The fate of typical pharmaceuticals in wastewater treatment plants of Xi’an city in China

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Eight typical pharmaceuticals in four wastewater treatment plants (WWTPs) of Xi’an city in China were investigated to determine their occurrence and removal efficiencies. Target pharmaceuticals were extracted from wastewater and sludge samples by solid-phase extraction (SPE) and analyzed by gas chromatography equipped with tandem mass spectrometry (GC–MS/MS) after derivatization. The results indicated that the concentrations of the pharmaceuticals ranged from 0.39 to 642μgL−1 in the influents, which were similar with or one order magnitude higher than that of previous reports, and phenacetin, gemfibrozil and caffeine were main contributors. The concentrations in the effluents were between 0.075 and 7.01μgL−1, and 80–100% pharmaceuticals were removed in the WWTPs except diclofenac, which was removed nearly 72–85%. Three main removal pathways including physicochemical process, biodegradation and sludge adsorption were involved in the removal of the pharmaceuticals. Almost 20–50% of the pharmaceuticals were removed through physicochemical operating units, and high concentration pharmaceuticals were examined in the floating oil from aerated grit chamber. Nearly 11–89% and 0–15% pharmaceuticals were removed by biodegradation and sludge adsorption, respectively. Aerobic condition was advantageous for the biodegradation of phenacetin, gemfibrozil and caffeine, while cholesterol was easily decomposed by anaerobic microorganism. It showed that high temperature was beneficial to the biological removal of gemfibrozil, and acidic condition could be more helpful to the biodegradation of diclofenac and its removal efficiency reached 60% at pH 4.5. However, biodegradability of diclofenac should be further investigated to eliminate its adverse effects on human health and ecological environment.