The “Number Two” Threat to Climate Change: Implications of Methane Emissions from Wastewater Treatment Plants

Abstract

The processes involved in the treatment of municipal wastewater at sewage treatment plants emit large quantities of trace gases into the atmosphere, which can have a significant negative impact on air quality and contribute to the adverse effects of greenhouse gases on the environment and climate. This study focuses on methane as the primary greenhouse gas emitted from wastewater treatment plants. It aims to accurately identify and quantify the contributions of these methane emissions and propose potential solutions to mitigate the impact they have on the environment.

This investigation combines air quality and weather data collected from field measurements of 13 different wastewater treatment plants throughout New Jersey, Pennsylvania, and New York, with the utilization of atmospheric dispersion models to estimate the emissions and the impacts of wastewater on the environment. It also uses information from interviews conducted with various plant supervisors and engineers to deduce information about the potential for mitigation of these emissions as well as resource recovery opportunities for methane as a source of fuel. While field measurements were collected in conjunction with other members of the Zondlo Research Group at Princeton as required by safety considerations, the analyses and data interpretations in this thesis are original work. I also led or co-led most of the field measurements in this thesis, though to widen the dataset, a few additional sampling campaigns were conducted by other researchers in the Zondlo group that are included in the analyses for this thesis. While the majority of sampling site data was collected during the academic year, to provide a more complete set of data and analysis, field data collected in the summer of 2019 were re-analyzed during the senior thesis to be consistent with the techniques used from academic year sampling.

Results from this research suggest that of the wastewater treatment plants sampled, emission rates are consistently lower than the IPCC emission factor for methane from wastewater treatment plants, within an order of magnitude. Further analysis also suggests that larger wastewater treatment plants emit less methane into the atmosphere per gallon of wastewater treated. This finding appears to contradict the current recommendation that a distribution of wastewater treatment on a more local scale will reduce environmental impacts. These results also suggest a policy recommendation of wastewater treatment consolidation. The investigation of complexities from individual plants emphasizes the importance of understanding the dynamics of wastewater treatment on a plant-to-plant basis in order to accurately deduce an emission rate.