial wastewater limited nitrogen removal. Coupling SO42- reduction with sulfide autotrophic denitrification provides a novel strategy. Herein, bioelectrochemical sulfate reduction was coupled with heterotrophic sulfate reduction to drive sulfide autotrophic denitrification. In this coupled system, total nitrogen (TN) removal efficiency was increased from ~25% to ~85% by inputting −45 mA electricity. With the help of supplying electrons to denitrification through SO42− reduction, coulomb efficiency was improved to 61.5%. Also, bioelectrochemical sulfate reduction could improve sulfur recovery and thus increase TN removal efficiency. Furthermore, through tuning turnover numbers of SO42−, high TN removal efficiency can be obtained at various concentrations of SO42−. Moreover, main functional bacteria in this system were identified. Finally, ~75% TN removal efficiency was achieved with real wastewater in this system. Overall, this work offered a new approach for efficient nitrogen removal from industrial wastewater containing SO42−. © 2021 American Institute of Chemical Engineers

Metal-free electrocatalysts have been widely used as cathodes for the reduction of hexavalent chromium [Cr(VI)] in microbial fuel cells (MFCs). The electrocatalytic activity of such system needs to be increased due to the low anodic potential provided by bacteria. In this study, graphite paper (GP) was treated by liquid nitrogen to form three-dimensional graphite foam (3DGF), improving the Cr(VI) reduction by 17% and the total Cr removal by 81% at 30 h in MFCs. X-ray absorption spectroscopy confirmed the Cr(VI) reduction product as Cr(OH)3. Through the spectroscopy characterizations, electrochemical measurements, and density functional theory calculations, the porous structures, edges, and O-doped defects on the 3DGF surface resulted in a higher electro-conducting rate and a lower mass transfer rate, which provide more active sites for the Cr(VI) reduction. Additionally, the scrolled graphene-like carbon nanosheets and porous structures on the 3DGF surface might limit the OH− diffusion and result in a high local pH, which accelerated the Cr(OH)3 formation. The results of this study are expected to provide a simple method to manipulate the carbon materials and insights into mechanisms of Cr(VI) reduction in MFCs by the 3DGF with in situ exfoliated edges and O-functionalized graphene. © 2020 Elsevier B.V.

Low organic carbon-to-nitrogen ratio and existing sulfate (SO42−) in industrial wastewater limited nitrogen removal. Coupling SO42- reduction with sulfide autotrophic denitrification provides a novel strategy. Herein, bioelectrochemical sulfate reduction was coupled with heterotrophic sulfate reduction to drive sulfide autotrophic denitrification. In this coupled system, total nitrogen (TN) removal efficiency was increased from ~25% to ~85% by inputting −45 mA electricity. With the help of supplying electrons to denitrification through SO42− reduction, coulomb efficiency was improved to 61.5%. Also, bioelectrochemical sulfate reduction could improve sulfur recovery and thus increase TN removal efficiency. Furthermore, through tuning turnover numbers of SO42−, high TN removal efficiency can be obtained at various concentrations of SO42−. Moreover, main functional bacteria in this system were identified. Finally, ~75% TN removal efficiency was achieved with real wastewater in this system. Overall, this work offered a new approach for efficient nitrogen removal from industrial wastewater containing SO42−. © 2021 American Institute of Chemical Engineers

Up to now, computational modeling of microbial electrosynthesis (MES) has been underexplored, but is necessary to achieve breakthrough understanding of the process-limiting steps. Here, a general framework for modeling microbial kinetics in a MES reactor is presented. A thermodynamic approach is used to link microbial metabolism to the electrochemical reduction of an intracellular mediator, allowing to predict cellular growth and current consumption. The model accounts for CO2 reduction to acetate, and further elongation to n-butyrate and n-caproate. Simulation results were compared with experimental data obtained from different sources and proved the model is able to successfully describe microbial kinetics (growth, chain elongation, and product inhibition) and reactor performance (current density, organics titer). The capacity of the model to simulate different system configurations is also shown. Model results suggest CO2 dissolved concentration might be limiting existing MES systems, and highlight the importance of the delivery method utilized to supply it. Simulation results also indicate that for biofilm-driven reactors, continuous mode significantly enhances microbial growth and might allow denser biofilms to be formed and higher current densities to be achieved., BT/Bioprocess Engineering

