Comparative assessment of four ballast water compliance monitoring devices with natural UV-treated water using IMO's monitoring approaches

Compliance Monitoring Devices (CMDs) are instruments indicating if the 10-50 μm organism abundance in ballast water complies with the International Maritime Organizations' discharge standard. For that, they trade the presumed accuracy of detailed methods for speed and simplicity. In an experiment using UV-treated water, four CMDs were compared, using a Cohen's kappa analysis (ISO 3725), with two detailed methods: Fluorescence Microscopy (FM) and the Most Probable Number (MPN). Of two CMDs, BallastWISE and B-QUA ATP, the standard (non)-compliance limits were adapted. Correlated to FM (non)-compliance results, ranking resulted in: 1) BallastWISE, 2) MPN, 3) Ballast-Check-2 and 4) WALZ-PAM. The ATP method had too few data for this ranking. MPN proved problematic: the abundance of 10-50 μm organism decreased while that <10 μm organisms increased. It is concluded that in case of UV-treatment, the outcome of CMD-validations will depend on the detailed method, the CMD instrument, and the (non)-compliance limits chosen.