I've Seen The Light

By Bob Kappel

What would you say if we told you that it is now possible to eliminate chloramines in your swimming pool without using chemicals? How much safer would you feel if we told you that all microorganisms that pass through the filtration system could be fully inactivated? What would you think if you were told you that the only task you had to perform to eliminate those pesky chlorination byproducts and germs was to flip a switch? Well, believe it or not, these things are possible; and it is all because of the magic of light – ultraviolet light to be specific. Follow me through PPOA’s first non-technical primer on the benefits of ultraviolet light technology.

Ultraviolet light, aka UV, comprises a small portion of the larger light spectrum. (Remember ROY G BIV from science class?) The range of our normal experience of light is: near Infrared (heat lamps); red, orange, yellow, green, blue, indigo, violet and, of course, ultraviolet (of tanning-lamp fame). UV can be further broken down into UVA, UVB, UVC and Vacuum UV. Each “color” of light can be organized by wavelength. A wavelength is simply a measurement used by scientists to describe the unique properties of each light color, based on their respective frequency.

The measurement unit of wavelength for light is called a nanometer (nm) which is 1/1,000,000,000 of a meter. Heat lamps produce relatively longer wavelengths in the range of 700-1000 nm. The visible light range falls in the range of 400 – 700 nm. UVA, which are the tanning rays of the sun, fall in the range of 315 – 400 nm. UVB, which are the burning rays of the sun, fall in the range of 280 – 315 nm. UVC, which are the cancer causing rays of the sun, fall in the range of 200 – 280 nm. Finally, there is vacuum UV which falls within the range of 100 – 200 nm. It is interesting to note that vacuum UV is absorbed quickly by water and by oxygen, and is the catalyst that forms ozone in our upper atmosphere.

Let’s first talk about microorganism inactivation. We’d like to be clear that UV does not kill an organism. It simply keeps it from replicating, which is the secret for biological success and the cause of illness. Our bodies’ immune systems can handle a small bunch of virus pathogens or a few cryptosporidium cysts, but when that organism propagates millions or billions of times our immune systems are overwhelmed and we get sick.

Remember, in our discussion above, UVC with a wavelength between 200 – 280 nm causes cancer? Well, it so happens that DNA and RNA, the key codes for replication, absorb UVC very well at 254 nm. This absorption scrambles the DNA and RNA in these pathogenic life forms, thereby preventing their normal replication (as with cells, in the case of cancer). For all practical purposes these critters are rendered sterile and harmless to us.

Now let’s talk about chloramine destruction. For all of us pool folks, there have traditionally been three chemical means to destroy chloramines: (1) breakpoint chlorination; (2) potassium monopersulfate addition; (3) ozone injection. All these processes involve typical chemical reactions. Add one chemical to another and you get a byproduct of that reaction. Now for the cool part… You can also achieve similar results by exposing a chemical to serious UV light. This process is called photochemistry. Simply stated, the light absorbed by a molecule can produce a change in the molecule. If there is enough power in the light and the light is of the right wavelength, we can change molecular structures without additional chemicals! The ramification of this fact is that if we expose chloramine-laden water to the right power and wavelength of light, we can break down the chloramines into less volatile and less irritating compounds!

The heart of any UV system is its lamp. There are many types of lamps but, for our discussion, we will limit them to two: low pressure and medium pressure. A typical UV lamp is similar in construction to the fluorescent lights we see in offices and homes every day. In this case, the glass tube contains mercury; when electricity is applied, the tube emits light. While a florescent lamp contains a white coating, a UV lamp does not. A low-pressure UV lamp has a relatively low pressure inside, considered a monochromatic lamp because it radiates UV light centered around one wavelength: 254 nm. Since DNA and RNA are scrambled best at 254 nm, a low pressure lamp will inactivate microorganisms well but will do nothing about our chloramine problem. “Medium pressure” lamps have a higher internal pressure, considered polychromatic because they have a very wide spectral output in the range of 180 – 315 nm. Not only will a medium-pressure lamp inactivate microorganisms but also will photochemically change monochloramines at 245 nm, dichloramines at 297 nm and nitrogen Trichloride at 260 nm! Wow!

There are some cautions we must make you aware of before we go further with our discussion. Not only must you choose the correct lamp type for your application but your lamp must radiate enough power to scramble the DNA/RNA and cause photochemical reactions. Not all organisms are created equal; enough lamp power at 254 nm might do a fine job scrambling the DNA of a cryptosporidium cyst but a Norwalk virus would swim by with its RNA intact, ready for attack! Likewise, certain chemical reactions are successful at certain moderate power levels while others require more power. It is generally accepted in the aquatics industry that the minimum UV power output for medium pressure to successfully destroy chloramine and inactivate microorganisms is 60 mJ/cm2. I will spare you the gory details of that power measurement. Suffice it to say that the higher the number is in mJ/cm2, the more powerful the output of the lamp. Another caution is that, just as in normal chemistry, the amount of time a chemical is in contact with another dictates the success of the reaction. The amount of time a chemical is exposed to UV light is obviously important.

It is, therefore, critical that the UV chamber is properly engineered to provide the maximum contact time possible. This is done with computer modeling. Yet another caution is the amount of suspended particles in the processed water. The larger the amount of suspended matter that is in your water, the more UV light is scattered, reflected and absorbed. This results in less inactivation and fewer photochemical reactions. Finally, if you have high levels of metals in your water such as iron, manganese, copper or calcium, the transparent quartz sleeve which encases the UV lamp can quickly become fouled. The photochemical reactions and the heat produced by medium pressure lamps – all of which lower the effectiveness of the UV light.

Another significant fact is that UV will never replace chlorine in the pool. It is a supplement. Remember, you can only treat the water that flows through the filtration system. Based on Gauge and Bidwell’s law of dilution, less than 50% of the pool water actually flows through the treatment system in one turnover. We still need to maintain adequate levels of oxidizer/sanitizer in the pool basin.

How effective is UV? Extremely effective! So effective, in fact, that drinking water and waste water treatment plants around the world are turning to UV for help inactivating pathogens and minimizing harmful disinfection byproducts. Swimming pool system designers are getting on the band wagon. Among those UV applications newly in use, we have not seen or heard of a single case of properly sized medium-pressure UV system failing to significantly reduce chloramines in a pool!

So when you are ready to take the leap into UV for your facility, make sure you know what you want to achieve. Select a well engineered product of the right type, size and features for your application. Take into account all the variables involved, from gallonage to organic load to turnover and sanitizer choice. Have your system installed by a qualified technician who can provide the proper training and service.

If you keep these things in mind, you too will see the light and your customers will love you for it.