Ozonation of Cooling Tower Water: A Case Study by Stephen Osgood Water Conservation Unit East Bay Municipal Utility District June 1991 Completed under Contract to the California Department of Water Resources Water Conservation Office Ozonation of Cooling Tower Water: A Case Study by Stephen Osgood, Water Conservation Unit East Bay Municipal Utility District Summary In 1988, Providence Hospital in Oakland, California changed the method it uses to treat the water in two cooling towers, replacing a multiple chemical treatment program with ozone gas treatment As a result, the hospital reduced water use feeding the cooling towers by 13 percent In addition, after changing the cooling tower water treatment, the hospital: more than doubled the cycles of concentration (based on conductivity), eliminated fouling and scaling of exposed surfaces, experienced no new scaling of exposed surfaces, dramatically improved water clarity, greatly reduced bacteria levels, achieved low corrosion rates, experienced minor pitting and scaling of heat exchange tubes, discovered corrosion of condenser tube end bells, and replaced two fan motors due to corrosion On the whole, the hospital is pleased with the performance of the ozone system It values ozone's excellent microbiological control and environmental compatibility It does not believe there has been any serious destruction of equipment Consequently, the hospital has not only continued to use ozone in the cooling towers of the main building, it has also recently selected ozone to replace a multiple chemical treatment program at the cooling tower in a second building The experience at this site suggests that ozone treatment of cooling tower water should be considered at least where the following conditions are met: the cooling water's chief function is to remove heat from medium sized heating, ventilation, and air conditioning (HVAC) systems; the ozone system is well designed, monitored, and maintained: the makeup water quality is low in dissolved solids Report Contents The purpose of this report is to describe the technology employed and the results it achieved The next few sections provide background information on the use and treatment of recirculating cooling water systems Details then follow of the technology employed at the study site, the water savings, other results, and the costs and savings The report identifies factors that should be taken into account when ozone is considered for cooling tower water treatment, and ends with a brief discussion of the potential for ozone technology to be adopted throughout California Open Recirculating Cooling Systems Water gains heat when used for cooling To be reused, the water's temperature must be reduced, typically by passing it through a cooling tower In a cooling tower the warm water enters at the top and spreads down over numerous vertical panels The large surface area facilitates evaporation, which lowers the temperature of the water that remains behind When needed, a fan boosts air flow across the water, thereby increasing evaporation and heat loss The air expelled by the fan can also carry off water droplets ("drift") "Makeup" water is added to replace what is lost by evaporation and drift The cooled water collects in a basin at the bottom of the tower, from where it is recirculated to again perform its cooling function As water evaporates, dissolved solids remain behind and increase in concentration The extent to which this occurs is referred to as the cycles of concentration, also known as the concentration ratio, which is the ratio of the quantity of dissolved solids in (For the cooling tower water to that in the makeup water example, given makeup water with Total Dissolved Solids (TDS) of 58 parts per million (ppm), a cooling tower with water at 145 ppm TDS would be operating at- 2.5 cycles of concentration.) A continuing increase in dissolved solids can lead to salts of calcium, magnesium, or silica precipitating out of solution and forming scale deposits on cooling system surfaces To dilute the water and minimize scaling, the concentrated water of the cooling tower is discharged and is then replaced by an equivalent volume (The discharge is referred to as "bleed of fresh makeup water off", or "blowdown") A cooling tower operating at relatively high cycles of concentration will save water compared to a similar one operating at lower cycles This is because the tower with higher cycles has less blowdown and less makeup water use However, as shown in Figures and 2, the relationship between cycles of concentration and blowdown is not a simple linear one The most dramatic water savings are achieved when one moves from very low cycles of concentration to more moderate ones As the number of cycles increases further, more water is saved, but the incremental reduction in blowdown and makeup becomes less significant Operating a recirculating cooling system also presents other problems that need to be controlled Warm recirculating waters provide an ideal environment for microbiological growth, which can result in the formation of slimes on equipment surfaces Microbes, such as Legionnaires Disease bacteria (Legionella pneumophila), may