Occurrence and fate of eleven classes of antibiotics in two typical wastewater treatment plants in South China.

Wastewater treatment plants (WWTPs) are regarded as one of the most important sources of antibiotics in the environment. Two sampling campaigns over a period of one year in two wastewater treatment plants (plant A: activated sludge with chlorination, and plant B: oxidation ditch with UV) of Guangdong Province, China were carried out to assess the occurrence and fate of 11 classes of 50 antibiotics. The wastewater samples were extracted by Oasis HLB cartridges (6mL, 500 mg), while the solid samples (sludge and suspended solid matter) were extracted by ultrasonic-assisted extraction with solvents (acetonitrile and citric acid buffer), followed by an enrichment and clean-up step with solid-phase extraction using SAX-HLB cartridges in tandem. The results showed the presence of 20 and 17 target compounds in the influents and effluents, respectively, at the concentrations ranging from low ng/L to a few μg/L. Sulfamethoxazole, norfloxacin, ofloxacin, anhydro erythromycin and trimethoprim were most frequently detected in the WWTPs wastewaters. Twenty-one antibiotics were found in the sewage sludge from the two WWTPs at the concentrations up to 5800ng/g, with tetracycline, oxytetracycline, norfloxacin and ofloxacin being the predominant antibiotics. The total mass loads of antibiotics per capita in the two plants ranged from 494 to 901 μg/d/inhabitant (672±182 μg/d/inhabitant) in the influents, from 130 to 238 μg/d/inhabitant (175±45 μg/d/inhabitant) in the effluents and from 107 to 307 μg/d/inhabitant (191±87.9 μg/d/inhabitant) in the dewatered sludge, respectively. The aqueous removals for sulfonamides, macrolides, trimethoprim, lincomycin and chloramphenicol in the WWTPs were mainly attributed to the degradation processes, while those for tetracyclines and fluoroquinolones were mainly due to the adsorption onto sludge.