Chromium Nano-Mining with Electrified Bioreactors

This study demonstrates the feasibility of transforming Cr(VI) into Cr(III) nanoparticles with electrified bioreactors. Bacterial cells in suspension acted as a biocatalyst to reduce Cr(VI), using reducing agents. First, the influence of environmental factors (medium type, Cr concentration, headspace composition, pH, cell strain, cell concentration, and type of reducing agent) on the Cr removal was investigated. Based on the optimal conditions ( e.g., microaerophilic, pH 7, and Shewanella Oneidensis MR-1 cell strain), a second embodiment used these parameters wherein the chosen reducing agent (H 2 ) was replaced by a cathode polarized at -0.8 V SHE , electrogenerating it in situ . Here, 61% of the Cr(VI) was removed in 24 h through biological active and passive mechanisms, reaching a maximum removal capacity of 1121 mg Cr g cell -1 . Cr nanoparticles of 19 nm to 36 nm were found attached to the suspended bacteria. This technology opens new insights into the application of suspended bacteria in electrified bioreactors, stepping up from the conventional bioelectrochemical technology on the bioremediation and valorisation of Cr.