Selenium treatment via integrating flow electrode capacitive deionization (FCDI) and bio-electrochemical systems (BES)

Selenium pollution in aquatic environments is a major concern globally and there is a gap in effective treatment technologies. In this study, we explored a novel approach combining flow-electrode capacitive deionization (FCDI) with bio-electrochemical systems (BES) for removal and reduction of selenate and selenite ions within a single reactor. Our integrated system was electricity-driven, eliminating chemical usage. Up to 76% selenium removal from the waste streams was achieved, followed by up to 66% and 54% reduction of selenate and selenite to elemental selenium respectively. The addition of acetate, a carbon source, enhanced selenate reduction by 14% but lowered selenite reduction by 21%, highlighting the substrate-dependent and bio-electrochemical-driven nature of selenate and selenite reduction respectively. Metagenomic sequencing revealed that Geobacter sulfurreducens and Pseudomonas stutzeri two known Se-reducing species, likely contributed both selenite and selenate reduction through up-regulating functional genes related to sulfide reductase, fumarate reductase, and multi-heme c-type cytochromes. Thauera spp. and Alishewanella spp., previously not identified in selenium reduction, were likely involved in selenite reduction via up-regulation of genes related to sulfite reductase and selenium reductase.