threaten the health of people exposed to airborne water droplets Workers who clean the inside of condenser heat exchange tubes may also be exposed to At a hospital, where weakened patients are Legionella particularly susceptible to infectious organisms and health professionals are frequently exposed to pathogens, the control of microbial growth in cooling tower water is critical Corrosion is another problem to be minimized It not only destroys metal surfaces, it also produces deposits which can contribute to the fouling of surfaces Airborne particles (such as dust from construction) can enter the recirculating water and also contribute to fouling Scale, slimes, and other types of fouling, when present on heat exchanging surfaces, act as insulators, decreasing the efficiency of the heat transfer This can lead to inadequate cooling or, at the least, to an increase in the amount of energy expended to produce the same amount of cooling.2 Multiple Chemical Treatment Recirculating cooling waters are often treated by adding chemicals which are selected to control one or more of the problems of biological growth, scale, corrosion, and fouling The following types of chemicals are available: biocidal poisons (must be EPA registered), oxidizing biocides (must be EPA registered), corrosion inhibitors which form a protective film over metal areas, acids or other scale inhibitors which prevent mineral precipitation, conditioners which decrease the density of any scale particles which form, allowing the particles to be more easily carried off by the flowing water, dispersants which increase foulants' electrical charges, causing them to repel each other, and wetting agents which reduce the water's surface tension so that particles are less likely to adhere to surfaces Maintaining correct water quality involves controlling the rates of blowdown and makeup water flow and involves adding chemicals in correct amounts at proper times This, in turn, requires insuring the compatibility of the chemicals, and requires monitoring and controlling pH and conductivity Chemical treatment carries with it the risks and responsibilities of storing and handling hazardous materials In addition, it is undesirable to discharge toxic chemicals to aquatic ecosystems or to wastewater treatment plants that rely on bacterial activity Ozone Treatment Ozonation, in contrast to traditional chemical treatment, involves the on site generation of a single oxidizing agent which is mixed into the recirculating water Typically, ozone is produced by the corona discharge method, in which dry air is passed through a gap between a highly electrically charged surface and a grounded surface When electrical discharges occur across the gap, some of the oxygen in the air is converted to ozone gas Potential benefits As a highly powerful oxidant, ozone destroys microorganisms which may threaten health (including Leoionella pneumophila3), foul cooling system surfaces, encourage the buildup of other deposits, or contribute to corrosion Ozonation has also been reported to achieve higher cycles of concentration than multi-chemical treatment Since there is less blowdown at higher cycles, ozonation offers the potential to save water In addition, when slightly alkaline water (pH greater than 7) is concentrated, the alkalinity becomes even more pronounced Operating cooling towers at higher cycles of concentration thus creates a more alkaline condition, reducing corrosivity.5 Ozone also has been promoted as effective method of directly an controlling corrosion and scale Environmental and Safety Aspects Highly reactive, ozone resides only briefly in water (Its half-life in distilled water is 20 to 30 minutes, and in cooling tower water, where there are oxidizable impurities, to minutes.)7 As a result, the treated cooling water can be discharged safely to the sewer system Even if there were some residual ozone in the discharge, it would be quickly consumed by other wastes in the sewer line Thus ozone poses virtually no threat to sewage treatment plants or aquatic ecosystems Since an ozone generator will produce the gas at concentrations of just to percent by weight in air, the resulting ozone/air mixture is not explosive Ozone is a toxic gas The maximum average allowable ozone concentration to which workers in California may be exposed over an hour day is 0.1 ppm The short term exposure limit (maximum allowable average concentration over any 15 minute period) is 0.3 ppm By contrast, ozone gas1Ocan be detected by smell at concentrations as low as 0.02 ppm , well below the exposure limit It is conceivable, however, that a gradual increase in ozone concentration might not be noticed by someone working close to an ozonated tower Study Site Facility Providence Hospital ("Providence") in Oakland, California (a coastal city) receives fresh water and wastewater treatment services from East Bay Municipal Utility District (EBMUD) Equipped to provide both acute and chronic medical care, the hospital houses 228 beds and employs 720 people The main hospital building, which utilizes the cooling system discussed in this report, has a floor area of approximately 275,000 square feet Cooling system Air