Hybrid ozonation-ultrafiltration: The formation of bromate in waters containing natural organic matter

The effect of pH, inlet ozone injection rate, initial bromide concentration, membrane coating, hydroxyl radical scavenger, and membrane molecular weight cut off (MWCO) on the formation of bromate in a hybrid membrane filtration-ozonation reactor treating water containing bromide and natural organic matter (NOM) was studied. Variations in the TOC, UV254, SUVA (specific UV absorbance), color and turbidity of water as a function of these parameters were investigated. Bromate formation increased with increasing inlet gaseous ozone injection rate, and initial bromide concentration. The extent of bromate formation decreased with decreasing pH, with increasing TOC concentration, and in the presence of tertiary butyl alcohol (t-BuOH), an OH radical scavenger. The bromate concentrations that were observed with the Mn oxide coated membrane were less than that formed with the TiO2 membrane. An increase in the bromate concentration was observed with decreasing MWCO of the filtration membrane. Consistent with earlier work, experimental results indicated that ozonation can be used to mitigate membrane fouling. If dissolved ozone is present in the system, continuous operation of the hybrid ozonation-membrane filtration system at a permeate flux comparable to the clean water permeate flux can be achieved. An empirical model was developed using multiple linear regression method to estimate bromate formation in the system as a function of bromide concentration, dissolved organic carbon (DOC) concentration, inlet ozone injection rate, pH, and reaction time. Good correlation was achieved between the model predictions and the experimental data. According to the model, bromate formation was favored as bromide concentration, ozone injection rate, and pH increased. However, an increase in DOC concentration reduced bromate formation.