CIP Chemical Cleaning Technical Guidelines for Reverse Osmosis Systems

I. Cleaning Trigger Criteria

• Permeate flow decline: Standardized flow reduction >15% (vs. initial value)
• Salt rejection deterioration: System salt rejection drop >10% (e.g., 98% → 88%)
• Pressure difference increase: Inter-stage ΔP increase >15% (e.g., 0.5MPa → 0.58MPa)
• Visible contamination: Colored deposits on membrane surface (biofilm/iron scale)

II. Pre-Cleaning Preparation

1. System Inspection

• Verify pressure gauge/flow meter accuracy (<±2% error)
• Check cleaning pump capacity (1.5× system design flow rate)
• Ensure cleaning tank volume >1.2× system water volume

2. Safety Precautions

• PPE: Acid/alkali-resistant clothing, face shield, chemical-resistant gloves
• Set up pH monitoring in restricted zones

3. Chemical Formulation

Cleaning Phase	Chemical Formula	Concentration	Temperature
Alkaline Cleaning	NaOH + EDTA-4Na + Surfactant	0.1%-0.5%	35-40℃
Acid Cleaning	Citric Acid/HCl + Corrosion Inhibitor	1%-2%	25-30℃
Disinfection	Peracetic Acid/Sodium Bisulfite	0.5%-1%	Ambient

4. System Isolation

• Close permeate valve, fully open concentrate valve
• Keep membrane housing vent valves open
• Disconnect from pretreatment system

III. Step-by-Step Cleaning Procedure

Step 1: Low-Pressure Flushing

• Flush system with RO permeate for 30 minutes
• Flow rate: 50% of design flow
• Objective: Remove loose contaminants

Step 2: Alkaline Cleaning (Organic/Biofilm Removal)

1. Circulation:
   • Flow rate: 8-10m³/h (for 8-inch membrane)
   • Duration: 60-90 minutes
   • Transmembrane pressure: <0.2MPa
2. Soaking:
   • Turn off pump and soak for 4-6 hours
   • Maintain solution temperature ≥30℃
3. Drainage:
   • Check effluent turbidity (NTU <5)

Step 3: Acid Cleaning (Inorganic Scale Removal)

1. Circulation:
   • Flow rate: 6-8m³/h (prevent CaCO₃ re-precipitation)
   • Duration: 45-60 minutes
   • Monitor pH (2.5-3.5)
2. Endpoint:
   • Stop when conductivity change <5%/hour

Step 4: Disinfection

• For severe biofouling:
  • 0.1% peracetic acid circulation for 30 minutes
  • OR 1% sodium bisulfite soak for 2 hours

Step 5: Final Flushing

• Alternate forward/reverse flushing with RO permeate
• Continue until effluent pH 6.5-7.5
• Conductivity returns to baseline ±10%

IV. Post-Cleaning Evaluation

• Performance recovery:
  • Permeate flow recovery ≥95%
  • Salt rejection improvement ≥3%
• Membrane autopsy (if needed):
  • Contaminant weight: <50mg/cm²
  • SEM analysis of membrane pores

V. Targeted Solutions for Specific Fouling

Fouling Type	Symptoms	Recommended Solution
Organic Fouling	Rapid ΔP rise, stable conductivity	Alkaline cleaner (pH11-12) + 50℃ heating
Inorganic Scaling	Sudden flow drop, salt rejection decline	2% citric acid + NH3 (pH4) + 40℃ circulation
Biofouling	Odor, slimy deposits	Alternate 1% peracetic acid and 0.1% NaOH
Colloidal Fouling	SDI >5, gradual ΔP rise	0.025% SDBS + EDTA composite cleaning

VI. Safety Protocols

• Chemical compatibility:
  • Avoid mixing oxidizers (e.g., NaClO) with acids
  • Flush alkaline residues before acid cleaning
• Waste treatment:
  • Neutralize pH to 6-9
  • Precipitate EDTA with FeCl₃ (1:1 molar ratio)
• Membrane protection:
  • Set temperature alarm at 45℃
  • Limit Cl^– concentration <1000ppm during acid cleaning

Expected Outcomes:

• Flux recovery >90%
• Extended membrane lifespan (12-18 months)
• 8-12% energy consumption reduction

Note: Use rotary nozzle systems (e.g., GE TurboClean™) to enhance shear force by 3× and cleaning efficiency by 40%+