| Leachate from municipal solid waste (MSW) contains high concentrations of organics, ammonia, etc., also contain certain concentration of heavy metals. Leachate may cause serious pollution of soil, groundwater and surface water. Generally, mounts of relative reports are focused on the removal of pollutants. Most of studies about soil pollution focuses on heavy metals, salts, arsenic, selenium, fluorine compounds, pesticides, phenols, cyanide, oil, synthetic detergents etc. Few reports are found about leachate polluted soils. There is a serious demand for soil remediation technologies about leachate pollution.The paper studied the effects of MSW leachate on soil pH, enzyme activities, respiratory, leaching ammonia and leaching toxicity. Besides, cow manure compost (CMC) and natural zeolites were applied as remediation materials. Conclusions are as follows:(1) The ecological effects of leachate on soils. After leachate and soil were mixed together, soil ecological indicators varied with the dosages of leachate. Leaching toxicity was the most sensitive indicator to the leachate dosage. Various dosages of leachate were irrigated into red soils and the pots were kept in an incubator. The ecological indicators were measured periodically during the incubation. The results showed:low dosages of leachate showed no significant influence on soil pH decrease. Soil respiratory was inhibited slightly in the beginning of incubatio, while amylase, catalase and invertase activities could be promoted by leachate in a short period. Soil pH and leaching toxic showed a significant negative correlation (p<0.05). Tetrahymena pyriformis was proved as a excellent indicator for soil pollution.(2) The effects and mechanisms of CMC on polluted soils. CMC could be used to improve the ecological characters of leachate contaminated soils and get rid of the pollution risks. The research results indicated that CMC was able to improve the pH buffering capacity and increase the leaching ammonia content in a short period. Besides, CMC was effective to increase the activities of amylase, catalase and invertase due to the promotion of Soil fertility and particle morphology. Leaching toxicity was also decreased by CMC significantly. (3) The effects and mechanisms of Natural zeolite and its modified products on polluted soils. Natural zeolite and its modified products could change several parameters with various dosages. When the modified method was "6%NaC1+960W microwave", highest removal of COD and ammonia was found. Soil pH increased after zeolite treatment because of ion exchange and neutralization, but high dosages of zeolite may cause pH up to9-10. Respiratory, amylase and invertase were improved in with low dosage of zeolite, while high dosages cause inhibition to soil microbe. Catalase decreased after various zeolite treatments, probably because of alkaline hydrogen peroxide generation and high pH value. In addtion, leaching toxicity decreased with zeolite treatment and microwave modification could strengthen the effect.(4) The remeditation effects of CMC and zeolite on polluted soils. The combined remediation of CMC and zeolite for leachate polluted soils have been proved effective. The combined remediation improved the soil pH and kept it in a suitable range (7.0-8.5). Soil respiratory was promoted significantly with the best dosage of "25g CMC+15g zeolite". Amylase, catalase and invertase activities increased significantly with combined remediation. Besides, leaching ammonia content was lower than the control group. Leaching toxicity decreased greatly with combined remediation and the total effect was much better than remediation of each material. CMC dosage has a significant positive correlation (p<0.05) with soil pH and amylase activity, microwave time of the modified zeolite showed a significant positive correlation (p<0.05) with amylase. |
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