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Micellar-enhanced ultrafiltration (MEUF) processes of resorcinol, phenol, and 1-Naphthol with rhamnolipid as an anionic biosurfactant were investigated using polysulfone membrane. The effects of retentate/permeate concentration of phenolic pollutants ( C / C ), distribution coefficient of phenolic pollutions ( D), concentration ratios of phenolic pollutions ( α ) and rhamnolipids ( α ) and adsorption capacity of the membrane ( N ) were studied by operating pressure, pH condition, feed surfactant, and phenolic pollution concentrations. Results showed that C (with pH) increased and ranked in the following order: resorcinol > phenol > 1-Naphthol, which is same with C (with pressure), C (with surfactant), C / C (with pollution), α, and D, while C (with pH), C (with pressure), and C (with surfactant) ranked in the reverse order. The operating pressure increased the solubility of phenolic from 0 to 0.1 MPa and then decreased slowly above 0.1 MPa. The concentration ratio of rhamnolipid was nearly at 2.0 and that of phenolic pollution was slightly above 1.0. D of phenolic pollutants reached the maximum at phenolic pollution concentration of 0.1 mM and the feed rhamnolipid concentration at 1 CMC. Moreover, zeta potential in feed stream and retentate stream and membrane adsorption of phenolic pollutions were firstly investigated in this article; the magnitudes of zeta potential with the feed stream of three phenolic pollutions were nearly the same and slightly lower than those with the retentate stream. The adsorption capacity of the membrane ( N ) was calculated and compared to the former research, which showed that rhamnolipid significantly decreases the membrane adsorption of phenolic pollutions at a relatively lower concentration. It was implied that rhamnolipid can be substituted for chemical surfactants. [ABSTRACT FROM AUTHOR]

Solubilization of n-decane, dodecane, tetradecane and hexadecane by monorhamnolipid biosurfactant (monoRL) at concentrations near the critical micelle concentration (CMC) was investigated. The apparent solubility of all four alkanes increases linearly with increasing monoRL concentration either below or above the CMC. The capacity of solubilization presented by the molar solubilization ratio (MSR), however, is stronger at monoRL concentrations below the CMC. The MSR decreases following the order dodecane ＞ decane ＞ tetradecane ＞ hexadecane at monoRL concentrations below the CMC. Formation of aggregates at sub-CMC monoRL concentrations was demonstrated by dynamic light scattering (DLS) and cryo-transmission electron microscopy. DLS-based size (d) and zeta potential of the aggregates decrease with increasing monoRL concentration. The surface excess (Γ) of monoRL calculated based on alkane solubility and aggregate size data increases rapidly with increasing bulk monoRL concentration and then asymptotically approaches the maximum surface excess (Γmax). The relationship between Γ and d indicates that the excess of monoRL molecules at the aggregate surface greatly impacts the surface curvature. The results demonstrate formation of aggregates for alkane solubilization at monoRL concentrations below the CMC, indicating the potential of employing low concentrations of rhamnolipid for enhanced solubilization of hydrophobic organic compounds. [ABSTRACT FROM AUTHOR]

The success of effective bioaugmentation processes for remediation of soil and groundwater contamination requires effective transport of the injected microorganisms in the subsurface environment. In this study, the effect of low concentrations of monorhamnolipid biosurfactant solutions on transport of Pseudomonas aeruginosa in an ideal porous medium (glass beads) with hydrophilic or hydrophobic surfaces was investigated by conducting miscible-displacement experiments. Transport behavior was examined for both glucose-grown and hexadecane-grown cells, with low and high surface hydrophobicity, respectively. A clean-bed colloid deposition model was used for determination of deposition rate coefficients. Results show that cells with high surface hydrophobicity exhibit greater retention than cells with low surface hydrophobicity. Rhamnolipid affects cell transport primarily by changing cell surface hydrophobicity, with an additional minor effect by increasing solution ionic strength. There is a good linear relation between k and rhamnolipid-regulated cell surface hydrophobicity presented as bacterial-adhesion-to-hydrocarbon (BATH) rate of cells ( R 2 = 0.71). The results of this study show the importance of hydrophobic interaction for transport of bacterial cells in silica-based porous media, and the potential of using low-concentration rhamnolipid solutions for facilitating bacterial transport in bioaugmentation efforts. [ABSTRACT FROM AUTHOR]

