Improving the pharmaceutical compounds control in two activated sludge wastewater treatment plants: key operating conditions and monitoring parameters

Abstract

The control of pharmaceutical compounds (PhCs) in urban wastewater treatment plants (WWTPs) is an issue of health and environmental relevance, expected to become mandatory in the European Union and beyond, but studies at full scale are still scarce. A long-term (2.5-year) full-scale study addressing practical strategies for controlling PhCs was conducted in two activated sludge WWTPs with nitrification (BEI with A2O process; FNW with oxidation ditch). The results showed similar removal patterns in both plants – some of the most abundant influent PhCs were highly removed, others presented intermediate and variable removals, and some were recalcitrant. These behaviours validated a 4-class (A-D) PhC framework (based on biodegradation (kbio) and solid–water distribution (Kd)) for interpreting and predicting PhC removal, particularly sensitive to kbio, with a turning point at 1 L/(gSS.d). A statistical analysis conducted to unveil the key operation variables showed T254 is a good indicator of PhC removal and confirmed that favouring conditions for nitrifiers to grow is an operational strategy to improve PhC control. In BEI, F/M (food to microorganisms ratio) showed the most consistent role (over the sludge retention time), values below 0.08 d−1 being associated with effluent PhC concentrations 26–45 % lower. In FNW, the nitrification role was statistically expressed by the alkalinity reduction, values above 40 % (i.e., Nt-removals >80 %) being associated with effluent PhC concentrations 23–61 % lower.