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The performance of nanofiltraton (NF) membranes are characterized by a high selectivity for multivalent anions, whereas poor selective separation capacity for multivalent cations and heavy metal ions. In this work, a new positively charged NF membrane was prepared by using 2-chloro-1-methyliodopyridine as an active agent to graft polyimide polymer onto the membrane surface via covalent bonding with surface carboxylic groups. The results showed that the prepared membranes had a high selective separation for divalent and monovalent salts (MgCl2 97.1%, CaCl2 96.8%, Na2SO4 83.5%, MgSO4 87.3%, NaCl 49%, LiCl 32%), and also exhibited a high removal efficiency for toxic heavy metal ions and dyes (CuCl2 96%, NiCl2 95.8%, CrCl3 98.0%, Tropaeolin O 98.3%, Victoria blue B 99.2%, Semixylenol orange 99%, Neutral 98.2%).

GO is of great interesting for membrane materials due to its unique properties including antimicrobial activity and antifouling property. However, the differences between GO nanosheets and layered GO membranes gained little attention. Herein, we fabricated GO membranes that have a thickness of around 30 nm and a void d-spacing of 0.67 nm (wet state) with single layer GO nanosheets of 10–75 nm in lateral size and investigated their antimicrobial and antifouling potential for practical use. It exhibits typical nanofiltration performance, with the rejections of 65.23%, 17.79%, 42.10% and 12.47% to Na2SO4, NaCl, Mg2SO4 and MgCl2, respectively. The antimicrobial test demonstrated that GO nanosheets lose their antimicrobial activity after they stacked together. A 14-day test showing that GO membrane has excellent resistance for organic fouling, with reversible fouling of more than 98%. But when it comes to tapwater, the proportion of irreversible fouling is surging to more than fifty percent even after cleaning with 2000 mg/L of sodium hypochlorite. Thus, we suggested that there are more details should be investigated before put layered GO membrane into practical use. Surprisingly, GO membrane exhibits excellent mechanical stability during the 14-day test, showing its exciting potential in water treatment.

Membrane capacitive deionization (MCDI) is an effective water purification technology. In this work, a monovalent selective cation exchange membrane (CIMS) was assembled in MCDI system (denoted as MSCDI) to separate lithium from magnesium. The effects of feed water quality and operating conditions on the lithium removal selectivity were systematically investigated. Specifically, in optimized conditions, the lithium selectivity coefficient reached 2.95. Furthermore, a custom-made large MSCDI module was applied to the selective removal of lithium. The removal rates of Li+ and Mg2+ in large module reached 38.4% and 19.2%, respectively. It is worth noting that the specific energy consumption was 0.0018 kWh mol−1, which is much lower than that of electrodialysis (0.04–0.27 kWh mol−1). Therefore, relying on its low energy consumption and environmental friendliness, MSCDI has considerable economic benefits for the efficient lithium extraction.

A surface hydroxylation process with an alkali solution of low concentration was employed to recover surface silanol groups of SBA-15 prior to amidoxime (AO)-functionalization. The effect of concentration and temperature on surface hydroxylation were investigated, and the optimal conditions of 0.003 mol L−1 and 65 °C for the surface hydroxylation were determined. The silanol density was increased from 1.20 mmol g−1 of the untreated SBA-15 to 1.45 mmol g−1 of the hydroxylated SBA-15. Characterizations through scanning electron microscopy, transmission electron microscopy, X-ray diffraction, N2 adsorption-desorption proved that the hydroxylation process did not destroy mesopore structure and morphology of SBA-15. The hydroxylated SBA-15 could anchor more AO groups than the untreated SBA-15, resulting in higher U(VI) adsorption capacity (709 mg g−1) of the pristine AO-functionalized SBA-15 following hydroxylation than that of untreated sample (601 mg g−1). The adsorption capacity of the regenerated samples slightly decreased after three sorption-desorption cycles. Compared with other coexisting cations (Na+, K+, Mg2+, and Ca2+) in artificial seawater with rich uranium, the distribution coefficient (Kd) and concentration factor (CF) value of UO22+ were far larger, suggesting high selectivity of AO-H-SBA-15 for UO22+. These results indicate that the surface hydroxylation process can enhance U(VI) adsorption maintaining the high adsorption selectivity and long-term adsorption stability.

