Comparing UV and Chlorination Options

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Introduction

Air & Water Quality (AWQ) has installed many ultra violet (UV) systems and chlorination systems. We have investigated both techniques for the purposes of primary disinfection. We have considered the following key points when deciding the best approach.

Key points

  • Coliform bacteria are found in or on all living and decaying organic matter. The presence of Coliform bacteria indicates the presence of these materials. As a result, coliform bacteria are considered indicator organisms.
  • Typically, the coliform bacteria found in well water are, not dangerous to our health.
  • Since organic matter is not present in ground water, any indication of its presence means there is contamination leaking into the well directly from the surface. The easiest way to identify this contamination is to test for coliform bacteria.
  • The surface contamination indicated by the presence of coliform bacteria can bring with it many other pathogens of which some can and will be viruses. Viruses must be inactivated by 99.99% to meet current drinking water standards.
  • To achieve the 4 log (99.99%) inactivation of viruses with UV, the water would have to receive a dose of 186 mJ/cm2. Current NSF standards for UV systems only require a dose of 40 mJ/cm2. To obtain the required dose, at least 5 NSF rated units would be required.
  • The installation of a UV light will inactivate the only organism (coliform) that will indicate surface water contamination without removing the rest of the pathogens. With a UV system in place, a water test will show no coliform and you will think that you are safe, even though other pathogens may be present. In other words, the UV system will only cover up and not solve the problem .
  • It is easy for the homeowner to determine if a chlorination system is functioning by doing a simple chlorine test. Most installed residential UV systems do not have any kind of UV monitor to know if they are functioning properly. Many water treatment companies will not install UV systems with monitors because the monitors have been found to be very unreliable.
  • The Maine Drinking Water Program (DWP) discourages the use of UV systems. The following is the statement posted from the Maine Drinking Water Program (DWP) UV Policy  [i]

Conclusion

 

The safest and least expensive way to control microorganisms in well water is to use chlorine (sodium hypochlorite, also known as bleach) for disinfection.

 

[i] Note- the notice refers to E. coli which is a type of coliform bacteria.

 

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