Abstract
Methane is a highly potent greenhouse gas and contributes significantly to climate change. Recent studies have shown significant methane production in sewers. The studies conducted so far have relied on manual sampling followed by off-line laboratory-based chromatography analysis. These methods are labor-intensive when measuring methane emissions from a large number of sewers, and do not capture the dynamic variations in methane production. In this study, we investigated the suitability of infrared spectroscopy-based on-line methane sensors for measuring methane in humid and condensing sewer air. Two such sensors were comprehensively tested in the laboratory. Both sensors displayed high linearity (R2 > 0.999), with a detection limit of 0.023% and 0.110% by volume, respectively. Both sensors were robust against ambient temperature variations in the range of 5 to 35°C. While one sensor was robust against humidity variations, the other was found to be significantly affected by humidity. However, the problem was solved by equipping the sensor with a heating unit to increase the sensor surface temperature to 35°C. Field studies at three sites confirmed the performance and accuracy of the sensors when applied to actual sewer conditions, and revealed substantial and highly dynamic methane concentrations in sewer air.
Highlights
Methane is a highly potent greenhouse gas and contributes significantly to climate change
We investigated the suitability of infrared spectroscopy-based on-line methane sensors for measuring methane in humid and condensing sewer air
According to the data reported in a study conducted on 14 manholes in a sewer line in Melbourne[9], gas phase methane concentrations usually vary from 1000 to 50000 ppm, which was chosen as the basis for the calibration range
Summary
Methane is a highly potent greenhouse gas and contributes significantly to climate change. The studies conducted so far have relied on manual sampling followed by off-line laboratory-based chromatography analysis These methods are labor-intensive when measuring methane emissions from a large number of sewers, and do not capture the dynamic variations in methane production. In a US study, gas phase methane concentrations of 500–900 ppmv, i.e. 0.05–0.09% vol, were detected at the discharge of a 5.3 km rising main with a diameter of 406 mm, yielding a CH4 emission of 7.44 kg/d10. These data confirmed significant methane production and emission from sewers, which is currently not accounted for. Even though it is claimed that these sensors are applicable to methane detection in wastewater treatment facilities, sensor performance has not been fully studied and there have been no reports in the scientific literature evaluating the suitability of these sensors for on-line methane measurement in sewers
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