MARPOL, Annex - IV, International Regulations for the Prevention of Pollution by Sewage from Ship

 Sewage Means :-

• Drainage and other waste from any form of toilets and urinal. 
• Drainage from medical premises via wash basin, wash tubs and scuppers located in such premises. 
• Drainage from spaces containing living animals
• Other waste water when mixed with the drainage defined above. 

Image By - 2nd Mate nimit_chhetri

                   

Holding Tank :-

Holding tank means the tank used to store the sewage is called holding tank. 

The Provisions of this Annex Apply to

A) All ship ≥ 400 GRT 

B) All ships certified to carry more than 15 person. 

* The special area designated for Annex - IV is BALTIC SEA. *

Discharge of Sewage :-

Discharge of Sewage into the sea is prohibited except when

1. A) Sewage is comminuted and disinfected using an approved system discharged more than 3 NM from nearest land. 

B) If sewage is not comminuted and disinfected discharged more than 12 NM from nearest land. 

C)  Sewage from holding tank should not be discharged instantaneously but at a moderate rate when the ship is en-route and proceeding at more than 4 knots OR

2. The ship has in operation an approved sewage treatment plant which has been certified. 

3. Does not produce visible floating solids and not discoloured.