5. Conclusions
A long-term dataset of continuous nitrous oxide emission
measurements from a municipal WWTP was used to evaluate
different sampling strategies that have been used in previous
studies to monitor these emissions. A reliable determination of
the actual average nitrous oxide emission of a WWTP requires
long-term sampling, be it online or grab sampling, covering the
entire temperature range that can possibly be encountered. For
long-term grab sampling, night-time and weekend samples
contribute significantly to a more accurate estimate.
If the interest of the monitoring campaign is in the shortterm
variability, rather than in the mere average nitrous
oxide emission, (long-term) grab sampling is not sufficient. In
that case, e.g. when researchers want to compare the diurnal
dynamics of the emission with the diurnal dynamics of the
plant’s process conditions, high-frequency (online) sampling
is indispensable. Especially in the case of online sampling,
long-term sampling is very resource-demanding. As a guideline
to help balancing cost and precision, a method was presented
to obtain the number of grab samples or online
sampling periods that would have been required to obtain a
sufficiently precise estimation of the emission