Degradation of steroid estrogens by UV/peracetic acid: Influencing factors, free radical contribution and toxicity analysis

Steroid estrogens (SEs) are a group of refractory organic micropollutants detected in secondary effluent frequently. The advanced oxidation processes (AOPs) are usually used to deep remove the SEs from the secondary effluent. Herein, we first investigated the UV/peracetic acid (PAA), a PAA-based AOP, to degrade SEs. Using estrone (E1), 17 beta-estradiol (E2), estriol (E3), and 17 alpha-ethinyl estradiol (EE2) as representatives, the results showed that UV can effectively activate PAA to enhance the degradation of the four SEs, which degradation followed the pseudo-first-order kinetics (R2 > 0.99), and the rate constant (kobs) of degradation increased with increasing the PAA dosage in the range investigated. Little pH dependence was also observed in the degradation of SEs by UV/PAA. Furthermore, the degradation of SEs was improved in the presence of coexisting substrates (Cl , HCO- 3, NO- 3, and HA) in relatively low concentrations. Quenching experiments revealed that the carboncentered radicals (R-C center dot) produced from the UV/PAA process were recognized as the predominant contributors to the degradation of the four SEs. Also, we found that the estrogenic activity decreased by more than 94%, but the acute toxicity inhibition increased to 37% in the solution after 30 min UV/PAA treatment. In addition, the 130% additional total organic carbon (TOC) was generated after UV/PAA process. These findings obtained in this work will facilitate the development of the UV/PAA process as a promising strategy for the deep removal of SEs in secondary effluent.