This research investigated effect of nitrite and nitrate on the removal of profenofos (organophosphorous pesticide) in water using vacuum ultraviolet (VUV, wavelengths of 185 and 254 nm) in comparison with UV (254 nm). Effects of initial nitrite concentrations (0.1, 0.5, and 1 mg/L as NO2-) initial nitrate concentrations (1, 10, 50, and 100 mg/L as NO3-), and initial pH of 5, 7, and 9 were studied. Also hydroxyl radical exposure was determined. The results showed that the VUV (87.9%) had superior degradation performance than that by the UV (72.1%) for the initial concentration of profenofos 10 mg/L (pH7) at 10 minute. Nitrite at 0.1 mg/L yielded the highest profenofos removal rate constant comparing to other nitrite concentrations. In case of nitrate, the highest removal rate constant of profenofos was at 1 mg/L. These results were agreeable to the formation of hydroxyl radical (OH•). The OH• exposure confirmed that the presence of nitrite and nitrate can generate OH•. pH 9 was found to have the highest profenofos removal rate constant. The finding of the work suggests that nitrite and nitrate play important role in profenofos degradation under UV and VUV processes. At low concentration, nitrite and nitrate can induce OH• formation. However, high concentration resulted in adsorption of VUV which in turn inhibit the reaction.

Thesis (M.Sc.)--Chulalongkorn University, 2014