The efficiency of biodegradation processes for removal of tetracycline antibacterial drugs using activated sludge and river water inocula.

Purpose: Tetracycline, chlortetracycline, and oxytetracycline are commonly prescribed antibiotics. Their extensive use results in a large stream of tetracyclines entering wastewater treatment plants (WWTPs). However, they can still be found in surface waters, which may suggest their incomplete removal in the WWTPs. The study was designed to show (i) how much of tetracyclines may be removed before they enter the environment, (ii) how tetracyclines may be removed after they enter surface water, (iii) how the presence of tetracyclines influence the metabolic activity of bacteria. Method: Degradation of tetracyclines was studied using two types of inoculum, simulating degradation in WWTPs and rivers. Cell metabolic activity was assessed to show potential risks arising from their appearance in water. Results: Complete primary degradation in the test with wastewater sludge inoculum was achieved within not more than 14 days. In the test with river water inoculum removal of both tetracycline and oxytetracycline did not exceed 20% in 28 days. Chlortetracycline was transformed rapidly but without considerable structural change. Although no considerable removal was achieved, bacterial activity in the river water test after 28 days was 10 times greater than while starting the test. Conclusions: The study shows that appropriate retention of sewage in WWTPs must be provided. Otherwise, tetracyclines will accumulate in the environment, where their removal is limited, even though bacterial activity is still relatively high.