Total Recirculation Mode Research Articles

Reverse osmosis and nanofiltration opportunities to concentrate multicomponent mixtures of volatile fatty acids

The application of reverse osmosis (RO) and nanofiltration (NF) to concentrate and/or fractionate volatile fatty acids (VFAs, occurring in acidogenic effluents) was systematically assessed for the first time using three commercial spiral wound modules. A bench scale plant was used to test the polyamide membrane cartridges, namely: AG1812-34D, DK1812-34D and NFS-3B-1812F. The effects of main operational parameters (pH, temperature, applied pressure) were firstly studied in total recirculation mode, using different total and relative VFA compositions. Thereafter, batch concentration tests were carried out (at constant applied pressure, ca. 30 bar) to fully characterize the RO and NF modules. AG1812-34D performed as an RO module and it allowed concentrating target solutions almost 3 times without relevant VFA losses (<4%) in the permeate side. All tested parameters were observed to affect concentration performances. However, typical pH levels occurring in acidogenic effluents allowed to achieve fully satisfactory VFA rejections. DK1812-34D and NFS-3B-1812F performed as NF modules and could represent suitable solutions for VFA fractionation. Separation factors significantly increased by pH rise; in particular, high acetic and propionic acid separation factors over butyric acid were achieved at pH 9, with DK1812-34D module.

Performance of ultrafiltration as a pre-concentration stage for the treatment of oxyfluorfen by electrochemical BDD oxidation

The present work deals with the use of ultrafiltration as a pre-concentration stage in the electrochemical degradation of a non-polar organochlorine compound (oxyfluorfen) with boron-doped diamond (BDD) anodes. The first stage of the work consisted in evaluating the performance of a pilot scale ultrafiltration unit to concentrate a solution of a commercial formulation of oxyfluorfen (Barre®) at total recirculation mode. The ultrafiltration membrane exhibited a total rejection of oxyfluorfen, around 70% rejection of TOC and a permeate flux of 285.1 L h−1 m−2 at 4 bar and 25 °C. The rejection of oxyfluorfen is higher than expected due to the presence of surfactant compounds in the commercial formulation selected, which promotes a mechanism of micellar enhanced ultrafiltration. Next, a discontinuous ultrafiltration test was performed, maintaining this high rejection of oxyfluorfen and observing a limited contribution of fouling mechanisms, according to the adjustment of the data to fouling models. Regarding the electrochemical oxidation of the concentrate with BDD anodes, it was observed an increase in the specific power consumption from 590 kWh kg−1 for the raw solution to 882 kWh kg−1 for the concentrate. This unexpected result can be explained due to the limited rejection of the soluble fraction in the ultrafiltration stage, what produced a lower concurrence of oxidants in the electrochemical oxidation step. According to these results, it can be stated that it is worth using ultrafiltration as a concentration stage for commercial formulations of non-polar organochlorines with both high rejection and flux, although it should be combined with degradation technologies different from electrochemical oxidation.

Modelling of a recirculating photocatalytic microreactor implementing mesoporous N-TiO2 modified with graphene

• Photocatalytic degradation of 4-nitrophenol in microreactor under solar irradiation. • The used CFD model incorporates total recirculation mode of operation. • The CFD model accounts for adsorption in the dark. • The CFD model predicts experimental data in a wide range of reactant concentrations. The use of microreactors in (photo)catalytic processes offers new possibilities for studying and optimizing many mass and photon transfer limited reactions. In this study, we propose a scalable computational fluid dynamics (CFD) model for the prediction of photocatalytic degradation of a model pollutant (4-nitrophenol) using immobilized N-doped TiO 2 grown over reduced graphene oxide (N-TiO 2 /rGO) in a photocatalytic microreactor working in continuous flow-recirculation mode. The mode of operation used in this study allows the reduction of mass transfer limitations inherent to heterogeneous photocatalytic reactions taking place on immobilized catalysts. A CFD model was developed for effective prediction of experimental results using COMSOL multi-physics. The experiment and the model results clearly showed a good agreement. The model parameters were determined through fitting the model with the experimental data, adsorption rate constants were estimated to be 1.76 × 10 4 m 3 mol −1 h −1 and 0.0252 h −1 for monolayer ( k ads,m and k des,m ), 1.76 × 10 4 m 3 mol −1 h −1 and 0.0126 h −1 for multilayer ( k ads,n and k des,n ); and the intrinsic rate constant ( k s ) was 2.02 h −1 . This proposed model herein could serve as a practical tool to improve and optimize an extensive number of photocatalytic reactions for (waste)water applications in microreactors operating in recirculation mode.

