Sewage – The problem
- The main sources of human-produced sewage are land-based - such as municipal sewers or treatment plants. However, the discharge of sewage into the sea from ships also contributes to marine pollution.
- The discharge of raw sewage into the sea can create a health hazard. Sewage can also lead to oxygen depletion and can be an obvious visual pollution in coastal areas - a major problem for countries with tourist industries.
- It is generally considered that on the high seas, the oceans are capable of assimilating and dealing with raw sewage through natural bacterial action. Therefore, the regulations in Annex IV of MARPOL prohibit the discharge of sewage into the sea within a specified distance of the nearest land, unless they have in operation an approved sewage treatment plant.
Regulations on force:
Standards for Sewage treatment plant (guidelines on implementation of effluent standards and performance tests for sewage treatment plants)::
- installed prior to 1 Jan 2010: Resolution MEPC.2 (VI)
- installed on or after 1 Jan 2010: Resolution MEPC.159(55)
- installed on or after 1 Jan 2016 - Resolution MEPC.227(64)
Guideline on how to calculate the moderate rate of discharge: Resolution MEPC.157(55) – adopted on 13 October 2006
Special Area provisions and the designation of the Baltic, Resolution MEPC.200(62) January 2013
Discharge of sewage
Prohibited except when the following requirements are complied with:
- Comminuted and disinfected sewage: at least 3 nautical miles from the nearest land, or
- Sewage not comminuted or disinfected: at least 12 nautical miles form the nearest land. Sewage that has been stored in holding tanks shall be discharged at a moderate rate when the ship is in route and proceeding at not less than 4 knots (the discharge rate shall be approved by the Administration based upon standards developed by the Organization).
- The ship has in operation an approved sewage treatment plant which has been certified by the Administration
These requirements shall not apply to ships operation in the waters under the jurisdiction of a State and visiting ships from other States while they are in these waters and are discharging sewage in accordance with such less stringent requirements as may be imposed by such State
As with tank cleaning water, a physical-chemical and biological process is carried out for grey water.