Studies On Photo-degradation Of Organophosphorus Pesticide Wastewater By Advanced Oxidation Techniques

The technique of photocatalysis oxidation is a new kind of water treatment process for the degradation of organic substances with great potential application recently.. This paper mainly studied on preparation and Characterization of titanium dioxide(TiO₂) nanoparticles and investigated the photocatalytic degradation of trichlorfon by the means of UV/TiO₂ and UV/Fenton..The effect of adding concentration of catalyst, pH value of solution, UV irradiation intensity on photodegradation of trichlorfon are discussed in details. The key factors which influce the photocatalysis oxidation of trichlorfon and the optimal degradation conditions are also studied with the orthogonal experimental method. The proposed degradation pathway for the photocatalytic degradation of trichlorfon are speculated in this paper.The results show that: (1)The sol-gel method is a good method for preparing nano-TiO2 photocatalystic agent. The crystal structure of TiO₂ powder is anatase and the average particle size is 7.5 nm by XRD characterization when the experiment condition is controlled strictly (2)The photodegradation of trichlorfon simulated wastewater by using UV/TiO₂ can get a good result. Based on the orthogonal experimental method, the order of factors which influence the degradation is as follows irradiation intensity > pH > adding air > TiO₂ concentration. The rate of photodegradation can exceed 90% in 90 min when the conditions is controlled at the pH of 2, the TiO₂ concentration of 0.7 g/L, the rate of aerating air of 0.8L/min and UV irradiation intensity of 2000 uw/cm² to 9.3 mg/L.of the initial concentration of trichlorfon(3)By use of the orthogonal experimental method, the order of factors which influence the degradation is as follows:Fe²⁺ concentration > irradiation intensity > H₂O₂ > pH. The rate of photodegradation can approach 90% with the optimal conditions of pH of 3, the Fe²⁺ concentration of 0.72 mmol/L, the H₂O₂ concentration of 7mmol/L and the UV irradiation intensity of 2000 uw/cm². The rate of photodegradation of trichlorfon would be promoted after.addition of appropriate active compound such as K₂C₂O₄ in UV/Fenton sysytem. (4)The photodegradation of trichlorfon produce organic acid and inorganic acid molecules and result in pH continually declining in the solution .The mechanism may involved in high oxidation ability of active hydroxyl radicals(·OH) which are strongly enough to break the p-0 bond and p-C bond of organic phosphor pesticide .