Multiphase
Extraction System Treats Emulsified Jet Fuel
Multiphase extraction (MPE) is a proven technology for removing fuel and fuel constituents from the subsurface. However, the high-vacuum process may produce fuel/water emulsions, which can significantly increase extracted water treatment costs. A case study of a fuel recovery system at Site 17, Naval Air Station (NAS) Lemoore, demonstrates the successful treatment of a fuel/water emulsion and illustrates the importance of recognizing site conditions that promote the development of an emulsion early in the project. Fuel/water emulsions consist of small droplets of fuel, between 20 and 0.01 microns in size, suspended in water. Emulsified fuel droplets may remain in suspension indefinitely and typically are not removed by an oil/water separator. Furthermore, the fuel droplets are too large to be adsorbed by granular activated carbon (GAC) in a cost-effective manner. The Navy investigated the conditions and processes that enable an emulsion to develop after experiencing breakthrough of the GAC during a 12-hour performance test of the Site 17 MPE system . Shearing and mixing of fuel and water by the extraction process and centrifugal transfer pumps, and an increase in suspended solids from extraction well drilling and development were found to contribute to emulsification. A series of treatment tests were conducted, including filtration, in-well separation, adsorption on clay and on a proprietary resin, chemical treatment, and dissolved air flotation (DAF). The Navy found that the addition of chemical flocculants and coagulants followed by treatment with a DAF unit was most effective for treating the emulsion. The system now discharges water that is below detection limits with respect to total petroleum hydrocarbons. Although the Site 17 system was successfully modified to treat the emulsion, it is recommended that MPE system designers employ proactive techniques to identify emulsions and emulsion treatment options as early in the design process as feasible. |