UVc is often referred to as the germicidal wavelength, because of its ability to destroy micro-organisms. The lamps in all of our UV sterilisers emit a wide range of ultraviolet with its most significant part at a wavelength of 253.7nm, which has been found to be the most efficient for germicidal action.
When water is passed through a UV steriliser, microorganisms contained in the water encounter UVc radiation emitted from the germicidal lamp. The UVc radiation penetrates the cell membrane and thereby either destroys or debilitates the micro-organism by damaging the genetic material (DNA/RNA). Different micro-organisms vary in their susceptibility to UVc radiation. The most sensitive and hence, the easiest treated, are some bacteria and most phototrophic organisms such as those often found in ponds and aquaria (e.g. algae and cyanobactera). Bacteria, such as Escherichia coli which can contaminate drinking water supplies, are easily controlled by relatively low levels of UVc and therefore low level UVc radiation has been employed by the drinking water industry for many years. The most resistant micro-organisms to UVc are protozoans which may, when compared to simple bacteria, require several hundred times the radiation dose to destroy them. Generally, the larger the organism, the larger the UV dose required to damage it. There are many hazardous and pathogenic aquatic organisms that can be controlled with the application of the correct UVc radiation dose. Correct application will dramatically reduce the likely spread of most primary infections such as Oodinium sp. and Cryptocaryon sp., at the same time almost eliminating the risk of secondary bacterial infection which is so often the real cause of fish loss. This is achieved by controlling potential populations of heterotrophic bacteria which are often associated with an unhealthy aquatic environment.
Factors Affecting Germicidal Action
Lamp Temperature
It is important that the UV lamp reaches its optimum operating temperature of 40°C otherwise the lamp will not generate the maximum amount of UVc radiation possible, and the efficiency of the unit will be compromised. For this reason, all UV water sterilisers must be fitted with a protective fused quartz glass sleeve, which keeps the UV lamp from direct water contact, which would otherwise act as a coolant. Units should also feature sealed end caps which help to maintain the lamp and the air around it at its constant optimum running temperature. The protective sleeve employed must be manufactured from fused quartz glass, which allows the highest possible amount of UV light to penetrate the water. Other materials should not be used as they can have a significant impact on the effectiveness of the steriliser by significantly reducing the amount of UVc that reaches the water.
Water Clarity
Dirty or turbid water with suspended particles will absorb the UVc radiation and dramatically reduce the effectiveness of the unit. It is important to ensure that the UV steriliser is placed at the end of the filter circuit, before the water returns to the holding tanks to ensure that the water passing through the steriliser is as clear as possible. Dissolved organic compounds also reduce the distance of penetration of the UVc radiation. Typically, in any aquatic environment with fish or other animals present, there is a gradual build up of phenolic compounds and other organic dyes. This build up of organic dyes is often referred to as ‘yellow water syndrome’ and can be dramatically reduced by filtering through a good quality activated carbon (e.g. HR Carbon) or by using ozone gas.
Each TMC Commercial UV Steriliser uses a high frequency control gear, which should, ideally, be operated on its own power supply circuit. If this is not possible then it is important that the UV Steriliser is not installed on a circuit that may be susceptible to induced loads that lead to high energy surges (spikes), as these high energy surges will damage the UV control gear. Examples of equipment that could potentially cause high energy surges or spikes are: most large electric motors including some water pumps and light fittings with igniters, such as floodlights. High frequency control gears should not be operated on the same power circuit as traditional magnetic ballasts.
