Best Guide: What Should I Do If the Membrane Performance Cannot Be Restored After Cleaning?| Insights by AQUALITEK

1. When Membrane Cleaning Fails—What Does It Mean?

If RO membrane performance does not recover after a standard cleaning procedure (CIP), it typically indicates that the membrane has experienced irreversible fouling or damage.

Common symptoms include:

•Permeate flow remains low

•Salt rejection cannot return to normal

•Differential pressure stays elevated

•Cleaning effect lasts only briefly

•Required operating pressure continues to rise

In these cases, simply repeating the cleaning will not solve the problem.

2. Typical Causes of Unrecoverable Membrane Performance

1. Irreversible Organic Fouling

If organic contaminants have compressed into the membrane pores for too long, they can become impossible to remove.

2. Severe Scaling

Silica scaling or carbonate/sulfate scaling that has crystallized tightly often cannot be dissolved even with intensive acid cleaning.

3. Oxidation Damage (Chlorine Exposure)

Chlorine permanently destroys the polyamide layer, causing rising salt passage and low rejection—this cannot be repaired.

4. Membrane Compaction

High pressure or long-term over-pressurization compresses the membrane, reducing permeability permanently.

5. Biofouling Inside the Membrane Structure

Mature biofilm or EPS (extracellular polymeric substances) can penetrate deeply, making removal impossible.

6. Abrasion or Mechanical Damage

Incorrect handling, sudden pressure shocks, or particulates can physically damage the membrane surface.

7. End-of-Life Membrane Aging

After years of operation, the membrane surface simply deteriorates from wear, chemicals, and pressure.

3. What To Do When Membrane Performance Does Not Recover

Step 1: Verify That Cleaning Was Performed Correctly

Before concluding membrane failure, you should confirm:

•Proper chemical type was used

•Correct pH range and temperature

•Proper soaking time

•Proper flow velocity and cleaning contact

•No residual chlorine entering the system

Incorrect cleaning procedures can lead to poor results.

Step 2: Perform a Second Targeted Cleaning

Use a specialized cleaning formula based on the fouling type:

•Acid cleaning → for inorganic scaling

•Alkaline cleaning → for organic fouling

•Enzymatic cleaning → for biofouling

•Chelating agents → for silica or metal fouling

•Surfactants → for colloidal fouling

If performance still does not recover → the fouling is likely irreversible.

Step 3: Inspect the System for Operational Problems

Failure to recover may indicate broader issues:

•Pretreatment failure (UF damage, filter collapse, high SDI)

•Incorrect antiscalant dosing

•Bypass or leakage allowing dirty water into the RO

•Poor CIP frequency or timing

•Overly high system recovery

Fixing root operational problems prevents future membrane failures.

Step 4: Replace the Membrane Module

When all cleaning attempts fail, membrane replacement is the only option.

Replace in cases such as:

•Salt rejection severely degraded

•Permeate flow remains <70% of original

•ΔP remains significantly high

•Chemical or chlorine damage

•Membrane age exceeds typical lifespan (2–3 years)

Replacing the membrane restores system performance and avoids excessive energy consumption.

Step 5: Optimize System to Prevent Recurrence

After replacement, implement preventive measures:

1. Improve Pretreatment

•Lower SDI

•Add UF or multimedia filtration

•Enhance carbon filtration or SBS dosing

2. Optimize Antiscalant Program

Use correct type and dosage to prevent CaCO₃, sulfate, or silica scaling.

3. Monitor Key Parameters Daily

•Pressure

•Conductivity

•pH

•SDI

•Flow rates

•Recovery rate

4. Conduct CIP at the Right Time

Never wait until performance drops too severely; clean when:

•Permeate flow decreases 10–15%

•ΔP increases 15–20%

•Conductivity rises above threshold

5. Avoid Chlorine

Ensure complete dechlorination upstream.

4. When Should You Stop Cleaning and Replace the Membrane?

Replace the membrane when:

✔ Flow drop remains after two proper cleanings
✔ Salt rejection is permanently reduced
✔ ΔP does not normalize
✔ Membranes are older than 3 years in industrial conditions
✔ Cleaning cost exceeds replacement value
✔ Production capacity is compromised

Trying to “save” a permanently damaged membrane leads to higher electricity consumption and lower water quality.

5. Summary: Cleaning Cannot Fix Everything

If membrane cleaning fails to restore performance, the membrane is likely damaged, scaled, compacted, or aged beyond recovery. The best action is:

1.Confirm cleaning method

2.Run a targeted cleaning

3.Check system operation

4.Replace the membrane if still ineffective

5.Improve pretreatment and operating conditions

This approach ensures lower long-term cost and stable system performance.