Mitigating methane emissions during nitrogen removal in constructed wetlands

Abstract

As nitrogen removal requires anaerobic conditions for denitrification, which facilitates the production of methane (CH₄), a potent greenhouse gas, it is a challenge to achieve nitrogen removal with minimal CH₄ emissions in constructed wetlands (CWs). This study proposed a solution for mitigating CH₄ 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 nosZ/amoA ratio than on the surface. The anaerobic decomposition of organic matter was inhibited, yielding significantly lower CH₄/CO₂ ratios (<1.0 ​× ​10⁻⁵) than those of traditional CWs (0.07). The methanogen proliferation and CH₄ 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 ​× ​10⁶ and 38%, respectively). Overall, this study proposed a strategy for mitigating the greenhouse effect of carbon emissions from CWs in the future.