conditioning is commonly referred to as "comfort cooling," which suggests it is a luxury In a hospital, however, the air temperature is of vital concern, both in the operating room and in patient rooms Providence's cooling system depends on two chillers which use the water from the cooling towers (at 85°F) to produce chilled water (at 48°F) by means of a condensed refrigerant The chillers pump the chilled water to points in the hospital where it cools indoor air, or performs other functions After the chilled water absorbs heat at the point of application, it returns in a closed loop to the chillers, where the heat is transferred to an internally recirculated refrigerant The refrigerant warms and expands In the condenser section of the chiller, the refrigerant is passed over copper tubes through-which passes the water from the cooling towers The heat from the refrigerant is transferred to the water returning to the cooling towers Finally, the cooling towers release the waste heat to the environment, in the form of water vapor Table lists characteristics of the hospital's cooling system and cooling towers Table Cooling System Characteristics, Providence Hospital Chiller capacity 354 Tons (425,000 BTU/hr.) Chiller operation (ave.) 85% of capacity (300 Tons) Cooling temp change (at) 6°F 11 1800 gpm Water recirculation capacity 20 HP Recirculation pump 300 Tons (360,000 BTU/hr.) Cooling tower capacity (each) Cooling tower operation (average over year) 300 Tons (combined) - 75% of capacity primary secondary - 25% of capacity" Cooling tower type induced draft, crossflow towers, with connected basins corona discharge Ozone generation principle PCI Ozone Corp., modified by NWMC Ozone generator manufacturer Ozone generator capacity lb./day Ozone generator operation 65% of capacity Water flow, 03, injection loop 60 gpm Cooling towers The cooling towers are about 15 years old, each with a capacity to remove 360,000 BTU's of heat per hour (300 tons) Their basins are interconnected, and fans at the top of the towers induce an upward flow of air when they are engaged Although water flows continuously through both towers, during most of the year only one fan is needed to boost air flow, and it engages intermittently Only on the hottest days of the year does the extra heat load cause the fan on the secondary tower to engage With the primary tower operating at approximately 75% of capacity and the secondary tower operating in the vicinity of 25% of capacity together they bear an average heat load of 300 tons Effective biological control of cooling tower water is important at the hospital Windows in one of the hospital buildings which overlook the towers are often kept open for ventilation These rooms, which are used for office space, may at times be exposed to cooling tower drift Additionally, the engineering section must report quarterly on the biological condition of the cooling tower to the hospital's quality assurance team, which is charged with ensuring compliance with hospital accreditation requirements Windows in both the main hospital building and the valve," or to purge chemicals that were improperly added.*' Lastly, approximately 500 gallons of water are removed each time that NWMC's service representative vacuums out loose particles from the cooling tower basin.21 It is not known how much cooling tower water was actually discharged by these means Neither is the amount of evaporation known, for measured makeup water use is much less than the amount of evaporation that would be expected from the operational cooling load 22 that the engineering staff believe the cooling towers carry Consequently, no water balance for the towers has been included in this report Other Results Cycles of concentration With ozone, Providence Hospital generally achieved higher cycles of concentration than it did under the multi-chemical regime During multi-chemical treatment, monthly measurements of the conductivity of both the cooling tower water and the makeup water were taken by the chemical company representative From March 1987 to March 1988, these monthly measurements indicate that the cooling tower water's cycles of concentration varied greatly, from to 36 On the majority of these monthly reports, the measured concentration ratio exceeded the intended upper limit Between March 1987 and March 1988, the median concentration ratio was 9.8, based on conductivity In comparison; NWMC's water quality analysis in 1988 indicated that the ozonated water operated at 25.3 cycles of concentration, based on conductivity 1990 results showed an even higher level of conductivity in the tower water than in 1988.23 Fouling of exposed surfaces and microbial growth Prior to the use of ozone, water in the cooling tower basin was murky and biological fouling was plainly visible on tower surfaces The ozone vendor's analysis of the cooling tower water indicated an aerobic bacterial population in excess of 100,000 colonies per milliliter (col/ml), and an anaerobic bacterial population greater than 10,000 col/ml A laboratory hired by NWMC to verify the results could not quantify the number of bacteria because of interference from the particles in the water Appendix A