Bioaugmentation of a wastewater bioreactor system with the nitrous oxide-reducing denitrifier Pseudomonas stutzeri strain TR2

In bioaugmentation technology, survival of inoculant in the treatment system is prerequisite but remains to be a crucial hurdle. In this study, we bioaugmented the denitrification tank of a piggery wastewater treatment system with the denitrifying bacterium Pseudomonas stutzeri strain TR2 in two pilot-scale experiments, with the aim of reducing nitrous oxide (N₂O), a gas of environmental concern. In the laboratory, strain TR2 grew well and survived with high concentrations of nitrite (5-10 mM) at a wide range of temperatures (28-40°C). In the first augmentation of the pilot-scale experiment, strain TR2 inoculated into the denitrification tank with conditions (30°C, ∼0.1 mM nitrite) survived only 2-5 days. In contrast, in the second augmentation with conditions determined to be favorable for the growth of the bacterium in the laboratory (40-45°C, 2-5 mM nitrite), strain TR2 survived longer than 32 days. During the time when the presence of strain TR2 was confirmed by quantitative real-time PCR, N₂O emission was maintained at a low level even under nitrite-accumulating conditions in the denitrification and nitrification tanks, which provided indirect evidence that strain TR2 can reduce N₂O in the pilot-scale system. Our results documented the effective application of growth conditions favorable for strain TR2 determined in the laboratory to maintain growth and performance of this strain in the pilot-scale reactor system and the decrease of N₂O emission as the consequence.