Galactoglucomannan Recovery with Hydrophilic and Hydrophobic Membranes: Process Performance and Cost Estimations

In this study, we compared the GR51PP (hydrophobic/polysulfone) membrane with a series of hydrophilic (regenerated cellulose) membranes with the aim of increasing the retention of products and decreasing membrane fouling. The raw material used was a sodium-based spent sulfite liquor from the sulfite pulping process of spruce and pine. The results show that the hydrophilic membranes were superior to the hydrophobic membranes in terms of higher fluxes (up to twice the magnitude), higher product retentions and less fouling (up to five times lower fouling). The fouling was probably caused by pore blocking as observed in earlier studies. However, the hydrophilic membranes had a lower affinity for lignin, which was indicated by the lower retention and fouling. This also resulted in a separation degree, which was higher compared with the hydrophobic membrane, thus yielding a higher galactoglucomannan (GGM) purity. 2D HSQC NMR results show that no major structural differences were present in the hydrophilic and hydrophobic retentates. A techno-economical evaluation resulted in the RC70PP being chosen as the most cost-efficient membrane in terms of flux and product recovery.

A Simple Methodology to Estimate the Diffusion Coefficient in Pervaporation-Based Purification Experiments

A procedure to estimate the diffusion coefficient in solution–diffusion models of hydrophilic membranes used in pervaporation-based purification experiments is presented. The model is based on a series solution of the general permeation problem. It considers a membrane that can be filled with water or with the feed solution before the measurement. Furthermore, the length of the tubing between the permeation cell and the place of cold traps is also addressed. To illustrate the parameter estimation procedure, we have chosen the data for the separation of water and ethanol by chitosan membranes. It is shown that the diffusion coefficient can be estimated effectively from the time course of the transported mass and by the analysis of certain well defined time lags of the permeation curve.

Improved Hydrophilicity of Membrane by Ethylenediaminetetraacetic Acid Modification

Hydrophilic membranes exhibit good flux and low fouling tendency, which are the crucial criteria for a good membrane. Attempts have been done by researchers over the past decades to enhance the hydrophilicity of membrane by using nanoparticles and grafting. However, these processes are tedious and costly. This study improves the hydrophilicity of cellulose acetate (CA) membranes by using ethylenediaminetetraacetic acid (EDTA) via simple blending method. Recent study showed that fouled membrane which was cleaned by EDTA exhibited high water flux performance. However, the use of EDTA in formulating a membrane has not been disclosed elsewhere. Thus, the objective of this study is to conduct a series of experiments to find out the role of EDTA in improving the hydrophilicity of CA membranes. Membranes with varying EDTA concentration were prepared via dry-wet phase inversion technique. Contact angle, porosity and water flux of the resultant membranes were determined. Additionally, the morphologies of the membranes were imaged using FESEM. Results showed that EDTA was a good pore former, which can be seen clearly from FESEM images. This explains for the high porosity properties in CA-EDTA membranes. Membrane with 1 wt% of EDTA showed the highest water flux, which was ~15 L/(h.m2). Meanwhile, no water flux was observed after three hours when pure CA membrane was used in a dead-end filtration cell. In conclusion, EDTA is a promising additive in improving the hydrophilicity of membranes.

Dialysis Membranes Influence Perfluorochemical Concentrations and Liver Function in Patients on Hemodialysis

Introduction: Perfluoro-octanesulfonate (PFOS) and perfluoro-octanoic acid (PFOA) are two toxic perfluorochemicals (PFCs) commonly used as surfactants. PFCs are difficult to be eliminated from the body. We investigated the influence of different dialysis membranes on the concentrations of PFCs in patients under hemodialysis. Method: We enrolled 98 patients. Of these, 58 patients used hydrophobic polysulfone (PS) dialysis membranes, and the other 40 had hydrophilic membranes made by poly-methyl methacrylate (PMMA) or cellulose triacetate (CTA). Liquid chromatography tandem mass spectrometry coupled was used with isotope dilution to quantify PFOA and PFOS. Results: The predialysis concentrations of PFOA and PFOS in patients with hydrophobic PS dialysis membranes were 0.50 and 15.77 ng/mL, respectively, lower than the concentrations of 0.81 and 22.70 ng/mL, respectively, in those who used hydrophilic membranes (such as CTA or PMMA). Older patients have higher PFOS and poorer body function, with lower Karnofsky Performance Status Scale (KPSS) scores. The demographic data of the two groups were similar. However, patients with hydrophobic PS dialysis membranes had lower predialysis aspartate transaminase (AST) (p = 0.036), lower glucose levels (p = 0.017), and better body function (nonsignificantly higher KPSS scores, p = 0.091) compared with patients who used other membranes. These differences may be associated with the effects of different membranes, because PFOA positively correlated with AST, while PFOS negatively correlated with body function. Conclusions: This is the first study comparing PFC levels in uremic patients with different dialysis membrane. PS membrane may provide better clearance of PFCs and may, therefore, be beneficial for patients.

Semi-Continuous Reverse Membrane Bioreactor in Two-Stage Anaerobic Digestion of Citrus Waste

The presence of an antimicrobial compound called D-Limonene in citrus waste inhibits methane production from such waste in anaerobic digestion. In this work, a two-stage anaerobic digestion method is developed using reverse membrane bioreactors (rMBRs) containing cells encased in hydrophilic membranes. The purpose of encasement is to retain a high cell concentration inside the bioreactor. The effectiveness of rMBRs in reducing cell washout is evaluated. Three different system configurations, comprising rMBRs, freely suspended cells (FCs), and a combination of both (abbreviated to rMBR–FCs), are incubated at three different organic loading rates (OLRs) each, namely 0.6, 1.2, and 3.6 g COD/(L cycle). Incubation lasts for eight feeding cycles at 55 °C. Methane yield and biogas composition results show that rMBRs perform better than rMBR–FCs and FCs at all three OLRs. Volatile fatty acid profiles and H2 production show that the reactors are working properly and no upset occurs. Additionally, a short digestion time of 4 days can be achieved using the rMBR configuration in this study.

Thermo-osmosis in Membrane Systems: A Review

We give a first review of experimental results for a phenomenon little explored in the literature, namely thermal osmosis or thermo-osmosis. Such systems are now getting increased attention because of their ability to use waste heat for separation purposes. We show that this volume transport of a solution or a pure liquid caused by a temperature difference across a membrane can be understood as a property of the membrane system, i. e. the membrane with its adjacent solutions. We present experimental values found in the literature of thermo-osmotic coefficients of neutral and hydrophobic as well as charged and hydrophilic membranes, with water and other permeant fluids as well as electrolyte solutions. We propose that the coefficient can be qualitatively explained by a formula that contains the entropy of adsorption of permeant into the membrane, the hydraulic permeability, and a factor that depends on the interface resistance to heat transfer. A variation in the entropy of adsorption with hydrophobic/hydrophilic membranes and structure breaking/structure making cations could then explain the sign of the permeant flux. Systematic experiments in the field are lacking and we propose an experimental program to mend this situation.