Biokinetics of nitrogen removal at high concentrations by Rhodobacter sphaeroides ADZ101

• A new strain of denitrifying phototrophic bacterium was isolated.
• The ability of the strain to remove nitrate and ammonia were investigated.
• The strain can remove high amount of nitrate and ammonia without nitrite accumulation.
• The kinetic coefficients for the removal were determined.
• Denitrifying genes, napA and nirK were also detected in the strain.

Denitrification plays a significant role in both wastewater treatment and nitrogen cycle. But high amount of nitrate and accumulation of nitrite inhibit these processes. In view of this, a denitrifying phototrophic bacterium was isolated, characterized based on 16s rRNA analysis and its ability to remove toxic nitrogenous compounds investigated. Different initial concentrations were used to determine the effect of concentration on nitrogen removal and the biokinetic coefficients using Michaelis–Menten rate expression. The bacterium can remove 71% of nitrate at the initial concentration of 85 mg l−1 under photoheterotrophic growth condition without nitrite or ammonium accumulation. It can also remove 62% of ammonium at initial concentrations of 52 mg l−1 under anoxic growth condition without nitrate or nitrite accumulation. The results also showed that increase in concentrations led to decrease for both NO3− and NH4–N removal. Analysis and amplification of the possible genes that are involved in denitrification revealed the possession of napA and nirK genes. This strain can therefore serve as good candidate in wastewater treatment plants that are faced with the problem of nitrite accumulation and high amount of nitrogenous compounds that inhibit cell growth during biological nitrogen removal.