Cooling Tower Ionizer Articles

Water Treatment Problems in Cooling Towers

"Minimizing development of algae and bacterial slimes is important because they reduce heat transfer, decrease cooling water flow, localize corrosion, and serve as a mortar for permitting rapid buildup of deposits consisting of an agglomerate of sediments, corrosion products and scale," said Sidney Sussman, Ph.D., Technical Director for Olin Water Services at an annual meeting of the Cooling Tower Institute in Houston.

"The aim in cooling tower treatment is microbiological control to avoid significant slime deposits or algae growth," but "control is becoming increasingly difficult as a result of pollution abatement regulations and water conservation measures," he said."Yet a biologically fouled tower causes heat transfer losses, metal degradation and blockage of flow" while increasing the incident of costly equipment shutdowns and time spent on maintenance and prematurely deteriorating expensive capital equipment."

"At the same time, pollution control regulations limit toxicity to aquatic life of any blowdown discharged to a river, lake or the sea. This requires examination of the paradoxical requirements for microbiocides; they must be toxic to undesirable organisms in the cooling water, but, at the same time, nontoxic to organisms - large and small - that live in water to which the blowdown is discharged," Sussman continued.

Use of Chlorine to Control Problem Creates Another Set of Problems
"Chlorine and other chlorine-yielding compounds are both broadly effective and widely used. Their future use is likely to be restricted by governmental limitations because very low concentrations of chlorine have been shown to be toxic to some forms of aquatic life in waters receiving cooling tower blowdown and because of recent concerns about formation of traces of chlorinated organics that may make water less desirable for potable use," Dr. Sussman saidIn fact, according to an article in Business Week (5/7/84) scientists discovered that "chlorine can react chemically with organic materials in water to form a class of carcinogenic substances called trihalomethanes (THM's). The problem is especially serious for areas that obtain their water from rivers or reservoirs rather than wells."

"Such surface water contains high amounts of organic material from pollutants and animals which react with chlorine to produce such chemicals as chloroform, a known carcinogen." This resulted in a significant crackdown by the U.S. Environmental Protection Agency which, among other things, limited THM's in potable water supplies to 100 ppb.

Unlike ionization technology, the efficiency of chlorine is highly dependent upon pH control. In addition, chlorine is corrosive, and controlling some algae with it is difficult because of limitations established by the regulatory agencies.

Ionization Technology Is An Excellent Chlorine Alternative In Cooling Towers
Reporting the results of his research on Ionization, Dr. Charles P. Gerba, Department of Microbiology & Immunology at the University of Arizona2 stated: "As an alternative to chlorine compounds, electrolytically generated copper and silver ions have been introduced recently as a relatively safe and odorless method for water disinfection." "Both copper and silver are bactericidal and virucidal, and copper has been shown to be algicidal and possess fungicidal properties."

Gerba also found that ionization technology can be used in conjunction with chlorine to produce a sanitizer superior to either of the two operating independently. He noted the additional advantage that the level of free chlorine need be only about 15 or 20 percent of the concentration required without ionization. This also represents a significant economic advantage.

"Copper/silver ions in combination with free chlorine reduced bacterial numbers more rapidly than chlorine or copper/silver ions alone . The addition of copper/silver ions allowed concentrations of free chlorine to be reduced to 0.20 mg/L while still being able to meet guidelines for ... disinfectants."

Gerba's research team uncovered another significant finding, not previously understood using ionization technology: "While Streptococcus faecalis is reported to be more resistant than E. coli ... experiments showed it to be more sensitive after the first 20 seconds."

Destroying Legionella Pneumphila: Ionization Technology More Effective
"In further research published in Applied and Environmental Mcrobiology4 Charles Gerba concluded that metal ion generators, "combined with very low levels of chlorine produces a synergistic effect which enables the dual disinfectants to kill the Legionella bacteria much more rapidly and is up to 1000 times more effective than chlorine alone."The additional benefit ... is that there is always a disinfectant residual in circulation that is unaffected by sunlight and temperature and, in fact, the bactericidal effect is enhanced by sunlight and high temperatures."

"Legionella pneumophila is resilient to high levels of chlorine and is a most difficult bacteria to eliminate, especially within systems that are exposed to sunlight and temperature such as cooling towers and hot water lines where levels of chemical biocides are difficult to maintain, and in most cases, non-existent due to dissipation," he said.

"This breakthrough in water purification means that the combination now produces a far more effective constant disinfectant against Legionella pneumophila and other chlorine resistant strains of bacteria. These systems are automatic and are easily monitored once they are installed."

Finally, according to a NASA Tech Brief 3, laboratory tests of NASA's original sterilizer have "demonstrated essentially complete kill within eight hours of Staphylococcus aureus and Escherichia coli (E. coli) bacteria present in initial concentrations of approximately 5 x 10 5 organisms per milliliter.

