A comparison of various rural wastewater treatment processes for the removal of endocrine-disrupting chemicals (EDCs)

The removal of six endocrine-disrupting chemicals (EDCs), including estrone (E1), 17β-estradiol (E2), estriol (E3), 17α-ethinyl estradiol (EE2), bisphenol A (BPA) and 4-nonylphenol (NP), was investigated in 20 rural wastewater treatment facilities (WWTFs) located in a county of Zhejiang Province, China. These WWTFs adopted one of the four treatment processes: activated sludge (AS), constructed wetland (CW), stabilization pond (SP), and micro-power biofilm reactor (MP). Results indicate that all the six EDCs were detected in wastewater samples with NP showing a maximum detection frequency (97%) and a maximum influent concentration (5002 ng L(-1)). After biological treatment, the concentrations of E2, E3 and NP decreased remarkably, while E1, EE2 and BPA exhibited varying removal efficiencies that depended on the specific treatment process and sampling season. In general, the centralized AS process outperformed those decentralized processes (i.e., CW, SP and MP) and a higher removal of E1, EE2, NP and BPA in the AS process was observed in summer (>70%) than in winter. Among the three decentralized processes, the removal of EDCs in the SP process was limited, especially for E1, EE2 and BPA (18-46%) in winter. Due to an incomplete removal, the total concentration of target EDCs increased obviously in the mixing and downstream sections of a local river receiving the effluent from a typical WWTF (practicing AS). This study reveals that the design and operation of rural WWTFs should be optimized if an effective removal of EDCs is to be achieved.