UV-cured polysulfone-based membranes: Effect of co-solvent addition and evaporation process on membrane morphology and SRNF performance

Membranes consisting of a semi-interpenetrating network of polysulfone (PSU) and cross-linked polyacrylate were synthesized via non-solvent induced phase inversion followed by UV-treatment. Tetrahydrofuran (THF) or 1,4-dioxane (DIO) was added as co-solvent to the N,N-dimethylformamide (DMF)-based polymer solutions and cast films were subjected to evaporation prior to coagulation. Effects of synthesis variables on the membrane morphology and solvent resistant nanofiltration (SRNF) performance were investigated by using a Rose Bengal solution in isopropanol. By increasing the evaporation time from 0 to 100 s for the membranes prepared with THF and DIO as co-solvent respectively, rejections increased from 65.3% to 94.2% and 60.1–89.1%, while permeances decreased from 0.29 to 0.01 l/m2 h bar and 0.41–0.08 l/m2 h bar. A similar effect was observed when the co-solvent/solvent ratio was increased from 0/100 to 100/0: rejections increased from 63.1% to 94.9% and 59.2–90.6%, while permeances decreased from 0.43 to 0.01 l/m2 h bar for THF-based membranes and to 0.07 l/m2 h bar for DIO-based membranes respectively. A post-treatment was performed to increase the flux by immersing UV-cured PSU-based films in DMF for 48 h. The resultant membranes showed higher permeances and lower rejections, making them especially useful as potential candidates for stable supports to apply selective layers upon, such as e.g. in thin film composite (TFC) membranes. As observed in scanning electron microscopy, higher evaporation times and lower initial co-solvent concentrations resulted in less or even no macrovoids

Effect of operational parameters on the performance of a magnetic responsive biocatalytic membrane reactor

In this work, the performance of an innovative magnetic responsive biocatalytic membrane reactor (BMRSP) has been investigated under various operational parameters. In particular, feed concentrations, flow rates across the bed, temperature and amount of biocatalytic bead were varied to probe the flow-dependent transport and kinetic properties of the reaction and the subsequent hydrolytic performance of the BMRSP. The rate of fouling for the BMRSP was always lower than a corresponding control system. For a given enzymatic concentration, a constant foulant hydrolyzing capacity is identified. At 3 g/m2 pectinase containing bionanocomposites, the BMRSP hydrolytic efficiency was 1.5 g/m2 h. This efficiency was further increased by increasing the amount of bionanocomposites per membrane area. This further allowed the BMRSP to hydrolyze higher loads of foulants while keeping a low if not zero increase in TMP over time at constant flux. Identification of an optimal operating condition laid the platform for continuous operation of the BMRSP over 200 h, without visible transmembrane pressure drift while maintaining constant flux. Product assay in the permeate gave constant value in the entire duration, i.e., no enzymatic activity decay owing to stable enzyme immobilization and no leakage through the pores of the membrane owing to the synergistic magnetic interaction between the magnetic membrane and magnetic bionanocomposites. The obtained stability over a broad range of operational parameters and sustainable performance over long period gives a high prospect to the newly developed BMRSP to be utilized in continuous biocatalysis and separation, thereby significantly improved process efficiency

Pectinases immobilization on magnetic nanoparticles and their anti-fouling performance in a biocatalytic membrane reactor

Enzyme immobilization on commercial superparamagnetic nanoparticles (NPSP) was performed using covalent bonding. The biofunctionalized NPSP was then immobilized on the surface of the membrane using an external magnetic field to form a magneto-responsive biocatalytic membrane reactor (BMRSP). The magnetically formed smart nanolayer can be easily re-dispersed and recovered from the membrane when the enzyme is deactivated or whenever cleaning is required due to substrate over-accumulation. The system was used to hydrolyze pectin contained in different streams. Results are supported with complementary data from hydrodynamic, kinetic and morphological characterization in a flow-through reactive filtration. Wavelength-dispersive X-ray spectroscopy (WDS) elemental mapping revealed that the NPSP are uniformly dispersed on the surface of the membrane forming a thin biocatalytic layer. Both results of hydrodynamic studies and SEM micrographs of the membrane with the enzyme layer under various operating conditions, show that the immobilized enzyme effectively reduced membrane–foulant interaction. Comparison of filtration data using this commercial NPSP reveals good agreement with our previously used home-made NPSP. This implies that the scaling-up and commercialization of the developed BMRSP can be straightforward

