Long-term Effect of Trimethoprim on Nitrification of Aerobic Activated Sludge

The long-term effect of trimethoprim (TMP) on aerobic activated sludge was explored by investigating the changes of nitrification, microstructure and microbial community composition of the activated sludge. Different concentrations of TMP inhibited the removal of ammonia nitrogen during long-term operation. However, removal ability of ammonia nitrogen could be gradually recovered and returned to stable after 25 days. Typical cycle experiments were conducted after 30 days of continuous operation. The results indicated that the nitrification performance was still inhibited to some extent under different TMP concentrations during a cycle. However, ammonia nitrogen could be stably removed at the end of one cycle. In addition, nitrite nitrogen was accumulated under high concentration of TMP (10 mg/L). Scanning electron microscopy showed that the breaking degree of sludge floc was more serious and the particles were smaller with the increase of TMP concentration. The analysis of microbial community composition showed that Actinobacteria had better tolerance to TMP than Bacteroidetes. In addition, the relative abundance of Nitrospirae increased from 0.84% to 1.60% with the increase of TMP concentration, indicating that Nitrospirae was more resistant to TMP. At the genus level, TMP had the most obvious inhibition on Flavobacterium.