Concurrent removal of nitrate, arsenic and iron from simulated and real-life groundwater to meet drinking water standards: Effects of operational and environmental parameters

The aim of this work was to study concurrent removal of nitrate, arsenic and iron in an attached growth reactor (AGR) based on bio-sulphidogenesis treating simulated and real-life ground water. A lab-scale bioreactor system was monitored for a period of 511 days under conditions identical to those prevailing at full-scale to assess the relative influence of empty bed contact time (EBCT) (20-90 min), backwash strategies (water-nitrogen and water-air), temperature (20-50 degrees C), pH (6.6-8.4) and shut down on reactor performance and recovery. Complete removal of nitrate (50 mg/L) and over 95% removal of iron (3 mg/L) occurred. Arsenic removal efficiency was around 99% (500 mu g/L) and treated water arsenic concentration was in compliance with the World Health Organization and Indian Standard of 10 mu g/L. Port sampling along the depth of bioreactor shows shifting of terminal electron accepting process zones at lower EBCT of 20 min and after air assisted backwashing. The temperature range of 20-50 degrees C and pH range of 6.6-8.4 were applicable for arsenic removal in natural conditions. Precipitated biosolids were analysed using electron microscopy. Biogenic sulphides resulted in the precipitation of arsenosulphides and iron sulphides, which concurrently removed arsenic and iron. This study suggests that a sulphidogenic bioreactor may help to set the basis for concurrent removal of nitrate, arsenic and iron from real-life groundwater using mixed biofilm bacterial community.