Nanofiltration (NF) membranes have come a long way since it was first introduced during the late 80's. With properties in between those of ultrafiltration (UF) and reverse osmosis (RO), NF membranes ...have been used in many interesting applications especially in water and wastewater treatment and desalination. Other applications include those in pharmaceutical and biotechnology, food and non-aqueous types of application. This review will comprehensively look at the recent advances in NF membranes research. Significant development has taken place in terms of the fundamental understanding of the transport mechanism in NF membranes. This has been translated into predictive modeling based on the modified extended Nernst–Planck equation. Similarly various methods have been used to fabricate improved NF membranes especially through interfacial polymerization incorporating nanoparticles and other additives, UV grafting/photografting, electron beam irradiation, plasma treatment and layer-by-layer modification. New applications were also explored in many industries. However fouling is still a prevalent issue that may hinder successful application of NF membranes. Efforts towards NF fouling prevention and mitigation have also been reported. The review ends with several recommendations on the future prospect of NF membranes research and development.
•State-of-the-art overview of NF membranes and its approach on membrane fabrication and modification•The trend and progress in the development and application of NF membranes over the past 5years•Fouling and fouling mitigation in the application of NF membrane•Future direction in NF membrane development
Applications of membrane technology in water desalination and wastewater treatment have increased significantly in the past few decades due to its many advantages over other water treatment ...technologies. Water treatment membranes provide high flux and contaminant rejection ability and require good mechanical strength and durability. Thus, assessing the mechanical properties of water treatment membranes is critical not only to their design, but also for studying their failure mechanisms, including the surface damage, mechanical and chemical ageing, delamination and loss of dimensional stability of the membranes. The various experimental techniques to assess the mechanical properties of wastewater treatment and desalination membranes are reviewed. Uniaxial tensile test, bending test, dynamic mechanical analysis, nanoindentation and bursting tests are the most widely used mechanical characterization methods for water treatment membranes. Mechanical degradations induced by fouling, chemical cleaning as well as membrane delamination are then discussed. Moreover, in order to study the membranes mechanical responses under similar loading conditions, the stress-state of the membranes are analyzed and advanced mechanical testing approaches are proposed. Some perspectives are highlighted to study the structure-properties relationship for wastewater treatment and water desalination membranes.
•Experimental techniques to assess the mechanical properties of water treatment membranes are reviewed.•Mechanical degradation mechanisms of water treatment membranes are discussed.•Stress-state of the water treatment membranes are analyzed at different scales.•Advanced mechanical testing methods are proposed to study structure-properties relationship for water treatment membranes.
This study compared the filtration of produced water using two new and highly hydrophilic nanofiltration (NF) and reverse osmosis (RO) membranes to assess removal efficiency in ...pre-and-post-filtration processes, and to compare the quality of water obtained against standards for reuse as indirect potable water. The results show that NF membrane successfully attains 96% of overall drinking water standards, despite its inefficiency in removing boron, molybdenum and ammonia. The study also found that the NF membrane can be used as a pre-treatment for the RO membrane to produce high quality water and reduce contaminant concentrations, thereby minimizing the potential for fouling. In contrast, the produced water treated by the RO membrane successfully met the regulatory quality standards for drinking water, with the exception of the parameters for ammonia and molybdenum. The study concluded that treated produced water has potential for reuse as indirect potable water and that both of the hydrophilic NF and RO membranes studied are suitable for treating produced water to yield a promising source of water.
► The new hydrophilic NF/RO membranes were used for treatment of produced water. ► The hydrophilic properties are anticipated to show a low level of membrane fouling. ► The NF treated water met standards for drinking water except for three parameters. ► The RO treated water has potential for reuse as indirect potable water. ► The NF membrane may be used as a pre-treatment for the RO.
Nanofiltration membranes (NF) have applications in several areas. One of the main applications has been in watertreatment for drinking water production as well as wastewater treatment. NF can either ...be used to treat all kinds of water including ground, surface, and wastewater or used as a pretreatment for desalination. The introduction of NF as a pretreatment is considered a breakthrough for the desalination process. NF membranes have been shown to be able to remove turbidity, microorganisms and hardness, as well as a fraction of the dissolved salts. This results in a significantly lower operating pressure and thus provides a much more energy-efficient process. Similar to other membrane processes, a major problem in NF membrane applications is fouling. Several studies have investigated the mechanisms of fouling in NF membranes and suggested methods to minimize and control the fouling of NF membranes. For NF membrane characterizations and process prediction, modeling of NF processes and the use of atomic force microscopy (AFM) are very important. The ability to predict the performance of NF processes will lead to a lower number of experiments, saving of time and money, and help to understand the separation mechanisms during NF. A comprehensive review of NF in water treatments is presented including a review of the applications of NF in treating water as well as in the pretreatment process for desalination; the mechanism as well as minimization of NF membrane fouling problems; and theories for modelling and transport of salt, charged and noncharged organic compounds in NF membranes. The review will also address the application of AFM in studying the morphology of membrane surfaces as part of the NF membrane characterization.
