Ion exchange and vacuum UV: A combined approach for removing organic matter and microcystins from natural waters

UV based advanced oxidation exhibits promising potential for the degradation of cyanobacterial toxins from natural waters. However, degradation is hindered by the presence of natural organic matter (NOM), which absorbs both 185 nm and 254 nm photons and scavenges hydroxyl radical (?OH), affecting mechanisms of UV/ vacuum UV (VUV) degradation and requiring higher fluences (exposure times) to achieve microcystin reduction. In addition to obstructing UV/VUV degradation, NOM is associated with the formation of harmful disinfection by-products (DBPs) with drinking and recycled waters. Hence, technologies that are capable of removing NOM are desirable. In this study, we investigated the synergistic application of ion exchange (IX) resins and VUV for the removal of NOM and Microcystin-LR (MCLR) from natural waters. A pre-treatment with 1 mL/L dosage of IX resins removed >80% of the dissolved organic carbon (DOC) and UV254 absorbing compounds. This increased the MCLR degradation rates (up to three folds) in the tested surface waters. A progressive analysis on the degradation products indicated subsequent degradation of the toxic ADDA moiety of MCLR confirmed by the formation of compounds with a specific mass to charge ratio (m/z) of 835.5 855.3 and 791.4. More importantly, pre-treatment with IX resulted in reducing VUV?s electrical energy per order (EEO) by up to four folds and the overall chlorine demand by eight folds for surface waters. Hence, the results of this study indicate that a combined IX-VUV will be highly effective at reducing microcystins in impacted natural waters.

Automated summary

The study shows that the combined application of ion exchange resins and vacuum ultraviolet light can effectively remove organic matter and microcystin-LR from natural waters, improving the degradation rate of MCLR. By pre-treating with IX resins, a significant reduction in energy consumption and chlorine demand for surface waters was achieved.