Enhanced Removal of Saxitoxins by Far-UVC Advanced Oxidation Processes

Harmful algal blooms (HABs) are becoming an increasing concern for drinking water utilities due to the production and release of cyanotoxins, including saxitoxins, into source waters. Many conventional water treatment processes have proven to be slow or ineffective in the removal of saxitoxins. This work investigated the removal of six saxitoxin congeners by UV-advanced oxidation processes (UV/AOP), utilizing KrCl* excimer and low-pressure UV (LPUV) lamps with hydrogen peroxide (H₂O₂) as a hydroxyl radical (^•OH) promoter. After exposure to typical UV fluences, initial saxitoxin concentrations decreased by 30–75%, depending on congener and irradiation source. Degradation of all six saxitoxin congeners was 2.1–10.8 times faster in the KrCl* excimer system compared to the LPUV system due to the greater ^•OH steady-state concentrations at 222 nm. While the addition of 1 mg_C L^–1 of dissolved organic matter (DOM) did not significantly affect the degradation rate of one saxitoxin congener at 222 nm, removal of all other congeners was significantly inhibited in the presence of 5 mg_C L^–1 DOM in both UV/H₂O₂ systems due to ^•OH scavenging by DOM.