Accelerated azo dye degradation and concurrent hydrogen production in the single-chamber photocatalytic microbial electrolysis cell

[Display omitted] •Microbial electrolysis cell with a TiO2 coated photocathode was developed.•Accelerated azo dye decolorization was achieved in the single-chamber PMEC.•Azo dye degradation intermediates could be further degraded in the PMEC.•The effect of methyl orange concentration on PMEC performance was evaluated.•Methyl orange degradation mechanism in the PMEC was revealed. The single-chamber microbial electrolysis cell constructed with a TiO2-coated photocathode, termed photocatalytic microbial electrolysis cell (PMEC), was developed to accelerate methyl orange (MO) degradation and concurrent hydrogen (H2) recovery under UV irradiation. Results showed that faster MO decolorization rates were achieved from the PMEC compared with those without UV irradiation or with open circuit. With increase of MO concentrations (acetate as co-substrate) from 50 to 300mg/L at an applied voltage of 0.8V, decolorization efficiencies decreased from 98% to 76% within 12h, and cyclic H2 production declined from 113 to 68mL. As the possible mechanism of MO degradation, bioelectrochemical reduction, co-metabolism reduction, and photocatalysis were involved; and degradation intermediates (mainly sulfanilic acid and N,N-dimethylaniline) were further degraded by OH generated from photocatalysis. This makes MO mineralization be possible in the single-chamber PMEC. Hence, the PMEC is a promising system for dyeing wastewater treatment and simultaneous H2 production.