5.5.1 Administrations should ensure that the sewage
treatment plant is installed in a manner which facilitates the collection
of samples, see figure 1. Sampling should be carried out in a manner
and at a frequency which is representative of the effluent quality.
Figure 2 provides a suggested frequency for sampling, however, the
frequency should take account of the residence time of the influent
in the sewage treatment plant. A minimum of 40 effluent samples should
be collected to allow a statistical analysis of the testing data (e.g.
geometric mean, maximum, minimum and variance).
5.5.2 Influent sample point should be upstream
of any return liquors, wash water, or recirculates generated from
the sewage treatment plant. Where such a sample point is not readily
available on ships, the flows and concentrations of these return liquors,
wash water, or recirculates generated from the sewage treatment plant
should be measured, so that the load can be taken away from the load
of influent.
5.5.3 An influent sample should be taken and analysed
for every effluent sample taken and the results recorded to ensure
compliance with section 4. If possible, additional influent and effluent
samples should be taken to allow for a margin of error. Samples should
be appropriately preserved prior to analysis particularly if there
is to be a significant delay between collection and analysis or during
times of high ambient temperature.
5.5.4 Any disinfectant residual in samples should
be neutralized when the sample is collected to prevent unrealistic
bacteria kill or chemical oxidation of organic matter by the disinfectant
brought about by artificially extended contact times. Chlorine (if
used) concentration and pH should be measured prior to neutralization.
Figure 2 Suggested hydraulic loading factors and sampling frequency for testing
sewage treatment plants. May be modified as necessary to take account of
characteristics of individual sewage treatment plants