The sewage waste discharge from the ship is regulated under MARPOL Annex IV. The regulation states that:

– Every ship of 400 GT and above which is engaged in international voyages, and carrying a minimum of 15 persons onboard must be equipped with either a sewage holding tank of appropriate capacity or an approved sewage Treatment Plant (STP) or both


– The sewage discharge from the ship is allowed if it has an approved sewage treatment plant, which can treat the raw sewage and discharge comminuted and disinfected sewage. With this arrangement, the discharge is allowed at a distance of more than 3 nautical miles from the nearest land when the ship is proceeding with a speed of 4 knots and above


– Foreign going cargo ships may be allowed (depending upon the area they are plying) to discharge untreated sewage only at a distance greater than 12 nautical miles from the closest land only if the ship is proceeding with a speed of 4 knots and above


– The ship has to maintain the rate of discharge of sewage from the ship as recommended by the administration


– The rate of discharge from the ship is also limited to 1/200,000 (or one 200,000th part) of swept volume as follows:

DRmax = 0.00926 V D B

Where: DRmax is the maximum permissible discharge rate (m3/h)

V is the ship’s average speed (knots) over the period

D is Draft (m)

B is Breadth (m)


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