Towards sustainability of engineered processes: Designing self-reliant networks of technological–ecological systems

Sustainability of human activities is entirely dependent on the availability of ecosystem goods and services such as carbon sequestration, mineral and fossil resources, sunlight, biogeochemical cycles, soil formation, pollination, etc. However, existing methods in most disciplines, including sustainable engineering and industrial ecology ignore this crucial role played by nature. The use of such a narrow boundary can lead to misleading results and perverse decisions. This paper introduces the idea of designing networks of technological systems along with their supporting ecological systems. Such networks of technological and ecological systems exploit the synergy between them and can help in closing material loops and minimize exergy loss, leading to truly self-sustaining systems. Methods for designing such technological–ecological synergy (TES) networks could be developed by extending existing process synthesis and design approaches to include ecological models. Such an approach would integrate industrial ecology with ecological engineering and require collaboration between engineers and ecologists. It presents many new challenges and opportunities for process systems engineering to contribute to the sustainability of engineered systems. The idea of TES networks is illustrated via several practical case studies, with focus on the life cycle of corn ethanol and a typical American residential system.