•High current density achieved on modified Ti electrode heated in a H2 atmosphere.•Electrode specific surface area increased greatly after electrochemical oxidation.•Highest electrode/biofilm electron transfer rate achieved for H2 treated electrode.We investigated the effects of the heat-treatment atmosphere on the current generation of Ti electrodes in microbial fuel cells (MFCs). The maximum current density was achieved for TiO2 nanotube array electrodes heated in H2 (TNA-H2) (22.69 ± 0.18 A m−2). Physical analysis of the Ti electrode surfaces revealed that the specific surface area increased after electrochemical anodization. The crystallinities of the TiO2 nanotube array electrodes heated in H2 (81.66%), CH4 (74.48%), N2 (59.67%), and O2 (44.82%) showed a significant positive correlation with the corresponding current densities (P < 0.05, R2 = 0.9469). In addition, the highest electron transfer rate constant was achieved for TNA-H2 (2.38 s−1). The large specific surface area, good chemical stability, high electron transfer rate, and good biocompatibility of TNA-H2 suggest its great potential for application as an anode system in MFCs.

•Sludge pyrolysis gas modification used to improve titanium alloy hydrophilicity.•Modified titanium electrodes accelerated biofilm formation.•Modified electrode current density was 316-fold higher than that of bare electrode.•New method proposed to dispose of sewage sludge.Titanium is under consideration as a potential stable bio-anode because of its high conductivity, suitable mechanical properties, and electrochemical inertness in the operating potential window of bio-electrochemical systems; however, its application is limited by its poor electron-transfer capacity with electroactive bacteria and weak ability to form biofilms on its hydrophobic surface. This study reports an effective and low-cost way to convert a hydrophobic titanium alloy surface into a hydrophilic surface that can be used as a bio-electrode with higher electron-transfer rates. Pyrolytic gas of sewage sludge is used to modify the titanium alloy. The current generation, anodic biofilm formation surface, and hydrophobicity are systematically investigated by comparing bare electrodes with three modified electrodes. Maximum current density (15.80 A/m2), achieved using a modified electrode, is 316-fold higher than that of the bare titanium alloy electrode (0.05 A/m2) and that achieved by titanium alloy electrodes modified by other methods (12.70 A/m2). The pyrolytic gas-modified titanium alloy electrode can be used as a high-performance and scalable bio-anode for bio-electrochemical systems because of its high electron-transfer rates, hydrophilic nature, and ability to achieve high current density.

•Comparison of iron coagulants for treatment of leachate membrane concentrates.•Effect of anions (Cl−, SO42−, and NO3−) on Fe(III) coagulation.•Response surface method.•>80% COD and TOC removals at relatively low FeCl3 coagulant dose.Leachate membrane concentrates containing high concentrations of organics and trace toxic compounds pose a major threat to the environment, and their treatment is an urgent issue. In this work, various coagulants were used to treat leachate membrane concentrates. Appropriate pH values for treatments with FeCl2, FeSO4, polyaluminum chloride, and FeCl3 were 3, 5, 5, and 4, respectively. FeCl3 achieved the highest total organic carbon (TOC) removal efficiency. The effect of the various anions in ferric coagulants [FeCl3, Fe2(SO4)3, and Fe(NO3)3] on the TOC removal efficiency was negligible. The main organics remaining in the leachate membrane concentrates after coagulation were humic and fulvic acids. The conditions for coagulation with FeCl3 were optimized using the response surface method (RSM). The highest TOC, chemical oxygen demand (COD), and chromaticity reduction efficiencies, 81%, 82%, and 97%, respectively, were achieved at pH 4 using FeCl3 (5 g L−1) and polyacrylamide (PAM; 0.07 g L−1). The COD of leachate membrane concentrates was reduced from 4000 to 718 mg L−1. The mole ratio of removed COD and Fe(III) (2.4 mol) at 5 g L−1 FeCl3 (pH 4, PAM 0.07 g L−1) was lower than that (3.8 mol) at 3 g L−1 FeCl3 (pH 4, PAM 0.07 g L−1); based on the cost and COD removal efficiency, the latter conditions were the best choice. Our work provides guidelines for the treatment of leachate membrane concentrates in engineering.

This paper introduces a high-performance photo-microbial desalination cell (PMDC) based on photo-electrochemical interactions. The anode of the cell was successfully modified with nanostructured α-Fe2O3. The maximum current density of the PMDC during operation was 8.8 A m−2 at an initial salt concentration of 20 g L−1, which was twice that of the unmodified microbial desalination cell. The results of electrochemical impedance spectroscopy and cyclic voltammetry indicated the current increase of PMDC was mainly contributed by the high electron transfer rate at electrode/biofilm interface. The salt concentration of the effluent from the middle chamber was below ca. 1.4 mg L−1 and the salt removal performance of the PMDC was always higher than 96%. The calculated number of harvested electrons agreed well with NaCl removal. In conclusion, the present PMDC effectively offers simultaneous electricity generation and desalination.

