Experimental Study On The Effect Of Exogenous DOM On The Adsorption Behavior Of Organic Pollutants With Different Polarities

Exogenous DOM(dissolved organic matter)plays an important role for the adsorption behavior of organic pollutants in the soil.To evaluate the effect of DOM on pollutant adsorption and find the largest contribution factor to adsorption.Batch sorption experiment were conducted to explore the influence of DOM on PPCPs organic pollutants adsorption with hydrophobic-carbamazepine(CBZ)and polarsulfamethoxazole(SMX)as two types of typical pollutants and montmorillonite as typical medium.DOM was prepared by commercial humic acid through ultrafiltration classification.The paper mainly achieved the following conclusions:(1)Batch sorption experiment results show that the difference in polarity of organic matter makes DOM have the opposite effect on its adsorption.The adsorption of polar SMX is obviously inhibited,and the adsorption of hydrophobic CBZ is changed from inhibition to promotion with the increase of its concentration.Polarity differences result in organic compounds having different affinities to the surface of the media or DOM,which is the main cause.After adding DOM,competitive adsorption,solubilization,cumulative adsorption and co-adsorption will occur when two pollutants are adsorbed.The dominant role in the mixed system is different due to the difference in the polarity of the contaminants.DOM and SMX are dominated by competitive adsorption;low concentrations of CBZ and DOM are dominated by competitive adsorption and solubilization;high concentrations of CBZ and DOM are mainly co-adsorbed or cumulatively adsorbed.(2)The effect of DOM on the adsorption of target pollutants is controlled by the concentration of contaminants.The characterization of the fluorescence spectrum combined with the adsorption isotherm shape confirmed that after adding DOM,lowconcentration CBZ and HA had competitive adsorption or solubilization.The adsorption isotherm of CBZ is L-shaped,and adsorption is suppressed.Highconcentration CBZ can form a composite with DOM and adsorb to the surface of the medium.In addition to being first adsorbed on the medium,can form a stable complex with HA molecules to synergistically adsorb on the surface of the medium.HA adsorbed on montmorillonite changes the properties of the adsorbent,and CBZ can undergo cumulative adsorption.The adsorption isotherm of CBZ is S type,and adsorption is promoted.SMX has strong polarity,and its affinity with HA is always higher than that on the surface of the medium.Regardless of its concentration,SMX is more likely to bind to HA molecules.The infrared spectrum shows that the complex of SMX and HA molecules is higher.Therefore,the proportion of co-adsorption is small,so that the adsorption of SMX is not always suppressed with the change of its concentration.(3)The polarity and concentration of pollutants are the main cause of the difference in adsorption affected by DOM,while the molecular weight and concentration changes of DOM have little effect.With the increase of the molecular weight of DOM,its hydrophobicity is enhanced,and the ability to compete with SMX for adsorption sites is enhanced.The inhibition of SMX adsorption is enhanced.The effect of DOM on CBZ adsorption increases with molecular weight increase,because co-adsorption and cumulative adsorption increase.The higher the DOM concentration,the lower the inhibition of SMX and low-concentration CBZ adsorption,and the stronger the promotion of high-concentration CBZ adsorption.The reason is that SMX or low concentration CBZ and DOM not only have competitive adsorption,but also coadsorption.The higher the DOM concentration,the stronger the co-adsorption.