Prediction of ultrafiltration performance during clarification of stevia extract

Membrane separation processes for the extraction and purification of steviol glycosides: an overview

Steviol glycosides (SGs), as natural sweeteners from Stevia rebaudiana, are currently employed for replacing sugar and its derivatives in several food products and formulations. Such compounds play an essential role in human health. Their usage provides a positive effect on preventing diseases related to sugar consumption, including diabetes mellitus, cancer, and lipid metabolism disorders. The traditional extraction of SGs is performed by means of solvent extraction, which limits their application since the removal of residual solvents is a challenging task requiring further downstream purification steps. In addition, the presence of residual solvents negatively affects the quality of such compounds. Today, food technicians are looking for innovative and improved techniques for the extraction, recovery and purification of SGs. Membrane-based technologies, including microfiltration, ultrafiltration, and nanofiltration, have long been proven to be a valid alternative for efficient extraction and purification of several high added-value molecules from natural sources. Such processes and their possible coupling in integrated membrane systems have been successfully involved in recovery protocols of several compounds, such as metabolites, polyphenols, anthocyanins, natural pigments, proteins, from different sources (e.g., agro-food wastes, plant extracts, fruits, fermentation broths, among others). Herein, we aim to review the current progresses and developments about the extraction of SGs with membrane operations. Our attention has been paid to the latest insights in the field. Furthermore, key process parameters influencing the extraction and purification of SGs are also discussed in detail.

Simultaneous removal of Cd (II) and p-cresol from wastewater by micellar-enhanced ultrafiltration using rhamnolipid: Flux decline, adsorption kinetics and isotherm studies

Flux decline due to membrane fouling by surfactant micelles is the major problem limiting the use of micellar enhanced ultrafiltration (MEUF) for the treatment of wastewater. Understanding of underlying mechanisms of membrane fouling, adsorption kinetics and adsorption isotherm are very important for the successful application of MEUF studies. In the present study, an unsteady state model considering sequential occurrence of complete pore blocking and gel layer formation was proposed for explaining flux decline behavior during rhamnolipid based MEUF for simultaneous removal of Cd⁺² and p-cresol from aqueous solution under batch concentration mode. The model was developed based on the Hermia's complete pore blocking model and resistance-in-series model coupled with gel layer theory incorporating the effects of feed temperature, variation of viscosity and retentate concentration with time, and pressure dependent mass transfer coefficient. A good agreement between the experimental data and model predictions was demonstrated. The effects of operating conditions were found to have a significant effect on the flux decline behavior and onset of gel layer formation. The use of ultrafiltration membrane for the study of adsorption kinetics and adsorption isotherm was demonstrated. Kinetic studies disclosed that both Cd⁺² and p-cresol adsorption was better described by the pseudo-second order model for both single and binary solution. The results of isotherm studies revealed that adsorption of both Cd⁺² and p-cresol was spontaneous in nature and equilibrium data was best fitted by Langmuir model with the maximum adsorption capacity of RHL vesicles of 208.33 and 53.27 mg g^-1 for Cd⁺² and p-cresol, respectively at 299 K. The model parameters of membrane fouling, adsorption kinetics and adsorption isotherm evaluated in this study could be useful in designing and scale up of RHL based MEUF process.

Influence of bentonite in polymer membranes for effective treatment of car wash effluent to protect the ecosystem

In this study, modified polyethersulfone (PES) and cellulose acetate (CA) membranes were used in the treatment of car wash effluent using ultrafiltration. Hydrophilic sulfonated poly ether ether ketone (SPEEK) and bentonite as nanoclay were used as additives for the PES and CA membrane modification. Performances of modified membranes were compared with commercial PES membrane with 10kDa molecular weight cut off (MWCO). The influencing parameters like stirrer speed (250-750rpm) and transmembrane pressure (100-600kPa) (TMP) were varied and their effects were studied as a function of flux. In the treatment of car wash effluent, a higher permeate flux of 52.3L/m(2)h was obtained for modified CA membrane at TMP of 400kPa and stirrer speed of 750rpm. In comparison with modified PES membrane and commercial PES membrane, modified CA membranes showed better performance in terms of flux and flux recovery ratio. The highest COD removal (60%) was obtained for modified CA membrane and a lowest COD removal (47%) was observed for commercial PES membrane. The modified membranes were better at removing COD, turbidity and maintained more stable flux than commercial PES membrane, suggesting they will provide better economic performance in car wash effluent reclamation.