CIP Chemical Cleaning Procedure for DOW & Hydranautics RO Membranes
> Direct Answer: Clean-In-Place (CIP) is a chemical recirculation process designed to strip scale, silt, and biofilm deposits from spiral-wound Thin-Film Composite (TFC) RO membranes. A complete CIP requires a two-stage procedure: Stage 1 (Low pH 2.0–3.0 with Citric Acid) to dissolve calcium carbonate and iron oxide scales, followed by Stage 2 (High pH 11.0–12.0 with NaOH + EDTA) to dissolve organic fouling, silica, and bio-slime.
Two-Stage CIP Cleaning Protocol
```mermaid
graph TD
Flush1[1. Low-Pressure Permeate Water Flush] --> LowPH[2. Low-pH Acid Cleaning: pH 2-3 with Citric Acid]
LowPH --> Soak1[3. Recirculate 45m + Soak 60m]
Soak1 --> Flush2[4. Intermediate Pure Water Flush]
Flush2 --> HighPH[5. High-pH Alkaline Cleaning: pH 11-12 with NaOH + EDTA]
HighPH --> Soak2[6. Recirculate 45m + Soak 60m]
Soak2 --> FinalFlush[7. Final Flush & Normal Operation Return]
```
Stage 1: Acid Cleaning (Inorganic Scale & Metal Oxides)
- Target Fouling: Calcium carbonate (CaCO_3), barium sulfate, calcium phosphate, and iron oxide deposits.
- Chemical Solution: 2.0% Citric Acid (C_6H_8O_7) or 0.2% Hydrochloric Acid (HCl).
- Target pH: 2.0 – 2.5.
- Temperature: 25°C to 35°C (never exceed 40°C).
- Recirculation: Recirculate at low pressure (20–40 PSI) for 45 minutes, then soak for 60 to 90 minutes.
Stage 2: Alkaline Cleaning (Biofilms, Silt & Organic Slime)
- Target Fouling: Biofilm growth, dead microbial biomass, natural organic matter (NOM), and colloidal silt.
- Chemical Solution: 0.1% Sodium Hydroxide (NaOH) + 0.1% Sodium Salt of EDTA (disodium/tetrasodium).
- Target pH: 11.0 – 11.8.
- Temperature: 30°C to 35°C.
- Recirculation: Recirculate at low pressure for 45 minutes, then soak for 60 to 120 minutes until the wash solution turns amber or turbid.
Critical Safety & Operating Precautions
1. Always use pure RO permeate water to formulate chemical wash solutions. Never use raw or municipal water.
2. Recirculation Pressure: Keep pressure strictly below 40 PSI (2.8 bar) during CIP to prevent permeate production during cleaning.
3. Rinse to Drain: Always flush wash solutions directly to drain until pH returns to neutral (6.5–7.5) before routing permeate back to clean water storage tanks.