Equally as important is the compound’s unique self-distribution characteristics. When emplaced in the subsurface, 3DMe does not perform like emulsified oil substrates – irreversibly sorbing onto the soil matrix within a few meters of injection. Its unique features (patent pending) allow for a slow, continuous distribution in the subsurface, effectively treating deep or large plumes. This distinguishing feature reduces the number of application points and ensures excellent contaminant contact.
Successful Treatment Requires Successful Distribution
When employing a substrate for enhanced anaerobic bioremediation, initial subsurface distribution is the key to success. The engineer’s primary issue is cost-effectively achieving adequate distribution within the treatment zone. This requires maximizing the subsurface volume impacted by the electron donor from each injection location.
One of the most important factors influencing the distribution of injectable substrates is the Hydrophile/Lipophile Balance (HLB). The HLB is an index used to describe the tendency for a chemical substance to dissolve in water(hydrophilic) or oil (lipophilic). The more hydrophilic a compound (high HLB), the more readily it dissolves and distributes in the subsurface. Conversely, the more lipophilic (low HLB), the more likely it will bind to the aquifer or soil matrix and distribute poorly. A substrate with a very high HLB, such as lactate (HLB 30), will distribute rapidly through diffusion and groundwater flow. Unfortunately, the high solubility of this compound will most likely cause it to ferment too rapidly resulting in undesirable methanogenesis, significant pH lowering, and ultimately “washing out” of the target treatment area.
Adversely, emulsified oil substrates have a very low HLB (HLB -6), which significantly limits distribution. When injected into the subsurface, they tend to rapidly bind to the aquifer mineral surface. This generally occurs within the first 1 or 2 meters of the injection location. Field data and laboratory studies have shown that the distribution of emulsified oil substrates is independent of the concentration of the oil emulsion injected and the speed with which the emulsion is applied.2 Unfortunately, no additional water injected will push the emulsified oil droplets further since the immobility of oil occurs once it is bound to the mineral surface. Due to its low HLB and insolubility, emulsified oil will not re-dissolve and distribute via diffusion or groundwater flow. Instead, emulsified oil substrates remain sorbed to the aquifer directly in the area injected.
As a result, the proper use of emulsified oil substrates requires many injection point locations or wells packed closely together in order to achieve adequate coverage of the aquifer volume to be treated. Under this scenario, the amount of emulsified oil emplaced in the subsurface may affect the hydraulic conductivity of the treatment zone.
3DMe Optimizes Distribution
In an effort to lower the cost of applying electron donor substrates, researchers at Regenesis took a new approach in designing 3DMe. The result is an advanced chemical structure with a balanced HLB (HLB 7) and the ability to adsorb, yet also dissolve. 3DMe is injected into the subsurface as a very fine emulsion and has a tendency to sorb onto the aquifer matrix, similar to emulsified oil substrates. However, the majority of the microemulsion droplets then re-dissolve into the groundwater leaving behind only a thin coating of the substrate as opposed to a heavy layer of adhered oil droplets. The dissolved substrate disperses into groundwater until it re-adsorbs nearby onto the aquifer surface. Research has shown that if the dissolved concentration of 3DMe exceeds what is referred to as the critical micelle concentration (CMC), it will form molecular spheres (0.01 to 0.05 microns) called “micelles.” These micelles will move outward in the subsurface until adhering nearby to the aquifer matrix. This cycle of partial dissolution, transport, and adsorption repeats until a thin layer of substrate coats the entire targeted treatment area, stimulating anaerobic bioremediation. This “self-distributing” characteristic of 3DMe is a breakthrough in the treatment of chlorinated solvent plumes, providing effective distribution that has never been achieved in the past.