The ecological risks of scrubbers for the marine environment are ignored while at the same time the economic benefits are overestimated, German environmental organisation NABU (Nature and Biodiversity Conservation Union) said commenting on the results of a new study.

A new study, assessing the environmental impact of scrubbers and the economic viability of the technology, strongly doubts this technology to be a sustainable solution for cutting ships’ sulphur emissions.

The study has been undertaken by the Dutch research institute CE Delft on behalf of the German environmental organization Nature and Biodiversity Conservation Union (NABU). NABU CEO Leif Miller says the study demonstrates that the ecological risks of using scrubbers to clean ship’s exhaust fumes are ignored and that the economic benefits have been overestimated.

“It is clear for everyone that simply discharging harmful substances into the ocean instead of to the air will not result in an improvement for the environment. Our report shows that today scrubbers cannot be considered a solution, neither in ecological nor in economical terms,” according to Miller.

Environmental impact

Scrubbers are an accepted alternative method for complying with marine fuel sulphur limits under International Maritime Organization (IMO) and European Union (EU) regulations, allowing ships to continue to use high sulphur fuel oil (HSFO) as long as they achieve equivalent sulphur emission reductions and meet specific washwater discharge criteria.

About 80 out of a 55,000 world fleet have scrubbers installed, with up to 300 additional systems on order, according to the study. The market is dominated by hybrid and open-loop scrubbers, discharging washwater into the sea which, unlike closed-loop and dry scrubbers. This is an issue, as

pollutants of which long term accumulative impact has not been systematically investigated and are not properly assessed. Even if the pH in washwater discharges meets IMO guidelines, scrubbers may have an impact on ocean acidification and accumulation of hazardous substances, such as heavy metals polycyclic aromatic hydrocarbons (PAHs).  Some of the metals discharged may come from fuel or lubricants, such as vanadium, nickel, calcium and zinc, while others may be related to engine wear, tear and system components.

Water frame directive

“It should be evaluated if scrubbers can be used in accordance with the European water framework directive that sets maximum concentrations for certain hazardous pollutants, especially close to dense shipping routes and vulnerable estuaries,” the study says.

Germany has prohibited scrubber washwater discharges in inland rivers and certain ports, including the Kiel Canal. Belgium has prevented discharging within three nautical miles off its coast. And Swedish authorities consider banning open loop scrubbers because of potential conflict with the European water framework directive.

Apart from concerns about the long term impact on ocean acidification there is the impact on greenhouse gas (GHG) emissions, primarily carbon dioxide (CO2), where scrubbers seem to compare favourably with MGO. The study indicates that scrubbers reduce sulphur emissions by more than 90%, particulate matter (PM) emissions by 60-90% and NOx emissions by 10% or less. Moreover, the additional power needed to drive pumps and caustic soda consumption causes an additional 1.5% to 3.5% of GHG emissions, but that the production of MGO for use in ECAs would cause an increase of GHG refinery emissions of roughly 6.5%.