The Study Of The Adsorption Characteristics And Its Control Of The Aldicarb In The Purple Soil

There has been increasing concern on non-point source pollution of excessive usage of pesticides in which are drained from farmland ecosystem to water bodies.Environmental friendly biochar can effectively adsorb various pesticides and control the movement of pesticides in the soil.The study,with batch experiments and unsaturated transient flow method conducted,reveals the mechanism of biochar absorbing the research object—aldicarb and its degradation products,which uses purple soil of sloping farmland with biochar.Based on the layout advantage of the sloping land,a new in-situ remediation technique,ridged biochar-amended permeable reactive barrier,is proposed to prevent aldicarb and its degradation products from transporting.By monitoring of insecticide loss from the experimental plots,the effectiveness of the ridged biochar-amended permeable reactive barrier is tested.The research findings provide theoretical basis for risk assessment of using pesticide in purple soil areas and feasibility evaluation of application of biochar on controlling pesticide pollution of soil.The main research results indicate:(1)The speed of adsorption of aldicarb and its degradation products changes from fast to slow.Weak adsorption of aldicarb and its degradation products in the purple soil was observed,since the equilibrium adsorption of every pollutant is below 20%of the initial dosage.Moreover,Elovich equation and Freundlich equation can depict the adsorption kinetic and thermodynamic characteristics very well.(2)By adding different amount of biochar to the purple soil,the effect of biochar on adsorption characteristics of biochar-amended soil was studied.The results indicated that straw biochar enhanced adsorption capacity of the purple soil.In addition,linear positive correlation between adsorption amount of biochar-amended soil and biochar level can be observed,when the application rate was between 0g/kg-50gkg.The adsorption capacity of three pesticides followed:aldicarb>aldicarb sulfone>aldicarb sulfoxide.(3)The absorption capacity of the two kinds of aging biochar-amended purple soil,which was made by placing lOg/kg and 50g/kg biochar-amended purple soil under dry-wet alternate farmland circumstance,weakened.Due to the interaction between soil and water during aging process,K+ and organic components lost easily with water,the 0:C ratio increased,and the stability was enhanced.In addition,the pore structure of aging biochar was destroyed.(4)Aldicarb in the soil degraded into aldicarb sulfoxide and aldicarb sulfone quickly.Aldicarb and its degradation products easily migrated with soil water to deep soil layer and water bodies due to its weakly adsorption property.(5)Ridged biochar-amended permeable reactive barrier was built at the bottom of the experimental sloping farmland,and the loss of aldicarb from the experimental plots was monitored.The results showed that aldicarb can be intercepted by biochar-amended permeable reactive barrier.