Reading guidance：Sludge utilization in agriculture is mainly because it contains a high content of nutrients in sewage sludge, sludge use in agriculture can provide certain fertility soil. However, the sludge in agricu

   Sludge utilization in agriculture is mainly because it contains a high content of nutrients in sewage sludge, sludge use in agriculture can provide certain fertility soil. However, the sludge in agricultural use must control the content of sludge on the heavy metal content and pathogen, in order to make the sludge are capable of effectively used in agriculture.
    For a variety of harmful substances contained in the sludge, heavy metal objects should be given special attention. This is because the special heavy metal pollution: first, no microbial degradation of heavy metals; secondly, microorganisms can be transformed into some heavy metals more toxic pollutants. The agricultural sludge, heavy metals in sewage sludge one part will enter the food chain through the crop absorption, adversely affect human health; the other part will stay in the soil for a long time, therefore, if the amount of sludge application time is too long or too large, will lead to soil pollution. While the urban sludge in general are more or less containing heavy metals, whether it can be the key agricultural is the content of the heavy metals.
   At present, relevant data show that although individual sewage treatment plant of one or several heavy metal content is likely to remain high, but in recent years, the contents of heavy metals in China's urban sludge presented a clear downward trend, visible in the sludge of heavy metals pollution problem is gradually eased. Heavy metal bio availability and potential transfer of not only with the total relevant, greater extent by its chemical speciation in environmental media determined. According to Tessier proposed by sequential chemical extraction method, metals were classified into five types: exchangeable, bound to carbonate, iron and manganese oxide bound, organic state and residual state. The combination of organic bound and residual sludge and the force is very strong, after the transfer of land administration to the poor; and exchange occurs easily state and soil solution, have very strong migration; carbonate bound and Fe Mn oxidation state under certain conditions can be utilized by plants, there is migration sure. So the existence of heavy metals in organic state and residual state is called a stable state with heavy metals; exchangeable, carbonate bound and Fe Mn oxide bound heavy metal state is called the unstable state of heavy metals. Therefore, when the sludge for agricultural, contents and form of heavy metals in the sludge is the factor must be taken into account. In addition, it should also be considered for a period of time after the application of sludge in heavy metal accumulation in soil.
   Human and animal feces and food, such as meat processing waste water, containing a considerable number of pathogenic microorganism and parasite eggs, of which about 90% more than the sewage treatment is condensed into a sludge. Once these sludge without treatment into the farm, a variety of pathogens in sludge will spread through various channels, to human health that pose a threat to agricultural production and ecological security. Therefore, the sludge stabilization and harmless treatment is absolutely essential. The research shows that the sludge in the vast majority of pathogenic microorganism and parasite eggs only at a temperature of 50~60 DEG C heating about 30min will be killed, and will not cause plant nutrients in sewage sludge the loss of sludge. At present the common sterilization method with lime disinfection method, radiation processing method, drying method, digestion method (divided into anaerobic digestion and aerobic digestion reactor). Fertilizer law and so on, from the perspective of economics, the cost of the first three methods of treatment is higher, and then the cost of the two methods is relatively low.
 
   
 

：Municipal sludge disposal has a long history Using sludge to agricultural field is worth being carried out. ：We are in an awkward situation in the process of sludge disposal We should have a good command of present situation