Anaerobic filter combined with submerged aerated biofilter: sludge production, denitrification and removal of pathogens

Abstract

The present study aims to investigate the performance of an pilot-scale anaerobic-aerobic system, provided with hospital sewage, consisted of anaerobic fixed bed reactor (AFBR) followed by biological aerated filter (BAF). Effluent recirculation will be adopted with 0.5, 1.0, 2.0 and 3.0 ratios, seeking denitrification. The steps will be as following: forming active biomass and establishing the dynamic equilibrium in the AFBR (step 1); evaluating ammonia toxicity to organisms involved in the nitrification process along the support medium height (step 2); promoting denitrification using volatile organic acids present in the anaerobic reactor as carbon source (step 3) and adjust the aeration to maintain steady state with the least possible oxygen consumption (step 4). Alongside these steps, effluent system toxicity will be assessed for ecotoxicological quality indicator organisms. Preliminary results in bench scale systems have been indicating that set up and operation proposals are adequate to meet the needs of operational robustness and organic carbon and nitrogen removal efficiencies. Evaluating the concentration gradients of nitrification intermediate compounds and the stratification of the involved oxidizing microorganisms is likely to clarify the process of nitrification inhibition in small height support medium reactors. Increasing recirculation reduces C/N ratio in BAF, optimizing ammonia oxidation by regulating substrate competition between autotrophic and heterotrophic bacteria, and increases nitrate conversion rate in the AFBR. (AU)