Effects of backwashing strategy and dissolved oxygen on arsenic removal to meet drinking water standards in a sulfidogenic attached growth reactor

[Display omitted] •Effects of air as substitute to nitrogen on arsenic removal in absence of iron studied.•Effects of dissolved oxygen on arsenic removal in an anaerobic AGR investigated.•Use of air in backwashing shifted the TEAP zones of sulphate reduction.•An overlapping of DO and nitrate TEAP zones was observed.•Bacterial genera capable of using multiple electron acceptors were detected. Efficiency and feasibility of two backwashing methods (water-nitrogen and water-air assisted) on arsenic and its co-pollutants removal were assessed through running a sulfidogenic attached growth reactor (AGR) treating arsenic spiked simulated groundwater for about 600 days. Replacing water with nitrogen assisted backwashing (WNAB) by water with air assisted backwashing (WAAB) introduced dissolved oxygen (DO) as an additional electron acceptor, which required an increased empty bed contact time (EBCT) to retain the entire terminal electron accepting zones (DO, nitrate, arsenate and sulfate) within the reactor. Removal of arsenic to below 10 μg/L required a longer EBCT at higher influent DO in backwash water. Notably, MiSeq sequencing analysis confirmed the presence of diverse bacterial community on biofilm which can utilize multiple terminal electron acceptors present in the bioreactor.