Graduation Year

2020

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Civil and Environmental Engineering

Major Professor

Qiong Zhang, Ph.D.

Committee Member

James R. Mihelcic, Ph.D.

Committee Member

Mauricio E. Arias, Ph.D.

Committee Member

Changhyun Kwon, Ph.D.

Committee Member

Jhih-Shyang Shih, Ph.D.

Keywords

Cost Analysis, Life Cycle Assessment, Nitrogen Removal and Recovery, Stormwater Management, Systems Modeling

Abstract

The need for wastewater and stormwater quality control, especially the control of nutrients, has been recognized due to the widespread problem of water eutrophication. Sustainable nutrient management is essential to reduce nutrient-related impacts and supply the growing nutrient demands.

This research focused on the nutrients (nitrogen and phosphorus) in the urban water environment with nitrogen as the nutrient of interest since nitrogen is the primary nutrient responsible for eutrophication in the coastal areas. It aimed to enhance the sustainability of urban nutrient management through technology-level evaluation and system-level optimization of technology implementation with consideration of life cycle environmental impacts and cost. For the technology level, the research evaluated the environmental and economic impacts of individual technologies (i.e. bioretention systems, membrane bioreactors, and onsite wastewater treatment systems, in Chapters 2 – 4, correspondingly) associated with their nutrient management function using life cycle assessment and cost analysis. Life cycle assessment is a method for quantifying resource consumption, loads, and potential environmental impacts associated with all the stages of the life cycle of a product or service, while life cycle cost analysis is a similar method that calculates the economic performance of a product or service over its entire life. The study investigated the tradeoff between the nutrient removal performance, environmental impacts, and cost of each selected technology in terms of different technological configurations. For the systems level, the research developed a spatial optimization tool to determine the combination and spatial distribution of nutrient management technology implementation (i.e. green stormwater infrastructure) with minimal system-level environmental impacts and costs, with consideration of terrain characteristics, environmental properties, and technological configurations (Chapter 5).

In the first task, the environmental and economic impacts of alternative bioretention system configurations were evaluated relative to their flood control and nutrient management capabilities using life cycle assessment and cost analysis. The trade-off between the nutrient removal performance, some environmental impacts, and cost were also observed and discussed. Finally, this task suggests a proper depth of 45 cm for the internal water storage zone and the insignificance of selecting ground plant species. It also highlights the importance of nutrient focus for the scope of sustainability assessment by comparing a nutrient-related functional unit and a water quantity-related one.

In the second task, the environmental and economic impacts associated with full-scale aerobic and anaerobic membrane bioreactors were compared for municipal wastewater treatment under different end use scenarios (i.e., discharge or reuse) of the effluent using life cycle assessment and cost analysis. It shows that anaerobic membrane bioreactors have higher impacts (10-49% higher) than aerobic ones in the discharge scenario but opposite (25-94% lower) in the reuse scenario. It highlights the environmental benefits of reusing the effluent of an anaerobic membrane bioreactor and the potential benefits vary depending on the types of crops receiving the reclaimed water. The use of the anaerobic membrane bioreactor effluent for irrigation and fertilization could be a win-win solution to both irrigation water shortage and high environmental impact associated with nutrient removal.

In the third task, the life cycle environmental and economic impacts of onsite wastewater treatment systems were evaluated relative to their nutrient management capabilities and the influence of locational variation was highlighted. Changing the location resulted in a change of up to 34% in TN removal, 30% in environmental impacts, and 35% in cost. It reveals that the less permeable soil type and higher soil temperature improved the total nitrogen removal efficiency, reduced nutrient-related impacts like eutrophication, and improved cost-effectiveness, especially for the conventional system due to its strong reliance on the performance of the drainfield. It also unveils that locational variation of energy mix had a strong influence on the environmental performance of the advanced system with active treatment units in terms of greenhouse gas emissions and fossil fuel depletion.

In the fourth task, a framework was developed for a spatial optimization of green stormwater infrastructure implementation in terms of sustainable nutrient management. It also developed the methods to create green infrastructure inventory by identifying implemented and candidate green infrastructure within the study area, as the input to the spatial optimization. The developed optimization tool helps determine the optimal allocation of green infrastructure in terms of location, size, and type. The system-level environmental impacts and costs can be minimized when a certain amount of green infrastructure (approximately 50) is implemented in the study area. In addition, the optimal solutions show certain patterns in terms of green infrastructure’s location, size, and type.

This research advances sustainable nutrient management from the views of both technology-level evaluation and system-level optimization. It highlights the factors of assessment goal, effluent end use, technology design, and locational conditions for the sustainability of nutrient management. Besides, the deployment location, size, and type of green infrastructure for stormwater and nutrient management can be optimized to reduce the system-level environmental impacts and costs. This research provides decision makers with a tool to make informed decisions in terms of the implementation of nutrient management technologies.

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