•Cathodes were modified by peptide nanotube containing redox mediators (PNT/RMs/CP).•PNT/RMs modification improved electrocatalytic activity of cathode electrodes.•The MFCs using PNT/RMs/CP cathodes promoted the Orange II decolorization rate.•The MFCs with PNT/RMs/CP cathodes generated enhanced power densities than control.To enhance azo dye reduction in cathode of microbial fuel cells (MFCs) and power generation, a novel cathode modification method was developed on carbon paper (CP) through immobilization of redox mediators (RMs) with self-assembled peptide nanotubes (PNTs) as the carrier. Results showed that the optimum peptide concentration for PNT self-assembly on electrode and Orange II decolorization in MFCs was 2 mg mL−1. The PNT/RMs/CP electrodes exhibited higher electrocatalytic activities than PNT or RM solely modified electrodes and raw carbon paper electrode. MFCs loaded with the riboflavin (RF)/PNT modified cathode (PNT/RF/CP) or anthraquinone-2, 6-disulfonate (AQDS)/PNT modified cathode (PNT/AQDS/CP) showed an enhanced decolorization rate to Orange II compared to that with the control electrode, with the reduction kinetic constants increased by 1.3 and 1.2 folds, respectively. Furthermore, the MFCs with the PNT/AQDS/CP cathode and PNT/RF/CP cathode generated a higher maximum power density of 55.5 mW m−2 and 72.6 mW m−2, respectively, compared to the control (15.5 mW m−2). The PNT/RMs modification could reduce cathode total internal resistance and accelerate electron transfer from electrodes to dyes, which may result in the enhanced performance of MFCs.Download high-res image (213KB)Download full-size image

•Vanillin could inhibit mixed-culture biofilm formation by a non-biocide mechanism.•Vanillin could not disassemble pre-established biofilms.•Vanillin caused EPS reduction for both the suspended bacteria and attached biofilm.•Vanillin coupled with proteinase K or DNase I enhanced anti-biofilm efficiency.Biofilm control and prevention based on traditional biocides and antibiotics through a killing mechanism may increase the risk of evolved resistance. This study explored a novel biofilm control strategy based on a quorum sensing inhibitor vanillin and extracellular polymeric substances (EPS) enzymatic disruptors through a non-microbicidal mechanism. The inhibitory effects of vanillin on biofilm formation were explored at different vanillin concentrations and on different supporting substrates. Results showed that vanillin was effective in inhibiting biofilm formation by mixed-culture both under static state and hydrodynamic conditions, and vanillin alone at the dose of 0.30 mg/mL led to a biofilm reduction of 52%. Vanillin could not disassemble pre-established biofilms. Vanillin in combination with EPS enzyme disruptor proteinase K or DNase I was more efficient in biofilm inhibition than their single treatment. Vanillin coupled with proteinase K or DNase I increased biofilm inhibition rate by 76.31% and 60.62% compared to vanillin single treatment. Overall, vanillin and its combination with enzyme disruptors provide a new strategy for biofilms control by multi-species wastewater culture through a non-microbicidal mechanism.

•A composite anti-biofouling coating (TNTs-Ag-PLGA/norspermidine) was fabricated.•PLGA/norspermidine to the top of TNTs greatly retarded silver ion release.•PLGA/norspermidine to the top of TNTs also extended antimicrobial validity.•TNTs-Ag-PLGA/norspermidine coating inhibited biofilm formation by about 48.42%.•The inhibition was due to the combination of a killing and a non-killing mechanism.Detrimental biofilms in water and wastewater treatment systems have become a great concern. Norspermidine is a potent inhibitor for biofilm growth through a non-biocidal mechanism. Nanosilver is a widely used and efficient inorganic biocide. In this study, using a titania nanotube (TNTs) array as the loading carrier of nanosilver and a norspermidine-incorporated polymer poly(lactic-co-glycolic acid) (PLGA) as the top cap of TNTs, a composite anti-biofilm coating (TNTs-Ag-PLGA/norspermidine) with multiple effects was fabricated, and its anti-biofilm efficiency against biofilms by wastewater mixed culture was investigated. Results showed that the addition of a PLGA/norspermidine cap to the top of TNTs greatly retarded silver ion release and extended antimicrobial validity. The TNTs-Ag-PLGA/norspermidine coating showed a biofilm inhibition of 48.42 ± 2.71% after 16 days of leaching, much higher than that without the PLGA/norspermidine cap (4.10 ± 3.32%). Confocal laser scanning microscopy (CLSM) showed that the biofilm attached to the surface of the TNTs-Ag-PLGA/norspermidine showed a much lower exopolysaccharide/exoprotein ratio (0.44) compared to the control (0.94), indicating that norspermidine incorporated into the PLGA layer could act on biofilm bacteria by reducing exopolysaccharides and destroying the EPS matrix. The TNTs-Ag-PLGA/norspermidine coating inhibited biofilm formation both through a killing mechanism by silver and a non-killing mechanism of norspermidine biofilm disassembly. The combination of nanosilver-loaded TNTs and a norspermidine-incorporated PLGA cap provides a novel and effective strategy to mitigate biofilm formation by wastewater mixed cultures and has potential application in water and wastewater treatment systems.

