Characteristics and effect factors of CH4 emissions in single-family treatment wetlands

Single-family treatment wetland (SFTW) is increasingly used in developing countries to treat rural domestic sewage. But they can emit CH4, which will affect the global carbon balance. However, a detailed understanding of CH4 emissions in SFTW under long-term real operating conditions is still lacking. To understand the emission characteristics of CH4 from SFTW, a 50-month CH4 flux measurement was conducted in six SFTWs (namely ZHANG, HU, LUO, WEEC, WANG, GAO) of Anlong village, Chengdu, China. The results show that the monthly fluxes of CH4 ranged from −81.35 to 223.13 mg·m−2·h−1, with an average value of 37.41 ± 60.97 mg·m−2·h−1. Generally, CH4 emissions were higher in spring and summer than other seasons (p < 0.05). Besides, the mean annual CH4 flux of 2016 had a significant increase compared to 2014 and 2015 in SFTW (p < 0.05). On the other hand, the mean CH4 fluxes from HU (P < 0.05) and WEEC were lower in the influent tank than in the effluent tank. Moreover, precipitation, air temperature, and sunshine duration were three key factors of CH4 emissions from SFTW. Illumina sequencing shows that Methanoregula and Methanobacterium were dominant methanogenic populations in SFTW (accounting for 96.97%), and were both hydrogenotrophic archaea. A high level of CH4 global warming potential (GWP) was found in SFTW, with an average value of 9.63 kg·CO2-eq·m−2·year−1. WANG wetland was the most environmentally friendly SFTW, acted as a “carbon sink” of CH4 from 2013 to 2016. This study provides a foundational reference for future research on CH4 emission reduction in constructed wetlands (CWs).