Effect Of Biochar Derived From Cassava Dregs For Environment Behavior Of Avermectin

Biochar?BC?is a carbon-rich soild material produced by heating biomass in an oxygen linted environment,an effective sorbent for organic contaminants.As sorbents for removing avermectin from aqueous solutions and tropical soils,BCs were studied in the research.BC was producted under zero oxygen at 350 ?,550 ?,750?.Also its properties was characterized.The study explore the effects of biochars on the environmental behavior of avermectin in the soil planting banana.The objective of the study was to open a new road for tropical agricultural waste utilization,which provides a feasible method for the application of biochar in tropical agriculture and the control and remediation of pesticide pollution in the tropical soil.The main achievements are as follows.?1?BCs were generated from cassava wastes.With the increase of temperature,its productivity rate decreased,but the ash content,pH and specific surface area increased.The rise of the pyrolysis temperature of BC is a process of increase in aromaticity and reduction in polarity.?2?The adsorption of abamectin on BC included three steps:first a fast step,then a slow step,last achieve the balance.And the process fitted the pseudo second-order model very well.The Freundlich model can describe the difference between three BCs adsorption-desorption process.All the three adsorption belong to nolinear.Also with the increase of pyrolysis temperature,the adsorption affinity of BC for abamectin strengthens,showing an order of MS750>MS550>MS350.According to the desorption hysteresiscoefficient HI,it is an negative hysteresis effect in the desorption process.The study also disscussed the changs in adsorption capacity of BC,showed that the adsorption process was spontaneous and entropy driven endothermic reaction.When the pH value is between 3 and 6,the adsorption capacity of BC to avermectin decreased,while the adsorption capacity of BC increased when pH is from 6 to 9,and the adsorption capacity reached the maximum when the pH value was 9.The effect of K⁺ and Ca²⁺ on the adsorption of avermectin by biochars was not significant.Compared with the two cations talked before,Al³⁺,Cu²⁺ and Zn²⁺ can promote the adsorption of Abamectin on BCs.?3?The the adsorption process of abamectin on soils was the same as BCs,and the pseudo second-order model fitted the sorption kinetics for abamectin perfectly.By using isothermal adsorption model to explore the adsorption mechanism of abamectin in BC applied in the soil,we found that adding biochars can enhance the adsorption ability of soil to abamectin,and the adsorption capacity increased with the rise of the preparation temperature and the contents of BCs.Freundlich model was the best fitting for abamectin sorption isothermals,the changes of lgkf can represent the soil adsorption capacity to abamectin amended with BCs,lgkf values change is the same with the results,and the desorption process also exists negative desorption hysteresis.The thermodynamic study indicated that the adsorption of abamectin in BC-added soils was spontaneous and entropy driven endothermic reaction.Except the adsorption of 5%addition of Abamectin on MS750 was a chemical process,the others were physical process.The pH and cation type can impact the sorption.?4?The degradation rate of avermectin was higher in the sterilized soil than that unsterilized,the degradation rate was 97.66%and 95.45%respectively after 21d,its half-life was 3.92d and 4.59d.The pseudo-first order kinetic model can describe the degradation process very well.A low content of BC at low temperature could promote the degradation of avermectin in the soil,while the high content of BC at low temperature or the BC produced at high temperature all inhibited the degradation of Abamectin in soil.The degradation trends of Abamectin in the sterilized soil and unsterilized soil were the same,but the half-life of the same kind of BCs was significantly longer in the sterilized soil than that unsterilized at the same content of BC-added condition.