Laboratory Research On The Removal Of Steroidal Estrogens By Enhanced Nitrification Technology

Steroid Estrogens, a kind of chemical compounds with the highest oestrogenic activity, interferes with the normal function of the endocrine system of aquatic organisms at low(ng/L) concentrations. SEs are transported via the sewerage systems to municipal wastewater treatment plants, where reduced by biological treatment processes. However, their removal during treatment is variable, and concentrations of the residuals in effluent are also high. Some research found that nitrification sludge got better removal for SEs. Enhanced nitrification process, therefore, can be used for removing nitrogen, with the same time for increasing SEs removal. Taking natural estrone(E1), 17?-estradiol(E2) and the synthetic 17?-ethynylestradiol(EE2), the major contributors to the environment and endocrine disrupting activity, as objects in this study, we used sequencing batch moving bed biofilm reactor(SBMBBR) to cultivate activated sludge, and analyze the removal capacity for SEs of enhanced nitrification process, with using sequencing batch reactor(SBR) as a blank control. Research contents can be summarized: 1) compare the two reactors removal efficiency of conventional items in wastewater with and without adding SEs in influent; 2) observe the variations of conventional items in effluent and microbial community structure in activated sludge before and after adding SEs in influent; 3) analyze statistical significance effects of C/N and aeration rate on the removal efficiency of SEs by factorial experiment analysis. The major conclusions are extracted as follows:(1) Adding SEs to SBMBBR and SBR reactors, concentrations of COD, TN and NH4+-N in effluents can achieve Grade A < Discharge standard of pollutants for municipal wastewater treatment plant>(GB18918-2002). Removal efficiency of TN increased caused by enhanced denitrification in the reactors, contrasted with a slightly change for COD and NH4+-N. Both of the two reactors showed some removals for SEs, mainly occurred in aerobic phase(reaching 90% of total), and highest for E2, followed by E1, and lowest for EE2. Moreover, removal efficiency of SEs in SBMBBR was higher than SBR, indicating enhanced nitrification process indeed getting better removal for SEs during wastewater treatment process.(2) Activated sludge species abundance and diversity declined after adding SEs in two reactors, when compared with conventional cultivation. Difference in Phylum was little, but large in Genus, and 16 dominant genera of bacteria disappeared with new 8 appearing, which may play an important role in reducing SEs. From the classification aspect of genus, ammonia oxidizing bacteria abundance varied a little before and after adding SEs, but abundance of nitroso oxidizing bacteria and denitrifying oxidizing bacteria increased. Removal of SEs mainly happened in aerobic phase, meanwhile dominant genera of nitrifying bacteria abundance also showed an increasing trend, indicating nitrifying bacteria may contribute to reducing SEs via co-metabolism.(3) Removal efficiency of natural estrone(E1), 17?-estradiol(E2) and the synthetic 17?-ethynylestradiol(EE2) in the two reactor reached 90%?95% and 55%~75%, respectively. From regression analysis, we can see the significant influence of C/N on the removal of E1, E2 and EE2 for SBMBBR, and E1 and EE2 for SBR. Also, aeration rate on E1, E2 and EE2 for SBMBBR, and E1 and E2 for SBR. Significant influence of interaction(C/N and aeration rate) only on E1 was observed in the two reactors.(4) Removal of EE2 increased with C/N and aeration rate, but removal of E1 and E2 enhanced with increased aeration rate, and declined with increased C/N in two reactors. Tendency of E1 and E2 with C/N and aeration rate was similar with NH4+-N, corresponding to co-metabolism theory of nitrifying bacteria degrading SEs. Whereas EE2, a refractory compound for microorganism, mainly reduced by adsorption of activated sludge, which led to increased removal of EE2 with improving C/N and aeration rate, and new activated sludge volume. During factorial experiment, removal capacity for SEs of SBMBBR(an enhanced nitrification process) was superior to that of SBR.