Optimization of Cheese Whey Ultrafltration/Diafltration for the Production of Beverage Liquid Protein Concentrates with Lactose Partially Removed

The processing of cheese whey pre-concentrated by reverse osmosis is carried out through ultrafiltration in diafiltration mode to produce whey protein concentrates with lower lactose content to be incorporated in beverages. The initial cheese whey protein and lactose contents are 2.13g/100g and 13.22g/100g, respectively.The commercial membranes, GR95PP, supplied by Alfa Laval, Denmark, were characterized in terms of a hydraulic permeability of 1.21 l/(h∙m^2∙bar) and a molecular weight cut-off of 7500 Dalton. The permeation tests were carried out in a plate and frame Lab-Unit 20 from Alfa Laval, Denmark, and a membrane surface area of 0.072 m2 was installed.The ultrafiltration of cheese whey in total recirculation mode yielded two asymptotic variations of the permeate fluxes versus the transmembrane pressure. For operating pressures up to 12 bar the permeate flux increases linearly with the pressure. Then, with the increasing pressure, they deviate from linearity and reach a limiting flux of 8.79 l/(h∙m^2∙bar) at 30 bar. The slope of the asymptotic linear variation is 0.48 l/(h∙m^2∙bar). To have minimal effects of concentration polarization the operating pressure was set-up at 12 bar.The optimization of ultrafiltration/diafiltration was carried out in terms of the volumetric concentration factors and the frequency of diavolumes addition. At a volumetric concentration factor of 1.32 the lactose content decreased from 13.22% to 5.7%.

Process efficiency of casein separation from milk using polymeric spiral-wound microfiltration membranes

Microfiltration is largely used to separate casein micelles from milk serum proteins (SP) to produce a casein-enriched retentate for cheese making and a permeate enriched in native SP. Skim milk microfiltration is typically performed with ceramic membranes and little information is available about the efficiency of spiral-wound (SW) membranes. We determined the effect of SW membrane pore size (0.1 and 0.2 µm) on milk protein separation in total recirculation mode with a transmembrane pressure gradient to evaluate the separation efficiency of milk proteins and energy consumption after repeated concentration and diafiltration (DF). Results obtained in total recirculation mode demonstrated that pore size diameter had no effect on the permeate flux, but a drastic loss of casein was observed in permeate for the 0.2-µm SW membrane. Concentration-DF experiments (concentration factor of 3.0× with 2 sequential DF) were performed with the optimal 0.1-µm SW membrane. We compared these results to previous data we generated with the 0.1-µm graded permeability (GP) membrane. Whereas casein rejection was similar for both membranes, SP rejection was higher for the 0.1-µm SW membrane (rejection coefficient of 0.75 to 0.79 for the 0.1-µm SW membrane versus 0.46 to 0.49 for the GP membrane). The 0.1-µm SW membrane consumed less energy (0.015-0.024 kWh/kg of permeate collected) than the GP membrane (0.077-0.143 kWh/kg of permeate collected). A techno-economic evaluation led us to conclude that the 0.1-µm SW membranes may represent a better option to concentrate casein for cheese milk; however, the GP membrane has greater permeability and its longer lifetime (about 10 yr) potentially makes it an interesting option.

Efficient treatment of perfluorohexanoic acid by nanofiltration followed by electrochemical degradation of the NF concentrate

