Why scrubbers matter

Ian Adams, executive director of the Clean Shipping Alliance 2020, explains why the continued use of heavy fuel oil and scrubbers is vital to human health and the environment.

There should be no doubt about the importance of the marine exhaust gas cleaning system in helping to improve the health of those living and working around the world’s ports and harbours. There is currently no better solution.

Sulphur emissions, particularly Sulphur Dioxide (SO2), a by-product of burning fossil fuels in an internal combustion engine, is the major contributor to a raft of respiratory health problems. Yet while we now have the technology to improve the health of millions, especially those living and working around the world’s ports and harbours, there is a corner calling for these systems to be banished.

The presence of high levels of SO2 and PM, especially, has such a negative effect on human health and society in general, that we as an industry, should be embracing this technology and looking at ways of improving it rather than removing it. It is counterintuitive and I think the media frenzy surrounding the washwater debate has created something of a panic devil, with us forgetting the primary reason why more than 4000 ships have the system installed.

Inhaled, sulphur dioxide quickly dissolves with moisture on the lining of the lungs and nose, burning the mucous membranes. This is clear to anyone who accidently inhales the smoke from a match being struck. Chronic, or long-term, exposure to high levels of SO2 leads to breathing problems and respiratory illnesses. Children tend to be more susceptible due to their less developed lungs.

Indeed, World Health Organisation (WHO) statistics show that 92% of the world’s population lives in places where air quality levels exceed WHO Ambient Air Quality Guidelines. These guidelines stipulate a ‘safe limit’ for fine particulate matter (PM 2.5) at 10μg/m3, but only 24 countries meet this requirement meaning that billions of people around the world are breathing in unsafe air. On average there are 1-in-8 premature deaths linked to air pollution each year – that’s 7 million deaths a year! The use of HFO with a scrubber can reduce this.

It is the Particulate Matter (PM) that is so dangerous to human health. And when inhaled, particles of less than 10μm penetrate the lining of the lungs, seeping into the bloodstream, contributing to respiratory diseases, such as asthma, bronchitis, and flu; increased risk of lung diseases, such as emphysema, chronic bronchitis, and lung cancer; increased risk of cardiovascular conditions, such as heart attacks and strokes; and increased risk of dermatological diseases and other cancers.

Aside from the poor respiratory health of those living around ports and harbours, areas where shipborne air emissions are documented to have a major negative impact on human health, these pollutants also, of course, contribute significantly to climate change.

Fossil fuels contain sulphur compounds and their combustion generates SO2. Further oxidation of SO2, usually in the presence of a catalyst such as Nitrogen Dioxide (NO2), forms H2SO4 (Sulphuric Acid), which returns to Earth in the form of acid rain. So, removing the sulphur compounds from the exhaust gas, reducing the potential of the formation of acid rain and the impact on humans and other living organisms, must remain the primary reason for adopting the most effective solution – the scrubber, a proven technology commonplace in land-based power plants and refineries around the world without undue concern.

Exhaust Gas Treatment Systems treat the gases from the combustion process by spraying alkaline water into the exhaust. In a seawater scrubber system, the sea’s natural alkalinity largely neutralizes the results of SO2 removal before discharge back to the sea. In a freshwater system, the washwater used for scrubbing and neutralization is treated with an alkaline solution such as sodium hydroxide (caustic soda) or magnesium hydroxide. In both cases the sulphates resulting from the SO2 removal will be discharged with the washwater to the sea, a major constituent of which is sulphate, anyway.

Of course, low sulphur fuels are being used, but the continued use of HFO with a scrubber provides a higher quality of air emissions than any 0.1% compliant fuel, and higher quality in all respects than 0.5% compliant fuel.

It is anathema to me that given the evidence and acknowledged fact that scrubbers do a far better job in removing SOx (99%), PM (94%) black carbon (60%), mitigating the risks to human health and the corresponding burden on public health services, that we are still having a debate about the efficacy of these systems.

Removal of black carbon, especially, slows down ice melt, which would ultimately contribute to rising sea levels. And, from an air quality point of view, operating a ship on HSFO in combination with a scrubber produces cleaner air emissions than operating on LSFO or MGO. Less refining also means less GHG emissions associated with HSFO vs MGO.

This was pretty much confirmed in a study published last year by Norway’s SINTEF, one of Europe’s largest independent research organisations. Chief Scientist Dr Elizabeth Lindstad concluded that from well-to-wake the continued use of HSFO or HFO with an EGCS is the most environmentally beneficial means of meeting global Greenhouse gas (GHG) emissions targets.

She stated that based on the energy consumed during the global production of distillate fuels, the continued use of residual fuel will have a positive impact on global GHG emissions, given the energy required to produce distillates would result in higher levels of CO2 being released into the atmosphere.