Enzyme catalysis coupled with artificial membranes towards process intensification in biorefinery- a review

In this review, for the first time, the conjugation of the major types of enzymes used in biorefineries and the membrane processes to develop different configurations of MBRs, was analyzed for the production of biofuels, phytotherapics and food ingredients. In particular, the aim is to critically review all the works related to the application of MBR in biorefinery, highlighting the advantages and the main drawbacks which can interfere with the development of this system at industrial scale. Alternatives strategies to overcome main limits will be also described in the different application fields, such as the use of biofunctionalized magnetic nanoparticles associated with membrane processes for enzyme re-use and membrane cleaning or the membrane fouling control by the use of integrated membrane process associated with MBR

Micropollutant rejection of annealed polyelectrolyte multilayer based nanofiltration membranes for treatment of conventionally-treated municipal wastewater

The ever-increasing concentrations of micropollutants (MPs) found at the outlet of conventional wastewater treatments plants, is a serious environmental concern. Polyelectrolyte multilayer (PEM)-based nanofiltration (NF) membranes are seen as an attractive approach for MPs removal from wastewater effluents. In this work, PEMs of poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) were coated in a layer by layer (LbL) fashion on the surface of a polyacrylonitrile ultrafiltration support to obtain PEM-based NF membranes. The impact of PEM post-treatment, by applying salt and thermal annealing, was then investigated in terms of swelling, hydrophilicity, permeability, and ion rejection. While thermal annealing produced a more compact structure of PEM, it did not improve the ion rejection. Among the different salt concentrations examined for the salt-annealing process, the highest ion rejection was observed for (PAH/PAA)15 membranes annealed in 100 mM NaNO3, interestingly without any decrease in the water permeability. This membrane was studied for the rejection of four MPs including Diclofenac, Naproxen, 4n-Nonylphenol and Ibuprofen from synthetic secondary-treated wastewater, over a filtration time of 54 h. At an early stage of filtration, the membrane became more hydrophobic and a good correlation was found between the compounds hydrophobicity and their rejection. As the filtration continued until the membrane saturation, an increase in membranes hydrophilicity was observed. Hence, in the latter stage of filtration, the role of hydrophobic interactions faded-off and the role of molecular and spatial dimensions emerged instead in MPs rejection. To test the suitability of the membranes for the ease of cleaning and repeated use, the sacrificial PEMs and foulants were completely removed, followed by re-coating of PEMs on the cleaned membrane. The higher MPs rejection observed in salt-annealed membranes compared to the non-annealed counterparts (52–82% against 43–69%), accompanied with still low ion rejection, confirm the high potential of PEM post-treatment to achieve better performing PEM-based NF membranes

Influence of ionic liquid-like cationic pendants composition in cellulose based polyelectrolytes on membrane-based CO2 separation

Cellulose acetate (CA) is an attractive membrane polymer for CO2 capture market. However, its low CO2 permeability hampers its application as part of a membrane for most relevant types of CO2 containing feeds. This work investigates the enhancement of CA separation performance by incorporating ionic liquid-like pendants (1-methylimidazol, 1-methylpyrrolidine, and 2-hydroxyethyldimethylamine (HEDMA) on the CA backbone. These CA-based polyelectrolytes (PEs), synthesised by covalent grafting of cationic pendants with anion metathesis, were characterised by NMR, FTIR, DSC/TGA, and processed into thin-film composite membranes. The membrane performance in CO2/N2 mixed-gas permeation experiments shows a decrease in CO2 and N2 permeability and an initial decrease and then gradual increase in CO2/N2 selectivity with increasing HEDMA content. The amount of HEDMA attached to the CA backbone determines overall separation process in bifunctional PEs. This indicates that the hydroxy-substituted cationic pendants alter interactions between PEs network and permeating CO2 molecules, suggesting possibilities for further improvements

