Erythromycin oxidation and ERY-resistant Escherichia coli inactivation in urban wastewater by sulfate radical-based oxidation process under UV-C irradiation

Abstract

This study evaluates the feasibility of UV-C-driven advanced oxidation process induced by sulfate radicals (SO4-) in degrading erythromycin (ERY) in secondary treated wastewater. The results revealed that 10 mg L-1 of sodium persulfate (SPS) can result in rapid and complete antibiotic degradation within 90 min of irradiation, while ERY decay exhibited a pseudo-first-order kinetics pattern under the different experimental conditions applied. ERY degradation rate was strongly affected by the chemical composition of the aqueous matrix and it decreased in the order of: ultrapure water (kapp = 0.55 min-1) > bottled water (kapp = 0.26 min-1) > humic acid solution (kapp = 0.05 min-1) > wastewater effluents (kapp = 0.03 min-1). Inherent pH conditions (i.e. pH 8) yielded an increased ERY degradation rate, compared to that observed at pH 3 and 5. The contribution of hydroxyl and sulfate radicals (HO and SO4-) on ERY degradation was found to be ca. 37% and 63%, respectively. Seven transformation products (TPs) were tentatively elucidated during ERY oxidation, with the 14-membered lactone ring of the ERY molecule being intact in all cases. The observed phytotoxicity against the tested plant species can potentially be attributed to the dissolved effluent organic matter (dEfOM) present in wastewater effluents and its associated-oxidation products and not to the TPs generated from the oxidation of ERY. This study evidences the potential use of the UV-C/SPS process in producing a final treated effluent with lower phytotoxicity (<10%) compared to the untreated wastewater. Finally, under the optimum experimental conditions, the UV-C/SPS process resulted in total inactivation of ERY-resistant Escherichia coli within 90 min.

•Erythromycin was completely degraded during UV-C-activated persulfate oxidation.•ERY degradation was affected by the oxidant dose, pH and aqueous matrix composition.•Seven transformation products were identified retaining the ERY lactone ring.•Organic matter and its oxidation products were responsible for phytotoxicity.•ERY-resistant E. coli cells were eliminated at the end of the treatment.