Commercial Products

UV Filtration

Ultraviolet is a term used to describe the wavelength between the blue violet range of the visible spectrum and the shorter wavelength or X-rays.

The ultraviolet spectrum is divided into three separate bands:-

UVa From 315nm to 400nm

UVb From 280nm to 315nm

UVc From 200nm to 280nm

UVc is often referred to as the germicidal wavelength, because of its ability to destroy micro-organisms. The lamps in all of the UV sterilisers stocked by TMC 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, micro-organisms contained in the water come into contact with UVc radiation emitted from the germicidal lamp. The UVc radiation penetrates the cell membrane and thereby either destroys or debilitates the micro-organism. 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. Bacteria, such as Escherichia coli which can contaminate drinking water supplies, are easily controlled by relatively low levels of UVc and this is why 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 given 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 operating temperature. The protective sleeve employed must be manufactured from fused quartz glass, which allows the highest possible amount of UV light to penetrate into the water. Other materials should not be used as they can have a significant impact on the effectiveness of the steriliser by 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.

Choosing the Correct UV Steriliser

1. Select application level required bearing in mind the type of pathogen to be controlled or killed (see table below). Level 2 or 3 is adequate for most applications.

2. Decide on the flow rate that you require in m³/hour (thousand litres/hour) taking into account the recommendations below.

3. Divide this number by the flow rate per lamp given in the table below for your selected application level.

4. The result tells you the number of lamps that are required to treat your given flow rate. If you have an odd number or fraction of a number, you should round up to the nearest whole even number. If the number is greater than 12 then you should use 2 or more units to give the total required number of lamps.

5. Use the product data table to obtain the specification of the correct unit for your application.

Please note that all outputs are given for the end of the maximum lamp life of 8000 hours. However it is strongly recommended that lamps are replaced every 4000 hours (approx. 6 months) to ensure optimum efficiency of the steriliser.