Formatted Title
The Energy Cost of PFAS Destruction across the Range of Commercially-Available Technologies
Background/Objectives
The current state of the practice for addressing liquids impacted with per- and polyfluoroalkyl substances (PFAS) is multiple treatment technologies in series with the objective of concentrating a minimal volume in preparation of energy-intensive destruction. Considerable progress within research and development has yielded multiple technologies capable of either concentrating or destroying PFAS. The energy required to destroy PFAS can be a critical performance indicator of the practical relevance of a given technology. Unfortunately, the comparison of the energy requirement for PFAS destruction is not standardized across the available options despite being presented in similar units (i.e., energy per unit volume [1s to 100s of kWhr-m3]). The purpose of this work is to present a standardized comparison of the energy requirements of some PFAS-relevant destruction technologies by considering the mass of PFAS destroyed in matrices that are representative of those subject to destructive treatment. The technologies we selected for this comparison include electrochemical oxidation, nonthermal plasma, ultra-violet radiated sensitizers, and hydrothermal.
Approach/Activities
To complete the comparison of the energy requirements of PFAS-relevant destruction technologies, the electrical energy per order (EE/O) magnitude equation is used. In addition, the treated volume, the matrix, the PFAS concentration change, and the generation of fluoride are considered to compare the EE/O to the energy per mass of PFAS destroyed. Technology-associated current densities and residence times were obtained from relevant literature searches and/or input from technology vendors. To the extent practicable, the energy requirements are separated into groups of PFAS (e.g., perfluoroalkyl carboxylic acids, perfluoroalkyl sulfonic acids, perfluoroalkyl ether carboxylic acids, etc.) and specific to fluorine saturated carbon chains. Where information is available for polyfluoroalkyl compounds, it is included but it is recognized that the diversity and continued discovery of polyfluoroalkyl compounds inhibits the ability to complete a comprehensive comparison of energy requirements. Energy requirements are also grouped by water type (e.g., landfill leachate, membrane rejectate, ion exchange regenerant solution, and foam fractionate).
Results/Lessons Learned
An energy requirement comparison of power per volume (i.e., EE/O) is useful; however, it is inherently limited because EE/O varies considerably depending on the concentration and matrix type treated. Therefore, it is prudent to distinguish the energy comparison of these technologies by incorporating the mass of PFAS destroyed into the energy expended in typical aqueous waste concentrates. This work is intended to offer a more practical energy comparison for PFAS-relevant destruction technologies by expressing previously reported EE/O requirements as energy per mass of PFAS destroyed requirements to account for energy inefficiencies at lower order of magnitude changes. Expressing the energy consumption in matrices that are relevant to destruction enables accounting for the competitive effects of co-occurring constituents on process efficiency.