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Adsorption properties of two activated carbons were investigated as a function of several operating parameters such as initial dye concentration, contact time, pH, and temperature. Adsorption/desorption performance was related to the structural and thermodynamic properties of the adsorbent. To evaluate the effect of the adsorbate an acid dye (alizarin red S, ARS) and a basic dye (methylene blue, MB) were used. Results obtained suggest that a low basicity of the adsorbent is a key factor independent of the acid or basic nature of the adsorbate. Langmuir isotherms best represent the adsorption system. Reported maximum adsorption capacities for ARS and MB were 762 mg·g−1 and 742 mg·g−1, respectively. The adsorption process followed the pseudo-first-order model. The thermodynamic parameters such as Gibbs energy (ΔG°), entalphy (ΔH°), and entropy (ΔS°) indicate that the adsorption of the basic dye was significantly dependent on AC properties. Hydrophobic interaction played a dominant role in the adsorption of the basic dye, whereas acid dye was bound through electrostatic interaction. This coincided with the lower activation energy values reported for MB [(9.58 to 18.68) kJ·mol−1] in comparison to ARS [(23.79 to 27.67) kJ·mol−1]. Finally, for adequate desorption it is more important to enhance interaction between dye and surfactant rather than the repulsion between micelles and the adsorbent surface.

Adsorption of natural organic matter (NOM) by granular activated carbon (GAC) was studied. Three different carbons of different origin were initially used. The physical properties were studied by means of N 2 adsorption. Chemical properties were studied by means of thermogravimetric analysis (TGA), acid-base titrations, and FTIR. Only one of the carbons showed a broad adsorption band in the 1300-1000 cm -1 region in FTIR spectra, which can be assigned to C-O stretching and O-H bending modes of alcoholic, phenolic, and carboxylic groups. Adsorption of NOM was studied by batch adsorption experiments. Uptake of NOM by the different carbons was evaluated by UV absorbance, disinfection byproduct formation potential tests, and HPLC-SEC chromatography. Freundlich equation was used to fit equilibrium data. pH PZC and overall surface basicity were shown to improve the removal of THM precursors. Differences in the molecular weight distribution of the adsorbed material by different carbons were reported. A clear correlation was found between the reduction in the THM formation capacity of sample and the reduction in intensity of a specific peak in SEC chromatograms. Furthermore, THMFP tests showed the existence of some fractions of NOM not adsorbable with activated carbons and undetected by measurement of DOC.

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