Environmental Engineering Reference
In-Depth Information
Recommended Sample Quantity
During our earlier studies (Gollasch and David
2009
,
2010a
,
b
,
2013
) we conducted
sequential ballast water sampling over different time durations of the sequences,
i.e., 5, 10 and 15 min, with the average water fl ow rate ranging from 30 to 50 l per
minute. To obtain most representative results we recommended that:
•
m in minimum dimension between
300 and 500 l should be fi ltered and concentrated at the sampling point;
• for the organisms less than 50
for the organisms greater than or equal to 50
ʼ
ʼ
m in minimum dimension and greater than or
equal to 10
m in minimum dimension a “continuous drip” sample with a total
volume not less than 5 l should be taken. To achieve this we recommend to col-
lect about 0.5 l of sample water every minute during the entire sequential sam-
pling time duration. Alternatively 0.5 l of sample water may be collected every
30-45 l of the ballast water sampled. The resulting 5 l of collected sample water
should be mixed and sub-sampled in two sets. One set of samples should be kept
alive and another preserved. We recommend approximately 60-100 ml as sub-
sample volume;
ʼ
•
for indicator microbes samples, a sample of approximately 1 l should be collected
as a sub-sample after mixing from the 5 l continuous drip sample (see bullet
point above).
Other Recommendations
It is further suggested that the fl ow rates during sampling may have an additional
infl uence on the viability of organisms. In case lower fl ow rates are obtained by
partially closing valves at the sampling point this may result in sheer forces at the
valve which likely will damage (especially larger) organisms during the sampling
process. A similar negative viability effect may be caused by very strong fl ow rates,
which may affect mainly the organisms greater than or equal to 50
m in minimum
dimension. Hence, the fl ow rate or “valve” effect, may result in an underestima-
tion of viable organisms as organisms may have died during the sampling process.
To avoid this unwanted effect it is recommended that the valve at the sampling point
is opened as much as possible. However, the fl ow rate should not exceed 50 l/min so
that the water pressure in the sampling net is not too high during sample concentra-
tion because this may also negatively affect organism survival.
ʼ
Sampling Logistics Feasibility
Vessels of different types, sizes and cargo profi les have very different ballast water
discharge patterns (see chapter
“
Vessels and Ballast Water
”
). The ballast water dis-
charge may be carried out as a one time event “at once” or sequentially over longer
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