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Apolipoprotein A-I (apoA-I), the primary protein component of plasma high-density lipoproteins (HDL), is comprised of two structural regions, an N-terminal amphipathic α-helix bundle domain (residues 1-184) and a hydrophobic C-terminal domain (residues 185-243). When a recombinant fusion protein construct [bacterial pelB leader sequence - human apoA-I (1-243)] was expressed in Escherichia coli shaker flask cultures, apoA-I was recovered in the cell lysate. By contrast, when the C-terminal domain was deleted from the construct, large amounts of the truncated protein, apoA-I (1-184), were recovered in the culture medium. Consequently, following pelB leader sequence cleavage in the E. coli periplasmic space, apoA-I (1-184) was secreted from the bacteria. When the pelB-apoA-I (1-184) fusion construct was expressed in a 5 L bioreactor, substantial foam production (~30 L) occurred. Upon foam collection and collapse into a liquid foamate, SDS-PAGE revealed that apoA-I (1-184) was the sole major protein present. Incubation of apoA-I (1-184) with phospholipid vesicles yielded reconstituted HDL (rHDL) particles that were similar in size and cholesterol efflux capacity to those generated with full-length apoA-I. Mass spectrometry analysis confirmed that pelB leader sequence cleavage occurred and that foam fractionation did not result in unwanted protein modifications. The facile nature and scalability of bioreactor-based apolipoprotein foam fractionation provide a novel means to generate a versatile rHDL scaffold protein.

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Foam fractionation is a green and economical primary separation technique and it has excellent application prospect in the field of food industry. However, it is difficult to simultaneously obtain the high values of enrichment ratio and recovery percentage in a batch operation of foam fractionation due to the opposite effects of operating parameters on interfacial adsorption and foam drainage. In order to solve this problem, multiple process intensification strategies of foam fractionation are developed. In this work, the current studies on the intensification methods of interfacial adsorption and foam drainage were firstly reviewed. The advantages and disadvantages of these methods are analyzed. Subsequently, the research progress of foam fractionation in the separation of proteins, enzymes, saponins, polyphenols and biological preservatives are summarized. Based on the literature review and problem analysis, three future research respects are proposed to promote the industrial application of foam fractionation: Developing new methods which would simultaneously improve interfacial adsorption and foam drainage, designing new collectors with strong binding specificity for non-surface-active materials and good reusability, and inhibiting protein denaturation during desorption process.

Copyright of Food Research & Development is the property of Food Research & Development Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract Foam formation is a massive challenge in submerged aerated bioprocesses, e.g., in beer fermentation. While the use of antifoam may easily overcome foaming at laboratory scale, it is often an unattractive solution since the challenge remains in future upscaling, as reduced mass transfer and extra steps in product purification and analytics result in increased costs. Interestingly, the number of studies tackling this challenge is relatively low, although literature suggests a range of alternatives, from avoiding foaming to means of controlling or even using foaming as an in situ product removal. Here we give an overview of the topic in five subsections. (1) We argue that a sound understanding of the molecular origin of foaming can facilitate solutions for overcoming the challenge while introducing some long-known challenges (i.e., in beer fermentation). We then review in (2) the apparent avoidance of foam formation before we in (3) summarize possibilities to reduce and control foam after its formation. Subsequently, in (4), we discuss possible solutions that take advantage of foam formation, for example, via foam fractionation for in situ product removal. Finally, in (5), we provide an overview of microbial strain engineering approaches to cope with some aspects of foaming in fermentations. With this review, we would like to sensitize and inform the interested reader while offering an overview of the current literature for the expert, particularly with regard to the foam special issue in Discover Chemical Engineering.

Enzymes have become important tools in many industries. However, the full exploitation of their potential is currently limited by a lack of efficient and cost-effective methods for enzyme purification from microbial production. One technology that could solve this problem is foam fractionation. In this study, we show that diverse natural foam-stabilizing proteins fused as F-Tags to β-lactamase, penicillin G acylase, and formate dehydrogenase, respectively, are able to mediate foaming and recovery of the enzymes by foam fractionation. The catalytic activity of all three candidates is largely preserved. Under appropriate fractionation conditions, especially when a wash buffer is used, some F-Tags also allow nearly complete separation of the target enzyme from a contaminating protein. We found that a larger distance between the F-Tag and the target enzyme has a positive effect on the maintenance of catalytic activity. However, we did not identify any particular sequence motifs or physical parameters that influenced performance as an F-tag. The best results were obtained with a short helical F-Tag, which was originally intended to serve only as a linker sequence. The findings of the study suggest that the development of molecular tags that enable the establishment of surfactant-free foam fractionation for enzyme workup is a promising method. Key points: • Foam-stabilizing proteins mediate activity-preserving foam fractionation of enzymes • Performance as an F-Tag is not restricted to particular structural motifs • Separation from untagged protein benefits from low foam stability and foam washings [ABSTRACT FROM AUTHOR]

Foam formation is a massive challenge in submerged aerated bioprocesses, e.g., in beer fermentation. While the use of antifoam may easily overcome foaming at laboratory scale, it is often an unattractive solution since the challenge remains in future upscaling, as reduced mass transfer and extra steps in product purification and analytics result in increased costs. Interestingly, the number of studies tackling this challenge is relatively low, although literature suggests a range of alternatives, from avoiding foaming to means of controlling or even using foaming as an in situ product removal. Here we give an overview of the topic in five subsections. (1) We argue that a sound understanding of the molecular origin of foaming can facilitate solutions for overcoming the challenge while introducing some long-known challenges (i.e., in beer fermentation). We then review in (2) the apparent avoidance of foam formation before we in (3) summarize possibilities to reduce and control foam after its formation. Subsequently, in (4), we discuss possible solutions that take advantage of foam formation, for example, via foam fractionation for in situ product removal. Finally, in (5), we provide an overview of microbial strain engineering approaches to cope with some aspects of foaming in fermentations. With this review, we would like to sensitize and inform the interested reader while offering an overview of the current literature for the expert, particularly with regard to the foam special issue in Discover Chemical Engineering. [ABSTRACT FROM AUTHOR]

