Studies On The Photodegradation Of Triazophos In Water

Triazophos was a type of low-toxic, high-effective and broad-spectrum phosphorothioate pesticide and acaricide, which was developed in 1970s. It was thought to become the substitution of other pesticide such as methamidophos and dimethoate, so it had a good potential of application. On the other hand, it wound be inevitably into waters (rivers, lakes etc.) when it was used, which wound cause environmental pollution and ecological destruction. How to improve and prevention these problems had practical significance.Photooxidation was one of the main degradation approaches of pesticides in environment. Photo-stability had a direct influence on the effectiveness and persistent of pesticides. So the photooxidative degradation of triazophos in water was studied in this paper. Factors effecting the degradation rate, including types of light sources, photooxidation catalyzers and sensitizers, the pH value of water and the component of humus were investigated in the experiment, and the treatment of wastewater containing triazophos using UV-Fenton was also studied in this paper. The experimental results were as follows.(1) Effect of light sources. Among the three light sources, i.e. sun light , 300W and 500W high-voltage mercury lamp, the degradation rate of triazophos under mercury lamp was higher than sun light, and increasing with the raising of mercury lamp voltage. The half life of triazophos degradation under three light sources are 301.37minutes, 77.02minutes and 35.73minutes respectively.(2) Effect of photosensitizers. Acetone was selected as photosensitizer. It had a distinct effect on photodegradation of triazophos. When the concentration of acetone was 1%(V/V) in water, the half life of triazophos photodegradation under sun light , 300W and 500W high-voltage mercury lamp reduced to 43.87minutes, 16.43minut.es and 9.76minutes.(3) Effect of pH value. Experiment was conduct in four buffer which pH value was 5.0\7.0>9.0 and 11.0 respectively and triazophos photodegradation rate increasing with the raising of pH value. Under the irradiation of sun light and 300W, 500W high-voltage mercury lamp, when pH value increased from 5.0 to 11.0, the half-life of triazophos decreased from 266.60 minutes,75.34 minutes, 52.91 minutes to 154.03minutes, 47.80minutes, 35.01 minuteso(4) Effect of the humus. The two components of humus (fulvic acid and humic acid) had the same characteristic between photodegradation of triazophos, i.e. under the irradiation of high-voltage mercury lamp, the two components exhibited the obvious photoquenching effect, and under the irradiation of sun light, the two components showed the distinct photosensitizing effect.(5) Effect of photocatalyzers. TiO2 and H2O2 were used as photocatalyzers. Experiment results showed that H2O2 was better than TiO2,and the mixture of the two compounds was the best, because it had cooperation effect.(6) The treatment of wastewater containing triazophos using UV, UV-H2O2, UV-Fenton(Fe2+), UV-Fenton(Fe3+) were tested under the conditions with and without aerating air. The result showed that photooxidation can improve the biodegradability of this type of water; the removal rate of COD improved markedly by aerating air. Both UV-Fenton(Fe2+) and UV-Fenton(Fe3+) the removal rate of COD was reached above 80% after treating 120 minutes, distinctly higher than UVand UV/H2O2.Author: Zhou Zuo-ming(Environmental Science and Engineering) Directed by Prof. Yang Ren-bin...