Revealing the differences in metabolisms and nitrogen removal mechanisms of the full and shortcut nitrification-denitrification processes for the treatment of livestock wastewater

Abstract

The full nitrification-denitrification process (FN) and shortcut nitrification-denitrification process (SN) are both important approaches for treating livestock wastewater. However, most existing studies focus on pollutant removal performance in wastewater treatment, while the differences between the two processes in terms of bacterial communities, metabolic pathways, nitrogen removal mechanisms, and potential pathogen threats have been poorly investigated. In this study, the SN process exhibited lower oxygen demand, reduced sludge production, higher nitrogen removal rate, and lower pathogen threat for treating livestock wastewater. The bacterial communities, the primary participants of pollutant removal in wastewater treatment, were significantly different between the two processes. In the FN process, 15 genera were significantly enriched, including Saccharimonadales, Micropruina, Ferruginibacter, etc. On the other hand, the SN process showed enrichment of 10 genera, including Brachymonas, Tessaracoccus, Ottowia, etc. These enriched genera, such as Brachymonas, Tessaracoccus, and Ottowia in the SN process, were positively correlated with the denitrification genes, facilitating a higher nitrogen removal rate. Moreover, the FN process exhibited significantly higher amino acid metabolism and reproduction-related pathways, contributing to its higher alpha-diversity of the bacterial community. The significantly enriched genes involved in assimilatory nitrate reduction and nitrogen assimilation pathway suggested that nitrogen assimilation played a crucial role in ammonia nitrogen removal, but it also increased sludge production in the FN process. Additionally, the FN process had a higher number and abundance of potential pathogens, indicating a greater pathogen threat. In conclusion, this study provides valuable insights into the differences between the FN and SN processes in terms of bacterial communities, nitrogen removal mechanisms, and potential pathogen threats. It also offers theoretical guidance for adopting appropriate strategies in wastewater treatment.