Application and validation of tracer dispersion method for quantifying fugitive methane emissions from landfills, wastewater treatment plants and biogas production

The fugitive methane emission from landfills, wastewater treatment plants and biogas production plants is a significant anthropogenic source to atmospheric methane. To understand the size of these emissions and to evaluate possible mitigation initiatives, reliable methane emission quantification methods are needed. One of the best methods for quantifying the whole site emission from a large area source is the tracer dispersion method. The method is using a known release rate of a tracer gas placed at the methane source and measure the ratio of methane and the tracer gas far from the emission area. Combining the tracer release and the downwind concentration ratio, the whole site emission can be calculated. 

The tracer dispersion method has advantages and disadvantages compared to other available methods for whole site emission. One of the challenges of the method is the availability of a downwind road in a suitable distance to the emission source, while one advantage is that it is not dependent of accurate measurements of the atmospheric conditions. 

The method has been used for quantifying methane from Danish landfills and when the Danish EPA the summer 2016 started a governmental funded project using methane oxidizing biocovers for minimizing methane emission from landfills, where gas extraction and utilization were not practical or economical feasible, the tracer dispersion method was chosen as the best available method for quantifying the effect of the mitigation initiative. Since then, the tracer dispersion method was applied at more than 40 Danish landfills to find their methane emissions and select the landfills on which biocovers will be applied. 

The tracer dispersion method has also been used to quantify the methane emission from wastewater treatment plants and biogas production plants. Comparison studies have been performed, using different quantification methods and different analytical setup. Methane emission from landfills are influenced by the changes in atmospheric conditions and we therefore tested the tracer dispersion methods ability to make a time series of methane emission from the landfill during a significant change in the atmospheric pressure. The method measures the whole landfill methane emission and is independent of the atmospheric pressure, and thus the changes in measured emission is a direct result of the change in atmospheric conditions. 

This paper describes the application of the tracer dispersion method at landfills, wastewater treatment plants and biogas production plants. The robustness and possible errors at the different application is discussed. The process of assessing the uncertainties is described, including an overview of how accreditation was obtained, given by the national accreditation body in Denmark (DANAK). This paper also describes a validation process through intensive studies comparing various quantification methods performed, as well as side by side measurements of identical and similar analytical setups for the tracer dispersion method. The validation studies are going to be published during 2017 and the results will be summarized in this paper.

For further information on monitoring methane at landfill sites, click through to reveal the National Physical Laboratory's presentation on the use of differential infra-red absorption lidar at sites across the UK.