The Sorption Mechanisms Of Carbaryl And Oxytetracycline Onto Biochars

The long-term utilization of pesticides and antibiotics have resulted in widespread and co-existing contamination in agricultural soils,and posed a potential ecological environmental risk to humans and microorganisms.Therefore,reducing their environmental risk has received great attention recently.Sorption is a critical processes that govern the mobility,bioavailability,and the ultimate fate of the contaminants in soils.Biochars are receiving recognition as potential amendments in soil that could help increase the sorption ability of soils,thereby reducing contaminants' environmental risk because of their extraordinarily strong adsorption affinity for different kinds of organic contaminants.In this dissertation,researches advance on exposure levels and ecological risk of co-existing pesticide and antibiotic in the soil,as well as the sorption and the enhanced sorption to soil of organic pollutants by biochar were reviewed.Carbaryl(CBL)and oxytetracycline(OTC)were selected as model pesticide and antibiotic,respectively.Sorption characterization and mechanisms of different biochars for single-and bi-solute of CBL and OTC were studied,and enhancement for sorption ability of soil amended with different biochars were elucidated.Additionally,the impact of mineral components in biochars on the overall adsorption and competitive adsorption of CBL and OTC was evaluated.These results provide a theoretical basis for the application of biochars in reducing environmental risk of CBL and OTC.The main original conclusions of this work are listed as follow:(1)The main mechanism and structure-activity relationship of biochar sorption for CBL and OTC has been established.The aromatic and hydrophobic carbon contents of wheat straw biochars(WSBCs)and cow manure biochars(CMBCs)had a positive effect on the OTC and CBL adsorption,while their bulk polarity had the negative effect on the OTC and CBL adsorption.The dominant sorption mechanisms of OTC and CBL on biochars have been established as specific-site sorption.Competitive sorption was found between co-existing OTC on CBL on all biochars,and the competitive strength was more significant on high-temperature-derived biochars.Additionally,the competitive strength of OTC to CBL was more significant than CBL to OTC,because OTC can take priority over CBL in occupying the high-energy sorption sites available on the biochars.(2)The impact of demineralization treatment with cow manure biochars on the adsorption and competitive adsorption of CBL and OTC has been evaluated.After demineralization treatment,the bulk aromaticity and hydrophobicity of biochar dereased,while the bulk polarity of the biochars increased.Additionally,the surface area and the micropore volume of demineralized biochars increased much more significantly.Adsorption increased greatly for OTC but decreased slightly for CBL after demineralization.Mineral components made great contribution to the overall adsorption of CBL but had a slight side effect on that of OTC to original biochars.This discrepancy can be attributed to that the dominant sorption mechanisms of OTC and CBL on demineralized biochars have been established as pore-filling effects and specific-site sorption,respectively.Competitive adsorption was observed in the binary-solute sorption system,where OTC outcompeted CBL on original biochars,however,CBL showed a greater competitive adsorption to OTC on demineralized biochars.Furthermore,demineralization treatment weakened the competition strength of OTC to CBL but enhanced that of CBL to OTC.