N₂O emission from full-scale urban wastewater treatment plants: a comparison between A²O and SBR

The emission of nitrous oxide (N₂O) from full-scale anoxic/anaerobic/oxic (A²O) and sequencing batch reactor (SBR) processes was measured to evaluate N₂O emission from urban wastewater treatment plants (WWTPs). The results showed that N₂O flux in the A²O WWTP followed an order of A²O-oxic zone > aerated grit tank >> A²O-anaerobic zone > A²O-anoxic zone > final clarifier > primary clarifier, while in the SBR WWTP the order was SBR tank >> swirl grit tank > wastewater distribution tank and within the SBR tank in an order of SBR-feeding period > SBR-aeration period > SBR-settling period > SBR-decanting period. N₂O emission from the A²O WWTP was approximately 486.61 kg d⁻¹, 96.9% of which was from the A²O-oxic zone. In the SBR WWTP, the emission of N₂O was 339.24 kg d⁻¹ with 99.9% of the total emission coming from the periods of feeding and aeration. There was 6.52% of nitrogen-load in the influent being transformed to the emitted N₂O in the SBR WWTP; the percentage was 3.35 times higher than that in the A²O WWTP.