The concept of sustainability became a tour de force when the claim was made that society was becoming progressively worse off because anthropogenic economic endeavors at various scales have been creating harmful environmental and human health impacts. At the time the idea of sustainable development emerged, environmental regulations were already at work reining in industrial emissions and discharges that were unethical, harmful, wasteful, and possibly illegal as well. The sustainability movement called for governmental policies worldwide to regulate emissions of harmful chemicals and biological agents to air, water and land from all commercial and manufacturing activities while also achieving certain societal goals. Environmental and ecological economists were the first to examine the measurement of sustainability from a macro level. Engineering approaches to measuring sustainability arose from attempts to measure environmental and human health impacts while also assessing resource use efficiency of energy, material, and water. It has since been evolving into a system of measurement that also considers societal wellbeing, although not very successfully yet.
All engineering attempts to measure sustainability were relative among comparable products and processes, or for the same product or process over time. This is true because absolute sustainability does not exist, and the vast majority of technologies, even those that appear stunningly original, are but incremental improvements over technologies that already exist. Measurement began by identifying indicators of the most important factors that determine the success of a technology. For chemical processes, energy use, material use, water use, pollution generation and its toxicity to human health, and greenhouse gas emissions, all normalized by a unit of product, became those important factors to measure for comparison. In the past several years, however, a strong tendency appears to put heavier emphasis on the greenhouse gas emissions, even though from a health impact viewpoint these emissions are inconsequential. The indicator values collected for comparable processes or products can be presented in tabular form and inferences of comparative sustainability can be made by either heuristics or by statistical aggregation into a single index for comparison. This presentation will provide a state of the art look at what has been done in this area. However, these evaluations are always after the fact. A preferable way to approach would be to incorporate sustainability assessment in simulation and optimization based design tools, i.e. for purposive design for sustainability.
A popular way to view engineering sustainability is by a Venn diagram in which three intersecting circles, each circle representing one of the three domains of sustainability: environmental, economic, and societal. Conceptually, sustainability happens at the intersection of the three circles. The goal is to minimize environmental impact, economic impact, and societal impact. Since human health impacts and ecological health impacts belong in environmental and societal domains, perhaps a case can be made that the three domains are better identified with environmental (pollution emissions, resource use, GHG emissions), health (human toxicity as well as ecological toxicity), and economic cost. Process simulators can track all three as various process options are considered for optimality. The indicators for the environmental and health domains can be aggregated to a sustainability index, also called footprint, which would be a function of cost. The optimization problem thus reduces to finding the sustainability footprint at the minimum cost. This consideration will also be elaborated in this presentation.