High-Performance UV Sterilisation & Water Purification Systems

UV Filtration

What is UV?

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 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.

Tips and Tricks

Choosing the Correct UV Steriliser

Refer to the table below (Exposures needed to kill Micro-organisms) for the required dosage rate for your application.
Decide on the flow rate that you require in m³/hr for your application. Refer to the product information sheets for the appropriate TitanUV or Commercial UV steriliser. Please note that flow rates on the information sheets are given to a kill rate of 30,000µWs/cm², if a higher or lower value is required please speak to us for calculations.
As a rule-of-thumb, if the flow rate is halved the dosage rate is doubled and if the flow rate is doubled the resultant dosage rate is halved.

N.B. All outputs are given for the end of the maximum lamp life of 8000 hours (to 85% output). However, it is strongly recommended that lamps are replaced every 4000 hours (approx. 6 months) to ensure optimum efficiency of the steriliser.

Hyperion bulbs last 12000 hours, therefore it is recommended to replace after 6000 hours.

Contact

To maximise germicidal action, it is important to consider the contact time and distance between the UVc source and the microorganisms to be treated. The contact distance is set by the design of the UV steriliser. The actual time it takes for water to pass through the chamber - ‘the contact time’- is a function of the recommended flow rate per lamp. The overall volume of water in the livestock tank or system, and the frequency that the total volume comes into contact with the UVc source is also significant and must be considered for the correct operation of the filter on a given system. We have carried out extensive trials over many years to ascertain the best relationship between the ‘contact time’ and the total volume of the system, and the turnover requirements of the system. UV output, recommended flow rates and maximum system volume are given for each model in the product information sections.

System Turnover rate

The total volume of a system needs to be turned over regularly through the steriliser to achieve desirable levels of sterilisation. The following recommendations should be adhered to and used in conjunction with the tables listed here.
Shellfish depuration systems - Minimum 3 x per hour, recommended 5x per hour (Sea Fish Industry Authority Recommendation)
Marine/freshwater ornamental systems - Minimum 4x per hour, recommended 7x per hour
Public aquaria displays - Minimum 2 x per hour, recommended 3-5x per hour.

* UV dosage required to destroy 99.9% of micro-organisms

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