Membrane Bioreactor for Simultaneous Synthesis and Fractionation of Oligosaccharides.

Galacto-oligosaccharides (GOS) are prebiotic sugars obtained enzymatically from lactose and used in food industry due to their nutritional advantages or technological properties. Selective mass transport and enzymatic synthesis were integrated and followed using a membrane bioreactor, so that selective removal of reaction products may lead to increased conversions of product-inhibited or thermodynamically unfavorable reactions. GOS syntheses were conducted on lactose solutions (150 g·L-1) at 40 °C and 10 Uß-galactosidase.mL-1, and sugar fractionation was performed by cellulose acetate membranes. Effects of pressure (20; 24 bar) and crossflow velocity (1.7; 2.0; 2.4 m·s-1) on bioreactor performance were studied. Simultaneous GOS synthesis and production fractionation increased GOS production by 60%, in comparison to the same reactions promoted without permeation. The presence of a high-molecular-weight solute, the enzyme, in association with high total sugar concentration, leads to complex selective mass transfer characteristics. Without the enzyme, the membrane presented tight ultrafiltration characteristics, permeating mono- and disaccharides and retaining just 25% of trisaccharides. During simultaneous synthesis and fractionation, GOS-3 were totally retained, and GOS-2 and monosaccharides were retained at 80% and 40%, respectively. GOS synthesis-hydrolysis evolution was strongly dependent on crossflow velocity at 20 bar but became fairly independent at 24 bar.

The Effect of pH on Atenolol/Nanofiltration Membranes Affinity.

Nanofiltration has been shown to be effective in removing pharmaceutical compounds from water and wastewater, so different mechanisms can influence treatment performance. In the present work, we carried out a case study evaluating the performance of two nanofiltration membranes in the removal of Atenolol (ATN)-a pharmaceutical compound widely used for the treatment of arterial hypertension-under different conditions such as operating pressure, ATN concentration, and solution pH. By determining the B parameter, which quantifies the solute/membrane affinity, we verified that the solution pH influenced the performance of the membranes, promoting attraction or repulsion between the ATN and the membranes. At pH 2.5, both membranes and ATN were positively charged, causing electrostatic repulsion, showing lower values of the B parameter and, consequently, higher ATN rejections. At such a pH, the mean ATN rejection for the loose membrane (NF270) was 82%, while for the tight membrane (NF90) it was 88%. On the other hand, at 12 bar pressure, the NF70 membrane (5.1 × 10 -5 m s-1) presented mean permeate fluxes about 2.8 times greater than the NF90 membrane (1.8 × 10-5 m s-1), indicating that NF270 is the most suitable membrane for this application.

Experimental Design as a Tool for Optimizing and Predicting the Nanofiltration Performance by Treating Antibiotic-Containing Wastewater.

In recent years, there has been an increase in studies regarding nanofiltration-based processes for removing antibiotics and other pharmaceutical compounds from water and wastewater. In this work, a 2k factorial design with five control factors (antibiotic molecular weight and concentration, nanofiltration (NF) membrane, feed flow rate, and transmembrane pressure) was employed to optimize the NF performance on the treatment of antibiotic-containing wastewater. The resulting multiple linear regression model was used to predict the antibiotic rejections and permeate fluxes. Additional experiments, using the same membranes and the same antibiotics, but under different conditions of transmembrane pressure, feed flow rate, and antibiotic concentration regarding the 2k factorial design were carried out to validate the model developed. The model was also evaluated as a tertiary treatment of urban wastewater for removing sulfamethoxazole and norfloxacin. Considering all the conditions investigated, the tightest membrane (NF97) showed higher antibiotics rejection (>97%) and lower permeate fluxes. On the contrary, the loose NF270 membrane presented lower rejections to sulfamethoxazole, the smallest antibiotic, varying from 65% to 97%, and permeate fluxes that were about three-fold higher than the NF97 membrane. The good agreement between predicted and experimental values (R2 > 0.97) makes the model developed in the present work a tool to predict the NF performance when treating antibiotic-containing wastewater.

Atenolol removal by nanofiltration: a case-specific mass transfer correlation.

Concentration polarization is a phenomenon inherent to membrane separation operations and as a precursor of membrane fouling is frequently related to the decrease in the performance of these operations. In the present work, a case-specific mass transfer correlation was developed to assess the concentration polarization when nanofiltration, in different operating conditions, was applied to treat a pharmaceutical wastewater containing atenolol. NF runs with two membranes, two atenolol concentrations and three feed circulating velocities were conducted, and the corresponding experimental mass transfer coefficients were determined using film theory to describe the concentration polarization phenomenon. Higher velocities led to higher mass transfer coefficients and, consequently, lower concentration polarization. These mass transfer coefficients were correlated with the circulating velocity (Re), the solute diffusivity (Sc) and the membrane permeability (LP +) (the membrane is a permeable interface with effect on the concentration profiles developed from the interface towards the bulk feed), yielding the following correlation Sh = 1.98 × 104Re0.5Sc0.33LP +0.32. The good agreement between the calculated and the experimental results makes this correlation a valuable tool for water practitioners to predict and control the concentration polarization during atenolol-rich wastewater treatment by nanofiltration, thereby increasing its productivity and selectivity.

Wine lees from the 1st and 2nd rackings: valuable by-products.

Phenolic compounds of the first and second racking wine lees, including anthocyanins, were qualitatively and quantitatively analyzed by HPLC-DAD-MS. Wine lees from both rackings displayed similar chromatographic profiles. Therefore, it was impossible to differentiate the qualitative results regarding phenolic compounds. On the other hand, those from the second racking presented, on average, concentration of polyphenols twice as high. While the ones from the first racking displayed ca. 1600 mg phenolic compounds and 400 mg anthocyanins per kg of dry matter, those from the second racking have shown ca. 3300 mg phenolic compounds and 700 mg anthocyanins per kg of dry matter. These outcomes indicate that, although the wine lees from the first racking can be employed as a resource for phenolic compounds recovery, those from the second racking are more appropriate for this purpose.

Concentration Polarization in Ultrafiltration/Nanofiltration for the Recovery of Polyphenols from Winery Wastewaters.

Concentration polarization is intrinsically associated with the selective character of membranes and often means flux decline and which causes a subsequent decrease of ultrafiltration and nanofiltration performance. More important is the fact that it acts as a precursor of membrane fouling and creates severe fouling problems in the longer times range. The quantification of its dependence on the operating parameters of cross-flow velocities and transmembrane pressures makes recourse to the film theory to introduce mass-transfer coefficients that generally are calculated by dimensionless correlations of the Sherwood number as a function of the Reynolds and Schmidt numbers. In the present work, the mass-transfer coefficients are obtained through the fitting of experimental results by the pressure variation method. The ultrafiltration/nanofiltration of the winery wastewaters from the racking operation is carried out with the membranes ETNA 01PP (Alfa Laval) and NF 270 (Dow Filmtec) under a wide range of cross-flow velocities and transmembrane pressures up to 15 bar.