contains the ozone vendor's detailed description of the condition of the cooling tower prior to ozonation, including the bacteria data After installing the ozone system, the cooling tower water and exposed surfaces improved dramatically in appearance Pacific Gas and Electric Company (PG&E), which analyzed corrosion rates 20 at the hospital's ozone treated cooling tower in 1988, describes the improvement: "The circulating water turned clear as the existing deposits on the wetted surfaces within view gradually 24 disappeared " "There were no crevices, scaling, or signs of biological growth observed on surfaces of testing materials 25 or cooling systems structures The water was crystal clear " The virtual elimination of microorganisms from the cooling tower was confirmed by bacterial analysis of the tower water Just half of a month after the switch to ozone treatment, an analysis of a sample of tower water found a bacterial count of 29,000 per 100 milliliters (or, 290 per ml), an improvement of roughly orders of magnitude26over bacterial levels observed during multiSubsequent analyses showed an additional chemical treatment improvement of an order of magnitude: a water quality analysis done by NWMC in 1988 produced a result28of 20 cfu/ml; in 1989 NWMC reported less than 100 counts/ml; and in 1990 a laboratory hired by NWMC counted just 17 cfu/ml.29 Corrosion Although there are no data available on corrosion rates at the site during multi-chemical treatment, the corrosion rates of metals exposed to ozonated water have been low Of five metal types tested by PG&E in the summer of 1988, all but grey cast iron had rates of less than 0.1 mils (milli-inches) per year (mpy) , as shown in Table Table Corrosion Rates Measured by PG&E Metal Type Corrosion Rates (MPY) CDA 706 (90-10 Copper-Nickel) 0.01 - 0.02 CDA 443 (Admiralty Brass) 0.01 - 0.02 Grey Cast Iron 1.30 - 1.80 Carbon Steel 1018 0.07 - 0.08 Aluminum 6061 0.01 - 0.02 Note: MPY = milliinches per year (0.001 in./yr.) According to PG&E, "The higher corrosion rates of [grey cast iron] (below two mills per year) were caused by lower concentration of total dissolved solids, not allowing complete passivation of this material." (Selected characteristics of the ozonated water during the monitoring are presented in Table 10.)30 21 Table 10 Selected Water Quality Characteristics During PG&E Monitoring Parameter Units Value Ave Temperature Degrees Centigrade 28-30 (82.4-86.0 F) Ozone Concentration parts per billion 47-48 pH Standard Units 8.6 - 8.9 Source (Tables and 10): Paul A Burda and Salem A Attiga, Evaluation of Ozone Technology for Chemical Treatment Replacement in Cooling Tower Systems (San Ramon: Pacific Gas & Electric Co., January 1989), Status Report, Report No 006.2-89.2 Measurements taken by NWMC in 1989 and 1990 using corrosion coupons have also shown low corrosion rates: 1.0 - 1.5 mpy for mild steel and 0.05 - 0.1 mpy for copper.31 A slight increase in pitting of chiller heat exchanger tubes, however, did occur after ozone was introduced Very shortly after the multi-chemical treatment was replaced with ozone, tests of all of the condenser tubes found no defects in Chiller #l, and found one tube (out of 660) in Chiller #2 with 20% internal diameter (I.D.) pitting A year later, when Chiller #l was reopened, tubes (also out of 660) showed 20% I.D pitting By 1990, the number of tubes in Chiller #2 with 20% I.D pitting had also increased to three, although this condition was described as "not a problem at this time." In both chillers, the status of each pitted 32 tube was deemed acceptable by the company performing the testing Table 11 shows results from the 1988 - 1990 tests of the chiller tubes." 22 Table 11 Results from Tests of Chiller Condenser Tubes Year Chiller No Chiller No 1990 Not tested tubes w/ 20% I.D pitting; ea tube deemed '*acceptable;" overall deemed "not a problem at this time." "Light scale Recommend check water treatment." 1989 tubes with 20% I.D pitting; ea tube deemed "acceptable." "Rust and light scale Check water treatment." No defects "Recommend brushing the tubes." Not tested 1988 Note: Source: tube w/ 20% I.D pitting; tube deemed "acceptable." "Very minor defect; all remaining tubes no defects." I.D = internal diameter Non Destructive Eddy Current Test Reports from Pacific Coast Trane Service to Providence Hospital The 1989 inspection of Chiller #l also found rust in the condenser section The chemical supplier representative, present described when the chiller was open, took photographs of what he 34 The as "corrosion of the tube sheet (due to electrolysis)." photographs show what would appear to be serious galvanic corrosion of the condenser tubes end bell, where metals of different types are in close proximity The end bell corrosion, which extended to all of the condenser tube end bells, was also present when the chillers were first opened up in 1988 Providence staff believe the end bell corrosion would have occurred regardless of the water treatment method After the 1989 chiller inspection sacrificial pieces of 35 metal were installed, arresting the problem The 1989 and 1990 examinations also found "light scale" in the 36 The chemical