Laboratory and Semi-Pilot Scale Study on the Electrochemical Treatment of Perfluoroalkyl Acids from Ion Exchange Still Bottoms

Vanessa Y Maldonado,Suzanne E Witt,Michael G Nickelsen,Michael F Becker

doi:10.3390/w13202873

Abstract

The ubiquitous presence of perfluoroalkyl acids (PFAAs) in the environment remains a serious environmental concern. In this study, the electrochemical oxidation (EO) of PFAAs from the waste of ion exchange (IX) still bottoms was assessed at the laboratory and semi-pilot scales, using full boron-doped diamond (BDD) electrochemical cells. Multiple current densities were evaluated at the laboratory scale and the optimum current density was used at the semi-pilot scale. The results at the laboratory scale showed >99% removal of total PFAAs with 50 mA/cm2 after 8 h of treatment. PFAAs treatment at the semi-pilot scale showed 0.8-fold slower pseudo-first-order degradation kinetics for total PFAAs removal compared to at the laboratory scale, and allowed for >94% PFAAs removal. Defluorination values, perchlorate (ClO4−) generation, coulombic efficiency (CE), and energy consumption were also assessed for both scales. Overall, the results of this study highlight the benefits of a tandem concentration/destruction (IX/EO) treatment approach and implications for the scalability of EO to treat high concentrations of PFAAs.

Highlights

Even assuming equivalent concentrations of ClO3− generated, the percentage of chlorinated byproducts remains low when compared to the initial concentrations of Cl−. These results suggest that additional species present in the solution may be competing for direct anodic oxidation or scavenging Cl− oxidation
The results suggest that ClO4− generation with boron-doped diamond (BDD) electrodes solely depends on the applied current density, regardless of factors associated to scale performance differences
This work focused on the evaluation of the electrochemical treatment of perfluoroalkyl acids (PFAAs) from still bottoms at the laboratory and semi-pilot scales

Summary

Introduction

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The persistent nature, toxicity and bio-accumulation potential of per-and polyfluoroalkyl substances (PFAS) led to their classification as emerging contaminants [1,2]. Multiple treatment technologies have been developed to remove PFAS from water [3,4,5]. Separation technologies including granular activated carbon (GAC), ion exchange (IX), reverse osmosis (RO), and nanofiltration (NF) have shown high levels of PFAS removal in water [5,6,7,8]. IX was shown to be effective for removing long- and short-chain PFAS and has demonstrated higher sorption capacities and shorter contact times than GAC [3,6,9]

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