Chemistry: molecular biology and microbiology – Process of utilizing an enzyme or micro-organism to destroy...
Reexamination Certificate
2000-12-12
2002-06-25
Lilling, Herbert J. (Department: 1651)
Chemistry: molecular biology and microbiology
Process of utilizing an enzyme or micro-organism to destroy...
C075S712000, C075S743000, C075S744000, C423S024000, C423S027000, C423S029000, C435S168000, C435S262500, C435S264000, C435S281000, C435S282000
Reexamination Certificate
active
06410304
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the biotreatment of solid materials. In particular, the present invention relates to the ex situ biotreatment of solid materials in an aerobic process to degrade an undesired compound present in the solid material.
2. Description of the Prior Art
Biological treatment processes are finding application throughout industry. Such processes have been used in waste water treatment, hazardous waste remediation, desulfurization of coal, and biooxidation of refractory sulfide ores.
A variety of methods can be employed in the biological treatment of solid materials, including in situ treatment, landfarming, composting, heap treatment, and stirred or agitated tanks. In the ex situ biological treatment of solid materials, some sort of bioreactor is used to carry out the biotreatment. A bioreactor can be defined as a vessel or body in which biological reactions are carried out by microorganisms, or enzymes they produce, contained within the reactor itself. The main objective in the design of a bioreactor is to generate an optimal environment for the desired biological process to take place on a large and economic scale.
When a solid material is being biotreated, the desired biological reactions typically involve the degradation, either directly or indirectly, of some undesired compound present in the solid material. To accomplish this economically, the bioreactor needs to reduce the concentration of the undesired compound to an acceptable level in an acceptable quantity (in terms of flow rate) of solid material to be treated.
In general biotreatment processes are slow, and if they are aerobic, they require large amounts of oxygen for the aerobic microorganism(s) to metabolize, either directly or indirectly, the undesired compound. Oxygen transfer, therefore, is typically a major problem for the large class of aerobic biological treatment processes available. Current aerobic bioreactor designs attempt to ensure not only that the microorganisms being used have access to the material to be biooxidized or metabolized, but also that all areas of the bioreactor have an adequate oxygen and nutrient supply, as well as maintain the correct pH and temperature, for the biological process to proceed.
Stirred tank bioreactors are used in many types of aerobic biological processes, including biooxidation of refractory sulfide gold ores and bioremediation of contaminated soils. Stirred tank bioreactors provide very good contact between the bioleachant and the solid material to be treated. In addition, stirred tank processes typically have favorable oxygen conditions because the tank is sparged with air or oxygen. However, even in stirred tank bioreactors where oxygen is provided by air or oxygen sparging, the low solubility of oxygen in water (10 ppm) requires a large gas-water interface. This is generally achieved with impellers and significant expenditures of energy. The high energy costs associated with stirring and aerating the reactor make this type of bioreactor primarily applicable to bioprocesses that come to a desired end point relatively quickly, typically less than a week. For slower biological processes, a low energy cost, large scale, generally static batch process, is the best solution. However, the goal of providing the bacteria, or other microorganism, with an optimal environment is still of primary importance.
There are three primary types of static batch bioreactors used to biotreat soils contaminated with toxic organic compounds. One of these methods is landfarming. This is an above grade treatment of contaminated soil in a large open space. The soil is spread over a high-density polyurethane lined area generally covered with sand to allow for drainage. Air can be introduced by perforated pipes and by tilling the soil once or twice a week. This method has been widely implemented at sites contaminated with polynuclear aromatic (PNA's) and pentachlorophenol (PCP). One limitation of this process is that a large area is needed because the soil is spread relatively thinly to ensure adequate air flow. This method also requires tilling and may be limiting in air if the layer of soil is too thick or does not mix well.
Another technology used in the bioremediation of contaminated soil is composting. The compost is made up of contaminated soil and various amendments necessary for composting to be sustained such as wood chips, straw, or manure. These amendments increase the amount of biodegradable organics, structurally improve the compost matrix by reducing bulk weight and increasing air voids, and increase the amount of inorganic nutrients in the mixture. The composting can be carried out in a vessel with forced air flow or in open piles that are aerated by air pipes or by tilling. One disadvantage to the addition of organic amendments is that their biodegradation generates heat and requires oxygen. Composting is usually run in batch mode and a portion of the compost is used to inoculate the next compost. This process has been used effectively on many types of organic contaminates including diesel fuel, 2,4,6 trinitrotoluene (TNT), polyaromatic hydrocarbons (PAH), benzene, and xylene.
Heap bioremediation is another static bioprocess used in the bioremediation of excavated contaminated soil. In this process the soil is placed in piles 8 to 12 feet high over a lined area. To improve air flow, air can be introduced by perforated pipes. In such circumstances, the pipes are placed on approximately a 12 inch bed of the contaminated soil in regular intervals. The pipes are then typically covered with a layer of gravel to protect them from the heavy equipment. The excavated soil is then dumped in an 8 to 12 foot high pile on top of the gravel. Moisture is maintained with an irrigation system. The soil may need fertilizer or lime to adjust pH and may need sand to increase porosity. This process is low cost and thus is applicable to slow biological processes. However, this process may be too slow if the heap becomes air-limited due to compaction of the soil during or after pile construction.
Therefore, air and liquid access remain important rate limiting considerations in existing static batch bioprocesses used for soil remediation, such as heap pile bioremediation, composting and landfarming. Air flow is improved in existing processes to the extent possible by introducing air through perforated air pipes or by tilling the soil. However, any flow constriction within the bioreactor will interfere with the efficiency of the process. Also, if parts of the contaminated soil are not exposed to bacteria or other nutrients as well as oxygen, the overall bioprocess will be slowed or not proceed to completion. Similarly, in the case of heap biooxidation of coal and refractory sulfide gold ore, biooxidation of the sulfides is efficiently carried out by the bacteria only when the metal sulfides are exposed to bacteria, water, nutrients, and air. If the sulfides are buried in the ore or in the solid pieces of coal, the biooxidation will not proceed. In addition, if air or liquid flow in the heap becomes limited, the biooxidation will also become limited. Consequently, a need exists for an improved bioreactor design which will permit the biotreatment of solid materials with improved air and fluid flow throughout the bioreactor and the solid material to be treated.
The use of acidophilic, autotrophic bacteria to biooxidize sulfide minerals in refractory sulfide ores is one biotreatment that has gained particular vigor in the last ten to twenty years.
Gold is one of the rarest metals on earth. Gold ores can be categorized into two types: free milling and refractory. Free milling ores are those that can be processed by simple gravity techniques or direct cyanidation. Refractory ores, on the other hand, are not amenable to conventional cyanidation treatment. Gold bearing deposits are deemed refractory if they cannot be economically processed using conventional cyanide leaching techniques because insufficient gold is solubilized.
Geobiotics LLC
Lilling Herbert J.
Lyon & Lyon LLP
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