Scrubbers on ships

In ship construction, Scrubbers, or exhaust gas cleaning systems, are installed on ships to reduce air pollution caused by sulfur oxides (SOx) emitted when burning heavy fuel oil. ^[1] A prevalent type is the open loop scrubber, which uses seawater to wash exhaust gases and then discharges the resulting polluted washwater directly into the sea. ^{[2] [3]} These systems have sparked significant environmental debate due to their impacts on marine ecosystems. ^{[4] [5] [6]}

Open loop scrubbers became widespread after the International Maritime Organization (IMO) implemented a global sulfur emissions cap in 2020. ^[7] They allow ships to continue using less expensive, high-sulfur heavy fuel oil while meeting air quality regulations, shifting the environmental burden from air to water. ^{[8] [9]} As of 2022, in some regions like the Baltic Sea, the number of ships fitted with these systems has quadrupled in recent years. ^{[10] [11]}

Cruise-ship equipped with scrubbers in Norwegian fjord

Types of scrubbers

• Open Loop Scrubbers: Use seawater to neutralize SOx in exhaust gases and discharge the used water, now acidic and contaminated, back into the ocean. ^[12]
• Closed Loop Scrubbers: Use a recirculating alkaline solution to remove SOx, storing the wastewater on board for later disposal at port. ^[13]
• Hybrid Scrubbers: Can operate in either mode, depending on local regulations and conditions. ^[14]

Environmental impacts

Open loop scrubbers have been subject to intense scientific scrutiny. Research shows that:

• For every tonne of fuel burned, ships with open loop scrubbers can release up to 45 tonnes of acidic, contaminated washwater containing heavy metals, polycyclic aromatic hydrocarbons (PAHs), and other toxins into the ocean. ^{[15] [16]}
• In the Baltic Sea, open loop scrubber discharge accounts for up to nine percent of certain PAH emissions, which are harmful to aquatic life. ^[17]
• Scrubber effluent can cause local acidification, reduce water pH, and increase concentrations of hazardous substances in sediments, affecting marine organisms' development and reproduction. ^{[18] [19]}
• Socio-economic costs of this pollution in the Baltic Sea region alone have been estimated at more than €680 million between 2014 and 2022, not including broader environmental damage. ^[20]

Regulatory responses

Growing concern over the environmental impact of open loop scrubbers has led to increasing regulatory restrictions. ^{[21] [22]} Many ports and jurisdictions have banned or restricted the use of open loop scrubbers in their waters, requiring ships to use either closed loop systems or compliant low-sulfur fuels instead. ^{[23] [24] [25] [26]}

