The U.S. Department of Energy requests that no alterations
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Ozone Treatment for Cooling Towers New Energy and Water Saving Technology
to Reduce Cooling Tower Operating Costs
The use of ozone as a maintenance treatment for cooling towers has
good potential for operation and maintenance savings in the Federal
sector. A small amount of ozone acts as a powerful biocide that decreases
or nearly eliminates the need to remove quantities of water from the
cooling tower in order to decrease the concentration of organic and
mineral solids in the system. Ozone treatment can also reduce the
need for chemical additives added to the cooling tower water.
In a properly installed and operating system, bacterial counts are
reduced, with a subsequent minimization of the buildup of biofilm
on heat exchanger surfaces. The resulting reduction in energy use,
increased cooling tower operating efficiency, and reduced maintenance
effort provide cost savings as well as environmental benefit and regulatory
compliance with respect to discharge of wastewater from blowdown.
Cooling towers associated with chillers for air-conditioning are good
candidates for ozone application. Ozone may be a corrosion stimulant
rather than an inhibitor, and this can be a factor in some circumstances.
Nevertheless, it is easier to combat corrosion in a clean system than
in one that is biologically and mineralogically fouled.
This Federal Technology Alert (FTA) provides detailed information
and procedures that a Federal energy manager needs to evaluate most
cooling tower ozone treatment applications. The New Technology Demonstration
Program (NDTP) technology selection process and general benefits to
the Federal sector are outlined. Ozone treatment, energy savings,
and other benefits are explained. Guidelines are provided for appropriate
application and installation. Two actual case studies are presented
to give the reader a sense of costs and energy savings. Current manufacturers,
technology users, and references for further reading are included
for prospective users who have specific or highly technical questions
not fully addressed in this FTA.
About the Technology
Ozone is a molecule consisting of three oxygen atoms and is commonly
denoted O3. Under ambient conditions, ozone is very unstable and as
a result has a relatively short half-life of usually less than 10
minutes. Ozone is a powerful biocide and virus deactivant and will
oxidize many organic and inorganic substances. These properties have
made ozone an effective chemical for water treatment for nearly a
century. During the last 20 years, technological improvements have
made smaller-scale, stand-alone commercial ozone generators both economically
feasible and reliable. Using ozone to treat cooling tower water is
a relatively new practice; however, its market share is growing as
a result of water and energy savings and environmental benefits relative
to traditional chemical treatment processes. A typical system for
ozone treatment of cooling towers is shown in Figure 1. Ozone treatment
of cooling tower water is not feasible in all situations and hence
traditional chemical treatment of cooling tower water is the only
A cooling tower functions to cool a circulating stream of water. The
tower acts as a heat exchanger by driving ambient air through falling
water, causing some of the warmed water to evaporate (evaporation
gives off heat--providing cooling), and then circulating cooler water
back through whatever equipment needs cooling (such as a chiller condenser).
Typically, chemicals such as chlorine and chelating agents are added
to cooling tower water to control biological growth (called "biofilm")
and inhibit mineral build-up (called "scale"). The control of biofilm
and scale is essential in maintaining cooling tower heat transfer
efficiency. As the water volume in the tower is reduced through evaporation
and drift, the concentration of these chemicals and their byproducts
increases. Cooling towers also pick up contaminants from the ambient
air. To maintain chemical and contaminant concentrations at a prudent
level, water is periodically removed from the system through a process
called "blowdown"or "bleed off". The blowdown water and the water
lost through evaporation and drift are replaced with fresh "make-up"
water (which will also contain minerals and other impurities).
Blowdown water must subsequently be discharged to a local wastewater
treatment facility or discharged onsite to the environment. The blowdown
water typically contains little organic material, and the local wastewater
treatment facility will charge extra sewage fees for accepting the
water. These costs can be quite significant in the overall costs of
operating a cooling tower. Discharge of the blowdown water to the
environment onsite is coming under increasing regulation due to stricter
regulation of the contaminants typically found in blowdown water.
Ozone will dissipate quickly and not be found in the blowdown water.
This reduces the overall chemical load found in the discharged water,
making it easier to comply with regulations.
Most cooling tower ozone treatment systems include the following components:
an air dryer, air compressor, water and oil coalescing filters, particle
filter, ozone injectors, an ozone generator, and a monitoring/control
system. Ambient air is compressed, dried, and then ionized in the
generator to produce ozone. Ozone is typically applied to cooling
water through a side stream of the circulating tower water.
Field tests have demonstrated that the use of ozone in place of chemical
treatment can reduce the need for blowdown, and, in some cases where
make-up water and ambient air are relatively clean, can eliminate
it. As a result, cost savings accrue from decreased chemical and water
use requirements and from a reduction of wastewater volume. There
are also environmental benefits as fewer chlorine or chlorinated compounds
and other chemicals are discharged.
There is also a belief within the industry (and some evidence) that
under certain conditions ozone acts as a descaling agent. The premise
is that ozone oxidizes the biofilm that serves as a binding agent
adhering scale to heat exchange surfaces. When scale buildup on condenser
tubes is reduced, higher heat transfer rates are achieved. Increasing
the condenser heat transfer rate will reduce the chiller head pressure,
which then allows the chiller to operate more efficiently and consume
There is a growing number of manufacturers and distributors of ozone
equipment in the United States, and the use of this technology is
encouraged by several major electric utilities and by electric utility
and cooling tower associations. Each new application of ozone for
cooling tower water treatment increases understanding of its overall
effectiveness and its applicability under differing physical conditions.
The technology has had both success and failure.
More information on the criteria for applicability and the potential
for the use of this technology in the Federal sector is provided below.
It is estimated that ozone treatment is applied on anywhere from 300
to 1,000 cooling towers in the United States. Most of these towers
dissipate heat generated by commercial heating, ventilating, and air-conditioning
(HVAC) systems and light industrial processes. The total number of
cooling towers requiring chemical treatment in the United States is
estimated at between 500,000 and 600,000.
Biological growth, scaling, and corrosion are the main maintenance
concerns with these cooling towers. Typical treatment involves the
application of chemicals such as chlorine, sulfuric acid, phosphorous,
and zinc compounds. Care must be taken in the storage, use, or discharge
of these chemicals. Care must be taken to ensure that the proper mixes
and proportions of chemicals are used, and to determine the corresponding
blowdown rates. Excessive application can increase the possibility
of corrosion and other undesirable impacts. As traditional chemical
water treatments are being restricted because of environmental concerns,
ozone is gaining acceptance as a viable biocide alternative.
Cooling tower water is continuously exposed to airborne organic materials,
and the buildup of bacteria, algae, fungi, and viruses presents hazards
to the tower system and to the health of humans encountering the water.
