Global scrubber washwater discharges under IMO’s 2020 fuel sulfur limit

A rapidly growing number of ships are being fitted with exhaust gas cleaning systems, or “scrubbers,” as a way to comply with the International Maritime Organization’s (IMO) 2020 global fuel sulfur limit. Scrubbers remove sulfur from ship exhaust by spraying a buffer solution, usually seawater, over it and then discharging the washwater overboard, often without treatment. The washwater is more acidic than the surrounding seawater and contains polycyclic aromatic hydrocarbons, particulate matter, nitrates, nitrites, and heavy metals including nickel, lead, copper, and mercury.

This webinar will discuss our new report, Global scrubber washwater discharges under IMO’s 2020 fuel sulfur limit, which is the first global assessment of the mass of washwater discharges expected from ships using scrubbers. We used 2019 ship traffic, as a pre-COVID-19 baseline, and considered approximately 3,600 ships that had scrubbers installed by the end of 2020. Results show that ships are emitting at least 10 billion tonnes of scrubber washwater each year. Approximately 80% of scrubber discharges occur within 200 nautical miles of shore, and there are hot spots in heavily trafficked regions, including the Baltic Sea, North Sea, Mediterranean Sea, the Strait of Malacca, and the Caribbean Sea. Scrubber discharges also occur in IMO-designated Particularly Sensitive Sea Areas (PSSAs), including those home to coral reefs.

Although several governments have banned the use of scrubbers in their ports, internal waters, and territorial seas, many have not. Policymakers concerned about the impacts of washwater discharges can consider several actions that will be discussed in the webinar.