The present study was aimed at the development of a strategy for removing and degrading perfluorohexanoic acid (PFHxA) from industrial process waters at concentrations in the range 60–200 mg L−1. The treatment train consisted of nanofiltration (NF) separation followed by electrochemical degradation of the NF concentrate. Using a laboratory-scale system and working in the total recirculation mode, the DowFilm NF270 membrane provided PFHxA rejections that varied in the range 96.6–99.4% as the operating pressure was increased from 2.5 to 20 bar. The NF operation in concentration mode enabled a volume reduction factor of 5 and increased the PFHxA concentration in the retentate to 870 mg L−1. Results showed that the increase in PFHxA concentration and the presence of calcium sulfate salts did not induce irreversible membrane fouling. The NF retentate was treated in a commercial undivided electrochemical cell provided with two parallel flow-by compartments separated by bipolar boron doped diamond (BDD) electrode, BDD counter anode, and counter cathode. Current densities ranging from 20 to 100 A m−2 were examined. The electrochemical degradation rate of PFHxA reached 98% and was accompanied by its efficient mineralization, as the reduction of total organic carbon was higher than 95%. Energy consumption, which was 15.2 kWh m−3 of treated NF concentrate, was minimized by selecting operation at 50 A m−2. While most of the previous research on the treatment of perfluoroalkyl substances (PFASs) focused on the removal of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS), these compounds have been phased out by chemical manufacturers. Our findings are relevant for the treatment of PFHxA, which appears to be one of the present alternatives to long-chain PFASs thanks to its lower bioaccumulative potential than PFOA and PFOS. However, PFHxA also behaves as a persistent pollutant. Moreover, our results highlight the potential of combining membrane separation and electrochemical oxidation for the efficient treatment of PFAS-impacted waters.

Pressure-driven membrane processes for the recovery of antioxidant compounds from winery effluents

Winery effluents are substantial sources for the recovery of antioxidant compounds, namely polyphenols and polysaccharides. In this study, aqueous extraction associated with microfiltration was used as a pretreatment for the recovery, by membrane processes, of polyphenols and polysaccharides present in effluents (wine lees) from the first racking of red winemaking. The study was carried out in total recirculation mode using a flat-sheet membrane and in concentration mode using a hollow fiber membrane. Although the most diluted permeates presented lower contents of polyphenols and polysaccharides, the solutes recovery did not follow this behavior. Higher dilution factors of the effluent resulted in higher permeate fluxes as well as in higher polyphenols recovery. At the best conditions, a solution diluted 50 V/V followed by microfiltration led to the achievement of a limpid permeate, representing a recovery of 1 g of polyphenols and 1 g of polysaccharides per liter of raw effluent.

Microfiltration for the recovery of polyphenols from winery effluents

Winery effluents are attractive sources for the recovery of antioxidant compounds, particularly polyphenols. In this study, the aqueous extraction associated with microfiltration for the recovery of polyphenols present in the effluent (wine lees) from the second racking of red winemaking was investigated. To decrease the charge of the suspended solids and then use the effluent as feed for the microfiltration, dilutions combined with vacuum filtration were tested. In total recirculation mode, two flat-sheet microfiltration membranes (V0.2 and MFP5 membranes) were studied, while in concentration mode a hollow fiber membrane (PAM-Membranas Seletivas) was used. Higher dilution factors of the effluent resulted in higher permeate fluxes, and the membrane with a larger pore size showed higher propensity to fouling. At the optimal conditions, a solution diluted 10v/v followed by microfiltration led to the achievement of a limpid permeate, rich in polyphenols. This represents a recovery rate of 21% of the total content of polyphenols.

Detoxification of hemicellulosic hydrolysates from extracted olive pomace by diananofiltration

Xylitol can be obtained from the pentose-rich hemicellulosic fraction of agricultural residues, such as extracted olive pomace, by fermentation. Dilute acid hydrolysis of lignocellulosic materials, produces the release of potential inhibitory compounds mainly furan derivatives, aliphatic acids, and phenolic compounds. In order to study the potential on the increase of the hydrolysate fermentability, detoxification experiments based on diananofiltration membrane separation processes were made. Two membranes, NF270 and NF90, were firstly evaluated using hydrolysate model solutions under total recirculation mode, to identify the best membrane for the detoxification. NF270 was chosen to be used in the diananofiltration experiment as it showed the lowest rejection for toxic compounds and highest permeate flux. Diananofiltration experiments, for hydrolysate model solutions and hydrolysate liquor, showed that nanofiltration is able to deplete inhibitory compounds and to obtain solutions with higher xylose content. Conversely to non-detoxified hydrolysates, nanofiltration detoxified hydrolysates enabled yeast growth and xylitol production by the yeast Debaryomyces hansenii, clearly pointing out that detoxification is an absolute requirement for extracted olive pomace dilute acid hydrolysate bioconversion.

