An aerobic denitrifier Pseudomonas stutzeri Y23 from an oil reservoir and its heterotrophic denitrification performance in laboratory-scale sequencing batch reactors

Biological nitrogen removal from wastewater is considered to be more economical and efficient than physicochemical methods. Furthermore, denitrifying strains with complete denitrifying capacity play crucial roles in biological denitrification of wastewater. In this study, a heterotrophic bacterium Y23 with high denitrifying efficiency was isolated from production brine of an oilfield, which was flooded by microbial-enhanced oil recovery technique through injecting carbohydrate and nitrate into oil-bearing strata. Strain Y23 identified as Pseudomonas stutzeri contains denitrifying genes that are responsible for converting NO3− to NO2− and sequentially to NO, N2O, and N2. Y23 with secreted extracellular polymeric substances formed flocs and biofilm and showed good sedimentation and immobilization properties. Strain Y23 grew well with NaNO3, NaNO2, and (NH4)2SO4 as nitrogen sources, and showed excellent denitrification performance under high dissolved oxygen (DO) concentration, which benefited nitrite reduction. The removal efficiencies of nitrogen and chemical oxygen demand were enhanced by the augmentation of strain Y23 back into a laboratory-scale sequencing batch reactor. The reactor with Y23 also showed stronger impact resistance. Further investigation of microbial communities within the sequencing batch reactor showed that Y23 coexisted with other denitrifiers during operation. Overall, this study isolated a promising denitrifier that performs complete denitrification at high DO condition, and found that the accumulation or reduction of nitrite can be achieved by regulating hydraulic retention time or increasing DO, respectively.