Cleaning of Reverse Osmosis Membrane Elements

Purpose: To ensure the normal operation of the reverse osmosis system

Purpose: To extend the service life of reverse osmosis membrane elements

When is cleaning required?

How to clean and what cleaning agents to use

When is cleaning the reverse osmosis system required?

• When the standardized permeate flow rate is 10% ~ 15% lower than after the last cleaning

• When the standardized permeate quality is 10% ~ 15% lower than after the last cleaning

• When the standardized pressure drop is 10% ~ 15% higher than after the last cleaning

• Before long-term shutdown

• As part of routine maintenance

What needs to be cleaned?

• Calcium carbonate scale

• Calcium sulfate, barium sulfate, and strontium sulfate scale

• Water and metal oxide scale (including iron, manganese, nickel, copper, etc.)

• Silica scale

• Colloidal deposits (inorganic)

• Colloidal deposits (inorganic and organic mixtures)

• Organic deposits (natural products)

• Organic deposits (anthropogenic products)

• Biological growth (bacteria, fungi, mold, etc.)

Note: You usually need to clean a mixture of the above contaminants.

How to Choose Cleaning Agents

• Identify the contaminants

• Contact membrane manufacturers, engineering companies, or reverse osmosis professional cleaning companies

• Choose general-purpose or specialized chemical cleaning agents

• Collect information on-site and perform cleaning (experimental and calibration methods)

• Provide membrane elements or scale samples to the reverse osmosis professional cleaning company for laboratory analysis

• Consider the cost of the agents

Precautions for Selecting and Using Chemical Cleaning Agents

• Follow the guidelines recommended by membrane manufacturers and reverse osmosis professional cleaning companies regarding agent type, dosage, pH value, and thermometer contact time.

• Optimal cleaning effect

• Minimize the use of strong chemical reagents

• For composite membranes and ultra-low pressure composite membranes, the typical pH range is 4-10.

• For composite membranes and ultra-low pressure composite membranes, the maximum pH range is 2-12.

• Clean at the recommended temperature, generally 30-40℃ is best.

• Consider the environmental impact of discharge.

• Do not mix acids and alkalis.

• Rinse the cleaning agent with high-pH permeate water.

• If oil contamination occurs, do not use a low-pH solution for cleaning initially.

Most Commonly Used Cleaning Formulas for Composite Membranes

Contaminants Cleaning Solution

Calcium Carbonate

Calcium Phosphate

Metal Oxides

(Formula A) Use KY-410, adjust pH to 4.0 (preferred)

(Formula B) 2% Citric Acid Solution + Ammonia Water Temperature 40℃

Sometimes, a hydrochloric acid aqueous solution with pH 2-3 can also be used for cleaning.

Calcium Sulfate

Mixed Colloids

Small Molecule Natural Organic Matter

Microorganisms

(Formula A) Use KY-420, adjust pH to 10.0 (preferred)

(Formula B) 2.0% Sodium Tripolyphosphate Solution + 0.8% Na-EDTA Solution (chelating agent) Temperature 40℃

Sometimes, a NaOH aqueous solution with pH < 10 can also be used for cleaning.

Large Molecule Natural Organic Matter

Microorganisms

(Formula A) Use KY-420, adjust pH to 10.0 (preferred)

(Formula B) 2.0% Sodium Tripolyphosphate Solution 0.25% Sodium Dodecylbenzenesulfonate Solution, Temperature 40℃

Most Commonly Used Cleaning Formulas for Acetic Acid Membranes

Contaminants Cleaning Solution

Calcium Carbonate

Calcium Phosphate

Metal Oxides, pH 4.0, 2.0% Citric Acid Solution, 0.1% Nonionic Cleaning Agent, Temperature 35℃

Calcium Sulfate

Mixed Colloids

Small Molecule Natural Organic Matter, pH 7.5, 2.0% Sodium Tripolyphosphate Solution, 0.8% Na-EDTA Solution, 0.1% Nonionic Cleaning Agent, Temperature 35℃

Large Molecule Natural Organic Matter, pH 7.5, 0.5% Sodium Perborate, 0.1% Nonionic Cleaning Agent, Temperature 35℃

Biological Growth, pH 7.5, 2.0% Sodium Tripolyphosphate Solution, 0.25% Na-DBS Solution, Temperature 35℃

Chemical Cleaning of Silica Scale

• Soluble silica deposited on the membrane is difficult to remove without damaging the membrane.

• Consult the membrane manufacturer or a professional reverse osmosis cleaning company before cleaning.

• Higher rinsing flow rates are beneficial for flushing away dirt.

• Repeated circulation and soaking are beneficial for descaling.

• For composite membranes, alkaline solutions with a high pH of 10-12 and high temperatures of 40℃ are beneficial for removing silica scale.

Cleaning of Biofouling in Composite Membranes

Coral Reef Syndrome: A complex mixture of inorganic scale, metal oxides, colloidal substances, organic matter, live and dead bacteria, biological slime, fungi, etc.

Solution 1:

Low pH cleaning

High pH cleaning

Disinfection with biological disinfectants

Solution 2:

Disinfection using disinfectants that can break down slime

High pH cleaning

Weekly shutdown for sterilization, each time using biological disinfectants for 20-30 minutes.