Effect of low-intensity direct current electric field on microbial nitrate removal in coal pyrolysis wastewater with low COD to nitrogen ratio

The coupling of bioelectrochemical system with the biological denitrification process (R1) was constructed for nitrate removal in coal pyrolysis wastewater (CPW) and the effect of low-intensity direct current electric field was investigated. Compared with control reactor (R2), the total nitrogen (TN) removal efficiency in R1 at the optimized voltage of 0.9 V was 94.20 ± 2.14%, which was 14.42% higher than that in R2. The biofilm on the cathode of R1 enhanced the nitrate reducing, however, nitrite was only reduced by bacteria in suspended activated sludge, which was confirmed by cyclic voltammetry measurement (CV). Microbial community network analysis revealed that exoelectrogenic bacteria of Pseudomonas was enriched on the anode of R1, and the “small world”, including Zoogloea, Pseudomonas and Arenimonas, was established under the stimulation of voltage. Therefore, Pseudomonas transferred electron to anode, and Arenimonas could utilize electron from anode to reduce nitrate, which enhanced TN removal in R1.