Study On Heavy Metal Removal From Sludge And Utilization

Some series environmental pollution problems has been risen following the pace of industrialization, urbanization and higher people’s living standards. The founding of the municipal sewage treatment plant to alleviate the industrial waste pollution, while sludge is an inevitable product of the sewage treatment plant. Sludge contains large amounts of N、P、K、organic matter and some trace elements which are necessary for plant growth and have great influence on them. But sludge contains a lot of indecomposable poisonous and harmful substances, such as organic matter, parasites, microbial and heavy metals. It causes serious secondary pollution in case that treated improperly, also effects on the normal operation of the sewage treatment plant. Therefore, we need to take some measures to deal with poisonous substances in the sludge.In this paper, the higher N, P, K nutrient elements in sludge were found by the analysis of the physical and chemical properties of sludge, which hints higher agricultural value, and heavy metal contents and their forms in sludge were studied. In conclusion, the Cd and Ni contents in sludge exceeded the national agricultural acidic soil standards for sludge, didn’t exceed alkaline soil standards. Pb, Cd, Cu, Ni were mainly existed in the form of residual state in sludge, their residual state proportion were 46.22%, 32.50%, 39.04%, 32.50%,respectively. According to the Geo-accumulation index and potential ecological risk index,there is a serious ecological risk with heavy metals in sludge.In this paper, chemical method, microbiological method and electrochemical methods were used to remove the heavy metals in sludge. The removal efficiency and economical effect were discussed. The results showed that the chemical method--treated with sulfuric acid and hydrogen peroxide at p H = 2 had the best economical effect of 5.1 RMB/m3, and the removal rate of Pb, Cd, Ni and Cu were 68.43%, 81.73%, 75.51% and 81.73%, respectively;The microbial leaching with 0.2g of Fe SO4·7H2O and S was the most economical of 2.86RMB/m3. The leaching rates of Pb, Cd, Cu, Ni were 74.72%, 81.54%, 70.46%, 77.35%,respectively; For electrochemical methods, the treating condition of 35 V, 80 m A current and6 h reaction time was the most effective and economical of 5.6 RMB/m3. The removal rates of Cu, Pb, Cd and Ni at anode were 57.35%, 48.42%, 68.63% and 49.85%, respectively.