1、 Item No. 24230 NACE International Publication 11206 This Technical Committee Report has been prepared by NACE International Task Group 151* on Biocide Monitoring and Control Techniques Biocide Monitoring and Control in Cooling Towers May 2006, NACE International This NACE International technical co
2、mmittee report represents a consensus of those individual members who have reviewed this document, its scope, and provisions. Its acceptance does not in any respect preclude anyone from manufacturing, marketing, purchasing, or using products, processes, or procedures not included in this report. Not
3、hing contained in this NACE International report is to be construed as granting any right, by implication or otherwise, to manufacture, sell, or use in connection with any method, apparatus, or product covered by Letters Patent, or as indemnifying or protecting anyone against liability for infringem
4、ent of Letters Patent. This report should in no way be interpreted as a restriction on the use of better procedures or materials not discussed herein. Neither is this report intended to apply in all cases relating to the subject. Unpredictable circumstances may negate the usefulness of this report i
5、n specific instances. NACE International assumes no responsibility for the interpretation or use of this report by other parties. Users of this NACE International report are responsible for reviewing appropriate health, safety, environmental, and regulatory documents and for determining their applic
6、ability in relation to this report prior to its use. This NACE International report may not necessarily address all potential health and safety problems or environmental hazards associated with the use of materials, equipment, and/or operations detailed or referred to within this report. Users of th
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9、rs of NACE International reports may receive current information on all NACE International publications by contacting the NACE International FirstService Department, 1440 South Creek Drive, Houston, Texas 77084-4906 (telephone +1 281 228-6200). Foreword Effective microbiological control is an import
10、ant aspect of a successful cooling water treatment program. It has often been said that more cooling water treatment programs fail because of poor microbiological control than for any other single reason. Consequences of poor biological control typically include biological fouling, microbially influ
11、enced corrosion (MIC), accelerated decay of cooling tower wood, and potential amplification of disease-causing microorganisms such as Legionella pneumophila. Bacteria, fungi, algae, and protozoa are the microorganism classes of concern in cooling water systems. To control the growth of these organis
12、ms, programs employing oxidizing microbicides,(1)nonoxidizing microbicides, and biodispersants are often used. This technical committee report discusses specific technologies used to control these classes of microorganisms. This report provides owners, engineers, contractors, and operators with spec
13、ific information on the types of organisms found in cooling systems, a list of common chemistries used for their control, and methods that are typically employed to monitor systems. Its intent is not to serve as a guide to set up a microbiological control program, but to assist users in understandin
14、g the components of in-place programs and discuss the treatment program typically used to avoid misapplication. While this report includes a list of common technologies used to treat biofouling, it is not meant to be exhaustive. This technical committee report was prepared by Task Group (TG) 151 on
15、Biocide Monitoring and Control _ * Chair Lynn G. Kleina, DCE Consulting, Perkasie, PA, and Vice Chair George Ganzer, Biolab Water Additives, Buckingham, PA. (1)While microbiocide and biocide are commonly used in the water treatment industry, microbicide is the technically correct term and will be us
16、ed in this report. NACE International 2 Techniques. TG 151 is administered by Specific Technology Group (STG) 11 on Water Treatment and sponsored by STG 46 on Building Systems and STG 62 on Corrosion Monitoring and MeasurementScience and Engineering Applications. It is issued by NACE International u
17、nder the auspices of STG 11. NACE technical committee reports are intended to convey technical information or state-of-the-art knowledge regarding corrosion. In many cases, they discuss specific applications of corrosion mitigation technology, whether considered successful or not. Statements used to
18、 convey this information are factual and are provided to the reader as input and guidance for consideration when applying this technology in the future. However, these statements are not intended to be recommendations for general application of this technology, and must not be construed as such. Mic