Antiscalants have been used to inhibit the formation of scales and reduce the risk of membrane scaling. However, issues such as the increased of biofouling tendency and contradictory observations of ...organic fouling propensity under the influence of antiscalants have been reported by other researchers. Such observations indicate the need for thorough understanding about the interaction between antiscalants and membrane/foulants in the solution. This study investigated the influence of antiscalant on the water characteristics and the performance of hybrid coagulation–nanofiltration membrane process for brackish water treatment. It was observed that scaling was mitigated with the addition of antiscalants but membrane fouling was exacerbated at higher dosage, probably due to the changes in foulant properties induced by antiscalants. Analysis carried out on the water showed that antiscalants altered the characteristics of the foulants and formed precipitates with calcium/aluminum and iron (from coagulant) ions, which eventually deposited as foulant layer on the membrane surface. This was proven with the existence of phosphorous element on the membrane surface using SEM–EDX. The findings demonstrated how the antiscalants altered the water characteristics and provided insight into the reactivity of antiscalants present in different concentrations, which could be used to interpret the contradicting findings from other researchers.
•Scaling could severely impair the performance of membrane desalination process.•Antiscalants have been used to prohibit and reduce the risk of scale formation.•Influence of antiscalant on coagulation–NF membrane process was investigated.•Interaction between antiscalant and foulants varied according to its concentration.•Membrane fouling tendency and water characteristic changed with antiscalant dosage.
•Performance and mechanism of chitosan and FeCl3 coagulation processes were studied.•Both coagulants were competitive in removing turbidity and HA in synthetic water.•Effect of chitosan and FeCl3 ...coagulation on NF/RO membrane fouling was investigated.•Chitosan resulted in more severe flux decline and membrane fouling issue.•Membrane fouling phenomena for all the hybrid processes were discussed.
Coagulation is the most common process used to remove the natural organic matter (NOM) for clean water supply and safe consumption. However, most of the time, the supernatant water quality produced did not meet the drinking water standard and several dispute issues currently exist about the impact of conventional inorganic coagulants on the environment and living organisms. In this study, hybrid coagulation–membrane processes were implemented for NOM treatment using chitosan as a natural coagulant. Its performance in terms of turbidity and humic acid (HA) removal was tested and compared with inorganic ferric chloride (FeCl3) coagulant. It was discovered that both coagulants were capable to remove 90% of the HA and produce supernatant water with acceptable quality for membrane processes; both nanofiltration (NF) and reverse osmosis (RO) membrane processes managed to remove nearly all of the turbidity and HA in the water. However, a hybrid process using chitosan had a more severe effect on membrane fouling compared to FeCl3 coagulation pre-treatment processes due to the smaller and neutral particles produced by chitosan coagulation, forming a compact foulant layer on the membrane surface. Therefore, the wise selection of a coagulant for the hybrid coagulation–membrane process is crucial for attaining high removal efficiency and low fouling propensity.
In order to reduce membrane fouling propensity, membrane technologies in water treatment and desalination processes have been coupled with coagulation process. However, the fouling issues still ...persisted. It is believed that coagulation might affect the fouling mechanisms involved. Hence, this study was intended to investigate the influence of water chemistry (solution pH, calcium concentration, and total dissolved solids) on hybrid coagulation–nanofiltration membrane processes. Assessment will be done based on permeate flux, salt rejection trend, and foulant layer autopsy. It was discovered that coagulation process altered the properties of the foulants in the solution and resulted in distinct membrane fouling phenomena compared to most of the standalone membrane fouling studies. This situation prevailed in the presence of calcium ions in the solution. It was postulated that coagulation process weakened the interaction between the oppositely charged calcium ions and foulants. Therefore, instead of forming complex with the foulants, calcium ions had higher affinity towards more negatively charged membrane. Consequently, calcium salts precipitated and formed scales on the membrane surface, as supported by membrane performance and SEM-EDX analysis. This indicated that membrane fouling study should consider the impact of pretreatment process for better understanding about the fouling mechanisms involved.
