Studies On Remediation Mechanism And Effect Of Green Waste Compost On Cadmium Contaminated Soil

Soil cadmium(Cd)pollution was one of the most concerned environmental problems in China.Once the Cd content in soil exceeds the standard,it will pose a great threat to human being's health and safety.Applying organic amendments to remediate Cd contaminated soil was a widely used chemical remediation method.At present,there were many studies on the remediation of Cd contaminated soil by organic compost such as sludge,straw,and manure,and there were few studies on green waste compost.In this study,the remediation mechanism and effects of green waste compost on Cd contaminated soil were studied.Through adsorption experiments,explore the adsorption performance and adsorption mechanism of Cd on green waste compost.Soil column leaching experiment to study the influence of green waste compost on the mobility and bioavailability of Cd.Seed germination experiment to explore the effect of green waste compost on early Cd stress.Through pot experiment,the remediation effect of green waste compost on Cd contaminated soil was tested.The conclusion will provide basis and reference for the application of green waste compost in the field of Cd remediation.The main results are as follows:(1)The results of the adsorption experiments showed that the optimal pH value for Cd²⁺adsorption in green waste compost was 7.0.The green waste compost dosage increased from5 g/L by 20 g/L,and the removal rate increased from 58.6%to 98.9%.The smaller the particle size of the green waste compost,the better the adsorption of Cd²⁺.The coexisting cation Ca2+in the solution inhibited the adsorption of Cd²⁺more than Mg²⁺and Na⁺.The study of adsorption kinetics showed that the quasi-secondary kinetic model could well fit the adsorption process of Cd²⁺in the solution,it was revealed that the chemical adsorption mechanism of green waste compost to Cd²⁺was mainly the complexation reaction between the oxygen-containing functional groups(-COO,-CO and-OH,etc.)on the surface of the green waste compost and Cd²⁺.(2)Soil column leaching experiment showed that the green waste compost increased the pH,EC and organic carbon content of the leaching solution,and at the same time increased the leaching loss of Cd.The application of green waste compost reduced the available Cd content in the soil,and at the same time changed the occurrence form of Cd.The percentage of Cd in acid extractable state was reduced by 4.6%?9.4%,and the percentage of Cd in reduced,oxidized and residual states was increased by 2.9%?7.1%,1.2%?1.5%,and 0.5%?1.0%,respectively,and reduced the bioavailability of Cd in soil.(3)The seed germination experiment showed that the application of green waste compost could significantly alleviate the inhibitory effect of Cd on the seed germination and seedling growth of pakchoi cabbage:it improved the germination rate,germination potential,germination index and vitality index of pakchoi cabbage seeds,and promotes the growth of pakchoi cabbage roots and buds.Protects cell membrane permeability,increased the chlorophyll content,and significantly reduced the Cd content in the roots and buds of pakchoi cabbage.(4)The pot experiment of using green waste compost to to remediate single Cd contaminated soil showed that:green waste compost increased soil pH,organic matter content,available phosphorus and available potassium content;significantly increased the activities of urease,catalase and dehydrogenase in Cd contaminated soils;and reduced the soil available Cd content,which reduces the mobility and bioavailability of Cd in the soil-plant system.Application of green waste compost increased the biomass and chlorophyll content of pakchoi cabbage,and significantly reduced the root Cd content of pakchoi cabbage by 30%?36%and the leaf Cd content of 43%?69%,and reduced Cd accumulation and transportation in pakchoi cabbage,leaf BCF decreased from 0.62 to 0.22,TF decreased from 0.94 to 0.46.(5)Remediation experiment of Cd,Zn,Cu,and As compound contaminated soil by using green waste compost showed that the green waste compost increased soil pH(0.11?0.26 units),EC(3.5%?15.2%)and organic matter content(3.1%?35.1%),and significantly increased the soil urease,catalase,and dehydrogenase activities;effectively reduced the content of available Cd,Zn,Cu,and As in the soil,of which the available Cd content decreased by 33%to 48%.Application of green waste compost significantly increased the root and leaf biomass of pakchoi cabbage by 40%?83%and 29%?59%,and significantly reduced the stress resistance of pakchoi cabbage such as SOD activity,POD activity,CAT activity,MDA content and free proline content,reduced the absorption of Cd,Zn,Cu,and As by the roots and leaves of pakchoi cabbage.Among them,the Cd content of the roots and leaves of pakchoi cabbage decreased by 21%?44%and 26%?53%,respectively.In conclusion,the green waste compost had a good passivation effect on Cd contaminated soil,which provide a theoretical basis and practical guidance for the cgreen waste compost to remediation of Cd contaminated soil.At the same time,it also opened up a new way for the resource utilization of green waste compost.