Algal-Rich Drinking Source Water: Effects of Chlorine Pre-oxidation on Algal Growth, Algal Organic Matter, and the Potential of Disinfection By-Products

Pre-oxidants are frequently used to eliminate algae and to enhance the removal of algae organic matter (AOM) at the intakes of drinking water sources; at the same time, they can cause the rupture of algal cells resulting in the release of AOM into the water sources, and AOM serves as a source of precursors for the formation of disinfection by-products (DBPs) during the final disinfection stage in the treatment process of drinking water. This study aims to investigate the effects of different doses of sodium hypochlorite pre-oxidation on algal growth, AOM, and potential DBPs in algal-rich drinking source water named Yanlong constructed wetlands and reservoir (YL CWs-R) ecosystem. DOC, UV254, and DON had a certain reduction, and K+ concentration increased slowly at low dosage (≤ 1 mg/L). When the dose exceeded 2 mg/L, part of the algal cells were damaged, resulting in a significant increase in DOC, UV254, DON, and K+ concentrations, and the characteristic peak value and the fluorescence volume increased significantly, with the humic acid-like fluorescence area experiencing the most significant increase. Total C-DBP and total N-DBP precursors can be partially removed under low dosage (≤ 2 mg/L), and high dosage of chlorine increased total C-DBP and total N-DBP precursors after oxidation. The precursors of DCAN, TCM, BCAA, and 1,1-DCP increased with increasing sodium hypochlorite dosage, and it had a better control of DCAA, DBAA, DBAN, and TCAM precursors when the dosage was less than 3 mg/L. With comprehensive algae removal efficiency, AOM release, and DBP precursors’ control, the ideal chlorine pre-oxidation dosage was 1 mg/L.