Augmented phototransformation of brominated disinfection by-products via surface water introduction during sunlit reclaimed water storage

Ozonation is widely used for reclaimed water disinfection; however, it inevitably produces harmful brominated disinfection by-products (Br-DBPs). When reclaimed water is replenished into surface water, one of its primary applications, Br-DBPs undergo complex phototransformation due to the interaction between surface water and reclaimed water matrices, which remains poorly understood. This study observed that mixing with surface water significantly enhanced both the photolysis rates of Br-DBPs and the detoxification efficiency of reclaimed water. The photolysis rate of adsorbable organic bromine (AOBr) increased significantly from 0.086h−1 to 0.20–0.23h−1 when mixed with surface waters (p<0.001). As a surface water proxy, Suwannee River natural organic matter accelerated the photolysis of three AOBr representatives: 2,5-dibromo-3,6-dihydroxyquinone, 3-bromo-4,5-dihydroxybenzoic acid, and 2-bromo-4-(hydroxymethyl)-6-methoxyphenol. The enhanced photolysis was attributed to DOM⁎ and derivative 1O2. High-energy 3DOM⁎ showed a stronger correlation with AOBr photolysis acceleration compared to low-energy 3DOM⁎. Furthermore, mixing with surface water enhanced the detoxification process, reducing toxicity equivalents from 8.5 to 2.9 mg-phenol/L in reclaimed water alone, and from 6.0 to 2.1 mg-phenol/L in mixed water. These findings suggest that mixing with surface water containing DOM with reactive optical properties is a promising strategy for improving water quality during surface storage.