Yet, here we are, and despite the clear benefits to our planet and those that live on it, we find ourselves in something reminiscent of a Franz Kafka novel, with some ports and harbours banning a solution adopted for their benefit based only on blind authority, hearsay and supposition.

Due to the unfounded view by several port and maritime authorities that scrubber washwater could be hazardous to the marine environment, bans or restrictions have been imposed because they think that scrubbers pose a risk to public health and increase the rate of corrosion of their port infrastructure. ‘Could’ and ‘think’ being the operative words here.

Despite the fact that for decades shore-based industries have been operating scrubbers and discharging washwaters into rivers and waterways without much ado, then surely what is good for the goose is good for the gander. If such discharges contravened any water quality requirements in any way, then it is logical to conclude that they too would be banned from operating them.

None of the studies on scrubber washwater to date have shown that the use of exhaust gas cleaning systems poses any significant risk to the marine environment or to public health. To the contrary in fact.

If the sulphur in the sea were spread out as an even layer, the total ocean area of the world would be covered by a 5-foot (1.5m) thick layer of sulphur. And if all the sulphur in all the known oil and coal reserves were added to this layer, then, as Nyman and Tokerud stated in 1991, the thickness would only increase by the thickness of a sheet of paper. What is more, vessels fitted with scrubbers spend most of their time in international waters, where they normally produce much less SOx than compliant fuel with a sulphur content of <0.5%.

Nevertheless, there is no doubt in my mind that use of an EGCS in port would improve the lives of those living and working around them.


  1. While I disagree with the notion that energy requirement for distillation of more refined fuel oils would mean higher CO2 emissions, since renewable energy sources can be used for that, I think the overall message here is pretty clear: stop burning complex hydrocarbons for energy! For all the financial and practical obstacles to its alternatives, the health and environmental impacts are simply unacceptable, and emphatically not sustainable. It’s a hard pill to swallow, for sure, but a wholesale change of the way the industry is powered is essential, so let’s knuckle down and figure out how to do it!

  2. ‘Despite the fact that for decades shore-based industries have been operating scrubbers and discharging washwaters into rivers and waterways without much ado, then surely what is good for the goose is good for the gander. If such discharges contravened any water quality requirements in any way, then it is logical to conclude that they too would be banned from operating them.’

    Well said! And fully agree!

    Now, can someone please confirm an open-loop scrubber does indeed exist in the shore-based industries?

  3. Quotes from a literature review by Professor John Heywood and Dr. Emmanuel Kasseris of the Massachusetts Institute of Technology (MIT).

    POLLUTION PREVENTION AND RESPONSE. Scrubber Environmental Impact Literature Review. (2019)

    “The first issue is the impact of scrubber effluent discharge on marine life and biogeochemical processes. This is especially concerning when discussing open-loop scrubbers which constitute the vast majority of installed EGCS. Scrubber effluent contains pollutants such as heavy metals and polyaromatic hydrocarbons (PAH),among others. It is also acidic, which can affect ocean chemistry and marine life. Although ocean dispersion modelling of scrubber effluent studies has been very limited, there is an almost complete consensus in the literature that there is cause for concern and justification for further scientific investigation.”


    “The second issue concerns whether ships equipped with scrubbers are truly equivalent to ships using low sulphur fuel regarding air emissions. In terms of gaseous sulphur oxides, scrubbers are effective in removing them. In terms of particulate emissions however,
    there are strong indications in the literature that ships equipped with scrubbers may not be equivalent to burning low sulphur fuel. This is mostly due to the fact that scrubbers may not be as efficient in removing small (less than 100 nm diameter) particulates (nucleation mode) that consist mostly of sulphuric acid, water and condensable organic molecules. There is limited work in this area and it needs to be investigated further. However, there are enough indications that there may be issues with current scrubber designs and regulations in terms of delivering emissions that are completely equivalent to those of low sulphur fuel.”

  4. A Study on the failure of overboard piping due to corrosion will quickly indicate the dangers of pumping the washwster into the Sea in an open loop Scrubber system. The fact that so many different materials have had to be experimented with for use in the Overboard systems due to the agressive nature of the discharge should have raised alarm bells.

  5. The easiest win seems to be slow steaming.

    Slow the fast ferries, car ships, and container ships to 14 knots.

    Bulkers and tankers to 11 knots.

    Racing to anchor for days is even dumber…. running the speed for inspection or the berth should be mandatory.


    1. Yep, Experts. Did you know, Popeye, it ttakes more than 10,000h of practice to even contemplate being perceieved as an expert. Without knowledge and research we would all be susceptible to climbing up the backside of ignorance to sit in perpetual darkness. Was it not an expert that performed the labotomy?

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