Liquid purification or separation – Processes – Treatment by living organism
Reexamination Certificate
1999-11-02
2002-01-08
Barry, Chester T. (Department: 1724)
Liquid purification or separation
Processes
Treatment by living organism
C210S616000, C210S617000
Reexamination Certificate
active
06337019
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to biological permeable barriers for creating a “bio-trench” or “bio-curtain” to clean contaminated groundwater. Specifically, the present invention relates to an apparatus and method to biodegrade contaminates in groundwater as the groundwater contacts and passes through the immobilized cells of the “bio-trench” or “bio-curtain” during groundwater flow or movement.
BACKGROUND OF THE INVENTION
Today's release of the contaminants to the groundwater is increasing. With over 50% of the fresh water used in the United States coming from groundwater, contamination of this resource by xenobiotic chemicals represents a potential serious health and environmental problem. Toxicity, accumulation, and persistence of contaminants found in groundwater are just a few of the reasons for concerns.
Several methods of on-site aquifer restoration have been utilized recently to remove contaminates from groundwater. Chief among these methods are the pump and treat method in which the water is pumped out and treated, and the permeable barrier in which some type of filtering agent or reactive agent is placed in the ground to contact the contaminated water.
Conventional aquifer restoration alternatives such as pump and treat or on site remediation are not generally commercially effective for most forms of contamination. These technologies have numerous problems associated with them which include: management of large volumes of water, potential production of undesirable by-products from the reaction with the contaminate, production of waste sludge from the reaction of the filtering agent with the contaminate, the exhaustion of the filtering agent or reactive agent and need to replace it to continue treatment, undesirable effects on hydraulic characteristics in uncontaminated parts of the aquifer (change in direction of water movement), and the labor or energy intensive nature of the process.
An alternative to conventional groundwater treatment processes is the use of barriers which are permeable to water, but prevent the migration of contaminants. They are referred to as permeable barriers. In-situ permeable barriers are a relatively new cost-effective technology that can be used in groundwater remediation of shallow aquifers. Permeable barriers are installed as permanent, semi-permanent, or replaceable units across the flow path of a contaminant plume. Permeable barriers allow water to move passively through while precipitating, sorbing, or degrading the contaminants. These mechanically simple barriers may contain metal-based catalysts for degrading volatile organics, chelators for immobilizing metals, nutrients and oxygen for microorganisms to enhance bioremediation, or other agents. Degradation reactions may break down the contaminants in the plume into harmless byproducts. Crushed limestone, peat, and powdered activated carbon are also several effective barrier mediums that have been used to adsorb or precipitate contaminants.
Advantages of these barriers include the following: simple installation, simple recovery and replacement of the material, low operation maintenance, less surface disruption, less labor, and less energy are required than other remediation technologies; and comparatively quick installation and containment of contaminants.
One example of such non-biological permeable barrier is a mixture of powdered activated carbon (PAC) and sand. The PAC/sand mixture has been shown to be a successful medium for benzene removal in trench-based permeable barrier. The physical uptake of different mixtures (3% and 10%) of PAC/sand and nonabsorbent material such as sand and zeolite have been used. Another non-biological permeable barrier containing an iron-based catalyst has been used to reduce the concentration of trichloroethene (TCE) by 95% and the tetrachloroethene (PCE) concentration by 91%.
Rael evaluated possible permeable barrier media designed to remove benzene in-situ from ground water. Effectiveness of several common material including coal, powdered-activated carbon (PAC), peat, and zeolite were evaluated in a series of batch and column studies with an initial benzene concentration of 50 mg/L. Silica sand was used as an inert matrix and was mixed with PAC to produce either 3% (by weight) or 10% PAC/sand mixtures. Based on their results, a mixture of PAC and sand was considered the most successful candidate. However, these authors observed that when the barrier reached its treatment capacity it had to be replaced with fresh media. The barrier medium allowed the flow of contaminated water but adsorbed the contaminant preventing further migration. This technology is limited to the depth accessible by trenching equipment and therefore would be applicable in shallow aquifer systems of less than 30 m.
Morrison and Spangler have explored chemical barriers as a passive in-situ water-treatment system. Precipitation barriers (hydrated lime) and sorption barriers (ferric oxyhydroxide) for removing uranium from ground water were studied. Chemicals used in the barrier were placed in the subsurface either by lining a disposal site, by trench and fill, or by injection. Dissolved contaminants became part of the immobile solids of the aquifer, by either precipitation or adsorption, as the contaminated groundwater passed through the chemical barrier.
In 1991 Thomson et al. examined the concept of designing permeable barriers to remove groundwater contaminants in-situ. Permeable barriers constructed by trenching had two advantages: 1) accessibility of the medium placement and 2) ease of recovery of medium by re-excavation. Permeable barriers were classified as either passive or active. An active barrier required continuous operation and maintenance while a passive barrier required no operation or maintenance once the medium is in place. An example of active barrier, in-situ air stripper was investigated and compared with conventional packed tower air stripping. It was determined that: 1) the trench-based stripping needed high pressure air compressors, but no water pumping equipment was needed which made the operating cost less; and 2) biostimulation did occur from the oxygen, resulting in a combined air stripping and biodegradation of volatile organic contaminants.
The drawbacks of physical or chemical barriers that were mentioned above are production of waste sludge from the reaction of the filtering agent with the contaminants, the exhaustion of the filtering agent or reactive agent and need to replace it to continue treatment.
One known method to completely destroy the contaminants into the harmless by products in the water is biological degredation. Biological processes are carried out by bacterial species that are capable of using organic compounds as their carbon source. Because of numerous advantages of biological processes, bioremediation has emerged as a viable technology to use microorganisms as effective agents to remove organic compounds from groundwater. The most common approach for large-scale bioremediation has been to inject nutrients into the ground water to simulate contaminant-degrading organisms. This approach has not proven to be reliable due to biofouling the stimulated population and contaminants into contact.
Another approach, called bioagugmentation, involves the addition of bacteria and nutrients to contaminated ground water. In this approach the microorganisms are exposed to the stress conditions in the environment where they are introduced. The losses of viable microorganisms as a result of stress conditions and migration of microorganisms are the major problems with this technology. Inadequate controls over the microorganisms under specific environmental conditions limit the biological process and result in incomplete contaminant transformation.
Key requirements for success of any bioremediation process are complete detoxification of the contaminants, high removal efficiencies, and process stability and control. Known in the art is the immobilization of cells can offer stability and control for biological processes. Also know
Barry Chester T.
Spencer Fane Britt & Browne LLP
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