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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]

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]

Abstract Nitrate groundwater contamination is a worldwide concern. In this study, a novel 2-stage, sequential biocathodic denitrification system was tested to perform autotrophic denitrification of synthetic groundwater. The system was operated at different nitrate loading rates (66–301 gNO 3 −-N m−3 NCC d−1) at constant NO 3 −-N concentration (40 mgNO 3 −-N L−1), by varying hydraulic retention time (HRT) during different trials from about 14 to 3 h. The system was able to achieve almost complete removal of nitrate (>95%) and Total Nitrogen (TN) (>92%) at NO 3 − loading rates between 66 and 200 gNO 3 −-N m−3 NCC d−1. The first stage reactor achieved lower values of effluent nitrate and nitrite than WHO guidelines for drinking water quality (<11.3 mg NO 3 −-N L−1, and 0.9 mgNO 2 −-N L−1, respectively) up to a nitrate loading rate of 167 gNO 3 −-N m−3 NCC d−1; in these conditions the second stage acted mainly as polishing step. From a loading rate of 200 gNO 3 −-N m−3 NCC d−1 on, N 2 O accumulation was observed in the first stage reactor, afterwards successfully removed in the second stage. Maximum nitrate removal rate of the 2-step process was 259.83 gNO 3 −-N m−3 NCC at HRT of 3.19 h. The specific energy consumption of the system (SEC) decreased with decreasing HRT, both in terms of mass of nitrate removed (SEC N) and volume treated (SEC V). The described combination of two bioelectrochemical systems system hence proved to be effective for groundwater denitrification. Graphical abstract Unlabelled Image Highlights • A 2-stage controlled biocathodic denitrification (CBD) system was built and operated. • The system was run at increasing nitrate loading rates (and decreasing HRT). • The system showed increasing nitrate removal rates, up to 259.83 gNO 3 −-N m−3 NCC d−1. • The specific energy consumption (SEC) decreased at the decrease of HRT. [ABSTRACT FROM AUTHOR]

Nitrates have been detected in groundwater worldwide, and their presence can lead to serious groundwater use limitations, especially because of potential health problems. Amongst different options for their removal, bioelectrochemical systems (BESs) have achieved promising results; in particular, attention has raised on BES-driven autotrophic denitrification processes. In this work, the performance of a microbial electrolysis cell (MEC) for groundwater autotrophic denitrification, is assessed in different conditions of nitrate load, hydraulic retention time (HRT) and process configuration. The system obtained almost complete nitrate removal under all conditions, while nitrite accumulation was recorded at nitrate loads higher than 100 mgNO 3 − L − 1 . The MEC system achieved, in different tests, a maximum nitrate removal rate of 62.15 ± 3.04 gNO 3 − -N m − 3 d − 1 , while the highest TN removal rate observed was 35.37 ± 1.18 gTN m − 3 d − 1 . Characteristic of this process is a particularly low (in comparison with other reported works) energy consumption: 3.17·10 − 3 ± 2.26·10 − 3 kWh/gNO 3 — N removed and 7.52·10 − 2 ± 3.58·10 − 2 kWh m − 3 treated. The anolyte configuration in closed loop allowed the process to use less clean water, while guaranteeing identical performances as in other conventional configurations. [ABSTRACT FROM AUTHOR]

Excess sludge production from wastewater treatment plants has significantly increased, and sludge disposal has become a serious social and environmental problem. In this study, we constructed a microbial electrochemical hybrid system (MEHS) for simultaneous electricity generation, acid and alkali production, desalination, alkali pretreatment, and degradation of sludge. The alkaline solution generated in the MEHS was used for in situ sludge pretreatment. Owing to the efficiency in alkali pretreatment, a higher sludge degradation efficiency was obtained by the MEHS (Total chemical oxygen demand (TCOD) removal efficiency of 57.2%) than by the SMFC (TCOD removal efficiency of 51.7%). Moreover, the MEHS (0.165C) could recover more electricity from the sludge than a traditional single-chamber microbial fuel cell (SMFC, 0.133C). Additionally, the MEHS exhibited excellent performance in desalination (> 50%) and acid production. The system developed in this study provides a new solution for sludge degradation and multifunctional utilization. Unlabelled Image • MEHS utilized in-situ generated alkali for sludge treatment. • MEHS shows better sludge degradation performance than SMFC. • MEHS can collect more electricity than SMFC. • MEHS can achieve acid production and desalination. • This study provides a new way for sludge treatment and degradation in BES. [ABSTRACT FROM AUTHOR]

