Study points to growing role of scrubber discharge water in Baltic Sea pollution

Discharge water from ships’ exhaust gas treatment systems (scrubbers) is responsible for up to nine percent of certain emissions of carcinogenic and environmentally harmful substances in the Baltic Sea, a study from Chalmers University of Technology reveals.

​The study was commissioned by the Swedish Transport Agency and the Swedish Agency for Marine and Water Management to investigate the environmental impact from scrubbers in the Baltic Sea compared to other sources of environmental contaminants. The number of ships equipped with scrubbers have more than tripled since the study was carried out.

Scrubbers have been a very attractive solution for meeting the IMO 2020 regulation on cutting the sulphur content in marine fuel, especially for bigger vessels. The IMO has found an estimated 77% drop in overall Sulphur Oxide emissions from ships since the entry into effect of the “IMO 2020” regulations in January 2020.

The reduction is equivalent to 8.5 million metric tonnes of sulphur oxides, which are linked to causing asthma, pulmonary, cardiovascular, and respiratory diseases. The majority of ships trading worldwide switched from using heavy fuel oil to using very low sulphuf fuel oil (VLSFO.) However, those that continued burning conventional fuels have fitted scrubbers on board their ships.

Many shipowners have opted for open-loop scrubbers that use sea water as the process fluid and discharge the treated water overboard.

The study from Chalmers says that washing the exhaust gases in seawater traps other contaminants in the seawater and results in the release of hazardous substances to the marine environment. ​

The researchers found that more than 200 million cubic meters of environmentally hazardous scrubber water were discharged from ships that used exhaust gas cleaning systems in the Baltic Sea – in just one year.

The study showed that scrubber wash water accounts for up to 9 percent of the emissions of certain cancer-causing polycyclic aromatic hydrocarbons (PAHs) into the Baltic Sea. The study also revealed that ships painted with copper-based antifouling paints account for a third of the total supply of copper to the Baltic Sea.

Erik Ytreberg​, Associate Professor and researcher at the Division of Maritime Studies at Chalmers University of Technology, who is the lead author of the scientific study, said that the study shows that shipping accounts for a significant proportion of hazardous substances released into the Baltic Sea, above all through antifouling paints and discharge of wash water from open loop scrubbers.

“PAHs are highly toxic to both humans and aquatic organisms as they are, among other things, carcinogenic. Worth noting is that the study’s data was collected in 2018, and at that time there were approximately 180 ships with scrubbers in the Baltic Sea. Since then, these ships have increased significantly and in 2021 there were almost 600 ships equipped with scrubbers in the Baltic Sea,” says Ytreberg. 

“For many years, we’ve flagged the fact that scrubbers account for disproportionately large emissions of hazardous and acidifying substances into the marine environment. In spite of this message, we have seen a significant increase in the number of scrubber installations as it is economically beneficial for the shipowner. Therefore, it is very important that authorities and decision-makers now react and implement measures to reduce shipping’s emissions and impact on the marine environment,” says Ida-Maja Hassellöv, Professor and researcher at the Division of Maritime Studies at Chalmers University of Technology.

The new research results have led the Swedish Transport Agency and the Swedish Agency for Marine and Water Management to propose a ban on the discharge of so-called scrubber water into the internal waters of the Baltic Sea. If the Swedish politicians follow the line of the researchers and the authorities, Sweden will be the first country in the Nordic region to introduce the ban.

Today, scrubbers are installed on over 4,000 ships around the world. In the Baltic Sea area, only Germany already applies the same legislation, even though several other countries in Europe regulate scrubber discharges in their ports.

“The proposal that Sweden should ban the discharge of wash water into Swedish inland waters is good, but at the same time it means that only 1 – 2 percent of the discharges that occur from scrubbers in the Baltic Sea today will be regulated. Sweden could also propose a ban in our territorial waters, which would mean that roughly 15-17 percent of emissions to the Baltic Sea could be regulated. But the biggest effect would obviously come from an international ban, where all the countries around the Baltic Sea agree on a joint regulation of the discharge of scrubber water,” says Ytreberg.

A growing number of countries are banning the discharge of scrubber wash water in their territorial waters. The latest ones to join the move were Turkey, Saudi Arabia,  Oman, Suez Canal Authority, Malaysia and Singapore.