Adsorptive mode of Phenol abatement from
aqueous solution using activated carbons

Abstract

Fresh water crisis has been emerged as one of the most acute issues in the current global scenario, forcing the waste water reutilization concept a must. The reutilization of waste water again demands proper yet effective treatment. Among organic contaminants of waste water phenolic compounds are the principal components, which due to its toxic and carcinogenic nature forces people for its removal from waste water. Adsorption being the highly efficient, simple, cost effectiveness and the availability of a wide range of adsorbents is used as one of the most indispensable method for treatment of phenolic waste water.
In the present study, two different types of activated carbons were used as adsorbents namely, commercial granular activated carbon and laboratory prepared water hyacinth activated carbon prepared from roots of water hyacinth by chemical activation method with phosphoric acid impregnation. For batch adsorption process, operating variables studied were adsorbent dose, contact time, pH, initial phenol concentration, and temperature respectively. Sorption experiments indicated that the sorption capacity was dependent on operating variables and the process was strongly pH dependent. Adsorption of phenol onto GAC witnessed following optimal values of different operating variables as, w=3g/L, t=360mins, pH=9 and highest
uptake capacity of 39.0056 mg/g and those for phenol-WHAC system are 5g/L, 360 mins, 6 and 28.0049mg/g respectively. In both the cases adsorption capacity was shown to be
decreasing with increase in temperature. Kinetic measurements showed that the process was uniform and rapid. In order to investigate the mechanism of sorption, kinetic data were modelled using the pseudo-first-order and pseudo-second-order kinetic equations. Among the kinetic models studied, the pseudo-second-order equation was the best applicable model to describe the adsorption process of phenol onto both the adsorbents. Equilibrium isotherm
data were analyzed using the Langmuir, Freundlich isotherms. The Langmuir model yields a much better fit than the Freundlich model for phenol adsorption onto GAC, in contrast Freundlich model was better fitted for WHAC. Isotherm parameters have also been used to obtain the thermodynamic parameters such as free energy, enthalpy, and entropy of sorption. The value of ΔH° was found negative, supporting that the phenol adsorption by the GAC and
WHAC are exothermic in nature.