Research On The Influence Of Catalytic Ozonation On Bromate Formation

Ozone is used more and widely in water treatment as an efficient techniquerecently. However, ozonation has some deficiencies, such as the poor removalability of recalcitrant organic pollutants, and the formation of bromate whenozone is used in water containing bromide. Catalytic ozonation in the presence ofmetal oxides has many advantages compared to solelyozonation, and it's feasibleto substitute ozonation in existence technique. The understanding of bromateformation in metal-oxides catalyzed ozonation is important for the practicalapplication of catalytic ozonation and the control of bromate formation inozonation. The contents in this dissertation consist of the following: 1.Development a method to determe of inorganic-bromine in water (bromide,hypobromide, and bromate). 2. The influence of different metal oxides catalyticozonation on bromate formation. 3. The effect of cerium dioxide catalyticozonation on bromate formation in different reaction parameters.Methods for the determination of trace bromate, bromide and hypobromitein water by HPLC-UV were set up. In strong acid solutions, bromate can reactwith bromide and then with phenol. The product is 4-bromophenol, which hasgood linear relationship with bromate, bromide and hypobromite concentrationsin a certainly range. The interference of hypobromite in the determination ofbromate and bromide is overcome by controlling devertization condition. Thechemical quantitative relation of bromate, bromide and phenol is fixed.The influences of MgO, Fe2O3 and CeO2 catalytic ozonation on bromateformation were significantly different. In pure water, the addition of magnesiaand ferric oxide can increase bromate formation, while the addition of ceriumdioxide can significantly reduce bromate formation. In HOA solutions, theinfluence of catalytic ozonation on bromate formation was weakened for theexistence of organics, and the ability of cerium dioxide on bromate formationcontrol was restrained.The effect of catalyst dose, bromide concentration, water pH, andtemperature on bromate reduction during catalytic ozonation was discussed whilethe principle of bromate formation reduction was also studied. The low bromate formation in catalytic ozonation is due to the inhibition of the reaction betweenmolecular ozone and hypobromite by cerium oxide. Since the inhibition ofbromate formation in catalytic ozonation was weakened when sulfate coordinatedwith surface Ce (IV) of cerium oxide, the function of the catalyst should berelated with surface Ce (IV) sites. Lab scale experiments show that catalyticozonation can decrease 85% bromate formation by increasing cerium oxidedosage from 0mg/L to 250mg/L. Catalytic ozonation can decrease 69.2%, 82.5%and 15.2% bromate formation when the bromide concentrations are 0.5, 1.0 and2.0mg/L respectively. It is not clear that the effect of bromide concentration onthe reduction of bromate in the catalytic ozonation. The increase of water pHshows negative effect on reducing bromate in the catalytic ozonation. Catalyticozonation can decrease 43%～59% bromate formation while the temperature isin the range of 5℃～25℃(Bromide concentration is 1.5mg/L). Thetemperature of water has no significant influence on the inhibition of bromateformation in catalytic ozonation.