AQUACHAIN GUIDE
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Illustrated guide · Operating diagnostics

What do acid and caustic CIP remove?

Match RO/NF CIP chemistry and sequence to the deposit, control circulation and soak conditions, and accept the clean on normalized performance rather than solution color.

Direct answer

Direct answer

Acid and caustic CIP are not interchangeable strong rinses. Acid cleaners mainly dissolve acid-soluble inorganic precipitates such as calcium carbonate and some iron oxides/hydroxides. Alkaline cleaners—often aided by surfactants, chelants or dispersants—remove natural organics, oils, colloids, silica-related deposits and biological matter by desorption, emulsification and dispersion. Formula, pH, temperature, velocity, time and deposit age matter as much as the acid/alkaline label. Sulfate, barium/strontium and aged silica scales are difficult; sulfuric acid is unsuitable because calcium sulfate may precipitate. Most deposits are mixed. FilmTec guidance normally places alkaline cleaning first to open organic, colloidal and biofilm layers, followed by a thorough rinse and acid cleaning of remaining mineral scale. Acid first is reserved for a deposit known to contain only calcium carbonate or iron oxide/hydroxide. CIP must be triggered from normalized flow, salt passage and stage pressure-drop trends; selected from evidence; mixed with RO permeate or DI water; introduced at low pressure; circulated stage by stage at adequate crossflow; and monitored for pH, temperature, flow, pressure drop, color and turbidity. Replace loaded solution, rinse thoroughly and judge recovery only after stable normalized operation.

Answer four questions before choosing acid or caustic

Deposit identity and membrane compatibility drive the recipe.

What is the deposit—not merely its color?

Combine stage location, normalized trends, feed chemistry, cartridge evidence and deposit analysis to separate carbonate/metal, sulfate/silica, colloid, organic and biofilm.

What pH–temperature–time envelope does this membrane allow?

Polyamide, cellulose acetate and individual RO/NF products differ. The more extreme the pH, the lower the permitted temperature may be.

Is it a single or composite layer?

Organic and biological matrices commonly encase mineral particles. Mixed deposits generally need alkaline-first sequencing.

Was cleaning early enough and at the right hydraulics?

Aged deposits compact or recrystallize. Low flow cannot carry debris; excessive vessel pressure drop risks damage.

1

A field CIP controls chemicals, tank, pump/filter and an isolated membrane stage

PPE and segregated drums, a mixed temperature-controlled tank and temporary low-pressure return hoses form one controlled loop.

A field CIP controls chemicals, tank, pump/filter and an isolated membrane stage：Segregated acid/alkali and PPE、Mixed, temperature-monitored CIP tank、Pump, filter, flow/pressure and return、Isolated RO pressure-vessel stage1234

What to identify

  1. 1Segregated acid/alkali and PPE
  2. 2Mixed, temperature-monitored CIP tank
  3. 3Pump, filter, flow/pressure and return
  4. 4Isolated RO pressure-vessel stage

What the image proves

CIP is a chemical-hydraulic system, not chemical poured into a running RO. Containment, compatibility and waste routing are part of the job.

How to verify it

Verify SDS, isolation, valves, tank volume, filter, heat/cool, instruments, eyewash and waste receiver; prevent incompatible chemical contact.

2

White mineral and brown organic/biological layers follow different chemical paths

A carbonate coupon reacts in acid while a brown matrix disperses in alkaline solution; probes show chemical demand.

White mineral and brown organic/biological layers follow different chemical paths：Carbonate/metal inorganic deposit、Acid solution and pH demand、Organic/colloid/biofilm layer、Alkaline dispersant/surfactant and pH1234

What to identify

  1. 1Carbonate/metal inorganic deposit
  2. 2Acid solution and pH demand
  3. 3Organic/colloid/biofilm layer
  4. 4Alkaline dispersant/surfactant and pH

What the image proves

Acid favors acid-soluble minerals; alkaline chemistry favors organics and biology, but silica and sulfate cannot be classified by appearance.

How to verify it

Retain deposit and blank; use solubility, TOC/ash, elemental, microscopy or ATP tests and trend return pH.

3

The transparent loop shows displacement, recycle, filtration, soak and return

A mixed tank feeds one vessel through flow and pressure control; a return filter and timed samples capture removed material.

The transparent loop shows displacement, recycle, filtration, soak and return：Mixed tank pH/T inventory、Low-pressure pump and flow/ΔP、Vessel feed-to-concentrate recycle、Return filter and timed solution samples1234

What to identify

  1. 1Mixed tank pH/T inventory
  2. 2Low-pressure pump and flow/ΔP
  3. 3Vessel feed-to-concentrate recycle
  4. 4Return filter and timed solution samples

What the image proves

Low pressure suppresses permeation; sufficient crossflow supplies shear and transport. Both are required.

How to verify it

Displace at roughly half flow, then use the manufacturer vessel flow; monitor ΔP, clean stages separately and recirculate during soak.

4

Four parallel tests reveal chemistry matching and sequence effects

Untreated mixed fouling, alkaline removal, acid-first residue and the full alkaline–rinse–acid result are compared.

Four parallel tests reveal chemistry matching and sequence effects：Untreated composite baseline、Organic/biofilm removal after alkali、Residue after wrong acid-first sequence、Alkali–rinse–acid combined result1234

What to identify

  1. 1Untreated composite baseline
  2. 2Organic/biofilm removal after alkali
  3. 3Residue after wrong acid-first sequence
  4. 4Alkali–rinse–acid combined result

What the image proves

pH alone does not guarantee removal; formulation and order decide whether material disperses or fixes/redeposits.

