About the author: Adam Donnellan is vice president of Sunlight Systems, in Allendale, N.J. He can be reached at [email protected].
Adam Donnellan, Sunlight Systems
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The benefits of ultraviolet (UV) light in destroying waterborne diseases are well established. In fact, the industrial world was one
of the first users of the technology.
Today, almost all industries have integrated UV into the water system infrastructure. These include food and beverage, pharmaceutical, cosmetics, healthcare, manufacturing, high tech and a host of others.
While germicidal water and wastewater disinfection are the primary use, the industrial marketplace has found other uses for UV light technology. These include ozone destruction, total organic carbon (TOC) reduction, liquid sugar disinfection, chlorine reduction, surface and air disinfection and cooling towers.
This article will provide an overview
of each of these “other” uses.
Germicidal Overview
For germicidal applications, water is exposed to UV light in the 254 nm wavelength. The light targets the
DNA, the very life center of a cell. Exposure to even low doses of UV
light scrambles the DNA, which prevents reproduction. This inability to reproduce renders the microbe harmless and, for all intents and purposes, “dead.”
As with all UV light applications, the sizing of the system is a function of intensity (lamp strength and efficiency) ¥ residence time (the amount of time that the water, liquid or air is exposed to the light).
Ozone Destruction
Industry has found ozone to be highly effective at sanitizing and treating process waters. Due to ozone’s excellent oxidization powers and the fact that it is a residual, it is often necessary to remove the ozone before it enters the main process loop.
UV light in the same 254 nm germicidal wavelength also is effective at destroying ozone residuals. UV light decomposes the ozone to oxygen. While sizing varies, a typical ozone destruct system requires three times the UV output of a traditional germicidal system.
Total Organic Carbon Reduction
In many high tech and laboratory settings, organics can interfere with the production of high purity water. There are a number of ways to remove organics from the water. Some of the more popular include activated carbon and reverse osmosis.
UV light in a lower wavelength
(185 nm) is effective at reducing
TOC (note that these lamps also produce 254 nm and, therefore,
are providing germicidal protection
as well). The lower wavelength
carries more energy and is able to decompose the organics. This occurs through the creation of what is known as a hydroxyl-free radical. While extremely complex, it basically oxidizes the organics into water
and carbon dioxide molecules. As
with the ozone destruction, these systems are sized three to four
times the output of a traditional germicidal system.
Liquid Sugar
Most food and beverage companies
use large quantities of liquid sugar. The sugar creates a breeding ground for bacteria due to the ample food supply. Since liquid sugar is opaque,
it is difficult to disinfect.
UV light in the 254 nm range will disinfect the product. In order to compensate for the thickness and
color of the liquid, the UV lamps
are spaced tightly together to form what is known as a “thin film” reactor. The close proximity of the lamps allows the UV light to effectively
treat the liquid. These units require extremely high doses of UV that
range from seven to 10 times the output of a traditional system.
Chlorine Destruction
As municipalities continue to add
large quantities of chorine to their water supplies, manufacturers are dealing with ways to remove it. The primary ways to remove chlorine is through activated carbon beds or through chemical treatment. The downside of carbon treatment is that
it needs to be regenerated and often becomes a breeding ground for microorganisms.
UV light in the 185 nm and 254 nm has been proven effective at breaking the chemical bonds of chlorine and chloramines. While it takes massive amounts of UV energy to perform the function, it does have some benefits. The benefits are that it does not add anything to the water; that there is no need for chemical storage; it is easy to maintain; and it also destroys bacteria and organics.
Surface and Air Disinfection
UV light has been used in air disinfection for as long as it has been used in water. Air disinfection units have been used in hospitals, clinics and clean rooms for many years. Today, the trend is moving into the plant, office and home.
The same water disinfection mechanisms are used in air. Basically, UV lights are installed into the ductwork, in front of coils or in wall-mounted fixtures. As air passes by, airborne microorganisms are rendered harmless. The same is true for surface disinfection. Surface disinfection is used in the food and beverage industries to disinfect products as they pass by on conveyors.
Cooling Towers
In order to cut down on the expense of biocides (purchasing, storage and insurance) as well as the health issues associated with chemical treatment, UV systems are being installed into cooling tower loops.
In combination with a filter, UV can control the biogrowth in both large
and small loops. While a residual is required, the use of biocides can be dramatically lowered.
The preceding applications have provided you with a basic overview
of the various applications in this growing field.
