The bromate formation in bromide-containing water during the Co(II)/peroxymonosulfate (PMS), Ag(I)/peroxydisulfate (PDS) and Fe(II)/persulfate (Fe(II)/PMS and Fe(II)/PDS) processes was investigated. The highest concentration of bromate was formed in the Co/PMS process, while insignificant concentration of bromate was formed in the Ag/PDS and Fe/persulfate processes. In the Co/PMS process, yields of bromate were up to 100% under test conditions, with the maximum formation at near neutral pH. The presence of NOM or chloride inhibited the formation. The bromate formation is a two-step process involving free bromine as a key intermediate. In the first step, free bromine is oxidized to bromide by sulfate radicals (SO₄^•–) and Co(III). The latter one is produced from the oxidation of Co(II) by...[ Read more ]

The bromate formation in bromide-containing water during the Co(II)/peroxymonosulfate (PMS), Ag(I)/peroxydisulfate (PDS) and Fe(II)/persulfate (Fe(II)/PMS and Fe(II)/PDS) processes was investigated. The highest concentration of bromate was formed in the Co/PMS process, while insignificant concentration of bromate was formed in the Ag/PDS and Fe/persulfate processes. In the Co/PMS process, yields of bromate were up to 100% under test conditions, with the maximum formation at near neutral pH. The presence of NOM or chloride inhibited the formation. The bromate formation is a two-step process involving free bromine as a key intermediate. In the first step, free bromine is oxidized to bromide by sulfate radicals (SO₄^•–) and Co(III). The latter one is produced from the oxidation of Co(II) by PMS and SO₄^•–. In the second step, bromate is oxidized essentially from free bromine by SO₄^•–. However, in the Ag/PDS process, the loss of soluble bromide by its precipitation with Ag(I) and the insufficient amount of SO₄^•– lead to the insignificant bromate formation. In the Fe/persulfate process, the rapid reduction of free bromine to bromide by Fe(II) results in the zero bromate formation.

The bromate formation in the Co/PMS process is significant and demands remedial actions. To control the bromate formation, four strategies including the chlorine-ammonia process, the ammonia-chlorine process, ammonia addition and Fe(II) addition, were evaluated. Increasing the ammonia, chlorine or Fe(II) dosage decreased the bromate formation. Generally the chlorine-ammonia and ammonia-chlorine processes are much more effective than ammonia addition and Fe(II) addition in controlling the bromate formation at all the tested Co(II) and bromide dosages. A 70% decrease in the bromate formation was observed in both processes with addition of 15 μM chlorine and 20 μM ammonia. The slow reaction of ammonia with free bromine at low concentration of reactive ammonia at pH 4 and fast consumption of Fe(II) lead to the ineffective control of bromate by ammonia addition and Fe(II) addition, respectively.