90% of People Don’t Know: The Truth Behind RO Membrane Clogging

90% of People Don’t Know: The Truth Behind RO Membrane Clogging

Clogging is a common issue when using reverse osmosis (RO) membranes. It is an inevitable phenomenon—it’s only a matter of time before it occurs. If clogging happens frequently, it’s essential to identify the causes and find appropriate solutions. This article primarily discusses common causes of RO membrane clogging and their solutions.

Causes and Solutions for Reverse Osmosis Membrane Clogging
1. The system’s pretreatment equipment is not suitable for the raw water quality and flow rate, or the system lacks necessary process equipment and steps.
2. The pretreatment equipment is not functioning properly; that is, the system’s existing pretreatment equipment has low removal efficiency for raw water SDI, turbidity, colloidal matter, etc., resulting in suboptimal pretreatment performance.
3. Inappropriate equipment selection or incorrect choice of materials (pumps, piping, and others).
4. Malfunction of the system’s chemical dosing system (acids, flocculants/coagulants, scale inhibitors/dispersants, reducing agents, and others).
5. Intermittent operation of the equipment or failure to implement appropriate protective measures after system shutdown.
6. Improper operation and management by operating personnel (recovery rate, product water flow, concentrate flow, pressure drop, cleaning, and others).
7. Long-term accumulation of insoluble precipitates within the membrane system.
8. Significant variations in raw water composition or fundamental changes in water source characteristics.
9. The reverse osmosis membrane system has experienced a significant degree of microbial contamination.

Symptoms of Scaling and Membrane Fouling Caused by Different Contaminants
1. Carbonate Scale
Symptoms after scaling: Decrease in standard permeate flow rate or decrease in desalination rate.
Cause: Increased concentration polarization on the membrane surface.
2. Iron/Manganese
Symptoms: Increased standard pressure drop (primarily in membrane elements at the front of the system), which may also cause a decrease in permeate flow rate. Manganese and iron are typically present simultaneously.
3. Sulfate Scale
If deposits form, they first affect the membrane elements at the rear of the system where salt concentration is highest, resulting in a significant increase in the pressure drop across the second stage. Specialized cleaning agents are required.
4. Silica
Particulate silica: Clogs the water flow channels of membrane elements, leading to increased system pressure drop. A 0.4% solution of dichloramine is effective against severely contaminated dissolved silica scale.
Colloidal silica: Similar to particulate silica.
Dissolved silica: Forms silicate precipitates; dichloramine cleaning should be used.
5. Suspended Solids/Organics
Contamination Symptoms: Decreased water flux and a significant increase in first-stage pressure drop. If the feedwater SDI exceeds 4 or turbidity exceeds 1, organic contamination is highly likely.
6. Microorganisms
Contamination Symptoms: Increased standard pressure drop or decreased standard water flux. Cleaning can be performed using non-oxidizing biocides combined with alkali.
7. Iron Bacteria
Contamination Symptoms: Increased standard pressure drop. Cleaning can be performed using sodium EDTA combined with alkali.

Cleaning should be performed when the following conditions occur:
1. Standardized water production has decreased by 10–15%;
2. Standardized operating pressure of the membrane system has increased by 15%;
3. Standardized salt rejection of the membrane system has increased by 10–15% compared to the initial normal value;
4. The operating pressure drop has increased by 15% compared to initial operation.

Reverse Osmosis Membrane Cleaning Methods
1. Vacuum Cleaning: Vacuum cleaning involves creating pressure on the reverse osmosis membrane side through the equipment’s vacuum suction, effectively removing contaminants from both the membrane surface and interior;
2. Backflushing: Backflushing involves using a high-pressure gas or liquid stream to clean the membrane surface, thereby removing contaminants from the interior of the membrane and restoring it to a clean state. Backflushing is currently one of the most commonly used methods for cleaning reverse osmosis membranes; 3. Chemical Cleaning: Chemical cleaning involves using chemical cleaning agents to clean reverse osmosis membranes. Because these chemicals target specific contaminants, they can effectively clean the membranes. This method is also one of the most commonly used cleaning methods.