supplier took a chillers' condenser tubes sample of the scale in 1989 at the same time as he photographed the electrolysis A consultant hired by the chemical supplier characterized the substance as principally composed of silicates and, secondarily, of what was probably calcium carbonate Appendix B contains the characterization report 23 Due to the observed scale and rust, the inspector(s) of the chillers in both 1989 and 1990 recommended that the hospital check its cooling water treatment Although one would probably assume that the slightly increased pitting and the presence of scale and rust in the chillers are due to the ozone treatment, this is not known with certainty For example, it is conceivable that some of the rust may have been related to the end bell corrosion, which Providence does not attribute to ozone treatment It is also conceivable that an externally caused change in the pH of the cooling tower water chemistry could have played a role A sudden drop in pH and a simultaneous increase in instantaneous corrosion rates did occur during PG&E's monitoring of corrosion rates during the summer of 1988 This suggested to NWMC that a foreign chemical had been added to the cooling tower water.37 In March 1989, too, NWMC found a foreign substance in one of the tower basins Appendix C is a copy of NWMC's letter to Providence on the subject An additional equipment problem at the hospital also developed after the switch to ozone treatment A fan motor was damaged by moist air penetrating into its housing Although the suitability of the motor for a moist environment and the adequacy of its seals were the fundamental issues, some Providence staff also worried that ozone might have contributed to the damage After the pump was replaced with one with adequate seals, epoxy, and paint, the problem appeared to have been resolved to the hospital's satisfaction In May 1991 the fan motor on the second cooling tower also had to be replaced due to corrosion This was not unexpected by Providence.38 The motor from the second tower also is being replaced by a new motor with a special epoxy coating Customer satisfaction On the whole, the hospital is pleased with the performance of the ozone treatment As explained by Providence's Chief Engineer, the hospital values the excellent microbiological control that ozone has delivered It also appreciates the environmental benefits, foreseeing more reasons in the future for facilities to switch to practices that are environmentally benign Providence believes that ozone has not resulted in any serious destruction of equipment As mentioned above, it does not attribute the end bell corrosion to the ozone treatment, and it feels that the replacement of the fan motors with ones that have special coatings was a necessity and a satisfactory solution It also sees the pitting and observed deposits in the heat exchange tubes 39 a minor problem which is not getting appreciably as worse The hospital's satisfaction is further evidenced by the fact that 24 it has not only continued to use the ozone system in the main building, it has recently selected ozone to replace a multiple chemical treatment program at the cooling tower in its recently constructed Medical Office Building Cost Effectiveness It is not known whether Providence's employment of the system has yielded net benefits or net costs This is uncertainty about the ozone treatment's effect on heat efficiency and on equipment longevity However, costs savings resulting from ozone treatment that are known, can be reasonably estimated, are listed in Table 12 in 40 dollars Table 12 Known Annual Costs and Monetary Savings COST / AVOIDED COST ITEM Avoided Chemical $5,582 Avoided Labor $1,260 Avoided Fresh Water $387 Avoided Sewer Conveyance $211 Avoided Wastewater Treatment $227 TOTAL KNOWN AVOIDED COSTS $7,667 Ozone Lease and Service $12,960 Electricity to Generate Ozone $418 Electricity to Recirculate Water in Ozone Injection- Loop $593 $1,011 Electricity to Compress Air $180 Phone Usage $15,162 TOTAL OZONE OPERATING COSTS $7,495 KNOWN NET ANNUAL COST 25 ozone due to the exchange and or that 1991 If ozone treatment caused a significant change in the heat exchange efficiency of the chiller tubes, it would make a great difference to the cost of running the cooling system For instance, a 5.5% change in chiller energy use at Providence would be equivalent to a change in energy costs of more than 41 $9,000 A change in equipment lifespan would also impose significant, real costs or savings on the hospital Chiller energy use Unfortunately, no baseline data exists on the condition of the chiller heat exchange tubes prior to ozone treatment As indicated earlier, the hospital began to employ a company to inspect and test the chillers only after ozonation began Since there is no separate electricity meter serving the chillers, it cannot be determined with certainty whether chiller energy consumption increased or decreased There are conflicting indicators of the probable condition of the chiller heat exchange tubes during multi-chemical treatment On one hand, the fouling of exposed cooling tower surfaces and the presence of numerous bacteria in the cooling tower water