Cleaning RO and NF Membrane Elements

Introductory Remarks
When to Clean
Cleaning Method Selection
Defining a Foulant and Scalant
pH and Temperature Limits
FT30 Resistance to Cleaning Agents
Cleaning Carbonate Scaling
Cleaning Sulfate Scaling

Cleaning Organic Fouling
Cleaning Biological Fouling
Cleaning Iron Fouling
Cleaning Silt Fouling
Cleaning Carbon Fouling
Chemical Attack
Permeate Back Pressure
The Cleaning Process
Safety

Cleaning Introductory Remarks

Cleaning is a means of removing mineral scale, organic matter, biological growth, colloidal particles, or insoluble constituents which build up on the surface of the membrane
Frequent cleaning should not be required for a properly designed and operated RO/NF system
Membranes may become fouled or scaled due to improper operation or change in feedwater quality

Cleaning Introductory Remarks (cont

Membranes’ elements can be cleaned effectively because:
chemical stability
broad pH tolerance
high temperature limits
Elements with oxidized membrane or mechanical damage must be replaced

When to Clean

Normalized flow declines by 10%
Pressure drop increases by 15%
Normalized salt passage increases by 5%*

*Dependent on individual system design

Cleaning Regimen based on System Performance and Water Chemistry
A wrong choice can aggravate a scaling/fouling problem
Acids for scaling
Alkaline for biological fouling
Alkaline with detergent for organic fouling
Frequently both alkaline and acid cleanings are required
Characterizing Foulant or Scalant
Analyze the normalized plant performance
Analyze feed water quality
Check performance after previous cleanings
Analyze cartridge/SDI filter residue

Characterizing Foulant or Scalant
Inspect lead element and feed scroll end for suspended solids fouling
Inspect scroll of tail element for scaling
Clean and analyze cleaning solutions (control samples required)
Destructive autopsy
pH Range and Temperature Limits During Cleaning

Recommend Feed Flow Rate Per Pressure Vessel

Carbonate Scalin

Cleaning System

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