Conclusions
The N2O and CH4 gas emissions from a plug–flow reactor present in
theWWTP of the city of Granollers were investigated in this study for a
period of 10 weeks. Also, dissolved data for these two gases across
different sections of the WWTP allowed investigating the sources and
their overall emission. The main conclusions of this study are:
• CH4 emissions from the plug–flow reactor presented a pattern which
was related with the regular inflow of influent and reject wastewater
containing dissolved CH4 into the bioreactor.
• N2O emission dynamicswere highly variable and mainly related with
the instability of the nitrification process occurring in the bioreactor.
Transient anoxic periods in the aerated zones resulted in N2O peak
emissions when aeration re-started.
• N2O peak emission events can significantly increase the overall
emission account of a WWTP. Sudden aeration stops should be
avoided in the nitrifying zones when possible, in order to minimize
N2O peak emissions.
• The production of N2O outside bioreactors (primary or secondary settlers)
could be relevant and needs specific additional research