2.2. CH4 and N2O monitoring and calculations
2.2.1. Gas emissions and emission factors
All the gas emission data recorded during this study was registered
in aerated and non-aerated zones of one of the activated sludge lanes
at GranollersWWTP. Wastewater is entering the first anoxic zone and
it is transported across the reactor passing through an aerated zone,
followed by a short anoxic zone (where mixed liquor is recirculated to
the first anoxic zone) to finally end in another aerated zone before
exiting the treatment lane. For the purposes of this study, the first anoxic
zone is divided into two sites (Site 1 and Site 2) with the first one
beingmore turbulent due to the flowof wastewater entering the bioreactor.
The main aerated zone is also divided into 2 sites (Site 3 and Site 4)
corresponding to the zones where two different air diffusers are present
and independently controlled. The two last monitoring sites correspond
to the second anoxic zone (from where mixed liquor is internally
recirculated, Site 5) and the final aerated part of the bioreactor (Site 6).
See Fig. 1 for locations of the monitoring sites.
CH4 and N2O emissions were monitored on-line for 48–72 h per
week during ten weeks between June and October, 2013. Measurements
of CH4 and N2O gases were performed using a commercial gas
collection hood (AC'SCENT® Flux Hood) connected via gas tubing to a
commercial gas analyser (VA-3000, Horiba, Japan) equipped with a
sample conditioning system (series CSS, M&C Tech group). Off-gas
was collected continuously (at 0.5 L/min) from the reactor headspace
and concentration data was logged every 15 s. Oxygen concentration
was also analysed using the same analyser for estimation of the Qgas
2.2. CH4 and N2O monitoring and calculations
2.2.1. Gas emissions and emission factors
All the gas emission data recorded during this study was registered
in aerated and non-aerated zones of one of the activated sludge lanes
at GranollersWWTP. Wastewater is entering the first anoxic zone and
it is transported across the reactor passing through an aerated zone,
followed by a short anoxic zone (where mixed liquor is recirculated to
the first anoxic zone) to finally end in another aerated zone before
exiting the treatment lane. For the purposes of this study, the first anoxic
zone is divided into two sites (Site 1 and Site 2) with the first one
beingmore turbulent due to the flowof wastewater entering the bioreactor.
The main aerated zone is also divided into 2 sites (Site 3 and Site 4)
corresponding to the zones where two different air diffusers are present
and independently controlled. The two last monitoring sites correspond
to the second anoxic zone (from where mixed liquor is internally
recirculated, Site 5) and the final aerated part of the bioreactor (Site 6).
See Fig. 1 for locations of the monitoring sites.
CH4 and N2O emissions were monitored on-line for 48–72 h per
week during ten weeks between June and October, 2013. Measurements
of CH4 and N2O gases were performed using a commercial gas
collection hood (AC'SCENT® Flux Hood) connected via gas tubing to a
commercial gas analyser (VA-3000, Horiba, Japan) equipped with a
sample conditioning system (series CSS, M&C Tech group). Off-gas
was collected continuously (at 0.5 L/min) from the reactor headspace
and concentration data was logged every 15 s. Oxygen concentration
was also analysed using the same analyser for estimation of the Qgas
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