In 2008 the IMO decided to significantly lower the permissible sulphur levels in marine fuels, particularly in Northern Europe and North America. Technology providers then scrambled to develop solutions that were much more affordable than switching to expensive low-sulphur fuel.

The alternatives that emerged included on-board Exhaust Gas Cleaning Systems (EGCS), also known as scrubbers. These shower the exhaust gas with water, which absorbs most of the sulphur oxides to make the emissions much cleaner.

The sulphur is now in an aqueous solution that still needs to be managed. Typically, this is done either by diluting with large amounts of sea water – in which the salt acts as a neutraliser – or by adding a reducing agent such as caustic soda to neutralise this otherwise quite acidic solution.


Many member states, especially those within the European Union (EU), encouraged shipowners to invest in scrubbers. Their use in ports and coastal areas has gradually become more and more prevalent but also increasingly contentious, notably among certain EU Member States and in the US, due to the potential composition of the effluent.

Within the wider maritime community, the issue of scrubbers also raises commercial concerns. Some countries see it as being uncompetitive and some question whether the technology itself is environmentally sound and defensible. Furthermore, there is no EU regulatory framework in place. This means it is left to individual member states, or even municipalities, to decide if they allow the use of open-loop scrubbers, which discharge into the sea, as opposed to closed-loop units that discharge into a tank for further treatment ashore.

The discussion on stricter requirements for discharge water from scrubbers has been on-going for many years without much scientific background. In recent years, several studies have indicated that the current prevalence of EGCS is not a cause for concern. However, the introduction of a global sulphur cap in 2020 has seen a rapid increase in scrubber uptake, so modelling should be made on the potential implications if installations are carried out by a significant proportion of the world merchant fleet.


Revised guidance for new EGCS installations has been developed and is awaiting approval by the IMO Maritime Environmental Protection Committee – the timing of which is unclear due to the current COVID-19 situation. The guidance, in its non-approved form, can be found as Annex 9 of the PPR 7 Report to MEPC 75.

Meanwhile the Interferry Operators Policy Committee has agreed the following position:

  1. Existing installations have been made in good faith and, so long as they comply with contemporary requirements, they should not be affected by any future changes
  2. Any new requirements should be based on scientific facts