Abstract
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.