For example, Legionnaire's Disease is caused by the bacterium Legionella
pneumophila that frequently thrives in cooling tower environments.
High levels of bacteria can also lead to an increased risk of microbially
influenced corrosion. Certain sulfate-reducing and iron-metabolizing
bacteria can destroy iron piping in as little as 9 months. Moreover,
a biofilm coating on heat exchanger surfaces reduces heat transfer
efficiency. Ozone kills bacteria by rupturing their cell walls, a
process to which microorganisms cannot develop immunity. Residual
ozone concentrations greater than or equal to 0.4 mg/L have been shown
to result in a 100% kill in 2 to 3 minutes for Pseudomonas fluorescens
(a biofilm producer) in a biofilm, while residual concentrations of
as little as 0.1 mg/L will remove 70-80% of the biofilm in a 3-hour
exposure. Studies have also shown that ozone concentrations less than
0.1 mg/L will reduce the populations of Legionella pneumophila in
cooling tower waters by 80%.
Another phenomenon requiring treatment in cooling towers is mineral
buildup. Minerals such as calcium and magnesium, which are common
dissolved solids in water, are deposited by two different mechanisms,
thermal and biological. As the water in a tower evaporates, dissolved
solids concentrate in the recirculating water. Biofilms also start
to form on the walls and other components of the tower. In essence,
the biofilm acts as an adherent for mineral micro-crystals. Over time,
deposition of organic and inorganic matter increases scale thickness.
Ozone can loosen and remove the scale if the biofilm is present, but
if the biofilm is not present the ozone may be ineffective in removing
the scale. Biofilm may not be the dominant fraction of scale where
the temperature of the heat exchanger is in excess of 135°F. Scale-forming
minerals are less soluble at these higher temperatures and can deposit
from solution directly onto pipe walls.
One operating concern of a cooling tower is the gradual corrosion
of various parts of the tower. Much of the corrosion in cooling towers
is associated with bacteria that create conditions favoring microbiologically
induced corrosion. When adequate quantities of ozone are injected,
control of the microbial population is accomplished. On the other
hand, due to its high chemical oxidation potential, ozone can be quite
corrosive. However, because a very small amount of ozone performs
effectively as a biocide, and because of its very short half-life,
the corrosive effects are minimized.
There is also an observed phenomenon of ozone-treated cooling tower
water, wherein the pH of the system rises above 8.5 and corrosion
protection of the cooling tower components takes place. This phenomenon
may also be dependent upon make-up water characteristics such as alkalinity
and hardness, so it does not release the operator of the cooling tower
from the obligation of making regular corrosion measurements.
Energy and Water Saving Mechanisms
Scale and biological deposits reduce the ability of refrigerant condensers
and industrial-process heat-exchangers to transfer heat. By removing
and inhibiting biological deposits and scale more effectively than
chemical treatment, ozone cooling tower water treatment can improve
chiller system performance. Manufacturers claim an average efficiency
gain of 10%; case studies range from no improvement in efficiency
to a 20% improvement in chiller performance. Energy savings should
be estimated for each individual application and based on the actual
operating condition of the condenser or heat exchanger and the type
of scale present. Further, any projected electrical savings must be
weighed against energy consumed by ozone generators and auxiliaries,
typically 9 kWh to 14 kWh per pound (0.45 kg) of ozone generated.
Water is lost from a cooling tower in three ways: drift, evaporation,
and blowdown. Drift occurs when the water droplets become entrained
in the discharge airstream and can be controlled through cooling tower
design. Evaporation is from air passing through the cooling water
and absorbing heat and mass. Blowdown is intentional bleed-off (replaced
by make-up water) to reduce the concentration of contaminants.
The capacity of a cooling tower is typically measured in tons, the
rate at which the tower rejects heat. One ton of cooling is equal
to rejecting 12,000 Btu (British thermal units) per hour (3.5 kW).
This heat is released through evaporation. The rate of evaporative
water loss is about 12 gallons (45.4 L) per minute for every 500 tons
(1,750 kW) of cooling tower tonnage. Ozone will not increase or decrease
the rate of evaporation. However, compared to chemical treatment at
the allowable dosages, ozone treatment contributes far less to the
tower's dissolved solids loading in the circulation water and is therefore
more amenable to operation at higher cycles of concentration.
"Cycles of concentration," "number of cycles," or "concentration ratio"
are some of the terms used to describe the relationship between the
quantity and quality of make-up water and the volume and constituents
of the bleed-off. This concentration ratio can be thought of as an
indicator of the number of times water is used in the cooling tower
before it is discharged, based on a mass balance between dissolved
solids entering the system in make-up water and dissolved solids leaving
the system in blowdown. The higher the cycles of concentration, the
lower the blowdown.
Blowdown water from a cooling tower can be sent to a municipal drain,
or it may require onsite pretreatment prior to disposal to a drain.
In some cases, blowdown may be stored onsite and then retrieved by
a disposal service. The savings are a direct function of the costs
associated with these three disposal processes and the blowdown volume
reduction achieved by the ozone system.
If water and sewer services are purchased from a municipal or public
utility, reducing blowdown and make-up water requirements will trigger
a series of resource and cost savings for those municipal utilities.
If the site operates its own water treatment and wastewater treatment
facilities, reducing blowdown and make-up water requirements will
allow the facility to realize these benefits directly as follows:
-reduced pumping power to extract water from source wells or reservoir
and pump to water treatment facility
-reduced chemical, filtration, and maintenance costs associated with
treating and purifying at the water treatment facility
-reduced pumping power for distributing the water from the water treatment
facility to the end-user
-reduced pumping power and associated costs to transport wastewater
(blowdown) to the sewage treatment plant
-reduced chemical and maintenance costs, and reduced pumping power
associated with sewage treatment at the plant reduced costs associated
with permits allowing the discharge of treated sewer water to a river
Besides its potential to reduce water and energy requirements, ozone
treatment can reduce or eliminate chemical use, eliminate infectious
bacteria, and improve regulatory compliance. Environmental and health
benefits occur as potentially harmful molecules are broken down into
less toxic byproducts. Properly controlled ozone applications decrease
the levels of both bacterial and mineral substances in the waters
discharged through blowdown or bleed-off.
Chemical treatment costs vary according to the size and chemical requirements
of the tower. These costs can be reduced by using ozone as the treatment
technology. Case studies indicate that chemical cost savings are a
large contributor to the cost-effectiveness of an ozone system.
