Environmental Engineering Reference
In-Depth Information
Recommended Sampling Duration
The organisms greater than or equal to 50
m in minimum dimension are negatively
affected by longer sampling times as sampling study results have documented.
The fi ndings of our studies also showed that shorter sampling times result in repre-
sentative samples, so that we recommend a sampling time for a sequential sample
of approximately 10 min. It was concluded that longer sampling times will likely
result in an underestimation of the viable organism concentration in the ballast
water discharged. This is especially the case for organisms greater than or equal to
50
ʼ
ʼ
m in minimum dimension.
Recommended Sampling Timing
We documented that organism concentrations vary considerably if the sampling
event is conducted at the very beginning or at the very end of the ballast water
discharge process because at these times the patchy organism distribution inside
ballast water tanks was the greatest indicating that organism are not homoge-
nously distributed inside the tank. Therefore, it is recommended to avoid taking a
sample at the fi rst 5 min or at the last 5 min of the ballast water discharge event
because an under- or overestimation of organism concentrations may have to be
expected. It is therefore recommended that the sampling is conducted with ran-
dom sequence(s) of approximately 10 min duration anytime in the middle of the
ballast water discharge from a tank, starting not before 5 min from the start of
discharge and ending not after 5 min before the end of the ballast water discharge
event from a tank.
Recommended Number of Samples
It was previously documented that the organism concentration of all organism
groups addressed by the D-2 standard varies in ballast water samples due to
their patchy distribution inside the tanks. Due to this variation a single 10 min
sequential sample may under- or overestimate the real concentration of organ-
ism discharged. It was also observed that the average organism concentrations
of two random sequential samples provide a very similar result to the average of
three random samples. Therefore, we recommend that compliance control sam-
pling is carried out by undertaking at least two random samples, and that the
samples are analysed immediately after each sampling event has ended. For the
fi nal result the organism concentrations of the two sequences sampled should be
averaged.
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