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Abstract: An ultrafiltration–nanofiltration (UF–NF) integrated membrane system (IMS) was operated for 500h to examine the performance of the NF membrane in seawater desalination pretreatment. The rejection of divalent ions, TDS, TOC and UV254 by the NF membrane as well as the permeation flux decreased gradually with operating time before each chemical cleaning procedure, while the calculated Stiff and Davis Stability Index (S&DSI) increased gradually from negative up to positive. The result indicates that there exists inorganic fouling during the long run. However, the IMS produced excellent effluent with 93.6% removal of total organic carbon (TOC) for long-term operation. The TOC concentration of the NF permeation samples was in the range of 0.06–0.35mg/L. The chemical cleaning results indicated that inorganic fouling should be preferentially paid attention to, and a combination of citric acid cleaning and NaOH cleaning may achieve an optimal cleaning efficiency. The long-term operation reveals that the membrane is more prone to fouling gradually after chemical cleaning. [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]

A pilot-scale ultrafiltration (UF)–nanofiltration (NF) integrated membrane system (IMS) which included a self-cleaning crossflow UF filtration process and a dual-stage NF process with a capacity of 100 m 3 ·d − 1 NF permeation water was established for seawater softening investigation. The separation performance of the dual-stage NF process under different conditions, such as operating pressure, recovery rate, and inlet flowrate, was extensively investigated; long-term performance and energy consumption of the dual-stage NF process were analyzed as well. The results showed that during the long-term operation, UF could provide qualified filtrate for NF. The dual-stage NF process achieved high separation performance with good permeate quality, especially high rejection of Ca 2 + and Mg 2 + (> 90%). In addition, the dual-stage NF process showed good anti-fouling characteristics, with the normalized NF permeate flux maintaining at an essential constant value of about 14 L·m − 2 ·h − 1 at 3.5 MPa, and DOC rejection around 90% during the long-term experiment. Energy consumption of the dual-stage NF process increased with the increase of the operating pressure and the decrease of the raw seawater temperature, which was about 1.8 kWh·m − 3 at 3.5 MPa and 25 °C. [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]