Exploring influence mechanism of small-molecule carbon source on heterotrophic nitrification-aerobic denitrification process from carbon metabolism, nitrogen metabolism and electron transport process.

The heterotrophic nitrification-aerobic denitrification (HNAD) process can remove nitrogen and organic carbon under aerobic conditions. To get the in-depth mechanism of the HAND process, a strain named Acinetobacter johnsonii ZHL01 was isolated, and enzyme activity, electron transport, energy production, and gene expression of the strain were studied with small-molecule carbon sources, including sodium citrate, sodium acetate, sodium fumarate, and sodium succinate. The HNAD pathway of ZHL01 was NH4+→NH2OH â†’ NO, and nitrogen balance analysis shows that ZHL01 could assimilate and denitrify 58.29 ± 1.05 % and 16.58 ± 1.07 % of nitrogen, respectively. The assimilation, the nitrification/denitrification, and the respiration processes were regulated by the concentration of reduced nicotinamide adenine dinucleotide (NADH) produced from the different metabolic pathways of small-molecule carbon sources. The HNAD process occurs to reduce intracellular redox levels related to NADH concentrations. This discovery provides a theoretical basis for the practical application of HAND bacteria.

Influence mechanism of C/N ratio on heterotrophic nitrification- aerobic denitrification process.

A heterotrophic nitrification- aerobic denitrification (HNAD) bacterium, Acinetobacter junii ZHG-1, was isolated, meanwhile, the optimal conditions for the strain were evaluated, moreover, the influence mechanism of the C/N ratio on the HNAD process was investigated from the perspective of electron transport and energy level. The increasing of C/N ratio enhanced the reduced/oxidized nicotinamide adenine dinucleotide (NADH/NAD+) ratio, NADH concentration, electron transport system activity (ETSA), ATP content, as well as enzymes activities, consequently, the HNAD performance of the strain can be improved, however, when the C/N ratio was higher than 30, the activities of enzymes relating to the HNAD process and the ETSA had reached the maximum, which might limit the further improvement of the nitrogen removal with the increasing of C/N ratio. As the interaction between different biochemical reactions in HNAD process, more efforts should be devoted to the influent mechanism of different environmental factors on the HNAD process.

Revealing the effects of static magnetic field on the anoxic/oxic sequencing batch reactor from the perspective of electron transport and microbial community shifts.

The effects of static magnetic field (SMF) on an anoxic/oxic sequencing batch reactor were investigated from the perspective of electron transport via determining the variations of reduced/oxidized nicotinamide adenine dinucleotide (NADH/NAD+) ratio, NADH concentration, electron transport system activity (ETSA), poly-ß-hydroxybutyrate (PHB), extracellular polymeric substances (EPS), as well as the gene expression under different conditions. Moreover, the shifts of microbial community were also analyzed. The application of SMF with an appropriate intensity significantly improved the performance of the process, the abundance of the anoxic denitrifiers, and the activity of the aerobic denitrifiers. The NADH content, as well as ETSA were also enhanced, therefore, the total nitrogen removal efficiency of the process was increased. However, the overhigh SMF intensity resulted in the change of microbial community, meanwhile, had negative effects on the metabolism of microorganisms. Selecting a proper intensity is crucial for the SMF-enhanced biological wastewater treatment process.