Question: We just found out that our well is contaminated with fecal coliform. The only things we currently have installed is a water filter and water softener. We have had two different companies make different suggestions as to how to resolve this problem. One want’s to install a chlorine injection system, and the other suggested a ultraviolet sterilization system. Which is right?
Answer: Both companies are suggesting different, but correct, technologies for resolving this problem. The first design that you mention is chlorine injection. Injecting chlorine disinfects the water, as long as you have the correct equipment design. A good package includes a static mixer, which aids in mixing the chlorine and well water, a quality pump, and sufficient retention time so that the chlorinated water is in contact long enough to ensure that disinfection is accomplished. You need a minimum of 20 minutes retention time, and this is normally accomplished with a 120 gallon retention tank. Chlorine injection will also typically include a backwashing carbon filter to remove any chlorine from the household water. This would be an important consideration in your case, as very high levels of chlorine can be damaging to the cation exchange resin found in a water softener – and you will want to remove it first. The specific design may vary depending on household flow rate & water quality, but you can look at a design that we offer for this purpose on our site.
The second solution may be a better one for your application. Ultraviolet sterilization will resolve this problem by passing a high energy light wave through the water, thereby sterilizing any harmful organisms. For UV to operate properly you need to incorporate a 5-micron filter into the design, to first remove any sediment from the water. This is because a harmful organism may be able to “hide” in the pores of a sediment particle, and if not removed, might receive an incomplete exposure to the UV light. In addition (and depending on your water quality) a water softener may be required upstream of the UV, so that scale and iron deposits don’t build up over time in the reactor. You already have a sediment filter and water softener, so it would appear that you are a very good candidate for a UV system. And there is no concern here with the possibility of chlorine damage to the softener.