Effect of low-intensity electric current field and iron anode on biological nitrate removal in wastewater with low COD to nitrogen ratio from coal pyrolysis

Abstract

Mixotrophic nitrate removal in wastewater from coal pyrolysis was achieved in microbial electrolysis cell with iron anode (iron-MEC). The effect of voltage, iron anode and conductivity were investigated. The effluent TN concentration was 8.35 ± 1.94 mg/L in iron-MEC when the conductivity of the wastewater was adjusted to 3.97 ± 0.08 mS/cm, which was lower than that in no-treated reactor. The increase of current density, which was resulted from the elevation of conductivity, promoted the iron corrosion and Fe2+ ion generation. Therefore, more Fe2+ ion was utilized by nitrate reducing ferrous oxidation bacteria (NRFOB) used to reduce nitrate. The microbial community analysis demonstrated that NRFOB, including Acidovorax and Bradyrhizobium, possessed a higher abundance in iron-MEC. The enrichment of Geobacter in iron-MEC might imply that the part of Fe(III) produced by ferrous oxidation was reduced by Geobacter, which established an iron cycle. Moreover, the production of N2O was decreased by the formation of Fe2+ ion.