Fate of tetracycline in enhanced biological nutrient removal process

This study investigated the fate of tetracycline at four different concentrations of 20 μg L^-1, 50 μg L^-1, 2 and 5 mg L^-1 in the enhanced biological nutrient removal processes. At the tetracycline concentration below 50 μg L^-1, no obvious inhibition on the biological N&P removal was observed, while the inhibition appeared after the tetracycline concentration was increased to 2 and 5 mg L^-1. It was found that about 44%-87% of tetracycline was removed through biodegradation, while only 3%-6% of removal was due to biosorption. These results clearly suggested that a substantial amount of tetracycline eventually ended up in sludge with the tetracycline content of 23 mg to 4.5 g kg^-1 sludge depending on the tetracycline concentration. Obviously, this could pose an emerging challenge to the post sludge disposal and reuse. Furthermore, phthalic anhydride was detected as a biodegradation byproduct of tetracycline, which has been known to be more toxic than tetracycline to aquatic organisms. Consequently, this study offers in-depth insights into the fate of tetracycline in the enhanced biological nutrient removal process, highlighting on the emerging ecological risks associated with sludge disposal and effluent discharge.