Research On Remediation Effect And Mechanism Of Different Maturity Waste Composts On Heavy Metal Contaminated Soil

In recent years,the problem of soil pollution caused by industrial development has drawn enough attention from all social sectors.In order to protect peat resources and realize the resource utilization of waste,to explore the feasibility of improving the soil with municipal solid waste compost,and to reveal the ecological remediation effect of domestic waste compost on heavy metal contaminated soil.This study comparatively analyzed the physical and chemical properties of primary compost(PC),secondary compost(SC)and secondary compost treated with wood vinegar(WV-SC).Adsorption experiment,composting and pot experiment were used to systematically analyze the characteristics of adsorption and discuss the adsorption mechanism.The effects of different maturity compost and dosages on the heavy metal speciation,soil properties and plant growth in contaminated soils of were studied.1.The adsorption characteristics and adsorption mechanism of PC,SC and WV-SC on Cu,Zn,Cd and Ni were studied through simulated experiments.(1)Secondary composting improved the maturity and changed the morphology characterization.The diameter of secondary compost particles decreased obviously,and the surface became rough.Addition of wood vinegar increases the relative content of carboxyl and phenolic hydroxyl groups in compost.Humic acid content of WV-SC was 26.9 g/kg,significantly higher than the SC and PC(p>0.05),while WV-SC also has higher CEC.Secondary compost increased the proportion of stable forms of heavy metals in composting.(2)The secondary composting improved the heavy metal adsorption capacity.For the single-metal adsorption system,the optimum adsorption conditions were:the initial pH value was 5.0-6.0,the ionic strength was less than 0.1 mol/L and the composting dosage was 8 g/L.The maximum adsorption of heavy metals was Cd>Cu>Zn>Ni.The pseudo-second order kinetic can better explain the trend of heavy metal adsorption over time.Experimentl datas are better fitted with the Langmuir isotherm equation.Adsorption capacity of WV-SC is greater than SC,PC.The thermodynamic parameters showed spontaneous reaction when secondary composting adsorbed heavy metals.The heavy metals adsorbed by SC and WV-SC were mainly in the oxidizable fractions and the residual fractions.(3)The heavy metals adsorption mechanism by different maturity composts showed that the humic acid content and cation exchange capacity of compost determine the selectivity of four heavy metal ions.The distribution coefficient Kd indicates that the order of adsorption by compost is Cu>Cd>Zn>Ni.The functional groups analysis of composts before and after heavy metal adsorption showed that carboxyl group,aromatic structure and phenols play important role in heavy metal adsorption.Metal ions could react with silica-alumina minerals to form complexes.And the ion exchange between Ca and heavy metal ions occurs during the adsorption of heavy metals by SC and WV-SC.2.Pot experiments were conducted with different composts,SC,0.5%WV-SC,2%WV-SC and aging compost by adding different proportions(0%,25%,50%)into the contaminated soils so as to study the effects of different composts on the bioavailability of heavy metals and plant growth.(1)The secondary composting and addition of wood vinegar increased the composts standard.The the organic matter further degraded and humic acid content increased significantly.Total nitrogen,total phosphorus,germination index(GI)increased in secondary compost and wood vinegar treated secondary compost,the heavy metals form more stable fraction.(2)Addition of composts improved the soil property.With more addition of composts,the bulk density of mixed soil showed a decreasing trend.Saturated soil moisture content showed positive correlation with the addition amount of composts.With the increasing proportion of composts added,the content of organic matter,total N and total P in the soil also increased,and adding aging compost has the most significant impact on the nutrient supply to the soil.Adding compost effectively reduced the bioavailability of heavy metals in contaminated soils,the proportion of residual fraction of metals increased.(3)Adding 25%compost had a better effect on promoting plant growth.The addition of aging compost had a better effect on growth,biomass,root length of Sedum aizoon.The root volume of the AC treated group was larger than that of the control group,followed by 25%secondary compost treatments and 50%secondary compost treatments.Adding compost reduces the content of heavy metal in plants.Adding AC and 2%WV-SC had a better alleviating action on the root lipid peroxidation level.This research provided basic research for the establishment of a standardized system for the utilization of municipal solid waste compost resources.