In the present study, the treatment of a typical spent Merox caustic waste (SMC) was investigated by three methods of Fenton-like process, foam fractionation and combination of both methods. Immobilised TiO2/Fe0 nanoparticles on modified silica nanoparticles were used as heterogeneous Fenton-like catalyst. The characterisation of catalyst was carried out using Fourier transform infrared (FT-IR), X‐ray diffraction (XRD), diffuse reflectance spectra (DRS) analysis, thermal gravimetric analysis (TGA), differential scanning calorimeter (DSC) and transmission electron microscopy (TEM). The performance of the combined method was evaluated in terms of chemical oxygen demand (COD) residual parameter. The parameters including pH, gas flow rate to the separator column, concentrations of hydrogen peroxide/catalyst/surfactant/chelate agent, surfactant type, and chelate agent type were investigated to obtain the optimum conditions of the process by response surface methodology (RSM) based on eight-factors central composite design (CCD). Under optimum conditions of combining Fenton-like and foam fractionation methods, the minimum residue of COD was 10.98 ppm, corresponding to a COD removal of 99.7%. However, the measured values for the Fenton-like or foam fractionation methods alone did not exceed 88.9% and 58.4%, respectively. In addition, hydrogen peroxide consumption decreased by 63% compared to the Fenton-like method. Also, another important result shows that the use of cationic surfactants is more effective than anionic and amphoteric for wastewater treatment. [ABSTRACT FROM AUTHOR]

In biological wastewater treatment, the sorption process is an important removal pathway of organic micropollutants from the aqueous phase. Beyond the conventional sorption to biomass and particulate matter, organic molecules can also partition to gas bubbles commonly present in aerated biological processes. This study investigated the partitioning behavior of 21 selected pharmaceuticals to two types of aerobic granular sludge, and the foam generated by aeration. Batch sorption experiments were performed with biologically inactive granules of controlled diameters (0.5–1, 1–2, and >2 mm). Removal during sorption tests was observed for four positively charged micropollutants (sertraline, citalopram, clarithromycin, and erythromycin), four neutral compounds (levonorgestrel, estradiol, ethinylestradiol, and ketoconazole), and one negatively charged pharmaceutical (losartan). This highlights the importance of electrostatic interactions and lipophilic affinity with the solids. For some compounds, the removal increased with time, suggesting that sorption in thick biofilm is limited by molecular diffusion into the biofilm matrix. Furthermore, partitioning of pharmaceuticals to aeration-induced foam was confirmed in separate batch tests. Clarithromycin, erythromycin, ketoconazole, losartan, levonorgestrel, and ethinylestradiol exhibited concentrations in the foam 1.0–5.3 times higher than the initial test values, indicating potential adsorption at the liquid/gas interface for these compounds.

In Bacillus fermentation processes, severe foam formation may occur in aerated bioreactor systems caused by surface-active lipopeptides. Although they represent interesting compounds for industrial biotechnology, their property of foaming excessively during aeration may pose challenges for bioproduction. One option to turn this obstacle into an advantage is to apply foam fractionation and thus realize in situ product removal as an initial downstream step. Here we present and evaluate a method for integrated foam fractionation. A special feature of this setup is the external foam column that operates separately in terms of, e.g., aeration rates from the bioreactor system and allows recycling of cells and media. This provides additional control points in contrast to an internal foam column or a foam trap. To demonstrate the applicability of this method, the foam column was exemplarily operated during an aerated batch process using the surfactin-producing Bacillus subtilis strain JABs24. It was also investigated how the presence of lipopeptides and bacterial cells affected functionality. As expected, the major foam formation resulted in fermentation difficulties during aerated processes, partially resulting in reactor overflow. However, an overall robust performance of the foam fractionation could be demonstrated. A maximum surfactin concentration of 7.7 g/L in the foamate and enrichments of up to 4 were achieved. It was further observed that high lipopeptide enrichments were associated with low sampling flow rates of the foamate. This relation could be influenced by changing the operating parameters of the foam column. With the methodology presented here, an enrichment of biosurfactants with simultaneous retention of the production cells was possible. Since both process aeration and foam fractionation can be individually controlled and designed, this method offers the prospect of being transferred beyond aerated batch processes.

This work focused on the development of an inexpensive carbon source and the improvement of the fermentation-foam fractionation coupling system. The rhamnolipids production capacity of waste frying oil (WFO) was evaluated. The suitable bacterial cultivation of seed liquid and the addition amount of WFO was 16 h and 2% (v/v), respectively. A combined strategy of cell immobilization and oil emulsion avoid cell entrainment inside foam and improves the oil mass transfer rate. The immobilization conditions of bacterial cells into alginate-chitosan-alginate (ACA) microcapsules were optimized using the response surface method (RSM). Under the optimal conditions, rhamnolipids production using batch fermentation with immobilized strain reached 7.18 ± 0.23% g/L. WFO was emulsified into a fermentation medium using rhamnolipids as emulsifier (0.5 g/L). By monitoring dissolved oxygen, 30 mL/min was selected as a suitable air volumetric flow rate for fermentation-foam fractionation coupling operation. The total production and recovery percentage of rhamnolipids were 11.29 ± 0.36 g/L and 95.62 ± 0.38%, respectively. [ABSTRACT FROM AUTHOR]

α-Pinene is an intriguing monoterpene as it has been reported to undergo the self-disproportionation of enantiomers (SDE) phenomenon via gas chromatography (GC), the only compound to decisively demonstrate this. Examples of the SDE involving the gaseous phase—sublimation aside—are extremely rare. Attempts to replicate the GC results were unsuccessful, though the authors argued convincingly for the difficulty of observing the phenomenon. However, we could effect for α-pinene SDE via evaporation off silica gel and by foam fractionation—albeit the SDE magnitude for both was only very slight—to confirm that α-pinene can undergo the SDE for processes involving a gaseous phase and thus validate the plausibility of the GC report. The indications are that the molecular associations responsible for the various SDE observations of α-pinene occur not in the gaseous phase or the bulk phase but rather in two-dimensional (2D) adsorbed monolayers and are not based on conventional functional group-based intermolecular interactions and instead are, most likely, as a result of homo- and heterochiral packing differences in the 2D monolayers—a well-known 2D chiral-based association packing effect. These are also the first reports of the occurrence of the SDE using an adsorptive bubble separation process (foam fractionation) and involving a gaseous phase other than sublimation, GC, and distillation. [ABSTRACT FROM AUTHOR]

