Abstract. This study investigated operational factors influencing the removal of steroid 18 estrogens and alkylphenolic compounds in two sewage treatment works, one a 19 nitrifying/denitrifying activated sludge plant and the other a nitrifying/denitrifying 20 activated sludge plant with phosphorus removal. Removal efficiencies of >90% for 21 steroid estrogens and for longer chain nonylphenol ethoxylates (NP 4-12 EO) were observed 22 at both works, which had equal sludge ages of 13 days. However, the biological activity 23 in terms of milligrams of estrogen removed per tonne of biomass was found to be 50-60% 24 more efficient in the nitrifying/denitrifying activated sludge works compared to the works 25 which additionally incorporated phosphorus removal. A temperature reduction of 6°C 26 had no impact on the removal of free estrogens, but removal of the conjugated estrone-3-27 sulphate was reduced by 20%. The apparent biomass sorption (LogKp) values were 28 greater in the nitrifying/denitrifying works than those in the nitrifying/denitrifying works 29 with phosphorus removal for both steroid estrogens and alkylphenolic compounds 30 possibly indicating a different cell surface structure and therefore microbial population. 31The difference in biological activity (mg tonne -1 ) identified in this study, of up to seven 32 2 times, suggests that there is the potential for enhancing the removal of estrogens and 33 alkylphenols if more detailed knowledge of the factors responsible for these differences 34 can be identified and maximised, thus potentially improving the quality of receiving 35 waters. 36 37 Introduction 38

Due to concerns regarding the release of pharmaceuticals into the environment and the understudied impact of stereochemistry of pharmaceuticals on their fate and biological potency, we focussed in this paper on stereoselective transformation pathways of selected chiral pharmaceuticals (16 pairs) at both microcosm (receiving waters and activated sludge wastewater treatment simulating microcosms) and macrocosm (wastewater treatment plant (WWTP) utilising activated sludge technology and receiving waters) scales in order to test the hypothesis that biodegradation of chiral drugs is stereoselective. Our monitoring programme of a full scale activated sludge WWTP and receiving environment revealed that several chiral drugs, those being marketed mostly as racemates, are present in wastewater and receiving waters enriched with one enantiomeric form (e.g. fluoxetine, mirtazapine, salbutamol, MDMA). This is most likely due to biological metabolic processes occurring in humans and other organisms. Both activated sludge and receiving waters simulating microcosms confirmed our hypothesis that chiral drugs are subject to stereoselective microbial degradation. It led, in this research, to preferential degradation of S-(+)-enantiomers of amphetamines, R-(+)-enantiomers of beta-blockers and S-(+)-enantiomers of antidepressants. In the case of three parent compound - metabolite pairs (venlafaxine - desmethylvenlafaxine, citalopram - desmethylcitalopram and MDMA - MDA), while parent compounds showed higher resistance to both microbial metabolism and photodegradation, their desmethyl metabolites showed much higher degradation rate both in terms of stereoselective metabolic and non-stereoselective photochemical processes. It is also worth noting that metabolites tend to be, as expected, enriched with enantiomers of opposite configuration to their parent compounds, which might have significant toxicological consequences when evaluating the metabolic residues of chiral pollutants.