Effect of increased cathodic nitrogen levels on anodic COD removal efficiency and bioelectricity generation in microbial fuel cells

Abstract

Simultaneous nitrification and denitrification (SND) of nitrogen-rich wastewater in microbial fuel cells (MFCs) is a new-age technology capable of treating wastewater and concurrently generating bioelectricity. Compared to the conventionally used biological nitrogen elimination processes, SND in MFC is much more energy and cost-efficient because it uses less organic carbon and excludes the nitrified liquid circulation process. In this work with a dual-chambered MFC, carbon-rich synthetic wastewater (CRSW) with an invariable glucose concentration of 2 g/L has been treated in the anodic chamber and nitrogen-rich synthetic wastewater (NRSW) containing 1 g/L, 2 g/L, and 3 g/L ammonium chloride (NH₄Cl) concentration has been treated in the cathodic chamber and concurrently bioelectricity has been generated. Results showed that CCV-2 with 2 g/L NH₄Cl load in closed circuit (CCV) mode generated the highest cell voltage, current density, and volumetric power density of 80.56 mV, 23.69 mA/m², and 12.97 mW/m³. Removal of chemical oxygen demand (COD), total Kjeldahl nitrogen (TKN), nitrite, and nitrate was also highest in CCV-2 being 90.25%, 92.18%, 85.78%, and 86.53% respectively. With further increment of NH₄Cl concentration to 3 g/L concentration there was a decrement in COD, TKN, nitrite, nitrate, and power generation output because TKN concentration higher than 3 g/L slowed down the growth of exoelectrogenic bacteria and decreased organic and nitrogen removal rate along with power output. All experiments in CCV mode gave better results than their counterparts operated in open circuit (OCV) mode. In microbial community structure analysis, the dominant genus was found to be Brevendimonas, Sphingomonadaceae, and Achromobacter in the cathodic chamber treating NRSW.

Graphical Abstract