Utilisation of sewage sludge derived adsorbents for the removal of recalcitrant compounds from wastewater: Mechanistic aspects, isotherms, kinetics and thermodynamics.

In the present study, the performance of sewage sludge based adsorbents was examined for the removal of two recalcitrant pollutants (i.e. lignin and amoxicillin) from synthetic wastewater solutions (adsorbate concentration=50-250 mg/l). The effect of various reaction parameters such as wastewater pH, adsorbent dosage and temperature was studied. Possible mechanisms for the adsorption process have been proposed which depends upon the behaviour of adsorbent surface and adsorbate molecules under specific reaction conditions. Three-parameter Redlich-Peterson isotherm model was found the best fit to the equilibrium data. Pseudo first and second order models validated the kinetic data for lignin and amoxicillin adsorption systems, respectively and the corresponding activation energy was 3.5-4.5 and 12-22 kJ/mol. The nature of adsorption was elucidated from the thermodynamic parameters.