Best Guide: Main Types of RO Membrane Clogging and Their Solutions| Insights by AQUALITEK

✅ 1. Introduction

RO membranes are precision filtration components designed to remove dissolved salts and impurities through semi-permeable barriers. However, during continuous operation, the membrane surface can become clogged with various substances depending on the feedwater composition and system operation conditions.

Understanding the different types of membrane clogging and their specific treatment strategies is essential to optimize performance, prevent downtime, and extend membrane lifespan.

✅ 2. Main Types of RO Membrane Clogging

(1) Particulate and Colloidal Fouling

Description: Caused by suspended solids, silt, and fine colloids that accumulate on the membrane surface.
Common Indicators:

•Increasing differential pressure (ΔP) between feed and concentrate

•Decreasing permeate flow rate
Causes:

•Inadequate pretreatment (e.g., ineffective sand or cartridge filtration)

•High SDI (>3) or turbidity
Solutions:

•Improve pretreatment with microfiltration (MF) or ultrafiltration (UF)

•Backwash pretreatment filters regularly

•Maintain SDI < 3 before the RO inlet

(2) Scaling (Inorganic Fouling)

Description: Precipitation and deposition of inorganic salts such as calcium carbonate (CaCO₃), calcium sulfate (CaSO₄), barium sulfate (BaSO₄), or silica (SiO₂) on the membrane surface.
Common Indicators:

•Gradual increase in feed pressure

•Decline in recovery rate

•Reduced permeate flux
Causes:

•High hardness or alkalinity in feedwater

•Inadequate antiscalant dosing

•Poor pH control
Solutions:

•Use appropriate antiscalant chemicals based on water chemistry

•Adjust recovery rate and pH

•Periodically perform acid cleaning (citric or hydrochloric acid)

(3) Organic Fouling

Description: Adsorption of natural organic matter (NOM), oils, surfactants, or humic substances onto the membrane surface.
Common Indicators:

•Decrease in flux

•Increase in TOC (total organic carbon) in permeate

•Brown or oily film on membrane
Causes:

•Incomplete activated carbon filtration

•High TOC feedwater (especially from surface or wastewater sources)
Solutions:

•Use activated carbon filters or UF membranes before RO

•Clean with alkaline detergents or surfactant-based cleaners

(4) Biofouling

Description: Caused by microbial growth forming biofilms on membrane surfaces and spacers.
Common Indicators:

•Gradual pressure rise

•Slime formation inside pressure vessels

•Deteriorating water quality or odor
Causes:

•Nutrient-rich feedwater

•Inadequate chlorination/dechlorination control
Solutions:

•Maintain proper disinfection upstream

•Periodically apply biocidal cleaning agents

•Use alkaline cleaning (pH 11–12) for biofilm removal

(5) Chemical Attack and Oxidation Damage

Description: Irreversible degradation of the polyamide layer due to exposure to oxidants (chlorine, ozone) or harsh pH conditions.
Common Indicators:

•Sudden increase in permeate conductivity

•Sharp decline in salt rejection
Causes:

•Residual chlorine not fully neutralized

•Improper cleaning reagent concentration
Solutions:

•Keep residual chlorine <0.05 ppm before RO

•Use sodium bisulfite for dechlorination

•Avoid excessive chemical exposure during cleaning

(6) Metal Oxide Fouling

Description: Precipitation of iron, manganese, or aluminum hydroxides on the membrane surface.
Common Indicators:

•Red, brown, or black staining on membrane

•Reduced flux and pressure imbalance
Causes:

•High Fe/Mn content in feedwater

•Poor oxidation/filtration control
Solutions:

•Oxidize and filter metals prior to RO (e.g., using aeration or MnO₂ filters)

•Clean with citric acid or EDTA-based solutions

✅ 3. Comparative Table of Clogging Types

✅ 4. Preventive Maintenance Recommendations

•Maintain SDI < 3 and turbidity < 0.2 NTU

•Apply appropriate antiscalant and biocide dosing

•Conduct CIP cleaning when normalized flux drops 10–15%

•Regularly test feedwater and permeate quality

•Train operators for proper shutdown and restart procedures

✅ 5. Conclusion

RO membrane clogging is an inevitable challenge in long-term system operation, but it can be effectively controlled through systematic pretreatment, precise monitoring, and timely cleaning.

By understanding each clogging mechanism—particulate, scaling, organic, bio, and chemical—operators can optimize cleaning schedules, minimize downtime, and ensure consistent product water quality.

A proactive approach ensures longer membrane life, lower energy consumption, and higher reliability across all industrial water treatment systems.