Energy Accounting for PFAS Treatment: Endpoint Definition, Concentration Dependence, and the Service-Equivalence Constraint

Energy performance in per- and polyfluoroalkyl substance (PFAS) treatment is often reported on a volumetric basis, in kilowatt-hours per cubic metre of water processed. Volumetric energy is necessary for hydraulic design and utility sizing, but it is insufficient by itself for cross-study comparison because it does not reference the quantity of contaminant addressed. This paper develops the mass-normalised complement and, more importantly, establishes the conditions under which either metric may be used comparatively. Three results are presented. First, a taxonomy separating five distinct endpoints — transfer, removal, degradation, defluorination, and mineralisation — that are not interchangeable, and a corresponding pair of mass-normalised metrics whose denominators are defined by measurement rather than assumption. Second, a generalised break-even condition governing whether an upstream concentration step reduces the energy required per unit mass meeting a specified endpoint. The condition reduces to a simpler form only under an explicit assumption of process identity. Third, a service-equivalence gate requiring a two-stage architecture to deliver at least a declared fraction of influent mass to the specified endpoint before its energy result is compared with another architecture serving the same duty. A train recovering 50% of influent target mass and achieving 90% endpoint efficiency on that recovered fraction delivers 45% of influent mass to the endpoint, irrespective of how favourable its energy per gram may appear. The paper concludes with a minimum reporting standard. Its purpose is not to rank technologies, recommend equipment, or estimate plant cost, none of which the framework supports. Its purpose is to make published energy figures comparable, and to make the concentration dependence of treatment cost explicit where it is currently implicit. Published under The Prior Art Project. This preprint discloses a measurement and comparison framework — endpoint taxonomy, mass-normalised metrics, two-stage energy balance, service-equivalence gate, and reporting standard. It does not disclose a specific PFAS treatment reactor and does not establish freedom to operate for any underlying treatment technology. No patent application has been filed covering the subject matter of this paper and the author does not intend to seek patent protection for it. Not peer reviewed; independent technical review by a specialist in PFAS treatment is sought.