3 General
Clasification Society 2024 - Version 9.40
Statutory Documents - IMO Publications and Documents - Resolutions - Marine Environment Protection Committee - Resolution MEPC.227(64) – 2012 Guidelines on Implementation of Effluent Standards and Performance Tests for Sewage Treatment Plants – (Adopted on 5 October 2012) - Annex - 2012 Guidelines on Implementation of Effluent Standards and Performance Tests for Sewage Treatment Plants - 3 General

3 General

  3.1 An approved sewage treatment plant should meet the technical specifications in section 4 and the tests outlined in these Guidelines. However, section 4.2 on nitrogen and phosphorous removal applies to passenger ships operating within a special area intending to discharge treated sewage effluent into the sea. It should also be noted that, when ships are operating approved sewage treatment plants, MARPOL Annex IV also provides that the effluent shall not produce visible floating solids or cause discolouration of the surrounding water.

  3.2 In meeting the effluent standards in section 4, an approved sewage treatment plant should not rely solely on dilution of wastewater. Where amounts of dilution are deemed essential to a treatment process, the effluent standards in section 4 having concentration limits (mg/l) should be adjusted proportionally using dilution compensation factor Qi/Qe to take account of dilution Qd. In addition, for effluent standards in section 4 having a percentage reduction, the geometric mean of the daily percentage reduction values should be calculated using the accumulated flow Qi and Qe over each 24-hour test day, in terms of l/day, multiplied by the geometric mean of the corresponding concentration Ci and Ce for the same 24-hour test day, in terms of mg/l.

The overall percentage reduction over the entire test period n is:

where PR n is the daily removal value:

where:

  • n represents the test day number; and
  • s represents the sample number collected on test day n

  3.3 It is acknowledged that the performance of sewage treatment plants may vary considerably when the system is tested ashore under simulated shipboard conditions or on board a ship under actual operating conditions. Where testing ashore demonstrates that a system complies with the standards, but subsequent onboard testing does not meet the standards, the Administration should determine the reason and take it into account when deciding whether to type approve the plant.

  3.4 It is recognized that Administrations may wish to modify the specific details outlined in these Guidelines to take account of very large, very small or unique sewage treatment plants.


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