Improving the performance of bioelectrochemical sulfate removal by applying flow mode. undefined

Treatment of wastewater contaminated with high sulfate concentrations is an environmental imperative lacking a sustainable and environmental friendly technological solution. Microbial electrochemical technologies (MET) represent promising approaches for sulfate reduction. In MET, a cathode is introduced as inexhaustible electron source of reductive power via direct or mediated electron transfer promoting sulfate reduction. So far, this is mainly studied in batch mode representing straightforward and easy-to-use systems, but their practical implementation seems unlikely, as treatment capacities are limited. Here we investigated bioelectrochemical sulfate reduction in flow mode and achieved sulfate removal rates (Rsulfate) and removal efficiencies (Esulfate) being comparable to batch experiments. Different temperatures and hydraulic retention times (HRT) were applied. The best performance (Rsulfate= 3.1 mmol L−1 d−1, Esulfate= 89.6%) was achieved at HRT 3.5 d and 30°C. Microbial community analysis based on amplicon sequencing demonstrated that sulfate reduction is mainly performed by prokaryotes belonging to the genera Desulfomicrobium, Desulfovibrio, and Desulfococcus, indicating that hydrogenotrophic and heterotrophic sulfate reduction occurred by utilizing cathodically produced H2 or acetate produced by homoacetogens (Acetobacterium). The advantage of flow operation for bioelectrochemical sulfate reduction is likely based on higher absolute biomass, stable pH, decreased sulfide inhibition, and optimized ratio between sulfate-reducing prokaryotes and homoacetogens.