Understanding landfill gas behavior at elevated temperature landfills

Abstract

Landfill gas (LFG) wellhead data were compared to understand the range of observations due to unique conditions at five elevated temperature landfills (ETLFs) in the U.S. Correlations of the primary gas ratio, CH4:CO2, show distinct compositional indicators for (1) typical operation, (2) subsurface exothermic reactions (SERs), (3) high moisture content, and (4) air intrusion that can help operators and regulators diagnose conditions across gas extraction wells. ETLFs A, B, D, and E showed similar trends, such as decreasing CH4 and increasing CO2, CO, and H2 that have been previously described. ETLF C uniquely exhibited elevated CH4 and temperatures simultaneously due to carbonation (i.e., CO2 consumption) of a steel slag which was used as alternative daily cover (ADC). At the maximum gas well temperature, T = 82 °C/180 °F, CH4 and CO2 concentrations were 47% and 28%, respectively. At ETLFs A, B, and E, H2 > 50% were regularly observed in affected gas wells for several years. At the five ETLFs, maximum CO concentrations ranged from 1400–16,000 ppmv. Like the analysis of CH4:CO2, it is hypothesized here that H2 (%):CO (ppmv) may infer the types of waste that are thermally degrading. Co-disposal of industrial wastes and MSW and the use of potentially reactive ADCs should remain an important consideration for landfill operators and regulators because of their potential long-term impacts to LFG quality.