Effects Of Sewage Sludge Compost On Soil-plant Systems

With substantial increase in the sewage treatment rate, each year, China needs to dispose of a large number of sewage sludge. The rich organic matter and nutrients in sewage sludge are able to improve soil, increase soil fertility, and promote plant growth. Using the urban sludge in forestland, the sludge of heavy metals and other harmful substances will not enter the food chain; while, forest plants can purify heavy metals and other harmful substances. In this paper, we analysis the change of physical and chemical properties, nutrient content of the soil, and the change in growing plants, research the effect of urban sewage both on soil and plants. We conduct this research on the use of sewage sludge in forestland to provide a scientific reference.This study selected sludge compost products as a research object from Nanjing Jiangxinzhou sewage treatment plant sludge, which treated by rapid aerobic composting, and mixed with woodland 0-30cm soil layer to CK (0%),5%,10% and 20%(dry weight ratio).Then plant poplar and cockoo, research the impact of the mixtures of sludge to soil-plant system. Through soil leaching test, research the impact to the soil and water environment. The results are as followings:(1) When sludge compost is mixed with forest-land soil, the improved woodland soil has stable pH and water rates. Organic matter, hydrolysable N and available P increased with sludge compost increased gradually. It showed a 20% processing> 10% processing> 5% processing. Therefore, Sludge compost can improve soil nutrient content and improve soil fertility, which will has a long fertilizer efficiency duration, therefore, meet the requirements of continuous production plants.(2) Sludge compost can promote plants growth. Populus euramevicanacv's height and Rhododendron's crown are significantly increased. Populus's growth rate increased when sludge compost increased gradually, with a 20% processing> 10% processing> 5% processing; while Rhododendron increased with a 10% processing, its crown has a 20% processing> 10% processing> 5% processing rule.(3) After putting in sludge compost, heavy metal increased within the soil, however, all the numbers are lower than the third in value of soil environmental quality standard(GB 15618-1995). In spite of Cd element content in 10% of the 0-20cm treated soil layer,20% treated 0-20cm and 20-40cm soil, other heavy metals qualified by soil environmental quality standards (GB15618-1995) secondary standards. All the heavy metals decreased as time goes by. Heavy Metals content showed that Ni elements had maximum activity, Cd is the second, and Cr is the minimum.(4) Simulated leaching test results show that the leach ate phosphorus and total nitrogen content is increased with the increase of sludge in soil, but lower than limits set in irrigation water quality standards (GB 5084-92) standard. Heavy metal elements meet Surface Water Environment Quality Standard typeⅢ. Cd, Cr Cu, Ni, and Zn were lower than Surface Water Environment Quality Standard typeⅡ.Cd and Cr were not detected in the 5% treatment leachate samples.