UV treatment for drinking water is a technology that dates back to 1916. It’s one of the most popular means of treatment for drinking water and is used in a lot of RO plants. What it does is use UV-B waves of 280-315 nm to put water into the ‘germicidal zone.’ Some UV-C of 200-280 nm is used with a little longer exposure times, but these two UV types are most efficient at deactivating bacteria, viruses, and protozoa.
Now, the deactivation is what is so unique about this type of treatment, it doesn’t kill anything, instead it rips the DNA and RNA proteins and bonds rendering these microorganisms inactivated. Basically, meaning they are prevented from reproducing. The UV light damages the DNA and RNA and when a microorganism cannot reproduce, it cannot infect. BUT, microorganisms are highly evolved sneaky little guys that also have the ability to repair the bond breaks caused by UV light. To enhance the effectiveness of the treatment, adding some type of chemical usually chlorine to further disinfect is used or you can drink it quickly before these bonds are repaired usually within a few hours or days.
What are potential advantages and disadvantages? (Thought you would never ask!)
A disadvantage is that UV depends on a constant energy source, inaccurate measures of dose, and a lack of residual after treatment. If UV treated water is to be stored, then chemicals should be added as a disinfectant in order to prevent the reactivation I just mentioned. Another disadvantage is if using the mercury lamps, they must be disposed of properly due to the toxicity (not likely in a HA/DR situation) and therefore further investment into UVLED lamps is recommended although not as affordable. There are also potential risks for UV treatment, exposure to mercury again if using a mercury lamp, formation of disinfection by-products, and exposure to UV light from the device, all of which are considered to be minimal and doesn’t really happen, so moving on…
The advantages are using a physical method over chemical, which does not leave any by-products, extremely effective against protozoa, inexpensive and quick process to drinking water treatment. UV is easy to install and requires low maintenance costs. There is not any kind of chemical taste or smell and is not all that sensitive to pH or temperature. It does not take any minerals out of the water, improves taste because it kills some organics, requires little contact time, has no smell, has no volatile organic compound emissions, and is recently acknowledged in water treatment journals as a Cryptosporidium control.
UV technology is highly accepted in conjunction with another form of disinfection. It is mostly used on a large-scale community level and can be found all over North America and Europe.The design and instillation of large-scale water treatment projects in other countries also adopt this technology as part of their process. In a household, this method is not seen as often, but it is also great for humanitarian assistance and disaster relief applications. It is rather common to see UV as a treatment process during times of disaster and crisis due to the effectiveness of the treatment and the quick contact time, this method is remarkably efficient in delivering clean drinking water quickly. They are also portable and lightweight, which makes these systems even easier in times of need.
Costs vary from US$0.02/m3 to $US2.35/m3 for operating and maintenance of the system. It is affordable for low-income residences and communities, and environments with minimal electrical and water infrastructure. The initial investment of US$41 estimates for a household level and up to US$244,419 for the most up to date technology measuring high volumes (found in large treatment plants). The average for a community size UV treatment is between $300-900 USD.
So, to UV or not to UV? Is there even a question?
Kinda looks like the lightsaber of water treatment. Off to fight the Darth virus!