How to Judge the RO Membrane Performance?

Main Performance Indicators

• Salt Rejection
  It is used to describe the capacity of RO membrane in removing impurities from feed water stream and is generally expressed in percentage. The calculation formula is as follows:
  Apparent Salt Rejection = (1 - Permeate TDS/Feed TDS) ×100%
• Productivity
  It is an indicator that reflects the volume of pure water produced by RO membrane per unit time under certain test conditions.
  It is generally expressed in GPD (gallons per day), L/h (liters per hour).
• Flux
  It is used to describe the volume of water produced by RO membrane per unit area per unit time.
  It is generally expressed in GFD (gallons per square foot per day) and m³/m²/D (cubic meters per square meter per day).
  Membrane Element Productivity = Flux × Effective Membrane Area
• Recovery
  It is used to describe the percentage of the RO feed water which is converted into permeate.
  Recovery = Permeate Flow/Feed Flow × 100%

Main Influence Factors

Productivity and salt rejection are key parameters in the reverse osmosis process. They are intrinsic properties to certain system conditions. Meanwhile, the productivity and salt rejection of the membrane system are mainly subject to feed temperature, feed pressure, feed TDS, feed pH value and recovery.

Feed Temperature

As the feed temperature rises, the productivity of the RO membrane increases as well and the salt rejection slightly declines. The feed temperature of the RO membrane shall fall between 5–45 °C.

Take SW-LP-4040 RO Membrane As An Example

Temperature (°C)	5	10	15	20	25	30	35
Feed Pressure (PSI)	150	150	150	150	150	150	150
Productivity (GPD)	1250	1520	1850	2240	2700	3070	3500

Feed Pressure

The productivity and salt rejection of the RO membrane increase as the pressure rises.

Take SW-LP-4040 RO Membrane As An Example

Feed Pressure (PSI)	75	100	150	200	300
Productivity (GPD)	1340	1730	2700	3650	5190
Salt Rejection (%)	98.5	99	99.4	99.6	99.75

Feed TDS

The salt rejection declines as the feed TDS increases. Meanwhile, the productivity slightly goes down.

Take SW-LP-4040 RO Membrane As An Example

Feed Pressure (PSI)	150	150	150	150	150
Feed TDS (mg/L)	200	400	1000	2000	4000
Productivity (GPD)	3000	3000	2850	2700	2270
Salt Rejection (%)	99.7	99.7	99.6	99.5	99.2

Feed pH

As the feed pH goes up, the productivity changes little and the salt rejection grows gradually. When the pH=7, the salt rejection tends to be stable.