Catalytic ozonation of hazardous halogenated compounds with mixed-metal oxides.
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Date
2018
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Abstract
The study compares degradation of four hazardous halogenated pollutants, namely 2,3-DBP,
1,3-DCP, 2,4,6-TBP and 2,4-DCPA Acid in water, by ozonation alone and catalytic ozonation
using Co and Ni loaded on Fe respectively by co-precipitation and a simple mixing method.
The brominated pollutants showed a higher reactivity during ozonation than the chlorinated
pollutants. In ozonation alone dehalogenation of each compound improved with an increase in
the amount of hydroxide ions. TOC removal and DBP minimization was difficult to achieve in
ozonation alone, however, in catalytic ozonation with Fe:Co (Co-ppt) and Fe:Ni (Co-ppt)
significant improvements were noted. Fe:Ni (Co-ppt) catalyst material showed the best activity
for conversion of the pollutants, TOC removal and DBP minimization in water during ozone
treatment. BET and SEM data showed that the mixed metal oxides catalyst prepared by coprecipitation
had better textural properties than the mixed metal oxide catalyst prepared by
simple mixing, hence more superior catalytic activity for degradation of pollutants, TOC
removal and DBP minimization, however, Fe:Co (Mixed) was the only catalyst material to
effectively minimize bromate formation through lowering of solution pH. The chloride ion was
found be refractory towards ozone, which is an added advantage during water treatment
processes. NH3-TPD analysis and pZc values reveal that Fe alone has negligible acidic sites,
whereas, Fe:Co (Co-ppt) and Fe:Ni (Co-ppt) have more acidic sites than Fe:Co (Mixed) and
Fe:Ni (Mixed), hence improved decomposition of ozone to hydroxyl radicals on these active
sites. The presence of 𝐻2𝑂2 showed an improvement in the debromination efficiency of 2,4,6-
TBP. TOC data indicated that total mineralization of OBP’s occurred in the 𝑂3/𝐻2𝑂2 process,
which was not achievable in ozonation alone. Only 10% 𝐻2𝑂2 was able to effectively lessen
𝐵𝑟𝑂3
− formation. In basic water both 2,4,6-TBP conversion and TOC removal decreased with
an increase in 𝐶𝑂3
2−, hence minimizing 𝐵𝑟𝑂3
− formation.
Description
Doctoral Degree. University of KwaZulu-Natal, Durban.