Impact of Changing Waste Streams on Microbial Ecology and Biogeochemical Cycling in Deep Landfill Ecosystems

Abstract:

Municipal solid waste landfills can reach depths of >100m and can be characterized as extreme environments in many respects (deep, dark, hotter than ambient). Landfills are inherently heterogeneous and rich with organic and inorganic materials that fuel a diverse array of microbial metabolisms. These ecosystems are major players in carbon cycling as they are a leading source of anthropogenic microbially driven methane emissions. To date, however, the composition and diversity of landfill microbial communities are poorly understood due to sparse application of modern sequencing techniques. We constructed laboratory-scale landfill microcosms to study the impact of a variety of waste inputs on landfill microbial communities. Specific waste inputs included contaminants of emerging concern (CECs) such as antibiotics and microplastics, as well as sulfate to mimic the addition of gypsum wallboard from construction/demolition waste or local high sulfate cover soils. Microcosms were sampled for DNA six times over a 65-day period to capture temporal changes in the microbial community. Test inputs (antibiotics, microplastics, sulfur, and iron) were added after ~40 days and compared to control microcosms without additions. We applied 16S rRNA high-throughput sequencing methods to understand the changes in microbial diversity associated with specific process conditions. Results show markedly high heterogeneity between triplicate microcosms even when inputs are held constant. Moreover, altering waste inputs slightly can significantly alter the dominant microorganisms present as well as the landfill leachate geochemistry, which may have important implications for biogeochemical cycling in these subsurface ecosystems.