Microbial desalination cells (MDCs) have been experimentally proven as a versatile bioelectrochemical system (BES). They have the potential to alleviate environmental pollution, reduce water scarcity and save energy and operational costs. However, MDCs alone are inadequate to realise a complete wastewater and desalination treatment at a high-efficiency performance. The assembly of identical MDC units that hydraulically and electrically connected can improve the performance better than standalone MDCs. In the same manner, the coupling of MDCs with other BES or conventional water reclamation technology has also exhibits a promising performance. However, the scaling-up effort has been slowly progressing, leading to a lack of knowledge for guiding MDC technology into practicality. Many challenges remain unsolved and should be mitigated before MDCs can be fully implemented in real applications. Here, we aim to provide a comprehensive chronological-based review that covers technological limitations and mitigation strategies, which have been developed for standalone MDCs. We extend our discussion on how assembled, coupled and scaled-up MDCs have improved in comparison with standalone and lab-scale MDC systems. This review also outlines the prevailing challenges and potential mitigation strategies for scaling-up based on large-scale specifications and evaluates the prospects of selected MDC systems to be integrated with conventional anaerobic digestion (AD) and reverse osmosis (RO). This review offers several recommendations to promote up-scaling studies guided by the pilot scale BES and existing water reclamation technologies. Unlabelled Image • Recent standalone, assembled, coupled, and scaled-up MDCs are reviewed and discussed. • The performance of assembled, coupled, and scaled-up MDCs are comparatively analysed. • Prevailing challenges and potential solutions for scaling-up MDCs are discussed. • Integration of MDCs with conventional technologies as prospects are proposed. • Recommendations for future MDCs scaling-up studies are provided. [ABSTRACT FROM AUTHOR]

Ammonium removal in wastewater treatment plants requires a large number of energy input, such as aeration and the addition of organics. Alternative, more economical technologies for nitrogen removal from wastewater are required. This study comprehensively investigated the feasible of microbial electricity coupled with Fe(III) reduction promoting the anaerobic ammonium removal. It was found that electrostimulation coupled with Fe(III) reduction (bioelectrochemical systems-Fe(III) (BES-Fe(III)) reactor) enhanced the anaerobic ammonium removal by 50.38% and 38.8% compared with the BES reactor and Fe(III) reactor, respectively. The ammonium removal rate reached the highest value of 80.62 ± 0.26 g N m−3·d−1 in the Fe(III)-BES reactor comparable to conventional wastewater treatment plants (WWWTPs). The improvement of ammonium removal might be the synergistic effect of BES and Feammox process on reaction process and microorganisms. Firstly, the addition of Fe 2 O 3 could improve the electrochemical characteristics by enriching iron-reducing bacterial (FeRB). Secondly, the improved ammonium removal could be due to nitrite generated from Feammox process driving the anodic ammonium oxidation. Additionally, the ammonium removal improvement might be the effect of BES on the Fe2+ leaching so as to accelerate the Fe (II)/Fe(III) cycle. In agreement, higher abundance of FeRB and iron-oxidizing bacteria was detected in the Fe(III)-BES reactor. This study provides a lower energy consumption and operational cost technology compared with the conventional partial nitrification/denitrification, which was more than 800 times less than for the conventional wastewater treatment. Unlabelled Image • Electrostimulation coupled with Feammox could improve anaerobic ammonium removal. • The ammonium removal loading reached the highest value of 80.62 ± 0.26 g N m-3·d-1 in the Fe(III)-BES reactor. • More electroactive community was involved in the Fe(III)-BES reactor during anaerobic ammonium removal process. • 800 times less energy consumption for ammonium removal than conventional treatment. [ABSTRACT FROM AUTHOR]

Bioelectrochemical systems (BESs) have demonstrated great promise in augmented biodegradation of petroleum hydrocarbons in water-saturated soils. However, bioremediation of unsaturated soil in vadose zone has been a challenge due to poor mass transfer and low conductivity. This study proposed a moisture retention layer (2 cm thickness) around the BES anodes to enhance soil remediation under unsaturated conditions. The active soil BESs (closed circuit) includes two reactors with anodic moisture-retaining layers of soil-polyacrylamide hydrogel (SHB) and graphite granule-polyacrylamide hydrogel (GHB) mixtures, and another reactor filled with only soil (SB) without moisture-retaining layer. An open circuit SB was served as a control to simulate natural attenuation. This study demonstrated for the first time that moisture retention layers around the BES anodes could significantly extend and enhance hydrocarbon degradation in vadose zone soil. Results showed that SHB reactor could maintain 43–100% longer duration for electricity generation than other reactors. Correspondingly, SHB showed the best removal (average 21–37%) of total petroleum hydrocarbon (TPH) in spatial distribution, which was ~91% and ~164% higher than other BESs and control, respectively. This study demonstrated that by using low-cost and environmentally friendly hydrogel, BESs could become a viable remediation method for vadose zone soil. Unlabelled Image • Anodic moisture retention enhanced bioelectrochemical remediation of unsaturated soil. • Low-cost and environmentally friendly hydrogel used for moisture retention • Moisture retention maintains 43–100% longer duration for electricity generation. • Total petroleum hydrocarbon removal was enhanced by 91–164%. [ABSTRACT FROM AUTHOR]