Oxidative debromination of 2,2-bis(bromomethyl)-1,3-propanediol by UV/persulfate process and corresponding formation of brominated by-products

This study investigated the oxidative debromination of 2,2-bis(bromomethyl)-1,3-propanediol (BBMP), a widely used brominated flame retardant, and the corresponding formation of brominated by-products by the UV/persulfate process. The debromination of BBMP by the UV/persulfate process was primarily driven by sulfate radicals (SO4 center dot-) at pHs 4.0-6.0 and hydroxyl radicals (HO center dot) at pHs 9.0-12.0. The debromination rate increased with increasing pH from 4.0 to 9.0 and remained the same at pHs 9.0 and 12.0. Bromate was formed through the oxidation of bromide released from BBMP mainly by SO4 center dot-, with free bromine as a key intermediate. Bromate formation increased with increasing pH from 4.0 to 6.0, while it remarkably decreased with increasing pH from 6.0 to 12.0. This was mainly due to the transformation of SO4 center dot- to HO center dot and also the quenching of bromine atoms that were the key intermediate for the formation of free bromine, by hydroxyl ions at the alkaline pH. In addition, the oxidative debromination of BBMP resulted in a significant decrease in the concentrations of total organic bromine, but the formation of brominated acetic acids and unknown brominated organic by-products. The concentrations of brominated organic by-products firstly increased and then decreased with prolonged reaction time. Also, the formation of brominated organic by-products and genotoxicity at pH 9.0 were much lower than that at pH 6.0. In this study, we propose that the UV/persulfate process under mildly alkaline conditions not only debrominates BBMP efficiently but also eliminates the formation of bromate and brominated organic by-products and genotoxicity. (C) 2019 Elsevier Ltd. All rights reserved.`