Test cooling
tower bacteria in 15 minutes!
Take your lab with you on a cooling tower service visit. With a 15 minute bacterial test, conducted on site, you can:
- Prevent biofouling of heat exchangers,
- Prevent Microbially Induduced Corrosion (MIC),
- Control Legionella Pneumophila to non-dangerous levels,
Enhance your sales efficiency by increasing your service efficiency.
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A-HMB Bacteria Analyzer B-Spare Needles C-Syringe D-Test Tubes E-Coupons F- Venting Apparatus G-Reagent #1 H- Reagent #2 I-Portable Case |
How? It's easy:
You can use the portable HMB-S test kit to make the Microbiological measurements while on-site and conveniently carry other testing technology in the same easy-to-carry case.
Eminently affordable, easy to use. Read the paper below for more important information about Legionella Pneumophila.
THE BIOLOGY OF
CIRCULATING COOLING WATERS
I. Why Test for Bacteria in Cooling Water
II. Methods of
Testing
a) Growth Methods
b) Biochemical Methods
III. How to Perform the HMB Test
IV. Interpretation of Test Results in
Cooling Water Samples
I. WHY TEST FOR BACTERIA IN COOLING WATERS?
A. Biological Effects in Cooling Waters
Circulating water is used for the purpose of transporting unwanted heat. As a heat transfer agent, water is the most efficient compound on Earth. There are, however, two prominent undesirable effects associated with the use of water in aerated systems:
- Water promotes corrosion and,
- Biological things grow in contaminated water.
Corrosion effects from non-biological causes in cooling water are dealt with elsewhere.
Biological activity is the subject of this paper. The following pertains to problems caused by biological activity in cooling waters, about how to measure biological problems early, and how best to control them.
Classifying Biological Activity in Cooling
Waters
There are many ways of categorizing different life forms. For the purposes of this discussion, two classifications of microorganisms are convenient:
1. Freely circulating. This means rods, spheres etc; organisms suspended in the water that have some mobility, but do not, by their own action, attach to surfaces. These include pathogenic organisms---those that cause human disease.
2. Sessile organisms are those that naturally stick to surfaces, accreting mass and forming biofilms.
Circulating organisms
Most bacteria are in this category. They metabolize and reproduce while freely circulating as suspended particles or on the surface of other suspended particles (dirt). Because cooling waters tend to be low in nutrients, and usually contain inhibitory chemicals, freely circulating bacteria reproduce slowly in well-maintained systems.
Sessile organisms
These include the slime-forming bacteria. All forms of microorganisms compete for the nutrients that are available in a particular ecosystem. Freely circulating organisms have some limited mobility, being able to swim around and stumble upon food. Slime forming bacteria are sticky, without mobility. They stick to the surfaces and wait for the circulation to bring the food around. In heavily contaminated systems (machining fluids, e.g.;) the freely circulating organisms have an advantage and tend to dominate. In low nutrient circulating environments (cooling towers) where long times are available, the slime forming bacteria have advantages. Slime bacteria attach to a surface over which the water circulates. Whatever other tiny particles that are suspended in the circulation are carried past these sticky cells and some of this mass gets stuck on the slime. Over time, the stickiness causes more and more slime forming cells to accrete. Eventually, a layer of slime (biofilm) covers the surface. This biofilm acts as an excellent insulator so the water can't access the surface of the heat exchanger. The organic acids that are waste products of bacterial metabolism get between the biofilm and the heat exchanger surface and corrode the surface. This is Microbially Induced Corrosion (MIC). Other circulating solids stick in the slime layer (including freely circulating bacteria) and are consumed. In this way the slime-formers can dominate in low nutrient circulating systems.
By this action, bacteria and nutrient are "filtered" from the circulating waters by the successful slime, resulting in a low population density in circulation even when the system is badly fouled by the presence of biofilm.
Freely circulating bacteria have mobility to move around and stumble upon food. In low-nutrient systems where it is a long way between tidbits of food, freely circulating organisms tend to do poorly. Sessile bacteria stick to surfaces and wait for the circulation to bring the nutrient around.
