Date of Award

Spring 2021

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemical and Environmental Engineering (ENAS)

First Advisor

Chertow, Marian

Abstract

The UN Sustainable Development Goals (SDGs) set out a bold vision to advance global society on multiple dimensions by the year 2030. The 17 SDGs tackle key issues of human wellbeing in part by building infrastructure, industrializing, and growing economies. The SDGs simultaneously aim to prevent climate change and conserve the natural environment. There are synergies between many of the goals, but clear tradeoffs as well. Investments in capital assets like buildings, roads, equipment, vehicles, and information technology come at an environmental cost. Innovative strategies are needed to grapple with these tradeoffs and optimize paths toward sustainable development. Innovative tools are needed to assess environmental considerations of the existing situation and possible futures.Grounded in a systems perspective, the evolving field of Industrial Ecology (IE) is well suited to contribute such assessment tools. The common suite of IE tools includes environmentally-extended input-output (EEIO) analysis, life cycle assessment (LCA), and material flow analysis (MFA). EEIO analysis takes a top-down look at the monetary exchanges between sectors of the economy, while LCA creates a detailed bottom-up account of the physical exchanges to produce and use a product system; both trace potential environmental impacts and resource use along supply chains. MFA traces the movement and accumulation of materials throughout a system and over time. The goal of this dissertation is to utilize and innovate upon EEIO, LCA, and MFA to address a set of environmental issues related to a variety of capital-intensive product systems. The dissertation begins by enhancing the USEEIO model through endogenization of capital assets. The USEEIO model was developed by the US EPA to analyze environmental impacts of around 400 goods and services in the US economy. Due to the structure of EEIO models, the investment in long-lived capital assets is considered separately from the exchanges of short-lived goods and services between producing sectors. Considering the environmental intensity of creating capital assets, it is important to incorporate the use of these assets in production processes, especially when comparing environmental impacts of alternative product systems. The dissertation next focuses on metal footprints, with an emphasis on metal in capital assets. The approach combines multi-regional EEIO analysis with MFA. Existing metal footprints trace the gross ore from the source to the end product and final consumer, and do not endogenize capital. The gross ore is mostly comprised of rock; the desired metal that continues along the supply chain is only a fraction. Given the high variation in the ore grade between types of metals, the ore-based metal footprint differs substantially from that calculated based on the valuable metal contained in the ore. In this work, an approach is developed and demonstrated to trace the valuable metal from the source through the supply chain and compare results with the typical approach. These metal contained footprints are compared with and without the capital assets endogenized. The analysis explores drivers of change over time, national trends, and potential environmental impacts of metal production. The dissertation then pivots to an LCA case study of a specific innovative product system: commercial aircraft powered by liquid hydrogen combustion. A variety of strategies are being pursued in attempts to decarbonize civil aviation, which is very challenging due the technical constraints of commercial flight. Hydrogen has been considered as a fuel over the decades but has recently been re-proposed as a possible solution by Airbus, with a caveat that the hydrogen would need to be produced from renewable electricity to net an environmental benefit. Currently, most hydrogen in the world is produced from natural gas and coal. There are no recent comprehensive studies on the potential environmental and human health benefits and tradeoffs of transitioning from a fleet powered by conventional petroleum jet fuel to one powered by hydrogen combustion. Therefore, this study is a comprehensive, comparative Well-to-Wake LCA. The use of capital assets are of course included throughout the life cycle; the assets drive the relative performance of some hydrogen production pathways. Many forms of uncertainty are captured in a simulation model, and influential parameters are identified. Recommendations are provided on critical areas for further study necessary to determine whether and under what scenarios to initiate a shift to hydrogen-powered aviation. This dissertation addresses several aspects of environmental assessments of capital-intensive product systems. The tools of IE have been shown to be effective for distilling key metrics for comparison between nations and product systems. Though the chapters do not build upon each other linearly, they overlap, and each help fill in different pieces of the same sustainability puzzle.

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