Non-catalytic and catalytic ozonation of simple halohydrins in water

Abstract

This study compares degradation of two hazardous halohydrins, namely 2,3-dibromopropan-1-ol (2,3-DBP) and 1,3-dichloro-2-propanol (1,3-DCP) by non-catalytic ozonation in acidic, neutral and basic water and catalytic ozonation with Co loaded on Fe prepared by (i) co-precipitation (Co-ppt) and (ii) a simple physical mixing (Mixed) method. The brominated halohydrin showed a higher reactivity with ozone than the chlorinated halohydrin. With uncatalysed ozonation, dehalogenation rate of both pollutants improved with increase in hydroxide ion concentration, however, complete removal of total organic carbon (TOC) and efficient organic by-product (Org-BP) minimization could not be achieved. Bromide ion oxidation to bromate ion was slower in acidic water, but increased as the hydroxide ion content increased. Ozonation in the presence of Fe:Co (Co-ppt) and Fe:Co (Mixed) catalyst enhanced substrate degradation, TOC removal and considerably minimized Org-BP formation. BET and SEM data revealed that Fe:Co (Co-ppt) catalyst has better textural properties compared to Fe:Co (Mixed) catalyst, and it displayed superior catalytic activity for degradation of toxic pollutants and Org-BP minimization. The Fe:Co (Mixed) catalyst was able to significantly suppress the formation of toxic bromate through lowering of solution pH from 6.8 to 5.7. Unlike bromide, the chloride ion was found be refractory during ozonation. NH3-TPD analysis and pZc values indicate that Fe alone has negligible acidic sites, while 9:1 Fe:Co (Co-ppt) has more acidic sites (6 cm3 g−1 STP) than 9:1 Fe:Co (Mixed) (2 cm3 g−1 STP) catalyst, hence promoting the decomposition of ozone to hydroxyl radicals on the Fe:Co (Co-ppt) surface.