Occurrence and partition of antibiotics in the liquid and solid phases of swine wastewater from concentrated animal feeding operations in Shandong Province, China

Swine wastewater represents an important pollution source of antibiotics in the environment; however, regional data about residual antibiotics in swine wastewater are very limited at present. This study investigated the concentrations of three classes of commonly used veterinary antibiotics, including five sulfonamides (SAs), three tetracyclines (TCs) and one macrolide (tiamulin, TIA), in swine wastewater collected from 21 concentrated animal feeding operation (CAFO) sites in Shandong Province, China. Both the liquid and solid (i.e., suspended solids) phases of swine wastewater were analyzed to determine the total concentration of each studied antibiotic. Results indicate that sulfamethazine had the highest median concentration (14.56 mu g L-1), followed by oxytetracycline (OTC, 8.05 mu g L-1) and chlortetracycline (CTC, 6.01 mu g L-1). The maximum detected concentration reached up to 2.02 mg L-1 (OTC) and the highest detection frequency was 95.1% (CTC). The median concentrations and detection frequencies of antibiotics in winter samples were generally higher than those in summer samples (except CTC). The log K-d values were in the range of 1.31-1.96 for SAs, 2.05-2.33 for TCs, and 1.54-1.58 for TIA in swine wastewater. More TCs (14-28%) preferred to partition in the solid phase than SAs (2-10%) and TIA (5-10%), indicating that the suspended solids of swine wastewater may not be ignored.