In heavily trafficked waterways as well as in ports and estuaries environmental risks increase exponentially. Photo: © Shutterstock – Frederick Doerschem

Environmental impacts of ship scrubbers

Untreated wash water from open-loop scrubbers contains heavy metals, aromatic hydrocarbons and soot particles, and scientific tests have shown harmful effects on marine organisms.

The use of exhaust gas cleaning systems, also known as scrubbers, on ships as an alternative to switching to cleaner low-sulphur fuel, has been a hotly debated issue since the stricter global ship fuel sulphur regulations were adopted by the International Maritime Organization (IMO) more than ten years ago.

Since 2015, all ships travelling in designated Sulphur Emission Control Areas (SECA) have to comply with a fuel sulphur limit of 0.10 per cent. The SECAs cover two northern European sea areas, the North Sea and the Baltic Sea, as well as the coastal waters (out to 200 nautical miles) of the United States and Canada.

As from 1 January 2020, the global sulphur limit will be reduced from 3.5 per cent to 0.50 per cent, and will apply to all ships in international trade.

Ship operators have different options available to achieve these sulphur limits. The most straightforward option is to switch to using a compliant lower-sulphur fuel oil, i.e. with a sulphur content less than the mandatory limit values. A second option is to switch to using an alternative low- or zero-sulphur fuel, such as liquefied natural gas (LNG), liquefied biogas (LBG) or methanol. And the third is to equip the ship with an exhaust gas cleaning system that reduces the emissions of sulphur dioxide (SO2) to levels that are lower than those resulting from using compliant fuels. Under this last option, ships are allowed to continue to burn residual high-sulphur heavy fuel oil (HFO).

There are primarily two types of scrubbers – open-loop and closed-loop, but there are also hybrid scrubbers that can switch between the open and closed modes. Open-loop scrubbers in particular have been subject to debate, as they use seawater as the “cleansing agent” and produce large amounts of wash water which is discharged into the sea, usually without any treatment. The closed system recirculates the scrubbing water and discharges a lesser volume after treatment.

It is expected that by the end of 2019 nearly 3000 ships will be equipped with scrubber systems, and the vast majority of these (around 80 per cent) are open-loop scrubbers.

In an EU-funded study published this summer, researchers at the IVL Swedish Environmental Research Institute have analysed the environmental effects of both open and closed scrubbing systems.

In ecotoxicological tests, a number of marine organisms were exposed to varying concentrations of scrubbing water. The tests revealed negative effects on vital functions in several organisms. Most impacted were the copepods – a group of zooplankton that play a vital role in the food chain. Even low concentrations of untreated water from open-loop scrubber systems as well as treated scrubber water from closed-loop systems resulted in adverse effects on these organisms.

Wash water from both scrubber systems was found to be heavily contaminated with heavy metals, aromatic hydrocarbons and soot particles. Since the open systems discharge significantly higher volumes than the closed system, the discharges from open scrubbers all in all pose a greater risk to the marine environment than those from closed systems, according to the report. Also, the water from the closed system is treated before discharge and residues that are separated are taken ashore for disposal.

The researchers point out that individual ship passages do not impact the marine environment to any great extent, but in heavily trafficked waterways as well as in ports and estuaries environmental risks increase exponentially.

“Several of these pollutants break down relatively quickly but are at the same time acutely toxic. When the marine environment is continuously exposed to scrubbing water from vessels, this acute toxicity becomes permanent. In my opinion scrubbing is a real threat to biodiversity,” says Kerstin Magnusson, marine ecotoxicologist at IVL and one of the authors of the report.

“If we permit the discharge of scrubbed exhaust gases into the sea, we expose marine ecosystems to yet another source of pollution, in addition to all those they are already subject to. That conflicts with the UN global environmental goals, which require us to prevent or at least significantly reduce all kinds of pollution in the sea by 2025,” she continued.

“The new sulphur legislation is important as it reduces the impact of shipping on air quality, but unfortunately it ignores the consequences for the marine environment. If vessels continue to run on dirty bunker oil, the pollutants will instead end up in the sea where they will adversely impact the marine ecosystem,” said Hulda Winnes, project manager and researcher at IVL.

The study consists of several parts, including cost-benefit and life-cycle analyses. From an environmental risk perspective, it was concluded that: “The use of a low-sulphur fuel oil as marine fuel is favourable compared to the use of heavy fuel oil in combination with an exhaust gas scrubber. This statement is valid for closed-loop scrubbers and open-loop scrubbers and mainly based on the studies performed on eco-toxicity of effluent water.”

When analysing external costs of the different options it was concluded that: “The low-sulphur fuel option is less costly than the two scrubber options. The use of scrubbers on the vessels increased health and environmental costs from emissions compared to the case when they used low-sulphur fuel oil.”

“Creating new environmental problems in this way, by giving a green light to scrubbing technology is wrong from a sustainability perspective. All we do when we fit exhaust gas systems, especially open-loop scrubbers, is move pollutants somewhere else,” said Hulda Winnes.

Christer Ågren

Source: IVL reports and press release, 1 July 2019. Link:
Note: Several countries and/or ports have already either banned or flagged an upcoming ban on open-loop scrubbers, including California, Belgium (all ports), Germany (canals, rivers and ports located by rivers), Ireland (Dublin), Norway (five protected fjords), China (ports in ECAs), Singapore and Fujairah. Website with list of scrubber bans (North P&I):

Most impacted were the copepods – a group of zooplankton that play a vital role in the food chain. Photo: /Biodiversity Heritage Library CC BY



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