Low organic carbon-to-nitrogen ratio and existing sulfate (SO42−) in industrial wastewater limited nitrogen removal. Coupling SO42- reduction with sulfide autotrophic denitrification provides a novel strategy. Herein, bioelectrochemical sulfate reduction was coupled with heterotrophic sulfate reduction to drive sulfide autotrophic denitrification. In this coupled system, total nitrogen (TN) removal efficiency was increased from ~25% to ~85% by inputting −45 mA electricity. With the help of supplying electrons to denitrification through SO42− reduction, coulomb efficiency was improved to 61.5%. Also, bioelectrochemical sulfate reduction could improve sulfur recovery and thus increase TN removal efficiency. Furthermore, through tuning turnover numbers of SO42−, high TN removal efficiency can be obtained at various concentrations of SO42−. Moreover, main functional bacteria in this system were identified. Finally, ~75% TN removal efficiency was achieved with real wastewater in this system. Overall, this work offered a new approach for efficient nitrogen removal from industrial wastewater containing SO42−. © 2021 American Institute of Chemical Engineers

Metal-free electrocatalysts have been widely used as cathodes for the reduction of hexavalent chromium [Cr(VI)] in microbial fuel cells (MFCs). The electrocatalytic activity of such system needs to be increased due to the low anodic potential provided by bacteria. In this study, graphite paper (GP) was treated by liquid nitrogen to form three-dimensional graphite foam (3DGF), improving the Cr(VI) reduction by 17% and the total Cr removal by 81% at 30 h in MFCs. X-ray absorption spectroscopy confirmed the Cr(VI) reduction product as Cr(OH)3. Through the spectroscopy characterizations, electrochemical measurements, and density functional theory calculations, the porous structures, edges, and O-doped defects on the 3DGF surface resulted in a higher electro-conducting rate and a lower mass transfer rate, which provide more active sites for the Cr(VI) reduction. Additionally, the scrolled graphene-like carbon nanosheets and porous structures on the 3DGF surface might limit the OH− diffusion and result in a high local pH, which accelerated the Cr(OH)3 formation. The results of this study are expected to provide a simple method to manipulate the carbon materials and insights into mechanisms of Cr(VI) reduction in MFCs by the 3DGF with in situ exfoliated edges and O-functionalized graphene. © 2020 Elsevier B.V.

Up to now, computational modeling of microbial electrosynthesis (MES) has been underexplored, but is necessary to achieve breakthrough understanding of the process-limiting steps. Here, a general framework for modeling microbial kinetics in a MES reactor is presented. A thermodynamic approach is used to link microbial metabolism to the electrochemical reduction of an intracellular mediator, allowing to predict cellular growth and current consumption. The model accounts for CO2 reduction to acetate, and further elongation to n-butyrate and n-caproate. Simulation results were compared with experimental data obtained from different sources and proved the model is able to successfully describe microbial kinetics (growth, chain elongation, and product inhibition) and reactor performance (current density, organics titer). The capacity of the model to simulate different system configurations is also shown. Model results suggest CO2 dissolved concentration might be limiting existing MES systems, and highlight the importance of the delivery method utilized to supply it. Simulation results also indicate that for biofilm-driven reactors, continuous mode significantly enhances microbial growth and might allow denser biofilms to be formed and higher current densities to be achieved., BT/Bioprocess Engineering

Raw data of potentiostat, reactor checkup data, fatty acid concentrations over time and metal element concentrations.

