Chemical Cleaning of RO Membranes — Cleaning Agents and Procedures for Different Fouling Types| Insights by AQUALITEK
Chemical cleaning is an essential maintenance process for reverse osmosis (RO) membranes, restoring flux, maintaining salt rejection, and extending membrane life. This article explains how RO chemical cleaning works, the cleaning agents used, and procedures tailored to different fouling types.
- Introduction
- Principle of Chemical Cleaning
- ⚙️General Cleaning Principle
- Cleaning Agents for Different Fouling Types
- Standard RO Cleaning Procedure
- ⚙️Step 1: Preparation
- ⚙️Step 2: Chemical Circulation
- ⚙️Step 3: Soaking
- ⚙️Step 4: Rinsing and Neutralization
- ⚙️Step 5: Performance Check
- Example: Two-Step CIP Cleaning Flow
- Best Practices for Chemical Cleaning
- Conclusion
Introduction
In industrial reverse osmosis (RO) systems, membrane fouling inevitably occurs over time due to scaling, colloids, organics, or biological growth.
When performance indicators such as normalized flux decline (>10–15%) or pressure differential increase (>15%) are detected, chemical cleaning (CIP, Clean-In-Place) must be performed.
Effective chemical cleaning can:
•Recover system performance
•Prolong membrane lifespan
•Reduce energy and operational costs
Principle of Chemical Cleaning
The CIP process dissolves, disperses, or removes accumulated foulants on the membrane surface.
Each fouling type requires specific cleaning chemicals, chosen based on the chemical nature of the deposits and membrane material compatibility.
⚙️General Cleaning Principle
1.Low-pressure recirculation of cleaning solution through RO elements
2.Soaking to allow reaction and dissolution of foulants
3.Rinsing with permeate water to remove residues
4.System restart and normalization check
Cleaning Agents for Different Fouling Types
|
Fouling Type |
Typical Cause |
Cleaning Agent |
pH Range |
Key Action |
|
Scaling (Inorganic) |
CaCO₃, CaSO₄, BaSO₄, SiO₂ precipitation |
Acidic cleaner (citric acid, HCl < 0.1%) |
2.0–3.0 |
Dissolves carbonate and sulfate scales |
|
Colloidal Fouling |
Fe(OH)₃, Al(OH)₃, silica colloids |
Mild acid + dispersant |
3.0–4.0 |
Solubilizes hydroxides and breaks aggregates |
|
Organic Fouling |
Humic acid, oil, surfactants |
Alkaline detergent (NaOH + surfactant) |
10–12 |
Breaks organic bonds and emulsifies oils |
|
Biofouling |
Bacteria, algae, biofilm |
Biocide or oxidizing cleaner (H₂O₂, NaOCl) |
Neutral–alkaline |
Oxidizes and sterilizes biofilm |
|
Mixed Fouling |
Combination of scale + organics |
Two-step cleaning: acid then alkaline |
Sequential |
Targets both inorganic and organic fouling |
Standard RO Cleaning Procedure
⚙️Step 1: Preparation
•Stop RO operation and isolate cleaning loop
•Prepare CIP tank with permeate or RO water
•Heat solution (typically 25–35 °C) to enhance cleaning efficiency
⚙️Step 2: Chemical Circulation
•Circulate cleaning solution at low pressure (≤4 bar) to avoid membrane compaction
•Flow direction: Feed → Concentrate → Permeate blocked
•Duration: 30–60 minutes per stage
⚙️Step 3: Soaking
•Stop circulation and soak membranes for 30–60 minutes
•Promotes dissolution and chemical reaction with deposits
⚙️Step 4: Rinsing and Neutralization
•Flush membranes thoroughly with RO permeate until pH returns to neutral
•Discharge cleaning solution according to environmental safety standards
⚙️Step 5: Performance Check
•Restart RO unit
•Compare normalized flux and salt rejection before/after cleaning
Example: Two-Step CIP Cleaning Flow
Flow Chart:
1.Step 1 (Alkaline Cleaning): Remove organics, biofilm, and oils
2.Rinse with RO water
3.Step 2 (Acid Cleaning): Remove inorganic scales and metals
4.Final rinse and return to operation
This two-step sequence prevents acid-base neutralization and ensures full coverage of different foulants.
Best Practices for Chemical Cleaning
•Always analyze foulant composition before cleaning
•Use manufacturer-approved cleaning agents to protect membrane integrity
•Avoid excessive pressure or temperature (>35 °C) during cleaning
•Regularly monitor CIP frequency (typically every 3–6 months)
•Maintain SDI < 3 and TOC < 2 mg/L to reduce fouling rate
Conclusion
Chemical cleaning is the backbone of membrane maintenance in RO systems.
By selecting the right cleaning agent, controlling conditions, and following standardized procedures, operators can effectively restore performance, reduce downtime, and extend the service life of expensive RO membranes.
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