Effect Of Biochars Prepared By Cassava Dregs On The Environmental Behavior Of Norfloxacin In Soils

Biochar(BC)was produced from cassava waste by pyrolysis under oxygen-limiting conditions at 350,450,550,650 and 750℃ and its properties were characterized(referred to BC350,BC450,BC550,BC650 and BC750,respectively).The paper studied the effects of biochars on the adsorption-desorption and degradation of norfloxacin as the goal pollutant in southern soils.The objective of the study was to open a new direction of tropical agricultural waste resource utilization,predict the antibiotics migration destination and provide a theoretical basis for organic pollution restoration.Main achievements were shown as follows.(1)With the increase of pyrolysis temperatures,the pH values,ash content and surface area of BC increased,while the H/C、O/C and(O+N)/C ratios and the yield decreased,indicating an increase in aromaticity and a reduction in polarity.(2)The adsorption kinetics of NOR included two steps:a fast step and a slow step and the kinetic data were best fitted to the pseudo second-order model.The adsorption and desorption data were well described by the Freundlich model and there was a hysteresis effect.With the increase of pyrolysis temperature,the adsorption affinity of BC for norfloxacin gradually strengthened.Thermodynamic study showed that the adsorption of NOR onto biochars was spontaneous.The effects of K+and Ca2+ on the adsorption of NOR by biochars were not significant,while Al3+ displayed promoting effect.According to FTIR analysis,the main adsorption mechanisms of NOR to biochars might be ion-exchange,electrostatic interaction,hydrogen bond,hydrophobic interaction and π-π interactions.(3)The kinetics of NOR in soils amended with biochars were also completed in two steps:a fast step and a slow step,and the pseudo-second-order model perfectly fitted the sorption kinetics for NOR.Biochars added into soils could improve adsorption ability for NOR and the properties and contents of BC had a positive effect on adsorption strength and capacity for NOR,showing in an order of BC750>BC650>BC550>BC450>BC350 and 5%>3%>1%>0.5%>0.1%.Temkin model was the best fitting for AT isothermals of adsorption and desorption in soils amended with biochars and an apparent negative hysteresis effect happened in the adsorption-desorption process.A thermodynamic study indicated that the adsorption of NOR in BC-added soils was spontaneous and entropy driven endothermic reaction.The absolute values of ΔG0 were all less than 20kJ/mol,indicating that the adsorption process of NOR in BC-added soils was primarily controlled by physisorption,which was the comprehensive effect of Van Der Waals force,hydrophobic interaction and hydrogen bond.Moreover,the solution pH values could affect NOR adsorption in BC-added soils.K+ and Al3+ had little effect on adsorption of NOR in soils amended with BC,while an inhibitory effect appeared when exogenous Zn2+ and Cu2+ added.(4)The degradation of NOR in laterite without BC mainly controlled by microbial degradation and chemical degradation.The degradation process of NOR in laterite without BC fitted the pseudo-first order kinetics.The degradation rate of NOR in the soil without BC was 86.07%after 60d and its half life was 21.59d.BC could affect the degradation of NOR in laterite.A low content of BC at low temperature could promote the degradation of NOR in soil,while an inhibitory effect appeared when high levels of biochar at low temperature and high temperature added.