Research On Technology And Policy Of Municipal Sludge Disposal In Jiangsu Province

Municipal sludge is an inevitable byproduct from wastewater treatment plants. With the development of industry and the rapid process of urbanization, there is a dramatic increase in production of sewage sludge. There are lots of soil nutrients such as nitrogen, phosphorus and organic matter contained in municipal sludge. However, there are also heavy metals, organic pollutant and pathogenic bacteria in sludge. So the municipal sludge should be treated and disposed properly. Sludge disposal technologies include incineration, landfill, land application, etc.It is significant to choose the effective technology to dispose municipal sludge according to the actual condition of different area.There are three parts in this text. In the first part, the present situation of production, performance and disposal of sludge were introduced based on the detailed research of the wastewater treatment plants in Jiangsu Province. In the second part, the contents of organic matter, nutrients, heavy metals and heat in sewage sludge of Jiangsu Province were detected. In the third part, technology and management policies about disposal of municipal sludge were researched.The investigation on sludge production showed that wastewater treatment plants in Jiangsu Province pruduced 150000 ton sludge annual. Most of wastewater treatment plants in Jiangsu Province adopted landfill to dispose sludge. However, with the development of population, there is less land that can be used as landfill ground. What is more, the municipal sludge were refused to go to landfill ground. So the problem on disposal of municipal sludge in Jiangsu Province especially in southern Jiangsu is becoming more and more serious.The investigation on sludge character showed that the heat in municipal sludge in southern Jiangsu were higher than that in northern Jiangsu. The heat in sewage sludges of Suzhou, Wuxi and Changzhou city were between 10000-15000 kJ/kg, but the heat in sewage sludges of northern Jiangsu were under 10000kJ/kg. The average contents of organic matter, total N, total P and total K were 404, 36.0, 16.1 and 3.7g/kg respectively, which were all higher than their responding contents in stall manure, except for total K.The average contents of heavy metals in sewage sludge exhibited an order of Zn>Cu >Cr>Ni>Pb>Cd>As>Hg. The concentrations of heavy metals in 80% of sewage sludge samples were found to be lower than 120 mg/kg for Pb, 8.5 mg/kg for Cd, 411mg/kg for Cr, 140 mg/kg for Ni, 1410 mg/kg for Cu, 1650 mg/kg for Zn. The average concentrations of Hg and As were 2.75 and 5.86 mg/kg. As a whole, the heavy metal concentrations in sewage sludge in southern Jiangsu were higher than that in central part and northern part. The fractions obtained by the sequential extraction procedure indicated that Cd were dominantly associated with residual fraction. Cu and Cr were principally distributed in the oxidizable fraction and residual fraction. For Ni and Zn, the concentrations of the acid extractable metals were high, indicating their relatively high bioavailability.Except for Pb, Hg and As, the concentrations of Cd, Cr, Ni, Cu and Zn in several wastewater treatment plants exceeded the heavy metal limits of sewage sludge for land application in China and Cu was the most primary heavy metal pollutant in sewage sludge in Jiangsu Province. Most municipal sludge samples which exceeded the heavy metal limits for land application were in southern Jiangsu. The concentrations of some heavy metals in the municipal sludge of southern Jiangsu exceeded the heavy metal limits severely. Among them, three municipal sludge samples were identified as hazardous wastes.At present, there existed a lot of problems on disposal of municipal sludge. The problem should be solved from the aspect of technology and management. The sludge in Suzhou, Wuxi and Changzhou city were suggested to be disposed together and the best way to dispose them should be incineration or landfill after dried processing. We suggested that the best way to dispose sludge in Nanjing, Zhenjiang and central Jiangsu was landfill and it could be landfilled solely or with municipal solid waste. We also suggested that 0.14-0.20 yuan/m~3 should be added to the present water fee as the charge of municipal sludge disposal.