To improve the separation performance and durability of the aromatic polyamide thin-film composite reverse osmosis membrane in tertiary treatment of textile effluent, grafting of hydrophilic polymer brushes was performed in this work through sequential surface treatment using acidic aqueous glutaraldehyde and monomethoxy-poly(ethylene glycol) (MPEG) solutions. ATR-FTIR and XPS analyses confirmed that MPEG brushes were grafted on membrane surface at the sites of N H group of amide linkages and end amino groups in the polyamide active layer. The modification was found to enhance membrane fouling resistance, water permeability and rejections to both COD and conductivity in tertiary treatment of textile effluent. The steady-state flux of the modified membrane to secondary textile effluent was higher by 24.0% compared with the virgin membrane and comparable with that of the commercial membrane BW30FR. The grafting of MPEG brushes was also found to make the membrane less susceptible to chlorine. After ten times of intensified chlorine exposure, i.e. total chlorine exposure of 42,000 ppmh NaClO of 35.0 °C and pH 9.0, the membrane grafted with MPEG brushes maintained COD and conductivity rejections of 97.9% and 98.5%, respectively, to textile effluent, showing better durability against chlorine than the virgin membrane and compared membrane BW30FR.

Developing a durable and antifouling monovalent selective anion exchange membrane is critical in practical electrodialysis (ED) process. Herein, a commercial anion exchange membrane was modified by sulfonated reduced graphene oxide (S-rGO) and polydopamine (PDA). Inspired by biological adhesion from mussels, the PDA coating on the surface of S-rGO-PDA membrane enhanced the stability of S-rGO nanosheets due to strong adhesion. The monovalent anion selectivity was evaluated by means of the Cl - / SO 4 2 - permeselectivity, and stability property was measured by the ion concentration changes of Cl - and SO 4 2 - for a long time application of ED. Moreover, antifouling property was measured by recording the time course of the potential difference in the presence of sodium dodecyl benzene sulfonate (SDBS). The results show that permselectivity of S-rGO-PDA membrane is 2.50, which is higher than pristine membrane (1.08). In addition, S-rGO-PDA membrane is stable, the permselectivity did not change significantly during 70 h ED process. Besides antifouling property of S-rGO-PDA membranes is improved compared with S-rGO membranes.

Bio-fouling of membranes caused by microorganisms seriously limited the development of membrane technology in practical applications. Design and synthesis of antifouling and antibacterial membranes with high quality are of paramount importance. In this study, we report a facile and safe method of extended Mitsunobu reaction (EMR)-freeze drying (FD) method to achieve oxygen-containing azido functionalized GO (AGO) nanosheets and synthesize novel azido-group functionalized graphene/polysulfone mixed matrix ultrafiltration membranes with enhanced permselective, antifouling and antibacterial property. Unlike reported thermochemical or chemical reactions to modify GO nanosheets, GO nanosheets were functionalized at low temperature which effectively prevented the decomposition of structural frame of pristine GO materials and the self-stacking phenomenon. Because of strong interactions between oxygen-containing AGO nanosheets and polymer matrices, high dispersity and interfacial compatibility were obtained in polysulfone membranes, resulting in sharp decrease of interfacial defects. Different kinds of techniques include SEM, ATR-FTIR, XPS, XRD, TEM and EDX were used to investigate the structure and morphology of AGO nanosheets and blended membranes, and cross-flow filtration experiments, anti-fouling and antibacterial test were applied to predict the behavior of hybrid membranes. High performance AGO/PSF mixed matrix membranes with excellent anti-fouling ability were successfully synthesized, which exhibited pure water flux as large as 245.1 L m-2 h-1 with satisfactory rejection of 95.8% for BSA. Moreover, the prepared membranes displayed good antibacterial activity against E. coli and S. aureus in long-term duration.

