Liquid purification or separation – Processes – Chemical treatment
Reexamination Certificate
2000-01-19
2002-04-30
Hoey, Betsey Morrison (Department: 1724)
Liquid purification or separation
Processes
Chemical treatment
C252S175000, C422S028000
Reexamination Certificate
active
06379563
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to agents for deactivating biofilms on surfaces in a variety of aqueous systems, including but not necessarily limited to recreational and industrial water systems, including drilling systems.
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 waterbome 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.
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 eradicating 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 non-oxidizing biofilm agents for aqueous systems which are effective to deactivate biofilms at lower doses.
SUMMARY OF THE INVENTION
The invention provides an aqueous system comprising a biofilm deactivation agent consisting essentially of one or more alkylamines. In a preferred embodiment, the biofilm deactivation agent also comprises a synergistically effective combination of the alkylamine with specified monomeric quaternary ammonium salts. The biofilm deactivation agent has a “minimum biofilm deactivation concentration” of about 200 or less. The invention also relates to the method of treating an aqueous system with the biofilm deactivation agent.
DETAILED DESCRIPTION OF THE INVENTION
Very low concentrations of certain alkylamines completely deactivated biofilm bacteria during laboratory testing, both alone and synergistically in combination with certain monomeric quaternary ammonium salts.
The biofilm deactivation agents of the present invention are useful in a wide variety of aqueous systems, including but not necessarily limited to recreational and industrial systems, including aqueous base drilling systems. Industrial systems in which the present invention may be used 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.
A wide variety of alkylamines are capable of deactivating biofilm bacteria according to the present invention if they are used at a high enough concentration. Suitable alkylamines are those with a “minimum biofilm eradication concentration” (MBEC) of about 200 or less, preferably about 100 ppm or less, more preferably about 50 ppm or less, and most preferably about 30 ppm or less.
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 deactivation 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, New York, 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.
As a general rule of thumb, about 1 pound of a biofilm treatment agent will result in 10 ppm of actives in a 12,000 gallon aqueous system. Alkylamines and blends that are suitable for use in the invention have MBEC's of about 200 ppm or less, and require about 20 pounds of the alkylamine or blend to effectively treat about 12,000 gallons of water. Preferred alkylamines or blends have the following characteristics: an MBEC of about 100 ppm or less, requiring about 10 pounds/12,000 gallons of water; more preferably an MBEC of about 50 ppm or less, requiring about 5 po
Albemarle Corporation
Hoey Betsey Morrison
Pippenger Philip M.
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