Application Of Sludge Compost And Research Of Heavy Metals Fraction And Adsorption In Municipal Wastewater Treatment Plant

In urban sewage treatment plant, if the sludge, a by-product in the process of urban sewage treatment, is disposed in an improper way, the serious "secondary pollution" problem will be caused. This paper, through the testing and analysis of the basic physicochemical properties, the contents of nutrients and heavy metals and other physicochemical indicators of dewatered sludge in four sewage treatment plants in Xi’an City, selects the mixed cigarette, and manure and other additives of dewatering sludge in the fifth sewage treatment plant to do research on the aerobic composting process,analyses the change of nutrient content and form of heavy metals in the sludge before and after composting mixture. And the products of sludge composting are applied to fertilizer of urban landscaping plant and agricultural fruit and vegetable to study the effects of the sludge fertilizer on the growth of urban landscape plant and effects of heavy metals on growth of crops. Meanwhile, soil column leaching experiment is conducted to discusses the potential harm to soil and groundwater that may be caused by applying sludge fertilize, The main research results are as follows:(1) The organic matter, TN, TP and fertilizing ingredients of the dewatered sludge in Xi’an four sewage treatment plants is almost equal to the content of livestock manure,and the content of heavy metals in sludge accords with the related limit values of mud used in our country’s landscaping and agriculture. Since the dewatered sludge has a higher water content, and EC value, it is not suitable for direct use in land and thus sludge’s direct use in land needs harmless treatment.(2) Mixed additives and sludge composting can effectively reduce the content ofbio-available fraction of heavy metals in the sludge so as to achieve the purpose of deactivation of heavy metals and reduction of the biological toxicity of sludge, and alleviate the toxicity of heavy metals to plants in application of sludge to land;(3) Application of sludge composting can promote the growth of the plants in urban landscaping(Cotinus coggygria Royal Purple, Prunus cerasifera, plum and peach),and have a significant role in promoting plant height, basal diameter, and leaf growth.The content of Cr, Pb, Mn and Hg in the soil of garden greening plants is less affected by the amount of fertilization in 0~2.16kg/m2;(4) Applying proper amount of sludge composting can increase production of agriculture fruit and vegetable(strawberry, green pepper), and excessive application will inhibit the growth. The content of heavy metals in fruits of vegetables and fruit with sludge composting is higher than that with non-sludge composting;(5) The form of heavy metals in sludge composting can be transformed in the soil environment and the biological available content of heavy metal Cu and Zn increases slightly;(6) A soil column leaching experiment shows that soluble salt easily migrates with the leaching solution vertically into the soil column, heavy metal Cr, Pb has a strong ability of vertical migration, the vertical migration ability of heavy metal Hg is weaker than that of heavy metal Cr, Pb and heavy metal Hg has a greater influence on the EC of soil;...