Wastewater treatment has developed as a mature technology over time. However, conventional wastewater treatment is a very energy-intensive process. Bioelectrochemical system (BES) is an emerging technology that can treat wastewater and also recover resources such as energy in the form of electricity/hydrogen gas and nutrients such as nitrogen and phosphorus compounds. Microbial electrolysis cell (MEC) is a type of BES that, in the presence of an additional voltage, can treat wastewater and generate hydrogen gas. This is a promising approach for wastewater treatment and value-added product generation, though it may not be sustainable in the long run, as it relies on fossil fuels to provide that additional energy. Thus, it is important to explore alternative renewable resources that can provide energy to power MEC. Waste heat is one such resource that has not been researched extensively, particularly at the low-temperature spectrum. This was utilized as a renewable resource by converting waste heat to electricity using a device called thermoelectric generator (TEG). TEG converted simulated waste heat from an anaerobic digester to power an MEC. The feasibility of TEG to act as a power source for an MEC was investigated and its performance compared to the external power source. Various cold sources were analyzed to characterize TEG performance. To explore this integrated TEG-MEC system further, a hydraulic connection was added between the two systems. Wastewater was used as a cold source for TEG and it was recirculated to the anode of the MEC. This system showed improved performance with both systems mutually benefitting each other. The operational parameters were analyzed for the optimization of the system. The integrated system could generate hydrogen at a rate of 0.36 ± 0.05 m3 m-3 d-1 for synthetic domestic wastewater treatment. For the practical application, it is necessary to estimate the cost and narrow the focus on the functions of the system. Techno-economic an

Sufficient supply of oxygen is a major bottleneck in industrial biotechnological synthesis. One example is the heterologous production of rhamnolipids using Pseudomonas putida KT2440. Typically, the synthesis is accompanied by strong foam formation in the reactor vessel hampering the process. It is caused by the extensive bubbling needed to sustain the high respirative oxygen demand in the presence of the produced surfactants. One way to reduce the oxygen requirement is to enable the cells to use the anode of a bioelectrochemical system (BES) as an alternative sink for their metabolically derived electrons. We here used a P. putida KT2440 strain that interacts with the anode using mediated extracellular electron transfer via intrinsically produced phenazines, to perform heterologous rhamnolipid production under oxygen limitation. The strain P. putida RL-PCA successfully produced 30.4 ± 4.7 mg/L mono-rhamnolipids together with 11.2 ± 0.8 mg/L of phenazine-1-carboxylic acid (PCA) in 500-mL benchtop BES reactors and 30.5 ± 0.5 mg/L rhamnolipids accompanied by 25.7 ± 8.0 mg/L PCA in electrode containing standard 1-L bioreactors. Hence, this study marks a first proof of concept to produce glycolipid surfactants in oxygen-limited BES with an industrially relevant strain

The coexistence of different pollutants in groundwater is a common threat. Sustainable and resilient technologies are required for their treatment. The present study aims to evaluate microbial electrochemical technologies (METs) for treating groundwater contaminated with nitrate (NO3−) while containing arsenic (in form of arsenite (As(III)) as a co-contaminant. The treatment was based on the combination of nitrate reduction to dinitrogen gas and arsenite oxidation to arsenate (exhibiting less toxicity, solubility, and mobility), which can be removed more easily in further post-treatment. We operated a bioelectrochemical reactor at continuous-flow mode with synthetic contaminated groundwater (33 mg N-NO3− L−1 and 5 mg As(III) L−1) identifying the key operational conditions. Different hydraulic retention times (HRT) were evaluated, reaching a maximum nitrate reduction rate of 519 g N-NO3− m3 Net Cathodic Compartment d−1 at HRT of 2.3 h with a cathodic coulombic efficiency of around 100 %. Simultaneously, arsenic oxidation was complete at all HRT tested down to 1.6 h reaching an oxidation rate of up to 90 g As(III) m−3Net Reactor Volume d -1. Electrochemical and microbiological characterization of single granules suggested that arsenite at 5 mg L−1 did not have an inhibitory effect on a denitrifying biocathode mainly represented by Sideroxydans sp. Although the coexistence of abiotic and biotic arsenic oxidation pathways was shown to be likely, microbial arsenite oxidation linked to denitrification by Achromobacter sp. was the most probable pathway. This research paves the ground towards a real application for treating groundwater with widespread pollutants.

