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Feedwater pretreatment in reverse osmosis systems
RESEARCH TRENDS
that contains the agent, and an osmotic ‘engine’ that swells on contact with water, to cause the release of the beneficial agent over time. The osmotic delivery system has a membrane material that allows a controlled amount of fluid to enter from an exterior part of the capsule, while preventing the compositions within the capsule from passing out of the capsule. The membrane material is cast, calendered or extruded, followed by machining (that is die-cutting, stamping or otherwise cutting to shape) to provide a uniform non-ribbed membrane material. The capsule also includes
Research Trends Reuse of reverse osmosis membranes in advanced wastewater treatment In areas where tap water has a high salt content, wastewater is not appropriate for reuse in agriculture, particularly for sensitive crops. One alternative is reduction, via desalination, of the brackish character to the secondary effluent. A filtration stage is also required before desalination. On the other hand, used reverse osmosis membranes can be recycled and used as filters in the advanced treatment stage in order to reduce suspended matter contained in the secondary effluent. One advantage of this is the environmental recovery of solid waste. Used membranes can be treated with strong chemical oxidants to peel off the active separation layer in order to transform them into microfiltration or ultrafiltration elements. Preliminary tests have been carried out with 20-cm (8-inch) elements. The aim was to compare membrane performance before and after the peeling process. An index, denoted as peeling effectiveness (high flux, high salt passage), is used for comparison. It was observed that potassium permanganate was more effective than others, together with sodium hydroxide. Doses around 1000 mg/L KMnO4 provided the best results. It was also concluded that membrane cleaning, done with sodium bisulphite before peeling, was better when the cleaning solution was recirculated around the membrane, rather than soaking it. Future research will test the actual filtration capability of the peeled membranes using wastewater. J.J. Rodríguez, V. Jiménez, O. Trujillo and J.M. Veza: Desalination 150(3) 219–225 (10 November 2002).
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membrane material retainer that is positioned at a fluid-uptake end so as to keep the membrane material in the capsule, even under a period of high pressure. Patent number: WO 03/000230 Inventors: G.J. Scott, J.R. Peery and J.E. Brown Publication date: 3 January 2003
System for purifying wastewater Applicant/Inventor: J. Toro Galvez, Spain The invention relates to a system for purifying wastewater originating from dumps. It involves the following steps: coagulation-flocculation;
Concentration of a formic acid solution The authors’ previous work clearly showed that electro-eletrodialysis was an efficient way to concentrate a formic acid solution. Electroelectrodialysis can be easily scaled up as electrodialysis, but the equipment cost increases. Accordingly, an electrolysis process with a new cation-exchange membrane was tested in this research work. The effects of concentration, electric current density and the concentration difference between the concentrated side and the dilute side were studied. The experimental results indicated that electrodialysis was also an effective method to concentrate a formic acid solution. For the high concentration system the overall current efficiency was larger than 100%. The overall current efficiency for a low concentration system would be up to 90%. But the concentrated ratio was not as high as was required, and was limited by the operating system and conditions. In general, the overall current efficiency was increased to a maximum value with an increase of the current density. After a certain value, the overall current efficiency began to drop. The increase of the initial concentration helped to increase the overall current efficiency, but led to a decrease in the concentrated ratio. The volume change of the concentrated solution is seriously affected by the current density and the ratio of the initial concentration in the concentrated compartment compared with that in the dilute compartment. G.S. Luo, S. Pan and J.G. Liu: Desalination 150(3) 227–234 (10 November 2002).
