A passenger ship is like a floating hotel. Besides energy, provisions and equipment a lot of fresh water is needed to keep its functions running. After using the water in many different onboard processes it ends up as waste water.
Basically, waste water origins from the ship's hotel functions, from engine operation or from deck washing. Sewage (waste water) from the hotel comes either from toilets, then called 'black water', or from wash- and shower basins, referred to as 'grey water'.
Since many years, sewage on board TT-Line's ships has been cleaned in biological sewage treatment plants and no untreated waste water is pumped overboard. Nowadays, reception facilities for sewage from ships are available in one of the ports of call. Consequently, TT-Line has started to discharge sewage from a collection tank on board to the municipal sewage system ashore thus omitting any discharge into the sea at all. This is done as far as technical requirements are met and when harbour times allow for.
Process water from engine operation and wash water from cargo decks contains oil which should not reach the sea. In accordance with the rules, all ships are equipped with oily water separators for cleaning this water. TT-Line has even retrofitted on some ships a new generation of water treatment plant being able to clean oily water to much below the permitted limit. This new equipment is presently tested in daily operation.