Mediator‐based extracellular electron transfer (EET) pathways can balance the redox metabolism of microbes. However, such electro‐biosynthesis processes are constrained by the unknown underlying EET mechanisms. In this paper, we studied Pseudomonas putida to systematically investigate its EET pathway to transition metal complexes (i.e. [Fe(CN) 6 ] 3‐/4‐ and [Co(bpy) 3 ] 3+/2+ ) under anaerobic conditions. Comparative proteomics showed the aerobic respiratory components were upregulated in a bioelectrochemical system without oxygen, suggesting their potential contribution to EET. Further tests found inhibiting cytochrome c oxidase activity by NaN 3 and NADH dehydrogenase by rotenone did not significantly change the current output. However, the EET pathway was completely blocked, while cytochrome c reductase activity was inhibited by antimycin A. Although it cannot be excluded that cytochrome c and the periplasmic subunit of cytochrome c oxidase donate electrons to the transition metal complexes, these results strongly demonstrate that cytochrome c reductase is a key complex for the EET pathway.

Biofilm anodes based on Geobacter enrichment in one‐chamber and two‐chamber reactors are qualitatively and quantitatively investigated. The methanogenic community of biofilms in both types of reactors consists exclusively of hydrogenotrophs, mainly the genus Methanobacterium . As qPCR demonstrates in one‐chamber reactors, the abundance of Geobacter and methanogens increases due to the presence of cathodically produced hydrogen. In two‐chamber reactors, the abundance of methanogens is decreased by 98% compared to one‐chamber reactors. Adding hydrogen gas to the anodic compartment of two‐chamber reactors recovers the abundance of methanogens and Geobacter . Ratios of methanogens/bacteria are confirmed using cofactor F 420 autofluorescence of methanogens. The impact of the reactor setup for developing primary microbial electrochemical technologies is discussed reasoning that two‐chamber reactors have to be generally favored. Yet, their use inheres a trade‐off when cultivating biofilm anodes, as the indicated syntrophic interactions between methanogens and Geobacter are reduced but pH decrease might influence microbial processes.

Bioelectrochemical systems (BES) can provide an energy efficient way to recover nutrients from wastewaters. However, the electron donors available in wastewater are often not sufficient to recover the total amount of nutrients. This work investigates hydrogen (H2) as an additional substrate for bioanodes. This hydrogen can be produced in the fermentation of complex organic waste or could be recycled from the cathode. Understanding how to influence the competition of electroactive microorganisms (EAM) with methanogens for H2 gas from different sources is key to successful application of H2 as additional electron donor in bioelectrochemical nutrient recovery. Ethanol (EtOH) was used as model compound for complex wastewaters since it is fermented into both acetate and H2. EtOH was efficiently converted into electricity (e−) by a syntrophic biofilm. Total recovered charge from 1 mM EtOH was 20% higher than for the same amount of acetate. This means that H2 from EtOH fermentation was converted by EAM into electricity. Low EtOH concentrations (1 mM) led to higher conversion efficiencies into electricity than higher concentrations (5 and 10 mM). Thermodynamic calculations show this correlates with a higher energy gain for electrogens compared to methanogens at low H2 concentrations. Cumulatively adding 1 mM EtOH without medium exchange (14 times in 14 days) resulted in stable conversion of H2 to e− (67%–77% e−) rather than methane. With H2 gas as electron donor, 68 ± 2% H2 was converted into e− with no carbon source added, and still 53 ± 5% to e− when 50 mM bicarbonate was provided. These results show that under the provided conditions, electrogens can outcompete methanogens for H2 as additional electron donor in MECs for nutrient recovery.

