Degradation of 17α-ethinylestradiol by Enterobacter tabaci Isolate and Kinetic Characterization

Abstract

In the present study, the degradability of 17α-ethinylestradiol (EE2) by isolated bacterial strains from the activated sludge of the wastewater treatment plant of a factory manufacturing contraceptive pills was investigated. The strain with more degradation capacity of EE2 (strain S1) was identified as Enterobacter tabaci based on its morphology and analysis of the 16S rRNA sequence. The isolated strains were used in the form of pure (containing the identified bacterial strain) and mixed (containing the two isolated bacterial strains) cultures for degradation of EE2 as the sole carbon and energy source. The added substrate (0–4 mg L−1) was metabolized almost completely within 4 d at 30 °C. EE2 was used as the growth substrate by the bacterial cultures, since the biomass concentration was obviously increased. EE2 biodegradation was kinetically investigated according to the kinetic data obtained by fitted appropriate models (the Monod model and the allosteric sigmoidal model were used for the pure and the mixed bacterial cultures, respectively). The first-order kinetic rate constant ( $$ \frac{q_m}{K_s} $$ ) for EE2 utilization by the pure culture was noticeably higher than the value obtained by the mixed culture, probably due to preference of the isolated bacterial strain to estrogenic compounds as the growth substrate by producing specific enzymes. By comparing the degradation and also the growth kinetic parameters, it was concluded that the pure bacterial culture had better efficiency in degradation of EE2.