Competitive adsorption of surfactant–protein mixtures in a continuous stripping mode foam fractionation column

PFAS distribution in cascade derived foam at wastewater treatment plants: The role of non-linear drainage, collapse induced enrichment, and implications for removal

Per- and polyfluorinated alkyl substances (PFAS) enrichment in foam was investigated for the first time at a wastewater treatment plant cascade. A novel sampling device was utilized to allow spatial and temporal heterogeneity in PFAS concentrations and liquid content to be characterized. Concentrations of 8 PFAS compounds were normalized to liquid content and fit to a power law model revealing strong correlation (R2 = 0.91) between drainage induced enrichment and PFAS molar volume. Short chain PFAS such as perfluorobutanoate (PFBA) exhibited minor to no enrichment factors in foam (0.24-5.9) compared to effluent concentrations across the range of foam liquid contents (0.28-6.24 %), while long chain compounds such as perfluorooctane sulfonate (PFOS) became highly enriched with factors of 295-143,000. A conceptual model is proposed to explain higher than expected enrichment of more surface-active PFAS relative to liquid content, which combines continuous partitioning of PFAS to air bubbles during foam formation with additional partitioning during non-linear drainage and foam collapse, both controlled by their affinity for the air-water interface. Scoping calculations suggest the majority of PFOS and other long chain PFAS may be removed if foam is continuously collected with potential to reduce waste volume under economic barriers for current destructive technologies.

Ultrasound: a suitable technology to improve the extraction and techno-functional properties of vegetable food proteins

Vegetable-based proteins may be extracted from different sources using different extraction methods, among them, ultrasound-assisted extraction stands out. This review presents the current knowledge on ultrasound-assisted extraction (UAE) and the functional properties of extracted vegetable proteins. Ultrasound generates cavitation in a liquid medium, defined as gas and vapor microbubbles collapse under pressure changes large enough to separate them in the medium. Cavitation facilitates the solvent and solid interaction, increasing yield and reducing extraction periods and temperature used. Moreover, ultrasound treatment changed extracted protein properties such as solubility, hydrophobicity, emulsifying and foam, water and oil absorption capacity, viscosity, and gelatinization. Ultrasound-assisted extraction is a promising technique for the food technology sector, presenting low environmental impact, lower energy and solvent consumption, and it is in accordance with green chemistry technology and sustainable concepts.

Pore-scale dynamics of nanofluid-enhanced NAPL displacement in carbonate rock

This study presents a pore-scale investigation of two-phase flow dynamics during nanofluid flooding in subsurface formations containing non-aqueous phase liquids (NAPLs) such as crude oils. The goal was to gain fundamental understanding of the dominant displacement mechanisms of NAPL at different stages of nanofluid injection in a carbonate rock using x-ray microtomography integrated with a miniature core-flooding system. The nanofluid consisted of surfactant-based microemulsions with in-situ synthesized silica nanoparticles. After establishing its initial wettability state, the carbonate core sample was subjected to various pore volumes (PV) of nanofluid flooding (from 0.5 to 10) to examine the impact on NAPL flow dynamics. We found that most NAPL mobilization occurred within the first PV of injection, removing nearly 50% of NAPL from the rock. The nanofluid invaded into larger pores first due to a sharp decrease in NAPL/brine interfacial tension (from 14 to 0.5 mN/m) and contact angle (from 140 to 88°). With higher amount of nanofluid delivered into the pores through advection, over 90% of NAPL droplets were emulsified and their size decreased from 9 to 3 μm. Subsequent nanofluid injection could further remove NAPL from the smaller pores by altering the thickness of NAPL layers adsorbed on the rock. This dynamic solubilization process reached equilibrium after 5 PV of injection, leading to a reduced layer thickness (from 12 to 0.2 μm), a narrower in-situ contact angle distribution around 81°, and an additional 16% of NAPL removal.

Adsorption of Fluoroquinolone Antibiotics at the Gas-Liquid Interface Using Ionic Surfactants

The overuse of antibiotics in today's society has resulted in high concentrations of pharmaceutical contaminants in the natural environment. In this work, we investigated the surfactant-mediated adsorption of fluoroquinolone (FQ) antibiotics at the gas-liquid interface and their separation using a semi-batch foam fractionation process. FQs being a zwitterionic compound have an affinity to bind with both cationic and anionic surfactants. The adsorption of FQs to the gas-liquid interface was investigated using a cationic cetyltrimethylammonium bromide (CTAB) and anionic sodium dodecyl sulfate (SDS) surfactant. Ciprofloxacin (CF) was chosen as a model FQ antibiotic. The adsorption properties of the surfactant systems and CF were characterized using pendant-drop tensiometry and surface excess analysis. It was found that CF partitions to the gas-liquid interface more readily in the presence of SDS compared to CTAB. This was also corroborated in the foam fractionation experiments. At optimum operating conditions, CF showed a higher removal efficiency with SDS (96.3%) compared to CTAB (52%). In spite of strong molecular interactions between CTAB and CF, the preferential adsorption of DS^--CF complexes was far greater than CTA⁺-CF complexes. At optimized operating conditions, using SDS as the surfactant, other FQs such as norfloxacin, levofloxacin, and ofloxacin were recovered up to 97.9, 91.7, and 96.7%, respectively, with effluent concentration less than 100 nM. Overall, the work demonstrates foam fractionation as a novel and environment-friendly gas-liquid separation technique for the targeted removal of FQ antibiotics from waterbodies.

Ascertainment of Surfactin Concentration in Bubbles and Foam Column Operated in Semi-Batch

This paper describes a mathematical model for the convection, diffusion, and balance phenomena for predicting the depletion curves, i.e., variations in the timed surface-active molecule concentration for fractionation processes in bubbles and foam column, operated in semi-batch. The model was applied for the purification of the surfactin solution and the results were compared with experimental data. Gibbs adsorption curves were obtained for the biosurfactant at different temperatures, and then adjusted with estimated parameters, according to the Langmuir adsorption model. The gas bubble sizes were optically determined. The isotherm adsorption parameters and bubble average diameter are crucial for the attainment of the depletion curves, generated by the model described. The results demonstrate that the process is most effective when operating a column with reduced gas flow and low initial concentration. A top product with two or thirty times greater concentration than the initial one was achieved and the highest biosurfactant concentrations were attained for higher operating temperatures. It was also observed that bubble diameter increased with a higher gas flow. The adjustment obtained for the adsorption curves of Gibbs was satisfactory. Therefore, there was evidence that surfactin molecules adsorb in monolayers in the liquid–gas interface.