Performance of different peroxide sources and UV-C radiation for the degradation of microcontaminants in tertiary effluent from a municipal wastewater treatment plant

Abstract

Microcontaminants present in environmental aqueous matrices represent an emerging concern due to their recalcitrance to conventional wastewater treatment. This study aimed to (i) investigate the degradation of a mixture containing benzophenone-3, fipronil and propylparaben in a tertiary municipal wastewater effluent (100 µg L−1 each) by UV-C, UV-C/H2O2, UV−C/S2O82− and UV−C/HSO5− , and (ii) compare the degradation profile of this mixture with that of naproxen (a compound that reacts preferentially by electron transfer). Regarding the mixture, degradation increased from 50% (UV-C) to 74–87% by coupling UV-C with peroxides under the best peroxide concentration (400 μmol L−1) due to the generation of hydroxyl (HO•) and sulfate (SO4•−) radicals. In addition, the degradation efficiency was strongly dependent on the structure of the target compound, pH and peroxide source. Although high pseudo-first-order rate constants (kobs) were obtained at pH 3.0 for all peroxides, higher kobs were obtained at pH 7.0 (natural matrix pH) in the presence of H2O2. Kobs calculated for mixture degradation using different peroxides at pH 7 showed the following order: UV-C/H2O2 > UV−C/HSO5− >UV−C/S2O82−. In contrast, an opposite profile was observed for naproxen degradation (UV−C/S2O82− >UV−C/HSO5− > UV-C/H2O2). Finally, the analysis of energy efficiency and treatment costs showed that UV-C/H2O2 is highly cost-effective.