Kinetic and equilibrium modelling of the methylene blue removal from solution by adsorbent materials produced from sewage sludges

Sewage sludge utilisation must be the preferred management solution for a residue which does not show the desired improvement on wastewater treatment. This research work's aim was to study the dye binding capacity of adsorbents produced from sewage sludges. The quality of sewage sludges as starting materials has been investigated by using sludges both from an urban and from an agrofood industry wastewater treatment plant. Dried sewage sludges, pyrolysed sewage sludges and both chemically activated and pyrolysed sewage sludges have been used as adsorbent materials in single batch liquid-phase adsorption tests. The adsorption equilibriums of methylene blue by these materials have been described in terms of both Langmuir and Freundlich equations. In order to investigate the mechanisms of adsorption, the first- and second-order kinetic models have been used. All the sludge-derived adsorbents produced have been able to uptake methylene blue from solution, the second-order rate expression being preferred to the first-order one. Nevertheless, the time needed for reaching the equilibrium and adsorptive capacity have differed from one to another adsorbent. Equilibrium and kinetic results have showed that dried urban sewage sludges are the most efficient materials for removing the methylene blue from the solution. (C) 2002 Elsevier Science B.V. All rights reserved.