As is clear from the foregoing, the most important part of the process is reverse osmosis membrane (OI)
Basically there are two materials used in the construction of semi-permeable membranes for reverse osmosis:
cellulose acetate.
This material is made the first membranes used industrially .
Polyamide.
Since manufacturing methods and materials technology are making significant progress in recent years, is being membrane pore size and permeability controlled which allows the separation of organic and inorganic substances with sizes between 1 and 10 molecular weight and very close.
RO membranes are commercially grouped within the container, usually cylindrical, and arranged in different configurations.
The set membrane-container is called reverse osmosis module .
The container must be resistant to high pressure, remember that the pressures in industrial-type facilities between 14 and 60 bar or whatever it is the same 200 and 850 lbf/in2, containers have generally three jacks: one for water input and two for output or osmosis permeate water output and concentrated.
Basically there are two materials used in the construction of semi-permeable membranes for reverse osmosis:
cellulose acetate.
This material is made the first membranes used industrially .
Polyamide.
Since manufacturing methods and materials technology are making significant progress in recent years, is being membrane pore size and permeability controlled which allows the separation of organic and inorganic substances with sizes between 1 and 10 molecular weight and very close.
RO membranes are commercially grouped within the container, usually cylindrical, and arranged in different configurations.
The set membrane-container is called reverse osmosis module .
The container must be resistant to high pressure, remember that the pressures in industrial-type facilities between 14 and 60 bar or whatever it is the same 200 and 850 lbf/in2, containers have generally three jacks: one for water input and two for output or osmosis permeate water output and concentrated.
commercial configurations used are: Tubular
: They consist of long porous tubes with lengths ranging from 1.5 to 3 m. and with diameters between 0.5 and 1 inch which are, concentrically, inside the membrane. The raw water is circulated through the interior, collecting the water permeated from the outside wall of the inner membrane and the container tube. Hollow Fiber
: They consist of thousands of hollow fibers (capillaries) into a bundle inside the container and the ends are inserted into an epoxy resin support. The outer diameter of these capillaries ranged between 60 and 80 microns for the polyamide and 200 to 300 microns for acetate. Water is required to pass through the capillary wall thickness of about 20 microns.
Spirals: These consist of sheets of membrane that are placed on a porous support and a spacer, this set is wound on a PVC pipe to serve as permeate water collector. Today 60% of the membranes used are of this type.
The reason for this popularity are two significant advantages:
1) Good relationship membrane area / module volume.
2) A design that allows use in most applications, supports a turbidity of more than three times greater than other systems, and can work with turbulent flow.
According to materials that are made of membranes, the behavior with respect to different content in water or different parameters indicating the same is very different pH
Polyamide is stable within a pH range from 3 to 11, and can withstand short periods, maximum 30 minutes, a pH between 1 and 12.
cellulose acetate to be an organic ester is subjected to hydrolysis with acid and alkaline pH , so the optimal working range of pH is between 4 and 7. Oxidants
Polyamide is attacked by the oxidant, so that the free chlorine greater than 0.1 ppm destroys the membrane.
cellulose acetate resists the action of oxidants can withstand chlorine amounts of about 2 ppm. Temperature
The effect of feed water temperature occurs in the membranes is an important feature to consider for the proposed facility as a strong influence on performance.
yields all the modules are given in a preset conditions of salinity , recovery, pressure and temperature. For the parameter
temperature 25 º C are considered, favoring performance at high temperatures to a certain limit.
For every degree Celsius change over the base temperature will cause a decrease, in the case of colder water, or an increase in the case of warmer water, 2.5 to 3% in the performance of the system.
maximum working temperatures between 30 º C for acetate and 45 ° C for polyamide.
Working at high temperatures favors the compaction phenomenon experienced by the membrane due to pressure of work, producing over time a decrease in production.
Differences between Membrane
Depending on the configuration of membranes taken, there are also differences in performance and operation.
A fundamental difference between a hollow fiber module and a coil is the system of water circulation through it, be it laminar and turbulent hollow fiber to spiral.
This phenomenon is very important because depending on the flow regime that we will be, required in water supply levels more stringent filtration hollow fiber to spiral, since the deposition of particles on the surface membrane is favored in laminar regime.
other hand, ease of cleaning spiral membranes is superior to the hollow fiber, but in any case, with better cleaning conditions are tubular, as they enable mechanical cleaning is done with "balls" sponge circulate through the inside of the tubes taking advantage of hydropower .
This module is recommended for the treatment of highly loaded liquids, such as the concentration of fruit juices, typical case in which the "usable" is concentrated.
: They consist of long porous tubes with lengths ranging from 1.5 to 3 m. and with diameters between 0.5 and 1 inch which are, concentrically, inside the membrane. The raw water is circulated through the interior, collecting the water permeated from the outside wall of the inner membrane and the container tube. Hollow Fiber
: They consist of thousands of hollow fibers (capillaries) into a bundle inside the container and the ends are inserted into an epoxy resin support. The outer diameter of these capillaries ranged between 60 and 80 microns for the polyamide and 200 to 300 microns for acetate. Water is required to pass through the capillary wall thickness of about 20 microns.
Spirals: These consist of sheets of membrane that are placed on a porous support and a spacer, this set is wound on a PVC pipe to serve as permeate water collector. Today 60% of the membranes used are of this type.
The reason for this popularity are two significant advantages:
1) Good relationship membrane area / module volume.
2) A design that allows use in most applications, supports a turbidity of more than three times greater than other systems, and can work with turbulent flow.
According to materials that are made of membranes, the behavior with respect to different content in water or different parameters indicating the same is very different pH
Polyamide is stable within a pH range from 3 to 11, and can withstand short periods, maximum 30 minutes, a pH between 1 and 12.
cellulose acetate to be an organic ester is subjected to hydrolysis with acid and alkaline pH , so the optimal working range of pH is between 4 and 7. Oxidants
Polyamide is attacked by the oxidant, so that the free chlorine greater than 0.1 ppm destroys the membrane.
cellulose acetate resists the action of oxidants can withstand chlorine amounts of about 2 ppm. Temperature
The effect of feed water temperature occurs in the membranes is an important feature to consider for the proposed facility as a strong influence on performance.
yields all the modules are given in a preset conditions of salinity , recovery, pressure and temperature. For the parameter
temperature 25 º C are considered, favoring performance at high temperatures to a certain limit.
For every degree Celsius change over the base temperature will cause a decrease, in the case of colder water, or an increase in the case of warmer water, 2.5 to 3% in the performance of the system.
maximum working temperatures between 30 º C for acetate and 45 ° C for polyamide.
Working at high temperatures favors the compaction phenomenon experienced by the membrane due to pressure of work, producing over time a decrease in production.
Differences between Membrane
Depending on the configuration of membranes taken, there are also differences in performance and operation.
A fundamental difference between a hollow fiber module and a coil is the system of water circulation through it, be it laminar and turbulent hollow fiber to spiral.
This phenomenon is very important because depending on the flow regime that we will be, required in water supply levels more stringent filtration hollow fiber to spiral, since the deposition of particles on the surface membrane is favored in laminar regime.
other hand, ease of cleaning spiral membranes is superior to the hollow fiber, but in any case, with better cleaning conditions are tubular, as they enable mechanical cleaning is done with "balls" sponge circulate through the inside of the tubes taking advantage of hydropower .
This module is recommended for the treatment of highly loaded liquids, such as the concentration of fruit juices, typical case in which the "usable" is concentrated.
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