U.V. Filtration
January 25, 2011|
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Ultraviolet is a term used to describe the wavelengths 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:-
U.V.c is often referred to as germicidal wavelength, because of its ability to destroy micro-organisms. The tubes in all of our U.V. 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 U.V. steriliser, micro-organisms contained in the water come into contact with U.V.c radiation emitted from the germicidal lamp. The U.V.c radiation penetrates the cell membrane and thereby either destroys or debilitates the micro-organism. Different micro-organisms vary in their susceptibility to U.V.c radiation. The most sensitive and hence, the easiest treated, are some bacteria and most phototrophic organisms such as those found in ponds and aquaria. Relatively low levels of U.V.c easily control bacteria, such as Escherichia Coli, which can contaminate drinking water supplies, and this is why the low level of U.V.c radiation has been employed by the drinking industry for many years. The most resistant micro-organisms to U.V.c 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 U.V dose required to damage it. There are many hazardous and pathogenis aquatic organisms that can be controlled given the correct U.V.c radiation dose. Correct application will dramatically reduce the likely spread of most primary infections such as Oodinium sp. and Cryptocaryon, 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 the 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 U.V units used for killing or controlling micro-organisms in liquids, for human/animal consumption or where a high kill rate is required that the tube reaches its optimum operating temperature of 40°C otherwise the lamp will not generate the maximum amount of U.V.c radiation possible and the efficiency of the unit will be compromised. For this reason we have manufactured a specialised range of U.V water sterilisers and fitted them with a protective fused quartz glass sleeve, which keeps the U.V. tube from direct contact, which would otherwise act as a coolant. The Units also feature sealed end caps, which help to maintain the lamp and 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 U.V. 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 significantly reducing the amount of U.V.c that reaches the water. Water Clarity - Dirty or turbid water with suspended particles will absorb the U.V.c radiation and dramatically reduce the effectiveness of the unit. It is important to ensure that the U.V. 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 U.V.c radiation. Typically in any aquatic environment with fishes 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 carbon. The clarity of the water is an essential condition of the function. The transmission factor must be as high as possible. In the course of the experiments, water polluted with about 300 000 bacteria per millilitre was upgraded to the quality of drinking water with less that 10 bacteria per millilitre. In the case of dirty or turbid water which reduces the transmission factor to radiation at 254nm to 74.4 per cent. It was found possible to reduce the number of bacteria from 350 000 per ml prior to irradiation, to 70 per ml after irradiation. To maximise germicidal action it is important to consider the contact time and the contact distance between the U.V.c source and micro-organisms to be treated. The contact distance is set by the design of the U.V. steriliser. You should bear in mind that the larger the diameter of the steriliser, the greater the dwell time of the water resulting in an increase in the dosage. However, as the radius of the steriliser increases, so does the distance the radiation must travel. This causes a decrease in the generated dosage. The actual time it takes for the water to pass through the chamber –‘the contact time’ – is a function of the recommended flow rate per tube. The overall volume of water in the livestock tank or system, and the frequency that the total volume comes into contact with the U.V. source, is also significant and must be taken into account for the correct operation of the filter on a given system. Some common uses of U.V. units. · Koi Ponds |
Posted by Shane Dick.
