Energy-positive nitrogen removal using the integrated short-cut nitrification and autotrophic denitrification microbial fuel cells (MFCs)

Abstract

An integrated short-cut nitrification and autotrophic denitrification microbial fuel cell (SNAD-MFC) was developed to achieve energy-positive nitrogen removal from wastewater. Ammonium was reduced mostly to nitrite instead of nitrate (the ratio of nitrite to nitrate: 3.0) in the cathode chamber of the short-cut nitrification MFC at low dissolved oxygen concentration (⩽3.5mg/L), and nitrite was reduced to nitrogen gas through autotrophic denitrification in the cathode chamber of the denitrification MFC by using the electrons produced from anode chamber. The total nitrogen removal rate was 0.0125kgN/m3d and the removal efficiency was 99.9%. The power generation in the short-cut nitrification MFC was 294.9mW/m2 with the highest current density of 0.158mA/cm2. The accumulated coulombs of the whole SNAD-MFC were 87.17C at DO 3.5mg/L. Unlike the energy-negative and carbon-intensive biological nutrient removal (BNR) processes, the SNAD-MFC exhibits the distinct advantages of compact configuration, low aeration cost, no requirement of carbon sources, and produces the net electric power of 0.007kWh/m3, which has a high potential for self-sustained energy-positive nutrient removal.