Anaerobic digestion is an alternative technology for the pretreatment of waste activated sludge (WAS) before final disposal. Hydrolysis is the rate-limiting step in this process; therefore, pretreatment of WAS to allow for high-efficiency anaerobic digestion is beneficial. In the present work, an electrochemical system characterized by a gas diffusion cathode (GDC) was established to facilitate WAS pretreatment. This GDC was composed of a carbon black diffusion layer and a Ni/NiOx catalytic layer. H2O2, an essential component of the pretreatment, was evolved on the electrode surface at a rate of 27.3 mg cm–2 day–1. Upon varying the potential of the GDC from 0 to −1.0 V (versus Ag/AgCl), the soluble chemical oxygen demand (SCOD) and the protein and carbohydrate concentrations increased from 134 ± 6, 38 ± 6, and 20 ± 3 mg/L to 3617 ± 65, 1436 ± 121, and 470 ± 64 mg/L, respectively, over 8 h. The ratio of SCOD to the total chemical oxygen demand (TCOD) was 48 ± 1.3%. The total methane output of the GDC pretreated sludge at the end of 10 days was close to 234 mL/g TCOD, which was 33.8% greater than that of the control sludge. The Ni/NiOx-modified GDC also exhibited excellent stability performance. The results of this work demonstrate the pivotal role of the combination of H2O2 and alkali generated by the GDC in the enhanced pretreatment of WAS.

•An bioelectrochemically assisted microbial system was developed for treating 2-fluoroaniline.•The system significantly increased the removal and mineralization of 2-fluoroaniline.•Suitably weak current stimulated specific catechol dioxygenase activity.•Suitably weak current have the directional effects on specific microbial communities.Bioelectrochemical auxiliary for treating wastewater has gained extensive attention and it is a promising technology for wastes especially refractory wastes treatment. In this study a bioelectrochemically assisted microbial system (BEAMS) was developed for 2-fluoroaniline removal in organic fluorine wastewater. The effects of electricity on 2-fluoroaniline removal performance, metabolic behavior as well as bacterial community structures were investigated. The BEAMS showed excellent performance in removing 2-fluoroaniline, the maximum biological defluorination and mineralization rates achieved being 116.07% and 43.06% higher, respectively, than the rates in the biological control. Suitable current intensity had positive effects on biological metabolism and the key enzyme for 2-fluoroaniline degrading catechol dioxygenase was stimulated, which increased the ability of the system to mineralize 2-fluoroaniline. Moreover, the current intensity had directional effects on specific microbial communities for 2-fluoroaniline degradation. These results give us a more detailed understanding of the effects of electricity on the treatment of 2-fluoroaniline contaminated wastewater and the system offers promise as a way of treating persistent organic pollutants.

•Influence of current on biofilm formation in BES was investigated.•Biofilm formation activity supplying with organic differed with inorganic.•Discussed the influence of signaling molecule and EPS on biofilm formation.Bioelectrochemical systems (BESs) are a promising technology for generating energy while treating wastewater. By utilizing the electron transfer between the anode and cathode, nitrate can be effectively removed from the BES. Our previous studies show that the carbon source and C/N ratio influences nitrate removal performance. The study presented here investigates how biofilm formation, nitrate removal and signaling molecule release are related in the BESs fed with glucose, starch and HCO3−. The results indicate that increasing the current can benefit signaling molecule (DSF) release and extracellular polymeric substances (EPS) excretion, which improves biofilm formation. However, when the current exceeds the optimum value, the influence becomes adverse. Nitrate removal was also improved with increased current, though different carbon sources showed different trends. The highest nitrate removal efficiency of 1.23 ± 0.27, 1.38 ± 0.09, 1.80 ± 0.02 mmol L−1 d−1 for the BESs fed with glucose, starch and HCO3− were achieved, respectively. This paper studied the bacterial habits in a BES to better acquire and regulate the reaction process, with the aim of achieving good pollutant removal performance.

•We describe a novel composite modification of a stainless steel substrate.•The relative merits of five modifications on SS were evaluated systematically.•A high current density (16 A m−2) was achieved on a composite anode.In this paper, we first systematically investigate the current output performance of stainless steel electrodes (SS) modified by carbon coating (CC), polyaniline coating (PANI), neutral red grafting (NR), surface hydrophilization (SDBS), and heat treatment (HEAT). The maximum current density of 13.0 A m−2 is obtained on CC electrode (3.0 A m−2 of the untreated anode). Such high performance should be attributed to its large effective surface area, which is 2.3 times that of the unmodified electrode. Compared with SS electrode, about 3-fold increase in current output is achieved with PANI. Functionalization with hydrophilic group and electron medium result in the current output rising to 1.5–2 fold, through enhancing bioadhesive and electron transport rate, respectively. CC modification is the best choice of single modification for SS electrode in this study. However, this modification is not perfect because of its poor hydrophilicity. So CC electrode is modified by SDBS for further enhancing the current output to 16 A m−2. These results could provide guidance for the choice of suitable single modification on SS electrodes and a new method for the perfection of electrode performance through composite modification.

•The secretion of signal molecules in AnGS was affected by the culture medium’s pH.•AnGS diameter decreased in acid medium because of decreasing AI-2 and increasing DSF.•Neutral and weak media had a positive effect on AnGS due to high AI-2 and low DSF.The effects of several signal molecules on anaerobic granular sludge at different pHs were investigated. The results showed that pH affected the synthesis and maintaining of the signal molecules. In an alkaline medium (pH 9), sludge bacteria secreted less acyl-homoserine lactone (AHLs), which had an opposite variation with the synthesis of extracellular polymeric substances (EPS), and its effect did not present. Additionally, the synthesis of EPS (mainly loosely bound layer) was majorly promoted by auto-inducers-2 (AI-2), but a lower negative role of diffusible signal factor (DSF). In neutral and weak alkaline media, the combining regulation of increasing AI-2 content and decreasing DSF content enhanced relative hydrophobicity (RH) and granular strength in granular sludge, which made granules to have a greater diameter and a more glossy granular shape. Whereas, in acid medium, the decreasing AI-2 content and increasing DSF content made a decrease in RH and granular strength, resulting in the degeneration of anaerobic granular sludge.