Surface modification has been adopted to tune surface property of nanofiltration membrane for improved separation performance. However, it has rarely been explored to modulate membrane pore size distribution. Here, we reported a novel modification strategy combined with surface cross-linking and in-situ condensation for fabricating composite nanofiltration membrane with reduced and homogenized pore size. The strategy was fulfilled by soaking the surface of nascent polyamide-based membrane with an aqueous solution of 3-aminopropyltriethoxysilane (APTES). Membrane physico-chemical property analyses demonstrated that the hydrolyzed APTES molecules bonded onto membrane surface through amidation and esterification reactions with the residual acyl chloride groups, and chemically combined with each other through condensation reaction. Modification was found to hydrophilize membrane surface, homogenize pore size and reduce mean pore diameter. The modification under desired conditions led to an improvement in pure water permeance from 12.2 to 14.0 l/m2 h bar, a decrease in geometric mean pore diameter from 0.71 nm to 0.63 nm, and a decline in geometric standard deviation from 1.32 to 1.23. Permeation test results showed that the APTES-modified membrane also exhibited improved removal performance to methylene blue and cresol red removal and enhanced antifouling resistances to model foulants cetyltrimethylammonium bromide, humic acid and bovine serum albumin.

In this study, carboxyl group-functionalized carbon nanospheres (CNs–COOH) and silver-coated products (CNs–COOH/Ag) were successfully realized and used as nanofillers to fabricate thin-film nanocomposite (TFN) membranes via the interfacial polymerization of m-phenylenediamine (MPD) and trimesoyl chloride (TMC) solutions. The structure of the functionalized CNs modified TFN membranes (TFN–Cs–COOH, TFN–Cs–COOH/Ag) was significantly different from that of the CNs modified TFN (TFN–Cs) and TFC membranes, as the carboxyl groups in the nanofillers strongly influence the process of interfacial polymerization. The permeability and anti-fouling performances of the TFN membranes were significantly enhanced owing to the changes in the membrane structure. The water fluxes of the TFN–Cs–COOH and TFN–Cs–COOH/Ag membranes were respectively 91.9% and 73.2% higher than that of the TFC membrane, with the NaCl rejection exceeding 96%. The nanofillers of CNs–COOH/Ag with monodispersed silver nanoparticles (NPs) resulted in outstanding anti-bacterial performance in the TFN–Cs–COOH/Ag membrane. Overall, this work demonstrates that, when functionalized carbon NPs are used as nanofillers, the practical performance of TFN membranes can be improved for reverse osmosis.

Super-hydrophobic F-TiO2@PP membranes were developed from polypropylene (PP) non-woven fabric by in situ cross-linking polymerization of trifluorofluorooctyl methacrylate (FOMA) and sol–gel-derived titanium dioxide with vinyltriethoxysilane (VTES). Due to the formation of super-hydrophobic “coral”-like synapses on the filamentous surfaces of PP non-woven fabric, F-TiO2@PP membranes showed extremely high water contact angles up to 157° and capability of rapidly absorbing oil drops. The F-TiO2@PP membranes were also able to expel water from water-in-oil emulsions with robustly high oil permeate fluxes (up to 11,000 L m−2h−1 under gravity), water removing efficiency (up to 99.7%), re-usability and long-term stability even at the presence of surfactant and salts. Such superior performance could lead to potential applications in rapid collection and efficient purification of recovered oily organic components from waste liquids or accidental oil discharges in marine or continental situations.

Modified three-compartment electrodialysis (MTED), a novel process containing intermediate compartment with fluorinated ion exchange membrane, has been applied to the recovery of petroleum sulfonate from petrochemical dispersion. The fluorinated ion exchange membrane has higher degree of crosslinking than heterogeneous ion exchange membrane. The petroleum sulfonate is separated from the petrochemical dispersion during anion migration by the different steric effect of ion exchange membranes. In order to reduce the membrane fouling and increase the current efficiency, the 50 nm ceramic membrane was utilized as the pretreatment of MTED. The result indicated that in total of 99.4 wt% of petroleum sulfonate in the petrochemical dispersion could be recovered at the applied voltage 25 V, flux rate 30 L/h, temperature 40 °C and initial concentration 7.5 wt% (NH 4 ) 2 SO 4 . Simultaneously, the (NH 4 ) 2 SO 4 solution without petroleum sulfonate was received in concentrate compartment of MTED. The results verified the feasibility of MTED on separating the petroleum sulfonate and inorganic salt in petrochemical dispersion, and provided important technical basis for a large-scale procedure of MTED in petrochemical dispersion treatment.

