Study on removal of bromate by activated carbon By Weifang Chen.

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Study on removal of bromate by activated carbon By Weifang Chen

Benefits of ozonation a. Prevents the production of halogenated DBP b. Improve flocculation c. Help remove natural and synthetic organic compounds such as taste and odor compounds, pesticides. Disadvantages of ozonation a. Larger amount of aldehydes and other oxidized organic byproducts than chlorination b.Inorganic by-products. potential of formation of bromate (BrO 3 - ) during ozonation of raw waters containing bromide ion (Br - )

Mechanism of bromate ion formation HOBr/OBr - Br - O3O3 O3O3 BrO 3 - Disproportionation BrO·BrO 2 - BrO 3 - BrO 2 · · OH O3O3 Br 2 - CO 3 - ·

Regulations on bromate ion Bromate is a possible carcinogen, cause kidney, and possibly other tumors WHO: Maximum 25  g/L USA and EU: less than10  g /L.

Treatment of bromate ion Minimization strategies a. pH depression/acid addition influence the speciation of HOBr/OBr - high cost for high-alkalinity water b. Ammonia addition react with HOBr/OBr - to form bromamine c. Radical scavenger addition ethanol, formate, acetate, oxalate, and glucose do not react with molecular ozone but with OH radicals.

Removal strategiesRemoval strategies a. Ferrous iron b. Ultraviolet irradiation c. High-energy electron beam irradiation d. Heterogeneous redox catalysis e. Ion exchange f. Activated carbon

Strategies for removal of bromate ion TechniqueCondition requiredEffectivenessCapital cost Fe 2+ reductionDO: 10mg/L PH< % reduction, works as coagulant Low Powered activated carbon (PAC) (Flocculator) Contact time: 30-60min Dose=25-50mg/L PAC specific 10-30% reduction Remove DOC Moderate GACLow total dissolved solids, Treated water GAC specific % removal Remove DOC, Remove SOCs Moderate Ion exchangeLow total dissolved solids, Low DOC water 100% removalModerate UV irradiationDOC<2mg/L, low alkalinity, Contact time10-30s %removal No pH effect Ease of maintenance Added disinfection Low Electron beam krads Contact time:20s % removal TOC removal Added disinfection High

AC removal mechanism adsorption and reduction

Factors influence the removal of bromate by activated carbon Carbon surface chemistry carbon with higher PZC has the higher capacity Carbon #pHpzcCapacity (mg BrO 3 - /gCarbon) <0.1

Solution pH (1) reactivity of bromate ion is higher at low pH (2) surface charge positive at low pH

NOM and other inorganic anions (1) block the access to the pores (2) competition for active sites on carbon surfaces

Conclusions 1.Bromate ion occurs through both a molecular ozone and a free radical pathway. 2.pH depression, addition of ammonia or OH radical scavenger are possible ways to limit the formation of bromate ion during ozonation. 3.Fe 2+ reduction, activated carbon adsorption, ion exchange, UV irradiation and electron beam have been used in various scales to remove the bromate.

Conclusions 4.Mechanism of removal of bromate ion by activated carbon is first adsorption of bromate ion onto the activated carbon and then reduced to Br Carbon surface chemistry, solution, and NOM and anions in water can affect the performance of activated carbon.