Using nature as a model, industrial ecology views the industrial plant or system as an integrated set of cyclical processes in which the consumption of energy and materials is optimized, waste generation is minimized, and wastes from one process serve as feedstock for other production processes. Industrial ecology views industrial production as a “metabolic” process. It attempts to close the “open materials cycle” characteristic of industrial society, whereby materials and energy are lost to economic use, and harmful toxic substances are released to the environment. Industrial ecology tries to “close the loop” in two ways: (1) by eliminating waste from production processes, and (2) by redesigning wastes as useful by-products that can be used in other processes.