Effects Of Sewage Sludge Vermicompost On Land Application And Risk Assessment Of Heavy Metals

With the development of our country economic and urbanization and the population increasing continually,the sewage sludge yield increased year by year.The sewage sludge treatment and disposal issue have severely affected on the development of economy and security of environment and ecological in China.The sewage sludge was applicated in farmland in many distracts and countries in the world,because there were plenty of nutritions and orgenic matter in sewage sludge,which could amende the farmland soil and decrease the fee of sewage sluge treatment.However,the application of sewage sludge to farmland would increase the accumulation of heavy metals(HMs)in farmland soil,at the same time,the heavy metals in soil could enter the hunman body and be harmful to human health.In laboratory experiment,sewage sludge vermicompost were applied to the soils at seven percentage levels: 0(control),5,10,30,50,70 and 100%,respectively.The pakchoi growth condition and biomass were selected as the observation index.The result showed that the pakchoi reached the maximum biomass when the sewage sludge vermicompost proportion was 10%.In field experiment,pakchoi(Brassica campestris L.ssp.Chinensis(L.)Makino var.communis Tsen et Lee),maize(Zea mays L.),eggplant(Solanum melongena L.),cucumber(Cucumis sativus L.),pepper(Capsicum annuum L.),carrot(Daucus carota L.sativa Hoffm.)and black soya bean(Glycine max(L.)Merr)were selected as the tasted plants to explore the effects of sewage sludge vermicompost on land application and the growth of plants.The bioconcentration regularity of heavy metals in different plants was also been studyed.Result showed that the concentration of total organic matter,the total nitrogen and available phosphorus in sewage sludge vermicompost amended soil were 2.31,2.10,8.84 times than control soil,the amended soil pH reduced from 7.61 to 7.31 and the electrical conductivity increased from 0.344 mS/cm to 0.459 mS/cm,the sewage sludge vermicompost played a role in improving the soil chemical properties.The edible parts increase rate of eggplant,pepper,pakchoi,cucumber,carrots,black beans,maize were 86.96%,56.12%,86.76%,164.42%,41.67%,4.17% and 63.43%,compared with the plants grown in control soil,respectively.At the same time,the sewage sludge vermicompost promoted the synthesis of Chlorophyll and Vitamin C.Contents of HMs(Mn,Ni,Cu,Zn,As,Pb and Cd)in amended soil and plant edible parts(pakchoi,maize,eggplant,cucumber,pepper,carrot and black soya bean)were not exceeded the relevant national maximum allowable levels in soil and foods.The plants grown in amended soil showed different bioaccumulation for heavy metals,and the bioaccumulation of heavy metals was higher in root than leaf for pakchoi,at the same time,pakchoi had the strong bioaccumulation for Zn and Cd.The bioaccumulation of Mn,Ni,Zn,as,Cd in the stem and leaf was higher than root tuber for carrot,while Cu and Pb were instead.Heavy metals mainly accumulated in the roots and stems and weakly accumulated in edible parts for maize,eggplant,cucumber,pepper.Compared with other tissues,black soy bean seeds had the strong bioaccumulation of Mn,Ni,Cu and Zn and weak bioaccumulation of As,Cd and Pb.According to the risk analysis of heavy metals pollution and the potential ecological risk,soil wasn't polluted by sewage sludge vermicompost and the level of potential ecological risk belong to low ecological risk.The target hazard quotient of heavy metals were less than 1,which indicated that the concentration of heavy metals in edible parts were not harmful to human health.