•Anode electrode was modified using peptide nanotube containing riboflavin (RF/PNT).•RF/PNT modification improved electrochemical properties of anode electrode.•PNT as the carrier retained RF on electrode more effectively and persistently.•Anode modification with RF/PNT increased power density in MFCs by 2.9 folds.A novel anode modification method was established based on immobilizing a redox mediator riboflavin (RF) onto carbon cloth using bio-inspired and self-assembled peptide nanotubes (PNTs). The cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in Fe(CN)63−/4− solution showed that the RF/PNT electrode demonstrated a higher electrocatalytic activity and faradic charge capacity than the untreated electrode. The chronamperometry analysis showed that RF/PNT electrode in the presence of Shewanella oneidensis MR-1 generated a current density of 28.9 μA cm−2, increased by 263.3% compared to the bare electrode. The MFC operated with the RF/PNT anode generated a maximum power density of 767 mW m−2, which was 2.9 times larger than control. Besides, RF/PNT modification significantly reduced anode total internal resistance of MFCs. The self-organized PNTs could increase specific surface and electrical conductivity of anodes and provide a good carrier for redox mediator immobilization, which may contribute to the improved performance of MFCs.

•Pt-Pd alloy catalyst was fabricated on carbon paper via electro-deposition.•MFCs with Pt-Pd cathode of 15 deposition cycles generated a maximum power density.•Graphene decoration did not improve ORR activity of the Pt-Pd electrode.•CNT as the supporting material enhanced ORR activity of the Pt-Pd electrode.•CNT-Pt-Pd cathode demonstrates the potential of replacing Pt catalyst in MFCs.In this study, Pt-Pd alloy catalyst was fabricated on carbon papers via electro-deposition as an alternative catalyst for oxygen reduction in air-cathode Microbial Fuel Cells (MFCs). Effects of electro-deposition cycles and supporting materials (graphene and carbon nanotubes (CNTs)) on oxygen reduction reaction (ORR) activity of the Pt-Pd electrode and power generation in MFCs were investigated. The structural and electrochemical properties of the Pt-Pd catalyst were characterized by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). Results showed that the Pt-Pd electrode showed a good ORR activity. A MFC with a Pt-Pd cathode of 15 deposition cycles produced a maximum power density of 1274 mWm−2, comparable to that with a conventional Pt/C cathode (0.5 mg Pt cm−2). CNT as the supporting material further increased ORR activity of the Pt-Pd electrode and power generation capacity in MFCs, while graphene as the supporting material did not produce positive effects. XRD results confirmed the presence of Pt/Pd elements on the electrode. SEM results showed that decoration using CNT reduced Pt-Pd particle size and promoted them even dispersion on the carbon paper. The Pt-Pd electrode attained a comparable performance to the Pt/C electrode when controlling an optimum deposition cycles and using CNT as the supporting materials, which demonstrates the potential of replacing Pt as an oxygen reduction catalyst in MFCs due to high oxygen reduction activity and relatively low cost.

Aerobic granular sludge degrading recalcitrant compounds are generally hard to be cultivated. This study investigated the feasibility of cultivating 2,4-dichlorophenoxyacetic acid (2,4-d) degrading aerobic granules using half-matured sludge granules pre-grown on glucose as the seeds and bioaugmentation with a 2,4-d degrading strain Achromobacter sp. QXH. Results showed that bioaugmentation promoted the steady transformation of glucose-grown granules to 2,4-d degrading sludge granules and fast establishment of 2,4-d degradation ability. The 2,4-d degradation rate of the bioaugmented granules was enhanced by 36–62 % compared to the control at 2,4-d concentrations of 144–565 mg/L on Day 18. The inoculated strain was incorporated into the half-matured granules successfully and survived till the end of operation (220 days). Sludge granules at a mean size of 420 µm and capable of utilizing 500 mg/L 2,4-d as the sole carbon source were finally obtained. Sludge microbial community shifted slightly during the whole operation and the dominant bacteria species belonged to Proteobacteria.

Cassava alcohol wastewater produced from the bioethanol production industry is carbohydrate-rich wastewater with large quantities of insoluble organic compounds. Microbial fuel cells (MFCs) were used for electricity recovery and pollutants removal from this wastewater. Different pretreatment methods (solid–liquid separation, ultrasonication, pre-fermentation) and anode-aeration modes were explored in MFCs aimed to enhance the efficiency of power generation and pollutants removal. Pre-fermentation was found to be the most effective pretreatment method. A maximum power density of 437.13 ± 15.6 mW/m2 and TCOD removal of 62.5 ± 3.5 % were achieved using the pre-fermented wastewater, 150 and 20 % higher than the un-pretreated control. Aeration in anode chamber could promote the hydrolysis of organic matter and production of VFAs in the raw wastewater, and increase TCOD removal and power density. Pre-fermentation coupled with halfway anode aeration may be a feasible strategy to enhance power generation and pollutants removal from the cassava wastewater in MFCs.