Phytoremediation Technology Of Cadmium-Contaminated Soil Improved By Sludge-Turf Composite

In recent years,cadmium(Cd)pollution continues to rank first in soil heavy metal pollution,seriously endangering soil environment,plant growth,and threatening human and animal health through the action of food chain.Therefore,soil cadmium pollution is an urgent environmental problem to be solved.At present,extensive researches have been carried out in soil improvement and plant enrichment technology,but these researches have not been applied in production practice due to high technical requirements,great influence on soil and high cost.Therefore,an ecological remediation technology of heavy metal polluted soil was studied in this paper.In this study,the artificial simulation of cadmium-contaminated soil(25 mg/kg)was taken as the research object,and the composite conditioner of sludge and grass soil was added.Poa pratensis,Zoysia grass,Pinus tabulaeformis and Pinus sylvestris were selected as the test plants,and the remediation effects of these four plants on the soil contaminated by heavy metal cadmium were investigated through pot experiment.The main research conclusions are as follows:1.The basic properties of soil were changed by applying the composite conditioner made of sludge and turf soil(1:1,calculated by dry mass ratio)into the soil.The p H value decreased from 6.98 to 5.85 when 15%-45% compound improver was applied.The electrical conductivity value increased by 43.93%-192.5%compared with the control experiment.Soil organic matter increased by 81.9% to266.2% compared with the control experiment.2.The biomass of Poa pratensis,Zoysia grass,Pinus tabulaeformis and Pinus sylvestris were increased after the compound improver was applied.Under 25 mg/kg cadmium stress,the dry weight of underground and above-ground Poa pratensis increased by 19.1%-36.46% and 19.89%-33.83%,respectively,compared with the control group.The dry weight of the lower part and the above part of Zoysia grass increased by 22.47%-44.46% and 21.89%-37.59%,respectively.Dry weight of underground and above-ground parts of Pinus tabulaeformis increased by20.27%-28.37% and 13.14%-26.27%,respectively.The dry weight of underground and above-ground parts of Pinus sylvestris increased by 13.77%-25.97% and12.28%-22.77%,respectively,which indicated that the application of amendments in the scope of this study could promote the growth of plants.3.Under the same treatment conditions,the distribution characteristics of cadmium in different plants are different.The cadmium content of various organs of Zoysia grass was in the order of stem > root > leaf,Poa pratensis was in the order of root > stem > leaf,and Pinus tabulaeformis and Pinus sylvestris were in the order of root > stem > leaf.4.The concentration and migration ability of heavy metal cadmium in plant organs was increased by the application of complex amendments.The enrichment coefficients of the roots,stems and leaves of Poa pratensis,Zoysia grass,Pinus tabulaeformis and Pinus sylvestris were higher than those of the control group,and the enrichment coefficients of the roots,stems and leaves of Pinus tabulaeformis and Pinus sylvestris showed a trend of first increasing and then decreasing with the increase of the application ratio of compound conditioner.The migration coefficients of Poa pratensis,Zoysia grass,Pinus tabulaeformis and Pinus sylvestris were 0.5-0.78,0.64-0.87,0.36-0.40 and 0.49-0.61,respectively.The enrichment coefficients and migration coefficients of the two herbs were greater than those of the two woody plants.In the range of this experiment,25% of compound amendments had the best effect on the transfer of cadmium from ground to ground in Poa pratensis,Pinus tabulaeformis and Pinus sylvestris,and 35% of compound amendments had the best effect on the transfer of Zoysia grass.5.The application of amendments had an effect on the distribution of heavy metal cadmium in soil.The exchangeable state and Fe-Mn oxide binding state increased with the increase of the application proportion,the carbonate binding state and organic binding state decreased with the increase of the proportion of amendments,and the residue state did not change much with the application of amendments.The p H value,organic matter and electrical conductivity were significantly correlated with the morphology of cadmium.On the other hand,p H value was negatively correlated with the change of bioavailable cadmium content in soil,while organic matter and electrical conductivity were positively correlated with the change of bioavailable cadmium content in soil.6.There were differences in the application ratio of the four amendments with the best remediation effect on cadmium-contaminated soil.When the proportion was25%,the cadmium accumulation in Poa pratensis and Zoysia grass was the highest,and the lowest cadmium content in repaired soil was 21.17 mg/kg and 22.86 mg/kg,respectively.When the proportion was 15%,the cadmium accumulation in the body of Pinus tabulaeformis was the highest,and the cadmium content in the restored soil was the lowest at 24.43 mg/kg.When the proportion was 35%,the accumulation of cadmium in the body of Pinus sylvestris was the highest,and the minimum content of cadmium in the soil after restoration was 23.76 mg/kg.In terms of short-term remediation effect,Poa pratensis herbaceous plants had the best remediation effect when the proportion of compound improvers was 25%,which could be used as a technology for rapid remediation of cadmium-contaminated soil.