[Effect of Ferric-carbon Micro-electrolysis on Greenhouse Gas Emissions from Constructed Wetlands]

As the problem of global warming becomes increasingly serious, the greenhouse gas (GHG) emission reduction measures of constructed wetlands (CWs) have drawn significant attention. Ferric-carbon micro-electrolysis exhibits an excellent effect on wastewater purification as well as the potential to reduce GHG emissions. Therefore, to explore the impact of ferric-carbon micro-electrolysis on GHG emissions from intermittent aeration constructed wetlands, four kinds of different wetlands with different fillers were constructed. The four fillers were ferric-carbon micro-electrolysis filler+gravel (CW-Ⅰ), ferric-carbon micro-electrolysis filler+zeolite (CW-Ⅱ), zeolite (CW-Ⅲ), and gravel (CW-Ⅳ). Intermittent aeration technology was used to aerate the wetland systems. The results show that ferric-carbon micro-electrolysis significantly improved the nitrogen removal efficiency of the intermittent aeration constructed wetlands and reduced GHG emissions. Compared with CW-Ⅳ, the CH₄ fluxes of CW-Ⅰ, CW-Ⅱ, and CW-Ⅲ decreased by 32.81% (P<0.05), 52.66% (P<0.05), and 54.50% (P<0.05), respectively. Among them, zeolite exhibited a stronger reduction effect on CH₄ emissions in both the aeration and non-aeration sections. The ferric-carbon micro-electrolysis substantially reduced N₂O emissions. In comparison with CW-Ⅳ, CW-, and CW-Ⅱ achieved N₂O emission reduction by 30.29%-60.63% (P<0.05) and 43.10%-73.87% (P<0.05), respectively. During a typical hydraulic retention period, the comprehensive GWP caused by CH₄ and N₂O emitted by each group of wetland system are (85.21±6.48), (49.24±3.52), (127.97±11.44), and (137.13±11.45) g·m^-2, respectively. The combined use of ferric-carbon micro-electrolysis and zeolite effectively reduces GHG emissions in constructed wetlands. Overall, ferric-carbon micro-electrolysis combined with zeolite (CW-Ⅱ) can be regarded as one of the valuable filler combination methods for constructed wetlands, which can ensure high removal efficiency of pollutants and effective GHG emission reduction in constructed wetlands.