The role of suspended biomass in PFAS enrichment in wastewater treatment foams.

Foaming in aerated bioreactors at wastewater treatment plants (WWTPs) has been identified as an operational issue for decades. However, the affinity of per- and polyfluoroalkyl substances (PFAS) for air-liquid interfaces suggests that foam harvesting has the potential to become a sustainable method for PFAS removal from sewage. Aerated bioreactors' foams are considered three-phase systems, comprising air, aqueous and solid components, the latter consisting of activated sludge biomass. To achieve a comprehensive understanding of the capability of aerated bioreactors' foams to enrich PFAS, we analysed PFAS concentrations from WWTPs in both the solid and aqueous phases of the collapsed foams (foamate) and underlying bulk mixed liquors. Our findings show that PFAS enrichment occurs not only in the aqueous phase but also in the solid phase of the foamate. This suggests that previous field studies that only analysed the aqueous phase may have underestimated the capability of the aerated bioreactors' foams to enrich PFAS. Fractions of PFOA and PFOS sorbed to the solid phase of the foamate can be as high as 60 % and 95 %, respectively. Our findings highlight the importance of implementing effective foamate management strategies that consider both the aqueous and solid phases.

A review of foam fractionation for the removal of per- and polyfluoroalkyl substances (PFAS) from aqueous matrices.

The detection of per- and polyfluoroalkyl substances (PFAS) in aqueous matrices is an emerging environmental concern due to their persistent, bioaccumulative and toxic properties. Foam fractionation has emerged as a viable method for removing and concentrating PFAS from aqueous matrices. The method exploits the surface-active nature of the PFAS to adsorb at the air-liquid interfaces of rising air bubbles, resulting in foam formation at the top of a foam fractionator. The removal of PFAS is then achieved through foam harvesting. Foam fractionation has gained increasing attention owing to its inherent advantages, including simplicity and low operational costs. The coupling of foam fractionation with destructive technologies could potentially serve as a comprehensive treatment train for future PFAS management in aqueous matrices. The PFAS-enriched foam, which has a smaller volume, can be directed to subsequent destructive treatment technologies. In this review, we delve into previous experiences with foam fractionation for PFAS removal from various aqueous matrices and critically analyse their key findings. Then, the recent industry advancements and commercial projects that utilise this technology are identified. Finally, future research needs are suggested based on the current challenges.

Influence of static mixer on the development of aerobic granules for the treatment of low-medium strength domestic wastewater.

The present work investigates the feasibility of aerobic granulation for the treatment of low-medium strength domestic wastewater for long-term operation and effects of a static mixer on the properties and removal performances of the aerobic granules formed. The static mixer was installed in a sequential batch reactor to provide higher hydrodynamic shear force in enhancing the formation of the aerobic granules. Aerobic granules were successfully formed in the domestic wastewater, and the granulation treatment system was sustained for a period of 356 days without granules disintegration. Subsequent to the installation, aerobic granules with a low SVI30 of 41.37 mL/gTSS, average diameter 1.11 mm, granular strength with integrity coefficient 10.4% and regular shape with minimum filamentous outgrowth were formed. Mineral concentrations such as Fe, Mg, Ca and Na as well as composition of protein and polysaccharide in tightly bound-extracellular polymeric substance of the aerobic granules were found to be higher under the effect of the static mixer. However, no significant improvement was observed on the TCOD, NH4+-N and TSS removal performance. Good TCOD and TSS removal performance of above 85% and 90%, respectively and moderate NH4+-N removal performance of about 60% were observed throughout the study. Higher simultaneous nitrification and denitrification (SND) efficiency of 56% was observed after the installation of the static mixer, as compared to 21% prior. Therefore, it may be concluded that the installation of the static mixer significantly improved the properties of aerobic granules formation and SND efficiency but not the TCOD, NH4+-N and TSS removal performance.