Characterising and control of ammonia emission in microbial fuel cells

Abstract

The serious ammonia (NH3) emission of air-cathode microbial fuel cells (MFCs) was reported but how to control and mitigate the emission hasn’t been well studied. Considering the importance of the issue for the application of MFCs in wastewater treatment, this study focused on understanding the NH3 emission process in MFCs and investigating mitigation approaches. The study found that when feeding with dairy wastewater the typical flat-cathode MFCs can emit NH3 of more than 0.82 mg-N/L. The NH3 emission reduced with the grown of cathode biofilm and the decrease of ammonium concentration in the influent. Combined experimental and theoretical results showed that the current density rather than the total current was the determined factor for ammonia emission. The novel Cu-blended 3D cathode developed in this study significantly decreased the NH3 emission to 0.037 mg-N/L (or 0.068% of the total removed ammonium), which was 6.3% of that in the activated sludge wastewater treatment plants (WWTP). In addition, the good power performance and high pollutants removal (14.4 W/m3, 88.1%-COD and 92.8%-TN removal) were also obtained by the Cu-blended 3D cathodes. This study unveiled the ammonia emission process and proposed effective mitigation methods, which will promote the practical application of MFCs for ammonium-rich wastewater treatment.