The Dangers of Reverse Osmosis Concentration Polarization and How to Eliminate It

Understanding Reverse Osmosis Concentration Polarization

In reverse osmosis (RO) membrane separation processes, water molecules pass through the membrane, leaving behind a layer with increased salt concentration. This creates a significant concentration gradient between the membrane surface and the feed water stream, known as concentration polarization. Concentration polarization can severely impact the efficiency and effectiveness of the RO system.

The Dangers of Concentration Polarization

  1. Increased Osmotic Pressure High salt concentration at the interface layer raises the osmotic pressure, resulting in decreased water output under existing operating conditions. To maintain the original water output, the feed water pressure must be increased, which leads to higher energy consumption.
  2. Increased Salt Passage The elevated salt concentration at the interface increases the concentration difference (Δc) across the membrane, leading to higher salt passage into the product water.
  3. Membrane Fouling Higher concentration levels at the interface promote the precipitation of scaling substances, leading to membrane fouling. Frequent cleaning is required to restore performance, which may cause irreversible damage to the membrane.
  4. Colloidal Pollution The diffusion rate of colloidal substances is hundreds to thousands of times slower than that of salts. Consequently, concentration polarization significantly contributes to colloidal pollution on the membrane surface.

Measures to Eliminate Concentration Polarization

  1. Control Water Flux Strictly control the water flux through the membrane to avoid exceeding the membrane’s design limits, thereby reducing the formation of concentration polarization.
  2. Control Recovery Rate Follow the membrane manufacturer’s recommendations to strictly control the system’s recovery rate, preventing the exacerbation of concentration polarization.
  3. Adhere to Manufacturer Guidelines Operate the system according to the design guidelines provided by the membrane manufacturer to ensure optimal membrane performance.

Increasing Turbulence to Reduce Concentration Polarization

One effective method to reduce concentration polarization is to increase the turbulence of the brine channel. In spiral-wound RO element designs, the brine spacer design is already considered to enhance the turbulence of the brine flow.

Conclusion

Concentration polarization in reverse osmosis systems significantly affects operational efficiency. Implementing effective measures can mitigate its harmful effects and improve system performance and membrane longevity. Controlling water flux and recovery rate, following manufacturer guidelines, and increasing flow turbulence are essential strategies to eliminate concentration polarization.

Xi’an CHIWATEC Water Treatment Technology is a high-tech enterprise specialized in various water processing devices. Aside from these individual products, which cover a number of types and series, we can also help with related comprehensive engineering projects. Thanks to our hard work and dedication upon our founding, we are now one of the fastest-developing water treatment equipment manufacturers in Western China.

Further reading

Underground Reverse Osmosis Plant

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