International regulations regarding shipboard sewage discharge, governed by MARPOL Annex IV, strictly control black water (sewage) but generally exempt grey water from direct international rules, although this is changing due to local legislation.
Black Water vs. Grey Water
- Black Water (Regulated): Commonly understood as MARPOL’s definition of sewage. It includes drainage from toilets, urinals, medical facilities, and animal spaces. It contains harmful bacteria, viruses, and pathogens.
- Grey Water (Generally Not Regulated by MARPOL): Wastewater from sinks, showers, laundry, dishwashers, and galleys. Though considered less contaminated, it can still contain pollutants like detergents, oils, food particles, and microplastics.
Black Water Discharge Requirements (MARPOL Annex IV)
MARPOL Annex IV applies to ships of $\geq400$ GT or those carrying $\geq15$ persons. Such ships must be equipped with an approved sewage treatment plant, a sewage comminuting and disinfecting system with a holding tank, or a holding tank with sufficient capacity to retain all sewage.
| Treatment Status | Minimum Distance from Nearest Land | Ship Condition |
| Untreated Sewage | Greater than 12 nautical miles (nm) | Must be proceeding en route at greater than or equal to 4 knots, discharged at an approved rate. |
| Comminuted and Disinfected Sewage | Greater than 3 nautical miles (nm) | Permitted when using an approved system. |
| Treated Sewage | At all times (no distance restriction) | Must have an approved and certified sewage treatment plant meeting MEPC.227(64) standards. |
Stricter Area-Specific Regulations
Both Special Areas and Polar Waters impose stricter requirements on black water discharge:
- Baltic Sea (MARPOL Annex IV Special Area): Applies only to passenger ships and prohibits the discharge of all sewage, regardless of distance, unless the ship is using an approved sewage treatment plant (meeting MEPC.227(64) standards).
- Polar Code (Part II-A, Chapter 4): Prohibits the discharge of any untreated sewage, regardless of distance, from Category A, B, and all passenger ships in Polar Waters.
Grey Water Regulation Status
Grey water is not directly regulated by MARPOL Annex IV; therefore, in most international waters, ships can discharge it overboard without treatment.
- Local Legislation: Due to growing environmental concerns, local authorities and coastal states, such as the US (under the Clean Water Act), Turkey (restricting all sewage, including grey water), and those bordering the Baltic Sea, are increasingly imposing stricter local laws that restrict or prohibit grey water discharge in nearshore areas.
- Crew Compliance: Where local laws restrict grey water discharge, crews must manage the water by directing it to the sewage holding tank, ensuring the overboard discharge valve is closed and sealed, and arranging for use of shore reception facilities when necessary.
The maritime industry, supported by organizations like BIMCO and HELCOM, is working toward harmonized international standards for grey water to address its cumulative environmental impact.
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Source: North Standard