•Hybrid coagulation–NF membrane process for brackish water desalination was studied.•Influence of water chemistry on the performance of hybrid process was investigated.•Properties of the foulants in the solution were altered by coagulation process.•Distinct membrane fouling phenomena compared to single fouling study were observed.•Membrane foulant cake layer was inspected and linked to explain fouling mechanisms.
Atomic force microscopy (AFM) has been used to characterize five commercial nanofiltration (NF) membranes from three companies. High-resolution 3D images of the membranes were obtained without ...preparative treatment that may affect the membrane surface. Obtained images have been filtered to overcome the effect of tip convolution and the noises. Two sizes of the images were obtained 2 μm × 2 μm and small sizes. The first images were used to find the surface morphology data such as average roughness, mean height, root mean square (RMS), and maximum peak-to-valley. The small size images showing visible pores were used to determine the pore size and pore size distributions, which were used to calculate porosity of membranes. A fitted line using lognormal distributions was used to represent the pore size distribution of the nanofiltration membranes. The results show that the lognormal distribution is fitted well with AFM experimental data.
This study compared the filtration of produced water using two new and highly hydrophilic NF and RO membranes to assess toxicity removal efficiency in pre- and post-filtration samples for reuse as ...indirect potable water. The toxicity test was conducted using marine luminescent bacterium Vibrio fischeri to monitor changes in the level of light emission during exposure to unknown toxic substances present in the tested pre- and post-filtration samples of produced water. The results show that the quality of water obtained using the NF membrane was toxic at an effective concentration of 13.65% (EC50). However, the performance of NF membrane in rejecting 48% of total organic carbon indicates that it has high potential for use as a pretreatment for the RO membrane in treating produced water because this configuration will decrease the rate of fouling by organics. Toxicity test analysis further revealed that the RO-treated produced water was free of toxicity, whereby 100% of the effective concentration (EC50) caused no effects when exposed to V. fischeri. Therefore, converting produced water from a pollution source into a new water resource has been conclusively shown to be readily achievable, especially through the use of a combined membrane system rather than a single membrane.
► The NF-treated produced water was found to be toxic at EC50 of 13.65%. ► The additive chemicals have potential to contribute toxicity to NF-treated water. ► The NF membrane removed 48% of TOC and shows potential to be used as a pretreatment. ► The RO-treated produced water was free of toxicity when exposed to Vibrio fischeri. ► The RO-treated produced water shows potential for reuse as indirect potable water.
Minimally invasive pancreaticoduodenectomy (MIPD) is a demanding surgical procedure, thus explaining its slow expansion and limited popularity amongst Hepato-Pancreatico-Biliary (HPB) surgeons. ...However, three main advantages of robotic assisted pancreaticoduodenectomy (PD) including improved dexterity, 3D vision less surgical fatigue, may overcome some of the hurdles and ultimately lead to a wider adoption. This systematic review and network meta-analysis aims to evaluate the current literature on open and MIPD.
A systematic literature search was conducted for studies reporting robotic, laparoscopic and open surgery for PD. Network meta-analysis of intraoperative (operating time, blood loss, transfusion rate), postoperative (overall and major complications, pancreatic fistula, delayed gastric emptying, length of hospital stay) and oncological outcomes (R0 resection, lymphadenectomy) were performed.
Sixty-one studies including 62,529 patients were included in the network meta-analysis, of which 3% (n = 2131) were totally robotic (TR) and 10% (n = 6514) were totally laparoscopic (TL). There were no significant differences between surgical techniques for major complications, overall and grade B/C fistula, biliary leak, mortality and R0 resections. Transfusion rates were significantly lower in TR compared to TL and open. Operative time for TR was longer compared with open and TL. Both TL and TR were associated with significantly lower rates of wound infections, pulmonary complications, shorter length of stay and higher lymph nodes examined when compared to open. TR was associated with significantly lower conversion rates than TL.
In summary, this network meta-analysis highlights the variability in techniques within MIPD and compares other variations to the conventional open PD. Current evidence appears to demonstrate MIPD, both laparoscopic and robotic techniques are associated with improved rates of surgical site infections, pulmonary complications, and a shorter hospital stay, with no compromise in oncological outcomes for cancer resections.
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