The effects of low-concentration monorhamnolipid (monoRL) on the adsorption of Pseudomonas aeruginosa ATCC 9027 grown on glucose or hexadecane to glass beads with hydrophobic or hydrophilic surfaces was investigated using batch adsorption experiments. Results showed that adsorption isotherms of the cells on both types of glass beads fitted the Freundlich equation better than the Langmuir equation. The K f of the Freundlich equation for adsorption of hexadecane-grown cell to glass beads with hydrophobic surface was remarkably higher than that for adsorption of hexadecane-grown cell to glass beads with hydrophilic surface, or glucose-grown cell to glass beads with either hydrophilic or hydrophobic surface. Furthermore, it decreased with the increasing monoRL concentration. For both groups of cells, the zeta potential was close to each other and stable with the increase of monoRL concentration. The surface hydrophobicity of hexadecane-grown cells, however, was significantly higher than that of the glucose-grown cells and it decreased with the increase of monoRL concentration. The results indicate the importance of hydrophobic interaction on adsorption of bacterial cells to surfaces and monoRL plays a role in reducing the bacterial adsorption by affecting cell surface hydrophobicity. [ABSTRACT FROM AUTHOR]

In this article, a rhamnolipid-functionalized graphene oxide (RL-GO) hybrid was prepared by one-step ultrasonication and adsorptive removal of methylene blue (MB) from both artificial and real wastewater by the RL-GO was investigated. The Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Fourier transform infrared spectrum (FT-IR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Brunauer–Emmett–Teller (BET) area and Zeta potential analysis were used to characterize the adsorbent. The results showed that RL-GO had abundant functional groups and a mesopores feature. MB adsorption by the RL-GO increased with increase in adsorbent dose, pH, temperature and initial MB concentration, while it was insensitive to ionic strength variation. The adsorption kinetics fitted well to the pseudo-second-order model with correlation coefficients greater than 0.999. The Intra-particle diffusion and Boyd's film-diffusion models showed that the rate-controlled step was dominated by film-diffusion in the beginning and then followed by intra-particle diffusion. The adsorption isotherm was fitted by adsorption models with the suitability in order of BET > Freundlich > Langmuir > Temkin, based on comparison between correlation coefficients. Thermodynamic analysis of equilibriums suggested that the adsorption MB on RL-GO was spontaneous and endothermic. The adsorption mechanism was also proposed to be electrostatic attraction, π–π interaction and hydrogen bond. In addition, the real wastewater experiment, the regeneration study and the comparative cost analysis showed that the RL-GO composites could be a cost-effective and promising sorbent for MB wastewater treatment owing to its high efficiency and excellent reusability. [ABSTRACT FROM AUTHOR]

A role of rhamnolipid biosurfactant to enhance the biodegradation of hydrocarbons is known to be enhancing bacterial cell surface hydrophobicity (CSH) and adhesion of cells to hydrocarbons. Assumptions regarding the mechanism for rhamnolipid in changing CSH of Gram-negative bacteria are rhamnolipid-induced release of lipopolysaccharide (LPS) from the cell's outer membrane and adsorption/orientation of rhamnolipid on the cell surface. In this study, the relation between cell-wall LPS or rhamnolipid content and CSH of a Pseudomonas aeruginosa bacterium subjected to rhamnolipid treatment was investigated to add insights to the mechanism. Results showed that the initial CSH was determined by the type of substrate the cells grow on and the stage of growth. For glucose-grown cells with low initial CSH and high LPS content, rhamnolipid sorption in cell wall had no discernable effect on CSH. For cells grown on glycerol with medium initial CSH and low LPS content, rhamnolipid sorption increased CSH of exponential-phase cells but decreased that of stationary-phase cells. For hexadecane-grown cells with high initial CSH and high LPS content, rhamnolipid sorption decreased CSH of both exponential-phase and stationary-phase cells. The results indicated that CSH has a better correlation to the content of rhamnolipid in the cell wall than to the content of LPS in the presence of rhamnolipid treatment and that rhamnolipid adsorption may be an important mechanism for rhamnolipid to alter CSH of P. aeruginosa. [ABSTRACT FROM AUTHOR]

