Liquid purification or separation – Processes – Treatment by living organism
Reexamination Certificate
2002-03-18
2004-09-28
Barry, Chester T. (Department: 1724)
Liquid purification or separation
Processes
Treatment by living organism
C210S611000, C210S616000
Reexamination Certificate
active
06797171
ABSTRACT:
BACKGROUND OF THE INVENTION
1. The Field of the Invention
The present invention relates to a process of bioremediation for contaminated earth and solid waste, herein referred to as permeable “media”. More specifically, the present invention relates to a process of applying an emulsion containing an electron donor material to contaminated media to facilitate long-term anaerobic conditions for reducing harmful contaminants in the media to less harmful or insoluble material.
2. The Relevant Technology
Many industries, including mines, fossil fuel power plants, pulp and paper mills, chemical processing plants, oil refineries and phosphate fertilizer manufacturers create byproducts or waste that may contain environmentally harmful materials. These byproducts and waste materials are typically stored in waste sites that take the form of land fills, tailings piles, dumping grounds, spent ore heaps, sludge ponds, and the like. They can contaminate their surrounding environment adversely affecting the adjacent earth, surface water, subsurface ground water, and other media with which the contaminated media comes into contact. Additionally, meteoric water can cause certain contaminants to leach out of the contaminated media. Acid rock drainage is an example of a contaminated leachate.
Metal sulfates and sulfuric acid are constituents of acid rock drainage from tailings piles and the like. When in the earth, pyrite, other minerals and selenium are not susceptible to oxygen and aerobic conditions which may transform the solid sulfides, selenium, or other compounds into more dangerous soluble sulfates, selenates, and the like. However, once mined and brought to the surface, tailings piles and waste from mining and processing facilities etc., become susceptible to oxygen by exposure to air or rain. This creates the aerobic conditions which allow sulfide, selenium and other insoluble materials to transform into soluble sulfates and selenates. These soluble materials can leach out of the media in which they reside and may pose a problem to groundwater or the surrounding environment. This is especially true given the large quantities of waste rock and tailings in many mining operations.
Bioremediation is increasingly being used to destroy contaminants such as hazardous organic compounds, cyanide, and other potentially harmful byproducts of industrial processes. Many bioremediation processes require that contaminated water be pumped from the ground and treated by passage through bioreactor tanks. The problem with these processes is that the removal step is costly, requiring extra equipment and space for treatment facilities.
In situ bioremediation has been used to overcome some of the higher costs of offsite treatment. In situ bioremediation involves enhancing the activity of an indigenous bacteria consortium in order to accelerate a decontamination process at the site being treated. The enhancement is often accomplished by optimizing the availability of needed nutrients. This allows the bacteria consortium to facilitate conditions in which contaminants are transformed chemically or biochemically and rendered harmless in place, without requiring costly pumping, or other means of removal, or further processing of effluents above ground.
Bacteria derive their energy from oxidation-reduction reactions. In the absence of oxygen, anaerobic respiration can occur if other molecular species are present to provide oxygen or accept electrons. Soluble ferric, nitrate, carbonate, and sulfate ions have been used to provide oxygen or accept electrons.
The electron donor nutrient or material often used for in situ anaerobic bioremediation may be a form of organic carbon. Two common material forms of organic carbon are known in the art: (1) solid or semi-solid biomass and (2) soluble aqueous solutions which may include carbohydrates, organic acids, and/or organic salts. Both of these, however, suffer drawbacks. Solid biomass is difficult to introduce and disseminate within the media being treated. Aqueous solutions containing soluble materials are easily introduced by gravity infiltration or injection wells, but are leached out leaving no permanent protection against the reintroduction of oxygen into the media.
With respect to solid sources of carbon, U.S. Pat. No. 4,990,031 (Blowes et al.) teaches the treatment of mine tailings with a layer of biomass placed in the tailings impoundment below the elevation of the final saturated water level in it. Biomass (e.g. wood chips) can also be introduced with the tailings slurry stream entering the impoundment. U.S. Pat. Nos. 5,362,394 and 5,514,279 also by Blowes et al. teach the use of a reactive wall of porous material containing disseminated biomass to intercept and treat groundwater from a tailings impoundment. U.S. Pat. Nos. 4,519,912 and 4,522,723 (Kauffman et al.) treat wastewater, including mine wastewater, flowing through a treatment zone (reactive wall) consisting of a porous matrix containing nutrient and sulfate reducing bacteria.
However, direct injection of the bioremediation materials as slurries will result in the suspended solids occluding interstices of the media preventing, or at least making difficult, further flow. This is impractical, and commercial application would be costly and difficult. Furthermore, solid organic materials, such as those used in prior art applications, tend to seal the media interstices. Because of pore plugging, they cannot be used for surface infiltration into contaminated media. With the possible exception of colloids, solids are also unsuitable for treating groundwater plumes.
Solid sources of carbon, sewage, wood chips, and biomass have been used to treat sulfate waste water. U.S. Pat. No. 5,738,789 (Shugina) teaches metal immobilization in groundwater plumes using an injection of sulfate reducing bacteria cultures derived from natural materials such as organic containing clay, sawdust, and vegetable remnants, which are solid or semi-solid materials. However, solids are not suitable for in situ treatment of media such as ground, soil, tailings in piles, mine waste, etc. because it is difficult, if not impossible to disseminate solids into the media.
Some attempts to overcome the solid bioremediation source material problem include providing water soluble sources of carbon in aqueous solutions. For example, U.S. Pat. No. 5,833,855 (Saunders) teaches bioremediation of groundwater using sulfate reducing bacteria and a soluble source of carbon nutrient, preferably sodium lactate. U.S. Pat. Nos. 5,554,920 and 6,143,177 (Suthersan) precipitate heavy metals with sulfate reducing bacteria, using wells to inject carbohydrate solutions (and sulfate if needed) into a saturated zone of the media. Metal immobilization by sulfate reducing bacteria using a liquid base containing an appropriate nutrient supplement is taught by U.S. Pat. No. 5,632,715 (Harrington et al.). This patent mentions water soluble carbohydrates including molasses, hydrolyzed potato starch, and milk whey. U.S. Pat. No. 5,710,361 (Harrington et al.) extends the claims from industrial wastes to earth materials.
Although carbohydrate nutrient solutions work well for metal immobilization and destruction of already dissolved contaminants, these nutrients are readily leached out of the media by continued flow of recycled solutions, groundwater and infiltrating meteoric surface water. Accordingly, soluble bioremediation material is not available to provide an effective long term solution. Moreover, soluble carbohydrates are relatively expensive.
Thus, it would be an advancement in the art to provide a more permanent environmental protection process using a bioremediation material that can easily enter the permeable contaminated media without clogging the media. It would be a further advancement to provide such a process that would provide long term retention and bioremediating conditions in the media. It would be yet another advancement to provide such a process using low cost bioremediation material. Such a bioremediation process is described and claimed herein.
BRIEF
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