| The pesticide is one high poisonous compound. Its wastewater always has strong toxicity, high concentration and difficult degradation. So it is paid much attention by the society. The wastewater mainly comes from production process and washing of pesticide container recovery. It must be treatmented, otherwise it will cause the environment serious pollution, in particular for the river around. Photocatalytic oxidation is a newly developed method, which is to dispose organic compounds wastewater by photocatalyst. TiO2 is the most accustomed photocatalyst. However, as photocatalyst TiO2 has two shortcomings: first it has only a narrow responding width to natural light and then a rapid combination velocity of the stimulated excisions. So it has not high catalytic activities. Many studies showed that it is possible to heighten its activities by some modification methods. The development of photocatalytic oxidation technology and the treatment approaches of pesticide wastewater in the domestic and foreign were summarized in this paper. Beta-cypermethrin(BEC)and glyphosate used widely in domestic in recent years were elected as the model pollutant. The degradation kinetics and the photocatalytic treatment conditions were studied in the laboratory scale. The experimental results were as follows:1. Preparation and structural characterization of CdS/TiO2 /FP coupled photocatalystThe CdS/TiO2/FP coupled photocatalyst was prepared on float pearls (FP) by means of sol-gel method. The structure, morphology, and element of photocatalyst were researched with the tests of SEM, XRD, IR and power spectrum. The SEM indicates the surface of prepared photocatalyst is smooth and brightness. The elements of Cd and S were successfully doped in the TiO2 thin film, formed the CdS/TiO2 coupled thin film. The photocatalyst obtained at 500℃TiO2 mainly was anatase.2. Photocatalytic degradation experimentsThe photocatalytic activity of multi-photocatalyst was evaluated by the photodegradation of BEC and glyphosate, and the effects of various conditions on the photocatalytic characteristics were investigated.(1) The degradation of beta-cypermethrin: concentrations of CdS 20%, heat treatment temperature 500℃, amount of photocatalyst 3g·L-1,initial density of BEC 45mg·L-1, initial pH 6.5,air flow 200mL·min-1,125 W mercury lamp as light source, the degeneration rate of BEC was 87.9% in 60min. 5 W ultraviolet lamp and sunlight as lamp source the BEC degeneration rate respectively achieves 79.3% in 1h and 93.4% in 5h. It is shown that the CdS/TiO2 coupled photocatalyst is applied to pesticide wastewater for nice prospect.(2) The degradation of glyphosate: concentrations of CdS 20%,heat treatment temperature 500℃,coating cycles 3,amount of photocatalyst 3g·L-1,initial density of glyphosate 135 mg·L-1, initial solution weak alkaline,air flow 200mL·min-1,125 W mercury lamp as light source, the degeneration rate of glyphosate was nearly 100% in 40min. The ultraviolet absorption spectrum indicates the colored groups of glyphosate has been basically degraded in 40min, absorbance of glyphosate in 200nm～700nm approaches zero, so this indicated glyphosate has completely degraded. Sunlight as lamp source the degeneration rate of glyphosate achieves 82.4% in 5h.(3) The degradation of mixed pesticides: the CdS/TiO2/FP was input to the mixed pesticides wastewater. The ultraviolet absorption spectrum indicates that the absorbance of glyphosate in visible nearly approaches zero in 40min and the absorbance of glyphosate in ultraviolet only is 0.5 and the degeneration of glyphosate is 80%. Therefore the degeneration of CdS/TiO2/FP to mixed pesticides is hopefully applied in actual industry.(4) The degradation of BEC can be described by Langmuir-Hinshel wood (L-H) equation, and the photocatalytic reaction is a first-order reaction at lower concentration (<= 90mg·L-1). Under these experimental conditions, the reciprocal of initial reaction rate 1/v0 is directly proportional to that of initial mass concentration 1/c0: 1/v0= 0.0733+16.062(1/c0),R2 is 0.9784. And the reaction rate constant k=13.64mg·(L·min)-1,the adsorption constant K=4.564×10-3 L·mg-1.
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