19、robes Most microbiological problems associated with cooling water systems are caused by a heterogeneous population of microscopic organisms. Each class of microorganism has unique characteristics as well as a range of properties shared across the different species. Rarely is a single type of microor
20、ganism responsible for widespread operational problems in a system. No document on microbicide monitoring and control would be complete without discussing the types of organisms these compounds and procedures are meant to control in an effort to help in the identification of problems associated with
21、 their presence. Bacteria Bacteria consist of single-celled prokaryotes ranging in size from 0.1 to 10 m. They include the smallest organisms having a cellular structure. They can be classified on the basis of their shape as a coccus (round), bacillus (rod), or spirillum (spiral, corkscrew). The cel
22、ls are generally enclosed within a rigid cell wall, surrounded by a slime layer and a plasma membrane enclosing the cytoplasm, which does not contain compartmentalized membrane-bound organelles as found in eukaryotic (animal) cells. The deoxyribonucleic acid (DNA) of the bacterium is not found in a
23、nucleus. Bacteria show a wide range of nutrient requirements and energy-related metabolism. Bacteria may be aerobic (uses oxygen for metabolism) or anaerobic (growth is typically without oxygen). They can also be planktonic (free-living, free-floating) in the bulk water or sessile (attached to surfa
24、ces). On surfaces, the bacteria produce slime and excrete polysaccharides, forming biofilm. The biofilm is composed of a consortium of microorganisms. The biofilm microbes are physiologically different and more resistant to microbicides. The build-up of slime in the biofilm has negative consequences
25、 on heat exchange and interferes with corrosion-control programs. The biofilm creates anaerobic microhabitats where acid-producing anaerobes can thrive and destroy system metal surfaces. Fungi Fungi are a group of nonphotosynthetic eukaryotic organisms. They include the single-cell types, generally
26、referred to as yeasts. They range in size from 5 to 30 m in length. Most are strictly aerobic and can be found at or above the water line in a cooling system. Yeasts, however, grow both aerobically and anaerobically. Fungi are responsible for breaking down organic material in the environment. Commer
27、cially, they are essential because they produce a wide range of materials that include cellulose and other enzymes, solvents, and organic acids. In industrial systems, these attributes are negatives as the fungi can attack structural materials, causing dry or wet rot. Algae Algae can be described as
28、 single-cell plants that grow in aqueous environments without roots, leaves, or stems. They contain chlorophyll a and other pigments. The chlorophyll a is used for the process of photosynthesis, which allows the algae to produce their own carbon source (food) from carbon dioxide, water, and sunlight
29、. Phosphate is one of the most essential nutrients that the algal cell needs for growth. This is normally a limiting factor to their growth in the environment. Algae range in size from microscopic forms (the same size as bacteria), to very large “seaweed-like” plants that can be meters in length. Mo
30、st types of algae found in cooling systems are microscopic in nature. Algae can grow as single cells, strings of cells similar to beads, or slimy clumps. There are several general groups classified as algae, including green, golden brown, and blue-green algae (cyanobacteria), although cyanobacteria
31、are actually bacteria. They grow at pH values from 5 to 9 over a wide temperature range. In most open recirculating cooling systems, algae are commonly present in areas exposed to sunlight. Water is typically needed because the algal cells take in dissolved nutrients through their cell walls. Algae
32、enter cooling systems through make-up water, rainfall, or windblown contamination. They are often found attached to the surface inside or outside the system where water comes in contact with the surface by splashing or leaking. These areas are also exposed to sunlight. When extra phosphate enters th
33、e water system, the algae sometimes undergo rapid growth or “bloom.” They can cover distribution decks and cause plugging or fouling deposits. Protozoa Protozoa are a class of single-celled eukaryotic microscopic animals. The protozoan cells sometimes have specialized NACE International 3 parts such
34、 as cilia or flagella that are used for motion or grazing. Often they are found in algal biofilms that eat bacteria. Some form cysts, which are impervious to harsh conditions of drying and high-microbicide concentrations. When conditions are more favorable, they return to the vegetative state and co
