December 2012

Ships travelling in regions with fresh water conditions may face challenges

DESMI Ocean Guard has developed a system based on UV radiation and ozonation at low concentration which is the first non-chemical system on the market which has passed the land-based tests also in fresh water. The landbased testing was started in brackish water where the system performed flawlessly, but when DESMI Ocean Guard decided to put the system through the tests also in natural fresh water they were in for a surprise. It turned out that fresh water is more demanding to treat and therefore a few modifications had to be introduced in order to meet the IMO discharge requirements also in fresh water.

The main challenges related to fresh water are related to “soft” organisms and poor UV-Transmission. The soft organisms are capable of squeezing through the filters typically used in ballast water treatment systems, and the poor UV-Transmission means the UV light can only penetrate a few cm into the water before it has been absorbed.


These challenges has been overcome by DESMI Ocean Guard by introducing a unique and patent pending filtration concept where the filter is also engaged during de-ballast, and by reducing the flowrate through the UV-units when treating fresh water.


In combination these modifications allowed the DESMI Ocean Guard system to pass the landbased tests in fresh water. “The extensive testing we have conducted during the past years has taught us that fresh water is particularly challenging. If a system has not been put successfully through a series of landbased tests in freshwater you should not assume that it will be able to meet the IMO discharge standard in freshwater. We know from early versions of our own system that even though the performance in brackish and salt water was excellent, the system could not handle freshwater to the required standards”, says Rasmus Folsø, CEO of DESMI Ocean Guard.


The DESMI Ocean Guard system marketed under the name OxyCleanTM received type approval from Lloyd’s Register in November 2012 and is now available for the market through DESMI’s global sales and service organization.