The selection of an appropriate functional unit (FU) is a critical yet often overlooked aspect in the life cycle assessment (LCA) of activated carbon (AC) systems. Existing studies commonly rely on product-based FUs, such as impacts per kg of AC produced, or waste intake-based FUs, such as impacts per kg of precursor or waste feedstock processed. While useful for evaluating production efficiency or waste management performance, these FUs do not fully capture the functional role of AC in pollutan