Complete nitrogen removal from over-aeration treated black-odorous water via adding aerobic denitrifiers and iron-carbon micro-electrolysis carriers

Over-aeration is usually unavoidable for removing ammonia nitrogen from black-odorous water bodies, which consumes a large amount of organic matter and creates a long-term oxygen-rich environment, limiting the denitrification process in the water. This study aims to investigate the synergistic effect of aerobic denitrifying bacteria and iron-carbon micro-electrolysis (IC-ME) carriers on complete nitrogen removal from the over-aerated black-odorous water. For nitrification, aeration can completely oxidize ammonia nitrogen to nitrate. For denitrification, adding aerobic denitrifying bacteria Pseudomonas ATCC 9027 allowed the nitrate reduction to occur under conditions of excess oxygen and enriched indigenous denitrifying bacteria (1.45% increase in cumulative abundance). These changes brought by Pseudomonas ATCC 9027 reduced the total nitrogen concentration from 12.07 to 7.12 mg/L. Besides, research has shown that IC-ME carriers as electron donors can provide additional electrons and improve the electron transport system activity by 0.07 μg O2/(g protein∙min) in the denitrification process. Enzyme activity test and metagenome analysis revealed that enzymes and genes associated with denitrification were both upregulated with the addition of Pseudomonas ATCC 9027 and IC-ME carriers. Specifically, the improvement for activities of nitrate reductase (NAR), nitrite reductase (NIR), nitric oxide reductase (NOR), nitrous oxide reductase (NOS), and cumulative abundance of denitrification genes was 0.93 μmol NO2−-N/(g·d), 3.74 μmol NO2−-N/(g·d), 0.18 μmol N2O-N/(g·d) and 0.09 μmol N2O-N/(g·d) and 1.48%, respectively. These findings provide an understanding of the cooperative mechanism of aerobic denitrifying bacteria and IC-ME carriers in enhancing nitrogen removal from over-aerated black-odorous water bodies.