A novel amidoxime (AO) functionalized SBA-15 (AO@SBA-15) with platelet shape and short channels, was prepared by the amidoximation reaction of hydroxylamine with cyanoethyl (CN) functionalized SBA-15 (CN@SBA-15) under N 2 atmosphere. The precursor CN@SBA-15 was initially synthesized by co-condensation of tetraethoxysilane with 2-cyanoethyltriethoxysilane (CTES) using a triblock copolymer (P123) as a structural directing agent in acid medium or via the post-grafting of CTES onto SBA-15 with short channels. The AO@SBA-15 with platelet shape and short channels was employed as an adsorbent to remove U(VI) from an aqueous solution. The g-AO@SBA-15 (precursor prepared by post-grafting method) has higher adsorption capacity (625 mg g −1 ) than that of c-AO@SBA-15 (precursor prepared by co-condensation method) (516 mg g −1 ) at an optimum pH of 6, but with one more preparation step. Results indicated that both the adsorbents showed fast adsorption rate, high selectivity to Na + , K + , Mg 2+ , and Ca 2+ , and reusability for uranium extraction. Therefore, AO-functionalized SBA-15 with short channels is a promising adsorbent to remove uranium ion from an aqueous solution.

High energy consumption and membrane fouling are the two major obstacles that limit the extensive application of nanofiltration technology in treatment of textile and dyeing wastewaters. In this work, traditional polyamide (PA) thin-film composite (TFC) nanofiltration membrane was modified with diethanolamine (DEA) for improved water permeability and antifouling property in the removal of dyes from aqueous solution. The DEA-modified PA-TFC membrane was fabricated by a facile approach of pouring the DEA-aqueous solution on the surface of the nascent polyamide membrane prepared via interfacial polymerization between trimesoyl chloride and piperazine. The covalent attachment of DEA molecules was found to make membrane surface more hydrophilic and less negatively charged while having no influence on the morphological structure and compactness of the active layer. Compared with the traditional PA-TFC membrane, the steady-state water fluxes of the DEA-modified PA-TFC membrane to dye aqueous solutions of Congo red, methyl blue, sunset yellow and neutral red were higher by more than 37.0%, the flux decline ratios due to membrane fouling were lower by at least 35.0%, while the dye removal remained constant, and furthermore, the dye molecules adsorbed and deposited on membrane surface could be more readily washed off by simple hydraulic washing.

The separation of magnesium and lithium is the key issue of preparation of pure lithium product due to their similar chemical property. Thermodynamic analysis was conducted on the removal of magnesium from lithium chloride solutions with phosphate precipitation method. The thermodynamic equilibrium diagrams of Mg 2 + - PO 4 3 - - H 2 O, Li + - Mg 2 + - PO 4 3 - - H 2 O and Li + - Mg 2 + - NH 4 + - PO 4 3 - - H 2 O systems at 298 K were established, separately. The effect of process parameters on the removal of magnesium was also investigated. The results revealed that the existence of Li+ was not beneficial to the removal of magnesium, and the precipitation method of MgNH4PO4 performed better than that of Mg3(PO4)2 for the separation of magnesium from lithium chloride solutions. The equilibrium concentration of magnesium decreased with the increase in total concentration of NH 4 + and the decrease in concentration of Li+. With the precipitation method of MgNH4PO4, there are four regions of stable solid phase in the pH range of 4.5–13.0 in lithium chloride solutions containing 1 mol/L Li+, 0.03 mol/L NH 4 + , 0.01 mol/L Mg 2 + and 0.03 mol/L PO 4 3 - , which are MgHPO4 (5.9 ( NH 4 ) 3 PO 4 · 3 H 2 O at pH 8 and 25 °C, while the concentration of residual phosphorus in purified solution was only 0.004 g/L, which was consistent with the thermodynamic analysis.

