Study: Scrubbers Have Minimal Effect on Water Quality

Scrubber retrofit installation (file image)

Published Jun 14, 2019 2:02 PM by The Maritime Executive

The Clean Shipping Alliance, the association for exhaust scrubber manufacturers and users, has released initial results from a study of scrubber washwater from environmental research institute CE Delft. The findings are favorable: the authors determined that accumulated concentrations of scrubber washwater contaminants in seaports are at very low levels, and well below regulatory limits. The results are similar to those from a study conducted by Japan's Transport Ministry and from extensive data gathered aboard Carnival's scrubber-equipped cruise ships. 

Exhaust pollutants discharged in washwater are equivalent to or lesser than those found in the airborne exhaust stream from a conventional ship - they are the same substances from the same source - but several ports and regional authorities have banned open loop scrubber use over pollution concerns. CSA and its partners, noting the shortage of scientific study of scrubber effects, have backed several new reviews of washwater contents and petitioned ports to reserve judgment until conclusive evidence is available. 

The latest study, funded by CLIA and Interferry and carried out by CE Delft and Deltares, used a dynamic computer modeling system to estimate the effects of scrubber washwater in European ports. CE Delft, a consultancy in the Netherlands, conducts maritime environmental reviews for government agencies, industry groups and advocacy NGOs alike. Using models of common EU port configurations, the study is assessing the accumulated impact of scrubbers on water quality by evaluating the concentration of nine metals and 16 polycyclic aromatic hydrocarbons (PAH) over time. CE Delft researchers used wash water samples taken from the scrubber tower outlet of cruise ships, bulk carriers and ferries prior to any after-treatment as the basis for pollutant concentrations. For four substances - naphthalene, nickel, and the PAH compounds benzo(a)pyrene and fluoranthene - the authors found a slight increase in the equilibrium concentrations, though still only between 0.02 - 0.2 percent of the maximum regulatory standard. Increases in other pollutant concentrations were negligible.