Dissolution of creosote in groundwater: an experimental and modeling investigation

The dissolution of industrial creosote with water was investigated using a small physical model (generator column) in the laboratory. The column was packed with a creosote residual of 10% and the effluent was monitored for ten target polycyclic aromatic hydrocarbons (PAH's) including naphthalene, phenanthrene and benzo[a]pyrene. Tests were also conducted with variable contact time to evaluate mass-transfer rates and the rate of approach to equilibrium dissolution. For most components equilibrium between creosote and water was attained after a contact time of 60 h. During shorter contact periods, lower aqueous concentrations of PAH's were attained. However, the ratios of these concentrations were in proportion to their effective solubilities which were calculated using Raoult's law and the creosote compositional data. Comparison of the laboratory data with results from an equilibrium model indicated that creosote dissolution could not be described by equilibrium relationships between component concentrations in the two phases at the experimental groundwater velocities. As well as the equilibrium model, a kinetic model was used in an attempt to stimulate the flushout data. It is suggested that increasing mass-transfer rate limitations between the two phases and within the non-aqueous-phase liquid (NAPL) as dissolution proceeded accounted for the differences between the kinetic model and experimental results. Both the physical and mathematical models showed that the dissolution of creosote dense non-aqueous-phase liquid (DNAPL) would initially result in high concentrations of components having high effective solubilities. Complete depletion of creosote by dissolution alone, assuming equilibrium, would require a water/creosote volume ratio of > 270, 000. Therefore, water flushing as a remedial measure will be relatively ineffective for removing residual creosote. The properties of creosote and the aqueous phase, time of contact between the two phases, the degree of contact and the groundwater velocity are important factors in controlling mass transfer between the two phases.