Mineralization of polystyrene nanoplastics in water by photo-Fenton oxidation

Wastewater treatment plants (WWTPs) have been identified as hotspots for the spread of micro(nano)plastics (MPs/NPs) in water. Advanced oxidation processes (AOPs) have emerged as promising alternatives for tackling MPs/NPs pollution, however, the number of studies on this topic remains quite limited and needs further research. In this study, the feasibility of the photo-Fenton process (UV/ H2O2/ Fe3+) carried out at ambient conditions and using a broad-spectrum UV-Vis lamp was investigated for the degradation of polystyrene (PS) NPs in water. The impact of the main variables of the process, namely initial PS concentration, Fe3+ concentration, initial pH, H2O2 dose and particle size, was evaluated. Under optimized operating conditions ([PS NPs]0 = 20 mg L-1; [Fe3+]0 = 1 mg L-1; [H2O2]0 = 130 mg L-1; pH0 = 3 and T = 25 ºC), complete mineralization of PS NPs (140 nm) was achieved in 40 min. The outstanding performance of the process was mainly due to the wavelength and light intensity of the UV-lamp employed. To the best of our knowledge, this is the first study in the field of photoassisted AOPs reporting the complete and fast mineralization of PS NPs in water, under ambient conditions. According to our results, photo-Fenton process can be applied to higher loads and larger particle sizes by adjusting the supplied oxidant dose and extending the reaction time. Hence, the photo-Fenton process displays great potential for producing high-quality reclaimed water and/or to be combined with a conventional separation process to treat concentrate streams and mineralize NPs at WWTPs.