Fouling study of nanofiltration membranes for sugar control in grape must: Analysis of resistances and the role of osmotic pressure

Producción CientíficaThree membranes are analyzed attending to their retention, flux and fouling when used to nanofiltrate sugars in red grape musts. With high molecular weight compounds, fouling develops from initial pore blocking to final cake deposition. A decrease of resistance appears due to a decrease of the effective transmembrane pressure and cake compaction. The final effective pore size corresponds to that of the compacted cake. Attending to flux decay and sugar retention, two membranes, HL and SR3, are appropriate to reduce the content of sugar of red must. Specifically SR3 shows the best passage of sugar and less foulingJunta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA302U13

Alcohol reduction in red and white wines bynanofiltration of musts before fermentation

Producción CientíficaOne of the consequences of global warming is the early ripening of grapes which promotes a sugar content increase. Fermentation of their must leads to wines with an alcoholic degree higher than desired. The scope of this study is to select a nanofiltration (NF) technique to reduce the alcohol content of wines approximately 2 degrees by controlling the sugar content of grape must before its fermentation. For this purpose the performance of single-stage and two-stage NF processes using a spiral wound membrane unit were compared for white must (Spanish Verdejo) while for red must (Spanish Garnacha) a two-stage procedure was tested. During the singlestage NF intermittent backflush due to the osmotic pressure effect was tested. Results showed that backflushing had an undesirable effect because it increased the flux decay by disturbing the cake stabilization on the membrane. The corresponding wines obtained by adequate mixing of permeated and retained or control musts showed a 1 to 2 degrees alcohol reduction. Sensory evaluation and principal component analysis (PCA) revealed that there were no significant differences between the control and the filtered wines. Among the processes studied, the best NF technique was the two-stage process without backflush.Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA248U13

Recent advances in membrane-based biogas and biohydrogen upgrading

Producción CientíficaBiogas and biohydrogen, due to their renewable nature and zero carbon footprint, are considered two of the gaseous biofuels that will replace conventional fossil fuels. Biogas from anaerobic digestion must be purified and converted into high-quality biomethane prior to use as a vehicle fuel or injection into natural gas networks. Likewise, the enrichment of biohydrogen from dark fermentation requires the removal of CO2, which is the main pollutant of this new gaseous biofuel. Currently, the removal of CO2 from both biogas and biohydrogen is carried out by means of physical/chemical technologies, which exhibit high operating costs and corrosion problems. Biological technologies for CO2 removal from biogas, such as photosynthetic enrichment and hydrogenotrophic enrichment, are still in an experimental development phase. In this context, membrane separation has emerged as the only physical/chemical technology with the potential to improve the performance of CO2 separation from both biogas and biohydrogen, and to reduce investment and operating costs, as a result of the recent advances in the field of nanotechnology and materials science. This review will focus on the fundamentals, potential and limitations of CO2 and H2 membrane separation technologies. The latest advances on membrane materials for biogas and biohydrogen purification will be systematically reviewed.Ministerio de Ciencia e Innovación/Agencia Estatal de Investigación (AEI)/10.13039/501100011033 - (projects PID2019- 109403RB-C21)Junta de Castilla y León y Fondo Europeo de Desarrollo Regional (FEDER) - (grant CLU2017-09, UIC082, CL-EI-2021-07 and UIC 315

A systematic study of ammonia recovery from anaerobic digestate using membrane-based separation

Producción CientíficaAmmonia recovery from synthetic and real anaerobic digestates was accomplished using hydrophobic flat sheet membranes operated with H2SO4 solutions to convert ammonia into ammonium sulphate. The influence of the membrane material, flow rate (0.007, 0.015, 0.030 and 0.045 m3 h−1) and pH (7.6, 8.9, 10 and 11) of the digestate on ammonia recovery was investigated. The process was carried out with a flat sheet configuration at a temperature of 35 °C and with a 1 M, or 0.005 M, H2SO4 solution on the other side of the membrane. Polytetrafluoroethylene membranes with a nominal pore radius of 0.22 µm provided ammonia recoveries from synthetic and real digestates of 84.6% ± 1.0% and 71.6% ± 0.3%, respectively, for a membrane area of 8.6 × 10−4 m2 and a reservoir volume of 0.5 L, in 3.5 h with a 1 M H2SO4 solution and a recirculation flow on the feed side of the membrane of 0.030 m3 h−1. NH3 recovery followed first order kinetics and was faster at higher pHs of the H2SO4 solution and recirculation flow rate on the membrane feed side. Fouling resulted in changes in membrane surface morphology and pore size, which were confirmed by Atomic Force Microscopy and Air Displacement Porometry.Junta de Castilla y León - FEDER (VA088G19, CLU 2017-09 y UIC 071)Ministerio de Ciencia e Innovación (proyecto: PID2019-109403RB-C21/AEI/10.13039/501100011033

Evaluation of forward osmosis and low-pressure reverse osmosis with a tubular membrane for the concentration of municipal lwastewater and the production of biogas

