Effect of dissolved oxygen on efficiency of TOC reduction by UV at 185 nm in an ultrapure water production system.

The effect of dissolved oxygen (DO) on the degradation of methanol by ultraviolet (UV) light at 185 nm (UV-185) was examined in this study. The experiments were conducted using a bench-scale experimental apparatus that was operated under continuous conditions. In the control tests with various DO conditions, it was confirmed that UV irradiation of water without methanol produced approximately 54 μg/L of HO and removed 15%-90% of the DO. The production of HO was affected by the mixing conditions within the UV reactor and the dose of UV. The degradation efficiency of methanol by UV-185 irradiation improved linearly with increasing DO concentration, with more than 90% DO consumption. The maximum total organic carbon (TOC) removal rate was observed at 100 μg/L DO and 433 mW·sec/cm, the highest DO and dosage conditions in this study. The production of HO was also affected by DO concentration in the feed water, especially at the high UV dosage, in which lower HO production was observed at higher DO.