Sustainable treatment of nitrate-containing wastewater by an autotrophic hydrogen-oxidizing bacterium

Bacteria are key denitrifiers in the reduction of nitrate (NO3−-N), which is a contaminant in wastewater treatment plants (WWTPs). They can also produce carbon dioxide (CO2) and nitrous oxide (N2O). In this study, the autotrophic hydrogen-oxidizing bacterium Rhodoblastus sp. TH20 was isolated for sustainable treatment of NO3−-N in wastewater. Efficient removal of NO3−-N and recovery of biomass nitrogen were achieved. Up to 99% of NO3−-N was removed without accumulation of nitrite and N2O, consuming CO2 of 3.25 mol for each mole of NO3−-N removed. The overall removal rate of NO3−-N reached 1.1 mg L−1 h−1 with a biomass content of approximately 0.71 g L−1 within 72 h. TH20 participated in NO3−-N assimilation and aerobic denitrification. Results from 15N-labeled-nitrate test indicated that removed NO3−-N was assimilated into organic nitrogen, showing an assimilation efficiency of 58%. Seventeen amino acids were detected, accounting for 43% of the biomass. Nitrogen loss through aerobic denitrification was only approximately 42% of total nitrogen. This study suggests that TH20 can be applied in WWTP facilities for water purification and production of valuable biomass to mitigate CO2 and N2O emissions.