Producción CientíficaCurrently, freshwater scarcity is one of the main issues that the world population has to face. To address this issue, new wastewater treatment technologies have been developed such as membrane processes. Among them, due to the energy disadvantages of pressure-driven membrane processes, Forward Osmosis (FO) and Low-Pressure Reverse Osmosis (LPRO) have been introduced as promising alternatives. In this study, the behavior of a 2.3 m2 tubular membrane TFO-D90 when working with municipal wastewater has been studied. Its performances have been evaluated and compared in two operating modes such as FO and LPRO. Parameters such as fouling, flow rates, water flux, draw solution concentration, organic matter concentration, as well as its recovery have been studied. In addition, the biogas production capacity has been evaluated with the concentrated municipal wastewater obtained from each process. The results of this study indicate that the membrane can work in both processes (FO and LPRO) but, from the energy and productivity point of view, FO is considered more appropriate mainly due to its lower fouling level. This research may offer a new point of view on low-energy and energy recovery wastewater treatment and the applicability of FO and LPRO for wastewater concentration.Junta de Castilla y León y Fondo Europeo de Desarrollo Regional (FEDER) - (grant CLU 2017-09, CL-EI-2021-07, VA088G19, and UIC 082 and UIC 334)Ministerio de Ciencia e Innovación - (project PID2019-109403RB-C21/AEI/10.13039/501100011033

Prediction of single salt rejection in nanofiltration membranes by independent measurements

Producción CientíficaIn this work amethod is proposed to predict salt rejection by nanofiltration. The procedure starts fromthe steric, electric and dielectric exclusion model with charge (and permitivity) depending on the concentration along the pore, SEDE-VCh, for membrane characterization, and substitutes all fitting parameters by values obtained by independent methods. These parameters are the relative permittivity inside the pores and the two constants of the Freundlich isothermfor the volumetric charge density,which can be obtained by impedance spectroscopy techniques. Moreover, the pore size and shape and the active layer thickness are required to complement the model. The pore size was obtained by using a neutral solute rejection test and the active layer thickness was estimated by SEM. Therefore, the model also requires pore shape as input. AFM measurements suggest the assumption of a slit shape for the pores. A Desal-HL membrane has been structurally, electrically and functionally characterized. These data allowed the testing of the predictive model that was subsequently demonstrated; as far as results are good enough considering the complexity of the mechanisms involved. Consequently, it seems clear that once the model parameters have been obtained by independent methods, it can be used as a predictive tool.Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA302U13

Fabrication and characterization of polyethersulfone nanocomposite membranes for the removal of endocrine disrupting micropollutants from wastewater. Mechanisms and performance

Producción CientíficaThe addition of carbon nanotubes to improves the removal and adsorption of endocrine disrupting micropollutants (bisphenol A and nonylphenol). Increasing the SWCNT (single walled carbon nanotubes) content increases removal and diminishes reversible and irreversible fouling. The isoelectric point of the SWCNT containing membranes decreases when the content of nanotubes increases with more negative charges at alkaline pH. Because, the nanotube loaded membranes are also less hydrophilic and bisphenol and nonylphenol are hydrophobous, adsorption plays a key role in the removal of micropollutants. An increase in the transmembrane applied pressure decreases the removal and more steeply for the membranes containing more SWCNT. Higher porosities, leading to higher water permeabilities, are also obtained for more loaded membranes. Too high SWCNT contents lead to a saturation and decrease of removal probably because high porosities lead to a decrease in adsorption due to both a decrease in the available surface and a sweeping action of convection through the membrane.Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA302U13

Flux Kinetics, Limit and Critical F 1 luxes for Low Pressure Dead-end Microfiltration. 2 The case of BSA Filtration through a Positively Charged Membrane

Producción CientíficaThe influence of the applied pressure on the flux decay mechanism during Bovine Serum Albumin (BSA) dead-end microfiltration (MF) has been investigated for a polyethersulfone, positively charged, membrane (SB-6407) from Pall®11 . BSA solutions, at pH values of 4, 5 (very close to the protein isoelectric point, IEP) and 6, were micro-filtered through the membrane at different low applied transmembrane pressures. Although filtration was done in dead-end configuration, limit fluxes appeared for all pressures and pH values studied. The concepts of (long time) limit and critical fluxes and their correlation have been clarified and analysed too. The usual blocking filtration laws have been included in a common frame and both the cases with zero or non-zero limit fluxes have been incorporated. Within this frame, the standard model, that assumes an internal pore deposition, has been included as well; although, in our case, the acting mechanism seems to be mainly the so called complete blocking. Protein adsorption has been analysed in terms of the protein-protein and protein-membrane electrostatic interactions. There is a faster flux-decay for the protein isoelectric point with a slightly slower decline in flux when there are both membrane-to-protein and protein-protein repulsion. The slowest kinetics appears for membrane-to-protein attraction with protein-protein repulsion. Moreover, adsorption is stronger, and the limit flux smaller, when the protein is attracted towards the membrane and there is protein-protein repulsion.Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA302U13

Comparative study of red grape mustnanofiltration: Laboratory and pilot plant scales

Producción CientíficaA consequence of global warming is the early ripening of grapes which promotes, among others, a higher fermentablesugar (glucose and fructose) content. This leads to wines with an alcoholic degree higher than desired.In this work, the main differences between red grape must nanofiltration at laboratory and pilot plant scale werestudied in order to perform the scale-up of a nanofiltration process to reduce the sugar content. For this, previousresults of the nanofiltration of commercial red must using the SR3 membrane in a flat sheet crossflow module werecompared with those obtained for the filtration of natural red must using the same membrane in a spiral woundmodule at two different applied pressures.The aim of this publication is to analyze the main differences between red grape must nanofiltration at laboratoryand at pilot plant scale.Results: showed that the flow destabilization and eddy promotion caused by spacers in the spiral wound modulemitigate the rate at which the cake thickens and compacts on the membrane surface. This causes a less sharp fluxdecrease, less variable sugars rejection and osmotic pressure difference. Moreover, higher applied pressure promotesa higher membrane fouling and osmotic pressure that worsen the flux decayJunta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA248U13