Microbial electrolysis cells (MECs) with autotrophic biocathode are a promising technology for removal of pollutants in wastewater. The aim of this study was to investigate the effect of initial acidity of wastewater on performance of sulfate-reducing biocathodes. MECs with biocathodes were operated with initial pH values of catholyte ranged from 3.0 to 7.0. The optimum initial pH value was 6.0 with a maximum sulfate reductive rate and biomass of 57 mg L-1 d(-1) and 2.1 +/- 0.4 mg g(-1), respectively. With initial pH 7.0, the pH value of catholyte increased to 9.8 +/- 0.2 after an operation cycle, which resulted in low performance of the biocathode. A considerable sulfate reductive rate of 31 +/- 0.85 mg L-1 d(-1) was achieved with initial pH 3.0. Desulfovibrio sp. grew dominantly with abundance of 46%-66% in the cathode biofilm with initial pH values from 3.0 to 6.0 and contributed to the sulfate reduction. Clostridium and Parapedobacter also had high abundance in pH 6.0 cathode, indicated that interspecies electron transfer between electrochemical active and sulfate-reducing bacteria could play an important role in sulfate removal. The results suggest that acidity of catholyte is an important factor to be considered to utilize autotrophic biocathode MECs for wastewater treatment.(C) 2017 Elsevier Ltd. All rights reserved.