These findings coupled with the knowledge that ionization is effective over a wide range of pHs and the fact that it does not create the kind of difficult wastewater treatment problems found with chlorine, encouraged Carefree Clearwater to conduct testing on water cooling towers.

Carefree Clearwater's test objective was to evaluate our metal ion generator's ability to control the severe algae problems encountered in cooling water recirculatingsystems. However, our primary concerns were the effect of copper ions, in solution, on dissimillar metals in the recirculating system - mild steel, black iron, etc. - and the ability of copper ions to inhibit algae growths and blooms at low ion levels.

The first test assembly was constructed in September 1986, recirculating water at 3 to 5 gpm. While the exact formula and application conditions are proprietary, a solution of polyacylate, phosphonic acid and molybdate was added at use levels in cooling towers. CDA11O and C1O1O coupon strips were placed in the recirculating water for an exposure period of 60 days.

Prior to developing an appropriate formula consistent with metal ionizer operation in cooling towers, the mild steel coupons produced corrosion rates of 7.2 mils per year -far in excess of industry standards. These tests yielded significantly reduced rates of 3.1 mils/year in later testing. The CDA11O rates averaged only 1.5 mils/year.

The system reservoir was placed to receive maximum sunlight to encourage organic growth. No other algicide or biocide were added during any of the tests. Total copper ion levels were maintained below 0.5 ppm. Corrosion rates were favorable in that the CDA11O was calculated at less than 3 mils/year and the C1010 was less than 3 mils/year. No algae growth was observed at any time during this period.

These results were encouraging and the decision was made to field test an ion generator on a 400 ton condenser water system which had been experiencing an especially difficult algae problem. (This particular cooling tower has a sand filter,sidestreaming approximately 10 to 12 percent of the system volume.) Total copper ions were maintained below 0.5 ppm.

After ninety days exposure, coupons were evaluated and corrosion rates were in the aforementioned acceptable range. Algae was non-existent with no other biocides being employed. just as with our model cooling tower which had utilized ionization successfully in the laboratory, field testing proved that this technology satisfied both the algae and corrosion control objectives.

Summary and Conclusions
Electrolytically generated metal ions are effective in preventing algae growths and in maintaining a cleaner system. The ionization process seems to impart favorable charges to ions in solution and this apparently aids in filtration where filtration is employed.

Carefree Clearwater completed testing in early 1989 sufficient for product distribution and concluded that our ionization systems, along with proper controls, were suitable for use in this application. During the entire test period, the water remained clear and had an attractive, sparkling appearance. Systems remained exceptionally clear of algae and slime throughout the one year field testing.

Using traditional biocides, we would generally have expected to see a resistance built up to the biocide over a period of time and eventual development of algae. Since this was not the case, we rate this method of water treatment excellent for cooling tower applications provided that corrosion rates are properly monitored.

The economic value in utilizing this technology is its ability to reduce system downtime due to algae and slime formation, the reduction or elimination of other biocides, increased success in dealing with troublesome microbiological contaminants such as Legionella bacillus, and reduction in maintenance time.

The singlemost essential feature of any system utilizing this technology in water cooling towers is the ability of the ion generator to sense an overfeed due to equipment failure and subsequently shut down the ionizer. Carefree Clearwater has built this feature into all equipment for installation on water cooling towers.

Notes

(1) ASHRAE Journal, page 34: American Society of Heating, Refrigerating and Air Conditioning Engineers, from an article by Joseph T. Echols, Ph.D., professor of chemistry and the head of the chemistry department at Pfeiffer College. Sherman T. Mayne, Ph.D., is vice president of Radiation Disposal Systems, Inc.)

(2) From a research program evaluating the efficacy of copper and silver ions directed by Charles P. Gerba, Ph.D., Department of Microbiology & Immunology at the University of Arizona, published in the Journal of Environmental Health; Vol. 51, No. 5, May/June 1989, pgs. 282-285. Other members of the research team included Moyasar T. Yahya, Susan M. Kutz and Lee K. Landeen - all from Dr. Gerba's department.

(3) NASA Tech Brief 68-10555 by C.F. Albright of the Garrett Corporation under contract to the Manned Spacecraft Center; MSC-11827.

(4) From a research program: "Efficacy of Copper and Silver Ions and Reduced Levels of Free Chlorine in Inactivation of Legionella pneumophila" Charles P. Gerba, Ph.D., Department of Microbiology & Immunology at the University of Arizona, published in Applied and Environmental Ntcrobiologyi_ Vol. 55, No. 12, Dec. 1989, pgs. 3045-3050. (Copyright 1989 by the American Society for Microbiology.) Charles P. Gerba, Ph.D., and Lee K. Landeen, Department of Microbiology & Immunology at the University of Arizona. Moyasar T. Yahya, Dept. of Nutrition & Food Science, University of Arizona.