Formation and reverse osmosis removal of bromate ions during ozonation of groundwater in coastal areas

The generation of bromate ions during ozonation of groundwater samples affected by seawater intrusion was investigated. The ozone-water contact times studied were 2.5, 5, 10, 15, and 30 min, while the applied ozone rate was 4.5 mg/ min. Generation of bromate ions started right after the application of ozone. The level of bromates increased with time as more ozone was added to the reactor. Even after 30 min of ozonation, the concentration of bromates kept rising without reaching a plateau. The higher the initial concentration of bromide ions, the higher the level of bromate ions in the ozonated water sample. The experimental results obtained during ozonation of the specific groundwater samples ( low TOC and low ammonia concentrations) were used in order to develop a mathematical model capable of forecasting the generation of bromate ions. The empirical model containing two independent variables, conductivity and contact time, was: [BrO3-] = e(-10,157)*[Conductivity ](1,5466) *[Contact Time](0, 94031); R-2 = 0.8568 This model allows the prediction of bromate ion generation, when the groundwater conductivity and the contact time are known, for an ozone application rate around 4.5 mg/ min. Finally, the ozonated water was treated by reverse osmosis. The removal of bromate ions reached 96.1%. Equivalent reduction in the conductivity of the water was also achieved.