Feedwater pretreatment in reverse osmosis systems This paper deals with the conventional physical, chemical and biological unit processes that are widely applied in the Middle East for treating feedwater used by reverse osmosis (RO) systems that produce potable water from brackish groundwater and saline sea water. Depending on the quality of intake water,
alkalinization with sodium hydroxide; pressurized air injection and filtration in parallel; filtration with sand bed, nylon and active carbon; ozonization; filtration with sand bed, nylon, diatoms and active carbon; and reverse osmosis. This system can be used to produce completely disinfected, clear, odourless water that complies with all legislative standards. Moreover, it is economical, fast, effective, easy to manage and perfectly compatible with the environment and people. Patent number: WO 03/000600 Publication date: 3 January 2003
membrane process, post-treatment, and the desired quality of product water, a pretreatment system was designed. Such a system usually comprises a train of unit processes based on technical and cost considerations. The decisions that need to be taken for selecting unit processes involve a thorough evaluation of available alternatives. Results are reviewed of previous experiences and present guidelines, and schemes that have been developed which combine unit processes for pretreatment of RO feedwater. Through the process, the combination of pretreatment units is made in such a way that the quality of feedwater is improved at a minimal cost for pretreatment, and with minimal adverse effects on succeeding processes – the membranes, storage and supply systems. Conceptual layouts of several systems are presented, along with comparative data on expected system performance and cost. A.M. Shahalam, A. Al-Harthy and A. AlZawhry: Desalination 150(3) 235–245 (10 November 2002).
Preparation and characterization of NF composite membrane With a view to be able to prepare high performance nanofiltration (NF) membranes, the authors of this study performed experiments where NF composite membranes were prepared by interfacial polymerization, using an ultrafiltration membrane as substrate. Performance parameters, such as water flux, retention of Na2SO4 and PEG 600 were studied. The results show that under an operational pressure of 0.6 MPa, water fluxes of NF-1, NF-2 and NF-3 are 4.1, 6.0 and 26.5 l/m2 h respectively, while the retention of Na2SO4 is 78, 94 and 94%, respectively. The chemical composition and the surface image of NF membranes were obtained using IR and atomic force microscopy. The prospects of using the membranes in the dyeing industry is also explored. X. Lu, X. Bian and Liuqing Shi: J. of Membrane Science 210(1) 3–111 (December 2002).
Membrane Technology February 2003
that contains the agent, and an osmotic ‘engine’ that swells on contact with water, to cause the release of the beneficial agent over time. The osmotic delivery system has a membrane material that allows a controlled amount of fluid to enter from an exterior part of the capsule, while preventing the compositions within the capsule from passing out of the capsule. The membrane material is cast, calendered or extruded, followed by machining (that is die-cutting, stamping or otherwise cutting to shape) to provide a uniform non-ribbed membrane material. The capsule also includes
Research Trends Reuse of reverse osmosis membranes in advanced wastewater treatment In areas where tap water has a high salt content, wastewater is not appropriate for reuse in agriculture, particularly for sensitive crops. One alternative is reduction, via desalination, of the brackish character to the secondary effluent. A filtration stage is also required before desalination. On the other hand, used reverse osmosis membranes can be recycled and used as filters in the advanced treatment stage in order to reduce suspended matter contained in the secondary effluent. One advantage of this is the environmental recovery of solid waste. Used membranes can be treated with strong chemical oxidants to peel off the active separation layer in order to transform them into microfiltration or ultrafiltration elements. Preliminary tests have been carried out with 20-cm (8-inch) elements. The aim was to compare membrane performance before and after the peeling process. An index, denoted as peeling effectiveness (high flux, high salt passage), is used for comparison. It was observed that potassium permanganate was more effective than others, together with sodium hydroxide. Doses around 1000 mg/L KMnO4 provided the best results. It was also concluded that membrane cleaning, done with sodium bisulphite before peeling, was better when the cleaning solution was recirculated around the membrane, rather than soaking it. Future research will test the actual filtration capability of the peeled membranes using wastewater. J.J. Rodríguez, V. Jiménez, O. Trujillo and J.M. Veza: Desalination 150(3) 219–225 (10 November 2002).