In this study, a numerical investigation of the Marangoni flow in foam fractionation was conducted, with a specific focus on the film of micro-foams in both the interior and exterior regions. A three-dimensional node–film–plateau border system was employed to model the system, utilizing time-dependent mass conservation equations. The study emphasized the influence of the surfactant concentration in the foam fractionation column and the mobility of the air–liquid interface on the Marangoni velocity within the film. The results indicated that higher surfactant concentration in the reflux column resulted in a significant increase in Marangoni velocities. Furthermore, a mobile interface enhanced the Marangoni flow, whereas a rigid interface reduced its intensity. The behaviour of the Marangoni flow was explored in both interior and exterior foams, revealing distinct characteristics. The presence of a wall in the exterior foam altered the flow dynamics, leading to a reduced Marangoni velocity compared to interior films. [ABSTRACT FROM AUTHOR]

Cellobiose lipids (CL) are glycolipids secreted by many Ustilaginaceae species in aerobic fermentations characterised by excessive foaming. While increasing CL concentrations remains an aim for its industrial production, excessive foaming during fermentation presents a challenge even at laboratory scale. Foam fractionation (FF) provides a solution to the foaming problem and facilitates the proceeding purification of CL. Here, we present a first CL fermentation process applying FF. With our set-up, we manage to exploit the excessive foaming for continuous product separation. The set-up includes a foam collecting vessel (FCV) with inserts for CL accumulation and foamate recirculation to minimise biomass and nutrient loss. Integrating a foam column (FC) into the fermenter headspace enabled foam enrichment, resulting in the recovery of > 90% of the produced CL from the separated fractions consisting of foam depositions in the fermenter headspace and the FCV. We also increased the fermenter filling volume and thus achieved a higher fermentation capacity. The separated CL fraction was purified via ethanol extraction to obtain CL with purities > 90%. We further examined the effects of different culture media constituents, including biomass and CL, on foam generation and decay and assessed the effect of FC geometries on product enrichment and recovery. In this work, a FF set-up is presented that enables a stable CL fermentation without additional foam mitigation methods. At the same time, the application of FF separated a fraction that was highly enriched in CL during fermentation, resulting in highly pure CL after a simple ethanol extraction. [ABSTRACT FROM AUTHOR]

Gas, which is trapped in either solid or liquid pockets, results in foam formation. Foam formation is common in many industries, i.e., in detergents, food and beverage, cosmetics, and fire-fighting. Foam formation in excess causes biotechnology fermentation instabilities, including material loss and the danger of contaminating the fermentation and the environment. Many foam-controlling measures have been reported, including thermal, enzymatic, mechanical, ultrasound pretreatments, steam explosion, reducing digester mixing, and surface sludge spray. Using antifoaming agents for foam control in fermentation is the most common method, sometimes supported by mechanical foam breakers. However, antifoam can be costly and can complicate product purification. Indeed, effective foam control can significantly impact the economics of the whole process. This mini-review summarizes some unconventional foam destruction techniques, including their various challenges. [ABSTRACT FROM AUTHOR]

The discharge of surfactants through wastewater from numerous industries is a serious concern, since they can critically impact the health of human beings as well as other living creatures. In addition, oily effluents present in the wastewater (such as benzene, toluene, and hexane) make it more harmful so that it is essential to treat it before disposing off. The present work demonstrates the removal of an anionic surfactant [i.e., sodium dodecyl sulfate (SDS)] from water by foam fractionation in the presence of these effluents. The SDS concentration was above its critical micellar concentration. A foam fraction column was used in the batch mode. SDS concentration in the samples collected from the column was measured by two-phase titration. The airflow rate was varied in the range of 0.4–1.6 dm3 min–1. The adsorption of the surfactant at the air–water interface was measured by the surface tension. About 72% of the SDS was recovered in the form of a semi-solid cake. Nearly 97.5% of water was recovered in this process. The removal and recovery of SDS increased with increasing airflow rate. Foam stability had a serious impact on the recovery of SDS. The oils had an antifoaming effect which reduced the foam volume. The foam stability was higher in the absence of the oils. The foam stability was analyzed by the measurement of zeta potential, and the entering, spreading, and bridging coefficients. [ABSTRACT FROM AUTHOR]

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. [Display omitted] • Sampled wet foams forming at a municipal wastewater treatment plant cascade. • PFAS enrichment increases with molar volume and lower foam liquid content. • Partitioning during foam drainage and collapse further enrich long chain PFAS. • Introduced a drainage coefficient with a strong correlation to molar volume. • Collection of cascade foam may be conducive to removal of long chain PFAS. [ABSTRACT FROM AUTHOR]

Municipal wastewater has a relatively low content of per- and polyfluoroalkyl substances (PFAS), compared with other point sources such as landfill leachate and industrial effluents. Nevertheless, it is considered as one of the major point pollution sources. Foam fractionation was previously shown to effectively remove PFAS from different water matrices and to reach a high PFAS enrichment. In this study, the removal of PFAS from municipal wastewater of different origins was investigated. Despite the low foaming potential, it was possible to reach an average removal of the sum of perfluorooctanesulfonic acid (PFOS), perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), and perfluorohexanesulfonic acid (PFHxS) of 93 %, the removal of the sum of 21 PFAS of 56 %, and the removal of the sum of PFAS expressed as PFOA equivalents (ΣPFOAeq) of 91 %, without any surfactant addition utilizing a novel approach of foam collection. The PFAS content was reduced to below the limit values for drinking water in Sweden and the anticipated future limit values for surface water in the European Union. The addition of four commercial surfactants and an extract of extracellular polymeric substances (EPS) from waste activated sludge each enhanced the foam formation. Moreover, a cationic surfactant increased the removal of short-chain PFAS. Additionally, foam fractionation of activated sludge was performed. A considerably lower ΣPFOAeq removal of only 20 % was demonstrated, which was explained by a high proportion of PFAS sorbed to sludge. Finally, the study discusses the practical implications of the application of foam fractionation at municipal wastewater treatment plants., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Due to climate change and environmental pollution, natural lakes and reservoir water suffer increasingly serious algal blooms and associated water quality problems due to the presence of algal or algogenic organic matter (AOM) such as algal odour and toxins. Effective removal of these micropollutants, especially in the event of algal blooms, is critical to aesthetic values of water bodies, drinking water security and human health. The study investigated the removal efficiency of two common odorous compounds, trans-1,10-dimethyl-trans-9-decalol (geosmin) and 2-Methylisoborneol (2-MIB), using foam fractionation enabled by air nanobubbles with addition of two common cationic and anionic surfactants, sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB), to enhance foaming ability and stability. The results showed that the cationic surfactant (i.e., CTAB), a low pH, and high ionic strength significantly promoted the removal of geosmin and 2-MIB. For example, the removal tests using the synthetic water determined that the conditions of pH = 7, [CTAB] = 20 mg·L -1 and IS = 10 mM as NaCl resulted in both the highest geosmin removal rate of 91.81% and highest 2-MIB removal rate of 85.0%. The removal of two odorous compounds in real lake water was evaluated, which yielded removal rates of 83.2% for geosmin and 48.1% for 2-MIB, highlighting the minor inhibition from water matrixes on the removal performances. Compared to microbubbles, nanobubbles enabled greater surface areas of foam and higher removal efficiencies. The study provided new insights into the use of foam fractionation with air nanobubbles to enhance the removal of odorous compounds from impaired water and mitigate the negative environmental and health impacts of harmful algal blooms (HABs)., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

