Liquid purification or separation – Processes – Treatment by living organism
Reexamination Certificate
2000-06-26
2002-03-26
Upton, Christopher (Department: 1724)
Liquid purification or separation
Processes
Treatment by living organism
C210S610000, C210S613000, C210S916000
Reexamination Certificate
active
06361694
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
Wastewater biomass systems normally consist of a mixture of water, organic matter and a variety of bacterial genera whose food, to a large degree, consists of the organic matter component of the biomass and/or other organic waste materials (e.g., volatile solids). The products of anaerobic digestion of such biomass systems normally consist of: (1) a gas phase primarily comprised of carbon dioxide, methane, ammonia, small amounts of other gases (e.g., hydrogen sulfide and hydrogen) and trace amounts (e.g., less than one tenth of one percent by volume) of certain other gases (e.g., propane), which, in total, constitute what is commonly referred to as “biogas”; (2) a liquid phase (aqueous in nature) in which ammonia, nutrients and a host of organic chemicals and gases and inorganic chemicals are dissolved; and (3) a colloidal phase of suspended solids containing undigested organic and inorganic compounds, synthesized biomass and/or bacterial cells.
Progressive destruction of the organic matter in such biomass systems has been made more efficient by introducing various solubilized nutrients for the bacteria into such systems. Various gases also have been injected into these systems as gas stripping agents. In effect, these gas stripping agents dissolve those biogas molecules (e.g., methane, carbon dioxide, ammonia, hydrogen, hydrogen sulfide, etc.) that are produced as waste products of the bacterial metabolic processes carried out in such biomass systems. These waste product gases are produced within the bacteria cells, permeate their cell walls and collect, in the form of bubbles, on their outer cell wall surfaces.
Nitrogen and hydrogen, obtained from sources outside the biomass system, as well as recirculated biomass product gases (e.g., carbon dioxide, methane and hydrogen), have been used to strip waste product gas bubbles from the bacterial cell walls. Again, the waste product gas molecules on the outer surfaces of the cells are dissolved in the stripper gases. Consequently, newly produced waste product gas molecules are able to leave the outer surfaces of the bacteria cell walls more quickly—and thereby produce more efficient biomass digestive processes.
2. Description of Related Art
Many academic, patent and trade publications have recognized the above-noted biomass gas inhibition problems and have suggested various ways to solve them. For example, within the academic literature, the following articles give some particularly good insights into the nature of these problems. Finney, C. D., and R. S. Evans, Anaerobic Digestion—the Rate Limiting Process and the Nature of Inhibition, Science, 1975, Vol. 190, p. 1088; McCarty, P. L., Anaerobic Waste Treatment Fundamentals, Part I, Public Works, 1964, p. 107; and Obayashi, A. W., and J. M. Gorgan, Management of Industrial Pollutants by Anaerobic Processes in Industrial Waste Management Series, W. James (ed.), Lewis Publishers, Inc., Chelsea, Mich., 1985; and Anaerobic Digestion Processes in Industrial Wastewater Treatment, Stronach, S. M., Rudd, T., and Lester, S. N., Springer-Vertog, Berlin, 1986.
The Finney and Evans article, for example, postulates that the rate controlling step in anaerobic digestion processes of this kind may be the fact that the cells' gaseous waste products (e.g., CH
4
+CO
2
) must eventually undergo a transfer from the system's liquid phase to its gas phase. That is to say that, even though many previous investigators had considered the biological conversion of organic acids (such as acetic acid and propionic acid) into methane and carbon dioxide as being the overall rate controlling reactions, Finney and Evans postulated other rate limiting steps. These authors suggested that the rate of removal of gas bubbles away from bacterial cell walls might constitute the rate limiting step.
Finney and Evans also postulated that, by remaining attached to their cell walls, waste product gas bubbles effectively (a) decrease the cell wall's gas transfer, surface area, (b) decrease the cell wall/gas layer system's overall permeability and (c) reduce the cell's ability to absorb needed nutrients. They also considered the possibility that the presence of certain toxic compounds in the biomass may interfere with a bacterial cell walls' ability to pass dissolved nutrients into the cells.
Many patent references teach various specific processes for stripping gases, such as hydrogen sulfide, from anaerobic cells in digester systems. U.S. Pat. No. 5,651,890 (“the '890 patent”, to applicant) is a particularly relevant patent in this regard; hence, its teachings are incorporated herein by reference. The '890 patent teaches that anaerobic digestion of wastewaters can be made more effective by introducing propane gas (from an external source) into the biomass in order to strip bacterial waste product gases such as H
2
S from bacteria cell walls. This patent does not however teach or suggest (1) the beneficial effects of stripping CH
4
and CO
2
gases off of the volatile solids component of the biomass system (and thereby creating more surface area on the volatile solids to which waste product gases can adhere) nor (2) the reduction of H
2
S produced in the biogas. Moreover, the '890 patent does not teach or suggest intermittent introduction of propane gas into a biomass in order to make such processes more efficient. Indeed, the '890 patent (see col. 11, line 14) teaches away from the concept of introducing propane intermittently. It also should be noted that the '890 patent also very strongly teaches away from the concept of using propane as a bacterial nutrient (see col. 13, lines 33-53) or having propane interact in any other biological process.
U.S. Pat. No. 4,289,625 (the '625 patent) teaches use of a hybrid, bio-thermal system comprised of an anaerobic digester unit and a thermal gasifier unit. In effect, the anaerobic digester system of the '625 patent achieves greater methane production per unit of feed by “digesting” and “cracking” the anaerobic sludge material and, secondarily, by feeding the thermal gasifier's, gaseous products back to the digester unit as food sources for the microorganisms residing therein. Some of these gaseous products are characterized as “C
x
H
y
” in the '625 patent, but no particular emphasis is laid upon a propane gas component that may fall within the generalized term “C
x
H
y
”. This is not surprising because a thermal gasifier such as this would tend to produce an extremely varied source of hydrocarbons due to its “cracking” ability.
U.S. Pat. No. 5,298,163 teaches that a “neutral” gas (no disclosures are made as to the exact identity of such a “neutral” gas) can be introduced in a biodegration process in order to strip or otherwise displace hydrogen sulfide gas from a biomass system but no H
2
S reduction in the produced biogas was noted.
U.S. Pat. No. 5,015,384 teaches an anaerobic digestion process that injects “anoxic” gases to strip carbon dioxide gas from a biomass system so that its pH remains neutral or nearly so. This reference states: “The primary requirement is that the gas be anoxic, i.e., not contain oxygen or other constituents toxic to the anaerobic bacteria.”
U.S. Pat. No. 4,826,600 teaches a process for altering the pH of a anaerobic system by using methane gas to strip carbon dioxide gas from the system. This process also may employ an “inert” gas to aid in the withdrawal of gaseous products. The preferred “inert” gas is methane.
U.S. Pat. No. 5,185,079 teaches an anaerobic reactor that removes biogas from the top of a reactor and re-introduces it into the bottom of said reactor. This reference also notes the beneficial effects of applying a vacuum during its settling phase to promote removal of gas bubbles attached to bacterial cell walls.
U.S. Pat. No. 4,372,856 discloses a process wherein a sludge is sparged with methane gas in order to stimulate the growth of anaerobic bacteria and, thus, greater production of biogas. This reference als
Dorr, Carson , Sloan & Birney, P.C.
Upton Christopher
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