Membrane Fouling & Cleaning Glossary: 30+ Terms

This glossary covers key terms related to membrane fouling, scaling, and cleaning. Each term is defined with technical accuracy for membrane researchers, engineers, and water treatment professionals. For the complete glossary covering all 80+ membrane technology terms, see our comprehensive membrane technology glossary.

Membrane Fouling, Scaling, and Cleaning

Fouling

The accumulation of unwanted materials on the membrane surface or within its pores, causing a decline in flux and separation performance. Fouling can be caused by organic matter (biofouling, organic fouling), inorganic precipitates (scaling), or particulates (colloidal fouling). Effective fouling management through pre-treatment, cleaning, and membrane selection is essential for long-term membrane system operation.

Scaling

The precipitation and deposition of sparingly soluble inorganic salts on the membrane surface, typically occurring when the concentration of salts in the concentrate exceeds their solubility limit. Common scalants include calcium carbonate, calcium sulphate, barium sulphate, and silica. Scaling reduces flux and can cause irreversible membrane damage if not controlled through antiscalant dosing, pH adjustment, and recovery limitation.

Biofouling

The colonisation and growth of microorganisms on the membrane surface, forming a biofilm that increases hydraulic resistance and reduces permeate quality. Biofouling is the most challenging type of fouling to control because even a small number of surviving bacteria can rapidly re-establish the biofilm. Control strategies include chlorination, UV disinfection, and periodic cleaning with biocidal agents.

Concentration Polarisation

The build-up of rejected solute concentration at the membrane surface relative to the bulk feed concentration, creating a boundary layer that reduces the effective driving force and increases osmotic pressure. Concentration polarisation can increase apparent salt passage and promote fouling and scaling. It is mitigated by increasing crossflow velocity, using turbulence promoters, and optimising module design.

CIP (Clean In Place)

A systematic cleaning procedure performed on membrane systems without disassembly, using chemical cleaning solutions circulated through the membrane modules. CIP protocols typically involve alkaline cleaning to remove organic foulants followed by acid cleaning to dissolve inorganic scale deposits. Regular CIP is essential for maintaining membrane performance and extending membrane life. Tech Inc. membrane test systems are designed with CIP-compatible connections for efficient cleaning evaluation.

CEB (Chemically Enhanced Backwash)

A cleaning procedure used in UF and MF systems that combines a hydraulic backwash with a low-concentration chemical solution. CEB is performed more frequently than full CIP but with shorter contact times and lower chemical concentrations. It provides an intermediate cleaning intensity between standard backwash and full CIP, helping to maintain flux between major cleaning events.

Backwash

A hydraulic cleaning procedure where permeate or clean water is pumped backwards through the membrane to dislodge accumulated foulants from the membrane surface and pores. Backwashing is a standard maintenance procedure for hollow fibre UF and MF systems, typically performed at regular intervals ranging from 15 to 60 minutes. The effectiveness of backwash depends on pressure, duration, and the nature of the foulants.

Membrane Autopsy

The detailed examination and analysis of a used or fouled membrane element to determine the causes of performance decline. Autopsy procedures include visual inspection, SEM imaging, FTIR analysis, and chemical analysis of deposits. Membrane autopsies provide valuable information for optimising pre-treatment, cleaning protocols, and membrane selection for future installations.

Antiscalant

A chemical additive dosed into the feed water of a membrane system to inhibit the precipitation and crystallisation of sparingly soluble mineral salts on the membrane surface. Antiscalants work by threshold inhibition, crystal modification, and dispersion mechanisms. Proper antiscalant selection and dosing are critical for achieving target recovery rates while preventing scaling.

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Frequently Asked Questions

What is Fouling?

The accumulation of unwanted materials on the membrane surface or within its pores, causing a decline in flux and separation performance. Fouling can be caused by organic matter (biofouling, organic fouling), inorganic precipitates (scaling), or particulates (colloidal fouling). Effective fouling management through pre-treatment, cleaning, and membrane selection is essential for long-term membrane system operation.

What is Scaling?

The precipitation and deposition of sparingly soluble inorganic salts on the membrane surface, typically occurring when the concentration of salts in the concentrate exceeds their solubility limit. Common scalants include calcium carbonate, calcium sulphate, barium sulphate, and silica. Scaling reduces flux and can cause irreversible membrane damage if not controlled through antiscalant dosing, pH adjustment, and recovery limitation.

What is Biofouling?

The colonisation and growth of microorganisms on the membrane surface, forming a biofilm that increases hydraulic resistance and reduces permeate quality. Biofouling is the most challenging type of fouling to control because even a small number of surviving bacteria can rapidly re-establish the biofilm. Control strategies include chlorination, UV disinfection, and periodic cleaning with biocidal agents.

What is Concentration Polarisation?

The build-up of rejected solute concentration at the membrane surface relative to the bulk feed concentration, creating a boundary layer that reduces the effective driving force and increases osmotic pressure. Concentration polarisation can increase apparent salt passage and promote fouling and scaling. It is mitigated by increasing crossflow velocity, using turbulence promoters, and optimising module design.

What is CIP (Clean In Place)?

A systematic cleaning procedure performed on membrane systems without disassembly, using chemical cleaning solutions circulated through the membrane modules. CIP protocols typically involve alkaline cleaning to remove organic foulants followed by acid cleaning to dissolve inorganic scale deposits. Regular CIP is essential for maintaining membrane performance and extending membrane life. Tech Inc. membrane test systems are designed with CIP-compatible connections for efficient cleaning evaluation.

What is CEB (Chemically Enhanced Backwash)?

A cleaning procedure used in UF and MF systems that combines a hydraulic backwash with a low-concentration chemical solution. CEB is performed more frequently than full CIP but with shorter contact times and lower chemical concentrations. It provides an intermediate cleaning intensity between standard backwash and full CIP, helping to maintain flux between major cleaning events.

What is Backwash?

A hydraulic cleaning procedure where permeate or clean water is pumped backwards through the membrane to dislodge accumulated foulants from the membrane surface and pores. Backwashing is a standard maintenance procedure for hollow fibre UF and MF systems, typically performed at regular intervals ranging from 15 to 60 minutes. The effectiveness of backwash depends on pressure, duration, and the nature of the foulants.

What is Membrane Autopsy?

The detailed examination and analysis of a used or fouled membrane element to determine the causes of performance decline. Autopsy procedures include visual inspection, SEM imaging, FTIR analysis, and chemical analysis of deposits. Membrane autopsies provide valuable information for optimising pre-treatment, cleaning protocols, and membrane selection for future installations.

What is Antiscalant?

A chemical additive dosed into the feed water of a membrane system to inhibit the precipitation and crystallisation of sparingly soluble mineral salts on the membrane surface. Antiscalants work by threshold inhibition, crystal modification, and dispersion mechanisms. Proper antiscalant selection and dosing are critical for achieving target recovery rates while preventing scaling.