Abstract:

We aimed at studying the effects of calcium alginate immobilized bacteria and ultrasonic assistance on the enhanced biodegradation of estrogens in E1,E2,E3,EE2 and BPA soil. The central composite design was utilized for the experiment design of ultrasonic time, the concentration of calcium alginate and the amount of immobilized bacteria. At the same time, the design was combined with the response surface method to optimize, to find the optimal degradation conditions of estrogens in soil and provide a theoretical foundation and basis on estrogens removal. The enhanced biodegradation mechanism of estrogens in soil by calcium alginate was analysed qualitatively. In the meantime, quantitative structure biodegradability relationship (QSBR) was utilized to analyze the effects of estrogenic physicochemical properties on the enhanced biodegradation mechanism, which was from the perspective of external and internal reasons. The results of our experiments and analysis show that under the addition of calcium alginate assisted with ultrasonic, the optimal condi
tions for the biodegradation of five estrogens were as followed: ultrasonic time was 3 minutes, the mass concentration of calcium alginate was 5%, and the amount of bacteria liquid was 6 mL. Under the optimal conditions, if the system was degraded 3 d, the biodegradation rate of E1 approached 100%; degraded 7 d, the biodegradation rates of E3,BPA,EE2 and E2 achieved 52.65%, 96%,96.90% and 100% respectively. The mechanism analysis also demonstrate that polar surface area (PSA), hydrophobicity (represent by lg K_ow) and surface tension of estrogens were the dominant parameters affecting estrogen biodegradation. In addition, the interaction of PSA and log K_ow performed a synergistic effect on the degradation of estrogens, the interaction of lg K_ow and surface tension also performed a synergistic effect on the degradation of estrogens. Therefore, it is clear that calcium alginate with ultrasonic assistance can significantly improve the biodegradation rates of estrogens in soil.

Key words: estrogen, soil, calcium alginate, quantitative structure biodegrade relationship, biodegradation mechanism