The disinfection process is certainly one of the most important steps in achieving a safe pathogen-free source for any daily household drinking water demands. One of the most common misconceptions is that if a water source tests negative for bacteria contamination at any given point, it is assumed that the source will continue to yield favorable results in the future. This is not always the case. Something as brief as a heavy rainstorm may wash contaminants into previously unexposed sources, altering the condition of the supply. It is important to educate the consumer that the sole responsibility of the quality of his drinking water relies upon cooperation with his local water treatment specialist in regard to periodic water sampling and performing any preventive maintenance required to ensure continual optimum performance from any water treatment equipment.
Currently, several methods of disinfection are available including chlorination, distillation, ozonation and ultraviolet (UV) disinfection. UV technology, although seemingly new as a bacterial safeguard, has been recognized as a means of water disinfection for quite some time. In fact, federal guidelines were established in April of 1966 regarding the specifics for UV equipment as a means of disinfection. Many states have incorporated their own standards for UV equipment that are solely or partially based on the 1966 Policy Statement on the Use of the UV Process for Disinfection of Water. Contact state and local health officials for current guidelines and regulations.
What is UV?
UV energy is germicidal especially at the level of 2,537-Angstrom units or more commonly known as 254 nm (nanometers). Its effect is the result of the ability of the UV light to penetrate the organisms cytoplasmic membrane (protective layer) and attack the deoxyribonucleic acid (DNA) structure. The DNA is photochemically altered, damaging the cell by disabling its self-reproductive abilities, rendering the cell lifeless.
Why Use UV?
UV disinfection offers many practical advantages over other current methods of water treatment. UV light is a point of contact disinfection process. What this means is that no additional chemicals are required for the process, the taste of the water is not altered in any way by this process. In fact nothing is added to the water and nothing is taken away from the water, whereas with the use of chlorine there is growing concern of harmful side effects and the by-products produced such as trihalomethanes. It is impossible to over treat water with UV; the more UV exposure, the higher the safety margin. There is minimal maintenance required for a typical UV system (typically, they are serviced annually). Power consumption is minimal with the average 10 gpm household UV system costing approximately $2.50 each month in electricity cost.
UV equipment is so compact and easy to install it is perfect for confined spaces and easily adaptable to new and existing water systems. Comparatively, UV systems are economical for the consumer not only in the initial investment but also in routine maintenance.
Typical Household System
UV equipment comes in all shapes and sizes. Equipment is designed to mount either horizontally or vertically. Some options available today include quartz wiper systems, which allow quartz sleeve maintenance without removing the sleeve. UV intensity monitors are another option available. These monitors show the amount of UV energy inside the reaction chamber at any given time. Most UV monitors are designed that when a low reading occurs, devices such as solenoid valves are activated and shut off the water supply. Other options include elapsed time meters, remote alarm connections and flow controls.
UV systems designed for the home should be built to last. Most whole house systems are composed of the following components.
- Minimum 30,000 Micro-Watt/cm2 UV dosage at the end of lamp life.
- 304 SS pressure vessel.
- Heavy duty quartz sleeve.
- Low pressure UV lamp.
- Standard pipe fitting connections.
- Flow controls to maximize UV exposure time.
- Audio and visual alarms to provide quick assurance of operation.
- Easy access for mounting and maintenance service.
Installation of a UV disinfection system is easy. The system always is installed after any other water treatment equipment including pressure tanks, filters, water softeners and RO systems. Installation occurs right before the piping breaks off to distribute water throughout the house.
When installing the UV system, it is important to bear in mind the service requirements of the system. Allow enough service area to remove the UV lamp and the quartz sleeve. Also remember to locate the system near an electrical outlet (GFI outlets are recommended). Follow any mounting instructions for the equipment. Use plumbing unions to connect the equipment to pipes. This allows easy replacement or service in the future. Use shut off valves before and after the equipment to isolate the equipment and minimal water drainage during service. A boiler drain valve on the piping at the bottom of the unit will create a quick drainage of the UV disinfection chamber.
