Nonchemical Alternatives to Cooling Tower Disinfection
Cooling towers are needed to dissipate heat, but the
complications arising in doing so are maintenance headaches and, in some
instances, disease-causing problems. Bio-slimes and algae growth can and have
caused bacterial contamination in cooling systems. Legionnaires disease and
pneumonia have been blamed for deaths and traced back to cooling systems. Water
and air can transport many pathogens and are responsible for a host of problems
related to inadequate disinfection. Chemicals are used in cooling tower systems
to control scale, bio-slimes and algae growth. These chemicals flocculate iron
and manganese from the influent water and contain biocides to control bacteria.
Softened water is not used because the mineral deposits cause scale and reduce
the effectiveness of the cooling coils, in addition to increasing maintenance
and labor costs at keeping the coils clean and operating efficiently. There are
alternatives on the market that when applied properly offer greater control of
Ozone and ionization have been used for many years to combat
scale and bacterial issues associated with cooling tower operation. Ozone has
not been as widely adopted as chemicals because many times it is not applied or
implemented correctly and the end user does not experience the intended
chemical reduction and smooth operation of the cooling system. Ultraviolet (UV)
light has been used to control bacteria, fungus and bio-slimes. Scaling issues
and maintenance due to improper application have hindered UV from being widely
accepted. By explaining some tips and tricks, maybe more water treatment
dealers can understand these technologies and use them in their arsenal of
It is estimated that there are 500,000 to 600,000 cooling
towers in the United States that use chemicals because they are accepted and
proven methods of treatment. Of the half million or more towers, it is
estimated only 300 to 1,000 use ozone and even less use copper ionization.
Cooling towers that use ozone, copper ionization or UV light in conjunction
with each other are very few and far between. Why, you may ask, if these
treatment methods work so well, are they not used more often? Cost is a big
factor in using ozone, copper ionization and UV. The initial start up costs are
expensive, but the return on investment is rather quick when properly installed
and monitored. Most water treatment dealers who do not understand the
technologies simply do not use them, or if they do one job and it fails, they
don't find out why and they stop selling these great alternatives to chemical
dosing. Whatever the case may be, these systems do work when applied correctly.
Every water treatment system that is employed needs to have
the influent water addressed in order to effectively design proper treatment.
There is more to water than total dissolved solids (TDS), hardness and iron,
which many dealers test as part of a free analysis. Other contaminants such as
manganese, chlorides, tannins and nitrates can change the way the designed
system functions. City water or municipal water supplies are easier to work
with than well water supplies, since the water is treated and contains mostly
hardness minerals and chlorine. Well water, on the other hand, makes water
treatment a challenge. Iron, manganese, chlorides, sulfates, nitrates and
tannins can make the treatment of cooling tower water very difficult. The
influent water needs to be closely analyzed so that it can be treated properly.
The flow rates and equipment used also must be matched mathematically in order
to function optimally.
One of the biggest mistakes made in treating cooling tower
water is not pretreating the influent water. For example, without the
pretreatment of water for reverse osmosis and UV light drinking water systems,
these water treatment methods fail or do not work effectively. So, why not
treat cooling water in the same fashion. If there is iron and manganese in the
water, why treat the water after it is in the make up tank? Maybe chemicals
seem to cost less than removing the iron and manganese with filtration, but
after looking at labor, chemicals and blow down discharge costs, removing the
contaminants with filtration can be very cost effective. Blow down usually is
done once the water reaches a set saturation or TDS level. Without the use of
chemicals the TDS would not rise and there would not be a need to discharge as
much water. This would reflect a cost savings on chemicals, labor and discharge
fees. Pretreatment also can save money when purchasing alternative methods of
treatment such as ozone, ionization and UV. With the elimination of iron and
manganese, the amount of ozone needed to treat the water would be reduced,
since the ozone would not have to react with the contaminants first to be
effective against bacteria, algae, and bio-slimes. Since ozone is an oxidizer
it reacts with other contaminants that are referred to as biological oxygen
demands (BODs) and chemical oxygen demands (CODs). By reducing the demands on the
ozone, the amount of ozone needed is reduced, which, in turn, decreases the
cost of using ozone as a treatment method. UV light would not have as much
scaling and maintenance involved. Copper ionization would work more effectively
since the copper would not be binding to the iron and would reduce the copper's
ability to control bacteria.
Now that the water is free from iron and manganese or other
contaminants that are removed by pretreatment, what do we do with hardness
minerals since softened water is not used? Some companies have used magnets to
combat this problem and have been very successful. However, the magnet
controversy within the water industry still prevails. Again, if matched
mathematically with flow rates and contaminant levels then this could be an
An even bigger benefit would be using copper ionization. Due
to its electrical charge, this type of treatment has good scale reducing
properties, and the small amount of copper in the water reduces bacteria and algae.
