What is Ultraviolet and How Does it Work?
Light is electromagnetic radiation, or radiant energy traveling in the form of waves. Ultraviolet (UV)
energy is found in the electromagnetic spectrum between visable light and x-rays and can best be
described as invisible radiation. The energy employed for UV water treatment is further categorized into
two primary levels measured as wavelengths, 254 nm and 185 nm, where nm = nanometer and 1 nm =
1/1000 of a micron.
UV systems feature low pressure mercury discharge lamps. These lamps are constructed with a
special quartz envelope material that looks like glass, but is actually a discriminating filter. This
exclusive design allows predominantly 254 nm or 185 nm UV energy to be transmitted into a water
stream as it flows through the UV system's treatment chamber.
All living organisms contain DNA which provides the mechanism for all functions needed to sustain life.
Cleaner Pools Industrial disinfection systems emit 254 nm UV light that penetrates the outer cell
membrane of microorganisms, passes through the cell body, reaches the DNA and alters the genetic
material. The organism is thereby destroyed in a non-chemical manner and is unable to reproduce.
How is Ultraviolet Applied to Cooling Towers and Recirculating Loops?
Cooling towers and recirculation loops, in general, have the distinction of being very dirty, warm,
aerated and bio-nutrient rich. Therefore, these heat exchanger loops are perfect incubators for
microorganism development. The fast growth and migration of organisms throughout the loop presents
an ongoing battle for maintenance engineers to control the rate and degree of growth. The facility
engineer would routinely fight this biological threat with the application of biocides. This is often a
considerable operational expense and can be somewhat technical to apply correctly.
Toxic biocides in the form of halogen or non-halogen (oxidizing or non-oxidizing) compounds, or ozone,
are used on a frequent or intermittent basis (some fed continuously) to control the rate of biological
growth in evaporative cooling loops.
Typically these products are fed into the system two, and sometimes three, times per week. The intent
is to maintain an organism growth range of 10^3 to 10^4 colony forming units per milliliter (cfu/ml) - by
using simple dip slides. The desired target range is the industry standard for gauging an acceptable
degree of biological control. When loops are in this control range, they are maintained in the most
chemically efficient and economically sound manner.
UV can substantially decrease the costs of a biocide program while addressing the many safety and
environmental issues associated with their use. By using simple filtration at 40 to 50 microns in
combination with UV on a sidestream to the main header, a facility can match or exceed the desired
microbial ranges mentioned above. 40 micron filtration will be tight enough to catch most particles that
would otherwise settle out of suspension in an exchanger, as well as to protect the UV quartz sleeves
from becoming dirty to the point of impacting light transmission values. Since water quality needs in the
cooling process are not high purity or as "critical" in nature, the condition of the sleeves is not as great
an issue as it would be in such applications as pharmaceutical and semiconductor grade water. Plants
should remember they are seeking control and not complete sanitization of water loops, which would be
technically and economically unfeasible.
Consumption rates of biocides, and therefore cost, is "site specific." They depend on many variables,
such as product selection (concentration/formulations, etc.), how it is applied (parts per million or ppm
residual desired, frequency required, etc.), equipment load, climate, tower design, hours of operation,
degree of organism infestation and water chemistry within the tower or loop. All these factors play a
primary role in expenditures.
The use of UV in conjunction with filtration, however, results in a much cleaner system, with constant
suppression of microorganism growth far below those achievable with chemical biocides. The cfu/ml in
the bulk stream can be easily maintained at 10^2 or less using this approach. The end result is a more
efficient, economical and environmentally friendly water treatment program-all within a very attractive
payback period.
Filtration keeps the entire loop cleaner, thereby minimizing dirt load and any likelihood of a fouled
condenser or exchange bundle. In most cases, an operator can simply forego tube brushing when
taking down the condenser. The biggest savings are in efficient electrical consumption with a cleaner
exchanger running within the design specifications. Even slight dirt deposits or biofilm can become a
large "hidden cost" of running a chemical treatment program. Further, dirt precipitation can act as an
organism breeding area and hinder a biocide's effectiveness, which will result in an increased demand
for the biocide product or render it unsuitable. In addition, the loop piping can also experience "under
deposit corrosion" as well.
Many cost considerations exist in applying a chemical program:
Hard Costs - direct product costs, disposal costs, etc.
Variable or Soft Costs - training, State and Federal compliance costs, water and products costs
dependent on equipment loads and on-line capacities, etc., and
Hidden or potential costs - civil and environmental liability, spills, medical costs, etc.
Some of these costs are less obvious than others and require some effort and honest appraisal to
determine. For this reason, payback periods and return on investment (ROI) on equipment packages is
"site specific
What are the Benefits of Ultraviolet?
UV can present a non-chemical alternative to an industry previously dependent solely upon
chemical solutions for microbial control. UV offers the following benefits:
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It adds nothing to the water but ultraviolet light
UV continuously provides protection as the equipment runs
UV can be neither overdosed or underdosed
UV is virtually maintenance free (lamps are changed once per year)
It is environmentally safe, with no chemicals to handle or discharge
It does not require government licenses, permits or training
UV is more "cost effective" than chemical biocides
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Benefits of Bag Filtration of Condenser Cooling Water Systems
Due to removal of suspended solids down to five microns or less, cooling tower basins and pump
strainers will have to be drained and cleaned less frequently due to a reduction of fouling and
deposition. Downtime is minimized and eliminated.
Most of all particulate matter drawn into the cooling system is removed at the lowest point in the
recirculation loop where deposition of mud, sludge and transported iron oxide is most severe.
Removal of potential foulants throughout the system enhances micro-biological and corrosion control.
Reduction of iron oxide which circulates throughout the cooling loop minimizes the potential for "underdeposit" and "erosion" corrosion.
Feed of oxidizing and non-oxidizing biocides can be reduced due to a permanent reduction of organic
debris in the system which act as nutrients or foodstuffs for algae, bacteria or fungi.
Use of dispersants to control organic and inorganic deposition can be minimized.
Absence of dirt or silt in the cooling system reduces the potential for the growth of slime on heat
exchange surfaces and the occurrence of Legionella species.
Overall improvement in the system cleanliness reduces the potential for microbiologically induced
corrosion (MIC), which may lead to severe metal pitting and piping failures.
Reduces restrictions in water distribution systems (spray headers, nozzles, distribution trays) which
promotes even flow and reduced "channeling" potential.
Maintains clean tower fill for consistent airflow and water velocity, which assures maximum heat
rejection.