Removal of Pharmaceuticals in Biofilm and Activated Sludge Systems

Abstract: Abstract The present work investigates i) the occurrence and removal of pharmaceuticals at Swedish WWTPs, and ii) potential causes for differences in the removal efficiency of pharmaceuticals at wastewater treatment plants. Particular attention is directed at the biological treatment and the pharmaceutical removal capacity per unit biomass of activated sludges and carrier biofilms of different origins. Influent and effluent concentrations of pharmaceuticals at wastewater treatment plants are compiled from several Swedish screening programs. Based on the compiled data, 70 non-antibiotic pharmaceuticals have been detected in incoming wastewater at concentrations ranging from a few ng/L to several µg/L. For some of these pharmaceuticals, a higher removal degree is observed for activated sludge treatment plants with nitrogen removal than for trickling filter plants. The pharmaceutical removal capacity of activated sludge and carrier biofilms from several municipal wastewater treatment plants are assessed in batch experiments. Three notable differences in the removal capacity per unit biomass are observed. Activated sludges with oxic sludge ages of >7 days appear to have higher removal capacities for some pharmaceuticals than sludges with oxic sludge ages of <3 days. The anoxic and oxic conditions in nitrogen removal processes are shown to affect the pharmaceutical removal - some pharmaceuticals are being degraded both oxically and anoxically, while others appear to be stable in the absence of molecular oxygen. Compared to activated sludges, carrier biofilms show considerably higher removal capacities for several pharmaceuticals. From the broader perspective of micropollutant removal at wastewater treatment plants, the high pharmaceutical removal capacity of carrier biofilms suggests that new biological treatment solutions for enhanced micropollutant removal are within reach.