Cosolvent flushing

T0179 Constructed Wetlands for Acid Mine Drainage—General T0186 Cosolvent Flushing—General... 

T0181 Contamination Technologies, Inc., Low-Temperature Thermal Absorber (LTA) T0182 ConTeck Environmental Services, Inc., Soil Roaster T0186 Cosolvent Flushing—General... 

Cosolvent flushing is an in situ technology that enhances the remediation of contaminated soils and groundwater by injecting water and a cosolvent such as alcohol (e.g., ethanol, methanol, and isopropyl) into a contaminated area. Research has shown that an organic cosolvent can also accelerate the movement of metals through a soil matrix. The alcohol causes both an increase in aqueous contaminant solubility and lowering of non-aqueous-phase liquid (NAPL)-water interfacial tension. 

According to researchers, cosolvent flushing has the following potential advantages ... 

One of the primary components in the cost of cosolvent flushing technology is the cost of the cosolvent solution. Reuse of the flushing solution has shown the potential to greatly reduce the cost of treatment by reducing both chemical costs and the treatment and disposal costs of the extracted contaminants (D21314Z, p. 5). 

In 1998, a pilot-scale field demonstration of cosolvent flushing technology took place in Jacksonville, Florida. The cost of the demonstration was approximately 440,000. Plans were in development for a full-scale application of the technology. It was estimated that alcohol reinjection could reduce the cost of treatment by up to 50% (D21314Z, p. 10). 

More attractive are in situ remediation approaches, which often cost less. Cosolvents promote the mobilization of organic chemicals in soils, thus accelerating the cleanup of contaminated site. Cosolvent flushing has been developed using the same principles as those used in solvent flooding, a technique to enhance petroleum recovery in oil fields. It involves injecting a solvent mixture, mostly water plus a miscible cosolvent, into the vadose... 

The applicability of solvent flushing, however, is often limited by the characteristics of the soil, especially the particle size distribution. While sandy soils may result in xmcon-trolled fluid migration, clayey soils with partieles size less than 60 pm are often considered unsuitable for in-situ solvent flushing due to low soil permeability. In an attempt to remove PAHs from poorly permeable soils, Li, et alP investigated the possibility of combining cosolvent flushing with the electrokinetie technique. Electrokinetic remediation... 

For in situ soil flushing, large volumes of water, at times supplemented with surfactants, cosolvents, or treatment compounds, are applied to the soil or injected into the groundwater to raise the water table into the contaminated soil zone. Injected water and treatment agents are isolated within the underlying aquifer and recovered together with flushed contaminants.50-52,85... 

Soil flushing Flushes surfactants or cosolvents below water table to promote Can be inefficient in low-permeability zones or complex geologic... 

The effects of rate-limited solubilization, subsurface layering and flushing solution density on PCE recovery were evaluated in two separate box studies (Box A and Box B). Box A was flushed with 4% Tween 80 alone to serve as the control case, while Box B was flushed with 4% Tween 80 + 5% EtOH to evaluate the effects of cosolvent addition on PCE solubilization, cumulative PCE recovery, and surfactant delivery. Each box was packed with 20-30 mesh Ottawa sand as the background porous medium, with one rectangular layer of F-70 Ottawa sand above two side-by-side rectangular... 

To evaluate the effects of cosolvent on surfactant delivery and PCE recovery, Box B was flushed with 4% Tween 80 + 5% EtOH at a Darcy velocity of 4.8 cm/hr. The surfactant/cosolvent mixture, which had a density of 0.994 g/cm3, was also representative of a neutral buoyancy flood solution (Shook et al, 1998). It is important to recognize that "neutral buoyancy" refers to density of flushing fluid after solubilization of the DNAPL. Thus, the initial density of the surfactant formulation must be less than that of the resident aqueous phase. Figure 5b shows the location and shape of the 4% Tween 80 + 5% EtOH front after flushing Box B with 0.5 pore volumes of solution. The lower density of the 4% Tween 80 + 5% EtOH solution (0.994 g/cm3) relative to the density of resident pore water (0.998 g/cm3) caused the injected solution to flow preferentially along the top of Box B (Figure 5b). This effect can become severe at low flow rates (Taylor, 1999). The... 

