A new strategy to simultaneous removal and recovery of nitrogen from wastewater without N2O emission by heterotrophic nitrogen-assimilating bacterium.

Biological assimilation that recovery the nitrogen from wastewater in the form of biomass offers a more environmentally friendly solution for the limitations of the conventional wastewater treatments. This study reported the simultaneous removal and recovery of nitrogen from wastewater without N2O emission by a heterotrophic nitrogen-assimilating Acinetobacter sp. DN1 strain. Nitrogen balance, biomass qualitative analysis, genome and enzyme studies have been performed to illustrate the mechanism of nitrogen conversion by strain DN1. Results showed that the ammonium removal followed one direct pathway (GOGAT/GDH) and three indirect pathways (NH4+ → NH2OH → NO → NO2- → NH4+ → GOGAT/GDH; NH4+ → NH2OH → NO → NO2- → NO3- → NO2- → NH4+ → GOGAT/GDH; NH4+ → NH2OH → NO → NO3- → NO2- → NH4+ → GOGAT/GDH). Nitrogen balance and biomass qualitative analysis showed that over 70 % of the ammonium in the wastewater was converted into intracellular nitrogen-containing compounds and stored in the cells of strain DN1. Traditional denitrification pathway was not detected and the ammonium was removed through assimilation, which makes it more energy-saving for nitrogen recovery when compared with Haber-Bosch process. This study provides a new direction for simultaneous nitrogen removal and recovery without N2O emission by the heterotrophic nitrogen-assimilating bacterium.

Integrative chemical and omics analysis of the ammonia nitrogen removal characteristics and mechanism of a novel oligotrophic heterotrophic nitrification-aerobic denitrification bacterium.

A novel oligotrophic heterotrophic nitrification-aerobic denitrification bacterium designated as Pseudomonas sp. N31942, was isolated from a eutrophic lake. Strain N31942 exhibits high ammonia nitrogen removal ability in oligotrophic environment as ammonia nitrogen can be efficiently (86.97 %) removed within 10 h with no accumulation of nitrite. In the nitrification process, strain N31942 can convert ammonia into nitrate in the absence of hydroxylamine oxidase and nitrite oxidoreductase. As for the denitrification process, nitrate or nitrite were reduced to ammonia and further converted into glutamate by dissimilatory nitrate reduction pathway. Transcriptomic analysis detected 2080 differentially expressed genes. Among them, the expression of the related genes in dissimilatory nitrate reduction process was all up-regulated at low ammonia concentrations, which indicates that the strain has excellent nitrogen removal efficiency for further nitrogen removal. Integrative omics analyses revealed that strain N31942 may have two possible pathways for the NH4+-N removal as direct GDH/GS-GOGAT pathway (NH4+-N → Glutamate) and indirect GDH/GS-GOGAT pathway (NH4+-N → NH2OH → NO2--N → NO3--N → NO2--N → NH4+-N → Glutamate). Moreover, strain N31942 also has excellent nitrogen removal ability for real sewage and 77.21 % total nitrogen could be removed within 48 h. The results presented here provide new insights into ammonia nitrogen removal characteristics and mechanism of heterotrophic nitrification-aerobic denitrification bacterium under oligotrophic conditions.