Since the IMO laid out the regulations for ballast water treatment (BWT) (with the International Convention for the control and management of ships ballast water and sediments, 2004) many technologies to treat ballast water have been discussed and developed. After a few years of testing and now gaining more and more real life experience it comes obvious that one key to an effective and economical treatment is the filtration within the process of ballast water treatment. Not only because the convention states to eliminate sediments but also looking to the removal of organisms with mechanical – environmentally friendly – technologies there is no way to operate without effective filters.
For filtration solutions the company Mahle offers today one of the most effective systems to treat ballast water according to[ds_preview] the D2 standards proving 0 organisms left in the discharge of ballast water.
The OPS is a three-stage ballast water treatment system. It works as an in-line system during uptake and discharge of ballast water. During uptake the first step of treatment is a pre-filtration for separating particles larger than 200 m, followed by a second filtration for separating particles larger than 50 m. With this pre-treatment sediments and most of the organisms are removed from the ballast water. The sludge from the self-cleaning process will be discharged at the same place where the ballast water was taken on board. The uptake treatment finishes by disinfection via UV light with low pressure lamps.
The factor of success in this process are the self-cleaning filters. We are not talking about typical back flushing filters but filters designed for a continuous filtration which guarantee
• low loss of flow rate
• low pressure drop
• low maintenance
• and hardly any spare parts.
Continuous test results are showing that these filters remove already over 90 % of organisms larger 50 m and more than 60 % of organisms between 10 and 50 m.
At the on-board installation it has been experienced that existing sludge and sediments in the ballast water tanks of a 17-year-old ship had been removed by using the OPS for a certain period of time – it was not necessary to clean the tanks before using the OPS.
After this effective filtration the OPS uses low pressure UV lamps which emit a special wavelength of 254 nm for disinfection with the key benefits of
• very low power consumption (only 20 % of consumption compared to medium pressure)
• vow operating temperature in the UV lamps
• 100 % removal of all critical organisms
• long lifetime of the UV lamps (up to six times more than medium pressure).
The UV lamps are automatically cleaned by a cleaning fluid which is filtered after each operation and can be used for multiple cleaning processes. No mechanical scrapers are necessary.
Experiences in the use of this technology combination show that safe and reliable treatment can be realized for seawater, brackish water, and fresh water without changing the parameters of the water, e.g. ph value.
Another challenging item for ship operators is the integration of the system into the on-board control system. By a clear and simple definition of the interfaces to pump and valve control systems the company managed to successfully integrate their system on existing ships as well as new buildings. Beneficial is the fact that the filters are pure mechanical devices with a rather simple control – together with the control of the UV unit it is a system running independently and fully automatically – so only few major signals need to be exchanged between the OPS control and the ship’s on-board control system.
Since installation time is always crucial Mahle developed its OPS on a modular base. Mechanical units such as the filters are mounted on a frame including piping and electric wiring so they create one complete unit to be installed. The same is done with the UV chambers in order to easily mount these modules together. Experiences show that besides effective removal of sediments and organisms it is crucial to facilitate the installation and operation of ballast water treatment systems. Complicated multistage systems with difficult operation processes are not wanted by ship crews.
Another factor: by installing the OPS in a container the company managed to put the system in operation ten days after the container had been loaded into the ships storage room. And this was done on voyage.
As another solution – also for retrofitting existing ships – the system can be delivered in single components mounted together on small modules to ease the installation and shorten the time of integration into the onboard systems. Since these modules can be flexible designed enough space can be found on almost every ship.
Michaela Marquardt
