RO membrane cleaning method

With the increasingly strict emission standards of sewage pollutants and the large-scale localization of membrane material production, more and more membrane technologies are used in the treatment of municipal sewage and various industrial sewage. Life and operating costs.

The cleaning of membranes is generally divided into two types: physical cleaning and chemical cleaning, and the higher the frequency of chemical cleaning, the greater the damage to the membrane, which seriously affects the service life of the membrane system. Therefore, it is generally difficult to master the chemical cleaning of the membrane system.

The frequency of membrane cleaning is closely related to the degree of perfection of pretreatment measures. The more complete the pretreatment, the longer the cleaning interval; on the contrary, the simpler the pretreatment, the higher the cleaning frequency.

The general membrane cleaning is to follow (10% rule)-when the ratio of the corrected fresh water flow rate to the initial 200h operation (after compaction occurs) is reduced by 10% and / or the pressure difference is observed to increase by 10-20 % Need to be cleaned.

As far as possible, measures should be taken before the reduction in desalination rate is shown.

Regularly scheduled protective maintenance cleaning is not sufficient to protect the reverse osmosis system. For example, due to the abnormal operation of the pretreatment equipment, the water inlet conditions will change in a short time.

Backwashing is effective to prevent large particles from clogging certain forms of reverse osmosis membrane modules. But not all pollution can be removed by simple backwashing, and periodic chemical cleaning is also required.

In addition to the increase in chemical and labor costs, chemical cleaning also has a pollution problem, so it should not be too frequent. It should not exceed 1 to 2 times per month, and each cleaning time is about 1 to 2 hours.

The chemical cleaning system usually includes a chemical mixing tank and matching pumps, mixers, heaters, etc. Chemical cleaning is often determined based on operating experience (it can be based on the relationship between the pressure drop reading of each column of equipment and the operating time, or based on the water production, fresh water quality and membrane pressure drop, etc.).

The chemicals and methods used in chemical cleaning need to be determined according to the source of pollution (the content described below is for reference), but more attention should be paid to and applied the experience of the unit. In order to ensure the effect, rinse before chemical cleaning. Before rinsing, reduce the pressure, and then use 2 to 3 times the normal flow of water to rinse the membrane. By the stirring action of the fluid, the dirt is peeled from the membrane surface and washed away. Then, according to the pollution characteristics, the cleaning fluid is selected to chemically clean the membrane. In order to protect the reverse osmosis module, the liquid temperature should preferably not exceed 35 ° C.

If the system is disabled for more than 5 days, it is best to rinse with formaldehyde before putting it into use. If the system is disabled for two weeks or longer, it should be soaked with 0.25% formaldehyde to prevent the growth of microorganisms in the membrane. Chemical agents are best replaced once a week.

The cleaning agent used for various pollutants can refer to the content listed below, and the water quality of different places can be selected appropriately.

①Metal oxide precipitation

Choose 0.2mol / L ammonium citrate or 4% sodium bisulfite. The dosage of medicament is about 100L / piece of membrane.
1) Maintain 0.4MPa pressure, 15L / min flow rate, and circulate for 2h;
2) Maintain the pressure of 1MPa and rinse with water for 30min;
3) Normal operation.

②Calcium precipitate

Can choose hydrochloric acid (adjust pH = 4) or citric acid (adjust pH = 4). The dosage of medicament is about 100L / piece of membrane.
1) Maintain 0.4MPa pressure, 15L / min flow rate, and circulate for 2h;
2) Maintain the pressure of 1MPa and rinse with water for 30min;
3) Normal operation.

③Organic matter and colloidal matter

Choose citric acid (adjust pH = 4); hydrochloric acid (adjust pH = 2); sodium hydroxide (adjust pH = 12); or neutral detergent.

The dosage of medicament is about 100L / piece of membrane.
1) Maintain 0.4MPa pressure, 15L / min flow rate, and circulate for 2h;
2) Maintain the pressure of 1MPa and rinse with water for 30min;
3) Normal operation.

④Bacteria and slime

Choose a 1% formaldehyde solution. The dosage of medicament is about 100L / piece of membrane.
1) Maintain 0.4MPa pressure, 15L / min flow rate, and circulate for 2h;
2) Maintain the pressure of 1MPa and rinse with water for 30min;
3) Normal operation.

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