| Description |
Atmospheric methane and carbon dioxide have been deemed significant "greenhouse gases" (GHG) which are thought to be responsible for major climate changes. Wastewater treatment plants have seen quite a lot of attention with respect to methane release, but little study of sewer transport (pipeline) contribution has been reflected in recent literature. This lack of analysis on sewer systems could be because of the Intergovernmental Panel on Climate Change report stating that in most developed countries, sewers are closed and underground, and therefore would not make a large contribution to carbon emissions (especially CH4) emissions. Previous methods for quantifying sewer transport emissions have mainly utilized tracer gas coupled with measurement of flow or velocity rates within the sewer lines, or through lab studies. The purpose of this study was to develop a direct flux emissions measurement method based on existing technology, soil flux chambers, for CH4 and CO2 using lab calibration and field testing. Such chambers were designed for measuring diffuse soil fluxes exclusively, and decades of such measurements indicate the validity of the approach. In this thesis study, the soil chamber was used as a basis for designing a larger chamber capable of handling relatively larger magnitude point fluxes from sewer access covers. The University of Utah campus consists of a series of mixed gravity sewer designs and ages, spanning the past century. Assuming this system was representative of the range of urban gravity sewer infrastructure typical to U.S. cities, a case study was done as part of this thesis. For this work, 11 sewer access covers were analyzed using a specifically designed flux chamber to measure gas fluxes directly from the sewer access covers. Based on these surveys, a preliminary estimate of annual carbon emissions from these 11 access iv points was determined to be 1.066 Metric Tons CO2 equivalent per year (Mt CO2e). It is recommended that more calibration and continuous surveys of these, and all other sewer access points on campus, are done to facilitate the calculation and cumulative "carbon footprint" of the campus sewer system. Ultimately, the technology developed as part of this thesis work can form the basis of an effective methodology to measure CH4 and CO2 emissions from sewer lines and possibly other urban infrastructure, and quantify the relative major GHG emissions or "carbon footprint" of such emission sources. |
