The Effect of Potentiostatic Control on the Bioreduction of Hexavalent Chromium Using Bacillus cereus

Coupling microbial catalysis with electrochemical stimulation offers a promising strategy for heavy metal remediation. This study investigates how potentiostatic control influences the bioreduction of hexavalent chromium (Cr(VI)) by Bacillus cereus strain DIF1 in a bioelectrochemical system. Cr(VI) reduction was evaluated under various applied cathodic potentials, and the highest reduction efficiency (91.45%) was achieved at +0.04 V after 24 h. This performance significantly surpassed that of the abiotic control (82.55%) and the open-circuit biotic control (9.25%), indicating that the applied potential enhances microbial Cr(VI) reduction beyond contributions from abiotic processes alone. Cyclic voltammetry (CV) revealed a distinct redox feature at +0.04 V with no corresponding reverse peak, indicating kinetically favored electron transfer during Cr(VI) reduction under this condition. Microscopic imaging confirmed that, under the applied potential, Bacillus cereus DIF1 formed filamentous connections, exhibited higher chromium accumulation on bacterial cells than on the surrounding carbon paper electrode, and developed a robust biofilm on the cathode surface. The system maintained consistent Cr(VI) reduction performance over three consecutive cycles, demonstrating good short-term operational reproducibility. These findings highlight the critical role of precise electrochemical control in modulating microbial Cr(VI) reduction and provide mechanistic insights into the interplay between electrode potential and bacterial activity.