A Systems-level Framework for Understanding Sustainability and Resilience of the U.S. Food-Energy-Water Nexus

Global population growth, environmental change, and increasing urbanization are pressurizing already constrained resources such as food, energy, and water. Food, energy, and water systems are interconnected in myriad ways and require an integrated management approach (referred to as the FEW nexus) to avoid unintended consequences. This work focused on irrigation and phosphorus fertilizer as critical avenues to understand interdependencies between FEW systems in the United States (U.S.). Specifically, we focused on modeling and analyzing FEW systems through the lens of domestic food trade. Food trade networks represent pathways for displacing vast quantities of embodied environmental impacts associated with agriculture production. Therefore, quantifying the origin and destination of food flows and associated environmental impacts is central for understanding the sustainability and resiliency of the FEW nexus. Combining food trade data with information on water use, fertilizer application, irrigation energy expenses, and life cycle assessment methods, this work quantified embodied phosphorus fertilizer, irrigation water, energy, and greenhouse gas (GHG) emissions associated with food trade. Through a network theory approach, this work further characterized the network structure and its implications for the sustainability and resilience of the FEW systems. Finally, an optimization model was developed to assess the feasibility of rewiring the food trade network for enhancing the environmental sustainability of FEW systems. Results showed that the GHG emissions associated with irrigation are similar to emissions from the US cement industry. For food trade networks, proximity to a trading partner is an important factor driving the trade with neighboring states trading more, but it could be a potential risk if these states depend on the same water source for agriculture. The findings of this work also highlight the challenges in restructuring trade to avoid tradeoffs between water and energy use. The results of the interstate phosphorus trade model revealed phosphorus fertilizer use savings with states using phosphorus fertilizer efficiently exporting to less efficient states. Finally, this work discussed challenges and opportunities in improving our current understanding of resource use in the U.S. agriculture

Technoeconomic analysis for biofuels and bioproducts.

Technoeconomic analysis (TEA) is an approach for conducting process design and simulation, informed by empirical data, to estimate capital costs, operating costs, mass balances, and energy balances for a commercial scale biorefinery. TEA serves as a useful method to screen potential research priorities, identify cost bottlenecks at the earliest stages of research, and provide the mass and energy data needed to conduct life-cycle environmental assessments. Recent studies have produced new tools and methods to enable faster iteration on potential designs, more robust uncertainty analysis, and greater accessibility through the use of open-source platforms. There is also a trend toward more expansive system boundaries to incorporate the impact of policy incentives, use-phase performance differences, and potential impacts on global market supply

Design of Sustainable Biofuel Processes and Supply Chains: Challenges and Opportunities

The current methodological approach for developing sustainable biofuel processes and supply chains is flawed. Life cycle principles are often retrospectively incorporated in the design phase resulting in incremental environmental improvement rather than selection of fuel pathways that minimize environmental impacts across the life cycle. Further, designing sustainable biofuel supply chains requires joint consideration of economic, environmental, and social factors that span multiple spatial and temporal scales. However, traditional life cycle assessment (LCA) ignores economic aspects and the role of ecological goods and services in supply chains, and hence is limited in its ability for guiding decision-making among alternatives—often resulting in sub-optimal solutions. Simultaneously incorporating economic and environment objectives in the design and optimization of emerging biofuel supply chains requires a radical new paradigm. This work discusses key research opportunities and challenges in the design of emerging biofuel supply chains and provides a high-level overview of the current “state of the art” in environmental sustainability assessment of biofuel production. Additionally, a bibliometric analysis of over 20,000 biofuel research articles from 2000-to-present is performed to identify active topical areas of research in the biofuel literature, quantify the relative strength of connections between various biofuels research domains, and determine any potential research gaps

Food–Energy–Water Nexus: Quantifying Embodied Energy and GHG Emissions from Irrigation through Virtual Water Transfers in Food Trade

We present a network model of interstate food trade and report comprehensive estimates of embodied irrigation energy and greenhouse gas (GHG) emissions in virtual water trade for the United States (U.S.). We consider trade of 29 food commodities including 14 grains and livestock products between 51 states. A total of 643 million tons of food with a corresponding 322 billion m³ of virtual water, 584 billion MJ of embodied irrigation energy, and 42 billion kg CO₂-equivalent GHG emissions were traded across the U.S. in 2012. The estimated embodied GHG emissions in irrigation water are similar to CO₂ emissions from the U.S. cement industry, highlighting the importance of reducing environmental impacts of irrigation. While animal-based commodities represented 12% of food trade, they accounted for 38% of the embodied energy and GHG emissions from virtual irrigation water transfers due to the high irrigation embodied energy and emissions intensity of animal-based products. From a network perspective, the food trade network is a robust, well-connected network with the majority of states participating in food trade. When the magnitude of embodied energy and GHG emissions associated with virtual water are considered, a few key states emerge controlling high throughput in the network

Paths to circularity for plastics in the United States

In 2019, the United States consumed over 57 million metric tons (MMT) of plastic with less than 7% recovered for reuse. This study provides an updated material flow analysis at national and regional scales for all durable and single-use plastics in the United States. From this material flow analysis, we develop a series of alternative future national plastic flow scenarios that envision a scale-up of recycling technologies, incorporating technical limitations and sorting infrastructure constraints. The results suggest that a maximum of 68% (24 MMT) of plastic waste could be diverted from landfills by scaling up existing commercial recycling technologies. Based on the current technological landscape, reaching near-zero waste is only possible if processes that are operating at pilot and laboratory scales can be effectively scaled and coupled with improved sorting infrastructure. Through these scenarios with increased recycling, the availability of postconsumer resin stocks could increase by 22–43 MMT

Leveling the cost and carbon footprint of circular polymers that are chemically recycled to monomer.

Mechanical recycling of polymers downgrades them such that they are unusable after a few cycles. Alternatively, chemical recycling to monomer offers a means to recover the embodied chemical feedstocks for remanufacturing. However, only a limited number of commodity polymers may be chemically recycled, and the processes remain resource intensive. We use systems analysis to quantify the costs and life-cycle carbon footprints of virgin and chemically recycled polydiketoenamines (PDKs), next-generation polymers that depolymerize under ambient conditions in strong acid. The cost of producing virgin PDK resin using unoptimized processes is ~30-fold higher than recycling them, and the cost of recycled PDK resin ($1.5 kg-1) is on par with PET and HDPE, and below that of polyurethanes. Virgin resin production is carbon intensive (86 kg CO2e kg-1), while chemical recycling emits only 2 kg CO2e kg-1 This cost and emissions disparity provides a strong incentive to recover and recycle future polymer waste