Solar photocatalytic degradation of total organic halogen in water using TiO₂ catalyst

Disinfection byproducts (DBPs) in treated wastewater effluents pose environmental and health risks during water reuse. Solar-TiO₂ photocatalysis is a promising technology for degrading organic pollutants in treated effluents. In this study, total organic halogen (TOX) was used as an analytical tool to determine the efficiency of solar-TiO₂ photocatalytic process for the dehalogenation of DBPs in water. Natural solar photocatalytic experiments using TiO₂ particles were conducted to evaluate dehalogenation kinetics of different TOX groups formed by fulvic acid including total organic chlorine (TOCl), bromine (TOBr) and iodine (TOI). The results showed that the mixed phase TiO₂ (Aeroxide P25) was much more effective at TOX removal than the anatase (Hombikat UV-100) and rutile (TiOxide) TiO₂ particles. The TOX photocatalytic degradation rates of different halogen substituents ranked as TOI > TOCl (NH₂Cl) > TOBr > TOCl (Cl₂). The TOX removal followed first-order kinetics with half-lives of 42.8, 11.0, 5.0 and 2.7 min for TOCl (Cl₂), TOBr, TOCl (NH₂Cl), and TOI, respectively, at the 100 mg L^-1 TiO₂ dose. The TOX dehalogenation was enhanced at pH 9 compared to pH 5, and the addition of hydrogen peroxide had limited improvement in the TOX removal. Hydrophobic and molecular weight (MW) > 1 kDa fractions of TOCl (Cl₂) were more susceptible to the solar photocatalytic process than the hydrophilic and MW < 1 kDa fractions. The solar-TiO₂ photocatalytic process also effectively removed TOX in chlorinated and chloraminated wastewater samples. The results of this study suggest that the solar-TiO₂ photocatalysis is an effective treatment technology for TOX removal in water reuse.