Comprehensive study on the formation of brominated byproducts during heat-activated persulfate degradation

Abstract

Applying the highly oxidative sulfate radical (SO4-·) to pollutant degradation may cause it to react with the coexisting bromide (Br−) to form undesired byproducts. This study investigated the transformation of Br− during the degradation process of a contaminant (diethyl phthalate (DEP)) via heat-activated persulfate (PS). Dibromoacetonitrile and bromoform formed with Br− and natural organic matter (NOM) in the solution, while only bromoform was detected without NOM. The formation of these brominated disinfection byproducts (Br-DBPs) can be ascribed to the reactions between the phenolic groups of DEP degradation intermediates or NOM and reactive bromine species (free bromine and radical bromine) generated through the oxidation of Br− by SO4-·. Br-DBPs were degraded by excessive SO4-·, which indicates that organic bromine is a temporary phase during the turnover of Br−. The time-dependent formation of organic and inorganic bromines suggests that Br− may have cycled several times between organic and inorganic forms before eventually turning into bromate. The bromate formation showed a lag phase before continuously increasing. Generally, increasing the temperature, PS dosage, and Br− and organic matter (DEP and NOM) concentrations increased the maximum concentration of Br-DBPs. Additionally, these reaction parameters facilitated bromate formation except for organic matter, whose inhibitory effect is probably due to the consumption of reactive species by organic matter and the generated superoxide anion. The total organic carbon concentration of the solution exhibited a relatively quick reduction followed by a slow decrease. These results highlight the potential risks of PS activation technologies and can help prevent such risks in actual practice.