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Coupling of a bioelectrochemical system (BES) into the upflow anaerobic sludge blanket (UASB) was developed for enhanced p -nitrophenol (PNP) removal in this study. Compared to the control UASB reactor, both PNP removal and the formation of its final reductive product p -aminophenol (PAP) were notably improved in the UASB–BES system. With the increase of current density from 0 to 4.71 A m −3 , the rates of PNP removal and PAP formation increased from 6.16 ± 0.11 and 4.21 ± 0.29 to 6.77 ± 0.00 and 6.11 ± 0.28 mol m −3 d −1 , respectively. More importantly, the required dosage of organic cosubstrate was significantly reduced in the UASB–BES system than that in the UASB reactor. Organic carbon flux analysis suggested that biogas production from organic cosubstrate was seriously suppressed while direct anaerobic reduction of PNP was not remarkably affected by current input in the UASB–BES system. This study demonstrated that the UASB–BES coupling system had a promising potential for the removal of nitrophenol-containing wastewaters especially without adequate organic cosubstrates inside. [ABSTRACT FROM AUTHOR]