One manufacturer claims that in normal operation, chiller tubes are
usually brushed out once a year, and the tower sump is shoveled once
or twice per year. When performing a cost savings evaluation for a
potential customer, the manufacturer takes credit for eliminating
this maintenance requirement. Although it may not be necessary to
brush out the tubes more than once a year, it may still be necessary
to shovel the sump for a number of possible reasons. Therefore, it
is generally recommended not to accept maintenance and labor savings
estimates for a facility without consulting the facility's maintenance
personnel. In addition, it is more likely that maintenance savings
will come from the reduction in chemical treatment system labor. This
savings should be weighed against maintenance requirements of the
ozone system, which are reported to be minor.
Finally, with a reduction in biological growth, scale, corrosion,
and chemical use, the issue of liability decreases as well. From a
human resources perspective, reduced risk to personnel health enhances
the working environment and makes a positive public statement.
Ozone generation is accomplished by passing a high-voltage alternating
current (6-20kV) across a dielectric discharge gap through which air
is injected. As air is exposed to the electricity, oxygen molecules
disassociate and form single oxygen atoms, some of which combine with
other oxygen molecules to form ozone. Different manufacturers have
their own variations of components for ozone generators. Two different
dielectric configurations exist--flat plates and concentric tubes.
Most generators are installed with the tube configuration. Cylindrical
configurations offer the easiest maintenance.
Mass transfer of the ozone gas stream to the cooling tower water is
usually accomplished through a venturi in a recirculation line connected
to the sump of the cooling tower where the temperature of the water
is the lowest. Since the solubility of ozone is very temperature-dependent,
the point of lowest temperature provides for the maximum amount of
ozone to be introduced in solution to the tower. Mass transfer equipment
can take other forms: column bubble diffusers, positive pressure injection
(U-tube), turbine mixer tank, and packed tower. The counter-current
column-bubble contactor is the most efficient and cost-effective but
is not always useful in a cooling tower setting because of space constraints.
Hence, setups like a venturi followed by an in-line static mixer,
or an eductor followed by an in-line static mixer, are common in the
installation of an ozone system.
Some ozone treatment equipment vendors propose that the most effective
use of ozone is through controlled low doses proportional to the thermal
and organic loads of the water. Several factors can influence load,
or the oxidation reduction potential (ORP) of the water, including
temperature, air quality in the vicinity of the tower, and cooling
demands. To provide a proportional quantity of ozone, the ORP must
be measured frequently and the ozone generation system must be capable
of instant response to changes in ORP. The ORP is a useful criterion
because other biocides can accumulate in the tower when blowdown is
reduced. These biocides include chlorine from the make-up water and
bromate species resulting from the ozone oxidation of trace bromine
in the make-up water.
Unfortunately, the ORP probe is prone to fouling (usually by a fine
layer of calcium carbonate). Maintenance is simple--and it is essential.
If the probe is not cleaned, the ozone system is likely to stray from
proportional control. The benefit of proportional control and variable
ozone generation capability is that only the necessary quantity of
ozone is generated; thus, energy consumption costs are minimized,
as is the possibility of corrosion from excessive ozone.
Ozone generators create heat and require a cooling system. Some manufacturers
indicate that water is the coolant of choice; however, others prescribe
cabinet air-conditioning units to keep constant temperatures and reduce
air moisture content. Regardless of which system is employed, reliable
cooling is essential to preserve the dielectric and to optimize ozone
Federal Sector Potential
The potential cost-effective savings achievable by this technology
were estimated as a part of the technology assessment process of the
New Technology Demonstration Program (NTDP).
Technology Screening Process
New technologies were solicited for NTDP participation through advertisements
in the Commerce Business Daily and trade journals, and through direct
correspondence. Responses were obtained from manufacturers, utilities,
trade associations, research institutes, Federal sites, and other
interested parties. Based on these responses, the technologies were
evaluated in terms of potential Federal-sector energy savings and
procurement, installation, and maintenance costs. They were also categorized
as either just coming to market ("unproven" technologies) or as technologies
for which field data already exist ("proven" technologies). Note this
solicitation process is ongoing and as additional suggestions are
reviewed, they are evaluated and become potential NTDP participants.
The energy savings and market potentials of each candidate technology
were evaluated using a modified version of the Facility Energy Decision
Screening (FEDS) software tool, developed for the Federal Energy Management
Program (FEMP), Construction Engineering Research Laboratories (CERL),
and the Naval Facilities Engineering Service Center (NFESC) by Pacific
Northwest National Laboratory (PNNL) (Dirks and Wrench 1993).
During the solicitation period in which ozone treatment of cooling
tower water was suggested, 21 of 54 new energy-saving technologies
were assessed using the modified FEDS. Thirty-three were eliminated
in the qualitative pre-screening process for various reasons: not
ready for production, not truly energy-saving, not applicable to a
sufficient fraction of existing facilities, or not U.S. technology.
Eighteen of the remaining 21 technologies, including ozone treatment
of cooling tower water, were judged life-cycle cost-effective (at
one or more federal sites) in terms of installation cost, net present
value, and energy savings. In addition, significant environmental
savings from use of many of these technologies are likely through
reductions of CO2, NOx and SO2 emissions. Several of these technologies
that have a demonstrated field performance have been slated for further
study through Federal Technology Alerts.
Through laboratory testing, field testing, and theoretical analysis,
ozone treatment of cooling tower water has shown to be technically
valid and economically attractive in many applications. The technology
works by virtue of the ability of ozone to act as a disinfectant and
therefore as an alternative to traditional chemical treatment. Performance
of the technology, when properly applied, has been demonstrated effective.
However, like most traditional chemical treatment programs, ozone
is not a cure-all. Ozone is a potential alternative to traditional
chemical treatment methods. More information is needed on the effectiveness,
efficiency and potential other impacts of ozone. The remaining barriers
to implementation involve user acceptance and correct application.
This Technology Alert is intended to address these concerns by reporting
on the collective experience of ozone users and evaluators and by
providing application guidance for Federal-sector installations.
This section addresses technical aspects of applying ozone treatment
technology to cooling towers. The most appropriate applications are
To determine whether ozone is an effective alternative for treating
the water in a specific cooling tower, a technical feasibility screening
study and economic (life-cycle cost) analysis should be performed.
In general, cooling towers associated with chillers for commercial
HVAC and light industrial process cooling are good candidates. Manufacturers
claim to have treated both wooden and metal towers in sizes ranging
from 60 to 10,000 tons (210 kW to 35,000 kW). A list of manufacturers
is provided later in this Technology Alert.
Ozone is not a corrosion inhibitor; however, the higher concentration
ratios resulting from the reduced blowdown volumes raise the pH of
the recirculating water, which helps protect the system from corrosion.
This same pH condition will promote the precipitation of silicates
and calcium carbonate if sufficient pretreatment of make-up water
is not provided. Lower pH will remove the scale but will also increase
the corrosion rate from the ozone. For this reason, make-up water
must be of sufficient quality to avoid these problems.