Degradation of rhamnolipid-solubilized hexadecane and mass hexadecane as a separate phase by Pseudomonas aeruginosa CCTCC AB93066 treated with rhamnolipid biosurfactant was studied for better understanding on the roles of rhamnolipid in hydrocarbon biodegradation. The results of hexadecane solubilization experiment showed that solubility of hexadecane was linearly related to the concentration of rhamnolipid below or above its critical micelle concentration (CMC), and the ability of monorhamnolipid (monoRL) to solubilize hexadecane was stronger at concentration below CMC than above CMC. MonoRL was then used for treating cells in degradation experiment. Results showed that 75 μM (1 CMC) monoRL treatment had a small inhibitory effect on cell growth on glucose or mass hexadecane, however 750 μM (10 CMC) monoRL treatment accelerated degradation of mass hexadecane by reducing the lag phase of cell growth for 36 h; this effect was not caused by initial cell surface hydrophobicity enhancement. No degradation of hexadecane solubilized by 750 μM monoRL was observed for the cells treated with or without monoRL, indicating that the pseudo-solubilized hexadecane is not available to cells. It is inferred from the data that the effectiveness of rhamnolipid to accelerate degradation of hydrocarbons by enhancing solubilization of the hydrocarbons may not always be guaranteed, which is of importance for evaluation of rhamnolipid biosurfactant application to hydrocarbon-contaminated sites during remediation. [ABSTRACT FROM AUTHOR]

The widespread existence of hydrophobic organic compounds (HOCs) in soil and water poses a potential health hazard to human, such as skin diseases, heart diseases, carcinogenesis, etc. Surfactant-enhanced bioremediation has been regarded as one of the most viable technologies to treat HOCs contaminated soil and groundwater. As a biosurfactant that has been intensively studied, rhamnolipids have shown to enhance biodegradation of HOCs in the environment, however, the underlying mechanisms are not fully disclosed. In this paper, properties and production of rhamnolipids are summarized. Then effects of rhamnolipids on the biodegradation of HOCs, including solubilization, altering cell affinity to HOCs, and facilitating microbial uptake are reviewed in detail. Special attention is paid to how rhamnolipids change the bioavailability of HOCs, which are crucial for understanding the mechanism of rhamnolipids-mediated biodegradation. The biodegradation and toxicity of rhamnolipids are also discussed. Finally, perspectives and future research directions are proposed. This review adds insight to rhamnolipids-enhanced biodegradation process, and helps in application of rhamnolipids in bioremediation. [ABSTRACT FROM AUTHOR]

Biosurfactant rhmnolipids have been applied in many fields, especially in environmental bioremediation. According to previous researches, many research groups have studied the influence of rhamnolipids on microorganism characteristics and/or its application in composting. In this review, the effects of rhamnolipids on the cell surface properties of microorganisms was discussed firstly, such as cell surface hydrophobicity (CSH), electrical, surface compounds, etc. Moreover, the deeper mechanisms were also discussed, such as the effects of rhamnolipids on the structural characteristics and functional characteristics of the cell membrane, and the effects of rhamnolipids on the related enzymes and genes. Additionally, the application of rhamnolipids in composting was discussed, which is an important way for pollutant biodegradation and resource reutilization. It is believed that rhamnolipids will play more and more important role in composting. [ABSTRACT FROM AUTHOR]

