Life Cycle Optimization of Sustainable Water-Energy-Food Nexus Systems and Networks


As the global population grows, consumption of water, energy, and food will also increase, placing stresses on these sectors, raising the importance of the Water-Energy-Food Nexus (WEFN). However, operation of WEFN systems are currently not sustainable. It is thus crucial to design WEFN systems to be sustainable from local to global scales and to all stakeholders. This dissertation seeks to develop novel methods and applications from process systems engineering and a variety of other disciplines, ranging from ecology to economics, to model and optimize WEFN systems for sustainability. Novel modeling frameworks that consider global impacts, multiple objectives of multiple stakeholders, and impacts on ecosystems of WEFN and production systems are constructed and applied. This dissertation shows that holistically modeling not only the WEFN but also the multitude of connected and intertwined processes requires interdisciplinary approaches, large datasets, and comprehensive models. Many WEFN systems are globally pervasive and consequentially impact global economics and the environment. The second chapter of this dissertation uses computable general equilibrium approaches from economics to determine which biofuels feedstocks should be used and where to grow them to minimize land use change and greenhouse gas emissions. This work represents the first time computable general equilibrium models have been integrated directly into life cycle optimization to design sustainable production systems at a global scale. While this work focuses on biofuel impacts, the developed framework can be applied to any globally traded WEFN commodity. Sustainable WEFN systems must be designed that consider the objectives and needs of all affected stakeholders. The third chapter of this dissertation develops a multi-objective, bilevel modeling framework that models and optimizes multiple objectives of multiple stakeholders. A lower-level Pareto-optimal set generation method is proposed to handle multiple objectives in the lower level of the problem. The framework is applied to a discrete manufacturing system where a designer wishes to minimize greenhouse gas emissions from energy use while maximizing profits, and manufacturers bid to produce the product while maximizing the uptime of their equipment and minimizing their costs. While the framework was applied to a discrete manufacturing case, the framework and solution method remains general and may be applied to a variety of WEFN systems. Furthermore, manufacturing is an energy-intensive industry, and cannot be considered divorced from the WEFN. Ecosystems are often negatively impacted by WEFN systems, sometimes severely. However, these ecosystems provide valuable and essential services that enable and enhance local and regional life. The fourth chapter of this dissertation seeks to develop decision-making models that design WEFN systems to minimize loss of ecosystem services and/or maximize any synergistic benefits, using objectives that clearly and quantitatively show these losses and/or benefits. This chapter integrates work from ecological economics, spatial modeling with GIS, and mathematical programming to develop such models. Ecosystem services are given values through a variety of accounting and analysis methods. Losses and/or gains of these ecosystem services are calculated for a regional bioenergy production system and optimized through a Green GDP objective, which considers not only nominal GDP but also aggregates ecosystem value.

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