Desorption is an important phenomenon in the removal of trace organic contaminants with activated carbon. Under certain conditions, the release of a trace contaminant back into solution leads to a higher contaminant concentration in an adsorberMoreDesorption is an important phenomenon in the removal of trace organic contaminants with activated carbon.
Under certain conditions, the release of a trace contaminant back into solution leads to a higher contaminant concentration in an adsorber effluent than in the influent. The objective of this study was to investigate the competitive effect of background natural organic matter (NOM) on the desorption kinetics of a target contaminant.-Batch kinetic desorption experiments using powdered activated carbon (PAC) were conducted to study the kinetics of atrazine in the presence of background NOM. The effect of increasing surface concentration of the strongly-competing (SC) fraction of NOM was to increase the intraparticle diffusion coefficient of atrazine, which is consistent with a shift from surface diffusion to pore diffusion of the trace compound.
The effect of SC NOM on atrazine kinetics was demonstrated not only for desorption, but also for adsorption, as well as using three different sources of SC matter. Thus, SC NOM not only competes with a trace compound for carbon capacity, but increases the rate of its release into solution.-The effect of increasing surface loading of the pore-blocking (PB) fraction of NOM was to decrease the diffusion coefficient of the trace contaminant. Thus, PB NOM has a positive benefit of slowing down the release of a trace contaminant.
Only when the above SC NOM kinetic effect was factored out, the mathematical correlation describing the PB NOM effect on adsorption kinetics was adequate to describe the kinetics of desorption due to displacement by another adsorbate as well as desorption owing to a decrease in solution concentration below equilibrium concentration.-A mathematical model was presented to model the simultaneous effects of SC and PB background organic matter on both adsorption and desorption kinetics in a batch reactor. The model was applied to describe and compare kinetics using two PACs with different pore size distributions.
An analysis of important issues in modeling desorption led to several recommendations for future research to improve the understanding of trace contaminant desorption from activated carbon.