DEGRADATION AND TRANSFORMATION OF E2-3S IN HORIZONTAL FLOW CONSTRUCTED WETLAND

Conjugated estrogens (CEs) are important existing form of natural estrogens, which can be hydrolyzed into free forms (Free estrogens, FEs), producing strong endocrine interference effects in the environment. Therefore, they have potential environmental risks. The degradation and transformation behavior of CEs with complex structure is not clear in the sewage treatment system, which is the key to accurately assess the comprehensive removal of estrogens. This study adopted a methodology of simultaneous analysis and detection of 15 kinds of FEs and CEs, to study the degradation behaviour of 17β-estradiol-3-sulfate (E2-3S) in planted and unplanted horizontal flow constructed wetlands (HFCWs) and also the transformation relationship between various estrogens. The results showed that under the condition of hydraulic residence time of 1.5 days, the removal efficiency of E2-3S reached 98% in the substrate depth of 15 cm at the inlet end of HFCWs. E2-3S could be transformed into other estrogens, which were the most abundant in FEs (accounting for more than 70%). Plants could significantly increase the wetland DO concentration and reduce the residual concentration of FEs. The removal efficiency of total estrogens by planted CW(P-CW) and unplanted CW(U-CW) were 84% and 56%, respectively. The major transformation pathway of E2-3S in HFCWs was to break the thioester bond to E2 and then oxidize it to E1, followed by direct oxidation of E2-3S to E1-3S and then hydrolyzing to E1, while a small amount of path was hydroxylation to form E3-3S and then hydrolyzing to E3. In addition, E2-3S could also produce trace D-CEs (< 5% of total estrogen), and the residual quantity in P-CW was lower.