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This RO membrane cleaning solution can solve 99% of your problems!

1 Pollution and cleaning of reverse osmosis osmosis membrane

RO membranes may be suspended or insoluble salts in the feed water. The most common pollutants are calcium carbonate precipitation, calcium sulfate precipitation, metal (iron, manganese, copper, nickel, aluminum, etc.) oxide precipitation, silicon deposits, inorganic or organic deposition mixture, NOM natural organic substances, synthetic organic matter (e. g., scale retardant / dispersant, cation polymer electrolyte), microorganisms (algae, mold, fungi), etc.

The nature and rate of pollution depend on various factors such as feed water quality and system recovery. Usually pollution is gradually, if not controlled as soon as possible, pollution will damage the RO membrane in a relatively short period of time. Cleaning of the RO membrane is recommended to be contaminated, or before a long shutdown, or as a regular routine maintenance.

Chemical cleaning or physical washing is required when the reverse osmosis system (or device) has the following symptoms:

Under the normal water supply pressure, the water output decreased by 10 ~ and 15% compared with the normal value; to maintain the normal water output, the water supply pressure after temperature correction increased by 10 ~ and 15%;

The yield water quality is reduced by 10 ~ by 15%, and the salt permeability increases by 10 ~ by 15%; the feed water pressure increases by 10 ~ by 15%; and the pressure difference between the system segments increases significantly.

Stable operating parameters mainly refer to water production flow rate, water production back pressure, recovery rate, temperature and TDS. If these operating parameters fluctuate, it is recommended to check if contamination occurs, or whether the actual operation of reverse osmosis is normal if the key operating parameters change.

Regular monitoring of the overall performance of the system is a basic method to confirm whether the RO membrane is contaminated. The effect of pollution on the RO membrane is gradual and the extent of the effect depends on the nature of the contamination. Table 1 "RO membrane pollution characteristics and treatment methods" lists the common pollution phenomena and corresponding treatment methods.

The cleaning cycle of contaminated reverse osmosis film depends on the actual site. The normal cleaning cycle is once every 3 – 12 months.

When the RO membrane occurs only undergone mild contamination, it is important to clean the RO membrane. Heavy pollution will hinder the deep penetration of chemicals into the pollution layer and affect the cleaning effect.

What pollutants and how to be cleaned based on site contamination. For several complications of simultaneous contamination, cleaning was performed by alternating washes with low and high pH (first low pH after high pH)

Table 1 Pollution characteristics and treatment methods of RO membrane

2. Pollution situation analysis

Calcium carbonate scale:

Calcium carbonate scale is a mineral scale. Calcium carbonate scale may be deposited in the failure of the scale inhibitor / dispersant addition system or the failure of the acid pH regulation system. Early detection of calcium carbonate scale is extremely necessary to prevent crystal damage to the RO membrane on the surface of the membrane. Early detected calcium carbonate scale can be removed by a method of reducing the fed water pH to 3~5 and running 1 ~ for 2 h. For calcium carbonate scale with a long deposition time, cleaning can be removed with a low pH citrate solution.

Calcium sulfate, barium sulfate, strontium sulfate scale:

Sulphate scale is a mineral scale much harder than calcium carbonate scale, and is not easy to remove. Sulphate scale can be deposited in the failure of scale repellant / dispersant addition system or pH with sulfuric acid. Early detection of sulfate scale is extremely necessary to prevent crystal damage to the RO membrane on the surface of the membrane. Barium sulfate and strontium sulfate scale are more difficult to remove, because they are difficult to dissolve in almost all cleaning solutions, so special attention should be taken to prevent the generation of such scaling.

Metal oxide / hydroxide contamination:

Typical metal oxides and metal hydroxide contamination are iron, zinc, manganese, copper, aluminum, etc. The formation of this scale may be a corrosion product of the device line, container (tank / tank), or oxidized metal ions, chlorine, ozone, potassium, permanganate, or the use of iron or aluminum additives in a pretreatment filtration system.

Polyized silicon scale:

Silicon gel scale is caused by oversaturated state and polymer, and is very difficult to remove. It should be noted that this contamination of silicon is different from that of silicone colloids. Silicon colloidal contamination may be caused by association with metal hydroxide or with organic matter. The removal of silicon dirt is difficult and adopts traditional chemical cleaning methods. If the traditional approach does not address this scale removal, contact HeadEnergy Technologies. Existing chemical cleaning agents such as ammonium hydrogen fluoride have been successfully used in some projects, but must be protected against the operational hazards and damage to the equipment.

Colliidal contamination:

Colloids are inorganic particles suspended in water or of an organic and inorganic mixture that do not precipitate due to its own gravity. Colliids typically contain one or more of the main components, such as iron, aluminum, silicon, sulfur or organic matter.

