Optimization of Batch Conditions and Application to Fixed-Bed Columns for a Sequential Technique of Total Color Removal Using “Greek Coffee ” Residues as Materials for Real Dyeing Effluents

In this study, the decolorization of industrial textile wastewaters was studied firstly in batch mode and after the optimization of these conditions, in fixed-bed columns using “Greek coffee ” wastes (COF) as low-cost adsorbents. In this attempt, there is a cost potential given that there was no further modification of COF (just only washed with distilled water to remove dirt and colour, and dried in oven). Also, tests were realized both in synthetic and real textile wastewaters for comparative reasons. The optimum pH of adsorption was acidic (pH=2) for synthetic effluents, while experiments in free pH (non-adjusted) were carried out for real effluents. Equilibrium data were fitted to the Langmuir, Freundlich and Langmuir-Freundlich (L-F) model. The calculated maximum adsorption capacities (Qm) for total dye (reactive) removal at 25 oC was 241 mg/g (pH=2) and 179 mg/g (pH=10). Thermodynamic parameters were also calculated (ΔH0, ΔG0, ΔS0). Kinetic data were fitted to the pseudo-first,-second and-third order model. The optimum agitation rate and the optimum pH for desorption were determined. The reuse potential showed 10 cycles of adsorption-desorption, in which the reduction in adsorption percentages from the 1st to 10th cycle was 4 % for COF adsorbents. Furthermore, experiments dealing the increase of mass of adsorbent showed a strong increase in total dye removal. To direct apply the optimized batch conditions, the same adsorbents were used in fixed-bed columns, performing a complet