Mitigating CH4 Emissions in Semi-Aerobic Landfills: Impacts of Operating Conditions on Abundance and Community Structure of Methanotrophs in Cover Soils

Abstract

Methanotrophs are the most important sink of CH₄, which is a more highly potent greenhouse gas than CO₂. Methanotrophic abundance and community diversity in cover soils from two typical semi-aerobic landfills (SALs) in China were detected using real-time polymerase chain reaction (real-time-PCR) and denaturing gradient gel electrophoresis (DGGE) based on 16S rRNA genes, respectively. Real time-PCR showed that Type I methanotrophs ranged from 1.07 × 10⁶ to 2.34 × 10⁷ copies/g soil and that of Type II methanotrophs from 1.51 × 10⁷ to 1.83 × 10⁸ copies/g soil. The ratio of Type II to Type I methanotrophic copy numbers ranged from 5.61 to 21.89, indicating that Type II methanotrophs dominated in SAL. DGGE revealed that Type I methanotrophs responded more sensitively to the environment, changing as the community structure varied with different soil types and locations. Methylobacter, Methylosarcina, and Methylomicrobium for Type I, and Methylocystis for Type II were most prevalent in the SAL cover layer. Abundant interflow O₂ with high CH₄ concentration in SALs is the reason for the higher population density of methanotrophs and the higher enrichment of Type II methanotrophs compared with anaerobic landfills and other ecosystems, which proved a conclusion that increasing the oxygen supply in a landfill cover layer would greatly improve CH₄ mitigation.