The strong oxidation potential of ozone is what makes it most attractive
for use as a biocide in water systems. However, this same property
also makes it difficult to use ozone when there is a large chemical
oxygen demand (COD) present (this will consume available ozone) in
the water or if local air conditions bring in large quantities of
organics to the tower. The latter condition is the reason it is not
possible to implement ozone water treatment in towers within chemical
plants or at oil refineries. In addition, ozone is corrosive to some
materials such as rubber fittings, gaskets, and certain kinds of metals
and alloys. If these materials are present in a cooling tower, they
should be replaced before ozone system installation if it is practical
and economical to do so.
Once ozone is in the liquid phase, it will last only a short period
of time; thus, maintaining an ozone residual for more than approximately
10 minutes can be difficult. This limits the application of ozonation
in large cooling towers. In large towers with 100,000 or more gallons,
multiple injection points may be necessary.
Make-up water that is high in mineral content or dissolved solids
may not be conducive to effective treatment; testing should take place
before a system is installed and on a periodic basis during operation.
A side-stream filter may be required on cooling towers operating with
make-up water quality in excess of 150 ppm calcium hardness. In cases
where hardness is in excess of 500 ppm as CaCO3, or sulfates >100
ppm, ozone can be eliminated as a viable cooling tower water treatment.
A "Cooling Tower Worksheet" is provided in Appendix A and can be used
to characterize the quality of make-up water.
The U.S. Occupation Safety and Health Administration (OSHA) has established
an ozone exposure limit of 0.1 ppm in air over an 8-hour shift. This
could be a problem if the cooling towers are located on the ground
level and are excessively treated with ozone so that the tower is
operating as an ozone gas stripper (gives off ozone into the air).
Ozone produces oxidation by-products. There are several secondary
products that must be accounted for in the set-up of cooling tower
ozonation. Both iron and manganese will be oxidized by the ozone to
form insoluble particulates that collect in basins, on screens, or
in any scale that is forming. Excessive amounts of either of these
two chemicals in the make-up water will require pretreatment. In addition,
organic compounds that may either be in the make-up water or introduced
through the atmosphere will react with ozone to form ketones, aldehydes,
and amines. If bromide is present, ozone can convert bromide to hypobromous
acid and hypobromite ion. These two species are known biocides and
would be considered helpful in controlling biofilms but potentially
detrimental in the discharge of blowdown. Excessive ozone can further
oxidize the hypobromite ion to bromate, reducing the effectiveness
of these components as biocides.
What to Avoid
Ozone treatment failures are usually related to an inadequate quantity
of applied/dissolved ozone which can be caused by excessive organic
material in the water or high operating temperature. Therefore, ozone
treatment should be avoided in the following situations:
-high organic loading from air, water, or industrial processes that
would require a high COD (the ozone will oxidize the organics and
insufficient residual may remain for the water treatment)
- water temperatures that exceed 110°F (43.3°C) (high temperatures
decrease ozone residence time and reduce overall effectiveness of
the ozone treatment)
- make-up water is hard (>500 mg/L as CaCO3) or dirty make-up water
(softening and/or prefiltering make-up water is sometimes recommended)
- long piping systems which may require long residence time to get
complete ozone coverage (insufficient ozone residence time may result
in incomplete coverage)
Water temperature is critical to the success or failure of a system.
Above 110°F (43.3°C) the solubility of ozone is effectively zero for
all concentrations of ozone in the feed gas. Even at 104°F (40°C)
the solubility is very small (<3 mg/L). Although some operational
data suggest that ozone may be used at temperatures of up to 135°F
(57.2°C), most sources agree that ozone works best in bulk water temperatures
under 104°F (40°C), preferably even below 100°F (37.7°C). Many comfort
cooling systems commonly operate at between 85°F and 95°F (29.4°C
and 35.0°C). As temperatures rise, the ozone will dissipate too fast
and not dissolve into the water. This is one reason ozone is not appropriate
for cooling tower systems such as nuclear and fossil generating plants
and absorption refrigerant plants, where temperatures are generally
Problems can and do occur in the field. The following precautions
are not always covered in manufacturers' instructions but are recommended
to be taken during installation:
-Preparation of the inlet air is very important for the efficient
operation of an ozone unit as well as for the longevity of the unit.
The preparation of the gas includes removal of dust (particle sizes
>1µm), moisture (dewpoint <-76° F (-60°C)="99.98%" moisture removed),
and oil. This requires that the pretreatment system be checked periodically
by properly trained personnel and that the appropriate monitoring
equipment for the pretreatment process is installed.
-Make-up water should be free from noticeable sediment, mud, and discoloration
and should not have extremely high levels of sulfates (<100 ppm) or
hardness (<500 ppm as CaCO3). These values may be determined by having
the water tested by a qualified lab
-Material in the ozone-treated system should be compatible with ozone.
The ozone distribution line from the generator to the gas/water contactor
carries the highest concentration (1 to 4% by weight of ozone); therefore,
the line material should be constructed of stainless steel or PVC.
-For efficient operation, the ozone generator should be located in
an air-conditioned area. Excessive heat (greater than 90°F) could
damage the system or reduce generation capacity.
-The actual capacity of the ozone generator should be certified by
the manufacturer and checked yearly by the ozone vendor or a qualified
- Corrosion coupons for copper and steel should be placed in the system
and checked at least every 6 months.
Normally the cooling tower manufacturer or vendor furnishes operating
and maintenance manuals and training. Manufacturers' instructions
should continue to be followed after the system is installed.
Ozone concentration in the water can be measured. The measurement
of ozone concentration has been a source of some debate in the past.
Two measurement methods are in use today that are fairly well accepted.
These are Absorption of UV light as determined by the Beer-Lambert
Absorption Law (OREC) and the Indigo method 8311 of HACH Company.
The UV absorption method is useful for on-line monitoring of the ozone
concentrations in systems for cooling tower water treatment.
A useful indicator of scaling is proposed by Pryor and Buffum, called
Practical Ozone Scaling Index (POSI). This index is a correlation
for traditional scaling indices for use in ozone treated systems.
Tierney, Feeney, and Mott propose examining the solubility based on
activity coefficients as a function of ionic strength using the DeBye-Huckel
equation. This latter approach is a direct assessment of scaling under
super saturated conditions.
The ozone systems for cooling tower application on the market today
are typically modular and fully self-contained systems with an independent
circulation system for sidestream installation. Ozonators operate
from line voltage of 120 volts single-phase, 230 volts single- and
three-phase, and 440 volts single- and three-phase, at 60 Hz. The
higher the output, the more desirable it is to operate from a higher
voltage and multi-phase source. Electric service breakers are system-mounted
for single-point electrical connection. Units can arrive completely
wired and piped, with all components mounted on structural steel skids.
