Liquid purification or separation – Processes – Treatment by living organism
Reexamination Certificate
2000-03-29
2001-10-30
Upton, Christopher (Department: 1724)
Liquid purification or separation
Processes
Treatment by living organism
C210S609000, C210S631000
Reexamination Certificate
active
06309547
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to anaerobic treatment processes for converting waste materials containing biodegradable organic components to soluble and gaseous components that include the step of recycling or otherwise retaining anaerobic bacteria to an anaerobic reactor. More specifically, the invention relates to methods of removing non-biodegradable organic compounds from the treatment process in order to increase the efficiency of the anaerobic treatment process.
BACKGROUND OF THE INVENTION
It is known that the separation and recycle or otherwise retaining solids containing anaerobic bacteria will provide significant benefits during the anaerobic conversion of sewage or waste water streams to soluble and gaseous products. See U.S. Pat. No. 5,015,384 to the inventor of the subject application. Also, see U.S. Pat. No. 5,514,277 to Boris M. Khudenko. The separation and recycle process preserves the bacteria responsible for conversion of biodegradable organic material to gaseous and soluble products and maintains slowly metabolized solids for prolonged periods of time within an anaerobic reactor where the slowly metabolized solids can be effectively digested.
The recycle processes described in the two patents noted above are limited by the accumulation of solids within the anaerobic reactor. The accumulation can be countered by wasting such solids from the anaerobic reactor. Unfortunately, the wasting of solids from the anaerobic reactor not only removes inorganic materials and refractory organic materials (organic materials not digested in a timely manner), but also removes the desirable biomass and also biodegradable organic material that has yet to be fully digested. By wasting solids from the anaerobic reactor, the solids retention time is reduced which limits the maximum potential of the recycle system since conversion of the biodegradable organic material to soluble and gaseous products is directly related to the solids retention time.
The build-up of solids within the anaerobic treatment process also adversely affects the completeness of mixing and heat transfer that can occur in the anaerobic reactors because of the higher solids concentration. As mixing and heat transfer efficiency decreases, the effectiveness of the anaerobic digestion of the biodegradable organic materials is reduced. Additionally, as the solids concentration increases, it becomes more difficult and costly to separate biodegradable components from nonbiodegradable components. For example, as the solids concentration increases, more energy and chemical conditioning is required to drive water from the solids. This action can be counterproductive to bacterial viability and process performance. For example, there is a direct relationship between the energy used in centrifuge separations of yeast and bacteria cells and the centrate SCOD resulting from cell rupture. The efficiency of membrane separation is also a function of the solids content of the feed stream, or retentate, since it has considerable influence on the permeate rate and its purity.
SUMMARY OF THE INVENTION
The present invention relates to a method for improving the efficiency of an anaerobic treatment process that includes the step of recycling or otherwise retaining anaerobic bacteria to an anaerobic reactor wherein the anaerobic bacteria are contacted with an influent containing biodegradable organic material, nonbiodegradable organic material, dissolved inorganic material, and undissolved inorganic material. Examples of these types of processes are described in U.S. Pat. No. 5,015,384; 5,514,277; and 5,670,047, each of which is incorporated herein by reference. Generally, such type of anaerobic treatment processes which employ retained or recycled anaerobic bacteria involve the step of contacting anaerobic bacteria in the anaerobic reactor with the influent. In the anaerobic reactor, a portion of the biodegradable organic material is converted to gaseous products and soluble products followed by separation of a portion of the soluble products from a portion of the anaerobic bacteria. The separated anaerobic bacteria is retained or recycled at some point to the anaerobic reactor for further utilization.
The present invention relates to a method of improving the efficiency of such an anaerobic treatment process by separating the non-biodegradable organic material from the biodegradable organic material, anaerobic bacteria, undissolved inorganic material and dissolved inorganic material and subsequently removing a portion of the separated non-biodegradable organic material from the anaerobic treatment process without removing a significant quantity of the biodegradable organic material or anaerobic bacteria. Optionally, undissolved inorganic material may be removed with the nonbiodegradable organic material. By removing the non-biodegradable organic material from the anaerobic treatment process, in accordance with the present invention, the accumulation of such materials is reduced without wasting desirable anaerobic bacteria and biodegradable organic material. Through the practice of the present invention, the percent conversion of biodegradable organic material into gaseous and soluble products is increased, preferably without an increase in the volume of the anaerobic reactor.
In a preferred embodiment, the present invention relates to an anaerobic treatment process for the conversion of biodegradable organic material to soluble and gaseous products that includes the step of contacting in a first anaerobic reactor, an influent stream containing the biodegradable organic material with anaerobic bacteria recycled from a second reactor. The biodegradable organic material is maintained in contact with the anaerobic bacteria for a predetermined period to at least partially digest the biodegradable organic material. Thereafter, non-biodegradable organic material is separated from the anaerobic bacteria, biodegradable organic material, undissolved inorganic material and dissolved inorganic material and removed from the anaerobic treatment process without removing a significant amount of the anaerobic bacteria or the biodegradable organic material. Optionally, undissolved inorganic material may be removed with the nonbiodegradable organic material. After the non-biodegradable organic material is removed from the anaerobic treatment process, the anaerobic bacteria and wholly or partially undigested biodegradable organic material are separated from the soluble products and the separated anaerobic bacteria and the wholly or partially undigested biodegradable organic material is delivered to a second anaerobic reactor for further digestion of the biodegradable organic material. A portion of the anaerobic bacteria from the second anaerobic reactor is then recycled to the first anaerobic reactor.
In another preferred embodiment, the present invention relates to an anaerobic treatment process for the conversion of biodegradable organic material to soluble and gaseous products that includes the step of contacting in a first anaerobic reactor, an influent containing the biodegradable organic material with retained or recycled anaerobic bacteria. The biodegradable organic material is maintained in contact with the anaerobic bacteria for a predetermined period to at least partially digest the biodegradable organic material. Thereafter, non-biodegradable organic material is separated from the anaerobic bacteria, biodegradable organic material, undissolved inorganic material and dissolved inorganic material and removed from the anaerobic treatment process without removing a significant amount of the anaerobic bacteria or the biodegradable organic material. Optionally, undissolved inorganic material may be removed with the nonbiodegradable organic material. After the non-biodegradable organic material is removed from the anaerobic treatment process, the anaerobic bacteria and partially undigested biodegradable organic material are separated from the soluble products and the separated anaerobic bacteria and the partially undigested b
Christensen O'Connor Johnson & Kindness PLLC
Upton Christopher
Western Environmental Engineering Company
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