suggest there may have been slimes or other types of biological fouling present in the heat exchange tubes On the other hand, no significant problems with the heat exchange tubes were reported in 1988 less than a month after the multiple chemical treatment program was terminated Equipment longevity The lack of certainty about the effect of ozone on equipment longevity also is due to conflicting evidence On one hand are the observed pitting of the heat exchange tubes and the corrosion of the fan motors On the other hand are the low corrosion rates measured by PG&E and NWMC which would seem to suggest that ozone should cause little observable corrosion Chemical savings Chemical savings of roughly $5600 are based on logged manual additions of chemicals, using actual unit costs in 1987, adjusted upward by 3% per year in order to express in 1991 dollars Labor savings Providence Hospital saved approximately hours of labor per month that had been required to manually add chemicals, equivalent to about $1300 annually.43 Ozone system energy use Energy costs to run the ozone system, approximately $2000, have been estimated, since there is no separate electricity meter that measures electricity consumption of the ozone system components Estimates of electricity consumption by the ozone generator and by the water pump used in' the ozone injection loop have been derived using formulas provided by NWMC These formulas suggest a higher consumption of 26 electricity per pound of generated ozone than has been estimated 44 by PG&E The electricity used by the air compressor was assumed to be equal to both the generator consumption and the 45 consumption of the recirculating pump Conclusions Providence Hospital, after replacing multiple chemical treatment of cooling tower water with treatment by ozone gas: reduced makeup water use by 13%, more than doubled the cycles of concentration (based on conductivity), eliminated fouling and scaling of exposed surfaces, experienced no new scaling of exposed surfaces, dramatically improved water clarity, greatly reduced bacteria levels, achieved low corrosion rates, experienced minor pitting and scaling of heat exchange tubes, discovered corrosion of condenser tube end bells, and replaced two fan motors due to corrosion Based on the experience at this site, ozone should be considered for treatment of cooling tower water at least where the following conditions are met: the cooling water's chief function is to remove heat from medium sized heating, ventilation, and air conditioning (HVAC) systems; the ozone system is well designed, monitored, and maintained; the makeup water quality is low in dissolved solids Due to some observed pitting and scaling of heat exchange tubes and the corrosion of fan motors after introduction of ozone, an unequivocable recommendation for use of ozone to treat cooling tower water cannot be made Where ozone treatment is considered, a decision to use or not to use ozone at any one site should be based upon its expected cost effectiveness and on the perceived importance of factors that cannot be adequately expressed in dollar terms The cost effectiveness of any ozone system installation depends upon several factors One is the degree of avoided or increased fouling or scaling, which would affect energy consumption A second is the effect on equipment corrosion: if low corrosion rates extend the expected life of the equipment, a benefit would 27 be obtained; if equipment experienced increased corrosion, the cost to replace it would be borne sooner A third factor is the size of the cooling system, which not only affects the sizing of the ozone system, and thus the size of the ozonation contract fee, but also affects the water and energy consumption A final cost consideration is the makeup water quality, which affects the upper limits on the achievable cycles of concentration and thus affects the water related savings Other benefits which are not easily quantified in dollar terms need to be factored into the decision as well One is the value to the customer of the excellent microbiological control that ozone provides Environmental benefits include reduced water consumption and discharge, as well as reduced toxicity of facility discharges Tradeoffs, too, need to be weighed Ozone allows the tower operator to avoid storing and handling hazardous chemicals, yet presents the potential to increase exposure to ozone gas In addition, an ozone lease and service contract reduces customer labor and automates the treatment process, but this may also have a down side Facility operations staff might see the ozone system as a foreign black box over which they have limited control This could lead to operations staff developing attitudes of suspicion, perhaps even hostility, towards the ozone system or the ozone vendor, and ultimately could interfere with relations with the vendor, handling of the cooling tower system, or with the work environment itself if negative feelings were misdirected Potential for Adoption Statewide Direct purchase, installation, and operation of an ozone system would be limited to organizations with sufficient technical expertise to monitor, diagnose, and maintain