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How To Choose Reverse Osmosis Membrane

How To Choose Reverse Osmosis Membrane

As a frequently asking question by customers, what indicators do we need to consider when choosing a reverse osmosis membrane?

There are usually three:  rate of desalination, water production yield, and recovery rate.
1) Desalination rate of reverse osmosis membrane
The desalination rate refers to the removal rate of salt by the reverse osmosis membrane.
Desalination rate = (total salt content of input water - total salt content of output water) / total salt content of input water × 100%
Sometimes for convenience reasons, the following formula can also be used to approximate the desalination rate:
Desalination rate = (total feed water conductivity - total output water conductivity) / total feed water conductivity × 100%
The desalination rate of the reverse osmosis membrane element has been determined at the time of its manufacture and formation, and the degree of salt rejection depends on the density of the ultra-thin desalination layer on the surface of the reverse osmosis RO membrane element. The denser the desalting layer, the higher the salt rejection rate, but the lower the water production. The desalination rate for different substances is mainly determined by the structure and molecular weight of the substance. The salt rejection rate of high-valent ions and complex monovalent ions could exceed 99%, and the salt rejection rate of monovalent ions such as sodium ion, potassium ion and chloride ion is slightly lower, but it could also exceed 98%; removal rate of organic matter with molecular weight above than 100 could also exceed 98%,  but for the organic matter which molecular weight less than 100, the removal rate is low.

Note: The longer the reverse osmosis membrane is used or the more chemical cleaning times, the lower desalination rate of the reverse osmosis membrane.

2) Water production of reverse osmosis membrane
Water production of RO membrane refers to the water production capacity of a reverse osmosis system, that is, the amount of water per unit time through the RO membrane, usually expressed in tons per hour or gallons per day.
Besides, the permeate flow rate of the reverse osmosis membrane is also an important indicator that indicates the amount of water produced by the reverse osmosis membrane element.
The permeate flow rate of a reverse osmosis membrane refers to the flow rate of permeate per unit membrane area, usually expressed in gallons per square foot per day (GFD). Excessive permeate flow rates will result in faster water flow rates perpendicular to the surface of the RO membrane, exacerbating membrane fouling.
3) Recovery rate of reverse osmosis membrane
The recovery rate of the reverse osmosis membrane refers to the percentage of the pure water against the feed water in the reverse osmosis membrane system.
The recovery rate of the reverse osmosis system has been determined at design time based on the input water quality of pretreatment system and the final water quality requirements after purifying by the reverse osmosis system.
Recovery rate of reverse osmosis membrane = (water production flow / influent flow of reverse osmosis membrane) × 100%

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