Textile mill effluent decolorization using crude dehydrated sewage sludge

Crude dehydrated sewage sludge issued from an urban wastewater treatment plant (High-rate aeration, activated sludge process, Monastir, Tunisia) is used as an adsorbent for the decolorization of a textile mill effluent. The main objective of this work was to evaluate the crude material adsorption capability of the dye contained in wastewater. No treatment to modify any of the adsorbent properties was however considered. Starting with a synthetic effluent, two different kinds of textile dyes had been used: A direct dye, Direct Red 79 and a vat dye from the anthraquinonic class, Vat Blue 4. It was found that the used material, in fact “waste of waste”, has a capacity (Langmuir monolayer) of, respectively, 19.6 mg/g to fix the former and 248.3 mg/g to fix the latter. The experiments conducted with the real textile mill effluent to evaluate the material capacity to decolorize it showed that 8 mg/g of the dominant dye (Indigo) gets adsorbed. Langmuir, Freundlich, Redlich-Peterson, Höll-Kirch, Toth and Langmuir–Freundlich two sites equilibrium models were used to fit the experimental results. A sensitivity analysis of the fitted models parameters, made by using Markov Chain Monte Carlo (MCMC) method and the contour plots showed, from statistical point of view, the goodness of the obtained results and the most influential parameter in each used model.