Separation and Purification by Ultrafiltration of White Wine High Molecular Weight Polysaccharides

This work aims to develop a process of ultrafiltration in diafiltration mode to concentrate the fraction of white wine polysaccharides of high molecular weight (arabinogalactan-proteins and mannoproteins) and to purify this fraction in terms of polyphenols, organic acids, and minerals removal. The membrane ETNA 10PP from AlfaLaval was characterized by an hydraulic permeability, Lp, of 105 L/(h·m2·bar) and a molecular weight cutoff, MWCO, of 17 kDa. A membrane surface area of 0.036 m2 was installed in a Lab-Unit M20 from Alva Laval. The permeation operating conditions, in total recirculation mode, were a temperature of 25 °C, pressures ranging from 0.5 to 5 bar, and an average velocity of 0.94 m/s. The ultrafiltration in concentration mode was run up to concentration factors of 4.25, and when diafiltration was introduced the concentration factors went up to 6.3. The permeate fluxes were maintained at an average value of 58 L/(h·m2).

Zero-valent iron (ZVI) Fenton oxidation of reactive dye wastewater under UV-C and solar irradiation

In the frame of this work, photo-Fenton processes using the zero-valent iron (ZVI) as a catalyst have been applied for mineralization and decolourization of the model wastewater containing reactive azo dye, C.I. Reactive Black 1 (RB1). Experiments were performed in the enhanced configuration of laboratory cylindrical batch photoreactor under UV-C irradiation (CBPR) and the boat-shaped flow reactor (BSFR) in total recirculation mode, exposed to direct sunlight, both with the immobilized iron.In the first part of the study, optimization of UV-C/ZVI-Fenton process has been performed using the concept of experimental mixture design, whereas Fenton reagent composition (ZVI and H2O2) and pH condition were treated as a three-component mixture. Due to the strict boundaries and constraints of mixture design, a single point in the design space emerged upon each optimization cycle.Corresponding kinetics was studied at optimal conditions. Two approaches has been compared; in the first approach a heterogeneous catalytic pathway has been adopted, while the second approach assumed the pure homogeneous catalysis, exploring the crucial role of the Fe(II) ions in the bulk solution due to its leaching from the ZVI surface. Corrosion of ZVI surface was examined by the means of material characterization and Fe(II) leaching.

Recovery of cerium(III) from aqueous solutions by complexation—ultrafiltration process

ABSTRACTComplexation–ultrafiltration process was investigated for cerium(III) recovery from aqueous solutions by using poly (acrylic acid) sodium salt (PAASS) as a complexing agent. The adsorption of cerium(III) on PAASS was preliminarily studied at different pH values. Next, effects of pH, polymer metal ratio (PMR), calcium(II) and competitive complexing agents on permeate flux (J) and cerium rejection coefficient (R) were investigated in the total recirculation mode. Finally, the integrations of four experiments including concentration, decomplexation, regeneration of PAASS and reuse of regenerated PAASS were carried out. Obtained results show that the adsorption can be described well using the Langmuir equation. If pH is reduced below 4, J decreases rapidly. PMR has negligible effect on J. R increases with increasing pH or PMR. Calcium(II) and ethylenediaminetetraacetic acid disodium salt have the effects on R, but these effects can decrease by increasing pH. Tartrate sodium does not influence R. In the process of concentration, J declines slowly, and R is about 1. It takes 40 min to reach the decomplexation equilibrium at pH 3. The decomplexation percentage of cerium(III)–PAASS complex is about 70%. In the regeneration of PAASS, cerium(III) can be removed effectively, and the purification of regenerated PAASS is acceptably satisfactory. The binding capacity of regenerated PAASS is close to that of fresh PAASS, and the recovery percentage of binding capacity is higher than 90%. © 2012 Curtin University of Technology and John Wiley &amp; Sons, Ltd.

