Role of Particle Size and Ammonium Oxidation in Removal of 17(alpha)-Ethinyl Estradiol in Bioreactors

Laboratory scale bioreactors were used to investigate sorption and biodegradation of 17-(alpha) ethinylestradiol (EE2). EE2 is among many emerging micropollutants that may cause endocrine disruption of aquatic organisms in the environment. Results showed that the sludge taken from the membrane bioreactor (MBR) had a sorption distribution coefficient that was more than twice that of biomass derived from sequencing batch reactors (SBRs). The MBR biomass had smaller particles and was more hydrophobic than the SBR biomass. Experiments with nitrifying sludge showed that sorption was more important when the initial ammonia concentration was 48 mg/L or less, but at higher initial ammonia concentrations the role of biodegradation became more important. The ammonium monooxygenase enzyme extracted from a nitrifying mixed culture removed EE2 in batch experiments. These findings are the first that we are aware of to link biomass particle size, hydrophobicity, and sorption capacity. These results also support the notion that cometabolic biodegradation of EE2 can occur in nitrifying sludge