Environmenatal Security Of Heavy Metals In Sewage Sludge Compost Applicated On The Land Of Kunming

The main point of this study was to assess environmental safety of the sewage sludge compost of Kunming when being applicated to the land. To reach this goal, sewage and sludge treatment in Kunming was surveyed, and characteristics of soil and sewage sludge compost were identified. Then leaching and pot experiments were conducted. The main conclusions are as follows:The sewage sludge of the 2nd Sewage Treatment Plant of Kunming was characterized with high organic and nutrient contents but low trace metals contents. Accordingly it was proposed that the sewage sludge of the 2nd Sewage Treatment Plant should be used as the raw material of Kunming sewage sludge composting project.Particle distribution, nutrient contents and XRD analysis showed applying sewage sludge compost in soil improved the nutrient contents, breathability and tilth properties of soil, but not fundamentally changed the mineral composition. Heavy metal contents and mobility are higher in sewage sludge compost than in soil, The ratio of heavy metals leached to left in SSC are respectively 1.07, 2.32, 0.96, 4.99, 2.28, 7.02 times than in soil, so the potential of polluting soil existed when applying SSC to soil. Competive absorption are existed among 6 metals. Cr and Pb are easier absorbed by soil than As, Cd, Cu, Ni.Leaching experiment showed heavy metals are different in migration ability, expressed as Nickel>Cadmium≈Copper>Arsenic>Lead>Chromium. The main part of heavy metals in leachate come from the soil. Over 99% of heavy metals in compost are left in soil. The leaching process of heavey metals in soil were simulated by kinetic model, 4 parameters were obtained. The retention factor Kd showed metals rentention effect by soil were ordered as Cd> Pb> As> Cr> Cu> Ni, hydrodynamic dispersion coefficient DL showed the dispersion of metals ordered as Cr>Ni>Cu>As>Cd>Pb, the effective migration mass of heavy metals ma indicates only the leaching of Ni has been completed, and reaction constant λ showed the states of heavey metals can be irreversibly changed between valid and invalid in leaching process.Pot experiment show that under the loading rate of 24kg/m2, the SSC improved the growth of Oxalis corymbosa DC., but not affect heavy metals enrichment in plant tissues. Chlorophyll content, stem length and stem proportion of Oxalis corymbosa DC. are comprehensively improved. Copper and Nickel concentrations in soil are strongly correlated with the concentration in plant tissues. Different tissues are different in metal Enrichment and different metals are differently enriched in plant tissue. Finally, the heavy metals absorbed by Oxalis corymbosa DC. take only a small part to the total metal amount in sewage sludge compost. The amount of As, Cd, Cd, Cu, Ni, and Pb induced in soil by SSC are respectively 85, 78, 470, 458, 372, 124 times to the amount absorbed by Oxalis corymbosa DC..