Surfactant Floods
The Basics
A surfactant, which is a Surface Active Agent, is an interesting compound that has an affinity for both water and oils, making it an ideal molecule for the removal of petroleum hydrocarbons. Surfactants are most appropriate for the removal of light non-aqueous phase liquids (LNAPL).
If you get grease on your clothing, you do not attempt to clean them by just adding water. You also use a detergent. Soaps and detergents are examples of surfactants.
The subsurface is, of course, a much more difficult environment in which to work. Contact of the surfactant with the LNAPL and maintaining hydraulic control are very important. Choosing the right surfactant is critical and will depend on the LNAPL, the groundwater chemistry and mineralogy.
Nonionic surfactants, which are used in dishwashing liquids such as Dawn, are also readily available for subsurface remediation. These types of surfactants are stable in hard water, which is a good thing when you are cleaning dishes. Of course, environmental conditions are somewhat different.
Anionic surfactants provide considerable advantages. Please note that we recommend using anionic surfactants that readily biodegrade.
First, as soils are primarily negatively charged, the soil naturally repels anions (negatively charged ions). On the other hand, nonionic surfactants are easily adsorbed. Thus, when applying nonionic surfactants, you end up wasting a significant amount of money just dealing with the matrix demand. Soils remove nonionic surfactants from water just like activated carbon removes organic contaminants from water. The manufacturers of nonionic surfactants typically recommend using 4 to 8% surfactant in the injectate. Using anionic surfactants can reduce the volume by almost an order of magnitude.
Furthermore, a key efficacy metric for surfactants is the reduction of the interfacial force, which is the force that keeps the oil trapped within pores. Fine-tuning the balance of the attraction of the nonionic surfactant between the oil and the water is difficult. As a result, most nonionic surfactants reduce this trapping force by about an order of magnitude. Because it is easier to balance the anionic surfactants, they can reduce the interfacial force by three to four orders of magnitude, a huge advantage.
| Surfactant | Interfacial Force (oil and water) | Injection Vol. | Interfacial Force with Surfactant |
|---|---|---|---|
| Nonionic | 30 to 50 mNewtons/meter | 4 to 8% | 5 mNewtons/meter |
| Anionic | 30 to 50 mNewtons/meter | 0.5 to 0.9% | 10-2 to 10-3 mNewtons/meter |
Therefore, when you apply the correct anionic surfactant, you not only use much less of it, but it is also far more effective.
The Company Dajak Represents
Surbec was founded by three faculty members at the University of Oklahoma. Surbec’s core expertise lies in the understanding of surfactant chemistry, which yields significant benefits.
- Dramatic reduction in cost – almost an order of magnitude
- Minimal surfactant mass – less than 0.9 weight percent
- 1 to 1.4 pore volumes for up to 95% mass removal
- No creation of a micro-emulsion, which dramatically reduces treatment costs – the oil separates from the water in a holding tank in less than 30 minutes
- Essentially no waste stream
- Any surfactants remaining in the subsurface are easily biodegradable
Some important points follow:
- Surbec surfactant routinely removes up to 95% of the NAPL contaminant mass.
- Surbec optimizes the anionic surfactant formulation for the specific contaminant and site geochemistry.
- By removing NAPLs, surfactants can enhance the effectiveness of bioremediation and chemical oxidation technologies.