1 Purpose and Scope
This instruction standardizes chemical cleaning (CIP) of ceramic membrane filtration systems so that membrane performance is restored in time when flux or transmembrane pressure (TMP) degrades, extending element life and keeping permeate quality stable. It applies to cross-flow systems using ceramic membranes (multi-channel tubular, flat-sheet or honeycomb) and covers chemical cleaning only; actual cleaning parameters shall follow the membrane element datasheet of the project.
2 When to Clean
1. TMP rises 0.05 to 0.1 MPa above the initial baseline value.
2. Permeate flux drops 10% to 15% at constant pressure.
3. Permeate turbidity or quality clearly deteriorates while the feed condition is unchanged.
4. Scheduled maintenance cleaning (typically every 2 to 8 weeks, depending on duty).
5. Before long-term shutdown (over 7 days) and whenever microbial growth is suspected.
3. CIP Procedure
1. Drain the feed from the membrane and pre-flush with clean water for 5 to 10 minutes until the discharge is essentially clear.
2. Prepare the cleaning solution in the CIP tank and heat it to the set temperature; verify the concentration and pH.
3. Start the cleaning pump, circulate at low flow for 5 minutes, then raise the flow gradually to the normal cleaning rate and circulate for 30 to 60 minutes.
4. For heavy fouling, stop and soak for 2 to 12 hours depending on the severity.
5. The usual sequence is alkaline wash first, then acid wash; rinse with clean water to neutral (pH 6 to 8) between the two steps.
6. After cleaning, rinse with clean water for 10 to 20 minutes until the discharge pH is close to neutral and no chemical residue remains.
7. Measure the pure-water flux; recovery to more than 90% of the initial flux means the cleaning has passed, otherwise repeat (maximum 2 times).
8. Complete the cleaning record: date, foulant type, agent and concentration, temperature, flux recovery.
4. Acceptance Criteria
1. Pure-water flux recovers to more than 90% of the initial value, or TMP falls back to within 0.02 MPa of the initial baseline.
2. Rinse discharge pH is 6 to 8 and conductivity approaches that of the feed water, with no chemical residue or odour.
3. If flux recovery stays below 80% after two consecutive cleaning cycles, re-identify the foulant and inspect the membrane elements.
5.Safety and Cautions
1. Store chemicals separately with clear labelling; never mix acid with sodium hypochlorite.
2. Wear goggles, acid/alkali-resistant gloves and protective clothing when preparing and handling chemicals; keep the area ventilated.
3. Hot cleaning solutions can cause burns; confirm the temperature is below 45 °C before contact.
4. If chemicals contact skin or eyes, rinse immediately with plenty of water for at least 15 minutes and seek medical attention.
5. Never dismantle piping, clamps or housing end caps while the system is pressurized; depressurize and drain first.
6. Neutralize cleaning waste before discharge in accordance with local environmental requirements; never discharge it into the storm water system.
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