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

Abstract

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.