Nanofiltration of surface water for the removal of endocrine disruptors

The assessment of surface water nanofiltration (NF) for the removal of endocrine disruptors (EDs) – Nonylphenol Ethoxylate (IGEPAL), 4-Nonylphenol (NP) and 4-Octylphenol (OP) – was carried out with three commercial NF membranes – NF90, NF200, NF270. The permeation experiments were conducted in laboratory flat-cell units of 13.2 × 10−4 m2 of surface area and in a DSS Lab-unit M20 with a membrane surface area of 0.036 m2. The membranes hydraulic permeabilities ranged from 3.7 to 15.6 kg/h/m2/bar and the rejection coefficients to NaCl, Na2SO4 and Glucose are for NF90: 97%, 99% and 97%, respectively; for NF200: 66%, 98% and 90%, respectively and for NF270: 48%, 94% and 84%, respectively. Three sets of nanofiltration experiments were carried out: i) NF of aqueous model solutions of NP, IGEPAL and OP running in total recirculation mode; ii) NF of surface water from Rio Sado (Setubal, Portugal) running in concentration mode; iii) NF of surface water from Rio Sado inoculated with NP, IGEPAL and OP running in conc...

Hydrolysis of disaccharides over solid acid catalysts under green conditions

The hydrolysis of the three most important disaccharides: sucrose, maltose and cellobiose, has been comparatively studied in mild conditions (50–80 °C) in water over several solid acid catalysts. Strong acidic resins (Amberlite A120 and A200), mixed oxides (silica-alumina and silica-zirconia), and niobium-containing solids (niobic acid, silica-niobia, and niobium phosphate) have been chosen as acid catalysts. The hydrolysis activity was studied in a continuous reactor with fixed catalytic bed working in total recirculation mode. Rate constants and activation parameters of the hydrolysis reactions have been obtained and discussed comparing the reactivity of the α-1,β-2-, α-1,4-, and β-1,4-glycosidic bonds of the employed disaccharides. The following order of reactivity was found: sucrose >> maltose > cellobiose. The sulfonic acidic resins, as expected, gave complete sucrose conversion at 80 °C and good conversions for cellobiose and maltose. Among the other catalysts, niobium phosphate provided the most interesting results toward the disaccharide hydrolysis, which are here presented for the first time. Relations between activity and surface acid properties are discussed.

Polymer supported ultrafiltration as a technique for selective heavy metal separation and complex formation constants prediction

This work is aimed at evaluating the affinity of partially ethoxylated polyethyleneimine (PEPEI) towards industrially valuable metal ions (Cu 2+, Ni 2+, Cd 2+ and Zn 2+). To face this aim, a characterization of polymer and macromolecular complexes by acid–base potentiometry was carried out. Next, lab-scale total recirculation mode ultrafiltration experiments were performed, checking that the affinity order was the same as that calculated from acid–base potentiometric titrations. Moreover, the influence of pH and loading ratio (LR) on Cu 2+ and Zn 2+ selective separation was evaluated, obtaining a maximum Zn/Cu selectivity of 12.31 at the optimal working conditions: pH 6, T = 50 °C, Δ P = 3 bar, LR = 286.74 mmol Me 2+/mol PEPEI. Finally, a model based on the competitive reaction between polymer functional groups and the solution cations was proposed. This model accurately adjusts metal rejection coefficients when pH is close to neutrality. Moreover, in order to overcome the drawbacks of acid–base potentiometry method, this model was used to calculate new complex formation constants from metal rejection data.

Graphite-supported TiO 2 for 4-nitrophenol degradation in a photoelectrocatalytic reactor

Amorphous TiO 2, prepared at room temperature through a sol–gel method implementing hydrolysis of TiCl 4, has been supported on graphite rods and then annealed at 673 K. In this way graphite was completely covered by a porous anatase TiO 2 layer, with an external thickness of about 1 μm, with graphite pores completely filled by the semiconductor particles. The obtained electrode was structurally characterized by SEM microscopy coupled to EDAX mapping and by Raman spectroscopy. A Pyrex annular reactor was designed in order to test the prepared electrodes for the photoelectrocatalytic degradation of 4-nitrophenol, a target pollutant dissolved in aqueous conductive solution. The continuous reactor worked in total recirculation mode and the degradation runs were carried out by applying near UV-light, bias or both energy sources. The influence of flow rate, initial 4-nitrophenol concentration and applied potential on the degradation rate was studied.