The necessary piping (usually PVC) and circulation pumps
must be provided to connect the system to the cooling tower water
sump. Sometimes, filters must be installed to capture mineral deposits
that will occur from the ozone treatment. Installation can typically
be completed in one day provided the appropriate electrical service
is in place.
Monitoring and control packages can include integral alarms. Also,
interlocking features are available so that remote fans, blowers,
pumps, solenoid valves, etc. will be activated upon start up of the
ozonator and vice versa.
Different ozone systems have different dimensions or "footprints."
A system designed to treat a 1,000-ton (3,500-kW) tower may have width-height-depth
system dimensions of 37 x 32 x 55 inches (0.94 x 0.81 x 1.4 meters)
to 90 x 60 x 30 inches (2.3 x 1.5 x 0.76 meters). To maximize the
use of ozone during its short half-life, the ozone-containing water
should be returned to the sump of the cooling tower as close as possible
to the suction side of the circulation pumps, to ensure that the maximum
amount of oxidant is circulated through the piping and heat exchangers
and that some ozone remains to be returned to the top of the cooling
As with any technology, it is important to perform routine maintenance
in order to preserve overall efficiency and effectiveness, as well
as to extend equipment life. Preventive maintenance recommendations
are listed in Table 1.
Table 1. Recommended Preventive Maintenance
Change brushes on powerstat control
Remove dust from transformers
Check cooling water system
Check low pressure safety cut-out switch
Clean high voltage bushings
Change humidity sensor
Check relief valves for proper operation
General inspection for water leaks
||Check air dryer pre- and post-filter as specified by air dryer
Change air dryer desiccant (if used) every three years
Check air compressor system every six months
Ozone technology appears to be a reliable method for cooling tower
water treatment. As with any water treatment process, there are reported
successes and failures. As with most equipment, warranties vary between
manufacturers. Although a full comparison of warranty information
cannot be provided in this Technology Alert, one manufacturer warrants
the electrodes in the ozone generator for three years.
The reader should inquire into the ozone equipment warranty directly
from the ozone equipment manufacturer or sales representative. In
addition, the reader should inquire into the impact on the chiller
and cooling tower equipment warranties directly from the providers
of the chillers and cooling towers. Some ozone technology providers
disclaim any warranty with regard to the use of the ozone equipment.
The actual terms of the warranty are usually set forth in the specification
submittal or documents of sale. The reader is encouraged to investigate
the equipment warranties.
Costs for a typical ozone system capable of treating a 1,000-ton (3,500-kW)
cooling tower are estimated to range from $25,000 to $70,000, depending
upon manufacturer and actual system size. $36/ton of cooling may be
used to provide a rough cost estimate for an ozone system. The ozone
systems are sized according to need and range from 10 gr/hour to 3,700
gr/hour with corresponding prices ranging from $10,000 to $300,000.
The wide range in cost is a result of the fact that the size, and
subsequently the cost, of the system depends heavily upon the operating
temperature and operating environment of the tower.
Utility Incentives and Support
Although no utilities currently offer rebates for ozonation, a number
have sponsored seminars and disseminated information. Some have sponsored
field tests and comprehensive studies. The reader is urged to contact
your local utility to see if any energy savings rebates are available.
Texas Utilities (TU) has worked with one company since spring of 1994
and has completed four ozone installations for TU customers. Southern
California Edison has studied installations and offers information
to its customers. Pacific Gas & Electric evaluated a test installation
over a two-year period and concluded that ozone was "superior to the
current, conventional, multi-chemical treatment program." Georgia
Power, Alabama Power, and the TVA all sponsored onsite seminars on
cooling tower ozonation for their customers in 1994.
Technology Performance A large number of case studies have been reported
by manufacturers and others. Observations of field performance, obtained
from Federal- and private-sector analysts and users, are summarized
Pacific Gas and Electric reported effective use of ozone as a biocide
following a 2-year study of treatment of mechanical draft counterflow
water cooling towers at a large gas production utility site.
An Electric Power Research Institute (EPRI) case study focuses on
the Digital Equipment Corporation offices in Littleton, Massachusetts,
a 500,000 square-foot complex. The ozonation system was commissioned
in 1989. Digital engineers found ozonation to be economically and
environmentally superior to previous chemical treatments. In addition
to the biocidal effect, ozonation reduced blowdown and eliminated
the need for employees to handle chemicals. Tests over 2.5 years showed
no scale formation; corrosion rates were within industry standards
and equipment manufacturer recommendations. Operating costs were reduced
by almost $90,000 per year, and the payback period for capital investment
was only about 2 years.
In 1984-85, NASA performed an experiment in which a 600-ton cooling
tower was retrofitted with an "Ozone-Air HF-90" solid-state ozone
generator, which used 60% less electricity to make a pound of ozone
than a conventional transformer/glass-electrode generator (6.1 vs.
15.3 kWh/lb ozone). The generator cost a total of $16,057 for a 2-cfm
air compressor, air dryer, and ozone generator. Its use decreased
the cooling tower's bacterial count by four orders-of-magnitude and
turbidity by eightfold. Scale accumulations on the tower loosened
and fell off. The effect on chiller energy consumption was not measured,
but the condensers were found to be clean and looking as though they
were newly retubed. Negative impacts included ozone attack on galvanized
steel, copper, and nylon fittings; these were eventually replaced
with PVC and stainless steel.
Case Study I
This case study examines a system of four ceramic-filled concrete
cooling towers with a capacity of 2,500 tons (8,750 kW) each. The
towers reject heat from the air-conditioning system that provides
temperature and humidity control for Space Shuttle processing in the
Vehicle Assembly Building (VAB) at NASA's Kennedy Space Center (KSC),
The cooling towers that provide service to the VAB are located in
the Utility Annex (central plant) at KSC. The make-up water is purchased
from a Privately Owned Treatment Works (POTW) at a cost of $1.18/1,000
gallons ($0.31/1,000 liters) and blowdown was discharged to local
surface waters. Chemical treatment for the cooling tower was $10.18/ton
per year ($2.91/kW) and consisted of two phase scale and corrosion
inhibitors and alternating biocide application. In 1990, the Florida
Administrative Code (FAC) 17-302, Surface Water Quality Standards,
introduced stricter environmental regulations that made the blowdown
water unable to meet regulatory criteria for discharge to the local
surface waters. Hence, ozone treatment was installed in February 1994
in an attempt to reduce the amount of blowdown being discharged.
