C. Güell

Membrane fouling by turbidity constituents of beer and wine: characterization and prevention by means of infrasonic pulsing

Abstract During microfiltration of fermented beverages such as beer and wine, colloidal turbidity constituents play an important role in membrane fouling and therefore hinder the permeate flux. This paper studies polymeric membrane fouling by turbidity constituents of beer and wine and proposes a fouling prevention method to improve permeate flux. The model turbidity suspensions, based on gelatin and tannic acid, were microfiltered in a stirred cell using 0.2 μm cellulose acetate (CA), polyvinylidene di-fluoride (PVDF) and polycarbonate (PC) membranes under constant pressure (0.79 bar) and agitation (1350 rpm). Fouling caused by either a separate protein solution or a separate polyphenol solution was considerably lower than the fouling caused by a solution of both at the same concentration, which suggests that fouling is mainly caused by light scattering complexes formed by polyphenols and proteins. In all cases, during the microfiltration of model turbidity suspensions, the internal fouling mechanism dominated first and this was later followed by a period of external fouling. It was shown that membrane fouling depends strongly on the initial turbidity of the solution. A lower turbidity of the model solution resulted in a lower final total resistance. The initial turbidity also influenced the duration of the initial period of internal fouling. For the lower turbidity model solutions internal fouling lasted longer. An infrasonic pulsing was applied to remove foulant cake and improve permeate flux during microfiltration of model turbidity suspensions, and wine and beer samples. In infrasonic pulsing, high frequency pulses of permeate are periodically sent back in the direction of the membrane at a lower pressure than the transmembrane pressure. This causes the membrane to vibrate rapidly and removes a portion of the foulant cake. The model turbidity suspension (33±2 NTU) was filtered through a flat-sheet PVDF membrane at a transmembrane pressure of 0.65 bar. In the experiments with infrasonic pulsing a 0.2 duty cycle (Φ) was used. The improvement in net permeate flux depended on the infrasonic pulse frequency. For the highest frequency (6.67 Hz) net permeate flux improved fourfold in comparison with long-term permeate flux in normal cross-flow. These data fitted very well to the theoretical model first published by Czekaj [Reduccion del Ensuciamiento de Membranas Polimericas en Procesos de Microfiltracion Tangencial de Suspensiones Biologicas Mediante Utilizacion de Infrasonidos y de la Tecnica de Flujo Transversal, PhD Thesis, Universitat Rovira i Virgili, Spain] Experiments with wine and beer samples filtered through a PS hollow fiber membrane yielded approximately 2.4 and 2.1 times larger permeate fluxes with infrasonic pulsing than with normal cross-flow.

Oxidation of activated carbon: application to vinegar decolorization

This article reports studies on the feasibility of increasing the decoloring capacity of a granular activated carbon (GAC) by using oxidation with air at 350 degrees C to modify its surface activity and porosity. The GAC, obtained from olive stones, had a maximum decolorization capacity of 92% for doses of 20 g/l, while the maximum decolorization capacity of the modified granular activated carbon (MGAC) was about 96% at a dose of 10 g/l. The increase in decoloring capacity is thought to be due to an increase in mesopore area (from 129 to 340 m2/g) in the MGAC. The maximum decoloring values and the doses needed to attain them are very close to values obtained in previous studies using coconut shell powder-activated carbon (94 and 98% for red and white vinegar for a dose of 10 g/l, respectively).

Continuous vinegar decolorization with exchange resins

Vinegar decoloring by adsorption with exchange resins was studied and the decoloring capacity of three commercial resins as adsorbent material evaluated. The regeneration of the resins was also studied. The decoloring capacity of the selected resin (Lewatit S-6328-A) was compared with a powder activated carbon which is currently used as an adsorbent in the vinegar industry for decolorization. For a batch process with white and rose vinegars with resin Lewatit S-6328-A (10 g/l for white and 20 g/l for rose) at equilibrium the maximum decolorization efficiency was 69% and 72%, respectively. In the continuous process with a packed column on bench scale, the pseudo-contact time (ratio resin volume and vinegar flow-rate) is the operation factor which determines the decolorization level. The maximum level of decolorization for white and rose vinegars in continuous process was practically the same. The pseudo-contact time required to obtain the maximum decolorization for rose vinegar was almost three times that required for white vinegar. The adsorption of coloured compounds with exchange resins in continuous packed columns seems to be technically feasible, and the results of this work form the backbone of subsequent studies of scaling up for vinegar decolorization. The possibility of packing the resins into a column means that a new continuous process can be used for vinegar decolorization.

Direct formulation of a solid foodstuff with phenolic-rich multicomponent solutions from grape seed: effects on composition and antioxidant properties.

The aim of our work was to supplement a solid foodstuff with grape phenolics by osmotic treatment with an aqueous solution made of osmo-active agents (NaCl and sucrose) and a commercial grape seed extract. To investigate how the composition of the osmotic solution affected phenolic infusion, experimental conditions were set by a central composite design with two factors (the molality of NaCl and sucrose in the osmotic solution). In all experiments, the total phenolic content in the osmotic solution was kept constant (6300 +/- 45 mg gallic acid equivalents/kg), and the model food (an agar-agar gel) was processed for 8 h. Throughout the response surface, the osmo-treated model food was significantly supplemented with flavan-3-ols. At the central point of the experimental design, flavan-3-ol monomers and dimers were found in concentrations of 1334 +/- 126 and 486 +/- 55 mg/kg, respectively. Their penetration into the model food was limited by sucrose to a different extent. The Trolox equivalent antioxidant capacity of the osmo-treated gel was higher than that of fruits with a very high free radical scavenging activity.

Note. Vinegar Decolourization by Re-Activated Carbon

This paper describes a batch-system for the decolouring of vinegar with modified activated carbons. The carbon was modified using controlled oxidation with a mixture of Ar/air at a temperature of 350°C. The porosity and functionality of the carbon obtained was studied by nitrogen physisorption and FTIR. The BET area increased from 625 to 1126 m2/g and the functionality also increased, giving new bands around 1700, 1200, 1450 and 1550 cm-1, which contained most of the information about the functionality assignments of the activated carbons. The decolouring efficiency (DE) of a modified pelleted activated carbon (85.9 ± 2.2%) increased with respect to nonmodified pelleted activated carbon (14.1 ± 4.2%). This increase in DE is related to the increase in both the BET area and the functionality.

Application of pervaporation and osmotic membrane distillation to the regeneration of spent solutions from the osmotic food dehydration

Application of pervaporation and osmotic membrane distillation to the regeneration of spent solutions from the osmotic food dehydration Results of pervaporation (PV) of sucrose and calcium chloride spent solutions were presented. Additionally, osmotic membrane distillation (OMD) of sucrose solutions was investigated. It was found that the regeneration of spent sucrose solution for the reuse is possible by using PV or OMD processes. However, OMD process produces another spent stream i.e. CaCl2. Pervaporation membranes showed fluxes in the range of 0.5 - 0.9 kg m-2 h-1 in contact with 40° Brix sucrose solution, whereas OMD water permeate fluxes were in the range of 4 - 5 kg m-2 h-1 for the same feed concentration. Two different hybrid processes were suggested: i) pretreatment followed by OMD reconcentration of spent sucrose solution and independently PV for CaCl2 regeneration; ii) membrane pretreatment (MP) followed by PV of sucrose solution. Based on the experimental results, the membrane areas for both systems were calculated and compared. MP-PV system seems to be a better solution for the spent mixtures management.