It belongs to the key devices for prevention of pollution from ship in seas and oceans according to the revised Annex IV of the International Convention of the Prevention of Pollution (MARPOL 73/78).The resolution MEPC.2 (VI) adopted on 3 December 1976 is the present guidelines on implementation of effluent standards and performance tests for STP.which is called "old standards".This device is according to the resolution MEPC.159(55) enacted on 13 October 2006,which is called "new standards".