Anaerobic Treatment of Antibiotic Production Wastewater Pretreated with Enhanced Hydrolysis: Simultaneous Reduction of COD and ARGs

The presence of high concentration antibiotics in wastewater can disturb the stability of biological wastewater treatment systems and promote generation of antibiotic resistance genes (ARGs) during the treatment. To solve this problem, a pilot system consisting of enhanced hydrolysis pretreatment and an up-flow anaerobic sludge bed (UASB) reactor in succession was constructed for treating oxytetracycline production wastewater, and the performance was evaluated in a pharmaceutical factory in comparison with a full-scale anaerobic system operated in parallel. After enhanced hydrolysis under conditions of pH 7 and 85 oC for 6 h, oxytetracycline production wastewater with an influent chemical oxygen demand (COD) of 11,086 ± 602 mg L-1 was directly introduced into the pilot UASB reactor. With the effective removal of oxytetracycline and its antibacterial activity (from 874 and 900 mg L-1 to less than 0.61 and 0.84 mg L-1, respectively) by the enhanced hydrolysis pretreatment, a COD removal between 68.9 % and 83.2 % was achieved at an organic loading rate ranging from 3.3 to 5.9 kg m-3 d-1. At the same time, the relative abundances of the total tet genes and a mobile element (Class 1 integron) in anaerobic sludge on Day 96 were one order of magnitude lower than those inoculated on Day 0 (P< 0.01). The reduction of ARGs was further demonstrated by metagenomic sequencing. By comparison, the full-scale anaerobic system treating oxytetracycline production wastewater with an influent COD of 3,720 ± 128 mg L-1 after dilution exhibited a COD removal of 51 ± 4 % at an OLR 1.2 ± 0.2 kg m-3 d-1, and a total tet gene abundance in sludge was five times higher than the pilot-scale system (P< 0.01). The above result demonstrated that enhanced hydrolysis as a pretreatment method could enable efficient anaerobic treatment of oxytetracycline production wastewater containing high concentrations of oxytetracycline with significantly lower generation of ARGs.