Effect of preozonation on flux and water quality in ozonation-ultrafiltration hybrid system for water treatment

The effect of ozonation on membrane flux and water quality was investigated in an ozonation ultrafiltration (UF) hybrid system. Crossflow UF was performed in total recycle mode to study the effect of ozonation on membrane fouling and disinfection by-product formation potentials of organics. Total organic carbon (TOC), UV absorbance at 254 nm (UV254) and trihalomethane formation potential (THMFP) were measured as water quality parameters. The effect of ozonation on membrane flux was found to be largely dependent on raw water quality as well as ozone dose. In case of upstream water (A), preozonation achieved significant flux enhancement regardless of ozone dose. Whereas, for the downstream water (B), the steady state flux was increased or decreased depending on ozone dose. The analysis based on the resistance-in-series model provided the mechanistic interpretation on the membrane flux variation. Ozonation in an ozone-ultrafiltration system always brought about a decrease in cake resistance (R-c) and an increase in fouling resistance (R-f). Based on the measurement of particle size distribution and zeta potential, the reduction in cake resistance through ozonation was attributed to an increase in particle size due to ozone-induced particle destabilization. However, the increase in the fouling resistance seems to be caused partly by the microbial characteristics of raw water. Although there was little effect on TOC, ozone-UF treatment could get much higher removal of UV254, THMFP (1day) and THMPF/TOC ratio than UF treatment alone.