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Membrane technology plays important roles in drinking water treatment in last decades; ultrafiltration (UF) is typically used to separate natural organic matters (NOM) and nanofiltration (NF) is used primarily to reject divalent ions, due to the different pore sizes of the used membranes. However, high water production rate at low energy consumption will be achieved if NOM and heavy metals can be simultaneously removed via UF-based water treatment process, which is necessary nowadays due to the carbon neutrality target worldwide. Here, a polyethersulfone (PES)-based UF membrane, modified chemically by grafting and crosslinking polyethylenimine (PEI, 25,000 Da) in two steps, was used to simultaneously remove humic acid (HA) and copper (Cu) from water. The molecular weight cut-off of the PEI-modified membrane was ∼110 kDa, and results showed that the efficiencies of HA and Cu2+ removal substantially increased because of the smaller pore size and additional adsorption effects compared to pristine PES membrane. Although the flux of the PEI-modified membrane was reduced, the membrane fouling was significantly alleviated compared with the pristine UF membrane. In comparison with Fe-based coagulants, Al-based coagulants as pretreatment performed better on removing HA and Cu2+, and the membrane flux greatly improved compared to only UF. The higher the coagulant dosage, the better the membrane performance was, particularly the pollutants removal efficiency. In addition, the PEI-modified UF membranes presented excellent pollutants removal after 4 months of storage in water. Besides, the as-modified UF membrane has only limited influence on removing mineral substances (e.g., Ca2+, Mg2+), indicating a potential application in actual water treatment. Furthermore, the PEI-modified membrane can be easily chemically cleaned; the removal efficiencies for hybrid Al-coagulation and UF process were as high as 88.2% ± 0.8% (HA) and 82.8% ± 0.1% (Cu2+) even after 4 cycles of filtration and subsequent chemical cleaning. [Display omitted] • Modified UF membrane was used to simultaneously remove NOM and Cu2+. • Excellent membrane performance was observed after PEI modification. • Al-based salts performed better than that of Fe-based salts as pretreatment. • Modified membrane was stable and had little influence toward mineral substances. • Modified membrane can be easily chemically cleaned and performed well. [ABSTRACT FROM AUTHOR]

Abstract: The phase inversion parameters of membranes prepared from lab-synthesized poly(ether ether ketone) polymers BPAPEEK and TBPEEK are investigated to tune their performance towards nanofiltration. These PEEK polymers are suitable for producing phase inversion membranes as they are soluble in polar aprotic solvents, thanks to the presence of alkyl side groups. Firstly, the influence of polymer concentration on membrane performance was investigated and a volatile co-solvent was added to improve the retention. Evaporation time was then tuned, in addition to coagulation bath composition and casting thickness. The membranes were also tested with a smaller solute. Additional to this phase inversion study, stability of the membranes in alkaline conditions was investigated. The prepared polymers proved to have potential as solvent resistant nanofiltration membranes or as hydrophobic support materials for thin film composite membranes. [Copyright &y& Elsevier]

Abstract: In this paper RO colloidal fouling was predicted using an on-line Feed Fouling Monitor (FFM) combined with a monitor based on ultrasonic time domain reflectometry (UTDR) under constant flux filtration. The FFM incorporated the relevant cross-flow hydrodynamics and detected the development of foulant load and resistance from a continuous sample passing over a small UF membrane. A UF membrane was used in the FFM, rather than a RO membrane, because it was more sensitive to fouling resistance and this decreased monitoring time and increased accuracy. The UTDR was coupled to a RO membrane cell to monitor the rate of cake thickness increase, which is the required information for the estimation of cake-enhanced osmotic pressure (CEOP). A model was developed to predict fouling in RO using data from the two monitors and combined both the cake resistance and the CEOP effect due to cake formation. RO and FFM fouling experiments were performed at different constant fluxes using the same feed solutions (200mg/l SiO2, 2000mg/l NaCl) and the same cross-flow velocity (0.1m/s). The results showed that higher fluxes caused an increased fouling rate for both RO and the FFM. The foulant layer thickness measured by UTDR in the RO experiments increased faster at higher applied fluxes and the estimated CEOP effect was also strongly influenced by the flux. The results show that the model, combined with the FFM and UTDR measurements, can provide a good estimation of the RO fouling profile over a range of applied fluxes. This study also underscores the importance of CEOP in contributing to the increase in transmembrane pressure due to colloidal fouling in RO of saline feeds. [Copyright &y& Elsevier]

