TL;DR
Normalized permeate flow declining 10% or more below baseline means membrane scaling or biofouling. Review antiscalant dosing, check SDI, and plan a high-pH CIP to recover flux.
What you might see
- normalized permeate flow 10% or more below baseline
- feed pressure required to maintain flow has increased
- system recovery ratio dropping below design
- concentrate volume rising relative to permeate volume
Likely causes
Calcium carbonate or sulfate scaling on the membrane surface reducing permeability
Biofilm formation on the membrane feed surface reducing effective water passage
Pre-treatment SDI deteriorating above 5, sending colloidal foulants to the lead elements
Feed temperature drop increasing water viscosity and naturally reducing permeate flow
Required tools
- Flow meters at permeate and concentrate
- Temperature sensor at RO feed
- SDI test kit at cartridge filter outlet
- CIP pump and tank
Safety first
- CIP chemicals (citric acid and NaOH) are corrosive. Wear chemical gloves and face shield during preparation and circulation.
- Do not exceed the maximum operating pressure during CIP. Set a pressure-relief valve or pressure switch to limit pump output.
Procedure
- 1
Normalize permeate flow using the membrane manufacturer's temperature correction factor (TCF) formula. A temperature-corrected decline of 10% or more from baseline confirms real flux loss.[1]
- 2
Review pre-treatment performance: SDI at the cartridge filter outlet, antiscalant dosing rate, and multimedia or ultrafiltration pre-treatment differential pressure.
- 3
Confirm that the antiscalant dosing pump is operating and dosing at the correct rate per the current feed water analysis.
Warning: Antiscalant solutions are mildly irritating. Wear nitrile gloves when handling dosing lines and checking injectors. - 4
If flux loss is concentrated in the lead vessels of the pressure vessel array, biofouling is likely. Prepare a high-pH caustic CIP (pH 11-11.5) and circulate per the OEM procedure.
- 5
If scaling is suspected (hard water, high LSI), perform a low-pH citric acid CIP.
- 6
After CIP, re-normalize permeate flow and compare to baseline. If recovery is less than 80% of the pre-foul baseline, plan element replacement for that position.
Sources
Veolia (Suez) FilmTec BW30 / SW30 elements Reverse Osmosis (RO) System general technical documentation, Veolia (Suez)
RO membrane performance normalization, scaling and biofouling diagnostics, general water treatment references (general)
More guides for Veolia (Suez) FilmTec BW30 / SW30 elements
How to reduce high differential pressure across a FilmTec BW30 / SW30 RO membrane train
A rising normalized differential pressure across the RO train means feed channel fouling. Perform a low-pH citric acid CIP to dissolve inorganic or biological deposits. If that does not work, plan for element replacement.
How to investigate salt rejection decline and high permeate conductivity on a FilmTec BW30 / SW30 RO system
Rising permeate conductivity means a membrane element has been physically damaged, oxidized, or has a sealing defect. Sample each pressure vessel's permeate individually to locate the problem vessel.
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