The Denitrification Characteristics and Microbial Community in the Cathode of an MFC with Aerobic Denitrification at High Temperatures.

Jianqiang Zhao,Jinna Wu,Xiaoqian Ding,Sha Wang,Bo Hu,Xiaoling Li

doi:10.3389/fmicb.2017.00009

Abstract

Microbial fuel cells (MFCs) have attracted much attention due to their ability to generate electricity while treating wastewater. The performance of a double-chamber MFC with simultaneous nitrification and denitrification (SND) in the cathode for treating synthetic high concentration ammonia wastewater was investigated at different dissolved oxygen (DO) concentrations and high temperatures. The results showed that electrode denitrification and traditional heterotrophic denitrification co-existed in the cathode chamber. Electrode denitrification by aerobic denitrification bacterium (ADB) is beneficial for achieving a higher voltage of the MFC at high DO concentrations (3.0–4.2 mg/L), while traditional heterotrophic denitrification is conducive to higher total nitrogen (TN) removal at low DO (0.5–1.0 mg/L) concentrations. Under high DO conditions, the nitrous oxide production and TN removal efficiency were higher with a 50 Ω external resistance than with a 100 Ω resistance, which demonstrated that electrode denitrification by ADB occurred in the cathode of the MFC. Sufficient electrons were inferred to be provided by the electrode to allow ADB survival at low carbon:nitrogen ratios (≤0.3). Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) results showed that increasing the DO resulted in a change of the predominant species from thermophilic autotrophic nitrifiers and facultative heterotrophic denitrifiers at low DO concentrations to thermophilic ADB at high DO concentrations. The predominant phylum changed from Firmicutes to Proteobacteria, and the predominant class changed from Bacilli to Alpha, Beta, and Gamma Proteobacteria.

Highlights

Microbial fuel cells (MFCs) have gained widespread attention as an innovative wastewater treatment and energy recovery technology that combines sewage purification and electricity production (Janicek et al, 2014; Li et al, 2014)
In stage 1, the MFC with simultaneous nitrification and denitrification (SND) was operated at 31 ± 1◦C, 100 resistance and intermittent aeration (2 h aeration and 2 h static), and the dissolved oxygen (DO) of the cNaOth−2o-lyNtedwecarsea0s.5ed–1w.0itmh ga/Lg.raTdhuealcoinnccreenatsreatinionthseorfeNleaHse+4 -vNoltaangde of the MFC
The removal of total nitrogen (TN) began to increase sharply, and the concentration of NO−2 -N in the cathode effluent began to decrease correspondingly from the 6th day, while the voltage of the MFC increased slightly and stabilized. This might have been due to the high temperature in the cathode (36–48◦C), which was harmful for the growth of normal ammonia oxidizing bacteria (AOB)

Summary

Introduction

Microbial fuel cells (MFCs) have gained widespread attention as an innovative wastewater treatment and energy recovery technology that combines sewage purification and electricity production (Janicek et al, 2014; Li et al, 2014). Biocathod MFC with Aerobic Denitrification developments of nitrogen removal with MFCs have been achieved with various designs and configurations (He et al, 2009; Virdis et al, 2010; Zhang and Angelidaki, 2013). Nitrogen recovery with MFCs through NH3 stripping has been successfully developed to simultaneously produce energy and recover ammonium (Kuntke et al, 2012; Zhang and Angelidaki, 2015), SND in cathode of MFCs and its some new biochemical mechanisms still remain valuable to explore. Studies of simultaneous phenol removal, nitrification and denitrification using MFCs have indicated that phenoldegrading bacteria, nitrifiers, and denitrifiers in the aerobic cathode chamber are responsible for phenol oxidation, aerobic nitrification and aerobic denitrification, respectively (Feng et al, 2015). The SND mechanism in the aerobic cathode chamber is complex and remains unclear

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Conclusion