Formation of Bromate and Other Brominated Disinfection Byproducts during the Treatment of Waters Using a Hybrid Ozonation-Membrane Filtration System

Abstract

<p>In this research, ozone hydrodynamics and disinfection by-products formation in a novel hybrid ozonation-ceramic membrane filtration system was studied to minimize membrane fouling while also ensuring that the system meets regulatory criteria for disinfection by-products. The influence of important operating parameters including inlet ozone mass injection rate, initial bromide concentration, membrane molecular weight cut off (MWCO), membrane coating, hydroxyl radical scavenger (<em>t</em>-butanol), pH, and temperature on bromate concentration in the absence and presence of natural organic matter (NOM) was examined. Experiments were also conducted under various operating conditions to investigate the formation of total trihalomethanes (TTHMs) and halo-acetic acids (HAAs) in the water distribution system due to post chlorination. Moreover, variations in the TOC, UV₂₅₄, color and turbidity with respect to operating parameters were monitored.</p> <p>Bromate and TTHMs formation increased with increasing ozone mass injection rate, and initial bromide concentration. An increase in the bromate concentration was observed with decreasing membrane MWCO. Less bromate and TTHM was formed with the coated membrane and <em>t</em>-butanol significantly reduced bromate and TTHM formation. Bromate formation decreased significantly with decreasing pH. Increasing the temperature resulted in enhanced bromate formation. NOM exerted a favorable effect on bromate formation as the bromate concentration was observed to decrease as the NOM content was increased.</p> <p>Experimental results indicated that ozonation can greatly reduce color and turbidity of water and can be used to overcome membrane fouling. Ensuring a minimum ozone residual in the system enables the continuous treatment of water at a relatively high permeate flux (up to 85% of the clean water flux) and eliminates the need for membrane cleaning procedures.</p> <p>An empirical model was developed to predict bromate formation in the hybrid ozone- membrane system (R²=0.903). Theoretical models were developed to estimate the rate of bromate formation and to describe the ozone mass transfer in a hybrid system. In all cases, good correlation between the model predictions and the experimental data was achieved.</p>