| UV Disinfection, A Growing Trend In Safe Water When properly designed and maintained, UV disinfection is an effective technology to keep drinking water safe. UV disinfection systems can provide an alternative to conventional chemical chlorine disinfection, and can also provide an additional barrier to protect against harmful bacteria, viruses and parasites.The UV system design is simple. Its main component is a UV lamp enclosed in a protective quartz sleeve. As the water flows past the UV lamp, the microorganisms are exposed to a lethal dose of UV energy similar to the radiation given off by the sun. UV treatment doesn’t chemically alter the water as nothing is being added to the water except energy. UV systems do not remove chemicals, organics or particles from the water. One of the main advantages of using UV disinfection is that disinfection-by-products (DBPs) are not created when treating waters with a high organic content as can occur when using chlorine disinfection. Disinfection-by-products, such as trihalomethanes, are a concern as long-term exposure is a potential cancer risk. Another advantage of using a UV disinfection unit is that it is simple to install, operate and maintain. The main disadvantage
associated with using UV disinfection is there is no residual
protection downstream as with chlorine disinfection. With UV treatment,
bacteria is only destroyed at one point in the water distribution
system. Thus, UV is often the last device in a treatment train,
being located as close to the point-of-use as possible. There are two important variables in successfully disinfecting with a UV: the water quality and flowrate. If the water is too cloudy, dirty or colored, the UV rays cannot properly penetrate through the water to kill the bacteria. In this case, proper pretreatment is necessary before the water can be properly disinfected. If the flowrate is too high, water will flow past the lamp without enough UV exposure time to properly kill or inactivate the disease-causing organisms. All UV systems have a maximum flowrate capacity that must not be exceeded. Other important system design issues are flow control and electrical connections. It’s important to prevent untreated water from flowing through the UV unit in the event of a power failure. This can be prevented with the use of a solenoid valve. UV units must also be plugged-in to a dedicated circuit within the household wiring as electrical fluctuations caused by pumps and freezers can cause damage to the UV ballast and bulb. UV lamps gradually lose effectiveness with use, so UV lamps should be replaced at least once a year . Rather than burning out as fluorescent lamps do, the UV lamps solarize, which reduces their UV intensity to a dosage too low to kill bacteria effectively. To maintain effective UV light exposure to the water, the glass around the lamp must also be cleaned regularly. As water passes through the unit, minerals, debris, and other material in the water will deposit onto the quartz or Teflon glass sleeve. This limits the amount of UV radiation that can penetrate through the glass into the water. Cleaning frequency depends on water quality. For example, water treated by a reverse osmosis membrane will require minimal cleaning since the water is highly purified. UV systems are designed for continuous operation and should be shut down only if treatment is not needed for several days. If the flowrate is too low, or the system is not in use for an extended period of time, heat may build up which can damage the UV lamp. Plumbing systems should be throughly flushed following a period of no use. A few minutes is required to warm the lamp prior to operation following a shutdown. Whenever the system is serviced, the entire plumbing system should be disinfected with a chemical such as chlorine prior to relying on the UV system for disinfection. The plumbing following
the UV unit will need to be periodically sanitized with a chemical
disinfectant since the UV unit doesn’t provide any chemical
residual for disinfection. The water should be sampled and tested
for coliform and bacterial counts regularly to determine the frequency
of sanitization required for the plumbing. |