UV And Ozone Systems
Across the United States, several water recreational facilities are facing class-action lawsuits because their patrons became infected with cryptosporidium. Cryptosporidium is a parasite that is released into the water in the form of oocysts from a person who is experiencing or has had diarrhea within a two-week time frame, or has poor personal or poolside hygiene.
In fact, the number of cryptosporidium cases reported to the Centers for Disease Control and Prevention (CDC) has risen substantially in recent years. According to CDC data, “in 2005, 2006, and 2007 the number of non-outbreak-related crypto cases rose 41 percent, 24 percent, and 66 percent, respectively.” Additionally, considerable increases in outbreaks associated with recreational pools and water parks were recorded in 2006 and 2007.
Seeking A Solution
More water venues are selecting ultraviolet (UV) or ozone systems as their primary water sanitation because, although chlorine is a satisfactory secondary disinfectant, it does not do an adequate job of inactivating cryptosporidium.
“People who have had diarrhea in the last few weeks shouldn't be swimming in the water,” says Tom Lachocki, CEO of the National Swimming Pool Foundation. “Even if they don't have an accident in the pool, the cryptosporidium could be released.”
UV And Ozone To The Rescue
“UV and ozone play a very important role in disinfection,” says Beth Hamlin of ozone equipment manufacturer DEL Ozone. “In fact, with the two of them together, you get knock-your-socks-off technology for anti-microbial disinfection and destroying chloramines.”
"Both ozone and UV are strong oxidizers and are very effective at inactivating almost anything," says Lachocki. "Oxidation changes the chemicals in the water, making them easier to remove by filtration which improves water quality."
Oxidation is a chemical reaction that changes the structure of organics and inorganics dissolved in the water, causing them to be either eliminated or precipitated out of the water through a filtration system.
A UV system works by exposing the water directly to ultraviolet light in the germicidal range (UVc), which is light in the wavelength range between 250-300 nanometers (nm). The water is exposed to a dose of UV energy that breaks down the cell walls, preventing bacteria and viruses from replicating. There are two different types of UV systems--low and medium pressure. Low-pressure UV light operates at 254 nm, whereas medium-pressure UV light operates in the range of 250 to 350 nm.
"We use a medium pressure," says Kevin Shannon, vice president of sales with Aquionics, a supplier of ultraviolet and water treatment and disinfection equipment. “It provides a broader spectrum for disinfection. A medium pressure unit provides 250 to 300 nm wavelength, and has a better performance and faster reaction." Simply put--a medium-pressure UV system does a better job of breaking all the bonds in the cell, making it incapable of repairing or replicating.
The water passes through the pumps and filters before it continues through the UV system, which looks similar to fluorescent ceiling lamps, except that the lamps are housed in quartz sleeves to protect the electrical components from the water.
Only the water that is exposed to UV is sanitized; therefore, a secondary sanitizer is required. "UV systems are always used with residual chlorine or secondary sanitizers," says Shannon. "You’ll use less chlorine with the UV systems."
If your facility decides to purchase a UV system, Shannon suggests that you find a company with years of experience with sizing and installing. “There are a lot of companies entering the market today,” says Shannon. “You need to have someone who can properly size the system, which includes the calculation of flow, energy transmittance through the water, and dosage of UV needed to reach the log value or disinfect the water.”
Shannon also advises that the unit be installed with an automatic wiper--a device that clears the quartz tubes housing the lamps--because this decreases the amount of maintenance that will be needed for the unit.
Ozone is created when concentrated oxygen is exposed to a corona discharge in which dried air passes through high-voltage electrical energy, or a 185-nm wavelength UV light is used. “Typically, ozone generators from corona discharge are going to be able to produce a higher yield of ozone gas than those that are using a UV light system,” says Marc DeBrum, sales engineer with ClearWater Tech LLC, a manufacturer of commercial ozone generators.
Oxygen (O2) is split, forming two oxygen molecules (O). These molecules then attach to an O2 to form O3, or ozone. The third oxygen molecule is held only by a weak bond, and will readily attach itself to anything--including cryptosporidium. The released oxygen molecules then oxidize and destroy the tough shell of the oocyst, making it unable to replicate.
“The ozone is dissolved in the water, and when it comes in contact with organic or inorganic material, the ozone breaks down the cell walls of the organism and destroys or inactivates the organism,” says DeBrum.
The ozone system works by a portion of the water flow being diverted, injected with ozone, and retained in a contact vessel for a set period of time to allow for the ozone to oxidize and inactivate the contaminants. To determine the dosage rate, DeBrum calculates the maximum bather load, the size of the pool in gallons and the amount of time required to fully recycle the water once.
“Ozone is much more effective and one-and-a-half times faster-acting than chlorine is in oxidizing and inactivating cryptosporidium,” says DeBrum. "Chlorine sanitation systems have a problem with inactivating cryptosporidium because of the high CT value required of the chlorine to produce a significant log reduction of the cryptosporidium.” The CT value is the concentration of the sanitizer multiplied by the time it needs to be in contact with the water to disinfect it.
“An important factor to look for in a system is the gas transfer and mixture of the ozone gas into the water,” says DeBrum. “Ozone has different levels of concentration, and the higher concentration of ozone gas in the water the better.”
To achieve a higher concentration and yield of ozone, it is essential to properly prepare the air entering the ozone generator. Dry air systems can deliver 20 percent ambient oxygen, whereas an oxygen concentrator can filter out the moisture and nitrogen to deliver up to 95 percent pure oxygen to the generator. The higher the concentration of oxygen entering the ozone generator, the higher the yield and concentration of ozone produced.
Bathers commonly complain of red, itchy eyes, itchy skin and that not-so-appealing smell of chlorine, all of which can be attributed to chloramines. "Chloramines are a carcinogenic byproduct of chlorine sanitation, and for health and safety factors you need to get rid of them," says DeBrum.
UV and ozone systems both oxidize the chloramines, improving water quality and clarity as well as air quality within an indoor facility.
Recreational Water Illness (RWI)
Selecting a UV or ozone system is dependent upon the facility, budget and space restrictions. However, industry leaders advise that facilities need to provide better protection for their patrons, or risk facing class-action lawsuits when outbreaks of recreational water illness occur.
Tammy York is president of LandShark Communications LLC in Greater Cincinnati. She left her state public relations position to pursue her passion for outdoor recreation and marketing. Her upcoming book, 60 Hikes within 60 Miles of Cincinnati, is due out in spring 2009. You may reach her at firstname.lastname@example.org