Longevity prediction of reactive media in permeable reactive barriers considering the contamination level and groundwater velocity at the planning site, with a focus on cadmium removal by zeolite

Abstract

Zeolite is a versatile and effective reactive material used in permeable reactive barriers (PRBs) for remediating groundwater contaminated with heavy metals. In this study, we evaluated the influence of subsurface environmental conditions, namely contamination level (C₀) and groundwater velocity (v), on predicting the longevity of zeolite for cadmium (Cd) removal. Batch experiments were performed to investigate the effect of C₀ on Cd removal, and column experiments were performed to examine how Cd transportation through zeolite varies at different C₀ and v. Breakthrough curves (BTCs) were analyzed with an advection-dispersion equation (ADE) coupled with nonequilibrium sorption rate models. The reaction parameters indicating the performance metrics of zeolite were determined using an iterative fitting approach-retardation factor (R), partitioning coefficient (β), and mass transfer coefficient (ω). R exhibited dependence on C₀, but was unrelated to v; its rapid increase at lower C₀ was explained by Langmuir sorption isotherms. β and ω, integral to sorption dynamics and mass transfer, respectively, showcased functional relationships with v. β decreased gradually as v increased, described by the nonequilibrium sorption model, whereas ω increased steadily with v, guided by the Monod function. Using the relationship of these parameters, the fate and transport of Cd within zeolite was simulated under various subsurface environmental conditions to construct the longevity prediction function. Thus, this study introduces a method for predicting the longevity of reactive materials, which can be valuable for designing PRBs with high longevity in the future.

Keywords: Cadmium removal; Contamination level; Groundwater velocity; Parameter estimation; Permeable reactive barriers; Zeolite.