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 performing electromethanogenesis (EMG-BES) represent an emerging technology for Power-to-gas as well as wastewater treatment. Moreover, EMG-BES can be used as a high-capacity energy storage system to absorb surplus energy in the electrical grid. This paper presents a modelling approach, which is based on building an equivalent electric circuit of the EMG-BES, which can be used to emulate static and dynamic non-linear behaviour of EMG-BES for different input voltages, which is advantageous if compared to other existing models. This model is a suitable choice for future studies in the development of the electric converters for EMG-BES plants connected to the electrical grid. The proposed model consists of practical and commercial elements, including capacitors, resistors, voltage sources, and a diode. The modelling of non-linear behaviour is achieved by adding a diode to the model. Four simple tests were performed to determine the equivalent circuit parameters in a medium-scale EMG-BES prototype. This prototype was built by stacking 45 cells together and connecting them in parallel, and it was long-term operated and tested under different electric inputs to determine the model parameters. A comparative study was finally conducted as reported in this paper in order to validate the proposed model against experimental results and values collected with other models., The research leading to these results has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 712949 (TECNIOspring PLUS) and from the Agency for Business Competitiveness of the Government of Catalonia. Also, this work has been supported by the Spanish Ministry of Economy and Competitiveness under the projects RTI2018-100921-BC21. Any opinions, findings and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect those of the host institutions or funders. The authors wish to acknowledge the Leitat collaborators who took part in Power2Biomethane project, which was financially supported by the Spanish Ministry of Economy and Competitiveness (RTC-2016- 5024-3, 2016)., Peer Reviewed, Postprint (author's final draft)

Producción Científica, 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., Ministerio de Economía y Competitividad - FEDER (grant CTQ2015-68925-R), Ministerio de Economía y Competitividad FPU grant (FPU13/04014)

Producción Científica, 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., Ministerio de Economía y Competitividad - FEDER (grant CTQ2015-68925-R), Ministerio de Economía y Competitividad FPU grant (FPU13/04014)

Producción Científica, 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., Ministerio de Economía y Competitividad - FEDER (grant CTQ2015-68925-R), Ministerio de Economía y Competitividad FPU grant (FPU13/04014)

Producción Científica, 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., Ministerio de Economía y Competitividad - FEDER (grant CTQ2015-68925-R), Ministerio de Economía y Competitividad FPU grant (FPU13/04014)

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 chain 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 limitation. 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 phototrophs 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.

Industrial fermentation in aerobic processes is plagued by high costs due to gas transfer limitations and substrate oxidation to CO2. It has been a longstanding challenge to engineer an obligate aerobe organism, such as Pseudomonas putida, into an anaerobe to facilitate its industrial application. However, the progress in this field is limited, due to the poor understanding of the constraints restricting its anoxic phenotype. In this paper, we provide a methodological description of a novel cultivation technology for P. putida under anaerobic conditions, using the so-called microbial electrochemical technology within a bioelectrochemical system. By using an electrode as the terminal electron acceptor (mediated via redox chemicals), glucose catabolism could be activated without oxygen present. This (i) provides an anoxic-producing platform for sugar acid production at high yield and (ii) more importantly, enables systematic and quantitative characterizations of the phenotype of P. putida in the absence of molecular oxygen. This unique electrode-based cultivation approach offers a tool to understand and in turn engineer the anoxic phenotype of P. putida and possibly also other obligate aerobes.

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.

A Plant Microbial Fuel Cell (Plant-MFCs) has been studied both in the lab and in a field. So far, field studies were limited to a more conventional Plant-MFC design, which submerges the anode in the soil and places the cathode above the soil surface. However, for a large scale application a tubular Plant-MFC is considered more practical since it needs no topsoil excavation. In this study, 1 m length tubular design Plant-MFC was installed in triplicate in a paddy field located in West Kalimantan, Indonesia. The Plant-MFC reactors were operated for four growing seasons. The rice paddy was grown in a standard cultivation process without any additional treatment due to the reactor instalation. An online data acquisition using LoRa technology was developed to investigate the performance of the tubular Plant-MFC over the final whole rice paddy growing season. Overall, the four crop seasons, the Plant-MFC installation did not show a complete detrimental negative effect on rice paddy growth. Based on continuous data analysis during the fourth crop season, a continuous electricity generation was achieved during a wet period in the crop season. Electricity generation dynamics were observed before, during and after the wet periods that were explained by paddy field management. A maximum daily average density from the triplicate Plant-MFCs reached 9.6 mW/m2 plant growth area. In one crop season, 9.5-15 Wh/m2 electricity can be continuously generated at an average of 0.4 ± 0.1 mW per meter tube. The Plant-MFC also shows a potential to be used as a bio sensor, e.g., rain event indicator, during a dry period between the crop seasons.

