Municipal wastewater has been increasingly used to augment drinking water supplies due to the growing water scarcity. However, reuse of wastewater has raised concerns about the potential health risks of contaminants in the effluents. Chlorine is the most widely used disinfectant in wastewater treatment. Chorine can react with organic matter in the wastewater effluent to form different groups of disinfection byproducts (DBPs). Many of these DBPs are suspected human carcinogens. As water recycling and reuse become an increasingly used practice to mitigate water scarcity, management strategies are needed to control wastewater-derived DBPs to improve the safety of water reuse. Solar photolysis is a major natural biogeochemical process that can affect the concentration of DBPs in surface waters. Natural sunlight can also be used as an energy source in advanced oxidation processes to remove various contaminants in wastewater. The objective of this study was to determine the degradation kinetics of total organic chlorine (TOCl), bromine (TOBr) and iodine (TOI), and specific DBPs in water by natural sunlight photolysis and solar/TiO2 and solar/Fenton processes. Outdoor solar photolysis experiments were performed to investigate photolytic degradation of specific halogenated DBPs and the total organic halogen (TOX) formed by fulvic acid. The results showed that TOX degradation by sunlight irradiation followed the first-order kinetics with half-lives in the range of 2.6 to 10.7 h for different TOX compounds produced by fulvic acid. The TOX degradation rates were generally in the order of TOI &gt; TOBr = TOCl(NH2Cl) &gt; TOCl(Cl2). The efficiencies of sunlight photolysis of specific DBPs varied based on DBP species, and the results showed that the photosensitive cleavage of carbon-halogen bonds increased with increasing number of halogens (tri- &gt; di- &gt; mono-halogenated) and size of the substituted halogens (I &gt; Br &gt; Cl). Solar/TiO2 and solar/Fenton processes substantially increased the rates of reduction of DBPs compared to natural sunlight alone. The results of this study provide a better understanding of the degradation of TOX and specific DBPs by natural sunlight irradiation and solar/TiO2 and solar/Fenton processes, which can help evaluate photolytic degradation of wastewater-derived DBPs in surface waters and develop engineered processes to reduce the DBP concentrations during water reuse.

Removal of disinfection byproducts by natural sunlight photolysis during water reuse

ACS Fall 2021

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