Remediation Of Cu And Cd-Contaminated Soil By Joint Application Of Straw And Engineered Bacteria

The experiment is an in situ remediation of heavy metals. The experiment was conducted in Miaoyunao Village near a mine, Daye Country, Hubei province, China. The materials of remediation are rice straw, a cheap organic matter, and engineered bacteria, a high adsorption and resistibility of Cadmium. A field trial planted lettuce was carried out to evaluate the influence of rice straw (5.2、10.3 and 23.2 t ha-1) and engineer bacteria (108 CFU g-1) on the growth and quality of lettuce, the properties of soil, the distribution of Cu and Cd and the retention of these metals by organic matter fractions in the copper and cadmium polluted soil. The main results are outlined as follows:1. The growth of lettuce was significantly promoted after combined application of the rice straw and engineered bacteria. Rice straw treatment increased the height and yield of lettuce by 6～23% and 28～86%. No apparent changes were observed for the concentration of chlorophyll and vitamin C. The content of nitrate was increased by 7～34%, while the soluble sugar was depressed by 9～34%. The joint application of rice straw and engineered bacteria enhanced the height, yield and Vc of lettuce by 8～20%,44～72% and 22～38%, respectively. Straw (10.3 t ha-1)/bacteria treatment increased the content of nitrate by 15.85%.2. The content of Cu in lettuce roots and leaves was decreased after application of rice straw and bacteria. Rice straw treatment decreased Cu content in lettuce roots and leaves by 19～35% and 18～32%, respectively. More significant decreases in the content of Cu in lettuce roots and leaves were observed for the combined application of rice straw and bacteria (24～42% and 33～62%).3. With the increase of the application rate of straw and bacteria, the content of Cd in lettuce roots increased gradually, while the content of Cd in lettuce leaves decrease progressively. Rice straw increased the content of Cd in lettuce roots by 1～18% and decreased Cd in lettuce leaves by 33～55%. The combined application of rice straw and bacteria increased Cd concentration in lettuce roots by 6～40% and decreased Cd concentration in lettuce leaves by 51～67%.4. No apparent changes in pH and organic matter(OM) were observed in the rhizosphere soil. When the rice straw was applied alone, the non-rhizosphere soil pH increased by 0.23～0.59 units, and the OM increased by 24～40%.After application of engineered bacteria, soil pH was increased by 0.43～0.66 units, and the OM was increased by 22～36%.The dissolve organic matter (DOM) in rhizosphere soil was increased by 21.9～55.5% in the rice straw treatment, but no obvious changes were observed in non-rhizosphere soil. The combined application of rice straw(5.2 t ha-1) and engineered bacteria enhanced the DOM in non-rhizosphere by 24.2% and decreased the DOM concentration in rhizosphere soil by 17.3%.5. Along with the increasement of rice straw, the fine size POM (50～200μm) decreased gradually, but the coarse size POM (200～2000μm) increased. Rice straw (23.2t ha-1) increased the fine size POM significantly. The concentrations of coarse and fine size POM in the straw and engineered treatment were more than the straw treatment.6. The application of rice straw and engineered bacteria enhanced the concentration of Cu and Cd combined with POM. The concentration of Cu and Cd in the fine size POM was increased by 25～135% and 61～88%, respectively. And the concentrations of Cu and Cd in the coarse size POM were enhanced by 81～133% and 87～97%. The concentrations of Cu and Cd combined with coarse size POM were higher than the fine size.7. The application of rice straw and bacteria promote more soluble/exchangeable Cu and Cd change to organic matter-bound or Fe oxide-bound fraction. The combined application of rice straw and engineered bacteria decreased the consent of soluble/exchangeable of Cd by 3～18%, and increased poor crystalline Fe oxides-bound Cd. The soluble/exchangeable of Cu was decreased by 40～54%, and the organic matter-bound Cu increased by 11～27% in non-rhizosphere soil. The Cu fraction in rhizosphere soil did not change much..In summary, there is a good effect for immobilization of Cu and Cd applying rice straw and engineered bacteria. The concentrations of Cu and Cd in lettuce leaves were decreased apparently by the combined application of rice straw and engineered bacteria. With the increase of the the application rate of straw, the effect gets better.