Ultraviolet light has been used, and accepted, as a disinfectant for years. Microorganisms (for instance; Escherichia coli, Salmonella typhi, and Hepatitus A virus) are lethally affected when exposed to UV. However, not all species react to the same extent, and conditions vary depending upon the UV intensity and time (dose). Some microorganisms, for example waterborne protozoa, require such a very high dose of UV to be effective that filtration is still the recommended and most feasible means to disinfect. It is for these reasons that Harmsco has developed the Homeland Security Water Filters that utilize a multi-technology, flow through barrier cartridge filter along with a powerful ultraviolet disinfecting reactor in one convenient appliance.

The family of Harmsco's Homeland Security Water Filters consists of three different size models, 5, 10 & 15 gpm, and are selected based on need. For example, the 5 gpm model, HS-5, is intended for a single bedroom, single bathroom application. The 10gpm model, HS-10, is for a two bedroom/two bathroom, and the 15gpm, HS-15, is for a three bedroom/three bathroom. The filters can be plumbed in parallel for greater flow rates.

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Installation of these filters is recommended (intended) to be in one's household, just prior to point of entry, that is, downstream from any conditioning units. All units were designed to utilize pressure and flow from the supply source, city or well pump, thus negating the requirement of a booster pump.

Each model consists of a pressure vessel with two distinct compartments, an upper cartridge filter and a lower UV reactor, that are internally plumbed together. The upper filter compartment, or chamber, contains a sophisticated, single filtering cartridge element, and is accessed through a secure lockable, clampband closure. Vessel pressure is established by the engagement of the clampband closure with the housing, lid and the housing's sealing O-ring. The lower compartment contains two UV lamps that are enveloped by quartz sleeves and are seal mounted to the housing's sidewall. Access to the lamps is through the plumbed fittings engaged with the sleeves.

Cartridge: The cartridge element is a single unit comprised of three separate layers of filtering media. Water must flow through all three layers prior to entering the UV reactor. The first layer is a pre-filter that utilizes silver zeolite in the filtering media, and is to catch any rust, sediment or scales that may have migrated downstream from the water source. The silver zeolite protects the media from unwanted growth of bacteria and prevents the formation of biofilms. Unprotected pre-filters sometimes blind off due to these biofilms. The second layer is high quality activated carbon. Many consider activated carbon as the world's best adsorber of unwanted chemicals, such as disinfection by-products, and also improves the taste, odor, and the overall aesthetics of water. The third layer is an absolute, cyst rated, filter media, which provides a barrier to cysts that may have made it though the previous layers. This fine filtration also improves the turbidity of the water prior to the UV application.

All three Homeland Security models incorporate the patented Harmsco up-flow technology to evacuate the chamber of air and maximize the cartridge's effectiveness. Briefly described, water enters the housing and must first flow through all layers of the cartridge, rise to the top of the cartridge chamber, and then into a standpipe that leads downward to the UV reactor.

UV: Ultraviolet (UV) light, or radiation, is classified into three categories based on wavelength ranges; UV-A is from 315 to 400 nm, UV-B is from 280 to 315 nm, and UV-C is from 100 to to 280 nm. UV-C is germicidal, that is, it deactivates the DNA of bacteria, viruses and other microorganisms that could multiply and cause disease. Figure 1 shows the UV-C range and its corresponding germicidal relative effectiveness.

Harmsco incorporates low pressure mercury discharge lamps in the UV reactor of the "Homeland Security" product line because of their germicidal effect, UV-C output. These lamps are also made of a special glass, TUV, that filter out ozone-forming radiation, predominately the 185 nm wavelength. Ozone is highly reactive and has strong corrosive properties with downstream plumbing. Fig 2 illustrates the transmission characteristics of several glass materials including TUV.

Fig 3 shows the relative spectral power distribution of the TUV lamps and indicates that the primary radiation generated by these lamps consists almost exclusively of a spectral line at 254 nm, which is in the region of maximum disinfection (peak at approximately 265 nm., see Fig 1).

Ultraviolet dose is the product of UV intensity and time of contact and is expressed in mW•sec/cm2. The UV intensity is dependant on the strength of lamp(s) in watts and distance from source to target. And the time of contact is dependant upon flow rate and the reactor's shape. The reactor designed into the Homeland Security Water Filter is of a complex nature by incorporating two lamps that are angled to minimize/eliminate shadows, and to increase dose. Also, water is directed within the reactor to assure the highest contact time possible, and thus also maximizing UV dose. At 15 gpm, the Harmsco Homeland Security Water Filter UV reactor has been analyzed to deliver a UV dose of 26 mW•sec/cm2. In comparison, the NSF standard 55 for 3 log reductions in point-of-use water treatment devices is - 24.6 mW•sec/cm2.