3.2. CH4 and N2O emissions
Average CH4 and N2O gas emissions measured during the monitoring
period are shown in Table 2. The anoxic zones of the bioreactor presented
very low emissions of both gases. The largest emission of CH4
was registered in the first aerated area (Site 3) of the bioreactor
(1.15 kg CH4/d) sharply decreasing in the following sites to levels well
below 0.02 kg CH4/d. N2O emissions from each of the aerated zones
presented differences also, ranging from 0.45 (Site 3) to 0.14 kg N/d
(Site 6), as shown in Table 2. Additionally, the emissions of N2O in Sites
3 and 6 presented large variations, even between different days during
the same week, as shown by the large standard deviation resulted from
the calculation of mean values from triplicates. This is attributed to N2O
peak events registered for a period of some hours that increased significantly
the total amount of N2O emitted from these sites. These N2O
peak events are further described in Section 3.3.
The total gas emissions from the bioreactor lane under study were
1.35 kg CH4/d and 0.78 kg N2O–N/d which corresponded to 0.016%
and 0.116% of the influent COD or influent TKN respectively.