Abstract: Biofilms may interfere with membrane performance in at least three ways: (i) increase of the transmembrane pressure drop, (ii) increase of feed channel (feed-concentrate) pressure drop, and (iii) increase of transmembrane passage. Given the relevance of biofouling, it is surprising how few data exist about the hydraulic resistance of biofilms that may affect the transmembrane pressure drop and membrane passage. In this study, biofilms were generated in a lab scale cross flow microfiltration system at two fluxes (20 and 100Lm−2 h−1) and constant cross flow (0.1ms−1). As a nutrient source, acetate was added (1.0mgL−1 acetate C) besides a control without nutrient supply. A microfiltration (MF) membrane was chosen because the MF membrane resistance is very low compared to the expected biofilm resistance and, thus, biofilm resistance can be determined accurately. Transmembrane pressure drop was monitored. As biofilm parameters, thickness, total cell number, TOC, and extracellular polymeric substances (EPS) were determined, it was demonstrated that no internal membrane fouling occurred and that the fouling layer actually consisted of a grown biofilm and was not a filter cake of accumulated bacterial cells. At 20Lm−2 h−1 flux with a nutrient dosage of 1mgL−1 acetate C, the resistance after 4 days reached a value of 6×1012 m−1. At 100Lm−2 h−1 flux under the same conditions, the resistance was 5×1013 m−1. No correlation of biofilm resistance to biofilm thickness was found; Biofilms with similar thickness could have different resistance depending on the applied flux. The cell number in biofilms was between 4×107 and 5×108 cellscm−2. At this number, bacterial cells make up less than a half percent of the overall biofilm volume and therefore did not hamper the water flow through the biofilm significantly. A flux of 100Lm−2 h−1 with nutrient supply caused higher cell numbers, more biomass, and higher biofilm resistance than a flux of 20Lm−2 h−1. However, the biofilm thickness after 4 days at a flux of 100Lm−2 h−1 (97μm) was in the same order of magnitude as the thickness of a biofilm at a flux of 20Lm−2 h−1 (114μm). An increase of flux caused an increased biofilm resistance while a decrease of flux caused a decreased resistance. The effect was reversible. It is suggested that the biofilm resistance is mainly attributed to EPS, probably due to the tortuosity (“hair-in-sink-effect”) of the biopolymers to water molecules travelling across the biofilm. The data show clearly that biofilm resistance (6×1012 m−1) was high compared to the intrinsic resistance of the employed MF membrane (5×1011 m−1). However, in nanofiltration (intrinsic membrane resistance ca. 2×1013 m−1) and reverse osmosis membranes (intrinsic resistance ca. 9×1013 m−1), the biofilm will not contribute significantly to the overall resistance. [Copyright &y& Elsevier]

Abstract: This work describes the development of micro-scale hollow fibers (HF) ultrafiltration membrane module using asymmetric microtubes produced by the co-electrospinning technique. Poly(caprolactone) (PCL) microtubes of average inner diameter of 4μm with wall thickness of 0.9μm and poly(vinylidenefluoride-co-hexafluoropropylene) (PVDF-HFP) with average inner diameter of 1.4μm, wall thickness of 0.9μm have been successfully achieved. The retention of the water soluble polymer poly(acrylic acid-co-maleic acid), sodium salt (50kDa) (PAA) (as a model contaminant) was used to evaluate the performance of HF modules. Applying pressure of up to 3.5bars to the HF modules of PCL and PVDF-HFP of 5.4cm in length have shown typical flux of 30–60L/m2 h, typical rejection of 25–35% and 28–40% correspondingly, and typical recovery of 20–37%. These results show a great potential in the use of micro-scale HF membranes for water purification. [Copyright &y& Elsevier]

Abstract: Caseins, the main proteins of milk, are known to be responsible of flux limitations in tangential filtration of skim milk. These proteins are well known to be versatile with the pH. Their initial form, corresponding to the so-called “native casein micelles” is due to a complex aggregation of monomers through calcium phosphate bridges that can be disrupted by small pH variations. This paper deals with the determination of both critical and limiting fluxes during ultrafiltration of natural and modified skim milks. pH ranging from 3.7 to 11.5 allowed to consider skim milk ultrafiltration (UF) for production purpose (pH 6.6–6.7) as well as acidic and alkaline concentrated effluents. The physico-chemical characteristics of caseins, as diameter and zeta potential, were measured according to the pH variations obtained by the addition of HCl and NaOH. Then, both limiting and critical fluxes variations were correlated to these characteristics. The critical and limiting fluxes varied in a quite complicated way with the pH, leading to four different regions. At acidic pH, zeta potential was null and fluxes were controlled by large particles of caseins that precipitated in the solution. Around neutral pH, the diameter of casein micelles remained constant whereas the zeta potential varied strongly. In this region the fluxes increased linearly with the zeta potential of caseins. Then at alkaline pH, the zeta potential of caseins remained constant whereas the diameter varied showing successively partial destructuration and partial “restructuration” of new types of micelles, both different from native casein micelles. In this region the fluxes varied with the rate of large micelles. Finally, retention of lactose (main neutral solute of milk) and whole proteins, mainly responsible of COD, were measured and discussed in relationship with above-mentioned parameters. [Copyright &y& Elsevier]

Abstract: Poly(N-isopropyl acrylamide) (PNIPAAm) was grafted on a polysulfone UF membrane. The changes of permeability as well as retention of PEG (35kg/mol) and Dextran (500kg/mol) between 23 and 60°C were determined for both grafted and unmodified membranes. The results showed that the viscosity corrected water permeability and solute retention were almost constant for the unmodified membranes within the measured temperature range, the permeability of the grafted membranes increased and the retention of Dextran and PEG decreased with temperature. The variation of changes was most obvious in the temperature range 27–37°C for the modified membranes due to the lower critical solution temperature (LCST) of PNIPAAm. The location and profile of PNIPAAm inside and on the surface of the membrane were analysed by SEM and FTIR. Depth profile calculation for FTIR spectra showed that PNIPAAm was mostly placed inside the membrane (at a depth of 1.06–1.10μm from the surface) rather than on the surface. The amount of grafted PNIPAAm was low and did not significantly affect the morphology of the membrane. Therefore, a difference in SEM pictures of modified and unmodified membranes could not be seen. The modified membrane exhibited a clearly different thermal response compared to the unmodified one. [Copyright &y& Elsevier]