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Meeting human needs while addressing and adapting to challenges posed by environmental change, resource depletion, and ecological deterioration is among the grand challenges facing humanity today. Engineering has an important role in addressing this challenge, but for technological solutions to be truly effective, they should not cause unintended harm, and they should not demand more from ecosystems than can be supplied. Unintended harm may be caused due to the shifting of environmental impacts across boundaries of space, time, disciplines, or types of flows. For example, electric cars may shift emissions from the automotive tailpipe to the industrial smokestack, and more efficient light bulbs could increase overall energy use because as cost per lumen decreases, economics tells us that its demand will increase. In addition, all industrial activities rely on goods and services from ecosystems such as water, minerals, photosynthesis, and air quality regulation. If the demand for such goods and services exceeds nature's ability to supply them, it results in resource scarcities and ecological degradation.

Our research is developing new understanding, methods, tools and techniques to address such challenges to develop a Sustainable Engineering. Such work relies on the foundation of systems engineering and connects with disciplines beyond engineering such as ecology, environmental economics, public policy, applied statistics, and operations research. It also requires methods to consider the broad implications of technologies on society and ecosystems, and of environmental change and regulations on industrial activities. Insight and results of such work are of significant interest to businesses, governments, non-governmental organizations, and consumers.

Some areas of on-going research include the following.

Techno-Ecological Synergy. Like all human activities, industrial activities also depend on the availability of goods and services from nature. However, engineering decisions usually ignore nature or take it for granted. Systems designed with such ignorance tend to demand more from nature than can be supplied making them inherently unsustainable. The framework of techno-ecological synergy encourages development of mutually beneficial harmony between technological and ecological systems.  It encourages enhancement of technological efficiency along with restoration and protection of ecosystems.  At the scale of individual manufacturing processes, this approach incorporates ecosystems in engineering design in a manner analogous to unit operations. At larger scales such as the life cycle, ecosystems are considered at regional scales. Applications demonstrate the ability of this approach to develop innovative designs that are economically and environmentally superior than designs from conventional techno-centric methods.

Process to Planet Framework. Reducing the chance of unintended harm by shifting impacts outside the selected boundary requires integration of models from small to large scales. The process to planet framework 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. The process to planet and techno-ecological synergy frameworks are being used together to solve problems ranging from process design, supply chain optimization, and landscape design of agricultural and industrial sites.

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. The Eco-LCA software based on this work is also available.

Statistical methods for 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.

Applications. Due to the multidisciplinary nature of our research, our methods are applied to a large variety of products and systems. We have conducted life cycle studies of transportation fuels, polymer nanocomposites, ionic liquids, and bio-based materials. Such studies account for the direct and indirect role of ecosystems, and consider ecological solutions such as the use of wetlands for treating agricultural runoff, and obtaining biomass from native grasslands. Frameworks of techno-ecological synergy and process to planet are being used to select the best pathway for biorefinery design and chemical process design.  Other applications include assessment and design of buildings and urban regions, and of policies such as carbon taxes.