Microbial structure of nitrifying granules and their estrogens degradation properties

It has been known that endocrine disruption compounds such as natural estrogens estrone, 17β-estradiol, estriol, and synthetic steroid 17a-ethynylestradiol can be degraded by nitrifying bacteria. The aim of this research was to test biodegradation of estrogens by microbial granules containing nitrifying bacteria. Cultivation of microbial granules was performed in sequencing batch reactor in model wastewater with carbon to nitrogen ratio of 100:30 by weight. After the system reached the steady state, the mean diameter of granules, sludge volume index of granular biomass, and biomass concentration were 0.6 mm, 22 mL g⁻¹ and 7 g L⁻¹, respectively. Nitrite was not detected in the effluent, and conversion of the consumed NH₄⁺-N to NO₃⁻-N was 93%. Specific NO₃⁻-N production rate was 0.12 d⁻¹ at the constant NH₄⁺- loading late of 0.9 g L d⁻¹. The presence of ammonium-oxidizing and nitrite-oxidizing bacteria was confirmed by fluorescence in situ hybridization with 16S rRNA-targeted oligonucleotide probes Nsm156 and Nit3. The estrogen biodegradation by the granules was conducted in batch experiments. The complete biodegradation of the mixture of estrone, 17β-estradiol, estriol, and 17a-ethynylestradiol, 100 μg L⁻¹ each, by microbial granules was within 60 days. The order of biodegradation for estrogens by microbial granules was as follows: 17β-estradiol -> estriol -> estrone ->17a-ethynylestradiol. The degradation rate constants of estrogens by microbial granules were 0.19 d⁻¹, 1.26 d⁻¹, 0.14 d⁻¹ and 0.11 d⁻¹ for estrone, 17β-estradiol, estriol and 17a-ethynylestradiol, respectively.