UV-Transmission
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Selecting the right ballast water treatment system Limitations of Ballast Water Treatment Systems It should be acknowledged that ALL BWTS have limitations. Typically, chemical systems (e.g. electrochlorination) have limitations related to the salinity of the water to be treated, its temperature or the amount of organic material contained therein, whereas UV-based BWTS have limitations with regards to the UV-Transmission of the water to be treated. In other words, all BWTS have special circumstances under which they cannot be expected to treat the water according to the IMO discharge standard. The trick for the ship owner then becomes to select a BWTS that will work under normal operational conditions. However, this choice is currently difficult to make due to lack of information from makers of BWTS, and consequently lack of transparency. What is UV-Transmission? UV-T is a measure of the capability of UV light to penetrate into the water. When the UV-T is high, close to 100%, the water is very clear and the UV light can penetrate deep into the water. On the other hand, when the UV-T is low (below 50%) the water is very un-clear and the UV light can only penetrate a limited distance into the water. With a UV-T of 90% the UV intensity is 81% 2 cm away from the UV lamp, whereas it has dropped to a UV intensity of just 25% 2 cm away from the lamp when the UV-T level is 50%. See also table on the back page. Clearly, the UV-T of the water to be treated is of In the figure two cases with different UV-T are illustrated; one case with high UV-T of 90%, and one case with just 50% UV-T. In the graphs (table 7 next page) it is illustrated how rapidly the UV intensity decays away from the UV-lamp. 90% (90% of light remains after penetrating 1 cm into water) UV-T = 50% (50% of light remains after penetrating 1 cm into water) PROVEN TECHNOLOGY / www.desmioceanguard.com MARINE & OFFSHORE DEFENCE & FUEL

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utmost importance. To render an organism non-viable a certain UV-dose is required, and the applied UV-dose is directly proportional to the UV intensity. Therefore, when the UV-T is low, significantly more UV-power is needed to treat the water according to the required discharge standards, than what is required when the UV-T is high. Measured on two different days and two different locations in Shanghai port UV-Transmission limit of DESMI Ballast Water Treatment Systems Only a few systems can cope with UV-T level below 50%. The DESMI systems can and sets the industry benchmark regarding UV-T...

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