Physicochemical Transport Processes Affecting the Removal of Residual DNAPL by Nonionic Surfactant Solutions

• Published in: Environmental science & technology 1996-06, Vol.30 (6), p.1852-1860
• Main Authors: Okuda, Itaru, McBride, John F, Gleyzer, Simon N, Miller, Cass T
• Format: Article
• Language: English
• Subjects: Applied sciences; Bioremediation; Chemistry; Contamination; Exact sciences and technology; Groundwaters; Natural water pollution; Pollution; Surfactants; Water; Water treatment and pollution
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es9504395

Aquifers contaminated with dense nonaqueous phase liquids (DNAPLs) are extremely difficult to remediate with standard pump-and-treat methods. Enhanced remediation methods, such as flushing with cosolvent or surfactant solutions, promise to reduce remediation times but result in complex physicochemical systems for which we still lack both fundamental understanding and reliable process-based models. The overall objective of this work was to observe and quantify various physicochemical transport processes acting during the removal of a typical residual DNAPL (tetrachloroethylene, PCE) by solutions containing a nonionic surfactant (Triton X-100). To achieve this goal, we measured the phase behavior of the water/PCE/Triton X-100 system in batch systems and performed a set of glass bead column experiments to investigate residual PCE removal mechanisms, nonreactive tracer transport, and Triton X-100 transport. We observed and quantified removal of residual PCE by a number of processes (dissolution, micellar emulsions/microemulsion transport, macroemulsion transport, and DNAPL mobilization) as a function of the surfactant concentration used to elute the PCE from the porous medium. We concluded that macroemulsion transport was an important process, accounting for up to 30% of total PCE removala process which, to date, has not been accounted for in mathematical models of surfactant-enhanced remediation. We also observed that viscous fingering developed during elution of surfactant in the idealized one-dimensional column system, suggesting that this phenomenon will also affect the efficiency of surfactant recovery in field-scale applications.