Mn oxides changed nitrogen removal process in constructed wetlands with a microbial electrolysis cell

Intensified Mn redox cycling could enhance nutrient removal in constructed wetlands (CWs). In this study, Mn oxides (birnessite-coated sand) were used as the matrix in horizontal flow CWs (HFCWs) with amicrobial electrolysis cell (MEC) (E-B-CW) or without anMEC (B-CW). The model CWs were developed to investigate the capacities andmechanisms of nitrogen removal with increasedMn redox cycling. The results showed that E-B-CW had the highest average removal efficiencies for NH4-N, NO3-N and TN, followed by B-CW and control HFCW (C-CW). The Mn(III) oxides (MnOOH or Mn2O3) and the Mn(IV) oxide (MnO2) were all detected in E-B-CW and B-CW, while the matrix in E-B-CW had much more Mn(IV) oxides than B-CW. Interestingly, clustering heat map showed that ammonification and nitrate reduction were related to Mn-oxidizing bacteria and the relative abundance of Mn-oxidizing bacteria in E-B-CW was highest due to the re-oxidation of Mn(II) by the MEC. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

The study demonstrates that enhanced Mn redox cycling in constructed wetlands can improve nitrogen removal efficiency, and using Mn oxides as the matrix can accelerate the nitrogen removal process.