Cryptosporidium parvum is a parasitic organism that has been identified as one of the leading causes of waterborne illness in the U.S.
Commonly referred to as “crypto,” it lives in the intestinal tracts of humans or animals, and is shed from the infected organism’s stool. In the spore phase of its life cycle, cryptosporidium is protected by a tough outer shell, or oocyst, which allows it to survive outside the body for extended periods of time. Ingestion of a single oocyst can be enough to cause a cryptosporidiosis infection in humans, and infected individuals will continue to shed crypto oocysts weeks after their symptoms resolve, increasing the likelihood of person-to-person secondary and tertiary infections.
Young children, pregnant women and immunocompromised individuals are especially vulnerable to serious illness resulting from this infection.
In recent decades, cryptosporidium infections transmitted via exposure to recreational water have caused illness in thousands of individuals. In 2005, a waterpark in Seneca Falls, N.Y., was found to have two water storage tanks infected with cryptosporidium, causing more than 3,800 people to develop symptoms of cryptosporidiosis and resulting in a year-long closure of the park and a $5 million class-action lawsuit. This event led to the development of increased regulations regarding safety and sanitation at waterparks in New York state and elsewhere across the United States.
Cryptosporidium’s protective oocyst also makes it extremely resistant to chlorine disinfection. In fact, crypto can remain active in a well-maintained pool or spraypad for many days.
Luckily, secondary disinfection methods such as UV, ozone and advanced oxidant disinfection have been shown to be effective in killing and inactivating crypto oocysts at rates reaching or exceeding 99.9 percent. Understanding the treatment systems available and how to select a correctly sized NSF/ANSI 50-certified treatment system appropriate for each pool or spa application is key to preventing cryptosporidiosis outbreaks and to maintaining a safe and healthy facility.
Ultraviolet (UV) Disinfection
UV systems are typically installed after the pool filter. They generate high energy, short wavelength ultraviolet light within the 200-300 nanometer wavelength range. Influent water is continuously pumped through the reactor, where it is exposed to UV lamps shielded behind quartz sleeves. When bacteria, viruses and protozoa (such as cryptosporidium) in the influent water are exposed to this short wavelength light, the energy emitted is absorbed by the cell’s DNA or RNA, and cross-links are formed between adjacent nucleotides within the DNA or RNA molecule. Accumulation of these cross-links prevents the ability of the DNA or RNA to be replicated, which in turn eliminates the microorganism’s ability to reproduce and infect. An effective UV system will result in at least a 3-log (99.9 percent) reduction or inactivation of cryptosporidium in a single pass of water through the system. UV irradiation of pool water also provides the added benefits of breaking down chloramines.
Ozone is an unstable molecule with the chemical formula O3. In the lower atmosphere, ozone quickly breaks down to normal molecular oxygen (O2). During this transition, a free oxygen atom, or free radical, is formed. Under normal conditions, this free radical will only survive for milliseconds. Ozone is very unstable and it will degrade over a short time frame (half-life). Ozone is a powerful oxidizing agent. This property imparts ozone with the ability to kill bacteria, viruses and cysts such as cryptosporidium by destroying their cell walls and all other essential components of the organism, including enzymes, proteins, RNA and DNA. In addition to its ability to kill microorganisms, ozone also is able to oxidize and destroy chloramines, and causes microflocculation of organic and mineral contaminants, which then can be removed by the pool or spa filter.
Due to its short half-life, ozone cannot be transported and therefore must be generated on site for use in pools and spas. Ozone can be created from oxygen with the introduction of an outside energy source. Two methods of ozone production typically are used: corona discharge and ultraviolet light.
• Corona discharge (CD) ozone generators function by simulating lightning in the atmosphere. Air or purified oxygen gas is exposed to multiple high-voltage electrical discharges, creating a ring (or corona) of energy. As the feed gas flows through this ring, some of the oxygen molecules split apart and reassemble with O2 to form O3, or ozone.
• Ultraviolet light ozone generators, by contrast, simulate solar UV light. Air or purified oxygen gas is passed over UV lamps, and the energy from the lamps splits the oxygen molecules in the gas stream. The resulting single oxygen atoms recombine with O2 molecules to form the more stable O3 (ozone). UV ozone generators typically produce a lower output and concentration of ozone than CD ozone generators, so they are less common in larger commercial pools.
After generation, ozone is typically introduced into the circulation water via a venturi injection system located downstream of all operating equipment, but before the primary disinfectant injection point. In many applications, the ozone is introduced into a sidestream of the circulation water. The system is designed to allow the ozonated water sufficient contact time with the water to be treated.
Advanced Oxidation Technologies
Recent advances in recreational water disinfection systems have led to the creation of systems that utilize UV and ozone technologies. These technologies are known as advanced oxidation technologies.
For recreational water applications, advanced oxidation process (AOP) is most commonly the conversion of ozone by UV rays to form high-energy hydroxyl radicals that are able to efficiently disinfect the pool water. Hydroxyl radicals are another form of powerful oxidizer that can oxidize and destroy bacteria, viruses and cysts, as well as other organic compounds. AOP produces a short-term active residual, as well as the longer half-life hydrogen peroxide, which provides a measurably increased ORP.
Advanced oxidation systems typically combine a CD ozone generator with downstream germicidal UV lamps. Ozone is generated, mixed with a stream of water and then exposed to germicidal UV light. This produces hydroxyl radicals as well as hydrogen peroxide.
These newer technologies can be beneficial in applications where traditional UV or ozone treatment is insufficient to meet the system’s needs.
NSF International tests and certifies UV and ozone generation systems to NSF/ANSI 50 to ensure that they function effectively and do not pose risks to health and safety. Systems certified to NSF/ANSI 50 meet standard requirements for:
• Cleanability• Design pressure and hydrostatic pressure
• Head loss
• Basic design requirements
• Ozone destruct capabilities for ozone generators
• Complete operation instructions
• Disinfection efficacy demonstrating 3-log (99.9 percent) reduction of influent bacteria
• Operational protection
• Chemical resistance
• Output, pressure, and efficacy following 3,000 operating hours
Additionally, UV or ozone systems that claim inactivation of cysts such as cryptosporidium parvum must demonstrate a minimum 3-log (99.9 percent) inactivation of cryptosporidium parvum in a single pass.
The standard joint committee that oversees the maintenance of NSF/ANSI 50 has convened a task group to define performance requirements and testing criteria for advanced oxidation systems. Once in place, these criteria will provide a means to validate the performance and disinfection efficacy of this promising new technology.
When choosing any UV, ozone or advanced oxidation system, operators should consider the type of pool and the water volume and turnover rate. Additionally, operators of sprayparks or other high-risk venues should consider selecting a system with a greater cryptosporidium parvum inactivation efficacy of 4-log (99.99 percent).
You can find NSF-certified UV, ozone and advanced oxidation systems that comply with NSF/ANSI 50 on NSF’s official product listings: www.nsf.org/certified/pools.