Vessels operating in United States waters must follow the vessel discharge standards of the Environmental Protection Agency’s (EPA) Vessel General Permit (VGP). These define, among others, the maximum amount of organisms that may be present in ballast water discharge, much like the IMO’s D-2 standards for ballast water management systems (BWMS), in order to avoid the spread of invasive species.  Both the VGP and and the IMO D2 standards are“licenses to operate” for commercial vessels, but are fundamentally different standards. 

In this article, you can learn… 

  • The key differences between the Vessel General Permit rules and the IMO rules for Commissioning Testing of Ballast Water Management Systems,  
  • Which compliance testing equipment you, as a service provider, can use for testing and documenting compliance with both VGP vessel discharge regulations and the international D-2 standards 
  • How the VGP standards may change in the future to include discharge limits similar to IMO’s D-2 standards.

VGP vs IMO ballast water commissioning test requirements 

The main difference between the IMO D2 standards and the VGP rules for ballast water compliance testing is that the EPA requires only heterotrophic bacteria testing and, for BWMS that employ oxidant-based treatments,  Total Residual Oxident (TRO) measurements, as defined in VGP 2013. In contrast, the IMO’s D-2 standards for commissioning testing of BWMS instead define compliance based on the allowed presence of microorganisms in two size fractions: 10 – 50 µm and over 50 µm – meaning it is not necessary to test for the specific types of organisms, but for the overall presence.  

As a result, different ballast water testing equipment is needed to test compliance according to VGP vs D-2 standards. However, vessels in the US may need to test for both in future, as the EPA is proposing to add regulations like the D-2 standards. 

Full VGP vessel discharge compliance testing is not possible with portable compliance test instruments 

The EPA has deemed only specific analysis methods acceptable for testing for heterotrophic bacteria (such as E.Coli, V. cholera and Enterococci) – and these chosen methods are not suited for on-site testing with portable equipment. The accepted methods include heterotrophic plate count (HPC), Coilert, Enterolert , EPA-1600 and EPA-1603. These accurately measure heterotrophic bacteria using a growth medium and incubation technique over longer periods (most often 24 hours) – requiring a laboratory setting and highly skilled personnel.

Total Residual Oxidant (TRO) measurements for all BWMS with oxidant-based treatment 

For any BWMS that employs oxidant-based treatments, such as systems based on chlorine, the VGP analysis monitoring requirements include daily TRO. The daily maximum allowed TRO discharge concentration is ≤ 0.1 mg L-1. TRO measurement can be done with several methodologies, such as diethyl-p-phenylene diamine (DPD) method or by electrochemical sensors. A Chlorine Colorimeter is often used for field testing of TRO in Ballast Water discharge and is widely available in inexpensive field test kits. 

New proposed rules to include IMO-style discharge standards? 

The VGP regulations on ballast water discharge will be replaced by the new VIDA regulations. In 2018, the Vessel Incidental Discharge Act (VIDA) was signed into law, requiring the EPA to develop new national standards for vessel discharge. The EPA (Environmental Protection Agency) has indicated that new federal discharge standards for vessels will be published in late 2024 

One of the changes the EPA proposes for the new standards is to add numeric ballast water discharge standards – much as it is defined in the IMO’s D-2 standards. This additional requirement will help prevent the spread of algae and zooplankton and harmonise the discharge standards for ballast water worldwide. Currently, the VGP does not require vessels to test for different size fractions of organisms.  

If this addition is approved, vessels operating in US waters will, regardless of whether they travel to international waters, be required to test for the number of organisms in their ballast water with equipment like BallastWISE. 

We hope you found this article helpful, and we wish you smooth sailing in your ballast water compliance testing journey. feel free to reach out if you have any questions. 


You might like these other Blog Posts…

USCG & IMO Type Approved ballast water treatment systems

USCG & IMO Type Approved ballast water treatment systems

This list of BWTS suppliers is meant to provide an accessible overview of the available systems while it also provides information on each BWTS’s type-approval status and method of treatment employed as stated on each system’s website. It is not an exhaustive list of all the companies that produce…

What are the D-1 and D-2 regulation standards?

What are the D-1 and D-2 regulation standards?

The International Maritime Organization (IMO) is responsible for protecting the marine environment from the harmful impacts of shipping. The IMO develops global standards for ships to prevent the spread of invasive species and potentially harmful pathogens with the ability to destroy or disrupt foreign ecosystems…