Liquid purification or separation – Processes – Chemical treatment
Reexamination Certificate
2000-03-13
2002-07-16
Hoey, Betsey Morrison (Department: 1724)
Liquid purification or separation
Processes
Chemical treatment
C210S764000, C252S175000, C422S028000
Reexamination Certificate
active
06419838
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to synergistic combinations of oxidizing and non-oxidizing agents for static control and deactivation of biofilms on surfaces in a variety of aqueous systems, including but not necessarily limited to recreational and industrial water systems. The synergistic combination also may be used to prevent the corrosion of metal equipment when used in aqueous drilling systems. More particularly, the invention relates to synergistic combinations of alkylamines and oxidizing agents for such purposes.
BACKGROUND OF THE INVENTION
Biological fouling is a serious economic problem in both industrial and recreational water systems. Biological fouling is the buildup of a “biofilm” on the surfaces that come into contact with the water in the system. A “biofilm” is the buildup of layers of microorganisms and/or extracellular substances and the dirt and/or debris that becomes trapped in that buildup. Bacteria, fungi, yeasts, diatoms and protozoa are only some of the organisms that cause the buildup of a biofilm.
In recreational waters, biofilms tend to be “slimey” to the touch, and can create a health hazard. In industrial waters, biofouling can interfere with industrial processes, lowering the efficiency of the process, wasting energy, and reducing product quality. In drilling systems, biofouling contributes to the corrosion of expensive drilling equipment.
Biofilm problems are encountered frequently in cooling water systems used in power-generating plants, refineries, chemical plants, and air conditioning systems. Cooling water systems commonly are contaminated with airborne organisms entrained by air/water contact in cooling towers as well as waterborne organisms from the system's makeup water supply. The water in such systems generally is an excellent growth medium for these organisms. If not controlled, the biofilm that results from such growth can plug towers, block pipelines, and coat heat transfer surfaces with layers of slime, thereby preventing proper operation and reducing the efficiency of the affected equipment.
Biofilms traditionally are controlled using oxidizing agents, which typically are based on chlorine or bromine. Oxidizing systems are effective to control biofilms, but such systems also can corrode valuable metal equipment and may irritate delicate and/or sensitive skin. A system that would require treatment with a minimal amount of an oxidizing agent would be desirable.
Non-oxidizing agents are available to control biofilms, and should avoid the foregoing problems; however, oxidizing biocides tend to be much more effective than non-oxidizing biocides at deactivating a biofilm. Biofilms also tend to require exposure to much higher doses of non-oxidizing agents for much longer periods of time than the dosage and time required to kill microorganisms in a suspension. As a result, non-oxidizing agents tend to be much more expensive to use as biofilm deactivation agents than oxidizing agents.
The current trend is towards using continuous levels of oxidizing biocides to maintain clean water system surfaces and to decrease the risk of contamination by
Legionella pneumophila
, the bacteria responsible for Legionnaire's disease. A continuous need exists for means to minimize the quantity of an agent required to deactivate a biofilm, whether the agent is an oxidizing agent or a non-oxidizing agent.
SUMMARY OF THE INVENTION
The invention provides an aqueous system comprising a synergistic minimum biofilm eradication concentration (“MBEC”) of a synergistic combination comprising an amount of an oxidizing agent and a quantity of an alkylamine. The oxidizing agent has an “oxidizing MBEC” in the absence of the alkylamine and the alkylamine has an “alkylamine MBEC” in the absence of the oxidizing agent. The synergistic MBEC comprises a reduction in at least one of an MBEC selected from the group consisting of said oxidizing MBEC and said alkylamine MBEC.
DETAILED DESCRIPTION OF THE INVENTION
The invention provides a synergistic combination useful as a biocide and/or as a corrosion inhibitor in a wide variety of aqueous systems. The term “aqueous system” includes, but is not necessarily limited to recreational systems, industrial systems, and aqueous base drilling systems. Suitable industrial systems include, but are not necessarily limited to cooling water systems used in power-generating plants, refineries, chemical plants, air conditioning systems, process systems used to manufacture pulp, paper, paperboard, and textiles, particularly water laid nonwoven fabrics.
The synergistic combination comprises an alkylamine having an “alkylamine MBEC” and an oxidizing agent having an “oxidizing MBEC.” The synergistic combination reduces the quantity of at least one of these values to achieve a “synergistic MBEC.”
The “MBEC”
The MBEC is a valuable measurement for determining whether the quantity of given agent that will be required to eradicate a biofilm will be economically and environmentally feasible. The MBEC test was developed by the University of Calgary to evaluate the efficacy of antibiotics and biocides towards biofilms. H. Ceri, et. al., “The MBEC Test: A New In Vitro Assay Allowing Rapid Screening for Antibiotic Sensitivity of Biofilm”,
Proceedings of the ASM
, 98, p 525 (1998). Ceri, et. al., “Antifungal and Biocide Susceptibility testing of Candida Biofilms using the MBEC Device,” Proceedings of the Interscience Conference on Antimicrobial Agents and Chemotherapy, vol. 38, p. 495 (1998); H. Ceri, et. al., “The Calgary Biofilm Device: A New Technology for the Rapid Determination of Antibiotic Susceptibility of Bacterial Biofilms,”
Journal of Clinical Microbiology
37 (1999) 1771-1776. The exclusive license for the MBEC technique is believed to be held by MBEC Biofilm Technologies, 665-8th Street S.W., Calgary, Alberta T2P 4H5 Canada.
The MBEC technique consists of growing identical 24 -hour biofilms on 96 pegs arrayed in 12 rows and 8 columns. The biofilms then are challenged with decreasing concentrations of selected antibiotics and/or biocides. After a certain challenge time (generally one hour), the biofilms are placed in 96 individual wells of growth media and ultra-sonicated to deactivate any surviving organisms. After culturing overnight, the wells are checked for turbidity. Clear, transparent wells indicate complete deactivation of the biofilm. Conversely, turbidity (“growth”) indicates lack of complete deactivation of the biofilm.
The minimum biofilm eradication concentration (MBEC) is defined as the minimum concentration of an agent that completely deactivates biofilm bacteria. The MBEC technique provides a potentially powerful and reproducible tool to study the efficacy of biocides and additives towards biofilm deactivation. Unless otherwise indicated, the biofilms used in the examples below consisted of a pure culture of
Pseudomonas aeruginosa
(ATCC 15442). The reason for this is that
Pseudomonas aeruginosa
often represents the major biofilm component in industrial and recreational water systems. J. W. Costerton and H. Anwar, “
Pseudomonas aeruginosa
: The Microbe and Pathogen”, in “
Pseudomonas aeruginosa
Infections and Treatment”, A. L. Baltch and R. P. Smith (eds.), Marcel Dekker, N.Y., 1994. In addition,
Pseudomonas aeruginosa
is a gram-negative bacteria. Gram-negative bacteria tend to be more difficult to kill than gram-positive bacteria. In other words, if an agent is effective against
Pseudomonas aeruginosa
, then persons of ordinary skill in the art would find it reasonable to predict that the agent also would be effective against other microorganisms found in biofilms.
The Oxidizing Agent
A wide variety of oxidizing agents are known to control biofilm growth. Any of such oxidizing agents are suitable for use in the synergistic combination as long as they meet one of the synergistic parameters defined herein. Preferred oxidizing agents are capable of supplying a Cl
+
ion or a Br
+
ion. Examples include, but are not necessarily limited to HOBr and salts thereof, HOCl and salts thereof, and organ
Albemarle Corporation
Hoey Betsey Morrison
Pippenger Philip M.
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