Getting Ahead with BWTS

The industry has seen a flurry of environmental legislation coming into effect, none more so than the ballast water management convention (BWMC). The BWMC came into effect on 8th September 2017 after 52 states, representing 35% of the world merchant shipping tonnage had ratified the convention. 

Under the rule of the convention, all ships engaged in international trade are required to manage their ballast water so as to avoid the introduction of alien species into coastal areas, including exchanging their ballast water or treating it using an approved ballast water treatment system. There are two different standards relating to these options.

The D-1 standard requires ships to exchange their ballast water in open seas, away from coastal waters. This means at least 200 nautical miles from land and in water of at least 200 meters deep. By doing this, it is expected that fewer organisms will survive, and ships will be less likely to introduce these potentially harmful species from their ballast water.

D-2 is a performance standard which specifies the maximum amount of viable organisms allowed to be discharged, including specific indicator microbes harmful to human health. All vessels are required to meet the D-1 standard, whereas the D-2 standard will come into effect based on a ship’s International Oil Pollution Prevention Certificate (IOPPC) renewal survey, which must be undertaken every five years.

Further amendments to the G8 guidelines also came into effect as of 28th October 2020 for the type approval of ballast water treatment systems.

The revised G8 guidelines, also known as the BMWC code, were changed to be more robust and in line with the US Coast Guard (USCG) requirements.  Previously some systems although type approved according to the original G8 guidelines failed to meet the IMO D-2 standard.


What are the equipment options?

There has been a number of ballast water treatment systems that have come to market over the years with different options for treating ballast water. The main options, with many suppliers opting for a combination, are:


This was one of the first options to come to market for treating ballast water. It’s a simple concept of filtering water of all organisms in an eco-friendly and non-harmful way with no chemicals.


This option treats the ballast water through UV light, by passing the ballast water through  UV light both as water is coming onboard and then again when it is discharged. It has a high efficiency for eradicating all species. However, this option started to be questioned some years back as there were concerns that it wouldn’t be able to effectively deal with brackish waters. It has however gained popularity again and this is the preferred method of the cruise ship market.


Electrolysis is the treatment process that utilizes chlorine and electric sterilization in its treatment of ballast water. The process lends itself to smaller systems and capacities of treatment.

Gas systems

This option utilises inert gas to treat ballast water. Using inert gas, the oxygen is stripped from the water, which increases the CO2 levels in the water and this temporarily reduces the PH value. This induces a damaging condition known as hypercapnia in marine life. 


What’s next?

From 2024, all ships are required to have approved BWT Systems that comply with the D-2 standard. Existing ships are required to install an approved system. The IMO has release 14 guidance documents in regard to the convention including the G2 Guidelines for Ballast Water Sampling, G4 Guidelines for Ballast Water Management and G6 guidelines for Ballast Water Exchange.

The industry is now being pressed to take steps to comply with the convention in installing ballast water treatment systems onboard vessel. Currently, 50% of the world fleet have installed ballast water treatment systems. Due to the changes in the scheduling of IOPPC surveys the industry is now expecting to see more ballast water treatment systems being fitted in the summer of 2022.

Newport Maritime Services is helping clients to meet these stringent requirements utilizing its approved supplier list and e-platform which allows for faster and easier access to quotations.