Dissertation
Quantifying the amount of useful heat energy in sewage
Doctor of Philosophy (Ph.D.), Drexel University
Dec 2022
DOI:
https://doi.org/10.17918/00001466
Abstract
There is an international imperative to reduce global greenhouse gas emissions. Investments into renewable energy are being made, yet the prospect of recycling energy by recovering heat from sewage is not getting the attention commensurate with its thermodynamic potential. Exergy is the amount of useful energy in a system. 4.5 years of sewage temperature and flow data from 15 Philadelphia sewers were analyzed using a modified process model to calculate exergy. The modified process model uses the temperature of ambient air as the dead state reference. This method was superior to the natural environment subsystem model, which used 25 °C as the standard dead state. The modified process model predicts slightly more exergy, and more accurately describes the flow of heat. An ability to articulate the useful energy in sewage allows society to treat it as a resource. Widespread engagement in sewage heat recovery has financial merit but more importantly it reduces greenhouse gas emissions. Each million gallons of sewage can reduce greenhouse gas emission by 0.8 to 4 metric tons of CO₂e. Additionally, a regression analysis of the independent sewer data was conducted resulting in a second order autoregression model. This model was able to accurately predict the monthly average temperature of sewage. The significant parameters were air temperature, whether the sewer was constructed of reinforced concrete or not, and the month of year. Other parameters sewage flow, precipitation, cross sectional area, depth, drainage area, or even the proportion of sanitary flow compared to combined sewage flow were not statistically significant. Sewage is a predictable, stable, and useful source of heat. Sewage heat recovery systems are essential to continued sustainable development.
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Details
- Title
- Quantifying the amount of useful heat energy in sewage
- Creators
- Paul M. Kohl
- Contributors
- Charles Nathan Haas (Advisor) - Drexel University, Civil, Architectural, and Environmental Engineering
- Awarding Institution
- Drexel University
- Degree Awarded
- Doctor of Philosophy (Ph.D.)
- Publisher
- Drexel University; Philadelphia, Pennsylvania
- Number of pages
- x, 144 pages
- Resource Type
- Dissertation
- Language
- English
- Academic Unit
- Civil/Architectural/Environmental Engineering (1970-2026); College of Engineering (1970-2026); Drexel University
- Other Identifier
- 991020077010004721