14
membrane material retainer that is positioned at a fluid-uptake end so as to keep the membrane material in the capsule, even under a period of high pressure. Patent number: WO 03/000230 Inventors: G.J. Scott, J.R. Peery and J.E. Brown Publication date: 3 January 2003
System for purifying wastewater Applicant/Inventor: J. Toro Galvez, Spain The invention relates to a system for purifying wastewater originating from dumps. It involves the following steps: coagulation-flocculation;
Concentration of a formic acid solution The authors’ previous work clearly showed that electro-eletrodialysis was an efficient way to concentrate a formic acid solution. Electroelectrodialysis can be easily scaled up as electrodialysis, but the equipment cost increases. Accordingly, an electrolysis process with a new cation-exchange membrane was tested in this research work. The effects of concentration, electric current density and the concentration difference between the concentrated side and the dilute side were studied. The experimental results indicated that electrodialysis was also an effective method to concentrate a formic acid solution. For the high concentration system the overall current efficiency was larger than 100%. The overall current efficiency for a low concentration system would be up to 90%. But the concentrated ratio was not as high as was required, and was limited by the operating system and conditions. In general, the overall current efficiency was increased to a maximum value with an increase of the current density. After a certain value, the overall current efficiency began to drop. The increase of the initial concentration helped to increase the overall current efficiency, but led to a decrease in the concentrated ratio. The volume change of the concentrated solution is seriously affected by the current density and the ratio of the initial concentration in the concentrated compartment compared with that in the dilute compartment. G.S. Luo, S. Pan and J.G. Liu: Desalination 150(3) 227–234 (10 November 2002).
Feedwater pretreatment in reverse osmosis systems This paper deals with the conventional physical, chemical and biological unit processes that are widely applied in the Middle East for treating feedwater used by reverse osmosis (RO) systems that produce potable water from brackish groundwater and saline sea water. Depending on the quality of intake water,
alkalinization with sodium hydroxide; pressurized air injection and filtration in parallel; filtration with sand bed, nylon and active carbon; ozonization; filtration with sand bed, nylon, diatoms and active carbon; and reverse osmosis. This system can be used to produce completely disinfected, clear, odourless water that complies with all legislative standards. Moreover, it is economical, fast, effective, easy to manage and perfectly compatible with the environment and people. Patent number: WO 03/000600 Publication date: 3 January 2003
membrane process, post-treatment, and the desired quality of product water, a pretreatment system was designed. Such a system usually comprises a train of unit processes based on technical and cost considerations. The decisions that need to be taken for selecting unit processes involve a thorough evaluation of available alternatives. Results are reviewed of previous experiences and present guidelines, and schemes that have been developed which combine unit processes for pretreatment of RO feedwater. Through the process, the combination of pretreatment units is made in such a way that the quality of feedwater is improved at a minimal cost for pretreatment, and with minimal adverse effects on succeeding processes – the membranes, storage and supply systems. Conceptual layouts of several systems are presented, along with comparative data on expected system performance and cost. A.M. Shahalam, A. Al-Harthy and A. AlZawhry: Desalination 150(3) 235–245 (10 November 2002).
Preparation and characterization of NF composite membrane With a view to be able to prepare high performance nanofiltration (NF) membranes, the authors of this study performed experiments where NF composite membranes were prepared by interfacial polymerization, using an ultrafiltration membrane as substrate. Performance parameters, such as water flux, retention of Na2SO4 and PEG 600 were studied. The results show that under an operational pressure of 0.6 MPa, water fluxes of NF-1, NF-2 and NF-3 are 4.1, 6.0 and 26.5 l/m2 h respectively, while the retention of Na2SO4 is 78, 94 and 94%, respectively. The chemical composition and the surface image of NF membranes were obtained using IR and atomic force microscopy. The prospects of using the membranes in the dyeing industry is also explored. X. Lu, X. Bian and Liuqing Shi: J. of Membrane Science 210(1) 3–111 (December 2002).
Membrane Technology February 2003