As per the opinion of industrial experts, Reverse Osmosis is a proven technology to purify water. It follows the distinctive theory of contaminant-separation. So, it is useful for different ranges of application. This technology removes the dissolved salts and solids from the water.
It is one of the most decent water desalination theories as it can convert brackish water and seawater into both drinking water and usable water for industrial applications. RO membrane is the major component to execute this whole water purification technique.
What Is RO Membrane?
RO membrane is such a component that works as an executor of reverse osmosis based technique, cross-flow filtration. In this filtration, the RO membrane treats the solution, having high salinity. This component acts in a very effective way to purify the surface water, seawater, even brine.
The core aspects of cross-filtration ensure the purity of the water by the active mechanism of the RO membrane. The stream of feed water flows through the connective path to the surface of the membrane.
In step by step, the fraction of water molecules of the feed stream crosses the layers of the membrane. And the major part of the feedwater flow ranges along the membrane surface. In this process, the RO system collects two types of streams :
● Concentrate Stream – It holds a high concentration of dissolved ions and tiny solid particles.
● Permeate Stream – It contains low concentrated ions.
In the entire process of reverse osmosis, pressure plays a vital role. During the purification, the cross-flow filtration technique is a proven option. The high level of pressure than osmosis pressure is applied to the concentrated stream.
Thus the application of force pushes the fraction of water from the top concentrated side to the thinner side. And the potent layers of the RO membrane keep the solutes.
Description of RO Membrane Components
The major component of the RO system is the RO membrane. And holds an authentic structure, which can be both of flat sheet HFF (Hollow Fine Fiber) format.
The entire format of the RO membrane is defined with a support layer made of non-woven polyester, a barrier layer made of polyamide, and a polysulfone layer. Among these three layers, the polyamide layer is based on molecules.
How to Justify the Effective Scale of Purification in RO Membrane
To justify the range of effective purification, you must go through different parameters of the reverse osmosis operation. The following points describe the useful parameters of the RO membrane, which ensure the level of cross-flow filtration.
The evaluation of three streams in an RO device shows the level of performance of the RO membrane. These three streams are concentrate streams, permeate creeks, and feed streams. During operation, the act of RO membrane converts feed stream into the permeate stream and concentrate stream. The flow ratio of these three streams are estimated in gallons per minute.
The flow rate of the feed stream is defined by the ratio of water entered into the RO device. The ratio of water fraction passes through the RO membrane determines the flow rate of permeate. And, the proportion of stream, which can not cross the RO membrane and exits from the RO system with ion particles, defines the flow rate of the concentrate stream.
Permeate Flux Rate
During the process of purification, the amount of permeate produced by the adequate performance of the RO membrane per unit of time is called permeate flux. A liter is the unit, which measures the permeate flux ratio per square meters per hour.
Salt Rejection Rate
The ratio, which measures the amount retained solute, produced by the membrane, is called salt rejection.
The ratio of stream fraction of feed flow passes through the RO membrane defines the recovery rate. Generally, it is estimated in percentage.
Pressure Drop Rate
The difference of pressure between feed stream and concentrate stream during the operation of the RO membrane defines the rate of pressure drop.
The significant driving power for the entire performance of an RO membrane is TMP or Transmembrane pressure. The difference of pressure between the permeate side and feed side in the membrane area defines the transmembrane pressure. This pressure is estimated in psi and bar.
According to the theory of membrane separation, the increment of TMP pressure boosts the level of permeate flux in the membrane area.
Core Aspects of RO Membrane Performance
The major parameter of RO membrane performance is the ratio of permeate flux. In literal terms, the average ratio of permeate flux depends on the difference between the amount of permeate production and salt rejection. The average ratio of permeate flux ensures the quality level of permeate.
Different operating factors, such as temperature, feed pressure, feed concentration, influence the average ratio of permeate flux. So, the entire performance of an RO device depends on these core factors of RO membrane operation.
Reasons Behind the Change of RO Membrane Performances
● During the enhancement of feed pressure, permeate flux becomes proportional as feed pressure works as primary driving pressure. And the rate of dissolved particles in the feed water does not increase. So, the ratio of salt rejection and permeate flux increases.
● If osmotic pressure decreases the major driving pressure, while feed water contains less amount of salt, in this condition, salt rejection level is reduced as a random effect of RO membrane performance.
● Increment of temperature increases the permeate flux ratio. As temperature works to lower the viscosity of water, so the rate of solute permeation becomes higher than permeating flux with heat.
● The low flow rate of feed water leads to concentration polarization. And this fact leads to the osmotic pressure increment than the level of concentration across the membrane surface.
Besides, the presence of different chemicals influences the performance of the RO membrane. The following points discuss the effect of chemicals on membrane separation.
Reasons Behind the Change of Average Membrane Rejection Ratio
Low-acidity and high alkalinity-based compounds may change the level of RO membrane rejection. Because due to dissociation of acids at alkaline pH leads the charge repulsion between the compounds and the surface of the membrane. So, as a consequence, the membrane rejection enhancement occurs.
Elemental Construction of RO Membrane
The available designs of the RO membrane is defined based on some specific shape of elements. Those are the frame, hollow fiber, tubular, and plate. These elements are remarkably used to make membrane structure.
The most popular and common element device for the application of the RO membrane is spiral-wound. To assemble the potent structure of the RO membrane, a spiral-wound configuration is very suitable.
This format effectively enhances the performance of the RO membrane due to having an abundant amount of packing density. The module of the spiral-wound configuration uses a center pipe, wrapped with flat sheets. Glu is used to pack the membranes from three sides.
Thus, the reliable mechanism of spiral-wound shape makes the membrane leaves cling to the center pipe or permeate channel. This center pipe is packed with the exposed edge of the leaf of the RO membrane. The internal part of the membrane leaf holds a permeate tricot. This tricot is specially designed for supporting the membrane sheet to prevent the collapse during pressure enhancement.
For being spongy, the permeate tricot clings to the center pipe. The tricot of the feed channel is attached between the leaves to maintain the feed channel’s height. This specific format is highly suitable for mass transfer.
Thus, the highly robust structure of the RO membrane helps to execute the entire cross-flow filtration process. For the maintenance of RO devices, a technician must know the core structure of the reverse osmosis membrane. Understanding the proper configuration of the membrane modules helps to understand the reason for flaws in membrane performance.
To get more detail on the elemental format of the RO membrane and its mechanism, go to the WaterBug portal pages. It will guide on the core factors of RO membrane performance.