Overall Adsorption Isotherm of Natural Organic Matter

Adsorption equilibrium data in lumped water quality indices obtained for diluted solutions of a peat water and effluents from a wastewater treatment were analyzed using the ideal adsorbed solution theory with the Freundlich equation. The use of the same value for Freundlich exponent 1∕n in the ideal adsorbed solution theory resulted in a straightforward and less computationally demanding expression to describe an overall batch adsorption isotherm. A fictive component approach, assuming a logarithmic normal distribution of Freundlich K and a nonadsorbable fraction, adequately described and predicted the overall isotherms for different initial concentrations of diluted solutions presented as a lumped water quality index. The parameters in the distributed fictive component approach were independently sensitive to each portion of an isotherm curvature. Preferential adsorption of the smaller molecular weight (MW) components was observed by a size-exclusion high-performance liquid chromatography. Two-dimensional distribution analysis of organics in terms of Freundlich K and MW revealed a weak tendency of the adsorptive strength to decrease with the increase of the MW.