Process algorithms are used to calculate the mass and energy flows throughout the system during the operation and maintenance stage. These flows can be used to gauge the performance of the technology (e.g., calculating contaminant removal) and to determine the relevant inventory items required for sustainability characterization (e.g., raw chemicals consumed, generated products and wastes, electricity consumption, and fugitive emissions such as CH4, CO2, and N2O). Like design algorithms, the complexity of process algorithms can vary widely: from assumed performance based on theoretical values to calibrated and validated mechanistic models. Given the importance of algorithm selection in QSD, more nuanced guidance is provided in Section 3.2 (below).