Granular Activated Carbon versus Ion Exchange: A Decision Space for Navigating Economic and Environmental Tradeoffs during Water Treatment Technology Selection

Abstract Selecting between granular activated carbon (GAC) and ion exchange (IX) to remove hazardous contaminants from water is a critical but complex decision, since GAC and IX have different removal mechanisms, reactor designs, and operating specifications. Previous studies have either not comprehensively integrated economic and environmental analyses or have evaluated only a limited treatment performance range. This study characterized the economic and environmental decision space for GAC and IX over a large range of treatment performance scenarios to represent a wide range of utilities. Life cycle costing and life cycle assessment were employed to calculate the economic cost and global warming impact of each technology for 15,000 treatment performance scenarios, where each scenario represented a different functional unit with a unique treatment objective and influent water quality. There was an approximately linear economic threshold curve that designated if a scenario would have a lower cost with GAC or IX, and the curve was highly sensitive to engineering decisions (e.g., spent media management strategy) and uncertainty assumptions (e.g., fresh media price). An environmental threshold curve revealed which engineering decisions may have a lower global warming impact. Additionally, there were many scenarios where GAC had economic benefits but environmental disadvantages compared with IX. This GAC-IX decision space will enable utilities to calculate breakeven values and evaluate risks associated with technology selection. By integrating performance data with the economic and environmental data generated from this study, utilities can navigate tradeoffs to make defensible, site-specific decisions.