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In this study, the engineering-oriented three-dimensional (3D) bioanode concept was applied, demonstrating that spiral-stairs-like/rolled carbon felt (SCF/RCF) configurations achieved good performances in air-cathode microbial fuel cells (ACMFCs). With the 3D anodes, ACMFCs generated significantly higher power densities of 1535 mW/m 3 (SCF) and 1800 mW/m 3 (RCF), compared with that of a traditional flat carbon felt anode (FCF, 315 mW/m 3 ). The coulombic efficiency of 15.39 % at SCF anode and 14.34 % at RCF anode also is higher than the 7.93 % at FCF anode. The 3D anode ACMFCs exhibited favorable removal of chemical oxygen demand (96 % of SCF and RCF) and total nitrogen (97 % of SCF, 99 % of RCF). Further results show that three-dimensional anode structures could enrich more electrode surface biomass and diversify the biofilm microbial communities for promoting bioelectroactivity, denitrification, and nitrification. These results demonstrate that three-dimensional anodes with active biofilm is a promising strategy for creating scalable MFCs-based wastewater treatment system., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Nitrate promotes anodic denitrification and fasts organic matter removal in microbial fuel cells (MFCs). However, it suffers from poor total nitrogen (TN) removal and current recovery. In this study, some novel electroactive nitrifying/denitrifying bacteria (ENDB) were introduced in a single chambered air-cathode MFC to investigate the performance of this device and the microbial community shift by adding nitrate. Results showed a similar disturbance in current output by adding nitrate during a short-term operation. However, a stable and reproducible current increase was achieved in the continuous experiment. A maximum current of 0.76 A m -3 and a maximum TN removal of >99 % were accomplished. The corresponding corrected coulombic efficiency was approximately 18 %. Under repeatable batches, a sharp decrease in chemical oxygen demand (COD) with feeding nitrate confirmed the temporary competition on electron donors through heterotrophic denitrification. The later current increase and nitrite detection occurring without metabolized COD could be considered evidence of electroactive anodic nitrification. The ENDB biofilm successfully coupled mixotrophic denitrification and electroactive anodic nitrification. It eventually promoted TN removal. In the process, genera Pseudoxanthomonas, Thauera, and Pseudomonas were enriched in the anodic ENDB biofilms. Cyclic voltammetry data confirmed the promotion of the electron transfer process by biofilms. The bacterial function predication revealed that the genes related to nitrogen removal and electron transfer were upregulated. Therefore, mixotrophic denitrification and electroactive anodic nitrification processes facilitated power recovery with the high efficiency of pollutant removal, finally ensuring water body security., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Wastewater treatment using microbial fuel cells (MFCs) is a potentially useful technology due to its low cost, environmental friendliness, and low sludge production. In this study, a single-chambered air cathode MFC (SCMFC) was developed and investigated regarding its performance and microbial community evolution following nitrate exposure. During long-term operation, diverse denitrifiers accumulated on the electrodes to form a denitrifying MFC (DNMFC) with stable activity for nitrate reduction. The DNMFC presented considerably higher electroactivity, stability, and denitrification rates than the SCMFC. Though energy recovery decreased in the DNMFC by partial organics utilized for heterotrophic denitrification, the electron transfer efficiency increased. Geobacter as the absolutely dominant genus in the SCMFC anode was eliminated and replaced by Azonexus and Pseudomonas in the DNMFC. Furthermore, the biomass of Pseudomonas (151.0 ng/μL) in the DNMFC cathode was five-fold higher than that in the SCMFC, although the bacterial community compositions were quite similar. The DNMFC with highly abundant Pseudomonas exhibited much better performance in terms of electrochemical activity and nitrate removal. The evolution process of functional bacteria from the SCMFC to the DNMFC comprehensively reveals the significant role of denitrifying electroactive bacteria in a bioelectrochemical system for nitrogen-containing wastewater treatment. [ABSTRACT FROM AUTHOR]

• The proportion of denitrifying bacteria significantly increased in the presence of nitrate. • COD removal by denitrification was only 3.7 g ± 0.3 g COD/g NO 3 −-N. • The optimal COD/N ratio in MFC-D was 5. • Anodic microbial communities were changed by substrate and configuration. At the anode of a microbial fuel cell (MFC), denitrifying bacteria can coexist with exoelectrogens, enabling an MFC to achieve simultaneous nitrate reduction and electricity generation by the oxidization of organic matter. In this study, an anodic denitrifying MFC (MFC-D) was constructed by incorporating heterotrophic denitrification. This was compared to a control, MFC without denitrification (MFC-C). The results showed that MFC-D exhibited higher chemical oxygen demand (COD) removal and power density than MFC-C. Microbial community analysis showed that the proportion of bacteria of the genus Geobacter significantly decreased from 72.8% in MFC-C to 29.4% in MFC-D, and that denitrifiers in MFC-D increased by 36.8% in comparison with those in MFC-C. The COD used for denitrification was calculated to be 3.7 ± 0.3 g COD/g NO 3 −-N when MFC-D was fed with different COD/N ratios. The optimal proportion of COD/N in the MFC-D system was 5:1, at which the highest coulombic efficiency (CE) of electricity generation and anodic denitrification were obtained. The maximum voltage output was not inhibited at a low COD/N, but the cycle duration was decreased with decreasing COD/N. Additionally, the bacterial community was more diverse when complex organics were used as an electron donor or in a single-chamber MFC, which subsequently altered the electricity recovery and denitrification performance. This study provides a new strategy to improve the performance of MFCs in actual applications by the addition of denitrifiers to the anodic biofilms. [ABSTRACT FROM AUTHOR]

Owing to membrane penetration, a novel route of nitrogen removal was proposed in a dual-chamber microbial fuel cell with a proton exchange membrane (PEM). The results showed that NH 4 +-N rapidly migrated across PEM with a mass transfer coefficient (K A) of 1.79 ± 0.51 × 10−4 cm s−1, 50% of which was oxidized to NO 3 −-N in the cathode chamber, then the remainder being eliminated by short-cut nitrification/denitrification. Meanwhile, NO 3 −-N went across the PEM again with a low K A of 5.50 ± 0.24 × 10−6 cm s−1, and was subsequently reduced via anodic denitrification. In the anode, the functional microorganisms were divided into exoelectrogenic bacteria (46.2%) and denitrifying bacteria (37.3%), while the dominated bacteria were mainly affiliated with nitrifying bacteria (19.6%) and aerobic denitrifying bacteria (52.9%) in the cathode. These findings provide a new insight into nitrogen removal during bioelectrochemical treatment of actual wastewater. [Display omitted] • All forms of nitrogen can migrate across PEM in dual-chamber MFCs. • NH 4 + is removed by complete nitrification and short nitrification/denitrification. • Simultaneous nitrification and denitrification occur aerobically in the cathode. • Anodic denitrification is the main route of nitrate reduction. [ABSTRACT FROM AUTHOR]