Nitrogen Removal Characteristics and Constraints of an Alphaproteobacteria with Potential for High Nitrogen Content Heterotrophic Nitrification-Aerobic Denitrification

The discovery of heterotrophic nitrification-aerobic denitrification (HN-AD) microorganisms has opened a new window for wastewater treatment. The underlying mechanism of HN-AD, however, is not fully understood because of the phylogenetic diversity of HN-AD microbes. The isolation and characterization of new HN-AD microorganisms are encouraging for furthering the understanding of this process. In this study, we found an Alphaproteobacteria isolate W30 from a historically polluted river in China through an HN-AD microbes screening process, which we identified as Pannonibacter sp. A potential HN-AD pathway for W30 was proposed based on N conversion analyses and the successful amplification of the entire denitrification gene series. The isolate exhibited high efficiency of aerobic inorganic nitrogen transformation, which accounted for 97.11% of NH4+-N, 100% of NO3--N, and 99.98% of NO2--N removal with a maximum linear rate of 10.21 mg/L/h, 10.46 mg/L/h, and 10.77 mg/L/h, respectively. Assimilation rather than denitrification was the main mechanism for the environmental nitrogen depletion mediated by W30. The effect of environmental constraints on aerobic NO3--N removal were characterized, following a membrane bioreactor effluent test under an oxic condition. Compared to known Alphaproteobacterial HN-AD microbes, we showed that Pannonibacter sp. W30 could deplete nitrogen with no NO2--N or NO3--N accumulation in the HN-AD process. Therefore, the application of Pannonibacter sp. W30 has the potential for developing a felicitous HN-AD technology to treat N-laden wastewater at the full-scale level.