IMO guidance: temporary storage of sewage and grey water

The International Maritime Organization has published BWM.2/Circ.82 with guidance for the temporary storage of treated sewage and/or grey water in ballast water tanks.

This circular was published on 2 April 2024.

Guidance for the temporary storage of treated sewage and/or grey water in ballast water tanks

The Marine Environment Protection Committee, at its eighty-first session (18 to 22 March 2024), approved the Guidance for the temporary storage of treated sewage and/or grey water in ballast water tanks to establish a uniform procedure for minimizing the impact on the environment while ensuring practicability on ships, as set out in the annex.
Member Governments are invited to bring this Guidance to the attention of all parties concerned.

Introduction

The purpose of this guidance is to provide a procedure for the temporary storage of treated sewage and/or grey water in ballast water tanks.
Shipowners, ship operators, masters and officers of ships with temporary storage of treated sewage and/or grey water in ballast water tanks should properly implement this procedure.
There are exceptional situations where, to comply with coastal State regulations or inadequate reception facilities at ports, dry-docks and terminals, it may become necessary to store treated sewage and/or grey water in ballast water tanks.

Definitions

For the purpose of these guidelines:
4.1 "Ballast water" means water with its suspended matter taken on board a ship to control trim, list, draught, stability or stresses of the ship (article 1(2) of the BWM Convention).
4.2 "Treated ballast water" means water that is treated by a ballast water management system (BWMS) to comply with regulation D-2 of the BWM Convention.
4.3 "Treated sewage (TS)" (effluent) means treated wastewater that is produced by a sewage treatment plant in accordance with regulations 9.1.1 and 9.2.1 of MARPOL Annex IV.
4.4 "Grey water (GW)" means drainage from dishwater, galley sink, shower, laundry, bath and washbasin drains and does not include drainage from toilets, urinals, hospitals, and animal spaces, as defined in regulation 1.3 of MARPOL Annex IV, nor drainage from cargo spaces (paragraph 2.7 of resolution MEPC.227(64), as may be amended).
4.5 "Ballast water tank (BW tank)" means any tank, hold, or space used for the carriage of ballast water (paragraph 2.2 of Guidelines (G4) (resolution MEPC.127(53) as amended)).
4.6 "Ballast water capacity" means the total volumetric capacity of any tanks, spaces or compartments on a ship used for carrying, loading or discharging ballast water, including any multi-use tank, space or compartment designed to allow carriage of ballast water as per regulation A-1.2 of the BWM Convention. Combined tanks are, therefore, regarded as BW tanks for the purposes of the BWM Convention.

General matters for application

Temporary storage of TS/GW in BW tanks should only be used as an option in specific ports and areas which restrict the discharge of TS/GW and where the ship does not have dedicated tanks with adequate storage capacity for TS/GW.
Mixing ballast water and TS/GW in a BW tank should be avoided.
The storage of sewage not meeting the definition in paragraph 4.3 in a BW tank is outside the scope of this guidance.
In case a ship stores TS/GW temporarily in its BW tanks, the ship should make periodic inspections for those BW tanks' coatings and take measures to prevent impacts.

General guidance

If the use of a particular BW tank is changed for the temporary storage of TS/GW in line with this guidance, such a BW tank should be solely used for storing it. If the use of the BW tank needs to be reverted to storage of ballast water, the ship should follow this guidance again.
In case a ship uses BW tank(s) to store TS/GW, when transferring TS/GW to BW tank(s) the ship should take appropriate measures to prevent contamination of the ballast system by TS/GW and to prevent accidental discharge of TS/GW within restricted waters (e.g. closing the valves or using blanks, spectacle flanges and pipeline blinds or using isolated pump and pipeline, dedicated portable hose, and/or using a lockout/tagout).
In case a ship changes the use of a BW tank to store TS/GW, the BW tank should be fully emptied, including removal of any residual ballast water, as far as practicable, through the BWMS. The removal and disposal of sediments should be carried out as far as practicable and in line with paragraph 1.3 of part A of Guidelines (G4) (resolution MEPC.127(53) as amended).
In case a ship changes the use of a BW tank from TS/GW storage back to ballast water storage, the ship should follow the following procedures:
12.1 The contents of the BW tank(s) should be discharged. The BW tank, pipes, and dual-purpose pumps should be flushed with the normal maximum volume of the tank.
12.2 Water used to flush the tanks should not be discharged through the BWMS to avoid residue from the TS/GW entering the BWMS as this could potentially harm the BWMS.
12.3 Subsequent to the discharge and flushing, the ballast water tank should be reconnected to the ballast system and the tank should be flushed once more with treated ballast water to replace the residual water thus ensuring the tank is ready to return to ballast operations in accordance with the BWM Convention.
The hull strength and stability of the ship should not be compromised during the intended duration of the temporary storage of TS/GW in BW tanks including ascertaining that non-availability of a BW tank does not impact ship safety and operational performance.
The discharge of ballast water and TS/GW should adhere to the following principles:
14.1 the discharge of ballast water and sediments should be in compliance with the BWM Convention; and
14.2 the discharge of TS should be in compliance with MARPOL Annex IV where relevant. Any local TS/GW discharge requirements should also be considered.
The Ballast Water Management Plan (BWMP) of the ship should include a ship-specific change-over procedure, from ballast water storage to TS/GW storage and back to ballast water storage, including pump and piping associated with the dual-purpose BW tanks, with specific details on how the flushing is conducted. The BW tanks to be used for temporary storage of TS/GW should be identified in the BWMP.
The Ballast Water Record Book (BWRB) should have an entry made under the appropriate code related to additional operational procedures and general remarks containing the details as mentioned in examples 22 and 23 in BWM.2/Circ.80.

For more information, please see the document below (available only to subscribers):