Osmotic pressure estimation using the Pitzer equation for forward osmosis modelling.

Forward osmosis (FO) has received widespread recognition in the past decade due to its potential low energy production of water. This study presents a new model analysis for predicting the water flux in FO systems when inorganic-based draw solutions are used under variable experimental conditions for using a laboratory scale cross-flow single cell unit. The new model accounts for the adverse impact of concentration polarization (both ICP and ECP) incorporating the water activity by Pitzer to calculate the bulk osmotic pressures. Using the water activity provides a better correlation of experimental data than the classical van't Hoff equation. The nonlinear model also gave a better estimate for the structural parameter factor (S) of the membrane in its solution. Furthermore, the temperature and concentration of both the draw and feed solutions played a significant role in increasing the water flux, which could be interpreted in terms of the mass transfer coefficient representing ECP; a factor sensitive to the hydraulics of the system. The model provides greatly improved correlations for the experimental water fluxes.

Comparative power demand of mechanical and aeration imposed shear in an immersed membrane bioreactor.

The power demanded for the application of mechanically-imposed shear on an immersed flat sheet (iFS) membrane bioreactor (MBR) has been compared to that of conventional membrane air scouring. Literature correlations based on the Ostwald model were used to define the rheological characteristics of an MBR sludge. The correlation of specific power demand (P'¯, in Watts per m2 membrane area) with shear rate γ in s-1 was developed from first principles through a consideration of the force balance on the system in the case of mechanically-imposed shear. The corresponding aeration imposed shear correlation was interpreted from literature information. The analysis revealed the energy required to impose a shear mechanically through oscillation (or reciprocation) of the membrane to be between 20 and 70% less than that demanded for providing the same shear by conventional aeration of the immersed membrane. The energy saving increases with decreasing shear in accordance with a power demand ratio (aeration:mechanical) of 1400γ-1.4 for a specific sludge rheology. Whilst the absolute P'¯ value is dependent on the sludge rheology, the aeration:mechanical power demand ratio is determined by the difference in the two exponents in the respective correlations between P'¯ and γ. Consequently, aeration-imparted shear becomes energetically favoured beyond some threshold shear rate value (∼180 s-1, based on the boundary conditions applied in the current study). The outcomes qualitatively corroborate findings from the limited practical measurement of energy demand in MBRs fitted with reciprocating immersed membranes.

Benchmarking the Self-Assembly of Surfactin Biosurfactant at the Liquid-Air Interface to those of Synthetic Surfactants.

The adsorption of surfactin, a lipopeptide biosurfactant, at the liquid-air interface has been investigated in this work. The maximum adsorption density and the nature and the extent of lateral interaction between the adsorbed surfactin molecules at the interface were estimated from surface tension data using the Frumkin model. The quantitative information obtained using the Frumkin model was also compared to those obtained using the Gibbs equation and the Langmuir-Szyszkowski model. Error analysis showed a better agreement between the experimental and the calculated values using the Frumkin model relative to the other two models. The adsorption of surfactin at the liquid-air interface was also compared to those of synthetic anionic, sodium dodecylbenzenesulphonate (SDBS), and nonionic, octaethylene glycol monotetradecyl ether (C14E8), surfactants. It has been estimated that the area occupied by a surfactin molecule at the interface is about 3- and 2.5-fold higher than those occupied by SDBS and C14E8 molecules, respectively. The interaction between the adsorbed molecules of the anionic biosurfactant (surfactin) was estimated to be attractive, unlike the mild repulsive interaction between the adsorbed SDBS molecules.

Self-assembly of a surfactin nanolayer at solid-liquid and air-liquid interfaces.

Surfactin, a sustainable and environmentally friendly surface active agent, is used as a model to study the adsorption of biosurfactants at hydrophobic and hydrophilic solid-liquid interfaces as well as the air-liquid interface. Surfactin adsorption was monitored as a function of time and concentration using surface plasmon resonance (SPR) technique in the case of the solid-liquid interfaces or the drop shape analysis (DSA) technique in the case of the air-liquid interface. The results obtained in this study showed that surfactin adsorption at the "hard" hydrophobic (functionalized with octadecanethiol) solid-liquid and the "soft" air-liquid interface were 1.12 ± 0.01 mg m(-2) (area per molecule of 157 ± 2 Å(2)) and 1.11 ± 0.05 mg m(-2) (area per molecule of 159 ± 7 Å(2)), respectively, demonstrating the negligible effect of the interface "hardness" on surfactin adsorption. The adsorption of surfactin at the hydrophilic (functionalized with ß-mercaptoethanol) solid-liquid interface was about threefold lower than its adsorption at the hydrophobic-liquid interfaces, revealing the importance of hydrophobic interaction in surfactin adsorption process. The affinity constant of surfactin for the investigated interfaces follows the following order: air > octadecanethiol > ß-mercaptoethanol. Biosurfactants, such as surfactin, are expected to replace the conventional fossil-based surfactants in several applications, and therefore the current study is a contribution towards the fundamental understanding of biosurfactant behavior, on a molecular level, at hydrophobic and hydrophilic solid-liquid interfaces in addition to the air-liquid interface. Such understanding might aid further optimization of the utilization of surfactin in a number of industrial applications such as enhanced oil recovery, bioremediation, and detergency.

Lysozyme binding to tethered bilayer lipid membranes prepared by rapid solvent exchange and vesicle fusion methods.

Tethered bilayer lipid membranes (tBLMs) are important tools for studying protein-lipid interactions. The widely used methodology for the preparation of these membranes is the fusion of phospholipid vesicles from an aqueous medium onto an anchored phospholipid layer. The preparation of phospholipid vesicles is a long and tedious procedure. There is another simple method, rapid solvent exchange, for preparing lipid membranes. However, there is a lack of information on the effects of the preparation method of tBLMs on their interactions with proteins. Therefore, we present in this paper a comparative study on the binding of lysozyme onto tBLMs prepared by the abovementioned methods. The prepared tBLMs have either zwitterionic or anionic characteristics. The results show that lysozyme binding onto the prepared tBLMs is unaffected by the preparation method of the tBLMs, suggesting that the tedious fusion method might be replaced by the simple rapid solvent exchange method without altering the level of protein-lipid interactions.

Signature biomarkers in Crohn's disease: toward a molecular classification.

In an effort to develop a molecular classification scheme for Crohn's disease (CD), mucosal biopsies from 69 CD patients and 28 normal controls were analyzed for expression of the RelA subunit of nuclear factor (NF)-kappaB, A20 (a negative regulator of NF-kappaB), polymeric immunoglobulin receptor (pIgR), tumor necrosis factor (TNF), and interleukin (IL)-8. Principal component analysis was used to classify individuals into three subsets based on patterns of biomarker expression. Set 1 included normal subjects and CD patients with mild disease and good responses to therapy, thus defining "normal" biomarker expression. CD patients in set 2, characterized by low expression of all five biomarkers, had moderate to severe disease and poor responses to immunosuppressive and anti-TNF therapy. Patients in set 3, characterized by low expression of RelA, A20, and pIgR, normal TNF and elevated IL-8, had acute inflammation that responded well to therapy. Classification of CD patients by these biomarkers may predict disease behavior and responses to therapy.