Disinfection by Ultraviolet Light
But there are other ways to disinfect water. One advantageous alternative is ultraviolet light.
Light can disinfect? You're kidding, right? Nope. I'm not joking. Specific wavelengths of light do have disinfecting abilities. Sunlight is one of the best examples.
As you certainly know from the warm days of summer (and any accompanying sunburns), UV is one of the components of sunlight. It is this very component of sunlight that keeps microbes from ruling the Earth. If sunlight didn't keep at least some of the microbes on Earth in check, we'd all be covered in a gelatinous, gooey, microbial slime.
More refined sources of UV are adept at tackling even those organisms that chlorine has a difficult time coping with, such as Giardia or Cryptosporidium. Take a look at why: Researchers have irradiated Cryptosporidia-the same organism that got 400,000 people sick and killed almost 100 people in 1993 in Milwaukee, WI-with UV light, and then injected rats with the irradiated organisms.
Interestingly enough, the rats did not get infected. Meanwhile, an average observer looking at the organisms through a microscope after irradiation would see that the Cryptosporidia were still swimming around as if everything was okay.
InactivationWhile the irradiated Crypto was alive, the rats did not get infected because the UV light had "inactivated"
MaintenanceUV unit doses are also typically stated as the dose delivered at "end-of-life"
PretreatmentAs a disinfectant, UV holds plenty of advantages-no disruption of chemical feed, no disinfection byproducts and no chemical handling, etc.
However, light can be obscured by suspended solids or other components in the water. Any factor that could occlude the transmission of light, such as mineral scale formation or suspended solids, must be dealt with prior to reaching the UV unit. In other words, you are trying to reduce any factor that can shadow or protect microbes from exposure to UV light.
With almost every groundwater or surface water, some amount of pretreatment is required in order to achieve the minimum water specifications in Table 1.
There are many elements of UV unit construction that are important. As with any technology, there are also some "bells and whistles"
StandardsCurrently, there are several UV units on the market that are certified to the NSF/ANSI 55 Standard, Ultraviolet microbiological water treatment systems. There are two classifications for UV units per this standard: Class A and Class B.
In short, Class A systems are designed to inactivate and/or remove microorganisms, including bacteria, viruses, Cryptosporidium and Giardia, when applied on microbiologically unsafe water. Class A systems are not intended to convert wastewater into potable water, nor are they intended to be used on water that has obvious or intentional contamination, such as raw sewage, which would affect the original influent parameters for normal drinking water sources. Class A units must include UV sensing ability and some form of alarm indicator.
Class B systems are those intended for application on microbiologically safe sources, such as municipal water, which are tested and deemed acceptable for human consumption. In essence, Class B units are intended as a barrier to nuisance organisms.
UV has already shown great advantages in disinfection applications for a variety of application levels, ranging from household use to industrial and municipal water supply systems. It is a technology you are certain to see more of in the future of water treatment.