Degredation Of Propxour In Water By Ozone

Propoxur, a carbamate insecticide, is one of the public health pesticides recommended by the World Health Organization. It has been widely used in disease prevention in 2008 after the Wenchuan earthquake, resulting in a high propoxur residue in environment. Because of its high water solubility, propoxur is easy to transport in environment, then access to the surface and ground water and threaten drinking water safety. In order to eliminate propoxur micro-pollution and to ensure the safety of drinking water, technologies on the removal of propoxur micro-contamination are studied in this paper.First, potassium permanganate, chlorine, ozone and powdered activated carbon on the ability of propoxur removal were investigated. The investigation shows that propoxur is not well removed by potassium permanganate, chlorine and powdered activated carbon, but by ozone. When T = 13℃and pH = 6.5, ozone of the initial concentration of 0.65mg/L can completely remove the propoxur of the initial concentration of 200μg/L within 30min.Secondly, factors that influence the ozonation of propoxur were studied. The results show that increasing the initial ozone dosage conduce to the rapid removal of propoxur; pH affect the ozonation process of propoxur significantly, under acidic conditions the rate of the degradation of propoxur is relatively slow, while under alkaline conditions the removal rate of propoxur is fast; the radical inhibitor tert-butyl alcohol can significantly slow the degradation rate of propoxur, the greater tert-butyl alcohol dosage the more obvious inhibition on the degradation rate. when the dosage of tert-butyl alcohol increased to certain value, the inhibitory effect of tert-butyl alcohol is no longer enhanced; the chloride, sulfate and nitrate ions in aquatic environment do not affect the degradation of propoxur by ozone, while bicarbonate alkalinity inhibits the process, in conditions of the same pH value, the greater the alkalinity, the more obvious inhibition can be observed.The direct reaction rate constant between ozone and propoxur and the apparent rate constants under the different pH and temperature conditions are measured. When T = 18°C, pH = 6.95, using the tert-butyl alcohol as the hydroxyl radical inhibitor, the measured direct reaction rate constant k_D between ozone molecules and propoxur is 38.05 L/(mol·s); when T = 21°C, the corresponding apparent rate constants for pH 6.45, 7.06, 7.43 and 7.80 are 125, 199, 241 and 533 L/(mol·s), respectively; when pH = 7.07, the apparent rate constant corresponding to the temperature 7.0, 13.5, 21.0 and 28.0°C measured are 27.9, 112.6, 261.1 and 345.1 L/(mol·s), respectively; the analysis of the apparent rate constants versus temperature leads to the formula k_obs=1.36×10¹⁷exp(-10036/T), by which the apparent rate constant can be calculated when pH = 7.07.The identification of the products formed in the ozonation of propoxur was established by an HPLC-MS coupled with a photo diode array(PDA) detector. The result shows that there are several products of ozonation include two kind of [M+H]⁺ ions of the m/z 226 and 196. One of them is probably produced while the hydrogen on the benzene ring is replaced by hydroxyl, the other is formed when the C-N bond is broken resulting the separation of methyl from the propoxur molecule. Ion chromatography analysis shows that nitrogen in propoxur molecule can be transformed into nitrate finally.To ensure the safety of drinking water, the water-supply plant should be equipped with ozone generator, which can efficiently deal with unexpected propoxur and other pesticide contamination.