Factors Affecting UV Water System Performance December 11 2013
UV water treatment technology is a very robust water treatment solution that can be used effectively in many conditions. But like all technologies, it has it's limitations. For UV, it is the incoming water quality that has the greatest influence on system effectiveness. Identifying possible water quality challenges is the easiest and best way to make sure your UV system will deliver the performance you need it to.
In this article we go over the most important water quality parameters to consider. As you're reading this, please keep in mind that the vast majority of waterborne disease-causing organisms are actually very easy to destroy with UV. Most UV systems deliver at least 2 or 3 times the UV dose necessary to destroy these organisms. So, even a UV system that is only half-working (not ideal!) will still afford a great deal of protection. It's also important to distinguish between UV system manufacturers whose systems are designed to deliver the bare-minimum UV dose of 16mJ/cm² and the systems sold by aQuatell which deliver a minimum 30mJ/cm² dose. This difference in UV dose allows aQuatell UV systems to perform well even when water conditions are not ideal - making them a perfect choice for the myriad of applications in South Africa and beyond. Now, let's look at water quality and how it impacts system performance:
Water Quality Considerations
There are three main elements of water quality that can negatively impact UV system performance: Iron, Water Hardness, and UV Transmittance. There are two mechanisms by which a UV system can be impaired. Some minerals when dissolved in water absorb the germicidal wavelength of UV light leaving less UV energy available to disinfect the water. Other dissolved materials in the water can act as foulants where they deposit on the UV system quartz sleeve and prevent the light created by the lamp from entering the water column.
UV Transmittance, often abbreviated to UVT is the measure of how easily germicidal wavelengths of UV light can pass through the water. UVT has a major impact on the effectiveness of a UV system. There are a number of different substances that can affect the UVT of water:
- Particulate matter suspended in the water can lower UVT values. This is why all UV systems must be preceded by a 5-micron rated sediment filter
- Organic material dissolved in the water (primarily Tannins and Humic Acids) can give many surface waters a characteristic brown tint. This tint can absorb a large amount of UV light, making it unavailable for disinfection
- Dissolved minerals, namely Iron, can also act as UV absorbers in the same way as Tannins.