The potential use of heat flux to infer landfill gas flux
An assessment is made of how heat flux might be used to infer gas fluxes from municipal solid waste landfills. Thermodynamic principles are used to estimate the amount of heat generated per mole of anaerobically-produced methane gas. An equation is derived to relate a landfill's surface flux of methane to its flux of heat. A closed landfill in Christchurch, New Zealand, is used to demonstrate how the equation might be applied. An infra-red scan of the landfill by helicopter noted higher temperatures at the surface of one portion of the landfill. At six sites in that portion of the landfill, thermistor-fitted probes were driven to one meter depth and soil temperatures monitored. An estimate of methane flux from heat measurements is compared to an estimate based on literature and site-specific information. The two methods give similar results. Variability in the heat flux measured at the landfill raises concerns about the difficulties that might arise in attempts to improve the reliability of this new method of estimating methane generation rates. The ease of temperature monitoring suggests that further investigation of the technology is warranted.