Effect of solar photo-Fenton process in raceway pond reactors at neutral pH on antibiotic resistance determinants in secondary treated urban wastewater

Abstract

Solar photo-Fenton process in raceway pond reactors was investigated at neutral pH as a sustainable tertiary treatment of real urban wastewater. In particular, the effect on antibiotic resistance determinants was evaluated. An effective inactivation of different wild bacterial populations was achieved considering total and cefotaxime resistant bacteria. The detection limit (1 CFU mL^-1) was achieved in the range 80-100 min (5.4-6.7 kJ L^-1 of cumulative solar energy required) for Total Coliforms (TC) (40-60 min for resistant TC, 4.3-5.2 kJ L^-1), 60-80 min (4.5-5.4 kJ L^-1) for Escherichia coli (E. coli) (40 min for resistant E. coli, 4.1-4.7 kJ L^-1) and 40-60 min (3.9-4.5 kJ L^-1) for Enterococcus sp. (Entero) (30-40 min for resistant Entero, 3.2-3.8 kJ L^-1) with 20 mg L^-1 Fe²⁺ and 50 mg L^-1 H₂O₂. Under these mild oxidation conditions, 7 out of the 10 detected antibiotics were effectively removed (60-100%). As the removal of antibiotic resistance genes (ARGs) is of concern, no conclusive results were obtained, as sulfonamide resistance gene was reduced to some extent (relative abundance <1), meanwhile class 1 integron intI1 and ß-lactam resistance genes were not affected. Accordingly, more research and likely more intensive oxidative conditions are needed for an efficient ARGs removal.

Keywords: Antibiotic resistance genes; Antibiotic resistant bacteria; Raceway pond reactor; Solar photo-Fenton; Urban wastewater.