Mitigating methane emissions during nitrogen removal in constructed wetlands

As nitrogen removal requires anaerobic conditions for denitrification, which facilitates the production of methane (CH 4 ), a potent greenhouse gas, it is a challenge to achieve nitrogen removal with minimal CH 4 emissions in constructed wetlands (CWs). This study proposed a solution for mitigating CH 4 emissions while achieving nitrogen removal using porous fillers in CWs. We found that active denitrification occurred in the interior pores of these fillers in an oxygen-rich environment. The microbial analysis indicated that the internal pores of porous fillers created anaerobic habitats for denitrifiers as they had a higher nos Z/ amo A ratio than on the surface. The anaerobic decomposition of organic matter was inhibited, yielding significantly lower CH 4 /CO 2 ratios (<1.0 ​× ​10 −5 ) than those of traditional CWs (0.07). The methanogen proliferation and CH 4 production efficiency also remained at low levels (<1.1 ​× ​10 −3 and 0.045%, respectively), which was significantly lower than in traditional CWs (2.3 ​× ​10 6 and 38%, respectively). Overall, this study proposed a strategy for mitigating the greenhouse effect of carbon emissions from CWs in the future. • A novel solution was proposed for nitrogen removal with minimal CH 4 emissions. • Denitrification occurred in the pores of ceramic granules under oxic conditions. • Nitrification took place on the surface of ceramic granules. • Methanogen proliferation was inhibited with minimal CH 4 production.