Effect of organic matters in wastewaters on degradation of 17α-ethynylestradiol by nitrifying activated sludge containing ammonia-oxidizing bacteria

Abstract

17α-ethynylestradiol (EE2), a synthetic estrogen, is a key ingredient in oral contraceptive pill. This recalcitrant organic pollutant is reported as an endocrine disruptor, very high in estrogenicity. Previous studies on the occurrence of pharmaceutical compounds in environments suggested the existence of EE2 in several receiving waters (logKow = 4.15). Municipal wastewater is a potential source of EE2 since EE2 is released mainly to the environments by excretion of humans and animals through their urine and feces. Although wastewater treatment plants (WWTPs) are capable of removing EE2 from wastewater, the potential removals of EE2 by WWTPs are not enough to reduce the released amounts of EE2 to the safe levels. In batch experiment, EE2 appeared to be mainly stable in contact with activated sludge, while nitrifying activated sludge (NAS) could completely degrade EE2. In NAS, EE2 is proven to be degraded by ammonia-oxidizing bacteria (AOB) via co-metabolism. However, all the studies so far have provided only the information obtained from the study with single EE2 compound. In fact, other several types of organic matters are present in wastewater. Such organic compounds in wastewater can result in retarding EE2 degradation by competing EE2 for active site of ammonia monooxynase (AMO) enzyme. Therefore, applications of AOB in degrading EE2 in WWTPs require fundamental knowledge of AMO and its interaction with alternate substrates. This study aimed to investigate effect of organic matters in wastewaters on cometabolism of EE2 by AOB in NAS. Specific objectives included effect of types of wastewaters (municipal and industrial wastewaters), effect of initial ammonium concentration (2 and 10 mM), and effect of initial EE2 concentration (3.5 and 10 mg/l). To develop NAS, sludge taken from a municipal WWTP was enriched in a reactor receiving inorganic medium containing 2mM (28 mg-N/l) ammonium concentration. Each experiment was carried out with diluted wastewater to obtain various final chemical oxygen demand (COD) concentrations. Preliminary experiment on effect of pH and nitrite concentration (nitration) on abiotic transformation of EE2 suggested that abiotic EE2 transformation occurred at only pH < 6.8 and initial nitrite concentrations showed no effect on abiotic EE2 transformation. Degradation of EE2 under the presence of municipal or industrial wastewater showed that different types of wastewaters that may contain district compositions of organic matters exhibited inhibition behaviors differently. In the case of municipal wastewater, most amounts of organic matters may be noncompetitive inhibitors to ammonia which have the same binding site to EE2 causing no effect on ammonia oxidation but deceleration of EE2 degradation. In contrast, in the case of industrial wastewater, the major portions of organic matters may be competitive inhibitors to ammonia causing deceleration of ammonia oxidation. At low initial ammonium concentration, EE2 degradation can be deteriorated by COD concentrations. But when initial ammonium concentration increased, these phenomena disappeared. This is because when increasing the amount of the primary substrate, more AMO enzymes were produced resulting in unlimited degradation of all compounds in the medium reducing the effect of organic matters on cometabolism of EE2. However, although organic matters in municipal wastewater were more in noncompetitive forms to ammonia, COD concentrations were found to deteriorate ammonia oxidation at high initial ammonium concentration. This may cause by product toxicity when organic matters were more degraded. Initial EE2 concentration did not affect cometabolism of EE2.