CSA 2020 addresses scrubber concerns

Malcolm Latarche
Malcolm Latarche

19 October 2018

Ten of the main concerns over the use of scrubbers were addressed in a recent release by the newly formed Clean Shipping Alliance 2020 (CSA 2020). The association has now also added new members and now counts 25 leading maritime companies representing over 2,000 ships.

Among the most commonly voiced arguments against scrubbers addressed were those concerning the potential harmful effect of wash water on the environment. Referencing a widely quoted paper (Nyman GBG Tokerud A. (1991), CSA 2020 pointed out that, since scrubbers produce sulphur in the form of sulphate as the end product of the scrubbing process and sulphate is a naturally occurring constituent of seawater and therefore not harmful to the sea. The oceans are the Earth’s natural reservoir of sulphur and play a key role in the sulphur cycle. Sulphur is one of the most common elements and is both biologically necessary and critical to many metabolic processes.

In the paper referred to, it is stated that if all the sulphur in the oceans were accumulated at the bottom of the ocean the layer would be five feet thick; adding all the sulphur from all the oil and gas reserves in the world would add only the thickness of a sheet of paper. Compared with the quantity of sulphate existing in the oceans, the small amounts of sulphate contributed by exhaust gas scrubbing are insignificant and benign.

In addressing the question of scrubbers’ acidification effect on seawater, the CSA2020 release says that during the scrubbing process any decrease in the pH of the wash-water is largely neutralised by the natural alkalinity found in seawater. This ensures that the pH of the discharged water is in compliance with guidelines established by the IMO. The resulting discharge contains only a slight increase in the natural concentration of sulphate in water.

Direct measurements on 40 ships monitored by maritime classification societies while the ships were in port have shown that pH levels of scrubber discharge water revert to ambient seawater pH levels within two to four meters of the discharge point – exceeding the IMO requirement. As shown by a 2012 Danish Environmental Agency study, there is negligible acidification effect from scrubbers, even in semi-enclosed ocean areas with high traffic levels of scrubber-fitted ships.

In its release CSA2020 noted that adherence to the IMO guidelines on wash water will ensure that any harmful effects of scrubbing are controlled. In addition, independent studies and research demonstrate that scrubbers are capable of removing 60 to 90% of particulate matter (PM), including a portion of small PMs (10 and 2.5 micron, and ultrafine) which results in releasing fewer PMs in the atmosphere compared to using MGO. Scrubbers are also effective in removing black carbon (BC), of particular interest because of the potential impact in Arctic regions.