Effect Of Dissolved Organic Matter On Adsorption Of Carbamazepine By Mixture Of Biochar And Montmorillonite

When reclaimed water or polluted surface water infiltrates through soil aquifer system or irrigation,some pollutants may be brought into groundwater.Carbamazepine(CBZ)is a kind of psychotropic medicine commonly detected in groundwater.Due to the good adsorption capacity of biochar,it can be added to the soil to effectively sorb the pollutants in the reclaimed water.In this study,the effects of dissolved organic matter(humic acid(HA)and low molecule weight organic acids(LMWOAs))on the adsorption of CBZ on three commercial straws(wheat,corn and rice)biochar(production temperature 450 ?)and montmorillonite were studied by batch experiments.The main conclusions are as follows:(1)The ash content of the three biochar had no obvious effect on the adsorption of CBZ.After the removal of ash,the increase range of KD of CBZ was between 1.0% and 19.7%,which may be due to the exposure of more adsorption sites after the removal of ash.The adsorption mechanism of CBZ by three kinds of biochar includes partition and pore filling.(2)The addition of HA can inhibit the adsorption of CBZ by three kinds of biochar.With the increase of HA concentration in the solution,the adsorption capacity of biochar to CBZ first decreased and then gradually reached stability.At the same time,the adsorption of HA on biochar increased first and then remained stable.This is because HA and CBZ compete for the adsorption sites on biochar and HA and CBZ form complex to inhibit the adsorption of CBZ on biochar.(3)At high concentration,the adsorption of carbamazepine on montmorillonite creates the best interlayer environment for hydrogen bond interaction,which makes the isotherm adsorption curve "S" type.The adsorption capacity of the mixed system of biochar added to montmorillonite to CBZ is greater than its theoretical value.This is because the montmorillonite attached to the surface of biochar makes the specific surface area and pore volume of biochar increase,increasing the adsorption capacity of biochar.(4)The addition of small molecular organic acids(oxalic acid and citric acid)hindered the interlayer environment of montmorillonite to produce hydrogen bond,thus inhibiting the adsorption of CBZ by montmorillonite.For biochar,on the one hand,LMWOAs can make the organic matter in biochar dissolve and inhibit adsorption,on the other hand,it can also promote adsorption by increasing the specific surface area and pore volume of biochar.This makes LMWOAs have no obvious effect on the adsorption properties of biochar.Although biochar only accounts for 1%(mass ratio)in the mixture,its contribution to the adsorption is still the main one,so the coexisting small molecular organic acids in the solution will not obviously inhibit the adsorption of montmorillonite biochar mixture system.