How to verify it

Run compatible coupon tests at equal area, T, velocity and time; compare mass/microscopy and coupon flux/passage.

5

Before/after coupons, solution samples and normalized data close acceptance

Mineral, organic and clean coupons plus timed pH/turbidity samples connect surface removal to the pilot vessel.

Before/after coupons, solution samples and normalized data close acceptance：Mineral coupon and dissolution evidence、Organic/biofilm coupon and dispersion、Rinsed clean coupon and integrity、Timed pH, turbidity, color and samples1234

What to identify

  1. 1Mineral coupon and dissolution evidence
  2. 2Organic/biofilm coupon and dispersion
  3. 3Rinsed clean coupon and integrity
  4. 4Timed pH, turbidity, color and samples

What the image proves

Dark solution is not the endpoint; normalized flow, passage and stage ΔP must recover without new integrity damage.

How to verify it

Record stable pre/post normalized metrics. If appearance improves but performance does not, investigate aged scale, compaction, wrong chemistry or damage.

Nine steps from CIP trigger to acceptance

Keep diagnosis, chemistry, hydraulics, safety and results in one batch record.

  1. 1. Confirm trigger

    Normalized Qp↓ / passage↑ / ΔP↑

    Exclude temperature, salinity, pressure, recovery and instrument effects.

  2. 2. Localize/sample

    Stage profile + water/filter/deposit

    Identify organic/biological, mineral, mixed or mechanical causes.

  3. 3. Choose recipe/order

    Deposit + membrane → cleaner

    Usually alkaline then acid; acid first only for confirmed simple carbonate/iron.

  4. 4. Make up safely

    RO/DI water + chemical + pH/T

    Stay inside SDS, compatibility and membrane envelope.

  5. 5. Low-flow displacement

    Half-flow, low P → discard dilution

    Replace process water without pressing dirt onto the surface.

  6. 6. Recycle/soak

    High-flow shear ↔ intermittent soak

    Maintain chemistry and carry loosened deposit back to tank/filter.

  7. 7. Monitor/replace

    pH/T/Q/ΔP + color/turbidity

    Detect depletion, loading and redeposition risk.

  8. 8. Flush out

    RO/DI water → specified endpoint

    Prevent reactions with feed or the next chemistry.

  9. 9. Restart/accept

    Stable normalized Qp/passage/ΔP

    Prove recovery and correct the upstream root cause.

Four deposits and cleaning directions

A starting map, not a replacement for the element manual.

Carbonate and some iron oxides/hydroxides

Preferred direction
Acid dissolution/complexation.
Trap
Sulfuric acid may precipitate CaSO₄; mixed organic/silica layers complicate acid-first.
Confirmation
Elemental/acid-solubility, pH demand, location and normalized recovery.

Organic, oil, colloid and biofilm

Preferred direction
High-pH surfactant/chelant/dispersant removal plus crossflow.
Trap
NaOH alone may not handle oil, silica or mature EPS; killing is not removal.
Confirmation
TOC/ash, microscopy/ATP, solution load and Qp/ΔP recovery.

Silica and sulfate/Ba/Sr scale

Preferred direction
Early, manufacturer-specific alkaline chelant/salt or specialty chemistry.
Trap
Aged deposits may be poorly recoverable; extreme chemistry risks the membrane.
Confirmation
ICP/mineralogy, saturation, last-stage pattern and coupon trials.

Composite layer

Preferred direction
Usually alkaline to open matrix, rinse, then acid for remaining mineral.
Trap
Acid first can react with silica, humics and biofilm and worsen performance.
Confirmation
Stepwise solution analysis, performance response and surface evidence.

FilmTec general cleaning triggers include about 10% normalized flow loss, 5–10% normalized salt-passage increase, or 10–15% normalized pressure-drop increase. They are trend triggers, not universal limits; use the latest manual for the installed element.

Retain four synchronized evidence sets

Pre-clean baseline

Normalized Qp, passage and stage ΔP; feed, SDI/biology, location and recent events.

Chemistry

Lot/active strength, make-up water, initial/return pH, T, time, additions, compatibility and SDS.

Hydraulics/load

Stage Q/P/ΔP, displacement, soak/recycle timing, filter, turbidity/color and replacement points.

Outcome/root cause

Rinse endpoint, waste, stable normalized recovery, integrity and pretreatment/operation correction.

Interpret common observations

Observation
First-stage ΔP rise, slimy brown layer, ATP/TOC high
Likely direction
Biofilm/organic/colloid composite
Next action
Alkaline dispersant clean, stage-wise crossflow, correct pretreatment
Observation
Last-stage flow loss, white acid-soluble deposit, supersaturation
Likely direction
Carbonate or acid-soluble scale
Next action
Confirm mineral and membrane envelope, acid clean, correct recovery/pH/antiscalant
Observation
Solution quickly dark/turbid and pH drifts
Likely direction
High load or exhausted chemistry
Next action
Record demand, dose or replace before redeposition
Observation
Surface looks clean but normalized recovery fails
Likely direction
Aged insoluble scale, compaction, wrong chemistry or damage
Next action
Stop extreme repeat cleaning and analyze coupon/element

Four common mistakes

Acid removes every mineral; alkali every organic

Sulfates, silica, metal-organic complexes and mature biofilm need specific formulations.

Stronger, hotter and longer is better

pH–temperature–time must stay inside the element envelope; loaded cold soak can redeposit.

White deposit means acid first

Color is not mineralogy, and mixed layers can worsen under acid-first cleaning.

Dark return means success

Success is flush quality and normalized performance recovery plus root-cause correction.

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