Non-soluble natural organic matter contamination (NOM):

Non-soluble natural organic matter contamination (NOM——Natural Organic Matter) is usually caused by the decomposition of nutrients in surface water or deep well water. The chemical mechanism of organic pollution is very complex, mainly unit parts or graft acid, or yellow mildew acid. Adadsorption of non-soluble NOM to the membrane surface can cause rapid contamination of the RO membrane, and the gradual gel or block contamination process begins.

Microbial deposition:

Organic sediments are generated from bacterial clay, fungi, mold, etc., and this contaminant is more difficult to remove, especially if the water supply pathway is completely blocked. The blockage of water supply pathway will make it difficult for clean water to enter into the RO membrane. To inhibit the further growth of this sediment, it is important not only to clean and maintain the RO system, but also to clean the pretreatments, piping and ends, etc. When using oxidative sterilization for the RO membrane, please contact the technical support department of Yixing Fuhua Water Treatment Equipment Co., Ltd. to use the approved fungicide.

3. Selection and use of the cleaning fluid

The selection of appropriate chemical cleaning agent and reasonable cleaning scheme involves many factors. First, contact the equipment manufacturer, RO membrane manufacturer, or RO special chemicals and service personnel. Identify the main contaminants and select the appropriate chemical cleaning agents. Sometimes use a special chemical cleaning agent, when applied, and follow the product performance and instructions provided by the agent supplier. Sometimes, the contaminated single reverse osmosis film can be removed from the reverse osmosis device for testing and cleaning tests to determine the appropriate chemicals and cleaning scheme.

For optimal cleaning results, combined cleaning is sometimes used with some different chemical cleaning agents.

The typical procedure is to clean with a low pH range, remove mineral scale contaminants, and then perform high pH cleaning to remove organic matter. Some cleaning solutions are supplemented with detergent to help remove severe biological and organic debris scale, while other agents such as EDTA chelators are used to assist in the removal of colloidal, organic, microbial and sulfate scale.

Careful consideration needs to be given that the contamination gets worse if improper chemical cleaning methods and agents were selected.

4. Selection and guidelines for chemical cleaning agents

The specialized chemicals shall first ensure that they have been identified by the chemical supplier and meet the requirements for the RO membrane. The guidance / recommendations of the pharmaceutical supplier should not conflict with the cleaning parameters and limited chemical species recommended in this technical service announcement;

If the specified chemicals are being used, confirm that it is listed in this Energy Technical Service Bulletin and meets the requirements of its RO membrane (consult Anfeng);

The cleaning work is completed by a combination method, including appropriate cleaning pH, temperature and contact time parameters, which will be conducive to enhance the cleaning effect;

Clean at the recommended optimal temperature to achieve the best cleaning efficiency and extend the life of the RO membrane; clean with the minimum number of chemical contacts, beneficial to extend the membrane life;

Carefully regulated pH range from low to high extends the service life of the RO membrane.

Typically, the most effective cleaning method is by cleaning from low to high pH solution. Cleaning of the oil-contaminated RO membrane cannot start at low pH because the oil solidifies at low pH;

Cleaning and flushing flow direction shall be maintained in the same direction;

When cleaning multiple reverse osmosis devices, the most effective cleaning method is segment cleaning, which can control the optimal cleaning flow rate and cleaning liquid concentration, and avoid contaminants in the upstream section from entering the downstream RO membrane; washing detergent with higher pH product water can reduce the production of foam;

If the system has undergone biologic contamination, consider adding a fungicide chemical cleaning step after cleaning. The fungicide must be administered immediately after cleaning or at regular intervals (if once a week). We must confirm that the fungicide used is compatible with the RO membrane and does not pose any risk of harm to human health and can effectively control biological activity at low cost;

To ensure safety, when dissolving the chemicals, remember to slowly add the chemicals to sufficient water and stir simultaneously;

For safety purposes, acids cannot be mixed with harsh (corrosive) substances. The stranded former chemical cleaning solution was thoroughly rinsed from the RO system before using the next solution.

5 Selection of the cleaning solution

Table 2-The cleaning solution provided by the conventional cleaning solution formula is the addition of a certain weight (or volume) of chemicals to 100 gallons (379 liters) of clean water (RO product water or water without free chlorine). The solution was prepared in the proportion of the chemicals and water volume used. Solvents are RO product water or deionized water without free chlorine and hardness. Before entering the RO membrane, be thoroughly mixed and evenly, pH value should be adjusted according to the target value and the amine target temperature value is stable. The conventional cleaning method is set based on the operation of circulating chemical cleaning solution for one hour and an optional chemical immersion for one hour.

Table 2 General cleaning solution formula (based on 100 gallons, or 379 liters)

6 Introduction of conventional cleaning fluid

[Solution 1]

Wash solution vs. Low pH (pH = 3 ~ 4) of 2.0% (W) citrate (C6H8O7). It is very effective to remove inorganic salt scale (such as calcium carbonate scale, calcium sulfate, barium sulfate, strontium sulfate scale, etc.), metal oxide / hydroxide (iron, manganese, copper, nickel, aluminum, etc.) and inorganic colloids.

