Modeling The Adsorption Of Hazardous Organic Compounds By Activated Carbon In The Presence Of Background Dissolved Organic Matter.

Abstract

Adsorption by activated carbon in fixed beds is recognized as one of the fundamental treatment technologies for prevention and remediation of ground and surface water contamination by potentially hazardous organic substances. The site-to-site variability and complex composition of many waters, however, complicate the design and operation of carbon adsorption treatment processes. Although treatment objectives may be directed toward a specific target compound (or compounds), the interactions occurring among target compounds and other organic species in solution must be properly characterized and acknowledged in the engineering of adsorption systems. Prior evidence suggests that existing mathematical models and approaches, if properly modified, offer potential as useful design tools for tailoring adsorption processes to waters containing complex organic mixtures. This study focuses on the modification and application of a specific modeling methodology to such systems. A modified homogeneous surface diffusion version of the Michigan Adsorption Design and Applications Model was used to simulate and predict fixed-bed adsorber behavior with respect to two target organic compounds in the presence of various types and sources of background dissolved organic matter. The approach applied was one in which model coefficients specific to the system were evaluated for the target compounds, and the background organic material itself was considered only as unspecified background. It was determined experimentally that the unspecified dissolved organic matter in the background water significantly reduced adsorption capacities and rates for both target compounds relative to their respective values in waters containing no other organic species. System-specific rate parameters estimated by a short-bed adsorber technique provided adequate model predictions of both single-component and dual-component combinations of the target compounds with the various background waters. A more traditional methodology that utilizes literature correlations and completely mixed batch reactor rate data for estimation of rate parameters did not predict target compound breakthrough profiles as accurately as the short-bed adsorber technique.