Ultraviolet radiations
Ultraviolet radiations are not like other disinfectants. They do not deactivate the microorganisms with a chemical process. UV radiations deactivate microorganisms by absorbing light that causes a photochemical reaction the alters the essential components of the cell.
When a UV ray penetrates the microorganism's cell membrane, the ray' energy reacts with nucleic acids and other vital components of the cell. This causes important damage or death to the cell.
This proves that, with a sufficient dose, UV energy can kill most organisms. And UV rays can disinfect water at any degree.
Mixed management
|
Water quality |
Absorption |
Transmission % |
|
Excellent |
0,022 |
95% |
|
Good |
0,071 |
85% |
|
Poor |
0,125 |
75% |
Hardness can cause certain incrusting problems for the quartz. That's why it's important to keep it very clean. The presence of dissolved or suspended solids can provide a protective screen for the microorganisms against UV radiations. For example, iron, sulphur, nitrates and phenol can absorb ultraviolet light (Demers and Renner, 1992).
Therefore, before installing a UV unit, it is preferable to measure the absorption level of the water to determine it's absorption capacity for this specific case. The transmission percentage is a useful parameter to determine how easily or not the UV lamp will disinfect the water. Table reference: DeMers and Renner 1992.
UV currently available
There are two specific types of UV disinfection units on the market (standard and certified). Standard UV units are not recognized by an independent organism like the NSF. In Quebec, water professionals are required to sell and install NSF certified systems. These systems are also recognized by the MDDEP and the Régie du Bâtiment du Québec. Standard systems have been around for 20 years. They are more or less efficient. If the quality of the water changes, the quartz gets encrusted or the rays start to weaken, the lamp will not sound the alarm and contaminated water will get through.
Another system has been on the market for more then 10 years. It's the same as the standard system with an added probe that continuously reads the UV transmission.
This means that if the quality of the water changes or the quartz gets encrusted, this system will immediately sound an alarm and even stop the water flow if the option is activated. The alarm goes off when the UV dose reaches 40mj/cm2, the minimum dose considered secure enough to efficiently disinfect your water. These perfected systems are more efficient and can generate twice the power of conventional systems. And, they are certified by NSF.
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