The concept of incorporating foam fractionation in aerated bioreactors at wastewater treatment plants (WWTPs) for the removal of per- and polyfluoroalkyl substances (PFAS) has recently been proposed. The extent of PFAS enrichment in aerated bioreactors' foams, as indicated by enrichment factors (EFs), has been observed to vary widely. Laboratory evidence has shown that factors affecting PFAS enrichment in foams include conductivity, surfactant concentrations and initial PFAS concentrations. However, real wastewaters are complex heterogenous matrices with physical, chemical and biological characteristics potentially contributing to the phenomenon of PFAS partitioning into foams. In this study, we characterised mixed liquor suspensions, including conductivity, filament content, aqueous PFAS concentrations, surface tension and total suspended solids concentrations (TSS) as well as foams, including bubble size and half-life. We used statistical tools - linear mixed-effects model - to establish relationships between PFAS enrichment in aerated bioreactor foams and the examined characteristics. We found that some of the examined characteristics, specifically filament content, surface tension and TSS concentrations measured in mixed liquor suspension and foam half-life, are negatively and significantly associated with the enrichment of longer chain PFAS (with perfluorinated carbon number ≥ 6). Of these, filament content is the important determinant of PFAS enrichment, potentially leading to an increase in, for example, perfluorooctanoic acid (PFOA) EF from 3 to 100 between typical filamentous and non-filamentous suspended biomass. However, enrichment of shorter chain PFAS (with perfluorinated carbon number ≤ 5) is negligible and is not affected by the characteristics that were measured. The findings of our study may serve as valuable information for the implementation of foam fractionation at WWTPs by elucidating the drivers that contribute to the enrichment of longer chain PFAS, under conditions typically found at WWTPs., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Ltd.)

α-Pinene is an intriguing monoterpene as it has been reported to undergo the self-disproportionation of enantiomers (SDE) phenomenon via gas chromatography (GC), the only compound to decisively demonstrate this. Examples of the SDE involving the gaseous phase—sublimation aside—are extremely rare. Attempts to replicate the GC results were unsuccessful, though the authors argued convincingly for the difficulty of observing the phenomenon. However, we could effect for α-pinene SDE via evaporation off silica gel and by foam fractionation—albeit the SDE magnitude for both was only very slight—to confirm that α-pinene can undergo the SDE for processes involving a gaseous phase and thus validate the plausibility of the GC report. The indications are that the molecular associations responsible for the various SDE observations of α-pinene occur not in the gaseous phase or the bulk phase but rather in two-dimensional (2D) adsorbed monolayers and are not based on conventional functional group-based intermolecular interactions and instead are, most likely, as a result of homo- and heterochiral packing differences in the 2D monolayers—a well-known 2D chiral-based association packing effect. These are also the first reports of the occurrence of the SDE using an adsorptive bubble separation process (foam fractionation) and involving a gaseous phase other than sublimation, GC, and distillation.

Spent Merox caustic (SMC) is a hazardous waste that is produced during the Merox desulfurization process in the petroleum refinery industry and should be treated before discharging to environment. In the present study, treatment of SMC was investigated by three methods including Fenton-like process, foam fractionation, and a combination of both processes. Immobilized TiO2/Fe0 on modified silica nanoparticles was used as a heterogeneous Fenton-like catalyst. The chemical and physical characteristics of the catalyst were determined using Fourier-transform infrared spectroscopy, X-ray diffraction, diffuse reflectance spectroscopy, thermogravimetric analysis, differential scanning calorimetry, and transmission electron microscopy techniques. The treatment performance of the combined method was measured as a cost-effective method with chemical oxygen demand (COD) removal percentage. The effect of parameters including pH, gas flow rate, surfactant type and concentration of hydrogen peroxide, catalyst, and chelate were investigated. It is found that the prepared heterogeneous catalyst has high activity for the treatment of SMC. In addition, the results showed that the combined method achieved 97.6 ± 0.5% COD removal, while the measured values for Fenton or foam fractionation methods alone did not exceed 85.5 ± 1% and 47.2 ± 0.4%, respectively. The advantage of combination process over foam fractionation was the use of an advanced oxidation process in the separating column to eliminate or reduce the secondary phase contamination load. Besides, the role of the column in the effective contact of contaminants with the rising bubbles improved the degradation performance of the proposed process and reduced the consumption of hydrogen peroxide by 46% compared to the Fenton-like method. [ABSTRACT FROM AUTHOR]

Inherently occurring foam formation during aerobic fermentation of surface‐active compounds can be exploited by fractionating the foam. This also serves as the first downstream processing step for product concentration and is used for in situ product recovery. Compared to other foam prevention methods, it does not interfere with fermentation parameters or alter broth composition. Nevertheless, parameters affecting the foaming behavior are complex. Therefore, the specific foam fractionation designs need to be engineered for each fermentation individually. This still hinders a widespread industrial application. However, few available commercial approaches demonstrate the applicability of foam columns on an industrial scale. This systematic literature review highlights relevant design aspects and process demands that need to be considered for an application to fermentations and proposes a classification of foam fractionation designs and methods. It further analyses substance‐specific characteristics associated with foam fractionation. Finally, solutions for current challenges are presented, and future perspectives are discussed. [ABSTRACT FROM AUTHOR]