Micellar Enhanced Ultrafiltration for phosphorus removal in domestic wastewater

In this paper, a method of Micellar Enhanced Ultrafiltration (MEUF) with Hexadecyltrimethylammonium bromide (CTAB) is proposed to remove phosphate ions from treated domestic wastewaters from the reclamation station of University Campus of Toledo (Spain). This technique is able to reach phosphate rejection coefficients higher than 99% (a phosphate concentration in permeate of 1 mg/L if feed concentration is 95 mg/L). Additional experiments with Hexadecylpyridinium chloride (CPC) and Octadecylamine acetate (ODA) were performed to compare the behaviors of different surfactants. In the first stage, characterization (in terms of Chemical Oxygen Demand, Biological Oxygen Demand, Total Suspended Solids, Volatile Suspended Solids, phosphorus and nitrogen contents, pH, conductivity and turbidity) of real samples from reclamation station has taken place. After that, ultrafiltration experiments with semi-synthetic solutions in total recirculation mode were performed in order to optimize membrane hydrodynamic conditions and to analyze the influence of surfactant nature and concentration on permeate fluxes and phosphate ion rejection coefficients. Best results in terms of both phosphate rejection coefficient and permeate flux are 95% and 186.4 L/h m2 (LHM) at 1 mM phosphate concentration, 0.1 mM CTAB concentration, 25°C, tangential velocity 3 m/s and transmembrane pressure 4 bar. One of the novelties of this research lies in the surprisingly high performance of unusually low surfactant concentrations (even 10% CMC). Finally, two more additional variables (temperature and pH value) were analyzed to study the further surfactant regeneration. Unfortunately, none of these methods seem to be suitable since they do not abate phosphate rejection coefficients to low enough levels.

Performance and cost estimation of nanofiltration for surface water treatment in drinking water production

This work addresses the evaluation of nanofiltration (NF) and the minimization of NF membrane fouling in the treatment of surface water for drinking water production. The fouling characteristics of the natural organic matter (NOM) present in the surface water are dependent on the feed water composition and on the NF operating parameters. NF experiments were carried out in a DSS Lab-unit M20 with a membrane surface area of 0.216 m 2. Permeation experiments were performed both in total recirculation mode in order to optimize the operating conditions of pressure and recirculation flow rate and in concentration mode for design and optimization purposes. The concentration mode experiments were carried out at 15 bar and at a recirculation flow rate of 554 L/h. The water recovery rates (WRR) ranged up to 75%. A NF model was developed based on solute (NOM) and solvent differential mass balances and incorporating experimental data of the variation of permeation fluxes and total organic carbon (TOC) rejections with WRR. This model was used for the design of a NF plant with a permeate output of 100,000 m 3/d. The NF treatment cost was estimated to be €0.214/m 3.

Review of the treatment of seafood processing wastewaters and recovery of proteins therein by membrane separation processes — prospects of the ultrafiltration of wastewaters from the fish meal industry

The wastewaters generated in fish meal production (average flow rates of 1100 m 3/h for a plant capacity of 100 ton fish/h) contain a high organic load, and therefore they should not be discharged directly into the sea without effective treatment in order to prevent a negative impact on the environment. On the other hand, these effluents contain a large amount of potentially valuable proteins. These proteins can be concentrated by means of ultrafiltration (UF) and recycled into the fish meal process, improving its quality and the economic benefits from the raw material, whereas the treated water can be discharged into the sea or reused in the plant. Due to the high concentration of suspended matter in these effluents, microfiltration (MF) pre-treatment is required. An extensive review of the application of pressure-driven membrane separation processes in the treatment of seafood processing effluents and recovery of proteins therein is presented. Two effluents from a fish meal plant located in Talcahuano, Chile, were characterised and microfiltrated with a Whatman filter No. 1. A mineral tubular membrane, Carbosep M2 (MWCO = 15 kDa, ID = 6 mm and L = 1.2 m) was used in the UF experiments. The operating conditions were optimised in total recirculation mode, and the subsequent concentration experiments were carried out at 4 bar, 4 m/s, ambient temperature and natural pH. The results show that UF reduces the organic load from the fish meal wastewaters and allows the recovery of valuable raw materials comprising proteins. Moreover, they point out that further investigation should be dedicated to the use of UF membranes of lower molecular weight cut-off — or even NF membranes — in order to achieve complete recovery of the proteins contained in these effluents. Although the membrane undergoes severe fouling, it can easily be cleaned through a caustic washing.