Evaluating the removal and impacts of combined tetracycline, oxytetracycline, sulfadiazine, and norfloxacin during swine manure storage process at ambient temperatures

Manure storage is widely applied in intensive livestock regions with reporting elevated concentrations of combined veterinary antibiotics (CVAs), which raised serious environmental concerns. Four antibiotics (tetracycline (TC), oxytetracycline (OTC), sulfadiazine (SDZ), and norfloxacin (Norf)) were combined and their removal, fate and impacts on swine manure storage process under ambient temperatures for 90 days were examined. The results showed that temperature level, retention time, and CVAs' initial concentration significantly affected the biodegradation rates of CVAs and governed its impacts on the storage process stability. The storage temperatures of > 20 degrees C maximized the removal of CVAs, while it was minimized at 6 degrees C. The maximum removal efficiency of OTC was 94.8%, while 82.4%, 66.1%, and 61.4% were observed, respectively, for Norf, TC, and SDZ. However, no effective removal performance was achieved after day 60th for Norf and TC. Antibiotics degradation's halflives ranged from 26 to 150 d, affected by temperature level and CVAs' initial concentration. Due to a prolonged storage time, CVAs showed slight negative effects on swine manure's physicochemical properties (pH, COD, VFAs, TAN, and TN). According to the microbial diversity, Clostridium sensu stricto, Leucobacter, Advenella, Corynebacterium, and Turicibacter were the most dominant bacterial community abundance, where their abundance was enhanced by improving CVAs degradation. The recommended swine manure storage temperature was > 20 degrees C, with at least 60 days of incubation to facilitate the removal of CVAs and unstimulating their relative effects.