Existing Technology Description
The four cooling towers have a total capacity of 10,000 tons (35,000
kW) and contain a total of 204,000 gallons (772,000 liters) of cooling
water. The towers had an average make-up water volumetric rate of
146,000 gal/day (553,000 liters/day). Blowdown averaged 67,200 gal/day
(254,500 liters/day) with the rest being a combination of drift and
evaporation. The towers reportedly were operated with a concentration
ratio in the range of 4 to 7. Cooling water is circulated at 7,500
gal/min (28,400 liters/minute) through each tower. The tower water
temperature drops from 110°F (43.3°C) to 90°F (32.2°C).
Ozone Equipment Selection
Ozone vendors have well-developed specifications for the implementation
of ozone-producing equipment. These criteria consider all aspects
of the system. Many factors must go into the decision to use ozone
as a cooling tower water treatment. Among these factors are the operating
environment, operating temperature, material resistance to ozone,
and condition of the make-up water. However, it is important to have
an estimate of the size and cost of an ozone system before contacting
The size, cost, and operating conditions of the existing system should
be obtained so that a comparison can be made with using ozone. If
this information is not available, the inputs needed may be estimated
in the Cooling Tower Worksheet. It is necessary to know the nominal
rating of the cooling tower(s) under examination. Cooling tower capacity
is usually expressed in terms of tons. Once the tower capacity is
obtained, the system can be sized using the equations identified in
the Cooling Tower Worksheet.
A preliminary analysis will provide estimates that will be useful
in making a decision to implement ozone as a treatment for cooling
tower water. The estimation of the size and cost of an ozone system
can be done at several levels of detail. The highest level of estimation
is based on an average installed cost of an ozone system based on
the nominal tonnage of the tower. An installed cost of $10/kW ($36/ton)
is typical for smaller systems. As the ozone generators get larger,
the cost per ton can drop. An average chemical treatment program cost
is $10/ton per year while an average ozone treatment will cost around
$2/ton per year. The cost of make-up water and disposal of blowdown
can vary widely and should be obtained for the particular cooling
tower application under consideration. In addition, local energy costs
should be used for the ozone energy consumption. The estimated costs
and savings for the Utility Annex cooling tower system are listed
in Table 2.
Table 2. Estimated Cooling Tower System Operating Information
|Ozone equipment cost
|Annual water use
The estimates from the above calculations are to use a 690 gr/hr ozone
generator. Annual savings are estimated to be $124,465. Using the
Building Life-Cycle Cost software (BLCC 4.20-1995) available from
the National Institute of Standards and Technology (NIST), the total
life-cycle cost for the ozone technology is $663,850 compared to a
life-cycle cost of $1,463,555 for the conventional chemical treatment
program. A life cycle of 10 years was used in this analysis. The resulting
net present value (NPV) is determined to be $799,705 and the savings-to-investment
ratio (SIR) is 3.5. More information on Federal life-cycle costing
and the BLCC software can be found in Appendix B.
Implementation and Post-Implementation Experience
The ozone system installed at the Utility Annex has a generation capacity
of 600 gr/hr. For comparative purposes, the actual costs and savings
reported by Tierney and Mott are identified in Table 3. The overall
savings was determined to be $100,012/year. Experience at the Utility
Annex cooling towers has shown that ozone treatment is indeed a viable
water treatment method for cooling towers. The idea that zero blowdown
can be practiced is not feasible, since the calcium levels will eventually
get too high and scale will form. At 60 to 80 cycles, the cooling
towers were 60% plugged with scale in 8 months. In addition, the ozone
injection circuit was plagued by the same problem and was difficult
to keep on line. This forced the operators to reduce the concentration
cycles between 10 and 20. Research indicated that they could increase
the concentration cycles between 30 and 40, which is where they are
Table 3. Reported(a) Cooling Tower Operating Information
|Ozone equipment cost
|Annual water use
|(a) Reported from telephone interview with site
The ozone generator failed several times due to excessive heat but
was covered by the manufacturer's warranty. To remedy the failure
conditions of the ozone unit, an air-conditioned enclosure was built
to remove some of the cooling load on the ozone generator's cooling
system. This points out the need to have the cooling system for the
ozone generator serviced regularly to reduce failures in the unit
and to consider the cost of enclosing and cooling the unit if it must
operate in a high temperature environment.
Ozone injection systems are susceptible to scale build-up due to the
dry ozone/air stream coming into contact with the mineral-saturated
cooling tower water. This problem was solved by injecting potable
water (which is not mineral-saturated) at the site of ozone injection.
Overall, the results are good. The reduction in blowdown, make-up
water, and chemical costs usually will provide a simple payback time
of less than six years.
Case Study II
This case study concerns a system of two cooling towers with a capacity
of 300 tons each, located at the Lockheed Martin Electronics and Missiles
Ocala Operation in Ocala, Florida. Data were taken from a paper written
and presented at the DOE Pollution Prevention Conference XI in Knoxville,
Tennessee, on May 16, 1995 (See "Who Is Using the Technology" for
a contact at Lockheed Martin).
The Lockheed Martin Electronics and Missiles Ocala Operation is responsible
for the production of electronic assemblies, printed circuit boards,
and wiring harnesses for space exploration, defense weapon systems,
and defense communication systems. The cooling towers support a variety
of test and production equipment and also support secondary cooling
of HVAC systems.
The cooling tower system consists of two conventional Marley counterflow
cooling towers with an operating capacity of 500 gallons each. The
towers operate with an influent water temperature of 85°F (29.4°C)
and an effluent temperature of approximately 75°F (23.8°C), for an
overall temperature drop of 10°F (5.6°C). The facility was not connected
to a public works wastewater treatment facility, so the blowdown water
had to be transported offsite for disposal, at an annual cost of $45,360.
The cooling towers had an annual make-up water volume of 2.482 million
gallons. Since the installation was not connected to an outside water
source, the source of make-up water was treated wastewater recycled
from the manufacturing process. This make-up water had a total organic
carbon (TOC) content that was greater than 1500 ppm. This high TOC
concentration resulted in a large chemical demand in treating the
cooling tower water, which was reflected in the overall chemical treatment
costs. The water was soft (~=50 ppm as CaCO3) and contained ferrous
sulfate from the manufacturing process. Poor system control resulted
in either excessive chemical use or insufficient chemical feed, with
subsequent scale formation requiring acid cleaning. The tower required
acid cleans several times a year and the chiller condensers were cleaned
at least twice during the summer months due to biofilm growth that
resulted in excessive pressure head.
The existing multi-chemical treatment program consisted of the application
of chlorine gas, additional biocides, and corrosion inhibitors. The
total annual chemical costs were $24,733.
The savings data identified in Table 4 were generated by personnel
in charge of system operation. Significant savings were achieved in
all elements of the process: labor, energy, chemical, and blowdown
Table 4. Operating Cost Comparison for Cooling Water System Per
Savings with ozone treatment were $140,753/year with an NPV of $1,072,235
and an SIR of 31.9.
