Nitrite oxidation in oxygen-deficient conditions during landfill leachate treatment

Until recently, all known nitrite oxidation occurred in oxygen-rich conditions but now the oxidation of nitrite into nitrate within a low oxygen or anoxic environment has been observed in the ocean. However, this phenomenon is rarely reported in wastewater treatments and its mechanism is unknown. In this study, the partial nitrification and nitrite oxidation were conducted in no enough oxygen in order to remove nitrogen from landfill leachate, save energy, and save money. The results show that the NH4+-N removal efficiency was 99.4%. During phase I of the anaerobic sequential batch reactor (ASBR), no change in Chemical Oxygen Demand (COD) and ammonium were detected. The nitrite concentration decreased from 107 +/- 3 mg/L to 0.16 mg/L during 96 h of oxygen-deficiency, while NO3--N increased from 152.5 +/- 3 mg/L to 253.65 +/- 3 mg/L. The main microorganisms involved in this reaction in the ASBR were Nitrite-Oxidizing Bacteria (NOB), including Nitrospira and Nitrolancea, their relative abundances were 3.56% and 0.13%, respectively. The major NOB (Nitrospira) were confirmed by the further metagenomic binning analysis. This finding shows that nitrite oxidation can occur in oxygen-deficient conditions with specific NOB.

Automated summary

Until recently, nitrite oxidation was only known to occur in oxygen-rich conditions, but now it has been observed in low oxygen or anoxic environments in the ocean. However, this phenomenon is rarely reported in wastewater treatments and its mechanism is unknown. In this study, partial nitrification and nitrite oxidation were conducted in a low oxygen environment to remove nitrogen from landfill leachate. The results showed a decrease in nitrite concentration and an increase in nitrate concentration, and the main microorganisms involved were Nitrite-Oxidizing Bacteria (NOB).