Impact of biochar on greenhouse gas emissions from constructed wetlands under various influent chemical oxygen demand to nitrogen ratios

Biochar is widely used for nutrient removal in constructed wetlands (CWs); however, its influence on greenhouse gas (GHG) emissions from CWs remains unclear. Here, biochar was used to mitigate the global warming potential (GWP) from CWs and promote the removal of contaminants from simulated domestic wastewater under different influent chemical oxygen demand to nitrogen ratios (COD/N = 3, 6, 9, 12). Results demonstrated that biochar could improve the removal of COD, NH4+ - N, and TN. The average N2O and CO2 fluxes were significantly lower and CH4 fluxes were higher in biochar-added CWs than those in none-biochar CWs. Biochar reduced GWP values of N2O and CH4 from 18.5% to 24.0%. N2O fluxes and GWP decreased, while CH4 and CO2 fluxes increased as COD/N ratios increased. Additionally, biochar increased the abundance of Geobacter and denitrifiers such as Hydrogenophaga. Overall, biochar could not only promote the removal of nutrients but also mitigate GWP in CWs.