A novel process of anodic water denitrification in an upflow tubular microbial fuel cell: effect of C/N ratio

Abstract

BACKGROUND: A high nitrate concentration in groundwater in some parts of Iran has been detected due to untreated wastewater discharge and agriculture activities. Therefore, the development of treatment technology in this area using a new biological method was carried out. RESULTS: Activated sludge originating from slaughterhouse wastewater treatment plants and immobilized on graphite granules exhibited noticeable denitrification activity in a double chamber upflow tubular microbial fuel cell (UTMFC). The effects of three C/N values at different initial nitrate concentrations and external resistances on nitrate and chemical oxygen demand (COD) removal efficiencies as well as cell performance were studied at a fixed hydraulic retention time (HRT) of 12 h. Based on nucleotide sequence of 16S rRNA, four bacterial strains from anodic biofilm were also identified. The UTMFC operated in a continuous mode with C/N values of 20 and 10 was able to denitrify up to 150 mg L-1 nitrate without more accumulation of nitrite and ammonium ions than is permitted for drinking water. The maximum nitrate removal capacity of 0.25 ± 0.01 kg NO 3 −-N/ (m 3 net anodic compartment 'NAC'.day) was achieved at 400 mg L-1 initial nitrate concentration and at C/N = 10. Additionally, the maximum current density and power generation at this ratio were found to be 46.04 A m-3 NAC and 16.96 W/m 3 NAC, respectively. No efficient denitrification was observed at C/N = 5 while nitrite/ammonium formation increased. CONCLUSION: The experimental data documented the feasibility of bioelectricity generation and substrate removal utilizing acetate containing water under the adopted operating conditions of UTMFC, and the proposed system allowed the simultaneous heterotrophic denitrification/electricity generation.