| At present,desertification land in China accounts for a relatively high proportion,and the task of harnessing desertification is arduous and has a long way to go.The traditional methods of combating desertification are not efficient,and natural conditions and economic conditions are more restrictive.The sludge control system adheres to the concept of "treating wasteland for waste control" and is a sand control measure with development potential.Sludge sand control is a kind of sludge land use method.The sludge contains a variety of heavy metal elements that will enter the soil environment,which will cause pollution to the ecological environment and groundwater;the content of nitrogen and phosphorus in the sludge accounts for a large proportion.High,there is also a risk of eutrophication of groundwater.However,the soil ecological environment itself has certain tolerance and absorption effects on pollutants.The most important thing is the enrichment and absorption of pollutants by plants.In this paper,the environmental risks,comprehensive pollution risks and potential hazard ecological risks of single heavy metals in sandy soil and tall fescue sandy soil under different sludge application rates were investigated.The simulated soil column leaching test was carried out to analyze the soil heavy metal elements in the soil column.The total amount and morphological changes in the surface layer and each layer of soil,and the effects of planting tall fescue on the migration and transformation of heavy metals in the soil and the morphological changes were investigated.The contents of pollutants such as COD,TP,TN and heavy metals in the liquid were changed,and the main conclusions were as follows.(1)With the increase of the amount of sludge applied,the comprehensive pollution index and potential ecological risk index of the soil surface heavy metals increased accordingly;when the sludge application height was 5cm,10cm,15cm,the Mero comprehensive pollution index in the surface soil Compared with the original sand,it increased by 4.41%,19.64%,and 36.72%respectively;the potential ecological risk hazard index increased by 10.25%,18.72%,and 32.25%,respectively.Compared with the original sand,the relevant grading standards were 15cm in the sludge application height.The soil is also only slightly contaminated.Planting tall fescue reduced the Mero comprehensive pollution index and potential ecological risk hazard index in the topsoil.Under the condition of planting tall fescue,the Nemero comprehensive pollution index decreased by 4.47 compared with the control group when the sludge application amount was 15cm.%,potential ecological risk hazard index decreased by 2.44%.(2)Different types of heavy metals have different risks in the soil.The heavy metal form of Cd in the soil surface is the most unstable,and the risk of migration to the surrounding environment is the highest,followed by Ni and Zn.The forms of Pb,Cr and Cu are more stable than other heavy metals,and the risk of migration to the surrounding environment is less;The proportion of exchangeable states of heavy metals in the topsoil was reduced.Under the condition of planting tall fescue,when the sludge was applied at a height of 15 cm,the exchangeable state of Zn in the surface soil of the control group decreased by 51.77%after 80 days.The exchangeable state decreased by 32.70%and the Cd exchangeable state decreased by 26.67%;this indicates that the planting of tall fescue can reduce the risk of migration of heavy metals to the surrounding environment of the soil surface.(3)The more the amount of sludge applied,the greater the risk of migration of heavy metals to deep soils;the risk of different types of heavy metals moving to deep soils is different,and the risk of Cu migration to deep soils is the highest,which is about 6.5 higher than the original sand.Double;Cr and Pb increase the percentage in each soil layer,the maximum can be increased by about 2.5 times;Ni can be increased by about 1.9 times;Zn can be increased by about 1.35 times;Cd can be increased by 1.1 times;According to the distribution trend map in the soil layer,under the condition of planting tall fescue,the content of heavy metal elements in each soil layer was reduced compared with the control group.Planting tall fescue can reduce the migration of heavy metal elements into deep soil.risks of.(4)8 leaching simulation tests,the results show that the more the amount of sludge applied,the greater the risk of heavy metal elements pollution to groundwater,the higher the risk of groundwater pollution by Cd,Cr and Pb,and the certain concentration of groundwater by Ni and Cu.The risk of pollution,Zn has less risk of groundwater pollution;tall fescue has a certain control effect on the risk of leaching pollution of various heavy metal elements.The leaching risk of nitrogen,phosphorus and COD also increases with the amount of sludge applied.Planting tall fescue also has an inhibitory effect on this risk.. |
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