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Research reveals large emissions from ship scrubbers

25 October 2022

A study by the Chalmers University of Technology revealed that the discharge water from ships’ exhaust gas cleaning systems (EGCS), so-called scrubbers, is responsible for up to nine percent of certain emissions of carcinogenic and environmentally harmful substances in the Baltic Sea, which is considerably more than was previously known.

​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.

Scrubbers have been an attractive technology for meeting the IMO 2020 marine fuel quality regulation, where scrubbers can be used in lieu of low sulfur (<0.5%) marine fuels—primarily to reduce SOx emissions to the atmosphere.

The Chalmers study, published in the Marine Pollution Bulletin, found that more than 200 million m3 of environmentally hazardous scrubber water were discharged from ships that used open-loop scrubbers in the Baltic Sea—in just one year. The study showed that scrubber wash water accounts for up to 9% of the emissions of certain cancer-causing polycyclic aromatic hydrocarbons (PAHs) into the Baltic Sea. PAHs are highly toxic to both humans and aquatic organisms, are difficult to degrade and can spread widely in the environment before breaking down.

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. Copper in antifouling paints is already a known environmental problem as the metal cannot be degraded in the environment and therefore leads to high levels in water, sediment and soil.

The study’s data was collected in 2018. At that time, there were approximately 180 ships equipped with scrubbers in the Baltic Sea. By 2021, the number of ships with scrubbers in the Baltic Sea had increased to almost 600 ships. Today, scrubbers are used by approximately 4,000 ships around the world, which is 16% of all container ships and a third of all cruise ships.

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 scrubber water into the internal waters of the Baltic Sea. A number of ports and coastal areas worldwide have already adopted restrictions on overboard discharges of water from open loop scrubbers.

Source: Chalmers University