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Abstract: Because of the demand for acid solutions in seawater desalination pretreatment and the difficulty of transporting sulfuric acid or hydrochloric acid, seawater concentrate from an RO system was used as the feed for the production of mixed acid by bipolar membrane electrodialysis (BMED) after the removal of calcium ions and magnesium ions. In this experiment, the feasibility of the process was tested using a laboratory ED-cell with an effective area of 88cm2. Based on the configuration of the BP-C-A-BP, the mixed acid solution was produced in the acid compartment, and the base solution was produced in the base compartment. The results showed that 1mol/L mixed acid and sodium hydroxide could be produced continuously at a constant current density of 57mA/cm2 and a flow rate of 0.30L/h in the continuous-mode BMED. After the production of the acid and base solution, membrane fouling was inspected by measuring the stack resistance and using electron microscopy and surface elemental analysis. No visible fouling deposits on the surface of the CEMs (AEMs) were observed, and there was an increased stack resistance, thus proving that the BMED process for mixed acid production with pretreated RO concentrate is suitable for a long-term run. [Copyright &y& Elsevier]

Abstract: The antifouling property of poly(vinylidene fluoride) (PVDF) ultrafiltration (UF) membrane incorporating the amphiphilic copolymer additive, poly(vinylidene fluoride)-graft-poly(hydroxyethyl methacrylate) (PVDF-g-PHEMA) synthesized via atom transfer radical polymerization (ATRP), has been investigated. During casting, the PVDF-g-PHEMA additive segregates to form a PHEMA brush layer on all blend membrane surfaces, including internal pores. Polymerization time and monomer content are used as the independent variables to manipulate the amount of grafted PHEMA on PVDF, respectively. The grafting yield of PHEMA is determined by molecular number (Mn) which is increased with the polymerization time and monomer content. The polydispersity index of PVDF-g-PHEMA remains narrow Mw/Mn at around 1.21–1.45 throughout the reaction. The chemical compositions of copolymer and blend membrane are investigated by Fourier transform infrared spectrometer (FT-IR) and X-ray photoelectron spectroscopy (XPS). The morphology of blend membrane is investigated by scanning electron microscopy (SEM). It is found that PHEMA brushes provide higher pure water flux and better anti-protein absorption ability to PVDF membranes. Water permeability of blend membrane using PEG20000 as pore-forming agent is excellent than that using PEG400 due to formation of larger pore sizes on the PVDF membrane surface and some PEG20000 tangling up with copolymers in PVDF matrix. The exceptional anti-fouling performance holds promise for extending UF membrane lifetimes without need for aggressive cleaning procedures. [Copyright &y& Elsevier]

A novel nanofiltration (NF) membrane is developed via polyethyleneimine (PEI) deposition on a hydrolyzed polyacrylonitrile (PAN) substrate enhanced by an electric field and chemical cross-linking to achieve improved desalting properties. Compared to the PEI static-deposition process, dramatic increase in salt rejection and substantial reductions of deposition time and PEI concentration are achieved for the membranes prepared by electro-deposition. What's more, the resulting membrane exhibited both stable flux and salt rejection in filtrating seawater for a relatively long term due to a significant membrane stability attributed to the electro-deposition. Desalting properties in terms of salt rejection and flux were found to be strongly affected by both hydrolysis and electro-deposition conditions. Under the optimal fabricating conditions, the resulting NF membrane exhibited a high flux of 24 L/m 2 h, excellent MgCl 2 rejection of ∼92% and low NaCl rejection of ∼39% when filtrating 2000 mg/L salt solution at 0.5 MPa. Under filtration of raw seawater at 1.8 MPa, the resulting membrane exhibited a high flux of 30.2 L/m 2 h and a significant improvement in seawater softening efficiency compared to various commercial NF membranes, which is attributed to its excellent separation efficiency between divalent and univalent ions. The current investigation demonstrated that polyelectrolyte NF membranes fabricated by electro-deposition and cross-linking led to excellent separation performance and satisfactory stability and durability that can be used in seawater softening for a relatively long time. [ABSTRACT FROM AUTHOR]

Abstract: Dynamic layer-by-layer (LBL) self-assembly technology was used to prepare as few as three to five bilayers of poly(diallyl-dimethylammonium chloride) (PDADMAC) and poly(styrene sulfonate) (PSS) on negatively charged polysulfone (PS) ultrafiltration (UF) membranes of 50kDa MWCO and compared with those of the static assembly membranes. The prepared dynamic assembly (PDADMAC/PSS)4 nanofiltration (NF) membrane showed a permeation flux of 60Lm−2 h−1 at 1.0MPa, much higher than that of the commercial DL membrane (GE Osmonics, USA), but with a rejection of about 90% of SO4 2− which is relatively less than that of the DL membrane. The rejection performance showed that the dynamic–static assembly was more effective than others. Using dynamic–static assembly preparation, the rejection of (PDADMAC/PSS)3 membrane was about 90%, while the flux was about 55Lm−2 h−1 at 1.0MPa. The surface morphology of the prepared LBL membranes were characterized by SEM and AFM, and no defect was found. The surface morphology of the membrane prepared by dynamic–static assembly was almost the same as the commercial membranes. The analysis of filtration resistance indicated that the deposition of the first and second bilayer was crucial during the whole preparation process. [Copyright &y& Elsevier]