Removal of Humic Substances from Drinking Water Using GAC and Iron-Coated Adsorbents : Consideration of Two Kinetic Models and the Influence of Mixing

This paper investigated the removal of humic substances (HS) from drinking water supplies by adsorption onto granular activated carbon (GAC), iron-coated alumina (AAFS) and ferric oxihydroxide (b-FeOOH). The determination of the rate limiting step of the adsorption process was tested using the pseudo-first and second order kinetic models. Two mixing speeds were considered namely; 200 and 300 rpm. Disintegration (attrition) of the adsorbents occurred above 300 rpm while 200 rpm represented the minimum mixing speed required to keep the solution in suspension. During the first few minutes of adsorption at 300 rpm, strong instantaneous adsorption was observed. Among the three adsorbents, AAFS showed the least affinity for the HS with no instantaneous adsorption at all at 200 rpm. Furthermore, the pseudo-first order model failed to represent the whole range of data while the second order model was the best fit for all the experimental range considered in this study.