Tortuous mixed matrix membranes: A subtle balance between microporosity and compatibility

In this work, the effectiveness of metal-organic frameworks (MOFs) with sheet-like morphologies was assessed as function of the MOF microporosity and MOF-matrix compatibility. Zeolitic imidazolate frameworks (ZIFs, a MOF subclass) with sheet-like/platelet morphologies were incorporated in Matrimid/PBI matrices resulting in mixed matrix membranes (MMMs). The ZIFs were either permeable (ZIF-301) or impermeable (ZIF-95X) for gases with a kinetic diameter bigger than or equal to the kinetic diameter of CO2. Additionally, MMMs containing impermeable graphene nanosheets were fabricated as reference to confirm the ZIF-95X impermeability. The MMMs containing the ZIF-301 nanoplatelets showed enhanced CO2 permeabilities. Analysis of the N2 and CO2 solubility and diffusivity showed that this permeable additive enhances the solubility of both gases, but only increases the N2 diffusivity through the ZIF-301 MMM. This signified that for MMMs with sheet-like MOFs the MOF micropore volume should only be accessible for one gas such that the sheet-like morphology effectively increases the tortuosity for the other species. Contrarily, the MMMs containing impermeable ZIF-95X and graphene showed declined MMM separation performances. Analysis of the N2 and CO2 diffusivities showed the presence of defective interfaces in these MMMs and proved that an increased tortuosity is only effective if the additive-matrix interface is defect free

Bio-Hybrid Membrane Process for Food-based Wastewater Valorisation: a pathway to an efficient integrated membrane process design

