Sustainability News & Research

A Process Model for Sustainability

Several models have been developed to measure sustainability; most, however, are based only on the first law of thermodynamics and are therefore rough and incomplete. The rate of a sustainable process is maintained over time without exceeding the innate ability of the environment to support the process.

Michael Neuman of Texas A&M University (College Station) and Stuart W. Churchill of the University of Pennsylvania (Philadelphia) devised a model for measuring process sustainability that integrates the first and second laws of thermodynamics and the concept of rate processes to form a new synthesis (Ind. Eng. Chem. Res. DOI: 10.1021/ie1020156, Jan. 18, 2011). The degree of sustainability of a process (ecological, economic, social, chemical, or biological) is expressed quantitatively in terms of algebraic equations. It is a dynamic approach that applies at any scale and takes into consideration the spatial and temporal factors of processes. It therefore permits empirical applications that correspond to real-world conditions, that is, conditions that are dynamic, complex, and evolving. These characteristics make it especially suitable for applications in chemistry, chemical engineering, and ecology.

The authors give equations to illustrate the rate process model. The one shown represents a process carried out by continuous flow through a tube.

The authors also present a list of the characteristics of a rate process model of sustainability. The model

  • makes it possible to calculate the degree to which a process can be sustained over the long term by using the theories and methods of thermodynamics and rate processes;
  • allows a comprehensive consideration of the relevant factors that impinge upon sustainability: economic, ecological, technological, and social;
  • makes it easier to determine where in geographic space to draw the system boundary lines in the calculation of the degree of long-term sustainability;
  • allows a quantitative comparison of several processes to determine their relative degrees of sustainability and thereby direct technology and policy choices; and
  • combines long-term sustainability with short-term efficiency in the cost–benefit calculus of choosing processes, technologies, and materials.

The authors conclude by stating that their “theory of sustainability reflects a new manifestation of human will that does not merely shape and subjugate nature and ourselves along with it. Instead, sustainability embodies the will to work with nature [by] respecting it and adhering to its capacities and limitations while still realizing our own hopes and dreams.”