Characterization of sustainability can be performed either within or outside the system simulation platform. For economic sustainability, capital and operating expenditures can often be extracted from the commercial simulators, and some of these simulators have functionalities for profitability and cash flow analyses. However, these built-in functionalities often have little or no support for users to adjust parameter values (e.g., equipment and chemical costs). Therefore, additional analyses are often conducted outside these simulators to explore an expanded QSD problem space (e.g., using spreadsheets ).