In this study, the effects of cosolvent (EtOH) addition on the solubilization and recovery of PCE by a nonionic surfactant (Tween 80) was evaluated using a combination of batch, column and 2-D box studies. Batch results demonstrated that the addition of 5% and 10% EtOH increased the solubilization capacity of Tween 80 from 0.69 g PCE/g surfactant to 1.09 g PCE/g surfactant. For a 4% Tween 80 solution, this translates into a solubility enhancement of more than 50%, from 26,900 mg/L to 42,300. mg/L. When the surfactant formulations were flushed through soil columns containing residual PCE, effluent concentration data clearly showed that PCE solubilization was rate-limited, regardless of the EtOH concentration. Using analytical solutions to the 1-D ADR equation, effective mass transfer coefficients (Ke) were obtained from the effluent concentration data for both steady-state (A e ) and no flow conditions The addition of EtOH had... 

Radio frequency heating, 500 Steam stripping, 500 Vacuum extraction, 500 Aeration, 501 Bioremediation, 501 Soil flushing/washing, 502 Surfactant enhancements, 502 Cosolvents, 502 Electrokinetics, 503 Hydraulic and pneumatic fracturing, 503 Treatment walls, 505 Supercritical Water Oxidation, 507 Solid Solution Theory, 202 Solubility products, 48-53 Metal carbonates, 433-434 Metal hydroxides, 429-433 Metal sulfides, 437 Sorption, 167 See Adsorption Specific adsorption, 167 See Chemisorption Stem Layer, 152-154 Sulfate, 261... 

Jawitz, J.W., Dai, D., Rao, P.S.C., Annable, M.D. and Rhue, R.D. (2003) Rate-limited solubilization of multicomponent nonaqueous-phase Hquids by flushing with cosolvents and surfactants Modeling data from laboratory and field experiments. Environ. Sci. Technol., 37(9), 1983-1991. 

After these feasibility test data appeared (Li, Cheung, and Reddy, 2000), n-butylamine was employed in several electrokinetic tests as a flushing solution (Reddy and Ala, 2006 Reddy et aL, 2006 Maturi and Reddy, 2008). In a study by Maturi and Reddy (2008), the concentration of n-butylamine greatly influenced the amount of electroosmotic flow as well as phenanthrene mobility. When n-butylamine was present at 20%, greater phenanthrene removal was seen than when the cosolvent was present at 10% because of increased phenanthrene solubiUzation. Electroosmotic flow decreased, however, with increases in cosolvent concentration, resulting in an overall rather limited removal of phenanthrene. Therefore, optimization of cosolvent concentration is required to increase contaminant solubilization while permitting sustained electroosmotic flow. 

Reddy and Maturi (2005) examined the feasibility of using electrokinetic remediation for the removal of mixed contaminants (i.e. mixtures of heavy metals and PAHs) from kaolin (low permeability soU). Likewise, different types of flushing solution were evaluated by a laboratory experimental program, including a cosolvent (n-butylamine), surfactants (3% Tween 80 and 5% Igepal CA-720), and a cyclodextrin (10% hydroxypropyl-j8-cyclodextrin or HPCD). It was reported that... 

Another factor affecting the capability to rinse complex part structures are the forces of surface tension. Films of a solvent with a relatively high value of surface tension may block flushing of complex surface structures. In other words, an SA cosolvent which is perfectly miscible (Class III) or immiscible (Class II) with an RA cosolvent, can t either dilute or displace, respectively, the RA cosolvent if surface forces block /limit its passage to meet the SA cosolvent. 

Transfer the somewhat-cooled wet porous electrodes to another physically isolated cleaning chamber °, at a location adjacent to the primary cooling coils in the chamber (called the vapor rinse zone in Figure 3.33). Flush the electrodes with RA cosolvent vapor which easily condenses to liquid in the primary cooling coils. The SA cosolvent and RA cosolvents are adequately miscible, the exceptionally low surface tension of the RA cosolvent will aid in flushing the porous stmcture of these electrodes. 

L. Strbak, In Situ Flushing with Surfactants and Cosolvents. National Network of Environmental... 

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