Copper ionization's benefits are two-fold. Hardness minerals from municipal and
well water supplies can be controlled with ionization and, if UV were
installed, ionization would help keep the quartz sleeves or coiled tubes that
protect the bulb from scaling. In some applications, ozone may not be as
effective at controlling scale.
Sizing equipment can be time consuming, and this is another
reason many water dealers have not pursued this market arena. There is nothing
more disconcerting than spending valuable time designing a system and proposing
a bid and not getting the sale. What is even worse is getting the job and
having the equipment not function properly and ending up with a discontented
customer because his capital investment will see no return. One missed variable
in the calculation can cause a multitude of problems in the future. Not
understanding how the technologies perform are other factors that contribute in
design flaws of using chemical alternatives. The influent water analysis, the
amount of water and the flow rates are three of the most important parameters
in treating any water supply, but the compatibility of the application and
technologies used play a significant role.
Unfortunately there are no easily understood "cut-and-dried"
formulas for sizing equipment. There are some existing formulas, but they are
ambiguous and not pertinent to every application. Parameters that must be
considered are the size of the cooling tower, which is measured in tons; the
amount of water that is in the makeup tank; the amount of water that is in the
distribution system; the amount of evaporation that will take place; the
climate to which the cooling tower is exposed; the amount of blow down; the
amount of influent water needed to replace evaporation on hot or cooler days;
the types of materials of which the system is constructed that are compatible
with ozone; where the unit will be placed; the injection points of the ozone,
UV light or copper for proper dispersion; and off gassing of the ozone. As we
can see, there are many variables in figuring the proper treatment, and one
missed variable can render the system ineffective.
Ozone does not leave a residual. If there are areas too far
from the injection point, the amount of ozone at these areas might not be
effective enough to kill the bacteria, thus bio-slimes can form. UV light does
not add anything to the water so if there are microorganisms that are not
destroyed they, too, can cause growth within the system. Copper ionization will
help in this control, but improper copper levels also can lead to problems.
Ozone needs to be monitored and controlled with ORP meters or redox controllers
to be the most effective. A little bit of ozone goes a long way, and by
controlling the levels of ozone, such problems as corrosion or the destroying
of pumps and gaskets can be minimal. Trying to determine water usage can be
tricky and must be carefully calculated. Measuring the tank and piping can give
good approximations of how much water is in the system, but evaporation will
vary greatly depending on climate and weather conditions to which the cooling
tower is subjected. The amount of blow down will be reduced since chemicals are
reduced and TDS levels will not increase as rapidly.
Consider the Option
Filtration, ozonation, copper ionization and UV light may
not be an option on some water supplies or applications, but their usefulness
and alternatives to chemical dosing should be considered as an option. Water
supplies with contaminants, which are hard to remove might be treatable only
with chemicals, although when these technological advancements are understood,
there are ways to use the positive benefits synergistically. There is not one
water treatment method on the market that is a cure for all water problems or
uses, but when employed with each other, these methods can be extraordinarily
advantageous for the application and customer's needs.
Knowledge Is Power
There are many ozone, copper ionization, filtration and UV
manufacturers in the marketplace that have used their products in cooling tower
applications. Each has his own idea on how his equipment performs, but when
used in conjunction with other technologies he sometimes can be misinformed or
not educated enough on the capabilities of how his equipment can benefit, when
used in conjunction with other technologies. Jumping on the bandwagon to treat
cooling towers would be a mistake for many water dealers that are going to try
and make a fast dollar. This process is time consuming and educationally
taxing. Many types of water are not going to be favorable to this type of
treatment and the cost factors are going to keep companies from using the
technology unless a return on investment can be established. The impact that
chemical alternatives will have on the environment is huge and very positive
worldwide. With persistence and determination, many water treatment
professionals will be successful.
Studying articles and books (some listed at the end of this
article) would be wise, and doing research with pilot testing is recommended. A
good background in chemistry, physics and microbiology is very beneficial in
deploying a good system design that will give a return on investment for the
consumer. Understanding how bio-films form and how the technologies work will
help avoid the pitfalls of disinfection with chemical alternatives.
Unfortunately, this column does not provide enough space for a full explanation
of using these types of systems on cooling towers. Consultation with experienced
professionals and manufacturers is recommended.
Roger. "The O-Zone'Today's Lesson: Well, Ozone Again," Water Quality
Products, December 2002.
Quality Association Task Force. Ozone: A Reference Manual, Water Quality
Association, Copyright 2002.
Additional reading may be found at www.waterinfocenter.com.