Evaluation of the Temperature Range for Biological Activity in Landfills Experiencing Elevated Temperatures

Abstract

There have been reports of municipal solid waste landfills with waste and gas wellhead temperatures of at least 80–100 °C, which is in excess of temperatures reported at typical landfills. Landfills experiencing heat accumulation over a broad area present a number of challenges involving leachate and gas quality and quantity, and the associated collection infrastructure. The objectives of this research were to evaluate the impact of temperature on methanogenesis and fermentation in landfills, and to evaluate the extent to which microbial populations acclimate when perturbed to either lower or higher temperatures relative to their in situ temperature. Samples excavated from two landfills exhibiting elevated temperatures were utilized as inocula for small- and reactor-scale experiments. The optimum temperature for methane generation in the thermophilic range was 47.5–57.5 °C, with yields reduced by ∼37 and 75% at 62.5 and 67.5 °C, respectively. While microbial populations did not acclimate above 67.5 °C, methanogenic activity resumed when waste was cooled. 16S rRNA sequencing revealed that Methanothermobacter likely plays a key role in facilitating methane production in landfills operating in the thermophilic range and that microbial community diversity decreased at higher incubation temperatures. There was evidence that fermentation occurs up to 77.5 °C, well above the upper limit for methanogens measured in this study. Model simulations predict that fermentation reactions contribute a ∼3–10 °C rise in waste temperature.