Graduation Year

2019

Document Type

Thesis

Degree

M.S.E.V.

Degree Name

MS in Environmental Engr. (M.S.E.V.)

Degree Granting Department

Civil and Environmental Engineering

Major Professor

Qiong Zhang, Ph.D.

Committee Member

Sylvia Wilson Thomas, Ph.D.

Committee Member

Nancy Diaz-Elsayed, Ph.D.

Keywords

impacts of climate change, effects of population density, resource recovery, waste heat utilization

Abstract

Increasing resource demand and decreasing supplies necessitate a paradigm shift in wastewater management from treatment to resource recovery. As the economic and environmental performance of wastewater-based resource recovery systems is location-specific (e.g., terrain slope influences hydro-energy recovery), a holistic view of their sustainability requires a comprehensive analysis on the effect of the local conditions on these systems. Although the internal factors affecting such systems (e.g., water quality and end use) are well studied, there is limited literature on the effect of external factors such as topography, climate and population density. This study evaluated the role of climate and population density on the sustainability of drain water heat recovery systems (DWHRS) for regions across North America.

A MATLAB-based model was developed to compute life cycle energy consumption and net present value (NPV) of the DWHRS. Life cycle assessment (LCA) was performed to estimate carbon footprint, eutrophication potential and ecotoxicity. Energy recovered from the DWHRS was found to vary inversely with ambient temperature. For instance, 113% more energy is recovered in New York City as compared to Tampa, Florida. Regions with hot climates (e.g., Florida) are estimated to have a 5-6-year payback period, while colder regions like New York have a 1-2-year payback period. The DWHRS showed more economic benefits with increasing population density; NPV was −$125 for a one-person household and $513 for a three-person household over a 20-year lifespan in Tampa. The LCA reveals that the DWHRS performs better from an environmental standpoint than systems with no heat recovery. For example, in Tampa, heat recovery is estimated to reduce greenhouse gas emissions by 295% (3.97 g CO2 eq/ litre of water heated to 60 °C). The results were also compared with that of district heating in Canada. The DWHRS has about 3 times shorter payback period than the district heating system; however, the district heating system performs better than the DWHRS in all environmental impact categories except three indicators – non carcinogenics, eutrophication, ecotoxicity.

The model can be utilized to evaluate the sustainability of the DWHRS for specific locations and help consumers decide whether to invest in the DWHRS. Overall, this study provides a platform to evaluate the feasibility of wastewater-based resource recovery systems through sustainability assessment.

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