In this situation, prior to the installation of the ozone system,
the costs and maintenance were high enough to cause the facility to
examine alternative methods for cooling tower water treatment. The
result was a decision to use ozone for the treatment of the water.
A proposal from REZ-TEK International, Inc. was obtained in 1993 for
the installation. In February 1994, a REZ-TEK model S-1230 was installed
and put into service. The model S-1230 produces 0-30 grams of ozone
per hour and sold for around $35,000. The ozone system came completely
self-contained with a foot print of 37 inches by 30 inches and a height
of 55 inches. The appropriate electric service was already in place,
so the installation of the unit took one day. It should be noted that
the time and cost of installation will increase if the appropriate
electrical service is not available.
During initial start-up of the system, a significant amount of suspended
particles were observed. This was from the precipitation of the minerals
in the water and was an expected phenomenon. In this application,
the suspended solids were removed by application of hydrogen peroxide
as a make-up water pretreatment. Addition of ferrous sulfate was also
eliminated from the make-up water, and the sump water was filtered.
The bacterial count was reduced three orders-of-magnitude, from one
million to one thousand colony-forming units (CFUs), and blowdown
waste was reduced 90%. The operator reported that no chemicals had
been added to the cooling tower one year after the ozone system was
Labor savings were reported qualitatively: "Maintenance operator was
enabled to alternate one chiller and remove waste heat from air conditioning
and test chambers. System has allowed the maintenance operator time
to focus on the other facility issues." An important aspect of this
type of savings is that it will free up maintenance staff to address
other operation and maintenance issues at the facility.
Corrosion tests indicated that copper in the tower neither corroded
nor pitted, while iron showed 2.0 mils per year of corrosion and 0.37
mils per year of pitting. It was reported that the corrosion effect
of ozone was 50% of that of chlorine treatment.
The findings of the case study were very positive one year after installation
The Technology in Perspective
Much excitement has been generated around this technology. Manufacturers
and vendors see a huge market; cooling tower operators see the potential
costs savings, environmental benefits, and reductions in maintenance
and health hazards. As a result, many players have appeared in the
field along with a variety of products, services, and performance
With each installation, more is learned about actual performance,
cost, and benefits. There have been reports of success and of failure.
Manufacturers indicate that many of the failures were due to poor
design or inferior quality ozone-generating equipment. Sometimes the
application of ozone was inappropriate due to the make-up water condition
or the tower operating conditions. In these situations, a traditional
chemical treatment program will be more effective.
There are many reasons to consider ozone: when chemical costs are
high or chemical management is burdensome, when chemical water treatment
is not effective, when water and sewer charges are high or increasing,
or when local regulations require blowdown to be treated before discharge
to surface waters.
Potential users should carefully review their current and historic
costs related to cooling tower water treatment and the performance
of their associated cooling equipment. The guidance provided in this
Technology Alert should help indicate whether it would be worthwhile
to consider the technology.
Manufacturers and Suppliers
The firms listed below were identified as manufacturers and suppliers
of the technology at the time of this report's publication. This listing
does not purport to be complete, to indicate the right to practice
the technology, or to reflect future market conditions.
American Ozone Systems, Inc.
1301 North Elston Avenue
Chicago, IL 60622
7 Old Dock Road
Yaphank, NY 11980
or c/o MW Equipment, Inc.
(212) 643-7700 (attn: Dick Dabberdt)
Capital Controls Company , Inc.
3000 Advance Lane
PO Box 211
Colmar, PA 18915
Carus Chemical Company Ozone Systems
315 Fifth Street
Peru, IL 61354
Clear Water Technology, Inc.
850#E Capitolio Way
San Luis Obispo, CA 93401
Diversey Water Technologies, Inc.
7145 Pine Street
Chagrin Falls, OH 44022
3110 W. Story Rd.
Irving, TX 75038
(214) 257-0322 (attn: Patrick Hunt)
Emery-Trailgaz Ozone Company
11501 Goldcoast Dr.
Cincinatti, OH 45259-1643
Hankin Atlas Ozone Systems, Ltd.
690 Progress Avenue, Unit #12
Scarborough, Ontario M1H 3A6 Canada
Griffin Division of Ozonia North America
PO Box 330, 178 Route 46
Lodi, NJ 07644
Marley Cooling Tower
7401 W. 129th St.
Overland Park, KS 66213
(913) 664-7614 (attn: Terri Robee)
Mitsubishi International Corporation
875 North Michigan Avenue,
Suite 3900, John Hancock Center
Chicago, IL 60611
5951 Clearwater Drive
Minnetonka, MN 55343-8990
Ozonair International Corporation
903 Grandview Drive South
San Francisco, CA 94080
Ozone Research & Equipment Corp.
4953 West Missouri Ave.
Phoenix, AZ 85301
Ozone Technology Inc.
2113 Anthony Dr.
Tyler, TX 75701
Ozonia North America
2924 Emerywood Parkway
PO Box 70145
Richmond, VA 23229
2401 Oberlin Rd.
Yreka, CA 96097
Ozone Technology Incorporated
2113 Anthony Dr.
Tyler, TX 75701
79 Bond Street
Elk Grove Village, IL 60007
Sumitomo Precision Products Co., Ltd.
345 Park Ave.
New York, NY 10154
(212) 826-3634 PCI
Ozone & Control Systems, Inc.
One Fairfield Crescent West
Caldwell, NJ 07006
REZ-TEK International Corp.
15 Avenue E
Hopkinton, MA 01748
(800) 770-8554 (attn: Jim Daly)
Wheelabrator Engineered Systems, Inc.
P.O. Box 36, 441 Main Street
Sturbridge, MA 01566
Zelsman and Associates
329 Nebraska Ave.
Longwood, FL 32750
(407) 831-6268 (attn: Jack Zelsman)
For Further Information
The documents listed below were used in the preparation of this Technology
Alert and may be of further use to anyone considering application
of cooling tower ozone treatment. A list of pertinent associations
and organizations is also provided.
User and third party field and lab test reports and other technical
1994 ASHRAE Handbook, Equipment Volume, Chapter 20, Cooling Towers,
American Society of Heating, Refrigerating, and Air Conditioning Engineers,
Aqua-Chem, Inc. nd. "Ozone and the Environment." Aqua-Chem, Inc.,
Raleigh, North Carolina.
