The United States Coast Guard (USCG) has declined the use of the most probable number (MPN) method for evaluating the biological efficacy of UV-based treatment technologies in ballast water, which could cause a delay in the first type approval of any ballast water management system to the summer of 2016, according to international classification society DNV GL.
USCG said that the method, submitted individually by four BWMS manufacturers, does not evaluate the performance of a BWMS to that discharge standard.
The MPN method evaluates the ability of an organism to reproduce and hence its ability to colonize a new environment. As such, the method does not have the same results as the USCG’s preferred method vital staining.
Under the current USCG policy, BWMSs using UV technology need to apply a more conservative treatment dose to immediately kill organisms, therefore the new method, yet to be approved, will unlikely be a UV system.
However, DNV GL said that the MPN method is the most relevant method and is a reliable way of evaluating the performance of UV technologies.
“That method has been validated to a greater extent than most of the methods described in the Environmental Technology Verification (ETV) Protocol (prescriptive guidance incorporated by reference to US regulation), and UV technologies are commonly accepted in other water treatment industries,” DNV GL added.
DNV GL, having provided much of the MPN analysis done for the four BWMS manufacturers, said it expects the manufacturers will appeal the USCG decision.
DNV GL added that shipowners should consider possible operational limitations of UV-T, holding time, energy consumption and reduced flow rate when discharging ballast in US waters with UV systems.