GRANULAR ACTIVATED CARBON - THE VARIATION OF SURFACE-PROPERTIES WITH THE ADSORPTION OF HUMIC SUBSTANCES

Naturally occurring organic matter, such as humic and fulvic acids, is present in most surface water used for drinking water production. Such material interferes with the flocculation and chlorination steps of water treatment and is known to affect the efficiency and bed life of activated carbon filters. This study investigates the effect of known, small quantities of humic material adsorbed on the granular activated carbon (GAC) surface. It is found that the charge on the carbon surface, as determined by titration, is decreased by as little as 3.5-mg dissolved organic carbon adsorbed per gram of GAC. Higher surface concentrations decrease the charge further, although the concentration of negative charges at the surface leads to an overall decrease in the degree of ionization of the humic material, compared to bulk solution. Electrophoretic mobility measurements do not suggest any significant difference between new carbon and carbon with a small amount of adsorbed organic material. This is interpreted in terms of the sensitivity of the two techniques and their ability to examine different parts of a porous substance such as GAC. © 1993 Academic Press, Inc.