Burda, Paul A., Brian A. Healey, and Guna Selvaduray. 1993. "Performance
and Mechanisms of Cooling Tower Treatment by Ozone." Paper No. 488,
presented at Corrosion 93, the NACE Annual Conference and Corrosion
Show. Pacific Gas and Electric Company Technology Center, San Ramon,
Coppenger, G. D., B. R. Crocker, D.E. Wheeler, 1989, Ozone Treatment
of Cooling Water: Results of a Full-Scale Performance Evaluation,
Oak Ridge Y-12 Plant, Martin Marietta Energy Systems, Inc.
Donohue, J.M. 1972, Cooling Tower Treatment -- Where Do We Stand?,
National Association of Corrosion Engineers.
Dore, M. 1985. "The Different Mechanisms of the Action of Ozone on
Aqueous Organic Micropollutants." In Proceedings of the International
Ozone Association Conference, London, November 13-14, 1985.
Echols, Joseph T., and Sherman T. Mayne. 1990. "Cooling Tower Management
Using Ozone Instead of Multichemicals. ASHRAE Journal, June 1990.
Edwards, H., P.E. Banks. 1987. "Ozone--An Alternate Method of Treating
Cooling Tower Water." Paper No. TP87-17, presented at the 1987
Cooling Tower Institute Annual Meeting, New Orleans, February 25-27,
1987. Electric Power Research Institute (EPRI). 1992. Tech Application:
Ozonation of Cooling Tower Water. No. 3, EPRI Industrial Program -
Environment and Energy Management, Palo Alto, California.
HACH Company. 1992. Water Analysis Handbook. 2nd Edition. HACH Company,
Henley, Mike. 1994. "Ozone Review: Ozone Finding Small Niche as Cooling
Tower Treatment." In Industrial Water Treatment, March-April 1994.
Kaur, K., T.R. Bott, and B.S.C. Leadbeater. 1992. "Effect of Ozone
on Pseudomonas Fluorescens." In Biofilms--Science and Technology,
L.F. Malo et al. eds., pp. 589-94. Kluwer Academic Publishers, Netherlands.
Kenney, Ray. 1983, Ozonation as Cooling Tower Water Treatment: A
Pilot Study, IBM Technical Report TR 20.0430
Legube, B., J-P. Croue, D.A. Reckhow, M. Dore. 1985. Ozonation of
Organic Precursors Effects of Bicarbonate and Bromide, In Proceedings
of the International Ozone Association Conference, London, November
13-14, 1985 Masschelein, W.J. 1985.
Mass Transfer of Ozone Through Bubbling and Chemical Reactions in
Water, In Proceedings of the International Ozone Association Conference,
London, November 13-14, 1985.
Miltner, R. J., H. M. Shukairy, R. S. Summers, Disinfection By-Product
Formation and Control by Ozonation and Biotreatment, Journal of American
Water Works Association, V84 n11 pp. 59-62, November 1992.
Montgomery, James M., Consulting Engineers, Inc. 1985. Water Treatment
Principles and Design. John Wiley & Sons, New York.
Nebel, Carl. 1985, "The Oxidation Mechanism of the Oxyozonsynthesis
Process," In Proceedings of the International Ozone Association Conference,
London, November 13-14, 1985.
Nebel, Carl. 1994. "Design Consideration for Ozone Water Treatment
Systems in Cooling Towers." Paper No. TP94-07, presented at the 1994
Cooling Tower Institute Annual Meeting, Houston, Texas, February 13-16,
1994. PCI Ozone & Control Systems, Inc.
Nebel, Carl. 1995, Design of Ozone Systems for Cooling Towers, Engineered
Systems, April 1995.
Ozone, Kirk-Othmer Encyclopedia of Chemical Technology, Volume 16,
Third Edition, Copyright 1981, John Wiley and Sons, Inc.
Pacific Gas & Electric (PG&E). 1991. Evaluation of Ozone Technology
for Chemical Treatment Replacement in Cooling Towers (Power Plant
Systems): Final Report. Report 006.2-90.6, Pacific Gas and Electric
Company, San Ramon, California.
Patel, Arvind B. 1995. Pollution Prevention in Cooling Tower Water
Treatment. DOE Pollution Prevention Conference XI, Knoxville, Tennessee,
May 16, 1995.
Pope, Daniel H., Lawrence W. Eichler, Thomas F. Coates, Jeffrey F.
Kramer, and Reginald J. Soracco. 1984. "The Effect of Ozone on Legionella
pneumophila and Other Bacterial Populations in Cooling Towers." Current
Pryor, A.E., T.E. Buffum, "A New Practical Index for Predicting Safe
Maximum Operating Cycles in Ozonated Cooling Towers," Ozone Science
& Engineering, 17, 71-96, 1995.
Puckorius, Paul R. 1993. "Ozone Use in Cooling Tower Systems - Current
Guidelines - Where It Works." Ozone Science & Engineering 15:81-93.
Stumm, W., J.J. Morgan, "Aquatic Chemistry." 2nd Ed., John Wiley &
Sons, New York, NY, 1981.
Soeyink, V.L., D. Jenkins, "Water Chemistry," pp76-79, J. Wiley &
Sons, Inc., New York, NY, 1980.
Tierney, D.J. Cooling Tower Ozone Treatment at Kennedy Space Center.
EGG-8600/BOC-125 Tierney 407-867-1190.
Tierney, D.J., R.A. Mott. Ozone V. Chemical Treatment of Cooling Towers
at Kennedy Space Center: A Progress Report. Tierney 407-867-1190.
Tierney, D.J., E.S. Feeney, R.A. Mott. Case History: Performance Evaluation
of Ozone Cooling Water Treatment at Kennedy Space Center. Tierney
Wattinger, Ralph. 1993. "Ozone: An Environmentally Beneficial Means
of Treating Cooling Tower Water." Presented at the 2nd International
Energy and Environmental Congress, Minneapolis, Minnesota, August
4-5, 1993. REZ-TEK International, Inc., Mountaindale, New York.
Weisstuch, A., D.A. Carter, C.C. Nathan. 1971, Chelation Compounds
as Cooling Water Corrosion Inhibitors, National Association of Corrosion
Utility, Information Service, or Government Agency Technology
City of San Jose. 1992. Water Conservation Guide for Cooling Towers.
Environmental Services Department, City of San Jose, California.
Electric Power Research Institute (EPRI). 1992. TechApplication: Ozonation
of Cooling Tower Water. No.3, EPRI Industrial Program--Environmental
and Energy Management.
Electric Power Research Institute (EPRI). 1992. Ozonation of Cooling
Tower Water: An Alternative Treatment Technology. BR-100426, Electric
Power Research Institute, Palo Alto, California.
International Ozone Association. 1994. Ozone News 22:5 (1994).
Appendix A: Cooling Tower
Engineering Data Worksheet
Appendix B: Federal Life-Cycle
Costing Procedures and the BLCC Software
Produced for the U.S. Department of Energy by the Pacific Northwest