Effects Of Colloidal Organic Matter On Carbamazepine Transport In Saturated Porous Media

To explore the effects of colloidal organic matter（COM） on transport of carbamazepine（CBZ） in saturated porous media, column experiments were conducted with sand and two kinds of soil media, and with three different fractions of COM（hydrophilic, Hi; hydrophobic-basic, Ho B; mother liquor, M） prepared by commercial humic acid. The impacts of the background ion concentration, different fractions of the COM and the physical-chemical properties of the media were studied. The effluent data were fitted by CXTFIT software with equilibrium and nonequilibrium models, the breakthrough curves（BTCs） were fitted, and the transport parameters were obtained. The experimental results and characterizations showed the following issues.（1） In sand medium, R was relatively smaller in the column with high background ion concentration(0.01 mol L^-1) compared with the column with low concentration(0.01 mol L^-1). It was presumed that high background ion level does not favor CBZ getting trapped in the inter-pore of quartz sand medium. In the procedure of desorption, as the tailing was more significant in the column with high background level, the thickness of electric double layer of the COM particles was first compressed, and then the COM particles got released and came back into free movement. R was larger than 1 in the column with no injection of OM colloids, confirming the interactions between CBZ and quartz sand.（2） The results of all tested column in this study showed that the COM inhibitted the transport of CBZ. R was relatively smaller in the Hi column（4.50） compared with the Ho B column（5.60）, indicating that the inhibition effects of Ho B is greater than Hi on CBZ transport. The result of surface-enhanced Raman spectrum showed that the interactions between Ho B colloids and CBZ are quite significant. It was speculated that the large sized Ho B-CBZ complexes were trapped in the inter-pores of medium particles. Another portion of Ho B would connect CBZ to the soil particles as a bridge. In contrast, the interactions between Hi and CBZ as well as soil organic matter were quite weak, and Hi would rather migrate freely in the liquid phase than competing for the surface pores of mineral particles with CBZ. This guaranteed CBZ to interact directly with soil particles.（3） As the q_e c_in^-1of CBZ in soil columns were approximately twice as large as those in sand columns, and the value of ω（the ratio of the hydraulic retention time to the sorption time duration）, indicating that the sorption capacity of soil column is higher than that of sand column, and the sorption process is faster in soil column. The clay and soil organic matter components should be considered in key. CBZ would interact with soil organic matter prior to with minral components. CBZ could also attach to solid phase via the bridge of COM. The R value was smaller in standard soil column than in natural soil column. The desorption procedure in standard soil column was also faster. The primary difference between these two sample is that the standard soil contains more clay particles. The small sized clay particles, possessing more active sites and pores on its surface, are very attractive for CBZ. These particles were very likely to form into soil mineral colloids, under appropriate conditions, and then migrate along with water flow.According to the results aforementioned, a conceptual model was developed to describe the effects of different fractions of COM on the transport of CBZ in a relatively complexed soil medium.