TL;DR
TMP rising faster than normal or physical cleaning no longer recovering TMP means reversible fouling has crossed into irreversible. Perform a chemical clean-in-place (CIP) with hypochlorite and citric acid.
What you might see
- transmembrane pressure (TMP) rising above normal at the same flux
- filtration flux declining below target
- physical cleaning (backpulse / relaxation) no longer recovering TMP
- mixed liquor suspended solids (MLSS) elevated in the bioreactor
Likely causes
Biocake accumulation on the membrane surface faster than aeration scour can remove it
High MLSS concentration in the bioreactor exceeding the design operating window
Aeration scour diffuser fouling or air supply reduction decreasing cross-flow velocity at the membrane surface
Inorganic scaling from calcium or iron exceeding the chemical CIP interval
Required tools
- DCS TMP and flux trend data
- MLSS measurement kit or analyzer
- Sodium hypochlorite (chemical grade) and citric acid for CIP
- Confined-space entry kit including oxygen and gas detector
Safety first
- Sodium hypochlorite solutions are corrosive oxidizers. Wear chemical-resistant gloves, splash goggles, and work in a ventilated area.
- Do not mix sodium hypochlorite with citric acid or any acid in a concentrate. This produces toxic chlorine gas. Rinse completely between chemical phases.
- Bioreactor tanks are confined spaces. Follow confined-space entry procedures with atmospheric testing before entry.
Procedure
- 1
Review the TMP trend over the past 7 days. A TMP rising above 0.5 bar (or the OEM's CIP trigger threshold) after standard backpulse cycles confirms the need for a CIP.[1]
- 2
Check the MLSS concentration in the bioreactor. If MLSS is above the design range (typically 8,000-12,000 mg/L for a Memcor MBR), increase the waste activated sludge (WAS) rate to reduce loading.
- 3
Inspect the coarse bubble aeration diffusers beneath the membrane cassettes for scaling or fouling. Restricted air flow reduces membrane scour.
Warning: Confined-space entry procedures apply to any entry into the membrane bioreactor tank. Test for oxygen deficiency before entry and maintain continuous atmospheric monitoring. - 4
If physical cleaning does not restore TMP, proceed with a sodium hypochlorite maintenance clean (soaking the cassettes at 200-500 mg/L active chlorine for 30-60 minutes, per OEM guidance).
- 5
If calcium or iron fouling is suspected, follow the hypochlorite soak with a citric acid clean at pH 2-2.5 to dissolve inorganic scale.
Warning: Sodium hypochlorite at high concentration is an oxidizer. Do not mix with citric acid or any acid in a concentrated form. Flush the cassette thoroughly with clean water between chemical soaks. - 6
After the CIP, return the cassette to service and verify TMP is back below the alarm setpoint at the normal operating flux.
Sources
Veolia Evoqua Memcor MBR Wastewater Treatment (Clarifier / MBR) general technical documentation, Veolia
MBR membrane fouling, chemical CIP procedures, and MLSS control, general water treatment references (general)
More guides for Veolia Evoqua Memcor MBR
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DO below 1 mg/L in the bioreactor during normal loading means the aeration blowers are not delivering enough air. Check blower speed, discharge pressure, and diffuser condition before raising the DO setpoint.
How to investigate permeate quality deterioration and high turbidity on a Veolia Evoqua Memcor MBR system
Elevated permeate turbidity means a broken fiber or a failed o-ring is allowing mixed liquor to bypass the membrane. Run an integrity test to identify the damaged cassette.
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