Characteristics of Nitrate Reduction Using Fe (II) as Electron Donor in Activated Sludge

Static experiments were conducted to investigate the effects of environmental factors on nitrate (NO3−-N)-removal efficiency, such as NO3−-N loading, pH value, C/N ratio and temperature in activated sludge using Fe (II) as electron donor. The results demonstrated that the average denitrification rate increased from 1.25 to 2.23 mg NO3−-N/(L·h) with NO3−-N loading increased from 30 to 60 mg/L. When pH increased from 7 to 8, the concentration of NO3−-N and nitrite (NO2−-N) in effluent were all maintained at quite low levels. C/N ratio had little impact on denitrification process, i.e., inorganic carbon (C) source could still be enough for denitrification process with C/N ratio as low as 5. Temperature had a significant effect on the denitrification efficiency, and NO3−-N removal efficiency of 92.03%, 96.77%, 97.67% and 98.23% could be obtained with temperature of 25°C, 30°C, 35°C and 40°C, respectively. SEM, XRD and XRF analysis was used to investigate microscopic surface morphology and chemical composition of the denitrifying activated sludge, and mechanism of the nitrate-dependent anaerobic ferrous oxidation (NAFO) bacterias could be explored with this research.