A study by the International Council on Clean Transportation is suggesting individual governments to take unilateral action to restrict or ban scrubber discharges from both open-loop and closed-loop systems.
The IMO allows the use of scrubbers as an equivalent compliance option because they are expected to reduce sulfur dioxide emissions by the same, or more, as using compliant fuels. However, according to the study, when considering the total air pollution consequences of scrubbers, they may not be equivalent to using lower-sulfur fuels, such as marine gas oil (MGO).
While scrubbers are effective at reducing sulfur dioxide, the sulfur and other contaminants removed from the exhaust gas—including carcinogens such as polycyclic aromatic hydrocarbons (PAHs) and heavy metals—are dumped overboard in the form of washwater, also called discharge water. This happens even with so-called “closed-loop” scrubbers
The study estimated air and water emission factors for ships using HFO with scrubbers compared to other fuels based on the available literature and the methods of the Fourth IMO Greenhouse Gas Study. Regarding air emissions, it found that using scrubbers can substantially reduce sulfur dioxide emissions but carbon dioxide,
particulate matter, and black carbon emissions were higher when using HFO with a scrubber than using MGO.
For water pollutants, it found that scrubber discharges usually comply with IMO guidelines; however, compliance does not guarantee that scrubber discharges are safe.
In addition, the study concluded that all scrubbers discharge water that is more acidic and turbid than the surrounding water. Moreover, scrubbers emit nitrates, PAHs, and heavy metals, all of which can negatively affect water quality and marine life.
Based on this analysis, the International Council on Clean Transportation makes the following recommendations:
- Individual governments should continue to take unilateral action to restrict or prohibit scrubber discharges from both open-loop and closed-loop systems;
- The IMO should focus on harmonizing rules for scrubber discharges including where, when, and even if those discharges should be allowed, and to do so with urgency. The IMO should consider prohibiting the use of scrubbers as a compliance option for new build ships and work to phase out scrubbers installed on existing ships.
- Individual countries should take immediate actions to protect their air and waters from scrubber emissions and discharges.
Regarding the latter suggestions, these actions could include one or both of the following:
- An immediate prohibition on using scrubbers to comply with the Canadian portion of the North American ECA because they are not equivalently effective at reducing air pollution as ECA-compliant fuels;
- An immediate prohibition on all scrubber discharges in Canadian ports, internal waters, and territorial seas because they contribute to acidification and water pollution that can negatively affect marine life.