Foam fractionation (FF) is an effective water treatment technology used to remove fine particles in seawater recirculating aquaculture systems (RAS). However, there is only limited available information on the operation and efficiency of FF in freshwater. This study investigated the treatment efficiency of FF by measuring changes in bacterial activity and microparticle densities in freshwater from RAS. Thirty-six separate batch tests were performed with FF separately and in combination with addition of hydrogen peroxide (H2O2) and salt (NaCl). Both chemicals are commonly used for water treatment in freshwater aquaculture. The experiment was a 2 × 2 × 3 factorial design with 3 factors: FF (present or absent), H2O2 (0 or 10 mg L-1) and NaCl (0, 3, or 10 ppt). FF reduced the concentration of microparticles and turbidity in freshwater by 58.7 ± 5.4% and 27.5 ± 3.8% respectively. H2O2 had a significant antimicrobial effect, and the combination of H2O2 and FF resulted in an 80% reduction in bacterial activity in freshwater. Addition of NaCl improved the efficiency of FF by further reducing particle concentration and turbidity two-fold at 10 ppt compared to 0 ppt. This study provides new knowledge on the potential use of FF to improve the water quality in freshwater RAS, and this was further enhanced by the addition of H2O2 or NaCl. [ABSTRACT FROM AUTHOR]

• A novel self-designed foam fractionation device was assembled and built. • High enrichment ratios of 138.2 and 85.5 were achieved for MPD and OPD, respectively. • The mechanisms of key processes during foam fractionation were thoroughly discussed. • The method provided new insights for the detection of trace organic compounds. In this study, a foam fractionation technique was developed for the separation and enrichment of the trace m-phenylenediamine (MPD) and o-phenylenediamine (OPD) in solution. Firstly, a self-designed foam fractionation device was assembled and built, followed by a comprehensive characterization on gas types, foam fractionation column parameters, and porous sieve plate material used in the apparatus. Subsequently, the most crucial parameters for the separation and enrichment, such as surfactant species, solution pH, electrolyte categories, and gas flow rate, were identified and optimized. The mechanisms of key processes during foam fractionation under the influence of these parameters were thoroughly discussed. Other influencing factors, such as surfactant concentration, foam collection time, and solution volume in the fractionation column, were optimized using response surface methodology (RSM). Under these optimal conditions, maximal enrichment ratios of 138.2 and 85.5 were achieved for MPD and OPD, respectively. Finally, foam fractionation coupled with high-performance liquid chromatography (HPLC) was employed to detect MPD and OPD in the solution. The results demonstrated limits of detection (LOD) of 1.5 × 10−2 μg/L and 1.5 μg/L for MPD and OPD, with relative standard deviation (RSD) values of 4.1 % and 3.9 %. When testing various actual samples, the recoveries were in the range from 92.0 % or greater in all cases. The method exhibited advantages of high sensitivity, precision, and accuracy, attributed to the high enrichment efficiency of foam fractionation. In conclusion, the foam fractionation method established in this study offers simplicity in apparatus, operational convenience, environmental friendliness (minimized use of organic solvents), and high enrichment efficiency. It proves valuable for the quantitative analysis of trace amounts of MPD and OPD in solution, presenting a novel approach for the detection of trace organic compounds in solutions. [ABSTRACT FROM AUTHOR]

Several studies have demonstrated that air-bubbling and foam fractionation techniques can efficiently remove long-chain PFAS from contaminated water. However, removing short-chain PFAS is challenging due to its lower surface activity and inability to form self-assembly structures at the air-water interface. In this study, we tested various additives, including salts, surfactants, and polymers, to improve short-chain PFAS (e.g., perfluorobutanesulfonic acid (PFBS) and perfluorobutanoic acid (PFBA)) removal in non-foaming solutions using a bench-scale system. We found that in the presence of cetyltrimethylammonium chloride (CTAC) and salt, air-bubbling can significantly remove 0.5 μg L−1 of PFBS and PFBA in deionized water by >99% (15 min) and 81% (60 min), respectively. The decline of surface tension and the formation of thin foam-like layers during bubbling, controlled by the concentration of CTAC, significantly improved the removal of short-chain PFAS. Adding anionic and neutral surfactants showed no removal of short-chain PFAS during bubbling, suggesting the importance of the electrostatic interactions between short-chain PFAS and the cationic CTAC. We observed a 1:1 M ratio between CTAC and PFBS removed from the solution, suggesting the formation of ion pairs in the solution and enhancing the surface activity of the overall neutral (PFAS-CTAC) complex. A mass balance of the system revealed that the primary mechanism by which PFAS was removed from non-foaming waters was through aerosol generation (70−100%). Using the optimized condition, PFAS mixtures (short- and long-chain PFAS, including five recently regulated PFAS by USPEA, 2 nM each) in deionized water and natural groundwater were successfully removed to below detection (>99% removal; <2 ng L−1), except for PFBA (25−73% removal). These results provide an improved understanding of the mechanism by which PFAS is removed during foam fractionation and highlight the need for capturing aerosols enriched with PFAS to prevent secondary contamination. [Display omitted] • Cationic surfactant enhanced short-chain PFAS removal during foam-fractionation. • Ion-pair formation between PFAS and CTAC increased surface activity of short-chains. • Aerosolization was the primary pathway for PFAS removal in non-foaming waters. • Mass balance of PFAS in the system can achieve 70–100% when aerosols were measured. [ABSTRACT FROM AUTHOR]

[Display omitted] • Peanut meal protein (PMP) is developed as a frother and collector. • PMP displays nice foaming ability and stability. • Interaction mechanism between PMP and phenol is confirmed. • Eight-square bifrustum internal component can enhance phenol enrichment. • Phenol is effectively recovered under optimized conditions. Phenol, a prominent organic pollutant frequently found in water, poses considerable environmental risks due to its toxicity, high stability, and water solubility. To address this issue, a novel protein-enabled foam fractionation process was developed to efficiently recover phenol from water. The utilization of peanut meal protein (PMP) derived from agricultural waste as the collector/frother provides a sustainable and environmentally friendly alternative to chemical surfactants for phenol recovery. The optimally extracted PMP displayed outstanding foaming properties and collection capabilities, leading to a significant improvement in phenol recovery. Various techniques were employed to elucidate the underlying mechanism responsible for this collection ability, highlighting the crucial role of hydrogen bonds. Moreover, an innovative eight-square bifrustum internal component was designed to enhance phenol enrichment by approximately 1.3 times. The relationship between the foam fractionation performance and process variables were identified. Under optimized conditions involving a PMP concentration of 92.8 mg/L, pH of 6.0, and gas flowrate of 100 mL/min, impressive recovery percentages of 95.5–99.1 % and enrichment ratios of 9.0–13.1 were attained for phenol concentrations ranging from 10 to 50 mg/L. These results emphasize the importance of developing protein-based collectors/frothers and novel columns, ultimately advancing foam fractionation for the effective treatment of phenol-contaminated wastewater. [ABSTRACT FROM AUTHOR]

