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Mn oxides changed nitrogen removal process in constructed wetlands with a microbial electrolysis cell
Ning Zhang1, Chaoyu Li1, Huijun Xie1
1Environment Research Institute, Shandong University, Jinan 250100, China.
The Science of the Total Environment
|March 19, 2021
Summary
Engineered constructed wetlands (CWs) using manganese oxides enhanced nutrient removal. Microbial electrolysis cells (MECs) boosted manganese redox cycling, significantly improving nitrogen removal efficiencies in horizontal flow CWs (HFCWs).
Area of Science:
- Environmental Engineering
- Water Treatment Technologies
- Biogeochemistry
Background:
- Constructed wetlands (CWs) are effective for wastewater treatment.
- Manganese (Mn) redox cycling can enhance nutrient removal processes.
- Optimizing Mn cycling is key to improving CW efficiency.
Purpose of the Study:
- To investigate nitrogen removal capacities and mechanisms in CWs with enhanced Mn redox cycling.
- To compare the performance of CWs with and without a microbial electrolysis cell (MEC).
- To explore the role of Mn-oxidizing bacteria in nitrogen removal.
Main Methods:
- Utilized horizontal flow CWs (HFCWs) with birnessite-coated sand as the matrix.
- Implemented a microbial electrolysis cell (MEC) in one set of CWs (E-B-CW), comparing it to CWs without an MEC (B-CW) and a control (C-CW).
- Analyzed nitrogen species (NH₄-N, NO₃-N, TN) removal efficiencies and characterized Mn oxides and bacterial communities.
Main Results:
- E-B-CW demonstrated the highest removal efficiencies for NH₄-N, NO₃-N, and TN, followed by B-CW and C-CW.
- E-B-CW matrices contained significantly more Mn(IV) oxides compared to B-CW.
- Ammonification and nitrate reduction were linked to Mn-oxidizing bacteria, which were most abundant in E-B-CW due to MEC-driven Mn(II) re-oxidation.
Conclusions:
- Intensified Mn redox cycling, particularly with MEC integration, significantly enhances nitrogen removal in CWs.
- The MEC promotes Mn(IV) oxide formation and supports a higher abundance of Mn-oxidizing bacteria, crucial for nutrient removal.
- Engineered CWs utilizing Mn oxides and MECs offer a promising approach for advanced wastewater nutrient management.
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