Acetate as the dominant fraction of volatile fatty acids (VFAs) is an important intermediate in metabolic pathways of methanogenesis, which could reflect the stability status of anaerobic digestion (AD) process. Bioelectrochemical sensors for environmental or bioprocess monitoring have become increasingly attractive in recent years. Although it was more favorable, several challenges still need to be addressed for acetate detection, including large electrode spacing, low stability, biofouling at the cathode and low detection range. In this study, an innovative biosensor on the basis of a three-chamber microbial electrochemical system was proposed to monitor the acetate during the AD process. In such a system, acetate was first transferred from sample chamber through the anion exchange membrane (AEM) to anode due to the driven force of concentration difference and then oxidized by anodic biofilm as a substrate for the current generation. With such design, the influence of waste properties fluctuation in the cathodic reaction could be avoided. The response of current density to different acetate concentrations was investigated. The selectivity, the influence of the sample temperature and the external resistance were also evaluated. The correlation (R2 > 0.99) between the current densities and acetate concentrations (up to 160 mM) was established at specific reaction time (from 2 to 5 h). Current densities after 5 h reaction were improving about 20% when the sample temperature was high (e.g., 37 and 55°C). The detection range increased along with the decrease of external resistance. The acetate concentrations of AD effluents as determined by the biosensor where within 24.2% of the ones determined by gas chromatography. Nevertheless, the application of the biosensor for monitoring acetate in environmental samples could still be promising.

Background: A future bioeconomy relies on the development of technologies to convert waste into valuable compounds. We present here an attempt to design a biotechnological cascade for the conversion of vegetable waste into acetoin and electrical energy. Results: A vegetable waste dark fermentation effluent containing mainly acetate, butyrate and propionate was oxidized in a bioelectrochemical system. The achieved average current at a constant anode potential of 0 mV against standard hydrogen electrode was 177.5 ± 52.5 μA/cm2. During this step, acetate and butyrate were removed from the effluent while propionate was the major remaining component of the total organic carbon content comprising on average 75.6%. The key players with regard to carbon oxidation and electrode reduction were revealed using amplicon sequencing and metatranscriptomic analysis. Using nanofiltration, it was possible to concentrate the propionate in the effluent. The effluent was revealed to be a suitable medium for biotechnological production strains. As a proof of principle, the propionate in the effluent of the bioelectrochemical system was converted into the platform chemical acetoin with a carbon recovery of 86%. Conclusions: To the best of our knowledge this is the first report on a full biotechnological production chain leading from vegetable waste to the production of a single valuable platform chemical that integrates carbon elimination steps leading to the production of the valuable side product electrical energy., Baden-Württemberg, Ministerium für Umwelt, Klima und Energiewirtschaft, Bundesministerium für Bildung und Forschung

BTEX compounds (Benzene, Toluene, Ethylbenzene and Xylenes) are toxic hydrocarbons that can be found in groundwater due to accidental spills. Bioelectrochemical systems (BES) are an innovative technology to stimulate the anaerobic degradation of hydrocarbons. In this work, single chamber BESs were used to assess the degradation of a BTEX mixture at different applied voltages (0.8 V, 1.0 V, 1.2 V) between the electrodes. Hydrocarbon degradation was linked to current production and to sulfate reduction, at all the tested potentials. The highest current densities (about 200 mA/m2 with a maximum peak at 480 mA/m2) were observed when 0.8 V were applied. The application of an external voltage increased the removal of toluene, m-xylene and p-xylene. The highest removal rate constants at 0.8 V were: 0.4 ± 0.1 days−1, 0.34 ± 0.09 days−1 and 0.16 ± 0.02 days−1, respectively. At the end of the experiment, the microbial communities were characterized by high throughput sequencing of the 16S rRNA gene. Microorganisms belonging to the families Desulfobulbaceae, Desulfuromonadaceae and Geobacteraceae were enriched on the anodes suggesting that both direct electron transfer and sulfur cycling occurred. The cathodic communities were dominated by the family Desulfomicrobiaceae that may be involved in hydrogen production.

