Entropy and Energy: Toward a Definition of Physical Sustainability
Sustainable development is a growing concern expressed by many businesses, organizations and individuals. Yet, no workable quantifiable definition of sustainability is available for evaluation of specific projects or operations. This paper attempts to set a framework for such a definition in terms of the first and second law of thermodynamics. Specifically, the proposed description of sustainability relates the fundamental processes of chemical, physical or biological transformation, and mass transport to energy and entropy changes. Unlike previous applications of these concepts, the proposed definition is focused on the smallest unit operations and processes while allowing for aggregation into larger systems. The proposed description also explicitly considers the time horizon for sustainability. An example of sustainability analysis for a water treatment process is included.