Occurrence and fate of pharmaceutically active compounds in the largest municipal wastewater treatment plant in Southwest China: Mass balance analysis and consumption back-calculated model

• 21 and 18 Target PhACs were detected in the wastewater and sludge.
• Mass loads of PhACs per person were calculated and compared with other countries.
• Biotransformation/biodegradation was the main removal mechanism for the PhACs.
• Construct the back-calculated PhAC consumption model based on influent concentration.

The occurrence and fate of twenty-one pharmaceutically active compounds (PhACs) were investigated in different steps of the largest wastewater treatment plant (WWTP) in Southwest China. Concentrations of these PhACs were determined in both wastewater and sludge phases by a high-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry. Results showed that 21 target PhACs were present in wastewater and 18 in sludge. The calculated total mass load of PhACs per capita to the influent, the receiving water and sludge were 4.95 mg d−1 person−1, 889.94 μg d−1 person−1 and 78.57 μg d−1 person−1, respectively. The overall removal efficiency of the individual PhACs ranged from “negative removal” to almost complete removal. Mass balance analysis revealed that biodegradation is believed to be the predominant removal mechanism, and sorption onto sludge was a relevant removal pathway for quinolone antibiotics, azithromycin and simvastatin, accounting for 9.35–26.96% of the initial loadings. However, the sorption of the other selected PhACs was negligible. The overall pharmaceutical consumption in Chongqing, China, was back-calculated based on influent concentration by considering the pharmacokinetics of PhACs in humans. The back-estimated usage was in good agreement with usage of ofloxacin (agreement ratio: 72.5%). However, the back-estimated usage of PhACs requires further verification. Generally, the average influent mass loads and back-calculated annual per capita consumption of the selected antibiotics were comparable to or higher than those reported in developed countries, while the case of other target PhACs was opposite.