It is of significant importance to develop highly monovalent anion-selective membranes (MASM) having stable structure for a wide range of applications. To realize the efficient monovalent/bivalent anion separation, in this work, three amphoteric ion-exchange membranes (AIEMs) through blending were fabricated for use in electrodialysis (ED). The three membranes were prepared by blending amino-containing poly(arylene ether sulfone) (PAES-NH2) with 10, 15, and 20 wt% of sulfonated polysulfone (SPSf), respectively, followed by grafting imidazolium salt-terminated side alkyl chains on PAES backbone. Our investigations demonstrate that each transparent AIEM shows good miscibility between the two components, which has been verified by a homogeneous structure via SEM observation and by an even distribution of N element via EDX mapping. In the ED process at a current density of 2.5 mA cm−2, AIEM with 15 wt% of SPSf shows the superior perm-selectivity (Cl–/SO42–) of 21.8, relative to many reported MASMs having modified surfaces (

Innovative approaches to restraint bacterial adhesion and growth on membranes are significantly needed to avoid membrane performance decaying for biofouling. In this work, a series of thin film nanocomposite (TFN) reverse osmosis (RO) membranes has been prepared by incorporating nano-fillers of p-aminophenol-modified graphene oxide (mGO) into the polyamide skin layer via interfacial polymerization. Our investigations demonstrate that the introduction of mGO nano-fillers into the functional skin layers reduces the hydrophilicities with the water contact angles drop from 69.6° to 48.2° and meanwhile decreases the thickness of functional skin layers from 240 nm to 50 nm, relative to pristine polyamide RO membrane without nano-fillers. As a result, the as-prepared TFN RO membrane at optimized conditions shows a water flux of 23.6 L·m−2·h−1 and a NaCl rejection rate of 99.7%, reflecting a remarkable promotion in water flux (by 24.5%) compared with the pristine RO membrane. In addition, the data statistics of the live/dead fluorescent imaging assay demonstrate that TFN RO membrane with mGO exhibits bacterial killing ratios of 96.78% and 95.26% against E. coli and S. aureus at the additive loading of 0.005 wt%, which are much higher than RO membrane with GO (90.64%; 90.43%) and pristine RO membrane (4.95%; 2.48%). This work demonstrates a facile way to TFN RO membranes with good separation performance and desirable antibacterial capacities.

A large amount of acid wastewaters containing sodium chloride (NaCl) is usually generated during the production of HZSM-5 zeolite (H-form Zeolite Socony Mobile Five). It can cause contamination of the environment if discharged directly. In this study, a method was reported to regenerate hydrochloric acid (HCl) and sodium hydroxide (NaOH) from the acid wastewater by bipolar membrane electrodialysis (BMED). The effects of operation parameters, such as initial base concentration and current density, on the spent acid solution regeneration were investigated. The results indicated that the initial concentration of sodium hydroxide had little or no effect on the acid wastewater regeneration. But it was also demonstrated that current density have a great influence on the acid wastewater regeneration, and a higher current density applied to the BMED stack usually resulted in lower current efficiency and higher energy consumption. After the operation of BMED process, the comparison between the recycled acid solution and the pure acid solution illustrates the recycled acid solution by BMED process can replace the pure acid solution completely. Therefore, this experiment can not only achieve the elimination of environmental pollution, but also the recycling of resources.

Succinic acid is a key compound in the food, chemicals and pharmaceuticals, with increasing demand in industry. To produce succinic acid in an environmental friendly manner, bipolar membrane electrodialysis (BMED) was used to convert sodium succinate into succinic acid with 0.25 mol/L sodium sulfate as electrode supporting solution. Three stack configurations, such as BP-A-C-BP, BP-C-BP and BP-A-BP, were considered to find the most cost-effective configuration. These results suggested that succinic acid could be purified in a cost-effective manner by using BMED. The voltage drop, concentration, current efficiency, and energy consumption orders of three cell configurations for succinic acid production were U BP-A-C-BP > U BP-A-BP > U BP-C-BP , C BP-C-BP > C BP-A-C-BP > C BP-A-BP , ŋ BP-A-C-BP > ŋ BP-C-BP > ŋ BP-A-BP and E BP-A-BP > E BP-A-C-BP > E BP-C-BP , respectively. The BP-A-C-BP configuration was found to have the high current efficiency (90%) and the low energy consumption (2.3 kW h/kg).