See also

• Marine Pollution

References

1. Finch, George (March 2024). "Open-Loop Scrubbers Literature Review" (PDF). British Ports Association.
2. "DSpace". helda.helsinki.fi. Retrieved 2025-09-09.
3. Eisemann, Lea (2021-05-31). Environmental Impacts of Exhaust Gas Cleaning Systems for Reduction of SOx on Ships – Analysis of status quo (in German). Umweltbundesamt.
4. "Report: Scrubber Wash Damages Baltic as Shipowners Realize Profits with HFO". The Maritime Executive. Retrieved 2025-07-20.
5. "Study: Open-Loop Scrubbers Contribute to PAH Pollution in the Baltic". The Maritime Executive. Retrieved 2025-07-20.
6. Ytreberg, Erik; Hermansson, Anna Lunde; Hassellöv, Ida-Maja; Jalkanen, Jukka-Pekka; Majamäki, Elisa; Hänninen, Risto; Kukkonen, Jaakko; Granberg, Maria; Magnusson, Kerstin; Fridell, Erik; Jutterström, Sara; Johansson, Emilie; Moldanova, Jana; Guéret, Samuel; Winiwarter, Wilfried (2023). "EMERGE deliverable 6.1. Baltic and North Sea report". Research in Chalmers.
7. "Potential impact of wash water effluents from scrubbers on water acidification in the southern North Sea". ResearchGate. Archived from the original on 2022-02-09. Retrieved 2025-09-09.
8. "Air emissions and water pollution discharges from ships with scrubbers". International Council on Clean Transportation. Retrieved 2025-09-09.
9. Stallmann, Martin (2020-09-01). Environmental Protection in Maritime Traffic – Scrubber Wash Water Survey (in German). Umweltbundesamt.
10. Napolitano, Anna (2025). "How 'scrubbers' became a huge ocean problem". Eco-Business. Retrieved 2025-07-20.
11. "Discharges to the sea from Baltic Sea shipping in 2023" (PDF). helcom.fi.
12. Mansfield, Mike (2022-07-15). "Clean Air, Dirty Water - The Tradeoff of Scrubbers". More Than Shipping. Retrieved 2025-07-20.
13. Shagun (2020-01-09). "Huge increase in open-loop scrubber usage in ships: Report". Down To Earth. Retrieved 2025-07-20.
14. ICES (2020-09-24). ICES VIEWPOINT: Scrubber discharge water from ships – risks to the marine environment and recommendations to reduce impacts (Report). ICES Viewpoints.
15. Lunde Hermansson, Anna; Hassellöv, Ida-Maja; Grönholm, Tiia; Jalkanen, Jukka-Pekka; Fridell, Erik; Parsmo, Rasmus; Hassellöv, Jesper; Ytreberg, Erik (2024-05-07). "Strong economic incentives of ship scrubbers promoting pollution". Nature Sustainability. 7 (6): 812–822. Bibcode:2024NatSu...7..812L. doi: 10.1038/s41893-024-01347-1 . ISSN   2398-9629.
16. Achten, Christine; Marin-Enriquez, Octavio; Behrends, Brigitte; Kupich, Sandra; Lutter, Andreas; Korth, Richard; Andersson, Jan T. (2024-11-01). "Polycyclic aromatic compounds including non-target and 71 target polycyclic aromatic hydrocarbons in scrubber discharge water and their environmental impact" . Marine Pollution Bulletin. 208 116790. Bibcode:2024MarPB.20816790A. doi:10.1016/j.marpolbul.2024.116790. ISSN   0025-326X. PMID   39270562.
17. Ytreberg, Erik; Hansson, Katarina; Hermansson, Anna Lunde; Parsmo, Rasmus; Lagerström, Maria; Jalkanen, Jukka-Pekka; Hassellöv, Ida-Maja (2022-09-01). "Metal and PAH loads from ships and boats, relative other sources, in the Baltic Sea". Marine Pollution Bulletin. 182 113904. Bibcode:2022MarPB.18213904Y. doi: 10.1016/j.marpolbul.2022.113904 . ISSN   0025-326X. PMID   35878478.
18. "Scrubbing the Air, Poisoning the Sea: How "Clean" Shipping is Destroying Mediterranean Biodiversity | Earth Journalism Network". earthjournalism.net. 2025-07-01. Retrieved 2025-09-09.
19. updated: 2023-03-07, Last. "Researchers find scrubber water harmful at the tiniest of concentrations". www.ivl.se. Retrieved 2025-09-09.{{cite web}}: |last= has generic name (help)
20. Magazine, Hakai. "In the Baltic Sea, Ship Scrubbers Have Caused Millions of Dollars Worth of Environmental Damage". Hakai Magazine. Retrieved 2025-09-09.
21. "UN Ocean Conference 2025: The scrubber case – time for glocal solution". Swedish Institute for the Marine Environment. 2025-06-23. Retrieved 2025-07-20.
22. "Ministers meet in Vigo to take concrete measures to enhance protection of the North-East Atlantic Ocean". OSPAR Commission. 2025-06-27. Retrieved 2025-09-09.
23. "Where Are Open-Loop Scrubbers Banned?". liqtech.com. Retrieved 2025-07-20.
24. Comer, Bryan (2020-06-18). "Scrubbers on ships: Time to close the open loop(hole)". International Council on Clean Transportation. Retrieved 2025-07-20.
25. "No Scrubs: Countries and Ports where Restrictions on EGCS Discharges apply". NorthStandard | Marine Insurance. Retrieved 2025-09-09.
26. Rosenoegger, Joachim (2025-07-02). "OSPAR Scrubber Ban | An Executive Overview for Maritime Operations". Maritime-Innovations.com. Retrieved 2025-09-09.