Efficient and synergistic decolourization and nitrate removal using a single-chamber with a coupled biocathode-photoanode system.

•A single-chamber biocathode and photoanode coupled system was established.•TiO2/g-C3N4 nanosheet/graphene photoanode could efficiently absorb visible light.•Biocathode could improve the photocatalytic removal efficiency of methyl orange.•Synergistic decolorization of methyl orange and nitrate removal was verified.