It is significant to develop anion exchange membranes (AEMs) with efficient ionic transport and desirable stabilities (mechanical and dimensional) for various applications, including electrodialysis (ED). In this paper, three types of composite AEMs based on quaternized polysulfone (QPSU) and polyvinyl alcohol (PVA) blends: QPSU/PVA composite AEM (M0), potassium thioacetate (PT) modified QPSU blending with PVA (M1) and QPSU blending with 4-formylbenzoic acid (FBA) modified PVA (M2-X, X = mass ratio of the FBA with the values of 0.05 and 0.20), have been investigated. Our investigation demonstrates that the swelling ratios of M1 and M2-0.05 were significantly reduced to 10.9% and 4.7% at 20 °C, much lower than M0 (16.9%). This can be due to the formed hydrogen-bonding network via OH from PVA and >C O from PT structure on PSU within M1 or the ionic crosslinking interactions between COO– from FBA and >N+– on QPSU within M2. Though the free volume inside AEM matrix is reduced, the chloride ion conductivities of M1 and M2-0.05 reach 20.5 mS cm−1 and 23.5 mS cm−1 at 20 °C. In ED application, the optimized M2-0.05 has the highest NaCl removal ratio of 74.6% within 120 min (vs. 61.06% of the commercial AEM-Type II), and exhibits better desalination performance with high current efficiency (98.0% vs.92.8%) and lower energy consumption (2.2 kWh kg−1 NaCl vs. 2.4 kWh kg−1). The simple preparation process and good ED performance of M2-0.05 are indicative of its potential ED application.

Submerged nanofiltration of anionic dye aqueous solution by laboratory-fabricated sodium carboxymethyl cellulose (CMCNa)/polypropylene (PP) thin-film composite hollow fiber membrane was investigated in this paper. The CMCNa/PP thin-film composite membranes were prepared through dip-coating CMCNa skin layer on the outer surface of polypropylene microporous hollow fibers followed by cross-linking with FeCl 3 . The molecular weight cut-off (MWCO) and surface zeta potential of the tailor fabricated membrane were estimated through permeation tests using different PEG solutions and measurements of surface steaming potential, respectively. Submerged nanofiltration tests were then performed with anionic dye solutions under different conditions. It was found that, at neutral pH, the negatively charged CMCNa/PP composite hollow fiber membrane with a MWCO of about 700 Da could effectively remove anionic dyes (Congo red and Methyl blue) from aqueous solution with good long-term performance stability and anti-fouling property through submerged nanofiltration. The dye retention and water permeability was affected by the trans-membrane pressure, the dye concentration as well as the presence of salt in the solution. The dye retention, water permeability and salt rejection rate to aqueous solution containing 2000 mg/l Congo red and 10,000 mg/l NaCl were 99.8%, 7.0 l/m 2 h bar, and lower than 2.0%, respectively.

