Generally, the reverse osmosis membrane element can be used for about 2 ~ 3 years. If you want to prolong the service life, you can clean the reverse osmosis membrane elements, which are usually divided into physical flushing and chemical flushing. When the physical flushing can no longer restore the performance of the reverse osmosis membrane, chemical cleaning should be carried out.

Cleaning of reverse osmosis membrane

According to experience, if the reverse osmosis unit is cleaned every three months or more. If it is cleaned once every 1-3 months, the operating conditions need to be improved to improve the pretreatment effect.

one

Judge the cleaning condition:

(1) Standardized freshwater production fell by more than 10%.

(2) The standardized salt penetration rate increased by more than 10%.

(3) In order to maintain normal fresh water flow, the pressure difference between feed water and concentrated water increases by more than 10% after temperature calibration.

(4) There are serious pollutants and scale in the internal device.

(5) Before long-term shutdown of RO unit.

(6) Routine maintenance of RO unit.

Before determining whether to clean the reverse osmosis system, the following other reasons that may cause the above phenomena shall also be comprehensively considered:

☆ decrease of operating pressure (failure of pressure control device and abnormality of high-pressure pump);

☆ the inlet water temperature decreases (the heater fails or the water temperature decreases due to seasonal changes);

☆ the salt content of influent increases;

☆ preprocessing exception;

☆ concentrated water seeps into fresh water due to membrane damage, misalignment of central pipe of series membrane element, loose sealing of O-ring of pressure vessel, etc.

two

Contaminants

Common pollutants in reverse osmosis membrane elements mainly include CaCO3, CaSO4, BaSO4, SrSO4, metal oxide, silicon sediment, organic matter and biological slime. When the scale inhibitor dosing system or acid dosing system fails, CaCO3 may be deposited in the membrane element, and chemical cleaning method shall be adopted for cyclic cleaning or overnight immersion.

three

formula

Different pollutants cause different degrees of damage to the membrane, and different cleaning solutions shall be used for different pollutants.

four

Cleaning equipment

(1) Reverse osmosis cleaning system

It is generally composed of cleaning pump, reagent preparation box, 5-20um security filter, heater, relevant pipeline valves and control instruments.

(2) Operation  

The cleaning methods include static immersion and cyclic cleaning. Static immersion: soak the membrane with cleaning solution for about 1-15h depending on the degree of pollution. The general steps of cyclic cleaning are:

one

Pump fresh water from the reagent preparation tank into the pressure vessel and discharge it for several minutes.

two

Prepare cleaning solution with fresh water in reagent preparation tank.

three

Clean the pressure vessel with cleaning solution for 1H or reach the predetermined time. The cleaning flow can be determined according to the following table. When the pollution is serious, the cleaning flow can be increased to 150% of the resin in the table. At this time, the cleaning pressure drop is large, which is generally controlled not to exceed (0.10-0.14mpa) / root membrane element or 0.4mpa/root membrane module. At the beginning of dosing cleaning, 50% of the flow value in the table can be used to inject the heated cleaning solution into the pressure vessel to control the pressure, so as to overcome the pressure drop from inlet to outlet without fresh water outflow. In order to avoid dilution of the cleaning solution, open the concentrated water discharge valve to discharge the accumulated water in the system before cleaning. The reverse osmosis system can be cleaned in sections. The cleaning direction is the same as the running direction, and reverse cleaning is not allowed, otherwise the membrane roll may protrude and damage the membrane element.

four

After circulating cleaning, clean the reagent preparation tank with fresh water.

five

Flush the above pressure vessels with fresh water.

six

After the flushing, the reverse osmosis system will be operated under the opening of the fresh water discharge valve until the fresh water is clean, no foam or no cleaning fluid. It usually takes 15-30min time.

Replacement of reverse osmosis membrane

After the reverse osmosis equipment operates normally for a period of time, the reverse osmosis membrane element will be polluted by suspended solids or insoluble salts that may exist in the feed water, and the following symptoms will occur:

one

The weight of membrane elements of reverse osmosis equipment increases;

two

The removal rate of RO membrane increased or decreased significantly;

three

Under standard pressure, the water production of reverse osmosis equipment decreases significantly;

four

In order to reach the standard water production, the operating pressure needs to be improved;

five

The pressure drop between inlet water and concentrated water of reverse osmosis equipment increases;

six

Take out the membrane element from the pressure vessel and pour water on the water inlet side of the erected membrane element. If the water cannot flow through the membrane element, it only overflows from the end face, indicating that the water inlet channel is blocked.

Whether the reverse osmosis membrane element needs to be replaced or not depends on the actual situation.