Pore distribution effect of activated carbon in adsorbing organic micropollutants from natural water

Adsorption isotherms of organic micropollutants in coexistence with natural organic matter (NOM) were analyzed to evaluate the impacts of pore size di stribution of activated carbon (AC) on the competition effects of the NOM. Single solute adsorption experiments and simultaneous adsorption experiment s with NOM contained in a coagulation-pretreated surface water were perform ed for four agricultural chemicals and three coal-based activated carbons ( ACs) having different pore distributions. The results showed that, for all the carbons used, the adsorption capacity of the chemicals was reduced dist inctly in the presence of NOM. Such a reduction was more apparent for AC wi th a larger portion of small pores suitable for the adsorption of small org anic molecules and for the agricultural chemicals with a more hydrophilic n ature. Ideal adsorbed solution theory (IAST) incorporated with the Freundli ch isotherm expression (IAST-Freundlich model) could not interpret the impa ct of NOM on the adsorption capacity of the chemicals unless a pore blockag e effect caused by the adsorption of NOM was also considered. By taking int o account this effect, the adsorption isotherm of the chemicals in the pres ence of NOM was well described, and the capacity reduction caused by the NO M was quantitatively assessed from the viewpoints of the site competition a nd the pore blockage. Analytical results clearly indicated that pore blocka ge was an important competition mechanism that contributed to 10-99% of the total capacity reductions of the chemicals, the level depended greatly on the ACs, the chemicals and the equilibrium concentrations, and could possib ly be alleviated by broadening the pore size distributions of the ACs to pr ovide a large volume percentage for pores with sizes above 30 Angstrom. (C) 2001 Elsevier Science Ltd. All rights reserved.