Coupling UV-radiation with immobilized bacteria for the removal of 17-estradiol and 17 -ethynylestradiol

The ubiquitous presence of estrogens in the wastewater has raised global concerns due to the hazardous effects on ecosystems and human health. In this study, we intend to develop a coupled microbial immobilization degradation and UV photolysis in the same reactor to remove estrogens. The porous structure of the immobilized microbial carrier can prevent cell wall rupture caused by direct exposure to UV light, leading to inactivation of microorganisms. UV oxidation and biodegradation occur simultaneously, and the biodegradable products of UV degradation are timely processed by microorganisms. Results showed that the coupling technology significantly (p < 0.05) outperformed UV or immobilized bacteria alone for the degradation of 17 beta-estradiol (E2) and 17 alpha-ethynylestradiol (EE2). The synergistic effect of coupling UV with immobilized bacteria increased the removal of E2 and EE2 by 50-51 % in batch mode and resulted in an improvement of 10 % for E2 in continuous mode. Even though the UV photodegradation plays a major role, the functional microorganisms remain critical for the effective degradation of E2 and EE2. Further optimization, including an 8-hour hydraulic retention time and a 1.67 mM glucose system as carbon source, improved continuous-flow estrogens removal, consistently reaching rates of 94.6-100 % in the immobilized bacteria coupled UV-radiation column reactor. Our results have shown the immobilized microbial technology can effectively provide protection for microorganisms to prevent micro-bial losses and can be successfully applied in photodegradation coupled biodegradation technology.