The U.S. Environmental Protection Agency’s (EPA) Water Infrastructure Resiliency and Finance Center, in collaboration with the...
The objective of ozone use with cooling towers is to
maintain the highest purity of water with the least amount of water waste and
chemical use. Chemical use in cooling towers leads to ever-increasing total
dissolved solids (TDS), which must be reduced by eliminating water (blow
down/bleed off) and then refilling with raw/lower TDS water. This is a vicious
circle that will never end unless one of the TDS-increasing culprits (a.k.a.
chemicals) is eliminated or reduced.
Cooling tower water quality tends to be extremely poor.
Cooling tower traditional treatment is based on extreme chemical use only. This
means that you, the water treatment professional, have a chance to create an
entirely new income base and aid in environmental integrity and responsibility.
There are three main problems surrounding cooling towers.
quality control is difficult due to
dependence is promoted by an industry that serves and maintains cooling towers.
Most cooling tower manufacturers do nothing about recommending or selling
treatment equipment along with the towers. In most cases, it is left up to the
end users to set up the treatment method. The cost of chemicals is lower on the
front end than water treatment equipment, but far higher based upon the ongoing
nature of the use.
water waste issue. For example, it is not uncommon to see a 3,000-gallon
cooling tower constantly draining water, then constantly replenishing raw water
just to lower TDS. This ever-increasing TDS is contributed to a great degree by
the chemicals that are used for treatment.
Not only is there an extreme amount of water being wasted on
a daily basis, but the environmental impact from the chemical-laden wastewater
is deplorable. This chemical-laden wastewater eventually will make its way into
our lakes, streams, rivers and groundwater. That is why this wastewater is
becoming the subject of more stringent U.S. Environmental Protection Agency
Ozone is used in cooling tower treatment for
running temperatures where scale is inhibited or reduced
or elimination chemicals needed for algae control
Ozone is injected into the water flow created by a separate
circulation pump. This pump pulls the water from the tower's sump or basin and
sends it to the ozone injector, contact tank and scale removal/filtration
system. Lastly, the treated water returns back to the sump or basin. The
principle is to treat the water and eliminate/reduce the following
The clean water then is used to clean the entire sump,
basin, pipes and peripheral equipment.
The ozone treatment system is simple and can be broken down
into three easy steps.
injection. Ozone is injected into the side stream flow. Oxidation starts to take
place immediately on microbes, organics, bacteria and viruses.
A contact tank helps to further the ozone's ability to oxidize particles
allowing them time to react prior to returning to the system. As water flows
down the off-gas tank, ozonated water rises and strips any gas in the incoming
water. (The off gas tank is the same design as what was discussed in my column
"Ozone Installation," February 2003, and "Well-Ozone
Again," December 2002, Water Quality Products.)
scale control, particle removal. Possibly the most important aspect of any
water treatment is the removal of the particles that have been oxidized.
Without this step, all you have done with the ozone is change the structure of
the particles by making them larger, insoluble and/or heavier. This step is
necessary for systems that require scale control and particulate removal.
It is very important not to construct an ozone unit too
large to handle the bacteria, scale and algae. The problem encountered at this
point could be corrosion. If you carry an ozone residual too high to de-scale
downline you stand a chance of creating a corrosive situation in the sump and
its adjacent equipment. For this reason, it's important to utilize existing
water treatment technology and equipment in conjunction with ozonation. The
result is a system that works without high maintenance, dangerous chemicals,
extreme water waste and costly corrosion.