Influence Of Different Additives Ratios On The Efficiency And The Forms Of Heavy Metals During Sewage Sludge Composting Process

With the development of the economy and the acceleration of urbanization, the amount of sewage sludge produced in the city is increasing. The sewage sludge is recycled by aerobic composting, can not only solve the problems about its treatment and disposal, but also can provide high-quality fertilizer and plant nutrient soil for agriculture, forestry and city greening. It realizes biological recycling of resources and has significant economic, social and ecological benefits.An investigation on the influence of different ratios of conditioners including mushroom slag and waste clay on the composting effect of sewage sludge has been developed with the application of high-temperature aerobic composting process. With the determination of temperature, moisture, p H, conductivity, organic matter, total nitrogen, total phosphorus, total potassium, seed germination rate, content of heavy metals, content of diverse forms of heavy metals and other indicators, this paper discusses the rules of migration and transformation of heavy metals during the composting of sewage sludge in the expectation that the composting products meet the need of safe usage. The conclusions are as follows:1. Use the different ratios of additives including mushroom slag and waste clay on the composting effect of sewage sludge, after 26 days, six treatments can meet the requirements of the composting harmless, the moisture content down to below 20%, p H value was stable in the range of 7.4-7.8, EC value is maintained in the range of 1.62-1.73 ms/cm, in the safety range of crop growth; seed germination rate reached 80%, on plant growth and nontoxic. The sludge of each treatment is in accordance with the technical specifications of the sludge and organic fertilizer in the garden greening, and achieves the requirements of safe agricultural.2. After completion of compost, the six treatments of organic matter mass fraction were 27.24%, 26.36%, 30.02%, 31.55%, 38.72% and 38.80%, mass fraction of total nutrient are 4.00%, 4.17%, 4.58%, 4.57%, 4.95% and 4.95%. It is conformed to the requirements of organic fertilizer for agricultural technical indicators. Among them, due to the mushroom slag and waste clay add different proportions, the additives ratio 6(sludge: mushroom slag: waste clay =12:10:3) of the organic matter content of the highest nitrogen retention is the best and the total nutrient content of the highest compost effect is obviously superior to the other five.3. The content of heavy metals in the raw sludge was different, and the content of Zn and Cu was the highest, which was close to the control standard of the agricultural sludge in our country(p H<6.5). The content of Pb and Cd was lower. After composting, the content of heavy metals in each treatment was much lower than that in the standard limit of the soil and the quality of the agricultural sludge in the garden greening(p H>6.5). At the same time, the content of total Pb and total Cd is less than that in organic fertilizer, and achieves the requirements of safe agricultural; the overall trend of migration and transformation of heavy metals changed from easy-migrating form to difficult-migrating form, of which the influence on Zn and Cd is the best. On the whole, the additives ratio 6 reached the most remarkable result.4. Considering the effect of composting, the additives ratio 6(sludge: mushroom slag: waste clay =12:10:3) reached the most remarkable result on the efficiency and the passivation effect of heavy metals form during sewage sludge composting process. But from the point of view of economic considerations, the additives ratio 2(sludge: mushroom slag: waste clay =10:3:3) is more conducive to the utilization of sludge resources market prospects.