Mapping chemical impact
Professor Marja Kaarina Koski was one of the DTU researchers who, back in 2016, documented how chemicals from scrubber water influenced plankton, which is the base of the marine food chain.
In an ongoing study, DTU researchers are mapping how the cocktail of chemicals in scrubber water affects dominant zooplankton in Danish coastal waters, including organisms such as copepods. According to Marja Kaarina Koski, documenting how local species are affected is crucial.
"If we are to document how scrubber water affects the marine environment, we need to look at cocktail effects. Chemical substances react with each other, and the organisms' response is affected by the mixture of stress factors to which they are exposed. The strength of our research therefore lies in mapping the mechanisms of organisms' responses to cumulative effects that can be transferred to other areas, and in documenting specific effects on organisms that live in Danish waters," Marja Kaarina Koski says.
Air pollution from ships became pollution of the sea
The use of scrubbers gained momentum around 2015 when the International Maritime Organization (IMO) set stricter rules on how much sulphur ships were allowed to emit and introduced emission controls in areas such as the North Sea and the Baltic Sea. The IMO rules required that the sulphur content of marine fuel must not exceed 0.1% in these areas. In 2020, global rules became even stricter with new IMO requirements for a maximum sulphur content of 0.5% in marine fuel worldwide.
The sulphur content in ship fuel is not reduced by combustion, but is emitted in the smoke from the ship, primarily in the form of sulphur dioxide. Scrubbers are therefore a way of meeting the requirements without using the more expensive low sulphur fuel, because they wash the sulphur out of the exhaust gases and bind it in a liquid (e.g., sea water) that can be discharged into the sea. However, as a result of this process, the liquid also contains several heavy metals such as vanadium and nickel, and PAH substances such as naphthalene and phenanthrene.
Ban out to 22 kilometers
The ban on the discharge of scrubber water applies in the sea within 22 kilometers of the coast. The sea area beyond 22 kilometers is regulated by international rules, and the political parties behind the ban therefore agree that Denmark should work for a similar ban in the EU.
Under the new legislation, ships will in future have to switch to either low-sulphur fuel or closed scrubbers with zero discharge. This means that the residual product from the closed scrubber must be delivered to the ports' reception facilities. The ban will come into force on 1 July 2025 for ships with open loop scrubbers. For ships with closed scrubbers, the ban will come into force on 1 July 2029.
The research on scrubber water has been conducted by DTU's maritime centre, Maritime DTU, in collaboration with industry and authorities and with support from The Danish Maritime Fund and A/S D/S Orient's Fund.
