Enhanced nitrogen removal in constructed wetlands filled with iron-carbon substrates: Reexploring unique roles of iron-cycling and electroactive microorganisms.
Study Goal
The researchers aimed to determine the roles of iron-cycling bacteria and electroactive bacteria in nitrogen removal in constructed wetlands with iron-carbon substrates under different filling modes.
Results Summary
The study found that constructed wetlands with separately filled iron-biochar substrates achieved higher total nitrogen removal (81%) and lower greenhouse gas emissions compared to mixed filling modes. Iron-cycling bacteria and electroactive bacteria, rather than nitrogen-transforming bacteria, were decisive in nitrogen removal.
Population
Constructed wetlands treating low C/N ratio wastewater
Effective Dosage
Micro-oxygen regulation (2 h/d, 60 mL min-1)
Duration
240 days
Interactions
None mentioned
| Intervention | Direction | Endpoint | Population | Dosage | Impact | Claim # |
|---|---|---|---|---|---|---|
CWs amended with iron-biochar substrates separately (CW-D) | increase | total nitrogen removal performance | constructed wetlands (CWs) | 81 % | achieved a higher | #1 |
CWs amended with iron-biochar substrates separately (CW-D) | decrease | greenhouse gas emission (global warming potential) | constructed wetlands (CWs) | reduced by 3.07 × 10⁵ μg CO2-eq m⁻²h⁻¹ | lower | #2 |
nitrogen-transforming bacteria (NTB) | no change | relative abundance | constructed wetlands (CWs) | P < 0.05 | no significant difference | #3 |
iron-cycling bacteria (ICB, e.g. Pseudomonas) with electroactive | increase | abundance | CW-D | - | significantly enriched | #4 |
electroactive bacteria (EAB, e.g. Tetrasphaera) | increase | abundance | CW-E | - | significantly enriched | #5 |
iron-cycling bacteria (ICB) and electroactive bacteria (EAB) | decrease | NO₂⁻-N content | constructed wetlands (CWs) | P < 0.05 | significant negative correlations | #6 |
Bacteria involved in iron cycle and electroactivity are commonly found in intensified constructed wetlands (CWs) with iron-carbon substrates. However, their roles in nitrogen (N) removal remain unclear. Here, two types of CWs with different filling modes (separate and mixed) of sponge iron and biochar substrates under micro-oxygen regulation (2 h/d, 60 mL min-1) were constructed for nitrogen removal for 240 days. The results revealed that CWs amended with iron-biochar substrates separately (CW-D) achieved a higher total nitrogen removal performance (81 %) and lower greenhouse gas emission (global warming potential reduced by 3.07 × 105 μg CO2-eq m-2h-1) compared with Fe-C micro-electrolysis CWs (CW-E). In this process, although 41 genera of nitrogen-transforming bacteria (NTB) were detected in CWs, no NTB members had a significant difference (P < 0.05) in relative abundance between CW-D and CW-E. However, 11 genera of iron-cycling bacteria (ICB, e.g. Pseudomonas) with electroactive and 5 genera of electroactive bacteria (EAB, e.g. Tetrasphaera) were significantly enriched in CW-D and CW-E, respectively, both showing significant negative correlations (P < 0.05) with NO2--N content. It indicated that ICB and EAB rather than specific NTB members were decisive in N removal in iron and carbon CWs in low C/N ratio wastewater treatment and regulated by filling modes. Our findings expand the knowledge of the application of iron and carbon substrates in CWs and provide an initial assessment of the effect of different filling modes of iron and carbon on nitrogen removal in CWs.