Evaluating the Role of Microbial Internal Storage Turnover on Nitrous Oxide Accumulation during Denitrification

Biological wastewater treatment processes under a dynamic regime with respect to carbon substrate can result in microbial storage of internal polymers (e.g., polyhydroxybutyrate (PHB)) and their subsequent utilizations. These storage turnovers play important roles in nitrous oxide (N₂ O) accumulation during heterotrophic denitrification in biological wastewater treatment. In this work, a mathematical model is developed to evaluate the key role of PHB storage turnovers on N 2 O accumulation during denitrification for the first time, aiming to establish the key relationship between N₂ O accumulation and PHB storage production. The model is successfully calibrated and validated using N₂ O data from two independent experimental systems with PHB storage turnovers. The model satisfactorily describes nitrogen reductions, PHB storage/utilization, and N₂ O accumulation from both systems. The results reveal a linear relationship between N₂ O accumulation and PHB production, suggesting a substantial effect of PHB storage on N₂ O accumulation during denitrification. Application of the model to simulate long-term operations of a denitrifying sequencing batch reactor and a denitrifying continuous system indicates the feeding pattern and sludge retention time would alter PHB turnovers and thus affect N₂ O accumulation. Increasing PHB utilization could substantially raise N₂ O accumulation due to the relatively low N₂ O reduction rate when using PHB as carbon source.