Upscaling dissolution and remobilization of NAPL in surfactant-enhanced
aquifer remediation from microscopic scale simulations
Abstract
The dissolution and mobilization of non-aqueous phase liquids (NAPL)
blobs in Surfactant-Enhanced Aquifer Remediation (SEAR) processes are
upscaled using dynamic pore network modelling of three-dimensional and
unstructured networks. We considered corner flow and micro-flow
mechanisms including snap-off and piston-like movement for two-phase
flow. Moreover, NAPL entrapment and remobilization were evaluated using
force analysis to develop capillary desaturation curve (CDC) and predict
the onset of remobilization and complete removal of entrapped NAPL
blobs. The corner diffusion mechanism was also applied in the modeling
of interphase mass transfer to represent NAPL dissolution as the
dominant mass transfer process. Our model showed that although
surfactants enhance NAPL recovery during two-phase flow,
surfactant-enhanced remediation of residual NAPL through dissolution is
highly dependent on surfactant type. When sodium dodecyl sulfate (SDS),
as a surfactant with high critical micelle concentration (CMC) and low
micelle partition coefficient ( ) was injected into a NAPL contaminated
site, reduction in mass transfer rate coefficient (due to considerable
changes in interface chemical potentials) significantly reduced NAPL
recovery after the end of two-phase flow. However, Triton X-100 (with
low CMC and high ) improved NAPL recovery. This is because by enhancing
solubility at surfactant concentrations greater than CMC, Triton X-100
overcompensates the interphase mass transfer reduction.