an ozonation system over the long term For this reason, facilities that have attempted to piece together their own ozone control systems have not always achieved successful results Consequently, today the standard arrangement for using ozone to treat cooling tower water is to hire the services of a company that specializes in the installation, maintenance, and monitoring of ozone systems, such as National Water Management Corporation or TriOx, its chief competitor Adoption of this approach throughout California might be geographicly limited by the Principal service areas in availability of such services California in 1991 are the San Francisco Bay and Los Angeles areas, but rapid expansion by NWMc and TriOx is anticipated AS of 1991 there is little regulatory review of new installations 28 of ozone generating systems This is largely due to the youth of this technology in the United States: use of ozone to treat cooling tower water in the U.S appears to have begun less than 15 years ago: only since the late 1980s have ozone treatment services been available Sources of ozone are not specifically regulated by air quality agencies, for instance, because in the past ozone has not generally been emitted Rather it has been formed in urban smog by other emitted pollutants interacting with sunlight Nevertheless, laws aimed at attaining and maintaining state and federal ambient air quality standards for ozone could potentially be brought to bear on ozone generators Small generators, however, may not need specific approval from air quality districts, since ozone used for cooling tower treatment is produced in low concentrations and is almost completely consumed by oxidizable impurities in the cooling water The Bay Area Air Quality Management District (BAAQMD) suggests as a guideline that cooling water treatment systems or other small ozone generators of less than 20 lbs per day locating in its area of jurisdiction need not seek approval from it Larger generators, however, such as municipal drinking water or wastewater treatment systems, should contact the BAAQMD for the need to obtain a permit or for exemption, which the agency would evaluate on a case by case basis (These larger systems generally have abatement systems to reduce emissions.)46 One new area of regulation is likely to be the Uniform Fire Code (UFC) In 1990 changes were proposed to the UFC that would govern the installation of ozone generating systems.47 These, however, are not yet in effect.48 The above factors appear for the near future to be the only external constraints on the adoption of ozone technology for cooling tower water treatment in California 29 ENDNOTES H Banks Edwards, "Ozone: An Alternate Method of Treating Cooling Tower Water, " Journal of the Cooling Tower Institute, 8, No (1987), 10-21 For a discussion of the relationship between waterside fouling of condenser heat exchange tubes and condenser performance, see Charles E Middleton, Review of R&D Opportunities in Ozone Technology (San Ramon, Ca.: Pacific Gas & Electric Co., Dept of Research and Development, 1990), Report 008.1-90.2, pp 2-8 For a discussion of ozone's effectiveness in destroying Legionella, as well as background information about Legionnaires Disease and the bacteria which causes it, see Edwards See Douglas T Merrill and Joseph A Drago, Evaluation of Ozone Treatment in Air Conditionins Coolinq Towers (Walnut Creek, Ca.: Brown and Caldwell, 1979) and Leroy V Baldwin, Ellen S Feeney, and Rick Blackwelder, The Investigation and Application of Ozone for Coolinq Water Treatment (Kennedy Space Center, Fl.: EG&G Florida, 1985), from 46th Annual Meeting International Water Conference, Pittsburgh, Pa., 4-7 November 1985, IWC No 85-36 George Wofford, Cindy Slezak, and Michael Bukay, Corrosion Control in Ozonated Cooling Water Systems, rpt from Ultrapure Water Expo '90 West, pp 24-31 Also, Chris Morrison, District Sales Manager, NALCO Chemical Co., Pleasant Hill, Ca., verbal communication, April 1991 Ozone's effectiveness in microbiological control is acknowledged by vendors of ozone and multiple chemical treatment programs alike Ozone's ability to directly control corrosion and inorganic scale, however, is disputed For a description of corrosion control mechanisms using ozone, see Wofford et al For a description of ozone scale control mechanisms, see Marshall F Humphrey, Cooling Tower Water Conditioning Study (Pasadena, Ca: Jet Propulsion Laboratory, 1981) For other reports discussing mechanisms Of ozone scale or corrosion control, see Merrill and Drago; Kenneth R French, Ronald D Howe, and Marshall F Humphrey, "Ozone Inhibits Corrosion in Cooling Towers,*' NASA Tech Briefs, Fall 1979; and Edwards In addition, PG&E is expected to soon release a study of the use of ozone to treat cooling water at a natural gas compressor station, which is likely to discuss the issues of scale and corrosion 30 ENDNOTES Alan Pryor, Executive Vice President - Development, National Water Management Corp (NWMC), verbal communication, 16 October 1989 Alan Pryor, "Ozone Toxicology, Exposure Threshold Limit Values, and Safety Precautions," Ozone News, Nov./Dee 1990 Woody Hill, Industrial Hygienist, Cal/OSHA