Occurrence and removal of endocrine-disrupting chemicals in wastewater treatment plants in the Three Gorges Reservoir area, Chongqing, China

Abstract

Concentrations of six endocrine-disrupting compounds (EDCs), bisphenol A (BPA), estrone (E₁), 17β-estradiol (E₂), estriol (E₃), 17α-ethynylestradiol (EE₂) and diethylstilbestrol (DES), were assessed in influents, effluents and excess sludge in ten municipal wastewater treatment plants (WWTPs) in the Three Gorges Reservoir (TGR) area, Chongqing, China. Three types of activated sludge treatment processes, oxidation ditch (OD), reversed anaerobic–anoxic–oxic (rA²/O) technology and sequential batch reactor (SBR), were used in the surveyed WWTPs. These WWTPs were all combined landfill leachate–sewage treatment plants. All analytes were extracted by solid-phase extraction (SPE) in the dissolved phase and by accelerated solvent-based extraction (ASE) in sludge. Gas chromatography-mass spectrometry (GC-MS) was employed for the analysis of EDCs. Among these EDCs, BPA was the most frequently detected and abundant compound (100.0–10566.7 ng L⁻¹, 15.5–1210.7 ng L⁻¹ and 85.0–2470.4 ng g⁻¹ with respect to the influents, effluents and excess sludge samples). The greatest levels of steroidal estrogens in municipal influents were observed in E₃ which were all >100 ng L⁻¹, followed by E₁ (42.2–110.7 ng L⁻¹) and E₂ (7.4–32.7 ng L⁻¹), and in the effluents and sludge were E₁ > E₃ > E₂ which were all <31 ng L⁻¹ and 105 ng g⁻¹, respectively. Regarding synthetic estrogens, EE₂ was frequently detected in the influents, occurring below 50 ng L⁻¹, while DES was not detected at all. A high correlation coefficient was observed between the leachate–sludge ratio and concentrations of influent EDCs, and it was statistically significant (i.e., R > 0.65, P < 0.05), but removal efficiency of the EDCs did not show significant differences with OD, rA²/O and SBR processes. Furthermore, modification of treatment technology as well as operational parameters, such as hydraulic retention time (HRT), sludge retention time (SRT) and disinfection process (DP), were recommended to further eliminate the residual EDCs.