Discharge of sewage (Annex IV, Reg 11 MARPOL) into the sea is prohibited, except when:
1. The ship is discharging comminuted and disinfected sewage using a system approved by the Administration at a distance of more than 3 nautical miles from the nearest land, or sewage which is not comminuted or disinfected, at a distance of more than 12 nautical miles from the nearest land, provided that, in any case, the sewage that has been stored in holding tanks, or sewage originating from spaces containing living animals, shall not be discharged instantaneously but at a moderate rate when the ship is en route and proceeding at not less than 4 knots; the rate of discharge shall be approved by the Administration based upon standards developed by the Organization; or
2. the ship has in operation an approved sewage treatment plant which has been certified by the
-the test results of the plant are laid down in the ship’s International Sewage Pollution Prevention
-the effluent shall not produce visible floating solids nor cause discoloration of the surrounding water.
3. When the sewage is mixed with wastes or waste water covered by other Annexes of MARPOL, the requirements of those Annexes shall be complied with in addition to the requirements of Annex IV .