Effects of substrate type on enhancing pollutant removal performance and reducing greenhouse gas emission in vertical subsurface flow constructed wetland

Constructed wetlands (CWs), known as an alternative clean technology, have been widely used for sewage treatment. However, greenhouse gas (N2O, CH4 and CO2) emissions are the accompanying problem in CWs. To mitigate the net global warming potential (GWP) with the constant removal efficiency for contaminants is attracting wide attention recently. In this study, four CWs were established to explore the effects of substrate types (gravel, walnut shell, manganese ore and activated alumina) on contaminant removal and greenhouse gas emissions. CWs using manganese ore substrate with function of electronic exchange showed high removal efficiencies on COD (90.1%), TN (65.1%), TP (97.1%) and low greenhouse gas flux. The emission fluxes of N2O, CH4 and CO2 were 0.07–0.20, 2.00–252.30 and 337.54–782.57 mg m−2 h−1, respectively. Especially, the lowest average CH4 emission flux in the manganese ore CW was only 2.00 mg m−2 h−1 while those of N2O in walnut shell CW was only 0.07 mg m−2 h−1, which will make a significant contribution on the mitigation of GWP of CWs. High-throughput sequencing results indicated that microbial community diversity and richness changed significantly among different substrates. The high pmoA and low mcrA, caused by the introduction of manganese ore as substrate, also explained why there was little CH4 emission in CWs. Our study provided new insights into GWP mitigation and contaminant removal enhancement in CWs using optimal substrate.