Enhanced chromium recovery and simultaneous sludge degradation in a novel bioelectrochemical system assembled with bio/abio-cathodes

Abstract A novel five-chamber bioelectrochemical system (BES) consisting of bio/abio-cathodes and a precipitation chamber was constructed for enhanced chromium recovery with simultaneous sludge degradation. The results revealed that the BES obtained a Cr(VI) reduction efficiency of 99.93±0.63% and collected 82.2±4.2 mg precipitate/cycle on the bottom of the precipitation chamber instead of very little on the surface of the abio-cathode. Thus, it has the advantages of sustainably recycling more chromium and avoiding cleaning the cathode after every cycle. The Cr2O72- and HCrO4- were transformed into Cr3+, Cr(OH)2+, Cr2(OH)4+, and Cr3(OH)45+ and the precipitate that was mainly composed of Cr2O3 in the precipitation chamber ultimately. At the end of 147 h, the total chemical oxygen demand removal efficiency of the sludge was 9.37 ± 0.62%. The maximum power density of 3.68 ± 0.23 W/m3 was generated in the BES. This study provides an alternative technology to obtain a high rate of chromium recovery and synchronous sludge degradation.