The samples taken from a ballast water pipe system has to be “representative” in two ways:
(1) The composition of the suspended solids as well as the composition of the organisms in the sample should reflect the composition of the suspended solids as well as the composition of the organisms transported through the ballast water pipe system.
To ensure the composition of the sample is almost identical to the composition of the ballast water running through the pipe system the ballast water samples have to be taken via “isokinetic sampling ports”. The principle of isokinetic sampling describes a sampling pipe inserted into the main pipe system, from which the water sample has to be taken. The diameter of this sampling pipe and the technical installations attached to the sampling pipe ensure that the flow velocity in the sampling pipe is the same as in the main pipe system. Only these “isokinetic” conditions in both pipes will prevent the generation of turbulences right in front of the sampling pipe aperture. Turbulences, that would prevent suspended solids and floating organisms from entering the sampling pipe and subsequently generate a composition of suspended solids and organisms in the sample different from the composition in the main flow. Ideally isokinetic sampling ports may be shaped as an “L”-pipe (=pitot port) or as a straight pipe (=bend port).
Figure isokinetic sampling port: ”bend“ port
Figure isokinetic sampling port: ”pitot“ port
(2) The number of samples and the intervals in which these samples are taken have to respect the peculiar de-ballasting characteristics of the ship
Unfortunately there are only little experiences and results available from ballast water sampling procedures that try to ensure a representativeness respecting the peculiar conditions of the ship’s ballast water pipe system, which, of course, is of individual character. First preliminary results indicate that ballast water samples have to be taken across the entire time of de-ballasting, starting approximately 5 minutes after commencement of the de-ballasting process and ending approximately 5 minutes before the de-ballasting procedure stops in order to compensate different organism densities generated by the morphology of the ballast water tanks themselves.
It is expected that the BSH project will provide a broader insight into the conditions of representative sampling procedures during de-ballasting.
Live plankton after collection from filter mesh