Liquid purification or separation – Processes – Liquid/liquid solvent or colloidal extraction or diffusing...
Reexamination Certificate
2001-03-29
2003-01-28
Drodge, Joseph W. (Department: 1723)
Liquid purification or separation
Processes
Liquid/liquid solvent or colloidal extraction or diffusing...
C210S639000, C210S747300, C210S774000, C210S805000, C210S170050, C210S177000, C210S194000, C210S511000, C166S267000
Reexamination Certificate
active
06511601
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to methods for remediation of polluted bodies and sources of groundwater. More particularly, the present invention relates to a method and system for extraction of chemicals such as non-aqueous phase liquids from surfactant-based groundwater remediation effluent water.
2. Background Technology
Contamination of groundwater with liquid organic contaminants such as nonaqueous phase liquids (NAPL), including dense nonaqueous phase liquids (DNAPL) and/or light nonaqueous phase liquids (LNAPL), plagues sites in both the public and private sectors. For example, for many years little care was taken in the handling of organic solvents and other contaminants which were used in industry and at government installations, such as military bases. Through poor handling techniques and occasional intentional dumping, many industrial sites and military bases now have contaminated areas containing relatively high concentrations of contaminants such as chlorinated solvents or other organic liquids. If not removed, such contaminants can filter down into groundwater supplies, rendering the water unfit for consumption and other uses.
Such groundwater contamination is fairly common in groundwater sites, which are permeable bodies of rock that are capable of yielding quantities of groundwater to wells and springs. The Environmental Protection Agency (EPA), Region I, recently identified 20 groundwater sites requiring remediation, with an additional 10,000 contaminated groundwater sites believed to exist nationwide at industrial, municipal, and military installations.
Several methods have been tested at various scales to determine their effectiveness in removal of organic contaminants from groundwater, and several techniques, both in situ and ex situ, are currently employed for remediating contaminated groundwater. To date, most of these have been pump-and-treat methods where DNAPL liquids are involved. In such a method, wells are drilled into the contaminated area and contaminated groundwater is pumped above the surface, where it is treated to remove the contaminants. Such pump-and-treat methods typically suffer from low process efficiency due to the relatively low solubility of DNAPL in the groundwater and resulting long clean-up time.
Due to the general impractability of pump-and-treat methods, other technologies have been developed which utilize a process commonly referred to as enhanced solubilization. Such a process uses micellar surfactant solutions to increase the effective solubility of the dense non-aqueous contaminants to accelerate the rate of removal. The mechanism for solubilization displayed by surfactants arises from the formation of microemulsions by the surfactants, water, and the solubilized dense non-aqueous liquid molecules.
One such technology is surfactant enhanced groundwater remediation (SEAR), which is particularly effective in the removal of chlorinated contaminants such as trichloroethylene (TCE) and perchloroethylene (PCE) from contaminated groundwater. In the SEAR process, a surfactant and other process chemicals such as a thickener and alcohol are injected into a contaminated groundwater to enhance solubility of the organic contaminants. Following dissolution, the contaminants, surfactant, and other process chemicals are pumped back to the surface where the chemicals are stripped, and treated water is reinjected to the groundwater. The SEAR process is particularly suited to remediation of groundwater in groundwater sites having an aquiclude such as a clay layer, which prevents downward vertical migration of solubilized organic contaminants. While the SEAR process is effective in clean-up of source contamination, the process is not an endpoint for water treatment, but rather is primarily useful in the removal of concentrated contaminants.
The SEAR process generates effluent water containing high concentrations of PCE, TCE, surfactant, and other process chemicals. Typical TCE/PCE concentrations in the SEAR effluent range as high as 5000 ppm. Alcohol and surfactant concentrations may reach up to 12% and 4%, respectively. Effluent treatment is a significant cost burden to the SEAR process, with up to 40% of the total SEAR process cost arising from effluent treatment.
A related technique is surfactant enhanced groundwater remediation at neutral buoyancy (SEAR-NB), which is an enhanced pump-and-treat method for remediation of TCE and PCE contaminated groundwater that is disclosed in U.S. Pat. No. 5,993,660 to Shook et al. In this process, surfactant, alcohol, and other components injected into a contaminated groundwater, are optimized to provide a microemulsion with a substantially neutral buoyancy with respect to the groundwater. Thus, the SEAR-NB process is particularly suited to remediation of groundwater in groundwater sites that do not have an aquiclude to prevent downward vertical migration of solubilized contaminants.
Considerable chemical cost is associated with the SEAR-NB process. Significant capital and operating costs are associated with the operation of a SEAR-NB effluent treatment plant. Effluent treatment currently accounts for approximately 50% of the total cost of the SEAR-NB process, not including costs associated with the loss of high value chemicals. Such loss of high value chemicals has a significant detrimental impact on the overall economics of the SEAR-NB process.
Extraction of organic compounds from water using critical fluids and direct extraction of DNAPLs from solids have been previously demonstrated. For example, critical fluid extraction has proven an effective method for removal of organics from contaminated soils and regeneration of activated carbon. Techniques have also been developed for extraction of various hydrocarbons and other contaminants from aqueous solution. CF Technologies (Hyde Park, Mass.) has demonstrated steady state extraction of various organic compounds from wastewater with efficiencies in excess of 99% in a continuous extraction system. Extracted compounds have included acetone, methylene chloride, trichloroethylene, toluene, and methyl methacrylate.
Several technologies, including activated carbon adsorption, steam stripping, and membranes have been explored to determine their effectiveness in separation of DNAPLs and process chemicals from the SEAR or SEAR-NB effluent. These technologies are typically effective in removal of TCE and PCE from the effluent, but often result in destruction and loss of process chemicals.
Activated carbon, although effective in removal of organic contaminants from aqueous solution, is most effective in treatment of dilute, less than 1%, process streams. As the SEAR or SEAR-NB processes generate an effluent stream with relatively high total organic content, in excess of 16%, large volumes of granulated activated carbon (GAC) would be required to enact the separation. The large consumption of GAC would result in generation of a large volume of secondary waste requiring regeneration or incineration. GAC adsorption would ultimately result in SEAR or SEAR-NB process chemical destruction.
Although, steam distillation or stripping can separate PCE, alcohol, and surfactant from aqueous solution, the surfactant is generally damaged by the high temperature operation and cannot be reused. Foaming of the surfactant during distillation can also occur, making the separation impossible. Steam distillation would also be costly due to large energy requirements to enact the desired separation.
In the SEAR or SEAR-NB processes, a micro-emulsion is formed in which surfactant molecules surround molecules of PCE in the contaminated groundwater in micellular fashion. These micelles are then solubilized into the aqueous phase and pumped out of the groundwater with the alcohol/surfactant/water flood. Membranes, although capable of enacting the separation of highly dilute DNAPL from water, are generally not capable of breaking micellular microemulsions such as those encountered in the SEAR or SEAR-NB processes. To enact a separati
Barker Donna L.
Ginosar Daniel M.
McMurtrey Ryan D.
Moor Kenneth S.
Shook G. Michael
Bechtel BWXT Idaho LLC
Drodge Joseph W.
Workman & Nydegger & Seeley
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