The IMO BWMS Code (Formerly G8) and How Type Approval Works

Q: Is the BWMS Code the same as G8?

No. The BWMS Code (MEPC.300(72)) is the mandatory successor to the voluntary Guidelines G8. It standardized and tightened the test protocol and introduced mandatory System Design Limitations. Systems installed on or after 28 October 2020 must comply with the Code.

Q: What are System Design Limitations?

SDLs are the validated boundaries within which a system is proven to meet D-2, such as minimum UV transmittance, salinity range, temperature range and holding time. Operating outside the SDLs means the system has not been demonstrated to achieve compliant discharge in those conditions.

Q: Do I need a new system if mine was approved under the old G8?

Not necessarily. Systems installed before 28 October 2020 under the original G8 approval remain valid for those installations. However, any system installed on or after that date must hold BWMS Code approval, so retrofit and newbuild projects use Code-approved equipment.

Q: What is G9 approval and which systems need it?

G9 (MEPC.169(57)) is the IMO procedure that assesses the safety of active substances and disinfection by-products. Systems that generate or dose active substances, such as electrochlorination and chemical injection systems, require G9 Basic and Final Approval in addition to type approval.

Updated 2026-06-16

IMO type approval of a Ballast Water Management System is governed by the BWMS Code, adopted as MEPC.300(72), which replaced the earlier Guidelines (G8). The Code tightened test protocols, introduced mandatory reporting of System Design Limitations and made approval more robust. This article explains the testing regime, the role of G9 for active substances, and how to read a type approval certificate.

The IMO BWMS Code (Formerly G8) and How Type Approval Works

Key takeaways

The BWMS Code (MEPC.300(72)) replaced Guidelines G8 and is mandatory for systems installed on or after 28 October 2020.
Land-based testing requires valid replicate cycles in marine, brackish and fresh salinity bands against challenge water.
System Design Limitations (SDLs) define the validated operating envelope; operating outside them is unproven.
Shipboard testing and component robustness testing confirm real-service durability and sensor reliability.
Active-substance systems also need G9 approval (MEPC.169(57)), assessing TRO, by-products and neutralization.
A type approval certificate states the treatment-rated capacity and the SDLs the operator must match to trading waters.

From Guidelines G8 to the BWMS Code

For most of the Convention's early life, type approval followed the 2008 Guidelines for approval of ballast water management systems, known as Guidelines G8 (resolution MEPC.174(58)). Industry experience showed that the original G8 left too much interpretation to individual administrations, producing inconsistent results and systems that struggled in real-world service.

IMO converted the guidelines into a mandatory instrument by adopting the BWMS Code in resolution MEPC.300(72) in 2018. The Code became mandatory for systems installed on or after 28 October 2020, meaning new approvals had to demonstrate compliance with the stricter, standardized protocol rather than the legacy guidelines.

The headline change was rigor: tighter control of test conditions, mandatory measurement and reporting of System Design Limitations, and clearer rules on validating self-monitoring sensors. The aim was to ensure a type-approved system actually meets D-2 across the operating envelope claimed by the manufacturer.

Land-Based Testing

Land-based testing exposes the system to challenge water dosed with high concentrations of test organisms across three salinity bands: marine (>32 PSU), brackish (around 10-20 PSU) and fresh (<1 PSU). The challenge water must also meet minimum concentrations of organisms in the relevant size classes and minimum levels of dissolved and particulate organic carbon, plus a defined turbidity, so the system is tested against realistic loading.

Five valid replicate test cycles per salinity must demonstrate treated discharge meeting the D-2 limits, with control samples confirming the challenge organisms were present and viable. The BWMS Code requires that the most challenging conditions, such as minimum UV transmittance for UV systems or minimum temperature and salinity for electrolytic systems, are reflected in the declared System Design Limitations.

These System Design Limitations (SDLs) are a defining feature of the Code. They state the validated boundaries, such as minimum UVT, salinity range, temperature range and holding time, within which the system is proven to meet D-2. Operating a system outside its SDLs is effectively operating an unproven configuration.

Shipboard Testing and Robustness

Beyond the laboratory, the Code requires shipboard testing over a minimum operational period to confirm the system performs in actual service conditions. Shipboard testing includes a defined number of valid ballast and deballast cycles with sampling that confirms compliant discharge, demonstrating durability and integration with the ship's ballast system.

The Code also strengthened component robustness requirements, including environmental testing of electronic and electrical equipment for vibration, temperature, humidity and supply variation in line with marine equipment standards. Self-monitoring equipment such as TRO analyzers and UV intensity sensors must be validated so the control system reliably knows whether treatment is effective.

This combination of land-based and shipboard validation is intended to close the gap between certificate and reality that troubled early G8 systems. A system that passes the BWMS Code should hold up in the variable waters a trading vessel actually encounters.

Active Substances and Procedure G9

Systems that work by generating or dosing active substances, such as electrochlorination/electrolysis systems producing TRO or chemical injection systems, must also be assessed under the Procedure for approval of ballast water management systems that make use of Active Substances (G9), adopted as MEPC.169(57). G9 evaluates the environmental and human-health safety of the active substances and any disinfection by-products.

G9 approval is granted by IMO in two stages, Basic Approval and Final Approval, following review by the GESAMP Ballast Water Working Group. The process examines toxicity, persistence, bioaccumulation and discharge concentrations of TRO and by-products, and sets a maximum allowable discharge concentration that the neutralization stage must achieve before deballasting.

For operators this is why electrolytic and chemical systems include neutralization, commonly using sodium thiosulfate, and TRO monitoring before discharge. The G9 dossier underpins the discharge limits the crew must observe, typically requiring residual oxidant to be reduced to a safe level before ballast water leaves the ship.

Reading a Type Approval Certificate

A type approval certificate issued by a flag administration names the system, its model variants and treatment-rated capacity (TRC), and references the BWMS Code and, where relevant, G9 final approval. Crucially it lists the System Design Limitations, which the operator must check against the vessel's trading pattern.

If a ship regularly ballasts in very low UVT or low-salinity water that falls outside the SDL, the certificate alone does not guarantee compliant treatment in those conditions. The crew may need to manage operations, for example by avoiding ballasting in the most challenging water or treating during deballasting where the configuration allows.

When sourcing spares or service, the certificate and SDLs help confirm that components and consumables match the approved configuration. Sea Clean AS supports owners in interpreting type approval documentation for Headway OceanGuard and other systems so that maintenance and parts stay within the approved envelope.

Frequently asked questions

Is the BWMS Code the same as G8?