Aerobic Denitrification Is Enhanced Using Biocathode of SMFC in Low-Organic Matter Wastewater

Haochi Zhang,Hui Wang,Dengfeng Hou,Xian Cao,Xianning Li,Shuai Zhang

doi:10.3390/w13243512

Abstract

Nitrate (NO3−) in wastewater is a rising global threat to ecological and health safety. A sufficient carbon source, as the electron donor, is essential in the conventional biological denitrification process. It is not appropriate to add extra carbon sources into specific water bodies in terms of material cost and secondary pollution. Thus, innovative NO3− removal technologies that are independent of carbon sources, are urgently needed. This study constructed sediment microbial fuel cells (SMFCs) for aerobic denitrification in low-organic matter wastewater and explored the key factors affecting denitrification efficiencies. The SMFC treatments removed 72–91% NO3− through two main denitrifying stages which were driven by carbon sources (COD) and generated electrons, respectively. After COD was fully consumed, denitrification efficiencies were enhanced in SMFC treatments by 24–47% using the generated electrons within 3 days. In this stage, the NO3− removal efficiencies were positively correlated with external current intensities (p < 0.05). The improved denitrification efficiencies were attributed to two enriched phyla in the SMFC cathode. The dominant genera also demonstrated the heterotrophic denitrifying capacity of the SMFC biocathode. Furthermore, electrical characteristics could be used to monitor or regulate the denitrification process in the SMFC system. In conclusion, this study presents an innovative treatment strategy that is economical and eco-friendly compared with conventional physicochemical methods.

Highlights

Nitrogen (N) is one of the most common elements existing in the natural environment
Differing from the OC group, all four sediment microbial fuel cells (SMFCs) treatments of the CC group went through a slow decline period
Once chemical oxygen demand (COD) was fully consumed, the generated electrons via the external circuit of SMFC maintained autotrophic denitrification in the cathode region; 24–47% NO3− could be removed with different currents in the SMFC external circuit within 3 days

Summary

Introduction

Nitrogen (N) is one of the most common elements existing in the natural environment. The nitrogen released in surface water and subsurface aqueous environments is mainly in the form of domestic, agricultural, and industrial wastewater, resulting from fertilizer use, landfill leachates, and sewage wastewater discharge, etc. Since most released N in wastewater is converted to nitrate (NO3−) through biological systems [3], NO3− becomes one of the predominant nitrogenous species with high mobility and stability in the environment, especially in water bodies [4]. High concentrations of NO3− and its reduction product, nitrite (NO2−), have been demonstrated to damage the quality and yield of aquaculture species and even to threaten human health via drinking these water sources [8]

Methods

Results

Conclusion