Foam fractionation is a well-developed technology used to separate surface-active compounds from solution by exploiting their affinity for the air–water interface. The technology was founded in the 1940s and has since evolved into a key technology for treatment of many different pollutants from a variety of different industries such as textiles and dyes, heavy metals, proteins in food processing waste and even per- and poly-fluoroalkyl substances (PFAS). The technology has even progressed from a standard batch process to a continuous process with an applied reflux to being presently used as an in-situ groundwater remediation and soil remediation process. This review provides a snapshot of the historical evolution of foam fractionation, a discussion of the mechanism behind foam fractionation, the effect of key operating variables on the performance parameters, identification of the key transport processes that take place within a foam fractionation system, a review of the modeling of foam fractionation as a water treatment technology and a review of the applications of foam fractionation as a water treatment technology. [ABSTRACT FROM AUTHOR]

Locusta migratoria apolipophorin III (apoLp-III) possesses the ability to exist as a water soluble amphipathic α-helix bundle and a lipid surface seeking apolipoprotein. The intrinsic ability of apoLp-III to transform phospholipid vesicles into reconstituted discoidal high-density lipoproteins (rHDL) has led to myriad applications. To improve the yield of recombinant apoLp-III, studies were performed in a bioreactor. Induction of apoLp-III expression generated a protein product that is secreted from E. coli into the culture medium. Interaction of apoLp-III with gas and liquid components in media produced large quantities of thick foam. A continuous foam fractionation process yielded a foamate containing apoLp-III as the sole major protein component. The yield of recombinant apoLp-III was ~0.2 g / liter bacterial culture. Mass spectrometry analysis verified the identity of the target protein and indicated no modifications or changes to apoLp-III occurred as a result of foam fractionation. The functional ability of apoLp-III to induce rHDL formation was evaluated by incubating foam fractionated apoLp-III with phosphatidylcholine vesicles. FPLC size exclusion chromatography revealed a single major population of particles in the size range of rHDL. The results described offer a novel approach to bioreactor-based apoLp-III production that takes advantage of its intrinsic biosurfactant properties. • Apolipophorin III (apoLp-III) is a apolipoprotein with biosurfactant properties. • Recombinant apoLp-III with a pelB leader sequence is secreted from E. coli. • In a bioreactor, apoLp-III combines with gas and liquid in media to produce foam. • Foam fractionation can be used to streamline downstream processing of apoLp-III. • ApoLp-III has numerous biotechnology applications as a nanodisks scaffold. [ABSTRACT FROM AUTHOR]

The #25 teller rosette (TR) random packing was used to enhance foam drainage in foam fractionation under continuous steady‐state conditions and tested using sodium dodecyl sulfate (SDS) as a model surfactant. A column without the #25 TR served as control. The results demonstrated that the #25 TR was capable of enhancing the foam drainage and enrichment ratio while reducing the liquid holdup. The experiment was set up with optimized feed flow rate, liquid pool height, air flow rate, and SDS feed concentration. The enrichment ratio obtained by the #25 TR column was 1.76 times higher compared with the control column. Based on the mass balances and equilibrium relationship, a new method for graphical illustration of theoretical stages is also presented. [ABSTRACT FROM AUTHOR]

Foam fractionation is one of the novel techniques used nowadays for the wastewater treatment. The present paper discusses the removal of methylene blue dye by using a surfactant, sodium dodecyl sulfate, as a collector, by semi-batch foam fractionation technique. The influence of operating variables like aeration rate (150 - 250 mL.min-1), liquid height (600 - 900 mL), dye concentration (5 - 25 ppm), pH (3 - 10), surfactant dose (250 - 2000 ppm) on percentage removal, enrichment ratio and surface excess were investigated. The results revealed fairly high percentage removals at various operating conditions due to strong electrostatic interaction between dye and surfactant. Further, in order to augment separation, optimization was performed by employing Taguchi-based experimental design followed by Grey relational analysis (GRA) technique. The optimal conditions were found to be: 150 mL.min-1 air flow rate, 600 mL liquid loading and 5 ppm dye concentration for percentage removal of 95.7% and an enrichment ratio of 7.49. The analysis of variance (ANOVA) suggested dye concentration to be the most influencing operating variable. Lastly, the equilibrium relationship between bulk and surface phase was established which qualitatively indicates as to how much the actual process departs from equilibrium. [ABSTRACT FROM AUTHOR]

A multi-stage continuous bubble cap foam fractionation column was developed to achieve high separation performance using cetyltrimethyl ammonium bromide (CTAB) as a model surfactant. The effect of design and operating parameters on the overall performances was investigated at a steady state. The results illustrated that with increasing the airflow rate, the enrichment ratio of CTAB was decreased and its recovery percentage increased. When the feeding concentration of CTAB was greater than 0.2 g/L, the adsorption of CTAB at the gas-liquid interface was closed to equilibrium. Based on mass balances and equilibrium relationships, a new method of the number of theoretical stages by stage-to-stage calculation and graphics were presented on the foam fractionation column. [ABSTRACT FROM AUTHOR]

The isolation of dye (methylene blue) by employing a foam fractionation technique with the assistance of a surfactant (sodium dodecyl sulfate) has been dealt with in this paper. This study also incorporated the comparison between contrasted and experimental columns. Taguchi methodology and grey relational analysis techniques were used to ascertain optimal conditions at which the column should be operated to achieve maximum percentage removal and enrichment ratio, for both the columns. The analysis of variance study suggested dye concentration to be the most influencing parameter. The relationship between dye concentration in the bulk phase and the foam phase was also deduced. [ABSTRACT FROM AUTHOR]

Perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) are persistent anthropogenic chemicals that are widely distributed in the environment and pose significant risks to human health. Foam fractionation has emerged as a promising method to recover PFOS/PFOA from water. However, PFOS/PFOA concentrations in wastewater are often inadequate to generate stable foams due to their high critical micelle concentrations and the addition of a cosurfactant is necessary. In this study, we developed whey soy protein (WSP) as a green frother and collector derived from soybean meal (SBM), which is an abundant and cost-effective agro-industrial residue. WSP exhibited excellent foaming properties across a wide pH range and demonstrated strong collection capabilities that enhanced the recovery of PFOS/PFOA. The mechanism underlying this collection ability was elucidated through various methods, revealing the involvement of electrostatic attraction, hydrophobic interaction, and hydrogen bonding. Furthermore, we designed a double plate internal to improve the enrichment of PFOS/PFOA by approximately 2.3 times while reducing water recovery. Under suitable conditions (WSP concentration: 300 mg/L, pH: 6.0, air flowrate: 300 mL/min), we achieved high recovery percentages of 94–98% and enrichment ratios of 7.5–12.8 for PFOS/PFOA concentrations ranging from 5 to 20 mg/L. This foam fractionation process holds great promise for the treatment of PFOS/PFOA and other per- and polyfluoroalkyl substances. [Display omitted] • Whey soy protein (WSP) is developed as a frother and collector. • WSP significantly improves PFOS/PFOA foaming ability and stability. • Interaction mechanism between WSP and PFSO/PFOA is confirmed. • Double plate internal (DPI) have the ability to enhance the foam drainage. • PFOS/PFOA are effectively recovered by foam fractionation with WSP. [ABSTRACT FROM AUTHOR]

• Ozone foam fractionation removed over 90 % long-chain PFAS from landfill leachate. • Ozone removed short-chain PFAS 10 %–30 % less efficiently than air. • PFAS surface excess on ozone bubbles was 20–40 % lower than air bubbles. • Ozone's foamate volumes were 2–4 times smaller with 4 % lower wettability than air. Landfills are the primary endpoint for the disposal of PFAS-laden waste, which subsequently releases PFAS to the surrounding environments through landfill leachate. Ozone foam fractionation emerges as a promising technology for PFAS removal to address the issue. This study aims to (i) assess the effectiveness of the ozone foam fractionation system to remove PFAS from landfill leachate, and (ii) quantify equilibrium PFAS adsorption onto the gas-water interface of ozone bubbles, followed by a comparison with air foam fractionation. The results show that ozone foam fractionation is effective for PFAS removal from landfill leachate, with more than 90 % long-chain PFAS removed. The identified operating conditions provide valuable insights for industrial applications, guiding the optimization of ozone flow rates (1 L/min), dosing (43 mg/L) and minimizing foamate production (4 % wettability). The equilibrium modelling reveals that the surface excess of air bubbles exceeds that of ozone bubbles by 20–40 % at a corresponding PFAS concentration. However, the overall removal of PFAS from landfill leachate by ozone foam fractionation remains substantial. Notably, ozone foam fractionation generates foamate volumes 2 – 4 times less, resulting in significant cost savings for the final disposal of waste products and reduced site storage requirements. [Display omitted] [ABSTRACT FROM AUTHOR]

Demands for phosphoric acid are growing rapidly in various industries. This has highlighted the importance of optimizing its production and purification methods. Phosphoric acid can be produced by a wet process. However, due to the presence of many organic and inorganic impurities in the wet product, purification of the resulting product is a major concern in this industry. Removal of trace metal impurities (such as magnesium, cadmium, chromium, zinc, etc.) from produced phosphoric acid in a wet process was investigated by foam fractionation in a semi‐batch setup using sodium dodecyl sulfate (SDS) as the surfactant. Effects of inlet air velocity, surfactant concentration, and surfactant selectivity were investigated. The optimum air velocity and surfactant concentration were obtained as 0.020 cm/min and 0.7 g/L, respectively. At the optimum condition, the total removal efficiency and enrichment factor reached were 70.2% and 4.39, respectively, while the acid loss was 8.3%. The total metal removal efficiency was increased to 95.3% in a two‐stage experimental run. [ABSTRACT FROM AUTHOR]

In this work, copper (Cu) was recovered from the discarded printed circuit board (PCB) of personal computer through foam fractionation. The discarded PCB was treated by acid leaching. The leaching yield of Cu ion reached 97.61% under the conditions of temperature 40ºC, nitric acid concentration 6 mol/L and leaching time 60 min. A novel foam fractionation column was developed to strengthen foam drainage. Under the suitable conditions of pH 4.0, volumetric airflow rate 70 mL/min, SDS concentration 0.12 g/L and loading liquid volume 500 mL, enrichment ratio and recovery percentage of Cu ion were 29.1% and 90.2%, respectively. [ABSTRACT FROM AUTHOR]

Rhamnolipids are among the glycolipids that have been investigated intensively in the last decades, mostly produced by the facultative pathogen Pseudomonas aeruginosa using plant oils as carbon source and antifoam agent. Simplification of downstream processing is envisaged using hydrophilic carbon sources, such as glucose, employing recombinant non-pathogenic Pseudomonas putida KT2440 for rhamnolipid or 3-(3-hydroxyalkanoyloxy)alkanoic acid (HAA, i.e., rhamnolipid precursors) production. However, during scale-up of the cultivation from shake flask to bioreactor, excessive foam formation hinders the use of standard fermentation protocols. In this study, the foam was guided from the reactor to a foam fractionation column to separate biosurfactants from medium and bacterial cells. Applying this integrated unit operation, the space-time yield (STY) for rhamnolipid synthesis could be increased by a factor of 2.8 (STY = 0.17 gRL/L·h) compared to the production in shake flasks. The accumulation of bacteria at the gas-liquid interface of the foam resulted in removal of whole-cell biocatalyst from the reactor with the strong consequence of reduced rhamnolipid production. To diminish the accumulation of bacteria at the gas-liquid interface, we deleted genes encoding cell-surface structures, focusing on hydrophobic proteins present on P. putida KT2440. Strains lacking, e.g., the flagellum, fimbriae, exopolysaccharides, and specific surface proteins, were tested for cell surface hydrophobicity and foam adsorption. Without flagellum or the large adhesion protein F (LapF), foam enrichment of these modified P. putida KT2440 was reduced by 23 and 51%, respectively. In a bioreactor cultivation of the non-motile strain with integrated rhamnolipid production genes, biomass enrichment in the foam was reduced by 46% compared to the reference strain. The intensification of rhamnolipid production from hydrophilic carbon sources presented here is an example for integrated strain and process engineering. This approach will become routine in the development of whole-cell catalysts for the envisaged bioeconomy. The results are discussed in the context of the importance of interacting strain and process engineering early in the development of bioprocesses.

