A review on dissolution of multi-component non-aqueous phase liquids: recent studies, mechanisms and mass transfer limitations

Dense non-aqueous phase liquids (DNAPLs) are considered as priority pollutants in groundwater systems due to their low solubility and high toxicity even at low concentrations. The impact of their accidental release is irreversible as they mix with groundwater through dissolution such that complete remediation of the aquifer is nearly impossible. In this paper, the current status of research and recent developments in the experimental, analytical and mathematical approaches to study the dissolution of multi-component DNAPL compounds in the saturated, homogeneous/hetero-geneous porous media are summarised. It is observed that most of the earlier investigations have been confined to single-component dissolution either in lab-scale or in-situ studies. The existing mass transfer correlations are insufficient to estimate the dissolution rate of DNAPLs in a multi-component system where the velocity and non-aqueous phase liquids saturation are differently influenced by the aquifer heterogeneity. Considering the variability in the distribution pathways, a realistic quantification of the morphology and surface area of DNAPLs is quite challenging. Based on the insights from the recent literature, it is envisaged that a combination of solubility enhancement and remobilisation techniques can be further expanded to optimally remediate the contaminated sites.