Reading guidance：Municipal sludge is the urban domestic sewage, industrial wastewater treatment of solid waste generated in the process. Along with the development of social economy, sewage treatment rate and degree of

    Municipal sludge is the urban domestic sewage, industrial waste water treatment of solid waste generated in the process. Along with the development of social economy, sewage treatment rate and degree of improvement, increase in sludge production is inevitable, and sludge disposal contradiction is becoming more and more prominent.
  Sludge contains large amounts of organic matter and plant nutrients, is a valuable biological resources, scientific and reasonable land use can decrease the negative effect, so that sludge re enters the natural environment of material and energy cycle, sludge into a resource is the focus of world environment research in the field of attention. But sludge there are many harmful substances, especially the heavy metal is easy to enrichment and migration difficult, with great harm, is the main factor limiting sludge utilization in agriculture.
Generally speaking, sludge composting causes no obvious to the content of heavy metal, but may cause influence to the shape and activity of heavy metals.  Composted sludge water leaching concentrations of heavy metals in the state is usually less than 2% of the sludge after composting, which forms of heavy metals have great changes. General sludge after composting process, water leaching fractions of heavy metals in the amount of decrease, exchangeable and organic combined forms of heavy metals increased; and residual amount of different heavy metals vary, but than other forms of heavy metals in total.
   In order to ensure that after the application of sewage sludge can maximum reduce the degree of accumulation of heavy metal content in soil and to ensure that sewage sludge compost in heavy metal not ecological environment and human and animal health hazards, the compost must passivator. From for the passivation effect of fractions of heavy metals in the exchange, peat, fly ash and phosphorus slag is three effective passivation agent.
  The toxicity of extraction from low absorption not easily easily by leaching of heavy metals in sludge in different forms of biological effectiveness of different water states, exchangeable heavy metal uptake by plants and biological effectiveness of plant toxicity; organic bound and residual forms of heavy metals by plants and biological effectiveness of plant toxicity. Therefore, from the germination rate index changes can explain to the sludge compost added various passivation agent, change the sludge of heavy metals form, make it easy to be absorbed by plant water state, exchangeable to difficult for plants to absorb organic bound and residual state conversion, thereby reducing the sludge compost on plant.
  Adding fly ash, phosphate rock powder and peat passivation agent were conducive to the decrease in the composting of toxicity, especially reasonable passivation agent combination can strengthen the passivation effect of heavy metals in sewage sludge, in a greater degree reduces the toxicity of sewage sludge compost on plant, we are more conducive to the solid waste / harmless purpose. Adding fly ash, phosphate rock powder and peat passivation agent is conducive to reducing the phytotoxicity of compost, especially reasonable passivation agent combination can strengthen the passivation effect of heavy metals in sewage sludge and in a greater degree of reduced toxicity of sewage sludge compost on plant.
  Three passivating agent, fly ash, phosphate rock powder and peat, fly ash is alkaline substances, the addition of fly ash improves the pH of compost samples, reduce the solubility of metal ions, and enhance the stability of the metal organic complex; add ground phosphate rock and heavy metal ion formation is difficult to be absorbed by crops phosphate; peat humic substance, a kind of typical organic matter, toxic heavy metals can and organic matter in the formation of insoluble organic complex and difficult to be absorbed by crops. The results show that the addition of fly ash, peat and add a combination of fly ash and peat on heavy metal toxicity in plants decreased most significantly, which with the study results.
  By adding fly ash in sludge compost, phosphate rock powder and peat different heavy metal passivator can greatly reduce the phytotoxicity of compost, thereby reducing the sludge of heavy metals availability, prevent in agricultural sludge on the environment caused by secondary pollution, effectively ensure the human health. Worth in sludge composting and utilization of large area to promote the use of.
 
 
 

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