Effective wastewater treatment is needed to reduce the water pollution problem. However, massive energy is consumed in wastewater treatment, required to design an innovative system to reduce the energy consumption to solve the energy crisis. Integrated photobioelectrochemical system (IPB) is a powerful system to combine microbial fuel cells (MFCs) and algal bioreactor together. This system has good performance on the organic degradation, removal of nitrogen and phosphorus, and recover the bioenergy via electricity generation and algal harvesting. This dissertation is divided to twelve chapters, about various aspects of the working mechanisms and actual application of IPB. Chapter 1 generally introduces the working mechanisms of MFCs, algal bioreactor, and modeling. Chapter 2 demonstrates the improvement of cathode material to improve the structure and catalytic performance to improve the MFC performance. Chapter 3 describes the process to use microbial electrolysis cell (MEC) to generate biohythane for the energy recovery. Chapters 4 and 5 demonstrate the application of stable isotope probing to study Shewanella oneidensis MR-1 in the MFCs. Chapters 6 to 8 describe the application of models to optimize MFC and IPB system performance. Chapter 9 describes the strategy improvement for the algal harvesting in IPB. Chapter 10 describes the application of scale-up bioelectrochemical systems on the long-term wastewater treatment. Chapter 11 finally concludes the perspectives of IPBs in the wastewater treatment and energy recovery. This dissertation comprehensively introduces IPB systems in the energy recovery and sustainable wastewater treatment in the future.

BTEX compounds (Benzene, Toluene, Ethylbenzene and Xylenes) are toxic hydrocarbons that can be found in groundwater due to accidental spills. Bioelectrochemical systems (BES) are an innovative technology to stimulate the anaerobic degradation of hydrocarbons. In this work, single chamber BESs were used to assess the degradation of a BTEX mixture at different applied voltages (0.8 V, 1.0 V, 1.2 V) between the electrodes. Hydrocarbon degradation was linked to current production and to sulfate reduction, at all the tested potentials. The highest current densities (about 200 mA/m2 with a maximum peak at 480 mA/m2) were observed when 0.8 V were applied. The application of an external voltage increased the removal of toluene, m-xylene and p-xylene. The highest removal rate constants at 0.8 V were: 0.4 ± 0.1 days−1, 0.34 ± 0.09 days−1 and 0.16 ± 0.02 days−1, respectively. At the end of the experiment, the microbial communities were characterized by high throughput sequencing of the 16S rRNA gene. Microorganisms belonging to the families Desulfobulbaceae, Desulfuromonadaceae and Geobacteraceae were enriched on the anodes suggesting that both direct electron transfer and sulfur cycling occurred. The cathodic communities were dominated by the family Desulfomicrobiaceae that may be involved in hydrogen production.

Bioelectrochemical remediation of hydrocarbons is a technology that exploits the ability of specific microorganisms to use as electron acceptor an electrode, thus potentially lowering the operational costs related to classical bioremediation. Several well-characterized hydrocarbonoclastic strains might be electroactive, thus their biodegradation performances in Bioelectrochemical Systems should be studied. Cupriavidus metallidurans CH34 is a model metal-resistant strain whose capacity to degrade benzene aerobically has recently been described. In this study, toluene degradation under anaerobic conditions and the exoelectrogenic capacity of Cupriavidus metallidurans CH34 were determined. Strain CH34 was grown anaerobically with toluene as sole carbon source in sealed serum bottles and then inoculated in a Microbial Electrolysis Cell (MEC) to assess its exoelectrogenic capacity. It was demonstrated for the first time that strain CH34 is able to degrade toluene under nitrate-reducing conditions (up to 45 mgtoluene/L were removed within 17 days, corresponding to 73% of toluene amended). Nitrate consumption and cellular growth were observed during toluene removal. In the MEC, toluene degradation was linked to current production, showing current peaks after every toluene addition (maximum current density 48 mA/m2). Coulombic efficiency of the toluene biodegradation process increased with time, from 11% (first batch cycle), up to 77% (last batch cycle).

