Oxidation of bromide by heat-activated persulfate – Effects of temperature and the organic matter surrogate phenol on kinetics and stoichiometry

Abstract Reaction mechanisms of sulfate radical with bromide and organic substances can be largely altered at elevated temperature in heat-activated persulfate process due to different activation energies. This study investigated kinetics and stoichiometry of bromide oxidation in the heat-activated persulfate process. We postulated that reaction of sulfate radical with persulfate, which has relatively low reaction rate (6.3×105 M–1s–1), may become an important reaction at elevated temperatures. Persulfate decomposition was inhibited in the presence of sulfate radical scavenger phenol at low temperature (40℃) whereas phenol affected persulfate decomposition only at 50°C, which can be explained by a high activation energy (estimated activation energy: 311 kJ/mol). Bromate formation was inhibited in the presence of phenol. However, phenol oxidation was not affected by the presence of Br–, even though Br– reacts faster with sulfate radicals than phenol and was present in excess. This indicated that formed reactive bromine species such as Br• and Br2•– oxidize phenol under reformation of bromide. Formation of insoluble products was also observed indicating polymerization of phenol. This can be explained by lack of dissolved oxygen under conditions of heat-activation.