Sewage Treatment Plant

A marine sewage treatment plant produces effluent that meets the MARPOL Annex IV discharge standard so sewage can be discharged at sea. Plants installed on ships built on or after 1 January 2010 are type-approved to the effluent and performance standard in MEPC.227(64), which caps thermotolerant coliforms at a geometric mean of 100 per 100 ml, BOD5 at 25 mg/l, and suspended solids at 35 mg/l. Section 4.2 of MEPC.227(64) adds total nitrogen and phosphorus limits for plants on passenger ships intending to discharge in the Baltic Sea special area, the only Annex IV special area, with those nutrient limits phased in from 1 June 2019 and 1 June 2021.