25 May 2005
already attached to a surface that the light cannot reach or for controlling (destroying)
anaerobic bacteria that live underneath deposits that the light cannot penetrate. This
technology has limited effectiveness with highly turbid water.
Magnetic and Electromagnetic Devices. Magnetic and electromagnetic
devices use an unproven technology based on the theory that magnetic fields change
the physics of water and the water impurities. Water is a polar molecule. Most water
impurities are positively or negatively charged ions. These are the physical properties
that the magnetic fields are supposed to act on and to alter. The magnetic device is
installed at a point where the water passes by, usually at a point where the water enters
the system. A claim made commonly by the manufacturer of the device is that calcium
carbonate scale, and possibly other scales, can be conditioned and often prevented.
Most of the literature fails to provide a performance envelope of various water qualities.
Most manufacturers also fail to mention how corrosion or microbiological control is
achieved or even addressed. Magnetic filters used to remove magnetic iron oxide have
been shown to work, as described in paragraph 8-2.5.
Electrostatic Devices. Electrostatic devices use an unproven technology
based on the theory that an electric field changes the physics of water or the water
impurities. Some manufacturers market their devices for scale control only. Other
manufacturers state, without providing adequate verification data, that these devices
address corrosion and microbiological concerns. Performance results are not included
Non-Traditional Water Treatment Chemical Devices
Ozone. Ozone (O3) is a chemical gas consisting of three atoms of oxygen.
It has been used in cooling tower water systems. Ozone is a very effective disinfectant
for the control of aerobic bacteria and is somewhat effective for sessile bacteria. Ozone
has been shown to have a limited and unpredictable effect on calcium carbonate scale.
The scale that may form does not adhere to heat exchange equipment, but rather forms
SS that can be removed with filtration. The performance envelope for prevention of
calcium carbonate scale on heat exchange equipment is very limited and is much less
than what is possible when using traditional chemical treatment. Ozone does not
prevent corrosion of most metals. It provides some reduction of mild steel corrosion, but
will increase the corrosion of copper at rates up to 10 times versus traditional chemical
treatment. Ozone also attacks galvanized steel. Increasing the level of ozone in water
increases the corrosiveness of the water. Levels of 0.1 mg/l or less are acceptable.
Ozone has a short half-life and must be generated on-site. Ozone-generating
equipment can have high capital costs. It is difficult to maintain an effective residual of
ozone throughout the entire cooling water system because of the extreme reactiveness
of ozone. It is also very volatile and can be lost from the system as the water passes
through the cooling water system, resulting in biomass within the tower fill.
Copper and Silver Ionizing Devices. Copper and silver ionizing devices
use copper and silver metal rods that are electrically corroded and thus put copper and
silver ions in the cooling water. Copper and silver ions are known microbiocides. Both