Nitrogen Removal and Nitrous Oxide Emission in an Anaerobic/Oxic/Anoxic Sequencing Biofilm Batch Reactor

An anaerobic/oxic/anoxic sequencing batch biofilm reactor (A/O/A SBBR) was tested to treat carbon-limited wastewater without external carbon addition. Simultaneous nitritation–denitritation in the oxic period and poly-hydroxybutyrate (PHB)-driven denitritation in the anoxic period were implemented in the A/O/A SBBR. A high total nitrogen (TN) removal efficiency of 95.97 ± 2.85% was achieved, in which 57.62 ± 4.43% was removed during the aerobic period and 39.00 ± 4.07% was removed during the anoxic period. Simultaneously, 15.47 ± 2.65% of the removed TN was emitted as nitrous oxide (N2O), and 72.25 ± 4.86% of total N2O was produced during the anoxic period. As a result, PHB-driven denitritation improved TN removal efficiency while stimulating high amounts of N2O emission. High-throughput pyrosequencing analysis revealed an abundance of the genera Thauera and Denitratisoma as potential denitrifiers that improved TN removal efficiency. N2O was primarily produced by betaproteobacterial microorganisms, especially the genera Thauera, Denitratisoma, and Nitrosomonas.