Efficient degradation of polyethylene (PE) plastics by a novel vacuum ultraviolet-activated periodate system: Operating parameters, by-products, and toxicity

Abstract

This article presents a vacuum ultraviolet (VUV)-activated periodate (PI) system for the degradation of polyethylene (PE) plastics for the first time. The study compares the performance of the VUV/PI with VUV/sulfite, VUV/peroxymonosulfate, and VUV/persulfate degradation systems. At an oxidant concentration of 5 mM, reaction time of 6 h, PE plastics concentration of 0.1 g/L, PE plastics size of 12 mm, and pH 7, VUV/PI degradation system attained a mass loss ratio of 3.9 %, which was higher than the other degradation systems. The mass loss ratio increased to 4.9 % at pH 3, and 6.8 % for a plastic size of 6 mm. The degradation mechanism was found to involve iodate radicals and singlet oxygen as the main reactive species. Prolonging reaction time to 120 h resulted in a mass loss percentage of 61.8 %. SEM, FTIR, and water contact angle analyses after the degradation show cracks on PE plastics surface, an increase of carbonyl index, and a decrease of hydrophobicity affirming the efficient oxidation of PE plastics by the generated reactive species. The main oxidation by-products were alcohols, esters, acids, and ketones. Cytotoxicity and phytotoxicity analyses confirmed the efficient oxidation of PE plastics by the generated reactive species to result in low toxicity of the generated intermediates. The proposed study presents a simple and effective degradation system that can be implemented on a wider scale as a tertiary treatment in wastewater treatment plants for the degradation of plastics before release to the ecosystem.