RO Membrane Cleaning SOP (CIP) — Field Guide from 9 Plus Chemicals

Last week in a 2000-LPH plant, our tech Pratik called: “ΔP has crept up 18%, permeate flow is sagging, but SDI looks normal.”
This post is the exact SOP we follow in the field at 9 Plus Chemicals—written for technicians, not for textbooks. Use it as a checklist, then fine-tune to your membrane OEM’s manual and your plant’s data.

---

When should you clean?

Trigger a CIP if any one of these happens (normalized to design conditions):

• Permeate flow ↓ 10–15%

• ΔP ↑ 15–20% across a stage

• Permeate conductivity/TDS trending up abnormally

• Visibly slimy biofilm, oil, color, or scaling deposits in housings/elements

Pro tip: Regular dosing with 9 Plus Chemicals Antiscalant (10 ml single-dose trials available) helps delay mineral scale buildup between cleanings.

---

Choose the right chemistry (simple logic)

What you see	Probable foulant	First cleaner to use
Slimy film, organic smell, oily sheen	Bio/organic/oil	9 Plus Chemicals Organic Membrane Cleaner (Alkaline)
White/grey crust, hard water area, ΔP rises with stable SDI	Carbonate/sulfate scale, metals	9 Plus Chemicals Inorganic Membrane Cleaner (Acid)
Rust tint	Iron/manganese	Acid clean first, then quick alkaline
Mixed/unknown	Mixed foulants	Start alkaline, then acid (unless you’re sure it’s heavy scale)

Names made simple for SEO & clarity: Organic Membrane Cleaner (Alkaline) = for organic/biofouling; Inorganic Membrane Cleaner (Acid) = for mineral/metal scales.

---

Safety first (PPE & prep)

• PPE: chemical-resistant gloves, goggles/face shield, apron, closed shoes.

• Lock-out/Tag-out: isolate RO feed, high-pressure pump, and power.

• Dechlorinate: for polyamide RO, free chlorine < 0.1 ppm before CIP.

• Tools: pH meter, thermometer, TDS/EC meter, ΔP gauges, 5–10 μm bag filter on CIP loop, clean hoses, calibrated dosing jug.

---

Standard CIP flow (one stage at a time)

Always keep within OEM limits; these typical guardrails keep you safe:

• Flow: gentle turbulence in each vessel (avoid channeling), low pressure (< 2 bar), low ΔP across the stage (< 0.5 bar during CIP).

• Temperature: heat helps—30–35 °C for alkaline, 25–30 °C for acid (if allowed by OEM).

• pH set-points: Alkaline 10–11.5, Acid 2–3. Hold the pH—if it drifts, top up.

---

Mixing the cleaning solution (per 1000 L CIP tank)

A) For organics/biofilm/oil

9 Plus Chemicals Organic Membrane Cleaner (Alkaline)

• Target strength: 0.2–0.5% w/v (i.e., 2–5 kg per 1000 L)

• pH: 10–11.5  Temp: 30–35 °C

• Steps: Fill tank 70% with RO permeate → add cleaner slowly while circulating → top up water → check/adjust pH and temperature.

B) For mineral scale/metals

9 Plus Chemicals Inorganic Membrane Cleaner (Acid)

• Target strength: 1–2% w/w (i.e., 10–20 kg per 1000 L)

• pH: 2–3  Temp: 25–30 °C

• Steps: Same as above; always add acid to water (never water to acid).

SDS First: Read each product’s SDS for exact handling/storage. Concentrations above are field-proven starting ranges—optimize with your data and OEM guidance.

---

The cleaning cycle (timings you can trust)

1. Rinse (5–10 min)
   Flush the stage with RO permeate to remove loose solids.

2. Alkaline clean (if indicated)

   • Recirculate: 30–45 min (direction 1)

   • Soak: 30 min (circulation off)

   • Recirculate: 15–30 min (direction 2, if reversible)

   • Top-up pH: keep ≥10. If pH drops >0.3, add more cleaner.

   • Visual check: foam reduces, return line looks clearer.

3. Intermediate rinse
   Rinse with RO permeate until outlet pH 6–8.

4. Acid clean (if indicated)

   • Recirculate: 30–45 min (direction 1)

   • Soak: 30 min

   • Recirculate: 15–30 min (direction 2)

   • Hold pH: 2–3. If it rises (neutralized by scale), re-dose.

   • Rusty tint fading = good sign in iron-rich feeds.

5. Final rinse & return to service

   • Rinse to neutral pH 6–8, conductivity near permeate baseline.

   • Gradual start-up: low pressure first, then ramp to operating.

---

Quick math example (helps on site)

• Stage feed flow during CIP (example): 3 m³/h

• Alkaline clean chosen at 0.3% → 3.0 kg cleaner per 1000 L tank

• If your CIP tank is 500 L, use 1.5 kg; set pH to ~10.8, temp 32 °C

• ΔP drops from 1.2 bar → 0.8 bar after cycle = proceed to rinse/acid (if needed)

(Your numbers will vary—log everything and normalize.)

---

Technician notes (from our calls in the field)

• pH not holding? That means the chemistry is “working” (consumed by foulant). Re-dose to bring it back to set-point and continue.

• Foam party? Slight foam during alkaline is normal; excessive foam usually means oils—slow the flow and extend soak.

• Still dirty after two passes? Split the stage and clean train-by-train, or increase temperature (within OEM limit).

• Biofilm returning fast? Review pretreatment (chlorination/dechlorination window, biocide program) and check for dead zones in piping.

• Scale returns fast? Increase or optimize 9 Plus Chemicals Antiscalant dose (start 2–5 ppm as supplied) and verify LSI/SDI trends.

---

Post-CIP checklist (don’t skip it)

• Record before/after: ΔP, normalized permeate flow, permeate TDS, pH, temp.

• Inspect prefilters; replace if fouled.

• Update CIP log with chemical batch numbers and times.

• Schedule a follow-up check in 48–72 hours.

---

Why our products fit this SOP

• 9 Plus Chemicals Organic Membrane Cleaner (Alkaline): built with surfactants + dispersants to lift biofilm and oils at pH 10–11.5 without hurting polyamide.

• 9 Plus Chemicals Inorganic Membrane Cleaner (Acid): targets carbonate/sulfate scales and iron deposits at pH 2–3, leaving the membrane ready for service.

• 9 Plus Chemicals Antiscalant (daily dosing): reduces mineral scale formation so you clean less often and protect membrane life.