ACTIVATED CARBON AND SOLUBLE HUMIC SUBSTANCES - ADSORPTION, DESORPTION, AND SURFACE-CHARGE EFFECTS

Dissolved humic substances occur naturally in most surface waters. Suc h material interferes with conventional drinking water treatment proce sses and adsorbs on the surface of granular activated carbon (GAC), de creasing the effectiveness and life of GAC filters. An alkali treatmen t was investigated as a means of desorbing humic substances from the a ctivated carbon surface and possibly increasing the bed life of the fi lters. A maximum of 60% removal was achieved using this method. Surfac e titrations were undertaken using activated carbon samples with adsor bed humic material before and after the alkali desorption treatment. I t was found that the surface charge properties of the samples were not significantly altered by the treatment, and that the major influence on the surface properties was the concentration of the adsorbed humic material. The degree of ionization of the adsorbed material was found to be very strongly influenced by the surface concentration, and this effect was interpreted in terms of the orientation of the adsorbed mol ecules and the very strong electrostatic interaction between charged g roups of the adsorbed material. (C) 1994 Academic Press, Inc.