The quest for sustainability: Challenges for process systems engineering

La new strategic significance to the term “sustainability.” No longer confined to the economic realm, sustainability now embraces a broad spectrum of company characteristics related to social and environmental responsibility. This shift in thinking (dare we say enlightenment?) is due to growing recognition among business executives that profitability alone is inadequate as a measure of success, and that many of the nonfinancial concerns associated with sustainability are fundamental drivers of long-term shareholder value. Conversely, failure to recognize these strategic issues threatens the very survival of a business enterprise. For example, mounting concerns over the ability to curb industrial emissions of CO2 and other global warming gases are only the tip of this proverbial iceberg. The original concept of “sustainable development” (SD), defined over 15 years ago by a U.N. commission, suggested pursuing development in a way that respects both human needs and global ecosystems, assuring quality of life for future generations (WCED, 1987). It was clear even then that current trends in population growth and economic development were not sustainable. Without dramatic changes in the patterns of human activity, there will be severe challenges to the continued growth of global industries. Examples of these challenges include (World Bank, 2001): • Adverse environmental impacts such as climate change; degradation of air, water, and land; depletion of natural resources, including fresh water and minerals; loss of agricultural land due to deforestation, soil erosion and urbanization; and threatened ecosystems. • Adverse socio-economic impacts such as widespread poverty, lack of potable water, proliferation of infectious diseases, social disintegration resulting from displacement of traditional lifestyles, growing income gaps, and lack of primary education. Rather than ignoring these ominous signals, a number of visionary business leaders have risen to the challenge and developed a new model of industrial progress that marries economic growth with social and environmental responsibility (Holliday et al, 2002). Many corporations are beginning to partner with governments and nongovernmental organizations to seek sustainable solutions that preserve their freedom to operate. Pragmatically speaking, such voluntary initiatives are certainly preferable to resistance or indifference, which would invite an increasingly onerous regulatory regime that limits industrial growth through economic or technological constraints. Responding to the challenges of sustainability requires insight into the characteristics of a sustainable system, and a fundamental rethinking of how all industrial products and processes are designed, built, operated, and evaluated. Qualitative definitions of sustainability such as that given by the U.N. are not particularly helpful for engineering decision-making. The following definition is more useful: A sustainable product or process is one that constrains resource consumption and waste generation to an acceptable level, makes a positive contribution to the satisfaction of human needs, and provides enduring economic value to the business enterprise. The determination of an “acceptable level” represents a technical challenge, but it is common to assert that resource utilization should not deplete existing capital, that is, resources should not be used at a rate faster than the rate of replenishment, and that waste generation should not exceed the carrying capacity of the surrounding ecosystem (Robèrt, 1997). Since sustainability is a property of the entire system, and not of an individual subsystem, incorporating sustainability into engineering requires the boundaries of “the process” to be greatly expanded—beyond the plant and even beyond the corporation. As shown in Figure 1, the analysis boundaries might extend to the economy and the ecosystem. Moreover, the scope of analysis needs to be expanded beyond cost and performance issues to include environmental integrity and socio-economic well being. Life cycle assessment (LCA), now an ISO-standardized methodology, is an important example of the effort to expand the traditional process boundary. LCA considers both the upstream and downstream processes associated with a given product in terms of energy use, material use, waste generation, and business value creation (Consoli et al., 1993). The life cycle stages, shown in Figure 1, may include resource extraction, procurement, transportation, manufacturing, product use, service, and end-of-life disposition or recovery. The feedback loop indicates the importance of recycling, reuse, and reverse logistics. Careful consideration of life cycle implications can sometimes yield surprising results. For example, efforts to develop “green” plastics, such as polylactides, seem appealing because the feedstocks are renewable and the plastics are The Quest for Sustainability: Challenges for Process Systems Engineering