The used scrubbing material is then collected with wash water, which may be stored or disposed of immediately as the effluent. The cleaned exhaust is passed out of the system and into the atmosphere.
The scrubbing material is chosen for its ability to remove specific impurities – such as SOx or NOx – by chemical reactions. For de-sulphurization purposes, marine scrubbers use lime or caustic soda in order to produce sulphur-based salts after treatment, which can be easily discharged as they are safe for the environment.
Scrubbers may use sea water, or fresh water with added calcium/sodium sorbents, or pellets of hydrated lime, as the scrubbing medium due to their alkaline nature. On the basis of their operation, marine scrubbers can be classified into Wet and Dry versions.