Liquid purification or separation – Processes – Treatment by living organism
Reexamination Certificate
2000-07-24
2002-10-08
Barry, Chester T. (Department: 1724)
Liquid purification or separation
Processes
Treatment by living organism
C210S610000, C210S620000, C210S621000, C210S616000, C210S617000, C210S150000, C210S197000
Reexamination Certificate
active
06461510
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to novel ex situ processes for simple and economical destruction of air, water, and land contaminants.
2. Description of Related Art
Many industrial operations today utilize raw materials, solvents, and cleaners which result in the release of harmful pollutants into the environment. In addition, widespread use and improper disposal of toxic materials in the past have resulted in contamination of many soils and subsurface aquifers with harmful pollutants, particularly chlorinated aliphatic hydrocarbons (Council on Environmental Quality; U.S. Environmental Protection Agency, 1981). The National Priority List of the USEPA lists TCE as one of the most frequently reported contaminants at hazardous waste sites. In rural areas of the U.S., much of the drinking water supply is provided by groundwater. TCE is one of the most prevalent groundwater contaminants (Westrick et al. 1984; Lenhard et al. 1995), and due to the serious health threat these contaminated groundwaters pose, remedial action of such areas are of major concern. Traditional clean-up methods for contaminated water include air-stripping or air-stripping followed by granulated-activated carbon (GAC) adsorption. In either case, the contaminants are only transferred from one medium to another and must still be dealt with. In addition, traditional clean-up methods are often economically prohibitive due to the low concentrations of the contaminants. In contrast, biodegradation processes can convert toxic pollutants to non-toxic products such as carbon dioxide and water and are generally more economical than traditional clean up methods at low contaminant concentrations.
In industrial operations, tightening regulations are requiring more stringent controls on emissions and disposal, and chemical hygiene requirements are forcing the use of higher air volumes to provide worker safety, which results in high-volume, low-concentration contaminated air streams. Such contaminated air streams may be diluted to the point that traditional technologies, such as wet scrubbing, thermal oxidation, air stripping, or carbon adsorption may be either ineffective or too costly. Such dilute applications are well suited to biodegradation processes, which utilize microorganisms attached to natural or synthetic packing to actually biodegrade the target pollutants to non-toxic products rather than simply transfer them from one medium to another. Using biodegradation processes, contaminated streams are passed through packing containing microorganisms which degrade or mineralize the pollutants into harmless compounds such as carbon dioxide, salts, and water. In many cases, biodegradation processes provide cost-effective, environmentally friendly alternatives to traditional pollution control or remediation technologies.
The fate of chlorinated hydrocarbons, particularly TCE, is a major concern of the Department of Defense (DoD). Numerous DoD sites in the U.S. have been identified as having groundwater contaminated with chlorinated hydrocarbons as well as other hazardous organic compounds. The Army has prioritized “Solvents in Groundwater” as the fifth highest requirement in the area of environmental cleanup research and development. At some DoD sites, contaminated groundwater is pumped to air strippers which remove the contaminants from the groundwater and transfer them to an air stream. In many cases, these contaminated air streams from the strippers are simply released to the environment. In addition, painting, coating, paint stripping, solvent degreasing, and other operations at DoD sites result in the release of streams contaminated with TCE, methylene chloride, and other harmful VOCs (volatile organic compounds) and SVOCs (semi-volatile organic compounds) to the environment. Economical and practical processes are needed to degrade such contaminants to harmless by-products, either directly in groundwater or wastewater, or in the air streams emitted to the environment from air stripping operations, from soil vapor extraction processes, or from other operations which release harmful pollutants.
Traditional contaminated groundwater clean-up methods include air-stripping and/or granulated-activated carbon (GAC) adsorption. Generally, the contaminated groundwater is pumped to the surface and then to the top of an air stripper, which usually consists of a cylindrical column packed with material designed to maximize liquid-to-air contact. The contaminated water flows down through the packing by gravity as air is blown up through the column. The volatile organic compounds are thus counter-currently stripped from the water and enter the air during transit through the stripper. In some cases, this contaminated air stream is then blown through an activated carbon filter designed for removal of the particular contaminants in question. However, the contaminants are not destroyed. They are simply held and concentrated within the carbon filter. At some point in time the carbon filter becomes saturated with contaminants, and then the contaminants begin to pass through the filter to the environment. At this time, it is necessary to replace the contaminated carbon with fresh carbon and to either dispose of the contaminated carbon or to send it to a vendor for regeneration, both of which are costly and inconvenient operations. In some cases, the groundwater may be pumped directly through carbon filters without first air stripping. In other cases, the groundwater is air stripped, the air from the air strippers is emitted to the environment, and the water effluents from the air strippers are passed through carbon filters to remove less volatile compounds which may not be removed by the strippers. Unlike carbon adsorption, biodegradation processes such as biofiltration can destroy the contaminants and offer practical, cost-effective, and environmentally friendly alternatives.
Biofiltration technology is being developed as an economical and environmentally friendly solution for a variety of remediation and pollution control applications. Example applications include both point and non-point source industrial emissions (regulated by the 1990 Amendments to the Clean Air Act) as well as site remediation waste streams generated by soil vapor extraction and air sparging systems. Biofiltration technology has been accepted in Europe for the last 50 years for the control of odors. Within the last decade, the technology is gradually being adopted in the U.S., and the application base is broadening to include the control of volatile organic compounds.
In most biodegradation processes, the microorganisms actually consume and derive food value from the target pollutants, and the waste stream can be passed continuously through the processes to achieve continuous degradation of the target pollutants in the waste stream. In other words, the microorganisms directly metabolize the pollutants as a source of food and growth. Such biodegradation processes will hereinafter be referred to as direct-metabolism processes. Pollutants capable of being directly consumed (or metabolized) by microorganisms in biodegradation processes include methyl ethyl ketone, methyl isobutyl ketone, butyl acetate, toluene, xylene, styrene, benzene, carbon disulfide, hydrogen sulfide, ammonia, and many others.
However, with certain pollutants, such as chlorinated aliphatic hydrocarbons and in particular the chloroethylenes, naturally occurring microorganisms cannot directly consume and derive food value from the pollutants. In other words, the microorganisms cannot directly metabolize the pollutants. In such cases, certain alternate carbon (food) sources, or primary substrates, can be supplied that the microorganisms directly metabolize, and in so doing, the microorganisms thereby generate enzymes capable of degrading certain target pollutants that cannot be directly metabolized. In other words, the pollutants targeted for destruction are indirectly degraded by enzymes generated when the microorganisms directly metabolize another co
Boles Jeffrey L.
Gamble Johnny R.
Lackey Laura
Barry Chester T.
Tennessee Valley Authority
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