Abstract Biosurfactants offer environmental as well as health benefits over traditionally used chemical surfactants and heterologous production from engineered microorganisms has been demonstrated, offering containable as well as scalable production of these alternative chemicals. Low product titers and cost intensive downstream processing are the main hurdles for economical biosurfactant production at industrial scales. Increased biosurfactant concentrations are found in the liquid fraction of the foam formed during fermentation of producing microbes. Adsorption of biosurfactants from foam fractions in cultivations may offer a simple concentration and purification method which could enable their cost-effective production. Here, foam adsorption was applied as an in situ method for separation of the rhamnolipid biosurfactants during fermentation of Pseudomonas putida EM383. An integrated process was designed to capture the produced rhamnolipids on hydrophobic adsorbent in packed bed units while minimizing the impact of adsorption on the productivity of the system by recirculating cell-containing collapsed foam flow-through back into the reactor vessel. A stable rhamnolipid production by P. putida EM383 on glucose was performed coupled to this adsorption strategy for 82 h, after which no remaining rhamnolipids were found in the cultivation broth and 15.5 g of rhamnolipids could be eluted from the adsorbent. Rhamnolipid yield from glucose feed was 0.05 g g−1, when up to 2 g L−1 glucose pulse feeding was applied. After solvent evaporation, a product purity of 96% was obtained. The results indicate that the integrated adsorption method can be efficient for simultaneous production and recovery of rhamnolipid biosurfactants from microbial fermentations.

Background: Foam fractionation technology works on the adsorptive bubble separation principle. This technique involves adsorption of the surface-active substances on to a gas-liquid interface and separation of these components from the liquid along with bubbles as foam. The foam separation technology has been successfully utilized in the recovery of proteins from solutions containing either a single protein or binary mixtures. To develop a foam fractionation technology for selective enrichment and recovery of whey proteins, it is essential to investigate the effect of different feed and process variables that affect the foam fractionation process. The aim of the current study was to investigate the effect of two important feed variables, such as pH and initial protein concentration on recovery and enrichment of total whey proteins as well as α-lactalbumin and ß-lactoglobulin. Methods: All the experiments were conducted in Agriculture and biosystems engineering lab and Alfred Dairy Science lab at South Dakota State University, Brookings, South Dakota during 2011-2013. The experiments used four levels of initial protein concentration and five levels of feed pH. Yield and enrichment ratios were determined for total whey proteins, α-Lactalbumin (α-La) and ß-Lactoglobulin (ß-Lg). Result: Whey protein yields ranged from 51.58 to 90.92%, while the enrichment ratios were between 1.2 to 5. The yield of α-La varied from 59 to 94% and the highest enrichment ratio of 8.45 was obtained with the treatment combination of initial protein concentration of 109 mg/L and pH of 5.1. Selective enrichment of α-La over ß-Lg was observed at a pH of 4.65 with α-La to ß-Lg ratio of 0.49. These findings will be helpful in selective enrichment and recovery of valuable proteins from Cheddar cheese whey using the foam fractionation process. [ABSTRACT FROM AUTHOR]

• Surface activity of protein solution is finely adjustable via heat treatment. • Foamate volume and foamate flow are indicators for surface activity. • Impact of surface activity on foam fractionation is concentration dependent. • At high concentration destructive effects in foam are superimposed. • Bubble size reflects the surface activity determined in foam fractionation. Surface activity is an intrinsic protein feature, leading to the capability of aqueous protein solutions to form foam. This feature provides opportunities for downstream processing, such as usage of foam fractionation for purification. In order to investigate the impact of the surface activity on the performance of the foam fractionation process, protein solutions with different surface activity were produced by different thermal denaturation of aqueous β-lactoglobulin solutions. The effectiveness of the denaturation procedure was verified with circular dichroic spectroscopy, and the impact on surface activity was determined via dynamic surface tension measurement. The increased surface activity resulted in higher foamate flow rates. Furthermore, the effects could be correlated with secondary structure changes and with the dynamic surface pressure. The new result of this study is that the effect of the denaturation of a protein on foam fractionation depends on the protein concentration. At the lower feed concentration, effects became visible, which could not be observed at the higher concentration. [ABSTRACT FROM AUTHOR]

Foam separation promotes the removal of dissolved materials from solutions by adsorbing the molecules onto a surfactant. The zwitterion of rhodamine B was removed by using both anionic (sodium dodecyl sulfate: SDS) and cationic (dodecyltrimethylammonium chloride: DTAC) surfactants through foam separation. However, rhodamine B could not be removed from a strongly acidic DTAC solution (pH 2), because the molecular form changes from the zwitterion to cation. Moreover, the cationic dye of rhodamine 6G could not be removed from the DTAC solution. Therefore, these results demonstrate that the electrostatic interaction between a surfactant and target ion is an important factor in foam separation. [ABSTRACT FROM AUTHOR]

Foam separation can selectively remove a target substance from a solution via adsorption of the substance with the surfactant at the surface of the bubble. A cationic dye, methylene blue, and an anionic dye, Fast Green FCF, were prepared as substances to be removed via foam separation. Anionic (sodium dodecyl sulfate, SDS), cationic (dodecyltrimethylammonium chloride, DTAC), and amphoteric (3-(dodecyldimethylammonio)propane-1-sulfonate, SB-12) surfactants were used in the foam separation process. The effectiveness of the surfactants for removing the cationic methylene blue increased as follows: DTAC < SB-12 < SDS. On the other hand, the effectiveness of the surfactants for removing the anionic Fast Green FCF was in the opposite order. The dyes were effectively adsorbed by the foams via electrostatic interactions between the oppositely charged surfactant and the dye molecules. Since amphoteric surfactants have both anionic and cationic charges in a molecule, they could effectively remove both dyes in the foam separation process. Therefore, it was found that the amphoteric surfactant was highly versatile. Analysis of the kinetics of the removal rate showed that the aqueous solutions of monomers could remove the dyes more effectively than micellar solutions in foam separation. [ABSTRACT FROM AUTHOR]