Catalytic ozonation of hazardous halogenated compounds with mixed-metal oxides.

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.