Study On The Bioavailability Of Heavy Metal In The Sewage Sludge Stabilization Process

With the development of sewage treatment in cities of China, the production of sewage sludge increased dramatically. The main method of disposing the sewage is landfill in China, which is significant for the sustainable development by prolonging the life of landfill and recycling the landfill sites. The stabilized sludge is mainly employed as manure for agriculture, gardens and land improvement, heavy metals of sludge should comply with the pollution control standards after landfill. Studying on the migration and transformation of heavy metals and the effective of different additives on bioavailability of heavy metals is important for the exploitation and application of stabilized sludge in landfills.In the experiment, the sludge from Shanghai Bailonggang sewage plant was employed to study the bioavailability of heavy metals, form distribution and changes of different forms during landfill process, to compare the effect of different temperature and different additives on bioavailability.It is shown that total amount of heavy metals in pure sludge are different corresponding to the time in the landfill process. After landfill in indoor temperature, pure sludge can not be used for agriculture, gardens and land improvement, however, when temperature changes to 35℃, sludge is good for neutral and alkaline garden soils.After landfill of mixed sludge, total amount of heavy metals are lower than the pollution control standards of agriculture, gardens and land improvement. Construction waste sludg and fly ash are better and safer, the amount of Cr, Cu and Ni increase due to the utilizetion clay and aged refuse.The trend of total amount changes of heavy metals in pure sludge as well as the proportion changes of the total amount of heavy metals in each form is different. After landfill, most heavy metals like Cr, Ni, Cu, Pb and Zn are much more stable than before, bioavailability is greatly reduced, which in favor of reusing processed sludge.Sludge is a biosolid and biodegradable. Additives have little effect on content changes of Cd in vulcanized form and residual form. The effect of clay and aged refuse on passivation of Cr is significant. Passivation of Cu and Pb is accelerated by additives. Similar to Ni, the effect of additived is little. The content of Zn in vulcanized form of mixted sludge is higher due to various additives. In sum, the content of heavy metals in active form is reduced while it is enhanced in vulcanized form and residual form by additives, in addition to this, properties of heavy metals are more stable and bioavailability of heavy metals is greatly reduced.From the analysis, it can be seen that the percentage of Cu is decreased by mixed sludge with construction waste sludg, fly ash and aged refuse when the temperature is 35℃. Compared to indoor temperature, passivation of Cd is accelerated when landfill temperature is 35℃. Cr is more stable in mixed sludge with construction waste sludg, fly ash and aged refuse. Furthermore four additives reduce activity of Ni. How this temperature is not good for decreasing the bioavailability of Pb in mixed sludge with aged refuse.