The pathogen Legionella Pneumophila can prosper
in this environment. A brief discussion of this species in this context will be
useful in gaining an understanding of the biodynamics of cooling tower waters. Legionella
was first identified as the causative agent in a lethal outbreak of bacterial
pneumonia at an American Legion convention in
Legionella is a gram-negative, aerobic, motile, rod. This means that it will not absorb a gram stain, that it needs oxygen, that it can move about, and that it is shaped like a cigar. This description is included here for the purpose of completeness. Such "unfamiliar" terms will be avoided in this work wherever possible. Legionella is ubiquitous (See!) in soil and water. Most healthy adults have antibodies to Legionella, which means they have been exposed and their immune systems have succeeded in repelling the assault. The victims of Legionella are those who are in some way immuno-compromised (hospital patients, drug users, alcoholics, some of the elderly etc;). Normally functioning immune systems can defend against Legionella infection.
Legionella has rather complex nutritional requirements which limit the rate at which it can spread in most environments. It does have the ability to invade cooling water systems for reasons that will become clear.
When tissue sections taken from victims of Legionnaire's disease were examined, the Legionella were found to be growing inside macrophages (cells that eat other cells). Not only were the Legionella inside the phages, they were inside vesicles (a cell within a cell within a cell). In this manner, Legionella was protected from the outside world, and somewhat immune to biocide attack. When circumstances allow the Legionella to multiply sufficiently that a high concentration exists inside the host phage, the host phage is lysed (burst open), releasing the Legionella into the extracellular environment.
In cooling water systems, this same drama is played out with the slime forming cells that make up the biofilm taking on the role of the phages. Legionella "hides" inside vesicles inside the slime forming cells. This makes Legionella in cooling waters remarkably resistant to biocides such as Kathon and Chlorine. So, the biofilm is implicated in the production and preservation of Legionella in two ways: it nurtures Legionella by providing a nutrient rich environment, and it shields Legionella from traditional biocides. Without a biofilm, Legionella is severely limited in cooling waters; control the biofilm and the Legionella will be restricted to negligible levels.
Legionella is spread to humans by aerosol misting. When the biofilm on cooling water heat exchanger surfaces is allowed to prosper, it catches Legionella cells, which migrate to the interior of the slime cell and reproduce. When enough reproduction has occurred, a fairly large population of Legionella can be released into circulation where it is misted into the environment for unlucky humans to inhale. This is a particularly insidious occurrence when the intake vents for the building being serviced happen to be in the vicinity of the water surface, and the prevailing air currents push the vapors into the buildings being serviced.
Hospitals are especially vulnerable, in that they have many infectious agents (Chlamydia, Staph, e.g.;) present and a population of humans whose immune systems are weakened. Hospital devices used in inhalation therapy have become contaminated with Legionella, serving as sources of serious outbreaks.
To summarize, slime-forming bacteria represent the main source of problems in cooling towers. They have a tendency to prosper in low nutrient recirculating cooling water systems. Prevent the slime formers and the three prominent biological problems in cooling waters (heat exchanger fouling, MIC, and Legionella fears) are controlled. Population levels of Legionella sufficient to endanger humans seem to be coincident with successful formations of biofilm comprised of slime forming bacteria. Controlling biofilm formation suppresses the level of Legionella to below danger thresholds.
B. Controlling the Biology in Cooling
Waters
Controlling the biology in circulating cooling waters is usually done by adding biocides. The popular biocides used are typically broad spectrum, meaning that they can kill a wide range of cell types. From the earlier discussion, it is seen that biofilm formation is the culprit in the problem aspects of cooling waters: Biofilm is the mechanical agent that fouls heat exchange surfaces, making them inefficient; it induces corrosion; and, it can act as host to promote the growth of Legionella. In well-managed systems where biofilm formation is preventively controlled, Legionella will likewise be unable to grow to high concentrations. When systems are not managed, allowing biofilm to grow to gross proportions, it is likely that a wide spectrum of contaminating organisms will have success.
In addition to expense considerations, care should be taken that the proper dosage of biocides is administered. If too much is added there is danger to humans. If too little is added, cell mutation problems may occur
II. Testing
The best way to make efficient use of biocides is to monitor the systems with biological tests and administer the biocides as dictated by the test results. There are essentially two testing methodologies that may be used: Growth Methods and Biochemical Methods. Growth methods require placing a bit of the sample onto a nutrient mixture and incubating for 1-3 days. Viable cells from the sample may grow into colonies that are visible and these are counted as colony forming units per milliliter of sample (Cfu/ml). Growth methods provide an estimate of the count of cells that were in the original sample without saying what they were doing there.
