Microbial co-reduction of selenate and selenite in zeolite-packed columns in the presence of sulfate and nitrate: effects on removal efficiency and transformation of microbial community structure.

The escalating global concern over the presence of selenium species in aqueous systems, necessitates effective remediation strategies. Selenium, existing as selenite and selenate oxyanions, poses challenges due to its mobility in aqueous systems. Various technologies, particularly biological wastewater treatment systems, leverage microorganisms' unique abilities for waste removal. Challenges in selenium bioremediation, including interference from other anions and reoxidation, can be addressed with appropriate microorganisms. This study explores the responses of zeolite-packed (natural and modified) columns enriched with anaerobic sludge to selenium oxyanions and competing electron acceptors (SO42- or NO3-). After sulfate and nitrate amendments, the average selenium removal decreased by at least 17 % from the initial 99 %, demonstrating the influence of these anions. The series arrangement of columns in sulfate treatment led to increased selenium removal up to 93 % and sulfate removal up to 55 %, underscoring the potential for enhanced treatment capacity by increasing retention time by threefold. All columns achieved at least a 98 % reduction of nitrate. The 16S rRNA microbial community analysis indicates shifts in microbial composition with varying electron acceptors. Notably, the introduction of sulfate and nitrate led to increased diversity and dominance of sulfate reducers (Desulfovibrio (from 13 % to 38 %) and Enterococcus (from 2.5 % to 8.8 %)) and nitrate reducers (Chryseobacterium (from 0.5 % to 15 %), Sulfurospirillum (from 2.6 % to 11.0 %), and Anaeromusa-Anaeroarcus (from 2.6 % to 3.5 %)). Zeolite-combined microorganism systems showcase promise for selenium-laden wastewater treatment, achieving levels below permissible limits.