Temperature effects on ozonation: Impacts on kinetics of organic amines abatement, bromate formation and disinfection

• E a for O 3 reactions with neutral aliphatic amines were determined to be ∼75 kJ/mol • Dehydration of amine group during O 3 attack accounts for its relatively high E a • Temperature effect on micropollutants abatement during ozonation is assessed • E a for BrO 3 − formation during ozonation depends on R ct values of water matrices Ozonation has been applied in water treatment for disinfection and micropollutant abatement for decades. However, rate constants for predicting ozonation performance have been mostly measured at room temperature. To investigate the temperature effect on ozonation, the activation energies ( E a ) for ozonation of amine moieties and bromate formation have been investigated in this study and compared to other ozone reactive organic moieties as well as disinfection by ozone. The temperature dependence of second-order rate constants for ozone reactions with model aliphatic amines and micropollutants containing amino groups as the main reactive sites has been investigated in presence of an • OH scavenger ( tert -butanol) resulting in activation energies, E a of 75±10 kJ/mol. This is relatively high compared to E a (∼30 kJ/mol) for phenols, anilines and olefins. This difference could be ascribed to the strong hydration of amine moieties in water with a higher energy input for water exchange during ozone attack. For micropollutants with high reactivity with ozone, temperature has a negligible impact on their abatement. For those with moderate or low ozone reactivity, a comparison of E a for target compound oxidation and for ozone decrease in real water matrices is needed to access the overall temperature effect. The temperature effect on the tradeoff between micropollutants oxidation or microorganism inactivation and bromate formation during ozonation depends on their relative E a , and the overall E a of bromate formation depends on the R c t value (ratio of • OH exposure to O 3 exposure). For water matrices with low R c t values (< 5 × 10 −9 , e.g. lake water), where ozone reactions are more important, the ozone oxidation or disinfection efficiency ( E a = 20–100 kJ/mol) at different temperatures can be maintained without increase of bromate formation risk ( E a = ∼100 kJ/mol). However, bromate formation in high R c t water (> 1 × 10 −8 , e.g. WWTP effluent), where • OH dominates the reaction, may be problematic at low temperature due to its low E a (∼30 kJ/mol) and bromate mitigation approaches may be needed.