Effect of adding raw swine wastewater and anammox bacteria on N₂O emission reduction in liquid digestate partial nitrification and denitrification process

Due to the low C/N ratio of liquid digestate of swine wastewater, a large amount of greenhouse gas nitrous oxide (N₂O) is released in the denitrification process when liquid digestate is treated by partial nitrification and denitrification process. In order to solve this problem, we constructed two strategies, i.e. adding raw swine wastewater and anammox bacteria, based on sequencing batch reactor (SBR) and aerobic/ anoxic (A/O) reactors. The N₂O emission reduction potential of the two strategies was evaluated. The results indicated that under the strategy of adding raw swine wastewater, compared with the C/N ratio of 2/1, when the raw swine wastewater was added to the C/N ratio of 4.5/1, the N₂O emission of SBR and A/O could be reduced by 55% and 60%, respectively. After the bioaugmentation of anammox bacteria, the SBR and A/O could reduce N₂O emission by 89% and 7%, respectively. Under the strategy of adding raw swine wastewater, the denitrification activity and electron transport system activity of the sludge from A/O were higher than those from SBR, and A/O had higher denitrification ability than SBR. Therefore, A/O was suitable for adding raw water to reduce N₂O emission. Under the strategy of adding anammox bacteria, the anammox activity and the electronic system activity of the sludge from SBR were higher than those from A/O, and the anammox bacteria could quickly adapt to SBR reactor, so SBR was suitable for transforming into a short-range nitrification anammox process to reduce N₂O. The research results have important practical significance for mitigating the emission reduction of nitrous oxide during the biological denitrification treatment of liquid digestate.