Full Description

Naturally-occurring organic materials (NOMs) in dissolved, colloidal or particulate forms are ubiquitous in surface and groundwaters. The dissolved and colloidal forms (i.e., DOMs, those constituents passing a 0.45 micron filter) are the most problematic and undesirable fractions of NOM with regard to water treatment and supply. DOMs cannot be completelyremoved from water using conventional treatment processes. They can bind or complex synthetic organic chemicals (SOCs) and/or toxic metals and carry them through treatment facilities and distribution systems. DOMs can serve as substrates for bacterial growth in distribution systems and constitute the major precursors of disinfection byproducts (DBPs) formed during water treatment. The United States Environmental Protection Agency (USEPA) is planning to impose more stringent standards on DBPs because of their potential risk to public health. As a result, granular activated carbon (GAC) adsorption has been designated as a best available technology for DOM removal. In most current practical applications, GAC fixed-bed adsorbers are designed to remove dissolved pollutants, such as SOCs, from water. The presence of DOMs in water has been found to significantly reduce the performance and capacity of GAC adsorbers for target SOCs. Although meeting multiple objectives simultaneously in a single treatment process may be difficult, understanding the interactions between DOMs and GAC is essential to optimize their removal from water, to minimize their impact on the removal of the target pollutants, orboth. This study investigated the role of carbon surface chemistry on the adsorption of priority pollutants and DOMs using eleven GACs prepared by modifying the surfaces of one coal- and one wood-based GAC. Overall, the results indicated that the capacity of a GAC for a DOM is a function of two major factors: carbon surface acidity vs. DOM chemical composition; and, carbon pore size vs. DOM molecular size. Repulsive forces between strongly acidic functionalities (such as carboxylic groups) on the GAC surface and within the DOM structure appear to reduce adsorption capacity. Our results indicated that DOM removal can be maximized by selecting GACs with minimal surface acidity and large pore widths. Since we worked with two different carbons and our findings indicate that the relationship between carbon pore and DOM molecular sizes is important for the removal of DOMs from water by GACs, the objective of this research was to examine systematically the role of physical interactions during the adsorption of macromolecules by different carbon materials. Includes table, figures.

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Edition: Vol. - No. Published: 06/01/2001 Number of Pages: 7File Size: 1 file , 290 KB