Biochemical methods measure the presence of some marker molecule that results from biological activity. For example, the HMB test measures the enzyme Catalase which is produced by aerobic cells when they metabolize. Another biochemical method measures the level of the energy producing molecule ATP. As such, these methods are not counts, but measures of activity. Under certain conditions activity measurements and counts may be correlatable, but, in general, they won't be. Typically, results are available from biochemical methods in just a few minutes.
Because of the availability of immediate results, testing is usually done less frequently when biochemical methods are used. This saves money. Growth methods provide a count in 1-3 days, saying nothing about what the organisms are doing in the system; biochemical methods provide results in minutes, giving repeatable, digital information about how much the organisms are doing, but do not register organisms unless they are metabolically active.
Both methodologies are useful. But, none of this matters unless the sample tested can give information that can be used to treat the system in a meaningful way. As the earlier discussion shows, this information is not in the circulating waters. It is on the heat exchanger surfaces. Since quantifying this growth is a difficult if not insoluble problem, the solution is to use a surrogate. The test must produce information after the organisms have grown to detectable levels, but before any damage can be done to the system. The successful test procedure and associated products (pat. pending 11/99) are simple and elegant. They are described below. The goal of providing reliable testing information that allows the operator to treat in such a way as to prevent the fouling of the surfaces by biofilm, is achieved by this system.
III. How to Perform the HMB Test
Coupon Test for Slime Formation
This is the most important test for cooling towers. The coupons are installed on one service visit and read on a subsequent service visit. The test is simple: just drop the coupon into one of the test tubes, add a few drops of 50R reagent and 15 minutes later, read the result. After the reading, the coupon is cleaned and reinstalled. This test requires the appropriate coupons and the XMC test kit. See the operating procedure below for interpretations. Products required: HMB device, test kit, coupons.
IV. Interpreting Test Results in Cooling Water Samples
See the procedures for the test being performed.
HMB
TEST PROCEDURE---BIOFILM IN COOLING WATERS
Notes: This test uses specially made coupons
of a non-metallic material that have been installed in sidestream circulation
for an appropriate amount of time. Use test materials from the BioTech 50XMC
test kit.
- Remove
the coupon from the rack and without touching the surface of the coupon,
place it into one of the predispensed test tubes from the 50XBC test kit.
This tube contains a measured amount of diluent and reactants without
which test results will not be valid.
- Add
10 drops of HMB 50R reagent, dispensing it with the tube held at an angle
so the reagent runs down the side.
CAUTION: HMB 50R IS A STRONG OXIDANT. AVOID CONTACT WITH
EYES AND SKIN. WEAR PROTECTIVE EYEWEAR AND CLOTHING. IN CASE OF CONTACT WITH
EYES, IMMEDIATELY FLUSH WITH COPIOUS AMOUNTS OF WATER FOR AT LEAST FIFTEEN (15)
MINUTES. CALL A PHYSICIAN. CONTACT WITH SKIN WILL CAUSE A SLIGHT BURNING AND
BLEACHING OF THE SKIN. THIS WILL DISAPPEAR IN A FEW MINUTES.
- Without
agitating the tube unduly, insert the stopper securely into the test tube.
- Using
the needle apparatus provided in the kit, pierce the stopper for 1-2
seconds so that the head space within the tube is normalized to local
conditions.
- Holding
an index finger on the stopper, shake the tube a couple of times to mix
the contents. Place the tube in upright position for 15 minutes.
CAUTION: VERY HEAVILY CONTAMINATED SAMPLES MAY CAUSE
PRESSURES TO INCREASE IN THE HEAD SPACE SUFFICIENTLY TO BLOW THE STOPPER OUT OF
THE TUBE. KEEP THE TUBE POINTED AWAY FROM THE OPERATOR OR OTHER PERSONNEL. IF
THE STOPPER BLOWS, THAT TEST IS TO BE REGARDED AS VERY HEAVILY CONTAMINATED,
REQUIRING ACTION.
- After
15 minutes, repeat the mixing, and tap the tube on a solid surface to
assure that no liquid is trapped in the stopper.
- Turn
on the HMB IV, making sure it sets itself to 0.00 BMR within 3-4 seconds.
- Holding
the HMB IV vertically, in the left hand, impale the test tube on the HMB
IV needle.
- The
reading will flash once, then stabilize in about one second.
- Remove
the tube from the HMB IV, remove the stopper and discard the tube and its
contents.
INTERPRETATIONS OF THE
Read
the operator’s manual for further discussion.