Study On The Remediation Of Cd And Ni Co-Contaminated Sediment With Humic Substances Produced By Compost As Washing Agent

At present,the indiscriminate discharge of industrial and agricultural sewage has caused serious heavy metal pollution in rivers,lakes and other water bodies.Heavy metals in water exist in sediment with various forms and keep available to living organisms for a long period.However,heavy metals cannot be permanently immobilized in sediments.When the surrounding environment is disturbed,heavy metals in sediment may be released again,which poses a great threat to human health,food safety and eco-environment.Compared with other remediation technologies,soil washing is a relatively inexpensive and efficient method in soil remediation that can fundamentally remove the pollutants.The key to soil washing technology lies in the selection of washing agent.However,traditional soil washing agents such as EDTA and FeCl₃ have been reported with negative effects on environment and organisms.Therefore,in this manuscript,we used humic substances（HS）,an environment-friendly and low-cost washing agent,for remediation of heavy metals contaminated sediment.In this study,the physicochemical properties and heavy metal pollution status of contaminated sediment were determined and evaluated.The content of Ni in the samples of the two sediments was the lowest,both within the standard range,and the pollution degree of Zn,Cu and Pb was between no pollution and moderate pollution.Cd contamination was the highest,2.5 to 11 times higher than standard sediment samples.Next,HS selected from 8 composting groups（maize straw,sesame straw,peanut straw and fallen leaves,with or without grape marc）as washing agent were used to remove Cd and Ni from artificially contaminated sediments.Sesame straw compost appeared to have the highest removal capacity for heavy metals through a series comparison on Cd removal efficiency,yield of HS and fulvic acids（FA）,and seed germination index.The selected sesame HS was further used to wash two contaminated sediments of varying properties（a clay type for sediment 1 and a silty loam for sediment 2）.Batch desorption experiments were conducted to determine the optimum HS concentration,equilibrium time,pH,solid-to-liquid ratio,and washing frequency.Under optimum conditions,a triple washing removed 74.16%of Cd and42.91%of Ni from sediment 1,and 86.88%of Cd and 43.84%of Ni from sediment 2,respectively,whereas a commercial FA only achieved half of the efficiency.After washing,both sediments were identified with increased contents of total organic matter total nitrogen and phosphorus,but the change of pH was small.Furthermore,removing 1%Cd from contaminated sediment using our compost HS only cost 0.87US$t^-1,which has a significant economic benefit.Therefore,HS from the sesame straw compost is a cost-effective,efficient and environmental-friendly washing agent to remove heavy metals from contaminated sediments.