Degradation of organophosphate esters by UV/persulfate: Kinetic, mechanistic and toxicity evaluation

Abstract

With the ban of brominated flame retardants, organophosphate esters (OPEs) have been widely used. The ultraviolet combined sodium persulfate (UV/PS) process is a promising advanced oxidation process (AOPs), which effectively removes organic micropollutants by generating various reactive substances such as hydroxyl radical (•OH) and sulfate radical (SO• 4−). The degradation kinetics, influencing factors, degradation path, and toxicity of three organic phosphates, trimethyl phosphate (TMP), tris (2-chloroethyl) phosphate (TCEP) and triphenyl phosphine oxide (TPPO) were studied. The results showed that UV/PS could degrade OPEs efficiently, and 254 nm UV light was more conducive to the degradation of OPEs than 365 nm UV light, and the degradation of OPEs accelerated with the increase of PS concentration. Under acidic and neutral conditions, UV/PS was more conducive to the degradation of OPEs, and the concentration of NOM was inversely proportional to the degradation rate of OPEs, Cl− and SO42− had almost no effect on the degradation of OPEs, while HCO3− has an inhibitory effect on the degradation of OPEs. UV/PS also has a good effect on the degradation of OPEs in actual water. •OH and SO• 4−, as the main reactive radicals, participate in the degradation of OPEs. Hydroxylation, debenzene ring, demethylation, and ring opening reactions are the main reactions occurring in the process of OPEs degradation. The theoretical toxicity value of most intermediates is lower than that of the initial OPEs. This study reveals the transformation of OPEs in the UV/PS system and provides a new idea for wastewater treatment of OPEs.