First, the necessity of cleaning

Reverse osmosis membrane Under normal operating conditions, reverse osmosis membrane may be contaminated by inorganic scale, colloid, microorganism, metal oxide, etc. These substances are deposited on the surface of the membrane, which will cause the reverse osmosis force to drop or the salt removal rate to decrease. Therefore, in order to restore good water permeability and desalination performance, it is necessary to chemically clean the membrane. When the membrane is damaged, the membrane may be repaired by a repair solution provided by the membrane manufacturer to restore the salt rejection rate of the RO membrane.

Second, the reverse osmosis membrane pollution and cleaning methods

This article describes common contaminations affecting the performance of composite membranes and their cleaning methods. This article applies to reverse osmosis membrane modules of 4, 6, 8, 8 and 8.5 inches diameter.

Note 1: Under no circumstances should the water with free chlorine be in contact with the composite membrane module. If such contact occurs, the performance of the membrane module will be degraded and the performance will no longer be restored. After the pipeline or equipment is sterilized. It should be ensured that there is no free chlorine in the feed water sent to the reverse osmosis membrane module. It should be confirmed by laboratory tests that PH-011 should be used to neutralize residual chlorine and ensure sufficient contact time to ensure complete reaction.

Note 2: During the warranty period of the reverse osmosis membrane module, it is recommended to clean the membrane every time. At least during the first cleaning, the field service personnel should be on site.

Note 3: The use of cationic surfactants should be avoided in cleaning solutions, as irreversible contamination of the membrane modules may occur if used.

1. Contaminants in reverse osmosis membrane modules

After a period of normal operation, the reverse osmosis membrane module is contaminated by suspended matter or poorly soluble substances that may be present in the feed water. The most common of these pollutants are calcium carbonate scale, calcium sulfate scale, metal oxide scale, and silicon. Sediments and organic or biological deposits. The nature of the pollutants and the speed of pollution are related to the water supply conditions. The pollution is slowly developed. If no measures are taken early, the pollution will damage the membrane module in a relatively short period of time. The overall performance of the system is to confirm the contamination of the membrane module. A good method, different pollutants will cause different degrees of damage to the performance of the membrane module. The effects of common contaminants on membrane performance are listed.

2. Removal of pollutants

The removal of contaminants can be achieved by chemical cleaning and physical washing, sometimes by changing operating conditions. As a general rule, cleaning should be carried out when one of the following conditions occurs.

2.1 Under normal pressure, if the product water flow drops to 10-15% of the normal value.

2.2 In order to maintain normal product water flow, the temperature-corrected feed water pressure is increased by 10 to 15%.

2.3 Product water quality is reduced by 10 to 15%. The salt transmission rate is increased by 10 to 15%.

2.4 Increased use pressure by 10 to 15%

2.5 The pressure difference between the RO sections increases significantly (maybe there is no instrument to monitor this indication)

Third, common pollutants and their removal methods:

3.1 Calcium carbonate scale

When the scale inhibitor addition system fails or the acid system fails, the pH of the feed water rises. Then, calcium carbonate may be deposited. The precipitation of calcium carbonate scale should be discovered as early as possible to prevent the growth of crystals on the membrane surface. Damage is generated, such as early detection of calcium carbonate scale, which can be removed by reducing the pH of the feed water to between 3.0 and 5.0 for 1 to 2 hours. For calcium carbonate scales with longer precipitation time, PH-121 should be used for cyclic cleaning or overnight immersion.

Note: Make sure that the pH of any cleaning solution is not lower than 2.0, otherwise damage to the RO membrane module may occur, especially when the temperature is high. The highest pH should not be higher than 11.0. Ammonia water can be used to increase the pH, and sulfuric acid or hydrochloric acid can be used to lower the pH.

3.2 Calcium sulfate scale

PH-121 Wash 2 (see Table 2) is the best way to remove calcium sulfate scale from the surface of the reverse osmosis membrane.

3.3 Metal oxide scale

The deposited hydroxide (e.g., iron hydroxide) can be easily removed using the method of removing calcium carbonate scale as described above.

3.4 Silica scale

For silica scales that are not symbiotic with metallized or organic materials, they can only be removed by special cleaning methods.

3.5 Organic sediments

Organic deposits (such as microbial slime or mildew) can be removed using the cleaning solution PH-121. To prevent re-propagation, the company can use the PH-020 sterilization solution approved by the company to circulate and soak in the system. It usually takes a long time to soak. In order to be effective, if the reverse osmosis device is deactivated for three days, it is best to use disinfection. Please consult with the company to determine the appropriate disinfectant.

Fourth, the general steps to clean the reverse osmosis membrane module:

1. Use a pump to pump clean, free chlorine-free reverse osmosis product water from the wash tank (or corresponding water source) into a pressure vessel and drain for a few minutes.

2. Neutralize the cleaning solution with clean product water in the cleaning tank.

3. Circulate the cleaning solution in a pressure vessel for 1 hour or a preset time. For an 8 inch or 8.5 inch pressure vessel, the flow rate is 35-40 gallons per minute (133 to 151 liters per minute) for a pressure of 6 inches. The container flow rate is 15-20 gallons per minute (57-76 liters/min), and the flow rate for a 4-inch pressure vessel is 9-10 gallons per minute (34-38 liters/min)

4. After the cleaning is completed, drain the cleaning tank and rinse it, then fill the cleaning tank with clean product water for further washing.

5. Use a pump to pump clean, free chlorine free product water from the wash tank (or corresponding water source) into the pressure vessel and drain for a few minutes.

6. After flushing the reverse osmosis system, run the reverse osmosis system with the product water drain valve open until the product water is clean, free of foam or no cleaning agent (usually 15 to 30 minutes).