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

Yiwen Liu,Xueming Chen,Bing-Jie Ni,Zhiguo Yuan,Lai Peng,Jianhua Guo

doi:10.1038/srep15138

Abstract

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 (N2O) 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 N2O accumulation during denitrification for the first time, aiming to establish the key relationship between N2O accumulation and PHB storage production. The model is successfully calibrated and validated using N2O data from two independent experimental systems with PHB storage turnovers. The model satisfactorily describes nitrogen reductions, PHB storage/utilization, and N2O accumulation from both systems. The results reveal a linear relationship between N2O accumulation and PHB production, suggesting a substantial effect of PHB storage on N2O 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 N2O accumulation. Increasing PHB utilization could substantially raise N2O accumulation due to the relatively low N2O reduction rate when using PHB as carbon source.

Highlights

Biological wastewater treatment processes are usually experiencing dynamic conditions, with the microorganisms regularly experiencing rapid change of the availability of nutrients[4,5], such as sequencing batch reactor (SBR) and enhanced biological phosphorus removal (EBPR) processes
The model is applied to simulate a denitrifying sequencing batch reactor (SBR) and a denitrifying continuous system to reveal the impacts of the feeding pattern and sludge retention time (SRT) on storage formation as well as N2O accumulation
The model developed in this work considered the four-step simultaneous anoxic storage and growth processes as well as four-step anoxic storage utilization processes for describing all potential N2O accumulation steps in denitrification (Fig. 1 and Table S1 and S2 in Supporting Information (SI))

Summary

Introduction

Biological wastewater treatment processes are usually experiencing dynamic conditions, with the microorganisms regularly experiencing rapid change of the availability of nutrients (feast/famine regime with respect to the carbon substrate)[4,5], such as sequencing batch reactor (SBR) and enhanced biological phosphorus removal (EBPR) processes It is usual for the denitrifying microorganisms to www.nature.com/scientificreports/. In contrast to the existing denitrification models that directly couple carbon oxidation and nitrogen reduction, another denitrification model concept proposed by Pan et al.[15] described these two types of processes separately through introducing electron carriers to link them for each step of denitrification None of these currently available denitrifying models for N2O accumulation considered the potential effects of anoxic PHB storage turnovers on N2O accumulation. The model is applied to simulate a denitrifying sequencing batch reactor (SBR) and a denitrifying continuous system to reveal the impacts of the feeding pattern and sludge retention time (SRT) on storage formation as well as N2O accumulation

Objectives

Methods

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Conclusion