Studies On Degradation By In Situ For Organochlorine Pesticides DDT In Soil

In this paper, loam soil was selected by the moderate proportion of sandy and clay, which has both the advantages of sandy soil and clay soil. It has good gas permeability, and cultivated good, water security and supply manure for fertilizer and strong loamy soil as a test for soil. Selected representative of organochlorine pesticides DDT widely applied as insecticides in the 1960s and 1980s of last century, the degradation of ganochlorine pesticides in the soil was studied.According to the environmental acts of organic chlorine pesticides in the soil, the adsorption capability of loam soil for nano-TiO₂ was studied, photocatalytic degradation of soil leachate in the DDT and photocatalytic degradation of plant-specific, the joint effect of the specificity of plant and specifically microorganisms in the soil degradation of DDT, photocatalysis, plants, micro-organisms, even in conjunction with this ways repair DDT in the soil. By changed precipitation, precipitation intensity, light intensity, time, reaction temperature, humidity, pH, type of degradation of bacteria, repair, used of plant species, to take measures such as environmental conditions, optimization of degration of an organic chlorine pesticide DDT. In this paper, organic fertilizer contained dissolved organic matter, inorganic fertilizer contained transition metal elements and the degradation of DDT was studied too, the combination of these two types of substances in a variety of DDT degradation process in soil was studied.The major synopsis and results were summarized as the following:1. Effects of adsorption capability of soil for nano-TiO₂. The adsorption capability of loam soil for nano-TiO₂ affected by amount and intensity of leached water has been investigated by simulating the natural rainfall process under the leaching condition. The results showed that the amount and the intensity of leached water were two important factors affecting the adsorption capability of loam soil for nano-TiO₂. The results indicated that the depth of the loam soil containing a maximal amount of nano-TiO₂ was proportional to the amount of leached water, while it was inversely proportional to the intensity of leached water, at a constant amount of the leached water. It was also found that the adsorption capability of soils for nano-TiO₂, can be improved by adding other materials, such as dissolved organic matter (DOM), bentonite and straw. It was found that DOM was the best sorbent for improving the adsorption capability of the loam soil for nono-TiO2, followed by bentonite, while straw was not suitable for the modification of the loam soil. The improvement of adsorption capability of the loam soil depended on the amount of these additives. Nano-TiO₂ can effectively adsorb on the surface layer of loam soil containing appropriate amount of the additions.2. Study of photocatalyic degradation of DDT in leached solutions of soil by nano-TiO2. Trace elements of transition metal, such as copper, zinc, iron, manganese, molybdenum and non-metallic as element boron fertilizer, co-doped with nano-TiO₂ photocatalyst combined exudates on soil organochlorine pesticides DDT for photocatalytic oxidative degradation experiment. The experimental results showed that the specimen in the general trend of the degradation of DDT were the same under different experimental conditions, with the illumination time to increase gradually to reduce residuesIllumination time and soil effusions degradation of DDT was a direct correlations. In light of the initial four hours, they showed a good linear relationship, the level of DDT in soil was declining rapidly until the content was 15%. After four hours, with the growth of illumination time, the decomposition rate of DDTs was obviously slow down and its content was no longer change with time. In the reaction system of leachate in the soil, TiO₂ can not be easy to add the transition metal element method, which cannot improve the effectiveness of photocatalytic oxidation.3. Effects of various factors on the photocatalyic degradation of DDT on surface layer of soil. In order to got the optimum conditions for photodegradation experiment, the effects of various factors, including soil pH, dissolved organic matter (DOM), water content, soil depth, exogenous components and husbandry on the degradation performance of DDT were studied by choosing the brown soil samples spiked with DDT and exposed to the UV-light irradiation. The results indicated that the degradation rate increased with the increasing of the water content of the soil, but when it exceeded over 50%, the degradation rate decreased. The photocatalytic degradation rate of DDT increased with the rising of the concentration of DOM, however, when the concentration of DOM exceeded over 1.2%, the degradation rate reduced slightly. Acidic or alkaline environment was more effective for the photodegradation than the neutral environment. Fe and TiO₂ greatly accelerated the photodegradation of DDT in soil, DOM, Fe₂O₃ and all element fertilizer+DOM slightly positively influenced the photodegradation, while the all element fertilizer scarcely provode contributions. The degradation rate of DDT decreased with the rising of the soil depth; regular husbandry can enhance the degradation capacity of DDT effectively.4. Inducing effect of specific plants for remediation of DDT polluted soil. Both celery, a fond chlorine specific plant, and cole, an ordinary plant, have been employed to be contrastively investigated for the remendation of soil which was contaminated by dichloro-diphenyl-trichloroethane (DDT), an organic chlorine pesticide. By had been carrying out the glasshouse potted plant experiment in 50 days, the results have revealed that the content of DDT contained in the soil decreased with time increasing. Except for the instinct remendiation of soil by soil itself, crop growing strengthened the remendiation function of soil which contaminated by DDT. In addition, the degradation rate of DDT in soil will be increased by different crop planting. The result of the blank test has shown that the residual ratio of DDT in soil was 79.21% after 50 days degrading, owing to the larger molecular organics being degraded into smaller molecular weight organics. Therefore, the contamination of soil has been effectively decreased. The residual ratio of DDT in soil were 73.47%,66.96%,62.55%, and 53.29% in the potted cole and were 67.96%,58.39%,50.57%å’Œ34.37% in the potted celery treated with no fertilizer, inorganic fertilizer, organic fertilizer and organic-inorganic mixed fertilizer, respectively. However, the residual quantity of DDT in soil treated with growing celery, a fond chlorine specific plant, was remarkably decreased under the organic-inorganic mixed fertilizer conditions. The degradation ratio of DDT in this kind of soil was more 18.92% than that of growing cole at the same fertilizer conditions.5. The research on the process of microbial remediation of DDT in soil. By the means of isolating and cultivating indigenous micro-organisms, the strains that can tolerate DDT were screen and amplify. Then, the strains were placed into soil to degrade DDT. Meanwhile, did Phanerochaete sp., and compared the degradation effect of DDT with them. After initial identification, DB01 was Pseudomonas sp. bacteria; DB02 was Sphingobacterium sp. bacteria. The identification of fungal strains DF01, DF02 have to be further in-depth studied.After cultivating and amplifying these strains, the DDT in soil all can be degraded under the condition of organic matter provided as co-metabolism substrate. Adding organic matter as the co-metabolism substrate, FB01, FB02 and Pseudomonas sp. bacteria can degrade DDT much more effectively. However, Sphingobacterium sp.bacteria DB02, even if organic matter was not added as the co-metabolism substrate, still had a better effect on the degradation of DDT. Compared with the indigenous micro-organisms isolated from the soil, Phanerochaete sp.had a more significant degradation effect on DDT. Soluble organic matter was a co-metabolism substrate with good performance and effect.This study would be consistent with development of green agriculture, ecological agriculture , Ecological environment protection and the sustainable development of ecological economy. This was to save energy, mad full use of natural resources, avoided secondary pollution, which fundamentally to efficiently deal with this kind of organochlorine pesticide DDT and other persistent organic pollutants on the entire earth caused by a wide range of general pollution.This work provided a new method.