In this study, liquid culture systems containing rhamnolipid-solubilized, separate-phase, and multi-state hexadecane as the carbon source were employed for examining the effect of rhamnolipid solubilization on the bioavailability of hexadecane. Experimental results showed that the uptake of rhamnolipid-solubilized hexadecane by Pseudomonas aeruginosa ATCC 9027, a rhamnolipid producing strain, was enhanced compared to the uptake of mass hexadecane as a separate phase, indicating rhamnolipid solubilization increased the bioavailability of hexadecane for this bacterium. For Pseudomonas putida CICC 20575 which does not produce but degrade rhamnolipid, the uptake of either rhamnolipid-solubilized hexadecane or multi-state hexadecane was inhibited. The reduction of bioavailability was assumed to be the consequence of the blocking effect caused by the partition of rhamnolipid molecules at the hexadecane-water interface. The results show that how rhamnolipid solubilization changes the bioavailability of hexadecane depends on the bacterial compatibility to rhamnolipid. The study adds insight into the knowledge of biosurfactant-associated bioavailability of hydrophobic organic compounds (HOCs), and is of importance for application of biosurfactants in bioremediation of HOCs. [ABSTRACT FROM AUTHOR]

Abstract Effects of rhamnolipids on the removal of 2,4,2,4-tetrabrominated biphenyl ether (BDE-47) by Phanerochaete chrysosporium (P. chrysosporium) had been investigated, as well as the influence of carbon source (i.e. glucose). The results showed that the removal efficiency was over 90% in all treatments in 7 d. Rhamnolipids at low concentrations (0.05 and 0.1 CMC (critical micelle concentration)) could promote the removal of BDE-47, however, the inhibition effects occurred at high concentrations (0.5 and 1.0 CMC). The further study indicated that rhamnolipids at low concentrations not only promote the growth of mycelium, but also had obvious promotion on ligninolytic enzymes activity (i.e. manganese peroxidase (MnP), lignin peroxidase (LiP) and laccase (Lac)), especially for MnP and Lac. However, the opposite effect was generated at high rhamnolipids concentrations. Meanwhile, glucose played an active role for BDE-47 removal. For better understanding the degradation mechanism, the degradation product analysis and molecular docking had been introduced to this study. The degradation product analysis indicated that OH-PBDEs were the major degradation products and hydroxylation should be the important degradation pathway. The docking results showed that the ideal binding conformation occurred between ligninolytic enzymes and BDE-47, and hydrophobic interactions were the main interaction. Moreover, hydrogen bonds and hydrophobic interactions both existed in ligninolytic enzymes and rhamnolipids interaction. That might be the reason that rhamnolipids affected enzymes activity. These results indicated that P. chrysosporium might be a type of ideal microorganisms in the removal of BDE-47 pollution, and rhamnolipids could be a type of additives for better removal efficiency. Graphical abstract Image 1 Highlights • Glucose and rhamnolipids affected the removal of BDE-47 by P. chrysosporium. • Rhamnolipids at low concentrations promoted the activity of ligninolytic enzymes. • OH-PBDEs were the major degradation products of BDE-47. • Hydrogen bonds and hydrophobic interactions between ligninolytic enzymes and BDE-47/rhamnolipids were displayed. [ABSTRACT FROM AUTHOR]

The effects of rhamnolipids and Triton X-100 on phenol adsorption by Penicillium simplicissimum were studied. The optimum pH was 7 for phenol adsorption by all the test biomasses. The adsorption of phenol at pH 7 by biomass pre-treated with 0.05% Triton X-100, 0.2% Triton X-100, 0.05% rhamnolipids and 0.005% rhamnolipids was 3.4, 2.7, 2.4, and 1.8-fold, respectively, that of untreated biomass. The pseudo-second-order model and the Freundlich isotherms described the adsorption processes better than the pseudo-first-order model and the Langmuir isotherms, respectively. The pre-treatments by surfactants increased the zeta potential and hydrophobicity of P. simplicissimum . Analysis of the cell surface by Fourier transform infrared spectrometry, energy dispersive X-ray, and environmental scanning electron microscopy indicated that the pre-treatments by surfactants changed the cell surface functional groups, element concentrations and micrographs. The results indicated that surfactants can be potentially used to increase phenol adsorption. [ABSTRACT FROM AUTHOR]