Importance of culture history on 17α-ethinylestradiol cometabolism by nitrifying sludge

17 alpha-ethinylestradiol (EE2), a synthetic estrogen which interfere the endocrine and reproductive function in living organisms, has been found extensively to be deposited into municipal wastewater treatment plants and the environment via human excretion. EE2 has long been known to be efficiently cometabolized by ammonia-oxidizing bacteria (AOB) during ammonia (NH3) oxidation. Current study aims to investigate the effect of culture history on the biotransformation of EE2 by nitrifying sludge which was enriched under different ammonia loading rates in continuous flow reactors. Result showed that past growth condition largely affected not only the metabolic rate of NH3 oxidation but also EE2 cometabolism. Sludge previously acclimated with higher NH3 loads as well as sludge dominated with AOB belong to high growth cluster (Nitrosomonas europaea-Nitrosococcus mobilis) showed higher rate of EE2 biotransformation than those one being acclimated with lower NH3 loads because of its ability to provide more reducing power from NH3 oxidation. Moreover, the correlation between the degradation rates of NH3 and EE2 was higher in sludge being acclimated with higher load of NH3 in comparison with other sludge. Implication of the findings emphasized the role of volumetric NH3 loading rate in determining EE2 removal in wastewater treatment system.