Comparison of nitrous oxide emission between a partial and full nitrification enriched ammonia-oxidising culture

Nitrification systems are known to be a source of nitrous oxide (N₂O) emission, however, the contribution from partial and full nitrification systems remains controversial. In this study, N₂O emission from a partial and full nitrification culture was investigated. In all tests, nitrite, dissolved oxygen concentration and pH levels were controlled within a similar range limiting ammonium concentration to be the only variable. The results reveal with the same amount of ammonium removed, the full nitrification culture produced far greater N₂O than the partial nitrification culture for both pulse (25-36 times) and continuous feeding modes (2-110 times). The relative gene expression data indicate that under pulse feeding there is a decreasing trend of nirK and norB genes for the partial and full nitrification culture respectively while under continuous feeding, increasing norB trends were observed for both. This possibly indicated the hydroxylamine pathway was favoured for the partial nitrification culture while the hybrid N-nitrosation pathway maybe the major contributor for the full nitrification culture. These findings improve our understanding on N₂O production pathways and enable researchers to propose better mitigation strategies.