An IMarEST Explainer: The unanswered questions surrounding scrubber washwater discharge has been published to explore the concerns frequently raised in connection with the installation of exhaust gas cleaning systems, or scrubbers as they are commonly known, on ships. This Explainer focuses on the potential impact of washwater discharges from open-loop scrubbers on the marine environment and considers to what extent these concerns are grounded in science. It highlights current gaps in our knowledge, explains some of the practical difficulties impeding research and finally, offers some policy recommendations.
This explanation follows new regulations introduced by the IMO in January 2020 in a bid to reduce sulphur emissions from the marine sector by over 80%. These regulations (known as IMO2020) mandate that the prior maximum fuel oil sulphur limit of 3.50% m/m (mass by mass) will fall to 0.50% m/m. This is the largest reduction in the sulphur content of a transportation fuel undertaken at one time. In order for the shipping industry to comply, ships must consider one of three currently available options:
1. use of low-sulphur fuel oil
2. the installation of an exhaust gas cleaning system (ECGS or “scrubber”)
3. use of other fuels that have low or zero sulphur content such as LNG.
This IMarEST Explainer aims to set out the concerns that are frequently raised in connection with option 2 – the installation of scrubbers.