Extension of ASM2d to Model the Fate of 17α-Ethinylestradiol in Activated Sludge Systems

Abstract

The discharge of the synthetic estrogen, 17α-ethinylestradiol (EE2), in wastewater treatment plant (WWTP) effluents is an environmental concern as this compound can alter the reproductive system of aquatic wildlife at low ng L-1 concentrations. The impact of EE2 at such low concentrations indicates the need to identify activated sludge (AS) process designs that minimize WWTP effluent EE2 concentrations. An EE2 fate and transformation model was developed based on the following mechanism: (1) EE2 production from deconjugation of EE2-3-sulfate, a conjugated form excreted from humans, (2) EE2 removal from biodegradation by heterotrophic biomass growing on other substrates, and (3) EE2 removal from sorption to activated sludge. These mechanisms were incorporated into the International Water Association (IWA) Activated Sludge Model No. 2d (ASM2d) to model the fate of EE2 across aerobic and biological nutrient removal (BNR) AS systems. The model was calibrated and evaluated for mixed liquor solids, nutrients, and EE2 using lab-scale aerobic and BNR AS reactors fed primary effluent and amended with ng.L-1 estrogen concentrations. A sensitivity analysis predicted effluent EE2 concentrations were most sensitive to the biodegradation rate coefficient (kbio,H), the influent biodegradable chemical oxygen demand to EE2 ratio, and the aerobic solids retention time and were least sensitive to the deconjugation rate coefficient (kcle,H) and the solidliquid partitioning coefficient. Predicted effluent EE2 concentrations were more sensitive to the kcle,H/kbio,H ratio for AS systems with low kbio,H values.