Liquid purification or separation – Processes – Treatment by living organism
Reexamination Certificate
2000-10-31
2002-06-04
Upton, Christopher (Department: 1724)
Liquid purification or separation
Processes
Treatment by living organism
C210S747300, C166S296000, C166S305100, C166S310000, C405S128450, C405S128500, C405S129450, C435S262500
Reexamination Certificate
active
06398960
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the remediation of contaminated groundwater, and in particular, relates to a remediation method utilizing a microemulsion of an innocuous oil.
2. Description of the Related Art
There are numerous techniques employed for the remediation of contaminated groundwater in aquifers. The mechanisms for cleanup may be physical, chemical or biological. A typical physical remediation method for groundwater contaminated with volatile solvents includes recovery of the contaminated water using a series of wells followed by above-ground treatment by air stripping and/or activated carbon adsorption.
The most common approach for enhancing the anaerobic conversion of organic and inorganic contaminants in the subsurface involves continuously flushing a soluble readily biodegradable substrate such as lactate or molasses through the contaminated zone. There is, however, significant capital expense associated with the installation of the required tanks, pumps, mixers, injection and pumping wells and process controls required to continuously feed a soluble easily degradable substrate. Operation and maintenance costs can be high because of the frequent clogging of injection wells and the labor required for extensive monitoring and process control.
Treatment of contaminated groundwater in situ is often a less expensive approach for groundwater remediation. In situ treatment technologies generally rely on the natural migration of contaminated groundwater to the treatment zone where the transformation can occur via either chemical or biological mechanisms. Most previous in situ bioremediation approaches have also relied on the injection of oxygen or oxygen-containing chemicals into the aquifer to provide electron acceptors to enhance aerobic biodegradation processes, however, this approach is not applicable to chlorinated solvents and other oxidized compounds.
In many aquifers, the cleanup rate is controlled by the rate of contaminant dissolution and transport by the mobile groundwater. When dense non-aqueous phase liquids such as halogenated aliphatic organic solvents are present or contaminants are present in lower permeable zones, dissolution rates are slow and a long time is required for aquifer cleanup. Under these conditions high operation and maintenance costs are a major problem.
Impermeable barriers are used to restrict the movement of contaminant plumes in ground water. Such barriers are typically constructed of highly impermeable emplacements of materials such as grouts, slurries, or sheet pilings to form a subsurface wall. When successful, these barriers eliminate the possibility that a contaminant plume can move toward and endanger sensitive receptors such as drinking water wells or discharge into surface waters. However contaminated groundwater often bypasses around these barriers unless they are constructed to completely enclose the contamination source.
Technologies to improve the chances that contaminated groundwater will encounter subsurface reactive agents have been developed. One such technique is the permeable reactive barrier (PRB), which is a passive in situ treatment zone of reactive material that degrades or immobilizes contaminants as groundwater flows though it. In contrast to subsurface walls, permeable reactive barrier walls do not constrain plume migration, but act as preferential conduits for contaminated groundwater flow. In a PRB, reactive materials are placed where a contaminant plume must move through it as it flows, with treated water exiting on the other side.
PRBs are installed as permanent or semi-permanent replaceable units across the flow path of a contaminant plume. Natural gradients transport contaminants through strategically placed treatment media. The media degrade, sorb, precipitate or remove chlorinated solvents, metals, radionuclides, and other pollutants. These barriers may contain reactants for degrading volatile organics, chelators for immobilizing metals, nutrients and oxygen to enhance bioremediation, or other agents.
The choice of reactive media for PRBs is based on the specific organic or inorganic contaminants to be remediated. Most PRBs installed to date use zero-valent iron (Fe
0
) as the reactive media for converting contaminants to non-toxic or immobile species. For example, Fe
0
(can reductively dehalogenate hydrocarbons, such as by converting TCE to ethene, and can reductively precipitate anions and oxyanions, such as by converting soluble Cr
+6
oxides to insoluble Cr
+3
hydroxides. These barriers consist of a long trench constructed perpendicular to the groundwater flow that is backfilled with ground-up iron. As the chlorinated solvent and other contaminants flow through the barrier, they react with the iron and are transformed. The transformation reactions that take place in the barriers are dependent on parameters such as pH, oxidation/reduction potential, concentrations of the substrate(s) and contaminant(s) and reaction kinetics within the barrier. The hydrogeologic setting at the site is also critical, because geologic materials must be relatively conductive and a relatively shallow aquitard must be present to contain the system. The technology works well but is very expensive to construct. Examples include the work of Gillham et al. (1995, unpublished Communication to the International Containment Technology Workshop, Permeable Barriers Session, Baltimore, Md.). The disclosures of all patents and publications referred to herein are incorporated herein by reference.
Most PRBs are installed in one of two basic configurations: funnel-and-gate or continuous trench, although other techniques using hydrofracturing and driving mandrels are also used. The funnel-and-gate system employs impermeable walls to direct the contaminant plume through a gate, or treatment zone, containing the reactive media. A continuous trench may also be installed across the entire path of the plume and is filled with reactive media.
Pump-and-treat technologies and funnel and gate barriers are not conducive to broad site cleanup. These are interceptor technologies; there are no cost-effective technologies that address the entirety of the plume in situ.
Remediation techniques that have been employed for various contaminants are discussed more specifically below. Enhanced anaerobic bioremediation through reductive dehalogenation of halogenated aliphatic organic and inorganic compounds has been demonstrated as a method for remediating aquifers contaminated with chlorinated solvents (Holliger, 1995. Current Opinion in Biotechnol. 6:347-51; Beeman et al., 1994. In Bioremediation of Chlorinated and Polycyclic Aromatic Hydrocarbon Compounds, ed. Hinchee, et al., S K Ong, p. 14-27. Boca Raton: Lewis Publishers Ellis et al., 2000. Environmental Science and Technology. 34: 2254-2260). In this process an organic substrate is emplaced into the aquifer to stimulate the growth of anaerobic dechlorinating bacteria by providing an electron donor for energy generation and carbon source for cell growth (Lee et al., 1997. J. Ind. Microbiol. Biotechnol. 18(2/3):106-15; McCarty et al., 1994. Handbook of Bioremediation, Lewis Pub., Boca Raton, Fla., pp. 87-116). For example, tetrachloroethene (PCE) and trichloroethene (TCE) can be treated by the following reaction:
PCE->TCE->cis DCE >VC->ethene
Cis-dichloroethene (cis-DCE) and vinyl chloride (VC) are produced as intermediate compounds by this reaction. However, when a suitable microbial population is present, cis-DCE and VC are completely degraded to the non-toxic end product ethene.
Perchlorate can be biodegraded to chloride under anaerobic conditions through the sequence:
ClO
4
−
(perchlorate)→ClO
3
−
(chlorate)→ClO
2
−
(chlorite)→Cl
−
(chloride)
This process requires the addition of an organic substrate to remove dissolved oxygen, which can inhibit this process, and provide reducing equivalents to drive the reaction. (Herman et al., 1998. Journal of Environmental Quality, 27: 750-754). Studie
Borden Robert C.
Lee Michael D.
Olive & Olive P.A.
Solutions Industrial & Environmental Services, Inc.
Upton Christopher
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