Improved azo dye decolorization in an advanced integrated system of bioelectrochemical module with surrounding electrode deployment and anaerobic sludge reactor

•Integrated system with BES module and ASR was developed for azo dye treatment.•It improved decolorization and electrochemical performance without co-substrate.•COD can be removed after cleavage of the azo bond, different from biocathode BES.•Cooperation of cathode, biofilm, and sludge played an important role in treatment.

A new integrated system, embedding a modular bioelectrochemical system (BES) with surrounding electrode deployment into an anaerobic sludge reactor (ASR), was developed to improve azo dye decolorization. Results demonstrated that the AO7 decolorization and COD removal can be improved without co-substrate in such system. The kinetic rate of decolorization (0.54 h−1) in integrated system was 1.4-fold and 54.0-fold higher than that in biocathode BES (0.39 h−1) and ASR (0.01 h−1), respectively. COD can be removed after cleavage of azo bond, different from biocathode BES. The combined advantages of this integrated system were achieved by the cooperation of biocathode in modular BES and sludge in ASR. Biocathode was a predominant factor in AO7 decolorization, and anaerobic sludge contributed negligibly to AO7 reduction decolorization but mostly in the COD removal. These results demonstrated the great potential of integrating a BES module with anaerobic treatment process for azo dye treatment.