Effects and mechanisms of constructed wetlands with different substrates on N2O emission in wastewater treatment

Nitrous oxide (N 2 O) emissions from constructed wetlands (CWs) are accompanying problems and have attracted much attention in recent years. CWs filled with different substrates (gravel, biochar, zeolite, and pyrite) were constructed to investigate the nitrogen removal performance and N 2 O emissions, which named C-CWs, B-CWs, Z-CWs, and P-CWs, respectively. C-CWs showed the poorest nitrogen removal performance in all CWs. Although B-CWs exhibited the highest fluxes of N 2 O emissions, the percentage of N 2 O emissions in nitrogen removal (0.15%) was smaller than that of C-CWs (0.18%). In addition, microbiological analysis showed that compared with C-CWs, CWs filled with biochar, zeolite, and pyrite had higher abundance of nitrifying and denitrifying microorganisms and lower abundance of N 2 O producing bacteria. In conclusion, biochar, zeolite, and pyrite were more favorable kinds of substrate than the conventional substrates of gravel for the nitrogen removal and reduction of N 2 O emissions from CWs.