How to properly use the new RO reverse osmosis membrane?-Hezhong Environment (Beijing) Co., Ltd. was established in 2003

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How to properly use the new RO reverse osmosis membrane?

Published Time:

2022-10-09

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Technical points for using new RO reverse osmosis membranes:

1. First, rinse the quartz sand and coconut shell activated carbon thoroughly. Newly installed quartz sand and coconut shell activated carbon should be rinsed for a longer time.

2. Check for residual chlorine. If residual chlorine exceeds the standard, resolve the residual chlorine issue before proceeding to the next step of RO reverse osmosis membrane operation.

3. After installing the new membrane, flush it with water and soak the membrane for 1-2 hours. Because it is a dry membrane, the soaked membrane is more moist, preventing high pressure from damaging the membrane.

4. Then start the high-pressure pump, and the pressure should be increased slowly, from 2 kg to 8-10 kg, for better desalination efficiency of the new membrane.

5. Residual chlorine should be controlled below 0.003.

6. Open the concentrate valve before starting the high-pressure pump. After the high-pressure pump is turned on, slowly adjust the concentrate valve to control the single-membrane recovery rate at around 15%.

7. The produced water in the first half hour must be drained, because there is a protective liquid inside the membrane, to avoid affecting the taste of the water.

8. Check the influent pH value, above 6.5.

II. How to determine if the reverse osmosis membrane needs cleaning?

Reading

Reverse osmosis membrane elements can generally be used for about 2-3 years. To extend their lifespan, the reverse osmosis membrane elements can be cleaned. This usually involves physical and chemical cleaning methods. When physical cleaning can no longer restore the performance of the reverse osmosis membrane, chemical cleaning should be performed. Reverse osmosis membrane elements can generally be used for about 2-3 years. To extend their lifespan, the reverse osmosis membrane elements can be cleaned. This usually involves physical and chemical cleaning methods. When physical cleaning can no longer restore the performance of the reverse osmosis membrane, chemical cleaning should be performed.

Cleaning of Reverse Osmosis Membranes

Based on experience, if the reverse osmosis device is cleaned every three months or longer. If it is cleaned once every 1-3 months, the operating conditions need to be improved to enhance the pretreatment effect.

1 Judging the cleaning situation:

(1) The standardized freshwater yield has decreased by more than 10%.

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

(3) To maintain normal freshwater flow, the pressure difference between the feed water and concentrate water has increased by more than 10% after temperature calibration.

(4) There are serious pollutants and scaling inside the device.

(5) Before long-term shutdown of the RO device.

(6) Routine maintenance of the RO device.

Before determining whether to clean the reverse osmosis system, other possible causes of the above phenomena should also be considered comprehensively:

☆ Operating pressure drop (pressure control device malfunction and high-pressure pump abnormality);

☆ Influent temperature decrease (heater malfunction, or seasonal changes causing water temperature decrease);

☆ Increased influent salinity;

☆ Pretreatment abnormality;

☆ Membrane damage, misalignment of the central tube of the series membrane element, and poor sealing of the pressure vessel O-ring, causing concentrate water to seep into freshwater.

2 Pollutants

Common pollutants in reverse osmosis membrane elements include CaCO3, CaSO4, BaSO4, SrSO4, metal oxides, silicon deposits, organic matter, and biological sludge. When the scale inhibitor addition system or acid addition system malfunctions, CaCO3 may deposit in the membrane element, and a chemical cleaning method should be used for circulation cleaning or overnight soaking.

3 Formula

Different pollutants cause different degrees of damage to the membrane, and different pollutants require different cleaning solutions.

4 Cleaning Equipment

(1) Reverse osmosis cleaning system

Generally consists of a cleaning pump, chemical preparation tank, 5-20um safety filter, heater, related pipes, valves, and control instruments.

(2) Operation

Cleaning methods include static soaking and circulation cleaning. Static soaking uses cleaning solution to soak the membrane, the time depends on the degree of pollution, generally 1-15h. The general steps for circulation cleaning are:

1. Use a pump to send freshwater from the chemical preparation tank into the pressure vessel and drain for a few minutes.

2. Prepare the cleaning solution with freshwater in the chemical preparation tank.

3. Circulate the cleaning solution through the pressure vessel for 1h or until the predetermined time is reached. The cleaning flow rate can be determined according to the table below. When the pollution is serious, the cleaning flow rate can be increased to 150% of the resin in the table. At this time, the cleaning pressure drop is large, generally controlled to no more than (0.10-0.14MPa)/membrane element or 0.4MPa/membrane module. When starting the chemical cleaning, 50% of the flow rate in the table can be used to inject the heated cleaning solution into the pressure vessel, controlling the pressure so that it can overcome the pressure drop between the inlet and outlet water without freshwater flowing out. To avoid dilution of the cleaning solution, the concentrate discharge valve can be opened to drain the system water before cleaning. The reverse osmosis system can be cleaned section by section. The cleaning direction is the same as the operating direction, and reverse cleaning is not allowed, otherwise, the membrane may bulge and damage the membrane element.

4. After the circulation cleaning is completed, rinse the chemical preparation tank with freshwater.

5. Rinse the pressure vessel with freshwater.

6. After rinsing, operate the reverse osmosis system with the freshwater discharge valve open until the freshwater is clean, free of foam or cleaning solution, usually requiring 15-30 minutes.

Replacement of Reverse Osmosis Membranes

After a period of normal operation, reverse osmosis (RO) membrane elements can be fouled by suspended solids or sparingly soluble salts that may be present in the feed water, resulting in the following symptoms:

1. Increased weight of the RO membrane element;

2. Significant increase or decrease in RO membrane rejection rate;

3. Significant decrease in permeate water production of the RO system under standard pressure;

4. Operational pressure needs to be increased to achieve standard permeate water production;

5. Increased pressure drop between feed water and concentrate water in the RO system;

6. If the membrane element is removed from the pressure vessel and water is poured onto the feed water side of the upright membrane element, and the water cannot flow through the membrane element but only overflows from the end face, this indicates that the feed water channel is blocked.

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

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