Changes in algal organic matter under different pre-oxidants and dosages, and the formation potential of DBPs in algal-rich drinking water sources

During high-algae periods, the accumulation of algal organic matter (AOM) in source waters increases the risk of disinfection by-product (DBP) formation during subsequent disinfection, and pre-oxidation is therefore widely applied to regulate algal loading and DBP precursors; however, under a consistent algae-rich water matrix, the coupled effects of algal inactivation, AOM release or transformation, and DBP precursor evolution as a function of oxidant type and dose remain insufficiently quantified. In this study, algae-rich water from the Yanlong Lake constructed wetland–reservoir system (YL CWs-R) was used to compare sodium hypochlorite (NaClO), potassium permanganate (KMnO 4 ), and ozone (O 3 ) at dosages of 0–5 mg/L, with responses characterized using OD 680 , DOC, UV 254 , DON, K + release, and excitation–emission matrix (EEM) fluorescence. O 3 at 5 mg/L achieved substantial algal inactivation (OD 680 removal of 55.2%), but pronounced cell rupture induced organic release and elevated DBP formation risk. Low-dose NaClO (1 mg/L) suppressed AOM release, whereas higher doses (≥ 2 mg/L) promoted humic-like component accumulation and increased carbonaceous DBP formation potential. In contrast, KMnO 4 at 0.5 mg/L simultaneously reduced the formation potentials of carbonaceous and nitrogenous DBPs, decreasing total DBPs to 413.8 μg/L. EEM analysis further indicated that higher NaClO and KMnO 4 doses enhanced aromatic organic components associated with increased DBP formation. Overall, 0.5 mg/L KMnO 4 provided the most favorable comprehensive performance, while O 3 dosing should be carefully controlled to avoid secondary risks from oxidant-induced algal cell rupture, providing quantitative guidance for oxidant selection and dose optimization during high-algae periods in ecological purification source waters.