Biodegradation of oestrogens in nitrifying activated sludge.

The degradation of 17beta-oestradiol (E2) and 17alpha-ethinyloestradiol (EE2) was investigated in an aerobic activated sludge system fed with synthetic wastewater. The effect of different solid residence times (SRTs) and nitrification inhibitors, such as allylthiourea (ATU), was studied in order to assess which group of microorganisms plays a significant role in the degradation of oestrogens. E2 was effectively converted into oestrone (E1) under all the conditions encountered in the nitrifying activated sludge system. The degradation of E2 obeyed first-order reaction kinetics; with an increase in SRT from 12 to 20 days, the degradation rate constant, k, decreased from 2.3 h(-1) to 0.47 h(-1). The removal of EE2 did not change significantly with the addition of ATU and at different SRTs. Only about 20% of EE2 was removed from the system, which demonstrated that EE2 was more recalcitrant than natural oestrogens. The results are supported by other recent studies, which suggest that co-metabolic degradation of EE2 and E2 by ammonia-oxidizing bacteria is not an important removal mechanism. The primary mechanism for E2 and EE2 degradation in activated sludge is most probably the activity of heterotrophic bacteria.