TL;DR
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.
What you might see
- permeate conductivity rising above target
- normalized salt passage trending upward over months
- concentrate and permeate conductivity both rising
- permeate from a specific pressure vessel elevated compared to others
Likely causes
Membrane oxidation from chlorine or other oxidant exposure causing active layer degradation
Failed brine seal on one element allowing feed-side water to bypass the membrane
Telescoping element from a previous high-differential-pressure event damaging the element ends
Normal membrane aging reducing rejection to below acceptable limits
Required tools
- Portable conductivity meter with hose-end adapter
- Element removal tools (pressure vessel wrenches, element puller rod)
- Chemical-resistant gloves
Safety first
- Pressure vessels on high-pressure RO systems (up to 800 psi for seawater) must be fully depressurized and drained before opening end caps.
- Never expose polyamide RO membranes to free chlorine above 0.1 mg/L. Oxidation destroys the active layer irreversibly.
Procedure
- 1
Measure permeate conductivity at the outlet of each pressure vessel individually using a portable conductivity meter with a sample port at each vessel.[1]
- 2
Calculate the salt passage for each vessel using the standard formula. A vessel with significantly higher salt passage than adjacent vessels is the problem vessel.
- 3
Check the system operating log for any chlorine (or other oxidant) dosing events upstream of the RO system. Oxidant exposure is the most common cause of active layer damage in polyamide elements.
Warning: Before removing a pressure vessel end cap to pull elements, confirm the feed and concentrate isolation valves are closed and the vessel is fully depressurized and drained. End caps under pressure can fly off and cause injury. - 4
If no oxidant event is on record, depressurize the problem vessel and pull the elements for inspection. Check the interconnect brine seals for cracks or displacement.
- 5
If the membrane surface has a mottled or bleached appearance under the protective shell, oxidation damage is confirmed and the element must be replaced.
- 6
Replace the damaged element(s), re-normalize, and verify salt rejection returns to specification.
Sources
Veolia (Suez) FilmTec BW30 / SW30 elements Reverse Osmosis (RO) System general technical documentation, Veolia (Suez)
RO membrane salt rejection, normalized salt passage, element oxidation diagnosis, 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 diagnose low permeate flow and recovery decline on a FilmTec BW30 / SW30 RO system
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.
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