How to judge the quality of reverse osmosis membrane?
Generally, the main indicators for measuring the performance of reverse osmosis membranes include three indicators: recovery rate, water production and flux, and desalination rate.
Reverse Osmosis Membrane Performance Indicator 1: Recovery Rate
Recovery rate is an important indicator representing the efficiency of a reverse osmosis membrane element or system. It indicates how much of the feed water entering the membrane element becomes product water. The formula is: Recovery rate = Product water flow rate (pure water output) ÷ Feed water flow rate
Reverse Osmosis Membrane Performance Indicator 2: Water Production and Flux
Water production is an indicator of how much pure water volume is produced per unit time under certain pressure conditions. Common units include GPD (gallons per day) and LPH (liters per hour). Flux refers to the volume of water produced per unit area of reverse osmosis membrane per unit time, generally expressed in gallons/square foot × day (GFD) and cubic meters/square meter × day. Membrane element water production = Flux × Effective membrane area.
Reverse Osmosis Membrane Performance Indicator 3: Desalination Rate
Desalination rate indicates the ability of the reverse osmosis membrane to remove impurities from water. Generally, the removal rate of relevant impurities by the reverse osmosis membrane can be expressed as follows:
The removal rate of different substances by reverse osmosis membrane elements varies. Generally, the following rules apply:
1. The removal rate of multivalent ions is higher than that of monovalent ions; the removal rate of complex ions is higher than that of simple ions; the removal rate of organic substances with a molecular weight below 100 is lower; and the removal rate of nitrogen-containing elements and their compounds is lower.
2. Desalination rate is expressed as apparent desalination rate and actual desalination rate. Apparent desalination rate = 1 — Product water salinity / Feed water salinity
Actual desalination rate = 1 — 2 × Product water salinity / (Feed water salinity + Wastewater salinity) ÷ 2 × A, where A represents the concentration polarization coefficient (generally between 1.1 and 1.2).
