Scope and purpose

This protocol covers routine daily/weekly flushing, periodic backwash, and chemical clean‑in‑place (CIP) for polymeric MBR membranes used in municipal and industrial wastewater plants. Goal: restore permeability, control irreversible fouling, and minimize downtime while protecting membrane integrity.

Safety and prechecks

  • Personal protective equipment: chemical‑resistant gloves, goggles, face shield, apron, and respirator when handling strong chemicals.
  • Lockout and isolation: isolate the membrane skid; lock out blowers and pumps; tag valves.
  • Compatibility check: confirm chemicals and temperatures are compatible with RhyLOX membrane material and vendor datasheet.
  • Record baseline: note influent/effluent quality, TMP, flux, air scour rate, and operating temperature before cleaning.

Materials and chemicals

  • Softened or dechlorinated water for rinsing.
  • Alkaline cleaner (e.g., sodium hydroxide based) for organic fouling.
  • Acid cleaner (e.g., citric acid or dilute HCl) for scaling and inorganic deposits.
  • Oxidant only if membrane vendor permits (avoid uncontrolled chlorine on many polymeric membranes).
  • Antifoam and dispersant as required.
  • Flow meters, pH meter, conductivity meter, thermometer for monitoring.

Routine daily and weekly actions

  • Daily: monitor TMP and permeate flux; perform air scour checks and remove visible debris from screens.
  • Weekly: perform forward flush with permeate/backwash water for 10–30 minutes at design flow; inspect module housings and connections.

Step‑by‑step periodic backwash (mechanical cleaning)

  1. Isolate feed and switch to permeate/backwash source.
  2. Low‑pressure backwash: apply permeate at recommended backwash pressure for 5–15 minutes to dislodge cake layer.
  3. Air scour: run air scour cycle (intermittent pulses) for 10–30 minutes while maintaining low crossflow.
  4. Rinse: flush with clean water until turbidity and conductivity return to baseline.
  5. Return to service: gradually restore feed and monitor TMP and flux for 1–2 hours.

Chemical Clean‑In‑Place CIP procedure (when backwash insufficient)

Use vendor‑approved concentrations and temperatures. Example sequence (adjust to RhyLOX datasheet):

  1. Pre‑rinse
    • Circulate dechlorinated water at ambient temperature for 15–30 minutes to remove loose solids.
  2. Alkaline cleaning
    • Prepare alkaline solution (typical range 0.5–2.0% NaOH by weight; confirm with datasheet).
    • Heat to recommended temperature (commonly 30–40°C unless vendor allows higher).
    • Circulate for 30–120 minutes with moderate crossflow and intermittent air scour.
    • Monitor pH and conductivity; maintain target concentration.
  3. Rinse
    • Thoroughly rinse with clean water until pH and conductivity near feed values.
  4. Acid cleaning
    • Prepare acid solution (typical 0.5–2.0% citric acid or dilute HCl; vendor dependent).
    • Circulate at recommended temperature for 30–90 minutes to remove scale.
    • Use gentle air scour if allowed.
  5. Final rinse and neutralization
    • Rinse until pH and conductivity are stable.
    • If required, circulate a neutralizing solution or low concentration antiscalant.
  6. Sanitization (optional, vendor dependent)
    • If sanitization is needed, use approved oxidant at safe concentration and contact time; only if membrane material is compatible.
  7. Post‑CIP performance check
    • Record TMP, flux, permeate quality; compare to baseline.
    • If performance not restored, consider extended CIP or consult manufacturer.

Troubleshooting common issues

  • TMP not recovering after CIP: check for irreversible fouling, membrane damage, or module bypass; consider laboratory membrane autopsy.
  • High permeate turbidity after cleaning: incomplete rinsing or membrane fiber damage—stop and rinse longer.
  • Foaming during CIP: reduce circulation speed and add antifoam; check chemical compatibility.

Maintenance schedule and KPIs

  • Daily: TMP, flux, air flow, permeate quality.
  • Weekly: backwash cycles, visual inspection.
  • Monthly: performance trending, small CIP if TMP drift >15% above baseline.
  • Quarterly or as needed: full CIP; membrane autopsy if repeated failures.
  • KPIs to track: TMP (mbar), specific flux (LMH/bar), permeate turbidity (NTU), chemical consumption per m².

Documentation and recordkeeping

  • CIP log: date/time, operator, chemical batch, concentrations, temperature, duration, pre/post TMP and flux, observations.
  • Inventory: chemical lot numbers and MSDS on file.
  • Photos: before/after module housings and permeate clarity for audits.