Application of a Partial Nitrogen Lab-Scale Sequencing Batch Reactor for the Treatment of Organic Wastewater and Its N2O Production Pathways, and the Microbial Mechanism

Abstract

Partial nitrification (PN) is a widely used wastewater treatment process. Here a lab-scale sequencing batch reactor for PN (PN-SBR) was constructed and run with artificial organic wastewater for 225 days. Results showed that the SBR reached a stable PN state after 174 days of operation and >98% of NH4+-N was removed and >60% was converted to NO2−-N with low effluent NO3−-N content. In a PN-SBR cycle at stage IV, the release of N2O was accompanied by the production of hydroxylamine, occurring mainly in the conversion from anaerobic to aerobic phases, and the amount of N2O produced was about 6.3% of the total nitrogen. The N2O isotopic signature results suggested that hydroxylamine oxidation was the main pathway for N2O production. Illumina MiSeq sequencing results showed that Proteobacteria and Bacteroidetes were the dominant phyla throughout the operation period. Many heterotrophic nitrifiers were significantly enriched, leading to ammonia removal and nitrite accumulation, including Acidovorax, Paracoccus, Propionibacteriaceae_unclassified, Shinella, Comamonas and Brevundimonas. Representative strains were isolated from the reactor and they were capable of efficiently producing nitrite from ammonia. These results provide a guide for the direct running of PN reactors for treating organic wastewater and help to understand the microbial processes and N2O release pathways and the microbial mechanism of partial nitrification.