Comparison of association theory and Freundlich isotherm for describing granular activated carbon adsorption of secondary sewage effluent

Adsorption equilibria and kinetics are important to evaluate the effectiveness of an adsorption system. In this study, the adsorption behavior of organics in secondary effluent from a sewage treatment plant was investigated, using granular activated carbon (GAC) as an adsorbent. This paper provides details on the adsorption experiments conducted in a sewage treatment plant, and emphasizes the suitability of the association theory for describing adsorption characteristics of secondary sewage. The association theory was found to describe the overall adsorption equilibrium of the sewage system more precisely (with 0.33% error) than the more commonly-used Freundlich isotherm (with 9.9% error). The linear driving force approximation (LDFA) model and the fixed bed dynamics were used to predict the batch kinetics and the fixed bed adsorption experimental results respectively. The prediction was only slightly better when the isotherm parameters estimated from the association theory were used. Average errors in predicting batch and fixed bed experimental results were 0.25 and 0.55% with the association theory, and 0.34 and 0.75% with the Freundlich isotherm, respectively.