Analysis of the main factors affecting the performance of reverse osmosis membranes

1. The influence of inlet water pressure on Reverse Osmosis Membranes

The inlet water pressure itself does not affect the salt permeation, but the increase in inlet water pressure increases the net pressure driving reverse osmosis, which increases the water production. At the same time, the salt permeation remains almost unchanged. The increased water production dilutes the salt permeating the membrane, reduces the salt permeability, and increases the desalination rate.

When the inlet water pressure exceeds a certain value, due to the excessive recovery rate, the concentration polarization is increased, which will lead to an increase in salt permeation, offsetting the increased water production, so that the desalination rate will no longer increase.

2. The influence of inlet water temperature on reverse osmosis membranes

For every 1°C increase in inlet water temperature, the water production flux increases by 2.5%~3.0%, the reason is that the viscosity of water molecules passing through the membrane decreases and the diffusion performance is enhanced.

The increase in inlet water temperature will also lead to an increase in salt permeability and a decrease in desalination rate, mainly because the diffusion rate of salt through the membrane will be accelerated by the increase in temperature.

3. Effect of influent pH value on reverse osmosis membrane

The influent pH value has almost no effect on the water output, but has a greater effect on the desalination rate. Since the hydration radius of hydrogen ions is small, they can easily pass through the reverse osmosis membrane.

Therefore, the desalination rate is also low when the pH is low, and the desalination rate gradually increases with the increase of pH. The desalination rate reaches the highest between pH7.5 and 8.5, and then gradually decreases. This is because under alkaline conditions, CO2 dissolved in water exists in gaseous state, and after passing through the reverse osmosis membrane, it forms carbonate or bicarbonate, which reduces the desalination rate.

4. Effect of influent salt concentration on reverse osmosis membrane

The higher the salt content, the higher the osmotic pressure. When the influent pressure remains unchanged, the net pressure will decrease and the water output will decrease. The salt permeability is proportional to the difference in salt concentration between the positive and negative sides of the membrane. The higher the salt content of the influent, the greater the concentration difference, the higher the salt permeability, and the lower the desalination rate.