Study On Migration And Accumulation And Control Of Heavy Metal In Municipal Sludge Compost Amended Loess-Alfalfa System

Municipal sludge is a by-product of the sewage treatment process,and its disposal is the primary problem in sewage treatment around the world in the field of sewage treatment.With the vigorous development of China's construction of ecological civilization,it is imperative to explore a localized and economical sludge disposal methods to adapt to local condition.Combining the results of the study of sludge composting technology and sludge land application technology,in this paper,loess of Malan in the northwest area was the test material,amended with municipal sludge compost.In municipal sludge compost amended loess-plant system,Copper?Cu?,Zine?Zn?,Cadmium?Cd?,as the typical heavy,and alfalfa,as the tested plant,were determined to access the the safety and effectiveness of modified loess.The optimal ratio of municipal sludge compost to loess and bioaccumulation of heavy metals in municipal sludge compost amended loess-plant system were clarified.The main research contents and results are as follows:1.The physico-chemical properties of loess were effectively improved after municipal sludge addition.The content of organic matter,nitrogen and phosphorus of loess was increased.The organic matter content of the loess increases by 13.5%,36.3%,88.6%,159.2%,213.1%and 321.2%,respectively,when the proportion of sludge compost is applied by 0.5%,1.5%,3%,6%,10%and 15%.The content of ammonium nitrogen and available phosphorus increased 6.2%,and 183.5%respectively,when the ratio of sludge compost was 15%.Loess fertility and environment of plant growth with the improvement physical and chemical properties and fertilizer retention performance of loess had been improved.When the proportion of sludge compost is applied by 3.0%,the total plant height and total biomass of stems and leaves increased by 32.9%and263%,respectively,compared with the control group.2.Tthe extracted average concentrations of Cd,Cu and Zn in municipal sludge compost amended loess increased by 137.8%,20.1%and 44.5%with increasing municipal sludge compost application rates.In terms of the analysis of chemical fractionation indicated,Cd in loess of Malan was dominated mainly fraction of carbonate binding state and the fraction of exchangeable was low.However,the fraction of exchangeable concentrations of Cd increased higher than that the increased concentrations of Cu and Zn.The existence of Cu and Zn was mainly in residual fractions.From the perspective of single-step extraction of morphological content,the bioavailability of heavy metal Cd was higher than that of Cu and Zn.DTPA extraction was the highest in the phytoavailability of heavy metals.3.The variation range of Cd in municipal sludge compost amended loess was from0.103 mg�kg^-1 to 0.245 mg�kg^-1.When the proportion of sludge composting was 6%,the Cd concentration in stems and leaves increased by 46.5%,48.5%and 174.9%in the first,second and third cutting periods,respectively.under the conditions of the ratio of sludge compost modified loess,the content of Cd in the stems and leaves of alfalfa did not exceed the Feed Hygiene Standard.?GB13078-2017?related limits.4.The Cd accumulation range of stem and leaf of alfalfa on the ground was from4.89 to 11.48 ug�pot^-1.The Cu?Zn accumulation range of stem and leaf of alfalfa on the ground was from 0.35 to 0.514 mg�pot^-1,from 2.89 to 4.47 mg�pot^-1,respectively.Cd in alfalfa had lower transference and showed good tolerance to Cd.And it had better migration of Cu and Zn.When municipal sludge compost was applied at the same ratio,the accumulation of Cd and Zn was higher at the second mowing than at the other mowing stages,especially the accumulation of Cd was significantly different,while the accumulation of heavy metals in Cu was significantly higher at the second and third mowing than at the other mowing stages.To sum up,municipal sludge compost could be used as an amended of loess to improved loess property and planting environment.For the cultivation of alfalfa,when the ratio of sludge compost was 3%,the plant height and biomass can reach the optimal growth state.Alfalfa can be safely planted when the ratio of sludge compost is less than15%.It is essential to monitor Cd concentration in municipal sludge compost amended loess because of its high unavailability.