Pretreatment to reverse osmosis (RO) seawater desalination historically has been achieved using organic (polymer) ultra- and micro-filter (UF/MF) membranes. Newly developed inorganic (ceramic) membranes offer unique advantages over the currently employed membranes, and were recently introduced for the purpose. In this work, we investigate the performance of a zirconium dioxide ceramic membrane with 0.05 μm pore diameter to clarify raw seawater under different operating conditions. The influences of cross-flow velocity (2.7–4.9 m s −1 ), temperature (15–55 °C), transmembrane pressure (TMP) 0.1–0.2 MPa, and seawater pH (5.5–9.5) on permeate flux and rejection were assessed. The results show that the zirconium dioxide membrane at cross-flow velocity of 3.7–4.2 m s −1 , TMP of 0.14–0.18 MPa, temperature of 25–30 °C and seawater pH of 8.0–9.0 exhibited a high flux of 420–450 L m −2 h −1 with turbidity and COD Mn rejection of 99.0–99.5% and 32–35%, respectively. This work also introduces a new experimental procedure to determine different filtration resistance ( R m , R sads , R pads , R cp , R pb and R cr ) components, which helps the analysis of performance characteristics and the better understanding of interactions between the membrane and foulants. The present results show that the effect of concentration polarization was dominant in the ultrafiltration of raw seawater, and various fouling components contribute to the total in the order of R cp > R sr > R m > R sads > R pads > R irr . Further, reversible fouling was much more significant than irreversible fouling. The experimental method also showed interrelation between the reversible and irreversible resistances, whereby part of R sr is transformed into R irr within 20 min of filtration. The results of this study indicate that zirconium dioxide ultrafiltration pretreatment before RO desalination can achieve consistent permeate quality and low fouling potential at high permeate fluxes.

The combined membrane process of electrodialysis (ED) and reverse osmosis (RO) was carried out to recover the l -tryptophan from its crystallization wastewater which had 0.5–1.5% residual l -tryptophan and around 15% impurity of NaCl salt. In the process of ED desalination, the operating current should be controlled below the limiting current density to avoid the polarization phenomenon. The pH of dilute solution significantly affected the recovery ratio of l -tryptophan, and the salt removal ratio varied with current density and voltage. The operating current density also had a great impact on the performance of the electrodialytic desalination process. After ED desalination, two methods including raising the temperature and adjusting the pH of the dilute solution coming from ED process were used to increase the solubility of l -tryptophan in aqueous solution during the RO concentration process. It was observed that the recovery ratio of l -tryptophan was closely correlated with not only the pH of RO feed but also the salt removal degree of ED process. After the treatment of the combined ED and RO process, 60.4% of the optimal recovery ratio of l -tryptophan was achieved, and the purity of final product of l -tryptophan reached 98%.

Asymmetric and charged ultrafiltration membranes were prepared from blends with synthesized polyacrylonitrile (PAN) and hydrophilically modified polyacrylonitrile by the classical phase inversion technique in water. As hydrophilically modified polyacrylonitrile was added, the membranes were more hydrophilic and better anti-fouling performance. Collagen extract was separated by the resulted ultrafiltration membranes. The results showed that, compared to the pure PAN ultrafiltration membrane, the blend membrane possessed higher hydrophilicity and better anti-fouling property. Fouling of collagen particles on the blend membranes was able to reduce as the composition of hydrophilic polyacrylonitrile increased. And the resulted membrane can be used to purify and concentrate collagen extract effectively. The pH of the collagen extract and the hydrophilic polyacrylonitrile content in the blend membrane could influence the membrane separation performance during separating the collagen extract.

Interfacially polymerized polyamide thin film composite membrane was modified by electrostatic self-assembly of polyethyleneimine on the membrane surface, and the modified membrane showed significantly improved antifouling properties. The charge reversal on the membrane surface due to the application of the polyethyleneimine layer was shown to increase the fouling resistance of the membrane to cationic foulants because of the enhanced electrostatic repulsion, and the increased surface hydrophilicity would help minimize the flux reduction. The effects of parameters involved in the membrane surface modification (e.g., polyethyleneimine concentration and deposition time) on the membrane performance were investigated in terms of water permeation flux and salt rejection. The membrane modification was found to increase salt rejections when MgCl2 and NaCl were tested. The fouling behavior of the membranes was also studied with and without the presence of dodecyltrimethylammonium bromide (which is a common cationic surfactant present in waste water). It was shown that while the deposited polyethyleneimine surface layer tended to offer additional resistance to permeation, the improved fouling resistance and the increased surface hydrophilicity compensated for the reduction in membrane permeability due to the deposition of the polyethyleneimine layer.

