Role of granular activated carbon surface chemistry on the adsorption of organic compounds. 2. Natural organic matter

The role of granular activated carbon (GAC) surface chemistry on the adsorption of four model dissolved organic material (DOM) isolates and four surface water natural organic material (NOM) samples was investigated by using (I)ten carbons prepared by modifying the surfaces of a coal-based and a wood-based carbon and (2) seven different as-received GACs. Because changes in the pore structure resulting from surface treatment were small, while changes in the surface chemistry were significant, the impact on the DOM and NOM uptake by surface-treated carbons was systematically linked to the changes in the carbon surface chemistry alone. For the surface-treated coal-based carbons, there was (1) no significant capacity difference between acid-washed and heat-treated carbon samples, (2) oxidation of the carbon surface significantly decreased the uptake, and (3) the capacity was partially restored by subsequent heat treatment of the oxidized surfaces. A decreasing uptake with increasing surface acidity was evident, and the effects of surface acidity on uptake were qualitatively similar to the two SOCs studied in Part 1 of this series. The experiments with as-received coal-based carbons exhibited the same behavior; however, the reactivity of modified and as-received carbons for DOM and NOM uptake was significantly different. For the wood-based carbon, the impact of surface treatment on adsorption of DOMs and NOM was surprisingly minimal or absent. This finding was in contrast to the effects of surface acidity on uptake of the two SOCs studied in Part 1 in this series. Overall, the reactivity of carbon surfaces to DOM and NOM uptake depended on the raw material type, activation conditions and surface treatment.