Good, Better, Best
Molly McKain - August 9, 2016
Brief History of Water Disinfection
Evidence of water treatment has been found in ancient Greek and Sanskrit writings dating back to 2000 BC when boiling and physical filtration were the only methods known. At the time, water was only treated so it would taste better. Water safety did not become a concern until the 1670s when the invention of the microscope equipped scientists to view microorganisms in supposedly ‘clean’ water.
By the 1700s, domestic filters made of wool, sponge, and charcoal were gaining popularity and the world’s first municipal water treatment facility, based on slow sand filtration, was built in Scotland in 1804. The filtered water was delivered by horse-drawn carts until water distribution pipes were installed three years later. The establishment of a water treatment facility confirms safe drinking water was becoming a priority to public officials.
It was a few more years before the disinfection would be applied to drinking water. A sewage- contaminated water pump led to a cholera outbreak in 1854 London. The water flowing from the pump tasted and smelled fine, but the disease was still spreading, indicating taste and smell do not guarantee safe water. John Snow, a British scientist, used chlorine to disinfect the water. To this day, the chlorination of water is widely used as a method of disinfection. It’s good, but is it the best technology available today?
Chlorine, A Double-Edged Sword
It is true the chlorination of water has saved more lives by preventing disease than all medicines have saved through treatment, but chlorine is still a deadly pesticide. Unfortunately, scientists and doctors began to notice adverse side effects of chlorine consumption. Alternative disinfection chemistries have been developed, mainly different forms of chlorine and ozone, but they can lead to the presence of by-products in drinking water. Some of these by-products change the taste of water, but others cause carcinogenic, free radicals to form inside the human body. A North American study found, “women with breast cancer have 50% to 60% more organochlorines [chlorine by-products] in their breast tissue than women without breast cancer.”
An alternative to chemical disinfection is physical disinfection. Physical disinfection is not dependent on chemical reactions but utilizes filtration and/or ultraviolet (UV) light to clean the water. Micro filters are capable of removing organic material from the water, but they clog quickly and need to be replaced often.
Two English scientists, Blunt and Downes, proved that UV light has a disinfecting effect on water samples in 1877. UV light represents wavelengths that fall between visible light and x-ray on the electromagnetic spectrum. The UV-C portion represents wavelengths between 200 nm and 280 nm. It is now known that photons travel through water to penetrate organic cells and damage the nucleic acid, rendering them microbiologically inactive, or incapable of reproduction.
Traditional, mercury-based UV systems use pressurized mercury lamps to create UV light. Research has found that the most effective wavelengths lay in the 260-270nm range, with mercury naturally generating a wavelength of 254nm. Mercury systems place fragile mercury tube lamps (bulbs) inside large, tube-shaped reactors that use a lot of electricity. Most of a mercury lamp’s energy is lost as heat on the surface of the lamp, so the temperature of the water being disinfected may increase.
Mercury-based UV systems have usage limitations. They decay with each on/off cycle, so only a limited number of cycles are permitted before replacement is necessary. These lamps also require 10 to 20 minutes of warmup time before they are able to disinfect and a breakage during use would release mercury into the drinking water.
"UV-C LEDs open up UV applications never before possible with traditional, mercury-based UV systems."
UV-C LED Technology, The Next Revolution
UV-C LEDs effect the pathogens in the water with the same method as mercury lamps but with all the benefits of solid-state semiconductor technology. These semiconductors allow for a long list of new features not available with traditional UV systems. UV-C LEDs can be combined with a very efficient compact reactor to result in a UV system that does not require a warm up time and can endure infinite on/off cycles. LEDs can be designed for a specific wavelength so the optimum disinfection wavelength range can be used. This new technology allows for simple plug-and-play systems, requires low voltage power, and can be incorporated into existing treatment systems.
UV-C LEDs open up UV applications never before possible with traditional, mercury based UV systems. Semiconductor systems can be designed to easily mount below any sink or behind any shower head. This new technology is ideal for off-the-grid homes and RV’s, as well as emergency response, transportation, and industrial applications.