Application of novel continuous foam collection methods for removal of PFAS from cascade generated foam at wastewater treatment plants

Abstract

Three foam collection methods – passive overflow, mesh skimmer, and mesh-belt skimmer – were iteratively designed and evaluated for continuous collection of foam forming at a wastewater treatment plant (WWTP) cascade for removal of per- and polyfluorinated alkyl substances (PFAS). Surface tension, PFAS concentrations, and foamate collection rates were measured to assess their performance. Foam collection using a novel mesh skimmer and mesh-belt skimmer increased PFAS enrichment over that of the in situ foam, as the mesh facilitated drainage of PFAS-depleted liquid during collection. Enhanced enrichment and scalable foam collection with the mesh-belt skimmer may remove and concentrate most long-chain PFAS (>90 %) in under 270,000 L/d of foamate or 0.26 % of the wastewater volume when scaled up. For comparison, an estimated 900,000 L/d of foamate would need to be collected with the passive overflow method to achieve 90 % PFOS removal, but would only capture 20 % PFOA and 22 % PFHxS. Limiting the volume of final collected foamate is critical as it requires additional treatment, which can be cost prohibitive at large volumes. While a pilot scale study is required to accurately assess removal, the advantages provided by the mesh-belt skimmer suggest feasible foam collection for PFAS removal at the full WWTP scale.