The characteristic of N-nitrosodimethylamine precursor release from algal organic matter and degradation performance of UV/HO/O technology.

Seasonal cyanobacterial blooms in eutrophic water releases algal organic matter (AOM), which contains large amount of dissolved organic nitrogen (DON) and is difficult to be removed effectively by conventional treatment processes (e.g., coagulation and sand filtration) because of its high hydrophilicity. Moreover, N-nitrosodimethylamine (NDMA) can be generated by the reaction of AOM with disinfectants in the subsequent disinfection process. In this study, the formation of NDMA from different AOM components was explored and the control of algal-derived NDMA precursors by UV/HO/O was evaluated. The results showed that the hydrophilic and polar components of AOM with the low molecular weight had higher NDMA yields. UV-based advanced oxidation process (AOPs) is effective in degrading NDMA precursors, while the removal rate can be affected greatly by UV doses. The removal rate of NDMA precursors by UV/HO/O is higher than by UV/HO or UV/O which can reach 95% at the UV dose of 400 mJ/cm. An alkaline environment reduces the oxidation efficiency of UV/HO/O technology, while an acidic environment is conducive to its function. Inorganic anions such as HCO, SO, Cl and NO are potential to compete with target algal-derived NDMA precursors for the oxidants reaction and inhibit the degradation/removal of these precursors. The degradation of algal-derived NDMA precursors by UV/HO/O is mainly accomplished by the oxidation of DON with secondary amide groups, and the main degradation mechanism by UV/HO/O was through the initial decomposition of macromolecular organic compounds such as biopolymers and humic substances and the further degradation of resulting small molecular components.