Batch-scale remediation of toluene contaminated groundwater using PRB system with tyre crumb rubber and sand mixture

Abstract

The objective of the study is to examine the potential of TCR (tyre crumb rubber) particles to remediate toluene contaminated aquifers by using them as the reactive constituent of permeable reactive barriers (PRB). The objective is achieved by performing laboratory experiments to identify toluene adsorption capacity and rate of toluene removal of the optimal TCR-sand mix. Adsorption isotherms and Kc-Co relations (Kc: distribution coefficient, Co: initial toluene concentration) identified the optimum mix (2.5 % TCR-97.5 % sand mix) for remediation of toluene contaminated water. Batch experiments showed that toluene adsorption by TCR particles is endothermic and is energetically favoured at higher temperature. Adsorption of the non-polar molecule by TCR particles obeyed bi-linear, pseudo first order kinetics. The carbon-black component of TCR particles adsorbed significant amount of toluene during the initial contact period (10−60 min). Scatchard analysis, Freundlich isotherm and DR (Dubinin-Radushkevich) equation indicated that toluene is adsorbed by van der Waals attraction at energetically heterogenous sites of TCR particles. The near irreversible toluene adsorption in the laboratory experiment is attributed to physical entrapment of the non-polar molecules in the medium and fine pores of TCR particles. Batch experiment results predict that unit PRB column constructed with 2.5 % TCR-97.5 % sand mix can remediate 11,013 K L of toluene contaminated (0.15 mg/L) groundwater near instantaneously.