Degradation of 17α-ethynylestradiol (EE2) by nitrifying activated sludge containing different ammonia-oxidizing bacterial communities

Abstract

17α-ethynylestradiol (EE2), a synthetic estrogen, is a key ingredient in oral contraceptives pill. EE2 is reported as an endocrine disruptor, high in estrogenicity. Recent studies on the occurrence of pharmaceutical compounds in environments suggested the existence of EE2 in receiving water. Although previous studies suggested that EE2 persist in contact with activated sludge, more recent studies showed that EE2 can be degraded by ammonia-oxidizing bacteria (AOB) via co-metabolism. Nevertheless, all of the studies so far involved in only AOB enriched under high ammonium loads. The question still arises about whether AOB in municipal wastewater treatment systems (WWTS), as a potential reservoir for estrogens, which receive much lower ammonium loads than in the previous studies can degrade EE2. As a result, this study aimed to investigate the degradation of EE2 by nitrifying activated sludge (NAS) containing different AOB communities and factors affecting the degradation of EE2 by NAS (AOB communities, ammonia oxidation, and other organic matters). To develop NAS containing different AOB communities, sludge taken from a municipal wastewater treatment system was enriched in three reactors receiving inorganic medium containing different ammonium concentrations of 2, 10 and 30 mM. Community of AOB in each NAS was analyzed using specific Polymersase Chain Reaction amplification followed by Denaturing Gel Gradient Elecrophoresis and sequencing of 16S rRNA genes or amoA genes. The results showed that AOB community in each reactor differed depending on the ammonium load supplied. Predominant AOB species in the seed sludge related to Nitrosomonas communis cluster and Nitrosomonas oligotropha cluster, while that of NAS from 2 mM reactor related to Nitrosomonas communis cluster and that from 10 mM reactor related to unknown Nitrosomonas cluster, which was related closely to the strain Nitrosomonas sp. Is343 previously found in municipal, oil industry, and brewery WWTS. Whereas, that from 30 mM reactor related to Nitrosomonas europaea –Nitrosococcus mobilis cluster. Degradation studies suggested that EE2 can be degraded by all NAS under all different initial ammonium concentrations of 2, 10, and 30 mM. However, the degradation patterns varied among NAS. This result suggested that enzyme induction, enzyme expression, and enzyme activity may differ among AOB communities, and thus among distinct AOB species. Initial ammonium concentrations also affected the degradation of EE2. The results showed that the higher the initial ammonium concentration, more EE2 can be degraded. However, the amount of ammonia oxidized was not proportional to the amount of EE2 degraded. Study on the competition effect of other organic compounds on EE2 degradation showed that estradiol (E2), that have similar structure to EE2, competed the degradation of EE2, whereas organic compounds in canteen wastewater did not. The major finding of this study is that AOB found in municipal WWTS can degrade EE2. This will lead to the new means of treatment technology in removing EE2 and also other persistent organic compounds in wastewater using AOB.