Effects of feeding and aeration strategies on N 2 O production and emission by an aerobic granular sludge system for municipal wastewater treatment

The effects of a single feeding cycle followed by a continuous aeration phase (AND ) and a step-feeding cycle followed by intermittent aerobic/idle phases (AND ) on the production and emission of nitrous oxide (N O) from aerobic granular sludge (AGS) from real domestic sewage were studied. Higher N O emissions were observed in the AND treatment, and 9.2 ± 4.1% of the influent TN was emitted as N O, while in the AND treatment, 4.6 ± 2.5% of the influent TN was emitted as N O. Both strategies were similar for carbon and total phosphorus removal; but AND was advantageous for ammonium nitrogen and total nitrogen removal. Regarding the microbial populations associated with N O production, genera such as Thauera, a heterotrophic denitrifier, were found to have a relative abundance of 2.1% in AND and 3.8% in AND . Defluviccocus and Tetrasphaera, organisms capable of denitrification and phosphorus removal, especially the latter, were present in AND . Under AND conditions, these organisms may have been replaced by fast-growing organisms, such as Thauera. Principal component analysis (PCA) showed that incomplete denitrification was the dominant effect in the AND strategy. This may be related to the nitrate and phosphate concentrations and effluent characteristics (low C:N ratio). In the AND strategy, incomplete denitrification and low polyhydroxyalkanoate (PHA) consumption were the main effects. This is indicated by the high nitrite and phosphate concentrations. Therefore, according to the PCA results, the combination of the AND and AND strategies can play a crucial operational role in the dynamics of N O production and emission, especially considering that real domestic wastewater was used in the present research.