Remediation Of Cd-contaminated Soil By Annual Rotation Of Peanut And Rape And Resource Utilization Of Their Harvests

Plant rotation is one of the most widely used remediation methods for heavy metal contaminated soil in recent years.Previous studies have been carried out to repair heavy metal contaminated soil by the crop rotations of peanut-canola,rape-ryegrass-sweet sorghum,chicory-oil sunflower and other crops.Peanut and rape are oil crops and important economic crops in our country,and they have a certain enrichment effect on heavy metal Cd.Therefore,this paper reaserched the growth and absorption characteristics of peanut and rape in light and moderate cadmium（Cd）,and the effects on Cd contaminated soil by the different peanut cultivation methods（"Double-seeding"and"Single-seeding"）.In addition,peanut and rape are lignocellulosic biomass,and the straw contiminated can be processed into bio-energy.Therefore,this study liquelied the harvested peanut and rape straws by thermochemical technology under different parameters to generate bio-oil,discussed the influence of liquefaction parameters on the production process of bio-oil,and analyzed the main chemical composition in bio-oil using gas chromatography-mass spectrometry（GC-MS）,the volatile distribution of hydrocarbons in bio-oil by carbon number method,and the content and form of heavy metal Cd in bio-char and bio-oil produced after liquefaction.The main results are as follows:（1）The biomass in light Cd contaminated soil was greater than the same treatment in moderate Cd contaminated soil for the two peanut varieties（Zhonghua 16 and Zhonghua215）,and the aboveground biomass of rape（The previous crop was Zhonghua 16）was greater than the aboveground biomass of rape（The previous crop was Zhonghua 215）.The biomass of rape in light Cd contaminated soil was greater than the same treatment in moderate Cd contaminated soil in maturity under the two cultivation methods;moreover,the total content of Cd absorbed by Zhonghua 16 in moderate Cd contaminated soil was greater than the same treatment in light Cd contaminated soil,while Zhonghua 215 existed this characteristic under"conventional double-grain"cultivation.In summary,the total content of Cd absorption and Cd accumulation for Zhonghua 215 were greater than that of Zhonghua16,and the content of Cd in aboveground was greater than that of the underground,while Zhonghua 16 had the opposite trend.（2）Under the“Double-seeding”and“Single-seeding”cultivation methods,the Cd content in the soil of the two peanut varieties after harvest was higher than the standard limit of 0.3 mg/kg,but the DTPA-Cd content in the soil was lower than 0.3 mg/kg.Under different treatments,the Cd content of the rhizosphere soil of rape（The previous crop was Zhonghua 16）was the highest in maturity,while the Cd content of the non-rhizosphere soil was the lowest in flowering,and the Cd content of non-rhizosphere soil of rape（The previous crop was Zhonghua 215）was the lowest in flowering.In addition,the content of DTPA-Cd in the non-rhizosphere soil of rape（The previous crop was Zhonghua 16）,and the rhizosphere and non-rhizosphere soil of rape（The previous crop was Zhonghua 215）were the highest in buding.The rhizosphere soils of Zhonghua 16 and Zhonghua 215 had the same trend at maturity,and showed that the Cd content of rhizosphere soil was positively correlated with the content of DTPA-Cd,the Cd content of peanuts in aboveground and underground was positively correlated.The DTPA-Cd content of soil is significantly negatively correlated with the aboveground and underground biomass and Cd accumulation of peanut.Furthermore,there were similar correlations between the indicators during the growth of rape（The previous crop was Zhonghua 16）and rape（The previous crop was Zhonghua 215）.（3）The effects of liquefaction parameters on the liquefaction degradation behavior of peanut straw in ethanol solvent were as follows:with the increase of temperature and solvent filling rate,the bio-oil yield of peanut straw increased first and then decreased,and reached the maximum at 340°C.With the increase of solid-liquid ratio,the yield of bio-oil showed a continuous decline.The GC-MS analysis showed that the main types of compounds in peanut straw bio-oil were esters,hydrocarbons,alcohols,ketones,phenols,nitrogen-containing compounds and their derivatives.The carbon number analysis of peanut straw bio-oil showed that the carbon number range was between C₅ and C₂₃.The carbon number distribution of most hydrocarbons in bio-oil at different temperatures was similar,mainly concentrated in C₈,C₁₈ and C₂₀.Overall,the higher the temperature,the lower the boiling point.The Cd content in peanut straw liquefied biochar increased with the increase of temperature,but the content of F1（exchangeable/carbonate bound）decreased.（4）With the increase of liquefaction temperature,the yield of bio-oil from rape straw liquefaction increased first and then decreased.When the temperature was 340°C,the bio-oil yield reached the maximum.On the contrary,with the increase of temperature,the liquefaction residue yield decreased first and then increased slightly.When the solid-liquid ratio increased,the bio-oil yield continued to decrease,and the corresponding residue yield continued to increase.When the solvent filling rate increased,the bio-oil production decreased first and then increased.The yield of liquefaction residue increases first and then decreases with the increase of solvent filling rate.The carbon number analysis of bio-oil showed that when the temperature was 220°C,260°C and 300°C,the carbon number of hydrocarbons in rape straw bio-oil was mainly C₂₀,while when the temperature was 340°C and 380°C,the carbon number of hydrocarbons was mainly C₈ and C₉.The Cd content in liquefied biochar increased with the increase of temperature;compared with raw materials,the Cd content in liquefied biochar at different temperatures mainly exist in the form of F2（reducible）and F3（oxidized）.In summary,this paper discussed some changes in the crop rotation process based on crop cultivation methods,varieties and the soils with different Cd pollution concentrations,hoping to explore the appropriate crop rotation cultivation mode,which can not only repair heavy metal Cd contaminated soil,but also obtain economic benefits to lay a theoretical foundation;and carried out on the contaminated straw by thermochemical liquefaction treatment after crop harvest to provide a theoretical basis for the resource recovery and utilization of contaminated biomass.