The Research On Remediation Of Heavy Metal Contaminated Soil By Sewage Sludge And Sludge-derived Biochar

The characteristics of sewage sludge,such as large yield and difficult to deal with,make the disposal of sludge become a research hotspot.Sewage sludge contains so many nutrients that it is considered a waste of resources.The land use of sewage sludge can realize the reuse of resources.The land use of sewage sludge pyrolysis biochar has been widely concerned because of its porous structure,stable heavy metal property and stable carbon element.The survey results of soil pollution in China show that soil pollution is serious,especially heavy metal pollution.Therefore,the application of sewage sludge and sludge-derived biochar(SDBC)as remediation agents to heavy metal contaminated soil not only solves the problem of sludge outlet but also restores the soil,realizing the maximum utilization of resources.(1)The content of nutrient elements in soil was proportional to the application amount of sewage sludge and SBDC and increased with the increase of application amount.Except for N,the content of nutrient elements in soil in SDBC treatment group was higher than that in the sewage sludge treatment group.The increase of K element content was the lowest,and the increase of K content was 53.72% and97.52% respectively under the maximum addition of sewage sludge and SDBC.After the addition of sewage sludge and SDBC,the fertility level of organic matter and nitrogen increased,but the fertility level of K was still at a low level.Therefore,the supplement of inorganic fertilizer K fertilizer should be paid attention to in land use.However,P element content was at a high level in the soil of the control group,indicating that the soil did not need the supplement of P fertilizer.Both the application of sewage sludge and SDBC reduced soil pH value and bulk density,and increased soil porosity,which was conducive to promoting microbial activity and plant absorption of nutrients.(2)Sewage sludge and SDBC had the best repair effect on copper and cadmium under 5% and 10% respectively.For the Cu,in the 5% sewage sludge treatment group,acid soluble state decreased by 50% and residue state increased by 60.39% in the 5%sludge treatment,reducible state decreased by 77.21% and oxidizable state increased by 175.52% in the SDBC treatment group.For cadmium,the sludge significantly increased the proportion of residue state under the 5% application amount,an increase of 25.46%,and SDBC significantly increased the proportion of oxidizable state under the 10% addition amount,an increase of 153.13%.The analysis results of the total amount and morphology of Zn,Pb,Cr and Ni showed that the dynamic proportion ofNi increased with the increase of the applied amount.Attention should be paid to the pollution of Ni when applying sludge and SDBC to healthy soil.(3)The results of ecological risk assessment of soil heavy metals showed that the risk level and risk value of Cu and Cd decreased under the addition of 5% sludge and 10% SDBC.Sewage sludge and SDBC reduce the ecological risk of Pb,and the performance of SDBC is slightly better than that of sewage sludge on the other hand,the risk level of Ni in SDBC increases to the medium risk level under the application of high dosage,so the pollution of Ni should be concerned in the practical application.The health risk of the four heavy metals was ranked as Cr >Pb >Ni > Zn,and the risk of Cr was the highest.The risk of Cr was the largest,but the health risk of single element and total element did not exceed the critical value,so it did not cause health risk.