Dottorato di Ricerca in Ingegneria Chimica dei Materiali, Ciclo XXVII, a.a. 2013-2014The food industry is by far the largest potable water consuming industry that releases about 500 million m3 of wastewater per annum with very high organic loading. Simple treatment of this stream using conventional technologies often fails due to cost factors overriding their pollution abating capacity. Hence, recently the focus has been largely centered on valorization through combinatorial recovery of valuable components and reclaiming good quality water using integrated membrane process. Membrane processes practically cover all existing and needed unit operations that are used in wastewater treatment facilities. They often come with advantages like simplicity, modularity, process or product novelty, improved competitiveness, and environmental friendliness. Thus, the main focus of this PhD thesis is development of integrated membrane process comprising microfiltration (MF), forward osmosis (FO), ultrafiltration (UF) and nanofiltration (NF) for valorization of food based wastewater within the logic of zero liquid discharge. As a case study, vegetation wastewater coming from olive oil production was taken. Challenges associated with the treatment of vegetation wastewater are: absence of unique hydraulic or organic loadings, presence of biophenolic compounds, sever membrane fouling and periodic release of large volume of wastewater. Especially presence of biophenolic compounds makes the wastewater detrimental to the environment. However, recovering these phytotoxic compounds can also add economic benefit to the simple treatment since they have interesting bioactivities that can be exploited in the food, pharmaceutical and cosmetic industries. The first part of the experimental work gives special emphasis on the development of biohybrid membranes used to control membrane fouling during MF. Regardless of 99% TSS removal with rough filtration, continuous MF of vegetation wastewater using 0.4 μm polyethelene membrane over 24 h resulted in continuous flux decline. This is due to sever membrane fouling mainly caused by macromolecules like pectins. To overcome the problem of membrane fouling, biocatalytic membrane reactors with covalently immobilized pectinase were used to develop self-cleaning MF membrane. The biocatalytic membrane with pectinase on its surface gave a 50% higher flux compared to its counterpart inert membrane. This better performance was attributed to simultaneous in-situ degradation of foulants and removal of hydrolysis products from reaction site that overcome enzyme product inhibition. Although the biocatalytic membrane gave a better performance, its fate is disposal once the covalently immobilized enzyme gets deactivated or oversaturated with foulants. To surmount this problem a new class of superparamagnetic biochemical membrane reactor was developed, verified and optimized. This development is novel for its use of superparamagnetic nanoparticles both as support for the immobilized enzyme and as agent to render the membrane magnetized. This reversible immobilization method was designed to facilitate the removal of enzyme during membrane cleaning using an external magnet. Hence PVDF based organic-inorganic (O/I) hybrid membrane was prepared using superparamagnetic nanoparticles (NPSP) as inorganic filler. In parallel, superparamagnetic biocatalytic nanocomposites were prepared by covalently immobilizing pectinase on to the surface of NPSP dispersed in aqueous media. The synergetic magnetic responsiveness of both the O/I hybrid membrane and the biocatalytic particle to an external magnetic field was later on used to physically immobilize the biocatalytic particles on the membrane. This magnetically controlled dynamic layer of biocatalytic particles prevented direct membrane-foulant interaction, allowed in-situ degradation, easy magnetic recovery of the enzyme from the surface of the membrane, use of both membrane and immobilized enzyme over multiple cycles and possibility of fresh enzyme make up. The system gave stable performance over broad range of experimental condition: 0.01-3 mg/mL foulant concentration, 1-9 g per m2 of membrane area bionanocomposites, 5- 45 L/m2.h flux and different filtration temperatures. Under condition of mass transfer rate prevailing reaction rate, the system gave upto 75% reduction in filtration resistance. After optimization of the different operational parameters, it also revealed no visible loss in enzyme activity or overall system performance, when 0.3 mg/mL pectin solution was continuously filtered for over two weeks. In addition, the chemical cleaning stability of the O/I hybrid membrane was studied under accelerated ageing and accelerated fouling conditions. The ageing caused change in the physicochemical characteristics and enhanced fouling propensity of the membrane due to step-by-step degradation of the polymeric coating layer of used NPSP. But 400 ppm NaOCl solution at pH 12 was found compatible; henceforth it was used to clean the membrane. Second major limitation identified during the treatment of vegetation wastewater is presence of large volume of wastewater that comes in short period following the harvest of olive fruit. To alleviate this problem, FO was investigated to concentrate the wastewater. This process is believed to be less energy demanding, suppose that draw solution does need to be regenerated, and with low foul propensity. By operating at 3.7 molal MgCl2 draw solution and 6 cm/s crossflow velocity, single-step FO resulted in an average flux of 5.2 kg/m2.h. and 71% volume concentration factor with almost complete retention of all the pollutants. Moreover, the system gave a stable performance over ten days when operated continuously. After FO, both NF and UF were used to fractionate the recovered biophenols from the concentrate streams of FO. Compared to polymeric UF membrane, ceramic NF gave better flux of 27 kg/m2.h at 200 L/h feed flow rate and 7 bar TMP. Finally, when FO was used as a final polishing step to recover highly concentrated biophenols from permeate of the UF; it gave an average flux of 5 kg/m2.h and VCF of 64%. In conclusion, a great success has been made in tackling the two most important challenges of vegetation wastewater valorisation using the concept of biohybridization and FO. The bioinspired NPSP provides strong evidence that magnetically controlled enzyme immobilization have an immense potential in membrane fouling prevention and paves a potential breakthrough for continuous wastewater filtration. By setting bio-inspired NPSP biocatalytic membrane reactor at the heart, it is possible to successfully use integrated membrane process for continuous valorisation of food based wastewater. In addition to fouling prevention, they open a new horizon for applications in localized biocatalysis to intensify performance in industrial production, processing, environmental remediation or bio-energy generation.Università degli Studi della Calabri