Sulfate reducing microorganisms are typically involved in hydrocarbon biodegradation in the sea sediment, with their metabolism resulting in the by-production of toxic sulfide. In this context, it is of utmost importance identifying the optimal value for anodic potential which ensures efficient toxic sulfide removal. Along this line, in this study the (bio)electrochemical removal of sulfide was tested at anodic potentials of −205 mV, +195 mV and +300 mV (vs Ag/AgCl), also in the presence of a pure culture of the sulfur-oxidizing bacterium Desulfobulbus propionicus. Current production, sulfide concentration and sulfate concentration were monitored over time. At the end of the experiment sulfur deposition on the electrodes and the microbial communities were characterized by SEM-EDS and by next generation sequencing of the 16S rRNA gene respectively. Results confirmed that current production was linked to sulfide removal and D. propionicus promoted back oxidation of deposited sulfur to sulfate. The highest electron recovery was observed at +195 mV vs Ag/AgCl, and the lowest sulfur deposition was obtained at −205 mV vs Ag/AgCl anode polarization.

Removal of nitrogen, mainly in form of ammonium (NH4+), in wastewater treatment plants (WWTPs) is a highly energy demanding process, mainly due to aeration. It causes costs of about half a million Euros per year in an average European WWTP. Alternative, more economical technologies for the removal of nitrogen compounds from wastewater are required. This study proves the complete anoxic conversion of ammonium (NH4+) to dinitrogen gas (N2) in continuously operated bioelectrochemical systems at the litre-scale. The removal rate is comparable to conventional WWTPs with 35 ± 10 g N m−3 d−1 with low accumulation of NO2−, NO3−, N2O. In contrast to classical aerobic nitrification, the energy consumption is considerable lower (1.16 ± 0.21 kWh kg−1 N, being more than 35 times less than for the conventional wastewater treatment). Biotic and abiotic control experiments confirmed that the anoxic nitrification was an electrochemical biological process mainly performed by Nitrosomonas with hydroxylamine as the main substrate (mid-point potential, Eox = +0.67 ± 0.08 V vs. SHE). This article proves the technical feasibility and reduction of costs for ammonium removal from wastewater, investigates the underlying mechanisms and discusses future engineering needs.

It was recently demonstrated that a bioelectrochemical system (BES) with a redox mediator allowed Pseudomonas putida to perform anoxic metabolism, converting sugar to sugar acids with high yield. However, the low productivity currently limits the application of this technology. To improve productivity the strain was optimized through improved expression of glucose dehydrogenase (GCD) and gluconate dehydrogenase (GAD). In addition, quantitative real-time RT-PCR analysis revealed the intrinsic self-regulation of GCD and GAD. Utilizing this self-regulation system, the single overexpression strain (GCD) gave an outstanding performance in the electron transfer rate and 2-ketogluconic acid (2KGA) productivity. The peak anodic current density, specific glucose uptake rate and 2KGA producing rate were 0.12 mA/cm2, 0.27 ± 0.02 mmol/gCDW/h and 0.25 ± 0.02 mmol/gCDW/h, which were 327%, 477% and 644% of the values of wild type P. putida KT2440, respectively. This work demonstrates that expression of periplasmic dehydrogenases involved in electron transfer can significantly improve productivity in the BES.

Microbial electrochemical technologies (METs) and especially microbial fuel cells (MFCs) are considered to allow energy harvest from the fuel wastewater during its treatment. However, the majority of studies use either “artificial” wastewater, amended wastewater, (i.e. with addition of chemicals), or pre-enriched microbial anodes. As these strategies might not be transferable to large scale, this study uses exclusively amendment free municipal wastewater as inoculum and sole carbon and energy source. It is shown that electrons can be harvested, at maximum current densities of 0.01 mA cm−2. In weekly cycles using batch systems (with 90 cm2 L−1 anode surface) only a minor fraction (<10%) of the available charge from COD-removal was turned into electricity by a highly diverse anodic microbial community. This performance is below those achieved by pre-enriched anodes or in amended wastewater studies, illustrating the need for more fundamental, application relevant studies.