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Membrane fouling is the main problem during the nanofiltration (NF) process of brackish water desalination due to the existence of natural organic matter, especially humic acid (HA). Moreover, the conventional membrane cleaning method would do great harm to the environment because large amount of chemicals were employed. In order to control organic fouling, a novel cleaning method via direct osmosis backwash (DOBW) by injecting high salinity (HS) solution was developed. Different operating conditions for HS-DOBW technology in the actual process were systematically investigated. The results demonstrated that there was a strong driving force to lift and sweep the foulants from the membrane surface which would be carried over to the brine. The optimal conditions in terms of HS (150 kg/m 3 NaCl solution) flow rate of 0.121 L/min were selected for the subsequent experiments. The results showed that the fouling could be almost fully reversible (more than 99.78% permeate water flux recovery), and the membrane needed to be cleaned for about 10 min because of the appearance of HA on membrane surface at the fouling time of 24 h. Most importantly, the HS-DOBW technology is very effective in keeping the membrane continuously clean and ensuring stable permeate production. [ABSTRACT FROM AUTHOR]

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]

Abstract: An integrated membrane system (IMS) of ultrafiltration–nanofiltration (UF–NF) technology has been investigated extensively as a means of seawater softening for offshore oilfield water and polymer flooding. The results showed that the softened water generated by the selected NF membrane could meet the water flooding standard for offshore oilfield. At appropriate mixing ratio of softened water and formation water, scales may be avoided completely. Furthermore, the reservoir formation sensitivity evaluation proved the compatibility of NF permeation water with the formation core, which indicates that the permeation water of the selected NF membrane module could be safely used for offshore oilfield water flooding. The prepared aqueous polymer solution using NF softened seawater showed relatively high viscosity and stability at formation temperature for long time, which could meet the demand for offshore polymer flooding. Therefore, the UF–NF integrated membrane technology could efficiently resolve the softened water shortage problem in offshore oilfield water flooding and polymer flooding and ensure continuous and stable oil production. [Copyright &y& Elsevier]

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]

Abstract: The essential point for a successful seawater reverse osmosis (SWRO) plant is pretreatment that provides consistent and high-quality feed to SWRO membranes. Advances in membrane technology and increasing requirements on water quality have stimulated the use of ultrafiltration (UF) for SWRO pretreatment. In this study, inside-out (module A) and outside-in (module B) hollow fiber UF modules were adopted as the pretreatment prior to SWRO desalination at Qingdao Jiaozhou Bay, the Yellow Sea of China. The performances of the two modules were compared to operation parameters and permeate qualities. Based on the flux data, TMP and permeability, the outside-in UF module consistently performed better with an air enhanced backwash than the inside-out one using a chemical enhanced backwash, which was not particularly efficient for the outside-in module. As to permeate quality, both modules met the demand of the SWRO feed. [Copyright &y& Elsevier]

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: Nanofiltration (NF) membranes are playing a more and more important role in brackish and seawater softening process, wastewater reclamation and other industrial separation. In this study, ultrafiltation (UF) and NF (ESNA3, Hydranautics) were assembled to an integrated membrane system (IMS) as pretreatment prior to seawater reverse osmosis (SWRO) to evaluate the NF efficiency of seawater softening. The influences of NF feed property (the feed from UF1 with 100kDa MWCO and UF2 with 20kDa MWCO, respectively), operating pressure (0.5–3.0MPa), cross-flow velocity (0.028–0.048m/s) and feed temperature (5–17°C) on the softening efficiency in terms of the NF flux and ion rejection were investigated. The results showed that the high softening efficiency of NF membrane could be achieved using UF membrane with smaller MWCO (20kDa). NF system using UF2 as pretreatment process yielded a higher flux of 61.4L/(m2 h) with Ca2+, Mg2+, SO4 2− rejection of 44.37%, 73.26% and 99.82%, respectively, under the optimum operating conditions of operating pressure at 1.5MPa, cross-flow velocity at 0.035m/s and feed temperature at 12.5°C. And, the relatively excellent selectivity of divalent ions and univalent ions can be obtained by ESNA3 membrane compared to that of other NF membranes reported in the literature, indicating that the ESNA3 membrane seems to be appropriate for seawater softening process. [Copyright &y& Elsevier]