Consultation Service, San Mateo, verbal- communication, May 1991 Also, Air Contaminants - Permissible Exposure Limits (Title 29 Code of Federal Regulations Part 1910.1000), Occupational Safety and Health Administration Reprint, OSHA 3112 (1989) 10 Edwards 11 Based on 85°F average water temperature to chillers and 91°F average water temperature from chillers These averages were derived from values noted in the annual chiller preventive maintenance inspection reports from Pacific Coast Trane Service, 1988 - 1990 12 Steve Weber, Chief Engineer, Providence Hospital, verbal communication, August 1990 13 Although the generator produces a constant amount of ozone, it could be modified to automatically vary its output according to changes in the measured oxidation reduction potential (ORP) of the water in the ozone injection loop (Mark Fisher, Commercial Service Manager, NWMC, verbal communication, 17 October 1989.) 14 Weber, verbal communication, 26 June 1991 15 The overflow control comes out of adjustment periodically, and is a problem of equal magnitude from year to year (Weber, verbal communications, 26 October 1990 and 26 June 1991.) 16 Average evaporation of the hospital cooling towers, if operating at 300 tons of cooling with a 60F temperature drop, would be expected to be 5.4 gpm (7776 gpd), on average If the towers are actually carrying a cooling load of 200 tons, average expected evaporation with a 6°F temperature drop would be 3.6gpm (5184 gpd) The formula used to estimate evaporation is: Evap =(delta) t x 001 x gpm x Tons 17 It is NWMC's understanding that to prevent the ozone generator cooling water from creating overflow, the water level at which the float control would trigger makeup water 31 ENDNOTES 30 Burda and Attiga, p 31 Pryor, 20 February 1991 32 Pacific Coast Trane Service, Non-Destructive Eddy Current Test Analysis Reports for Providence Hospital TRANE Centrifugal Chillers, 1988-90 33 The ozone vendor questions the reliability of the reports of pitting, citing the fact that the tube in Chiller #2 identified in 1988 as having pitting was not so identified in 1990 Specifically, Tube No 18 of Row was found in 1988 to have some pitting, but in 1990 the tubes with pitting were Tube 13 of Row 16, Tube 16 of Row 17, and Tube 16 of Row 18 However, the system of reference used in 1988 was not the same as that used in 1990 In 1988, the test end was the right, the row direction horizontal, the row count top left to bottom right, and the facing panel tube count bottom left to top right By contrast, in 1990, the test end was the left, the row direction diagonal, the row count top right to bottom left, and the panel tube count top left to bottom right It is impossible for an untrained observer with access only to the written test results to decide whether or not the same tube was referred to in 1988 and 1990 34 Peter Gunderson, Aqua Treat Chemicals, Inc., Belmont, Ca., Consulting Service Report to Providence Hospital, March 1989 35 Weber, 26 June 1991 36 Trane 37 Pryor and Bukay Also, Steve Weber, verbal communication, 28 September 1989 38 Weber, 26 June 1991 39 Providence perceptions of ozone performance from Steve Weber, 26 June 1991 40 Ozone lease and service costs are the same in 1991 as they were in 1987, when the ozonation contract was signed 41 A change in heat exchanger fouling from a design clean state to slight fouling, or a decrease in fouling from moderate to slight fouling, could be considered equivalent to a 5.5% change in condenser energy use (NWMC, Technical Bulletin 32 ENDNOTES No 6: Energy Savings Through Cooling Tower Ozonation, Revision No (1988; San Jose, Ca.: NWMC, November 1988), p 2, Table 1.) The value of such a change in energy use was estimated for Providence assuming 300 tons of cooling and 8.48c per kilowatt-hour, and using the formula: Tons x 76 KW/Ton x % energy change x hrs x c/KW-hr (Formula from Keith Victor, Vice President of Project Development, NWMC, proposal to Steve Weber, 21 Aug 1987, and from Alan Pryor, verbal communication, 23 Oct 1989.) 42 A 3% annual increase to boost 1987 chemical costs to their 1991 equivalents was suggested by the chemical vendor, Peter Gunderson, Agua Treat Chemical Co., verbal communication, 19 May 1991 43 Weber, verbal communications, 29 June 1990 and 29 August 1990 44 Middleton 45 Information on typical air compressor energy consumption in an ozone system relative to that of an ozone generator and an injection loop water pump provided by William K McGrane, Applications & Development Engineer, TriOx Corp., Dublin, Ca., facsimile transmission (FAX) of 17 May 1991 33 ... extra heat load cause the fan on the secondary tower to engage With the primary tower operating at approximately 75% of capacity and the secondary tower operating in the vicinity of 25% of capacity... virtual elimination of microorganisms from the cooling tower was confirmed by bacterial analysis of the tower water Just half of a month after the switch to ozone treatment, an analysis of a sample... to ozonation, including the bacteria data After installing the ozone system, the cooling tower water and exposed surfaces improved dramatically in appearance Pacific Gas and Electric Company