link. To address this challenge, engineering solutions should not cause unintended harm, and they should not demand more from ecosystems than can be supplied. Developing such solutions requires research that not only cuts across disciplinary boundaries, but encourages the convergence of multiple disciplines into the emerging field of Sustainable Engineering. Our overall approach toward such convergence is illustrated in Figure 1, which shows how engineering needs to connect with other disciplines such as economics, sociology and ecology to develop technologies that help societal transformation toward sustainable development. Some areas of on-going and previous research include the following.Our research is motivated by the following grand challenge: how do we meet human needs while addressing and adapting to challenges posed by societal change, resource depletion, and ecological deterioration. More details about this motivation and the need for Sustainable Engineering are at this
Sustainability and Innovation by Seeking Synergies with Nature. All human activities are sustained due to the availability of goods and services from nature. However, most disciplines, including engineering ignore the role of nature or take it for granted. Designs based on such ignorance invariably exceed nature's carrying capacity, making them inherently unsustainable. We are developing the framework of techno-ecological synergy (TES) to encourage mutually beneficial harmony between technological and ecological systems, as illustrated in Figure 2. This framework encourages enhancement of technological efficiency along with restoration and protection of ecosystems. We are developing this framework for use at multiple scales: from an individual process, to a life cycle, to national and global systems.
- Process Design with Ecosystems as Unit Operations. At the scale of individual manufacturing processes, the TES approach incorporates ecosystems in engineering design in a manner analogous to unit operations. We have shown that such TES designs can provide novel solutions that are economically and environmentally superior to designs obtained from conventional, technology-only methods. Our applications include chemical processes, agricultural land use, urban biosolids management, watershed management, and industrial site design.
- Sustainability Analysis by Including Ecosystem Services in Life Cycle Assessment. We have developed a new framework for Techno-Ecological Synergy in LCA (TES-LCA). This framework quantifies the demand on nature imposed by human activities, and the capacity of ecosystems to meet this demand. It results in metrics for absolute sustainability that are calculated at multiple spatial scales.
This framework encourages not just technological improvements to reduce environmental impact, but also encourages restoration and protection of ecosystems to enhance their capacity to supply needed goods and services. On-going work is addressing differences in the spatio-temporal characteristics of technological and ecological systems. Technological systems are designed to be predictable and operate around a set point, while ecosystems are intermittent and unpredictable. We are also working toward accounting for all ecosystem services and developing tools for TES design and TES-LCA.
Multiscale Sustainable Engineering. This framework enables the systematic integration of models at the scales of individual equipment, manufacturing processes, life cycles, and the economy. As shown in Figure 2, this Process to Planet (P2P) multiscale modeling framework combines the benefits of engineering models (equipment scale) with models developed for LCA (value chain scale) and the economy (economy scale). It enables integration of nonlinear and fundamental models of engineering systems with linear and empirical models of the life cycle and economy. The resulting model can be used to design processes and supply chains while accounting for their life cycle environmental impact. It can also be used to determine the effect of macro-economic changes such as a carbon tax on individual processes. We are also developing ways of using the P2P and TES frameworks together to solve problems ranging from process design, supply chain optimization, and landscape design of agricultural and industrial sites.
Design for a Sustainable and Circular Economy. Many efforts toward sustainability aim to mimic the closed biogeochemical cycles of nature. The idea is that nature is sustainable because waste from one species is food for another. This is due to biotic (e.g. food web) and abiotic (e.g. carbon cycle) cycles in nature. The concept of a circular economy aims to mimic such cycles for technological products. Thus, in a circular economy, materials are retained in the economy for as long as possible so that the net input from nature is reduced, as is environmental impact. This is depicted in Figure 1 by the brown loop that goes back to technological systems. We have developed a computational framework for analyzing and designing sustainable and circular systems. Our current focus is on developing a circular economy of plastics.
Advances in Life Cycle Assessment. Given the popularity of LCA in industry and government, we continue to work on improving the theoretical foundation of this approach and addressing its practical challenges.
- Uncertainty in LCA. This work is addressing challenges posed by uncertain and incomplete data and models in life cycle assessment. We are working toward a statistically rigorous framework for combining data and models at multiple scales, and diverse sources of uncertain data. We have developed a novel approach for improving the quality of life cycle inventory data by imposing the laws of conservation on the data along with knowledge about their uncertainty. We are also developing new insight into the effect of methods for partitioning resource use and emissions among multiple products, and new ways of developing streamlined LCA models.
- Ecologically-Based Life Cycle Assessment. This method for sustainability assessment accounts for the role of ecosystem goods and services in supporting human activities. This has resulted in an integrated model of the United States economy and its direct and indirect dependence on ecosystem goods such as water, biomass, minerals, services such as carbon sequestration, and emissions such as reactive nitrogen and carbon dioxide. A similar model focusing on water has also been developed for the Indian economy. Thermodynamic methods are used for aggregating diverse material and energy flows and defining metrics for supporting decisions. These methods rely on the fact that both ecological and industrial systems are governed by the same laws and the flow of available energy (exergy) is a common currency for their integrated evaluation. Software for Eco-LCA was developed but is not available any more since the data have not been updated.
Applications. Due to the multidisciplinary nature of our research, our methods are applied to a large variety of products and systems such as the following.
- Design of chemical and manufacturing systems. This includes design of processes, supply chains, and entire life cycles. Applications include process design for net-positive impact manufacturing, corn ethanol supply chain design for net-zero contribution to harmful algal blooms, design of agricultural landscapes for sustainable bioenergy production.
- Sustainability assessment of emerging technologies. Assessing the sustainability at early stages of technology development is important for guiding future work. Our work has analyzed transportation fuels, polymer nanocomposites, ionic liquids, metal-organic frameworks, artificial photosynthesis, urban and conventional farming systems, etc.
- Assessment and design for carbon neutrality. Many corporations, universities and countries are aiming to achieve carbon neutrality in the near future. We have developed methods and tools for solving this problem, and are applying them to university campuses.
- Food-energy-water nexus. A trade-off often exists between food, energy and water. We have analyzed and designed watersheds and agricultural systems while accounting for this nexus.
Methods and Tools. Our research is computational and theoretical in nature. We use advanced computational methods such as mathematical programming, machine learning, and various statistical methods. We also used modeling tools and software packages such as ChemCAD, Aspen, EPIC, SWAT, ArcGIS, i-Tree, FVS, CALPUFF, OpenLCA, etc. Most projects involve some programming in languages such as R, Julia, GAMS, Matlab, and Python.
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