[Solution 2]

0.5% (W) Low pH hydrochloride cleaning solution (2.5) used primarily to remove inorganic scale (e. g. calcium carbonate scale, calcium sulfate, barium sulfate, strontium sulfate scale, etc.), metal oxide / hydroxide (iron, manganese, copper, nickel, aluminum, etc.), and inorganic colloids. This cleaning solution is stronger than solution 1 because hydrochloric acid (HCl) is a strong acid. The following concentration values of hydrochloric acid are effective: (18 ° Pomeric =27.9%, 20 ° Pomeric =31.4%, and 22 ° Pomeric =36.0%).

[Solution 3]

0.1% (W) sodium hydroxide high pH cleaning solution (pH = 11.5). For removing the polymerized silicon scale. This wash is a relatively intense alkaline cleaning solution.

7 RO membrane cleaning and flushing procedures

The RO membrane may be placed in a pressure vessel and cleaned at high flow rates with circulating clean water (RO product water or clean water without free chlorine) flowing through the RO membrane. The cleaning procedure for RO depends entirely on the circumstances, replacing the cleaning water for circulation if necessary.

Routine cleaning procedures for the RO membrane are as follows:

Low pressure flushing at 60psi (4bar) or lower, i. e., pump clean water from the cleaning tank (or equivalent water source) into the pressure vessel and discharge it and run for several minutes. The flushing water must be clean, removed hardness, free of transition metal or residual chlorine.

Prepare a specific cleaning solution in the cleaning tank. Preparation water must be RO product water or deionized water that removes hardness, no transition metal and residual chlorine. Temperature and pH shall be adjusted to the required values.

Start the cleaning pump and pump the cleaning fluid into the membrane assembly, circulating the cleaning for approximately one hour or the required time (consult the supplier's technician). At the start, before the cleaning fluid returns to the RO cleaning tank, discharge the original backflow to avoid the system stranded water uting the cleaning solution. For the first 5 minutes, the flow rate was slowly adjusted to 1 / 3 of the maximum design flow rate. This can reduce potential congestion caused by substantial deposition of dirt. In the second 5 minutes, increase the flow rate to 2 / 3 of the maximum design flow rate, and then, increase it to the designed maximum flow rate value. If required, the adjustment back to the original value when pH is greater than 1.

Circular cleaning and soaking procedures can be used alternately as needed. The soaking time is recommended to choose from 1 to 8 hours (please consult Fuhua Company). Be careful and maintain the proper temperature and pH.

After chemical cleaning, low pressure washing shall be performed with cleaning water (remove hardness, RO product water without metal ions such as iron and chlorine) to remove the residue of the chemical from the cleaning device / parts, discharge and rinse the cleaning tank, and then fully fill the cleaning tank with cleaning water for washing. Pump all flushing water from the cleaning tank to flush the pressure vessel to discharge. A second cleaning can be performed if required.

Once the RO system has been completely flushed with clean water in the water storage tank, the final pretreatment feed water can be performed with low pressure flushing. The feed water pressure shall be less than 60psi (4bar) and the final flushing continues until the flushing water is clean and free of any foam and detergent residues. Usually this takes 15 ~ and 60 minutes. The operator can sample with a clean flask, shake well, and monitor the residue of detergent and foam in the flushing water at the discharge outlet. The removal of the wash liquid can be performed by a method to test the conductance, such as the wash water to the discharge water is within 10~20% of the feed water conductance; the pH table can also be used to compare whether the wash water approaches the pH value of the feed water.

Once all stages have been cleaned and the chemicals have been washed, RO may resume in the operating procedure, but the initial product water will be discharged and monitored until RO can meet process requirements (conductance, pH, etc.). For stable RO production water quality, this recovery period sometimes takes from hours to days, especially after high pH cleaning.

8 RO membrane chemical cleaning and water washing

During cleaning, the cleaning solution is circulated on the high pressure side of the membrane with a low pressure and high flow rate, when the RO membrane is still installed in the pressure vessel and a special cleaning device is required to complete the work.

General steps for cleaning the reverse osmosis osmosis membrane:

1. Pump clean and free chlorine from the cleaning box (or corresponding water source) into the pressure vessel and discharge it for several minutes.

II. Prepare cleaning liquid in the cleaning water in the cleaning box.

3. Circulation the cleaning liquid in the pressure container for 1 hour or for a preset time.

IV. After cleaning, clean the cleaning box and rinse, and then the cleaning box is full of clean product water for the next step.

V. Use a pump to remove clean and no free chlorine product water from the cleaning box (or the corresponding water source) into the pressure container and discharge it for several minutes.

VI. After flushing the reverse osmosis system, run the reverse osmosis system when the product water discharge valve is opened until the product water is clean, without foam or has no cleaning agent (usually 15 ~ for 30 minutes).