Evaluating low-cost permeable adsorptive barriers for the removal of benzene from groundwater: Laboratory experiments and numerical modelling

Permeable adsorptive barriers (PABs) consisting of individual (compost, zeolite, and brown coal) and composite (brown coal-compost and zeolite-compost) adsorbents were evaluated for their hydraulic performance and effectiveness in removing aqueous benzene using batch and column experiments. Different adsorption isotherms and kinetic models and different formulations of the equilibrium advection-dispersion equation (ADE) were evaluated for their capabilities to describe the benzene sorption in the media. The batch experiments showed that the adsorption of benzene by the adsorbents was favourable and could be adequately described by the Freundlich and Langmuir isotherms and the pseudo-second-order kinetic model. Particle attrition and structural reorgani-zation occurred in the columns, possibly introducing preferential flow paths and resulting in slight changes in the final hydraulic conductivity values (4.3 x 10-5 cm s- 1-1.7 x 10-3 cm s- 1) relative to the initial values (4.2 x 10-5 cm s- 1-2.14 x 10-3 cm s-1). Despite the fact that preferential flow appeared to have an impact on the performance of the investigated adsorbents, the brown coal-compost mixture proved to be the most effective adsorbent. It significantly delayed benzene breakthrough (R = 29), indicating that it can be applied as a low-cost effective adsorbent in PABs for sustainable remediation of benzene-contaminated groundwater. The formulated transport models could fairly describe the behaviour of benzene in the investigated media under dynamic flow conditions; however, model refinement and additional experimental studies are needed before pilot/full-scale applications to improve the fits and verify the benzene removal processes. Our results generally demonstrate how such studies can be useful in evaluating potential reactive barrier materials.