2-Hydroxypropyltrimethyl ammonium chloride chitosan/polyacrylonitrile (HACC/PAN) positively charged composite nanofiltration (NF) membrane was prepared using HACC as active layer, PAN ultrafiltration (UF) membrane as support layer, and toluene diisocyanate (TDI) as cross-linking reagent. FTIR-ATR spectrum was employed to characterize the cross-linking on the resultant membrane surface. Besides, some characteristics such as the permeability of pure water and the rejection performance to different salt solutions were evaluated. At 20 °C and 30 L h −1 of cycling flow, the permeability of pure water through this membrane was 8.96 kg m −2 h −1 MPa −1 . The rejection to different salt solutions increased in the order of Na 2 SO 4 , MgSO 4 , NaCl and MgCl 2 .

A novel composite nanofiltration (NF) membranes were prepared using quaterinized chitosan as a selective layer, poly(acrylonitrile) UF membrane as a support layer and anhydride mixture as cross-linking reagent. The images of these membranes were characterized by scanning electron microscope, and the other characterizations such as pure water permeability, molecular weight cut-off, rejection and swelling were investigated. Molecular weight cut-offs tested were in the range of 550–580 Da (in NF range). Both pure water permeability and swelling in water decreased, whereas rejection increased with an increase in anhydride mixture concentration, indicating pore contraction and the increase in both hydrophobicity and pore tortuosity due to cross-linking. Besides, the rejection declined with the increasing feed concentration, whereas it was not affected by feed cross-flow rate. The order of rejection to different salts followed the decreasing of CaCl2, MgCl2, NaCl, KCl, MgSO4, Na2SO4 and K2SO4, suggesting the positively charged characteristic of the NF membranes. And the rejections to MgCl2, CaCl2 solutions reached up to 0.95, so the membranes developed can be used for the hardness removal in water treatment process.

A water-soluble copolymeric membrane material containing tertiary amine and carboxyl groups for CO2 facilitated transport have been synthesized by radical polymerization of DMAEMA (2-N,N-dimethyl aminoethyl methacrylate)–AA (acrylic acid). The composite membranes were prepared with copolymer of DMAEMA–AA as separation layer and polysulfone (PS) ultra-filtration membrane as support. The permeation rates of the membranes for pure CO2 and CH4 were investigated. The results show that the copolymeric membrane possesses a higher permeance of CO2. The membrane displays a CO2 permeance of 6.12 × 10−7 cm3 (STP)/cm2 s Pa, and a CH4 permeance of 2.4 × 10−9 cm3 (STP)/ cm2 s Pa at 299 K, 1.140 kPa of gas pressure. The results with the mixed gas are not as good as those obtained with pure gas because of the coupling effects between CO2 and CH4.

Elevated CO 2 levels in a closed space or room are of big concerns in many situations. Controlling the CO 2 level within a certain range is one of the most important tasks in a life support system. In this paper, a 10 l photobioreactor integrated with a hollow fiber membrane module was constructed to remove CO 2 from air by using the photosynthetic microalga, Chlorella vulgaris . The effects of the inlet CO 2 concentration and the introduction of the membrane module on microalgal CO 2 fixation were investigated. The results showed that the proper inlet CO 2 concentration was determined to be 1.0%, based on the description of the growth characteristics of the microalga, and the gas exchange efficiency was improved greatly when the membrane module was adopted. Compared with an ordinary photobioreactor, not only the retention time of the smaller and more uniform gas bubbles in the new membrane-photobioreactor increased from 2 s to more than 20 s, but also the dissolved oxygen (DO) dropped by a factor of 30, resulting in the enhancement of the CO 2 fixation rate from 80 to 260 mg l −1 h −1 . When the operating conditions were controlled at cell density of 2.0 × 10 7 cells ml −1 , inlet gas flow rate of 3 l min −1 , and light intensity of 157.6 μEm −2 s −1 at 25–30 °C, the 1.0% (v/v) CO 2 in the input aeration gas could be reduced to 0.3% in the discharged gas. Using normal room air (0.04% CO 2 ) as feed, the CO 2 concentration in the discharged gas could be decreased to the boundary value of 0.015%, indicating that the novel membrane-photobioreactor by intensifying the process of CO 2 conversion and fixation during the microalgal photosynthesis may be a promising solution to CO 2 removal in a closed space or room.