Wet waste carbon source recharge improves acetoclastic methanogenesis in aged landfills

The implementation of new waste sorting policies and "zero landfill" strategies has precipitated the premature retirement of municipal landfills and accelerated their aging, resulting in a significant decline in both the production and quality of landfill gas containing methane (CH₄), thereby impeding resource utilization and exacerbating carbon emissions. Waste-derived organic matter recharge can increase the availability of landfill gas, but the underlying mechanisms and influencing factors remain unclear. In this study, waste-derived organic matter (aged landfill leachate and wet waste slurry) available at the landfill campus was used as a supplemental carbon source to infuse into an anaerobic landfill column system to investigate the effects of exogenous carbon inputs on the performance of landfill CH₄ generation by using metagenomic sequencing. The results show that adding wet waste slurry and alkali-adjusted wet waste slurry increased the methane content by 50.75% and 58.31%, respectively, and significantly increased the concentration of volatile fatty acids (VFAs) in the leachate. Metagenomic sequencing revealed that wet waste slurry recharge enriched acidogenic bacteria, syntrophic bacteria, and acetoclastic methanogenic archaea and increased the expression of functional genes associated with acidification, direct interspecies electron transfer (DIET), and acetoclastic methanogenesis. A partial least squares path model (PLS-PM) revealed that functional genes and VFAs were the most important factors influencing landfill CH₄ production. The results of this study provide theoretical support for the scientific management, low-carbon operation and sustainable development of aged municipal landfills.