35、ntinue to grow and reproduce. This is of some concern, as protozoa serve as the host for the pathogen Legionella. The Legionella grow and multiply within the host cell and are incorporated into the cyst, making it difficult to kill them. Special Microbes Certain microbes are normally given special a
36、ttention as they pertain to cooling systems. One such group is the sulfate-reducing bacteria (SRBs), such as Desulfovibrio desulfuricans. SRBs reduce sulfate to sulfide in the presence of iron, thereby corroding the metallurgy of the cooling system. SRBs are anaerobic and can live at the metal-slime
37、 interface of a biofilm, where they are protected from microbicide attack while continuing to damage the system. Pathogens are microbes that sometimes cause disease in humans. One pathogen of interest with respect to cooling systems is the bacterium Legionella pneumophila, which causes the disease l
38、egionellosis. This organism and cases of the disease have been associated with aquatic habitats, domestic water systems, and cooling systems. Because of the life cycle of the organism and its association with protozoa, much interest and energy has been expended in preventing cooling systems from bei
39、ng the source of outbreaks. The probability of other pathogens existing in cooling systems is high, especially when poor or no microbiological control program is used. At this time, only Legionella microbes are of particular concern. Oxidizing Microbicides A wide variety of oxidizing microbicides ar
40、e used for microbiological control in cooling water systems. These microbicides can be grouped into five different oxidizing chemistrieschlorine, bromine, chlorine dioxide (ClO2), ozone, and peroxides. The monitoring and control of oxidizing microbicides depends to a large extent on the particular m
41、icrobicide chemistry. The following sections are grouped by chemistry and provide details on typical oxidizing microbicide monitoring and control. Table A1, located in Appendix A, provides a summary and overview on oxidizing microbicide monitoring and control. Chlorine and Bromine General Some commo
42、nly used microbicides in cooling water are oxidizing chlorine and bromine. Chlorine was one of the first products used to disinfect water. Bromine use for water disinfection is relatively new, but has gained wide acceptance because of changes in cooling water chemistry over the last 20 years. Bromin
43、e products are available in liquid or solid forms, and chlorine products are available as gas, liquid, or solid. Both oxidizing bromine and chlorine are effective in most situations and easy to measure. Common bromine- and chlorine-containing products are listed in Table 1. Table 1: Bromine- and Chl
44、orine-Containing Products Chlorine Products Bromine Products Chlorine (Gas) Activated Sodium Bromide (Liquid) Sodium Hypochlorite (Liquid) Brominated/Chlorinated Hydantoins (Solid/gel) Trichloroisocyanuric Acid (Solid) Mixed NaBr/Chlorinated Cyanuric Acid (Solid) Dichloroisocyanuric Acid (Solid) Sta
45、bilized Sodium Hypobromite (Liquid) Calcium Hypochlorite (Solid) Stabilized Bromine Chloride (Liquid) Lithium Hypochlorite (Solid) Chlorinated Hydantoins (Solid) Mode of Action The mode of biocidal activity of oxidizing chlorine and bromine is not completely understood. One of the reasons for this m
46、ay be because disinfection by oxidation is not specific, so there is no particular enzyme or metabolic pathway to focus on for investigation. It is believed that various enzymes and other proteinsincluding those in the cell membraneare oxidized, causing cell death. The nonspecific activity of oxidiz
47、ing chlorine and bromine is well known. They are broad-spectrum microbicides, i.e., effective against bacteria, algae, and fungi under the appropriate concentrations and conditions. There are also no known reports of organisms developing resistance to oxidizing halogen microbicides. Again, this is p
48、robably due to the nonspecific nature of the oxidation disinfection reactions. NACE International 4 The efficacy level of oxidizing chlorine and bromine is affected by several factors. These include: Nature of disinfectant (chlorine vs. bromine, hypochlorous acid HOCl, hypobromous acid HOBr, sodium
49、hypobromite NaOBr, sodium hypochlorite NaOCl, chloramines, bromamines, etc.) Concentration of disinfectant Contact time Temperature Concentration and type of organisms pH The above factors vary widely from water system to water system, so system-specific decisions are made based on which oxidizing chlorine or bromine material is the appropriate microbicide, and at what dosage level the product is fed to maintain effective biological control. Chemistry Upon dissolving in water, oxidizing chlorine and bromine dissociate to HOCl, NaOCl,
