This work describes a systematic approach to the development of a method for simultaneous determination of three classes of veterinary antibiotics in the suspended solids （SS） of swine wastewater, including five sulfonamides, three tetracyclines and one macrolide （tiamulin）. The entire procedures for sample pretreatment, ultrasonic extraction （USE）, solid-phase extraction （SPE）, and liquid chromatography-mass spectrometry （LC-MS） quantification were examined and optimized. The recovery efficiencies were found to be 76%-104% for sulfonamides, 81%-112% for tetracyclines, and 51%--64% for tiamulin at three spiking levels. The intra-day and inter-day precisions, as expressed by the relative standard deviation （RSD）, were below 17%. The method detection limits （MDLs） were between 0.14 and 7.14 μg/kg, depending on a specific antibiotic studied. The developed method was applied to field samples collected from three concentrated swine feeding plants located in Beijing, Shanghai and Shandong province of China. All the investigated antibiotics were detected in both SS and liquid phase of swine wastewater, with partition coefficients （logKd） ranging from 0.49 to 2.30. This study demonstrates that the SS can not be ignored when determining the concentrations of antibiotics in swine wastewater.
Three lab-scale vertical-flow constructed wetlands （VFCWs）, including the non-aerated （NA）, intermittently aerated （IA） and continuously aerated （CA） ones, were operated at different hydraulic loading rates （HLRs） to evaluate the effect of artificial aeration on the treatment efficiency of heavily polluted river water. Results indicated that artificial aeration increased the dissolved oxygen （DO） concentrations in IA and CA, which significantly favored the removal of organic matter and NH4＋-N. The DO grads caused by intermittent aeration formed aerobic and anoxic regions in IA and thus promoted the removal of total nitrogen （TN）. Although the removal efficiencies of CODEr, NH4＋-N and TN in the three VFCWs all decreased with an increase in HLR, artificial aeration enhanced the reactor resistance to the fluctuation of pollutant loadings. The maximal removal efficiencies of CODEr, NH4＋-N and total phosphorus （TP） （i.e., 81%, 87% and 37%, respectively） were observed in CA at 19 cm/day HLR, while the maximal TN removal （i.e., 57%） was achieved in IA. Although the improvement of artificial aeration on TP removal was limited, this study has demonstrated the feasibility of applying artificial aeration to VFCWs treating polluted river water, particularly at a high HLR.
