Reliability of the mass transfer factor models to describe the adsorption of NH4+ by granular activated carbon

Abstract

In spite of the adsorption of a solute onto porous material that can be described using the various models, the reliability of these models supported each other needs to be verified. In this work, the adsorption of NH4+ ions from domestic wastewater treatment plant effluent (DWTPE) onto commercial granular activated carbon (CGAC) was processed both in batch and column experiments. The Freundlich and Langmuir isotherm models and the pseudo-first-order (PFO) and pseudo-second-order (PSO) kinetic models were used for the analysis of data obtained from batch experiments. The bed depth service time (BDST), Thomas, and modified mass transfer factor (MMTF) models were used to describe the behaviors of NH4+ adsorption by the CGAC adsorbent using the data collected from column experiments. The results showed that batch experimental data better matched by the Freundlich isotherm model and by PSO kinetic model indicate the state of multilayer adsorption supported by electrostatic interaction of NH4+ ions with chemical functional groups on the surface of CGAC. The application and limitations of the BDST and Thomas models in the prediction of NH4+ adsorption behaviors require the MMTF models to predict the adsorption kinetics and mass transfer mechanisms of NH4+ ions transported from the bulk water to acceptor sites on the surface of the CGAC adsorbent. The resistance of mass transfer verified for adsorption of NH4+ onto CGAC is dependent on porous diffusion and this may contribute to the development of such porous material for increasing the removal performance of NH4+ ions from DWTPE.