Study On Effects Of Inorganic Salts On Forms Of Heavy Metals Pb And Zn During Municipal Sludge Composting

In recent years,with the rapid development of economy and the ascension of urbanization level,the yield of urban sludge is increased constantly.There being plenty of organic matter and nutrients exist in urban sewage sludge,which can make the sludge become a kind of useful biological resource and it is conducive to the improvement of soil quality.We can get more organic fertilizer and relieve stress of sludge accumulation,because the soil can be cleaned by itself.By adding fly ash,rice straw,ammonium carbonate,sodium silicate,potassium sulfate in sludge,we can analyze the effect of Pb and Zn forms when the inorganic salts deal with heavy metals in sludge aerobic composting,and we can explore the effective passivator to reduce the bioavailability of heavy metals.The experimental results show that the total amount of Pb is 200.7 mg·kg-1,and the total amount of Zn is 233.8 mg·kg-1.The exchangeable content of Pb is accounted for 36.97%with greater bioavailability.In the process of composting,the content of exchangeable Pb is decreased to 1.92%,which can obviously finish the passivation effect of exchangeable.The inactivation of ammonium carbonate,sodium silicate and potassium sulfate are accounted for 94.45%,86.51%and 84.69%.The inactivation of controlled experiment is 85.83%.Therefore,the composting quality of ammonium carbonate is the best,and the other inorganic salt is the same as controlled experiment.In the process of urban sewage sludge composting,the exchangeable content of Zn is accounted for 19.29%.The Sludge composting changes five kinds of forms and the content of exchangeable of Zn is decreased by 2.20%,and bioavailability is significantly decreased.The inactivation of ammonium carbonate,sodium silicate and potassium sulfate are accounted for 87.62%,73.54%,75.25%.The inactivation of controlled experiment is 74.36%.Therefore,the composting quality of ammonium carbonate is the best,and the other inorganic salts are no effect on sludge composting.So it can be concluded that ammonium carbonate is befitting for passivation agent to reduce the content of Pb and Zn in sewage sludge,and finish the purpose of reducing its biological effectiveness.