Once the necessary plumbing connections have been made, it is time to install the quartz sleeve. The quartz sleeve protects and insulates the lamp from the water and cold temperatures. The quartz sleeves are available in two distinct types—domed and open—referring to the quartz sleeve style. Domed quartz has one open end; its shape resembles a test tube. An open quartz sleeve has two open ends. Install the sleeve into the equipment (refer to the owners manual for specifics); if the quartz is domed, one O-ring will be necessary to complete the water-tight seal and if the quartz is open, two O-rings will be required (one for each end).
Then it is time to test the system to ensure all seals and plumbing connections are watertight. Do not plug the system in until you have verified that there are no leaks.
Next, install the UV lamp. UV lamps have connection pins on either one or both ends. Handle UV lamps by the bases (ceramic sections) to ensure that no fingerprints or contaminants get on the lamp surface. (If a UV lamp does not appear clean, use rubbing alcohol and a cotton cloth to clean it.) Insert the UV lamp into the quartz sleeve and make all electrical connections. Re-apply any access covers to complete installation.
After installation, it is important to sanitize all downstream piping prior to start-up.
Most UV systems are designed for the ease of service. Maintenance is usually limited to an annual change out of the UV lamp and cleaning of the quartz sleeve. Depending on the water quality and pretreatment equipment, the quartz sleeve cleaning may be more frequent.
UV lamps typically need to be replaced every 9,000 hours or approximately once a year. The reason for this is that while the UV lamp is in operation creating the UV waves, the mercury vapor that is produced inside the UV lamp oxidizes and plates itself to the interior. Over time this process diminishes the amount of UV energy that can be transmitted by the lamp and through the water. At the end of 9,000 hours, a typical UV lamp is emitting approximately 40 percent less UV energy than it did at 100 hours of operation. When finished, properly dispose of UV lamps; most manufacturers have recycling programs.
Quartz sleeves should be cleaned at least once a year. It is important for the quartz to be as clean as possible as any particles or scale may refract the UV rays and prevent proper transmission into the water. It is possible to clean the quartz sleeve with a dry cotton cloth, but sometimes dish detergent may be required. If there is mineral build up or scaling, use citric acid (usually found in a hardware/plumbing store). If the quartz sleeve is unable to be thoroughly cleaned, then it must be replaced.
Completing the System
Water softeners and UV. One of the more common water problems is hardness, a problem that produces white/gray scale deposits to the interior surfaces of household plumbing such as faucets, water heaters and other surfaces the water may come in contact with including UV disinfection systems. Water softeners are used to remove hardness (calcium and magnesium) and other minerals from the water supply. The water softener is applied as pretreatment. If the hardness levels are too high and no softener is installed, the calcium and magnesium may bond to the quartz sleeve over time reducing the ability of the UV energy to radiate throughout the reaction chamber. Water softeners offer the consumer higher quality water while at the same time enhance the performance of any water treatment equipment. It is important to remember that when a softener is installed on a chlorinated line, more often than not filters are put in place to remove the chlorine as it will damage some of the media used in softeners. This means there is no longer a means of disinfection on that system. A UV system will give adequate protection from possible bacterial growth in this scenario.
Reverse osmosis and UV. Point of use RO equipment is capable of producing very high quality water but at a slow rate. Because of the low water output, the water produced is stored in a holding tank. A small point of use UV system will ensure that the water flowing from the holding tank is free from any harmful bacteria. UV applied to pretreatment of an RO system assists in preventing premature bacterial fouling or failure of the RO membrane. By providing the UV pretreatment, the consumer can expect long-term cost savings by extending the life and effectiveness of the RO membrane.
Filters and UV. Most well water applications utilize at least one filter in the delivery process of the water. Usually this filter will be a sediment filter (a minimal 5-micron rating is recommended for use with UV systems) or of the type guarding against any loose particles/suspended solids in the water system. It also is common to find a carbon filter in use to reduce any unwanted tastes or odors that may be present. Filters as well as other standard equipment are excellent breeding grounds for bacteria. UV treatment installed after any filter will safeguard against unwanted harmful bacteria.
The application of a household UV system does not necessarily stem from a positive bacteria test. Installation of a UV system offers the consumer the satisfaction and reassurance that necessary measures have been taken to ensure that the water has been treated to disinfect against harmful bacteria that may be present in the drinking water supply.