Phytoremediation Engineering Practice And Effect Evaluation Of Zinc Contaminated Agricultural Soil

In recent years,the issue of soil zinc pollution has attracted widespread attention.Zinc is an essential trace element for the growth and development of animals and plants.However,when the zinc content in the soil is too high,it can lead to soil degradation,posing a great threat to plant growth and human health.As a bioremediation method,phytoremediation technology is widely used in the heavy metal pollution of agricultural land soil.Compared with chemical and physical remediation methods,phytoremediation can not only save costs,have certain remediation effects,but also not easily cause secondary pollution,and minimize the damage to agricultural land,which is worth popularizing.This study investigated the current situation of a soil pollution field in Chongming,combined with literature review,selected remediation technology,designed a phytoremediation project,implemented an ecological remediation project,and carried out a ten month follow-up monitoring.Finally,using the analytic hierarchy process and comprehensive evaluation method,an evaluation model was constructed to compare the remediation effects of remediation projects in each plot,and select the most suitable combination of phytoremediation for soil zinc pollution in the study area.It is expected to provide a reference basis for plant allocation for remediation of zinc contaminated soil of the same type,and provide engineering reference for phytoremediation of zinc contaminated sites of the same type,The main conclusions are as follows:(1)According to on-site research,the zinc concentration in the soil ranges from214 to 476 mg/kg,with 53.3% of the zinc exceeding the standard,indicating mild to moderate pollution.The overall soil is weakly saline alkaline.According to the type,degree,geographical location and other factors of heavy metal pollution in the study area,the advantages and disadvantages of different site remediation technologies and applicable scenarios are compared,and phytoremediation technology is determined to be used.The local plant metasequoia chosen for planting has a high survival rate and is easy to form a good landscape effect.At the same time,mixed planting of Ficus chinensis,Hemerocallis,Ryegrass,and Phragmites australis on different plots results in good plant growth and high coverage during the restoration process.(2)After restoration by various plant combinations,the soil zinc content in the study area ranged from 199 to 313 mg/kg.Except for the "metasequoia+ryegrass" plot(1.04 times the screening value),the soil zinc content in each plot was lower than the screening value(300 mg/kg).From the perspective of zinc indicators,the "metasequoia+ryegrass" plot has the largest decrease in total zinc content,at 26.24%.From the perspective of physical and chemical indicators,the soil pH values of each plot are stable between 8.0 and 8.3,and the conductivity is between 136 and 237 μBetween s/cm,the conductivity decreased significantly,and phytoremediation improved the soil salinity.From the perspective of soil fertility,the soil fertility after restoration is "Metasequoia+Hemerocallis fulva" > "Metasequoia" > "Metasequoia+Phragmites communis" > "Metasequoia+Ryegrass" > "Metasequoia+Miscanthus chinensis",which is generally at a medium fertility level.The soil can still maintain the nutrients required for plant growth in the process of phytoremediation.From the perspective of plant absorption characteristics,the root is the main organ for zinc enrichment in four herbaceous plants,with the highest zinc content in the upper and underground parts of the rye grassland,at 158.4 mg/kg and 477.5 mg/kg,respectively.The enrichment coefficients of reed and ryegrass in summer are greater than 1(1.34 and 3.02),indicating that reed and ryegrass have a strong enrichment effect on zinc in soil.From the perspective of soil microorganisms,the richness of soil microbial communities in each plot shows a trend of first increasing(from March to June)and then decreasing(from June to December),with no significant difference in diversity.(3)In the process of phytoremediation,six main weeds were found in the plot,namely Setaria viridis,Polygonum hydropiper,Erigeron breviscapus,Solanum nigrum,Echinochloa crusgalli and Zizania latifolia.Among them,Dogtail grass,Xiaopeng grass,and Solanum nigrum showed strong zinc enrichment ability,with BCF values greater than 1,1.52,1.46,and 1.08,respectively.Therefore,for this block,in the early stage of phytoremediation of soil zinc pollution,certain weeds can be retained without affecting the growth of main remediation plants.In the later stage of remediation,weed coverage can be adjusted according to the removal of zinc,which helps to shorten the period of phytoremediation of soil zinc pollution.(4)By using the Analytic Hierarchy Process to determine the weights of each indicator,and then using the Comprehensive Evaluation Method to calculate the comprehensive scores of each plant combination plot,from high to low,the order is "Metasequoia+Ryegrass"(3.663)> "Metasequoia+Wujie Mang"(3.044)> "Metasequoia+Hemerocallis"(2.965)> "Metasequoia+Phragmites australis"(2.509)> "Metasequoia"(2.166).The combination of "Metasequoia+Ryegrass" has the highest comprehensive score,indicating that the restoration effect of this plot is the best,When the soil zinc content is below 480 mg/kg,using a combination of "metasequoia+ryegrass" plants to repair zinc contaminated soil can control the soil zinc content within the screening value within about a year.