Formation Of Brominated By-products In Thermo Activated Persulfate Oxidation Processes

Sulfate radicals(SO₄^·-)are applied to degrade various organic pollutants.Due to its high oxidative potential,SO₄^·-is presumed to be able to transform bromide to reactive bromine species that can react with natural organic matter subsequently to form brominated products including brominated disinfection by-products?Br-DBPs?,which are proven to cause notable health risks and regulated world widely.In this,significant formation of bromoform and bromoacetic acids was verified in thermo activated persulfate oxidation process in the presence of bromide and humic acid?HA?.Yields of Br-DBPs increased monotonically at persulfate concentration of 1.0 mmol L-1 and working temperature of 70?.However,the time-depended formation profiles exhibited and increased and the decreased trend when persulfate was 5.0 mmol L-1,suggesting further degradation of organic bromine.HPLC/ICP-MS analysis demonstrated that the organic bromine eventually transformed to bromate at this condition.Thus,a transformation scheme was proposed in which the bromine could be recycled multiple times between inorganic bromide and organic bromine before finally transformed to bromate.when an oxidant excessive scenario in the treatment,bromide can be quantitatively transformed to bromate eventually,otherwise the final products of the reaction will be Br-DBPs.Phthalic acid and 3,5-dihydroxyl benzoic acid were seleted as humic acid model compounds to explore the formation mechanism of DBPs in persulfate oxidation processes.Phthalic acid generates almost no DBPs in bromination process while generates high yields of DBPs in the thermally activated persulfate oxidation process.This suggested that DBP precursors of phenolic feature could be temporarily generated through the oxidation of PA by SO₄^·-.Salicylic acid was detected as an intermediate of such function.This research revealed a DBP formation pathway potentially occurred SO₄^·-based oxidation but not conventional halogenation processes.Such a pathway has not been reported so far and highlights the potential risks associated with SO₄^·-based oxidation processes in the treatment of environmental matrices containing halides.