Post-anoxic integrated biofilm activated sludge wastewater treatment process for emerging contaminant removal

The study investigates the role of redox conditions and food-to-microorganism (F/M) ratio on emerging contaminants (ECs) attenuation in a laboratory-scale system. A Modified Ludzack Ettinger process integrated with a polyvinyl alcohol (PVA) gel-based biofilm reactor following the anaerobic tank was employed. Twenty ECs covering a wide range of physico-chemical properties were monitored across four treatment zones - aerobic, PVA, anoxic, and anaerobic reactors to understand the role of different redox conditions in removing ECs. Overall, the system achieved an average EC removal of 87%, with 9 out of 20 compounds removed by >80% and between 50 and 80%. The ECs removal contribution followed the trend: aerobic (42.7%) > PVA (33.4%) > anoxic (25.7%) > anaerobic (19.3%). The analysis revealed higher solid-water partition coefficients (K_d) in the settled sludge compared to the treatment reactors, with values varying based on the compound's chemical properties. The mass balance analysis showed biodegradation as the primary removal mechanism. Of the total EC mass load of 3.68, 0.5 and 0.022 g d^-1 was detected in the final effluent and sludge, respectively. Importantly, a strong negative correlation (r² = 0.83) was observed between the F/M ratio and EC removal efficiency, highlighting its critical role in process optimization.