What faults usually occur in RO membrane reverse osmosis equipment?

Author: Hongjie Water

Before using the reverse osmosis equipment after the festival, pay attention to check whether the appearance of the machine is normal, and connect the water and power only after confirming that all items are normal. If the equipment fails, try to find out the essence of the problem from these failures, so as to implement maintenance and repair as soon as possible.

The failure of RO membrane reverse osmosis system usually involves at least the following situations:

1、 When the working pressure and conductivity are normal, the water production decreases;

2、 After standardization, the desalination rate decreases, which is manifested as an increase in the conductivity of the produced water in the reverse osmosis system;

3、 After standardization, the water production decreases, and it is usually necessary to increase the operating pressure to maintain the rated water production, that is, the working pressure increases; 

Reduction in water production after standardization

The RO system experienced a decrease in water production after standardization, and the reasons can be identified based on the following three situations:

(1) If the water production of a section of the RO system decreases, there will be sedimentation of particulate pollutants;

(2) If the water production in the last stage of the RO system decreases, there is scaling pollution;

3. If the water production of all sections of the RO system decreases, there is pollution blockage;

The decrease in water production after standardization is one of the common system failures, which may be caused by:

(1) The reduction of membrane components requires operating according to the designed number of membrane components;

(2) The low-pressure operation of the reverse osmosis membrane refers to operating below the designed reference pressure (possibly with a throttle valve);

(3) It was found that membrane component compaction occurs when the reverse osmosis membrane operates under conditions that greatly exceed the reference pressure, and the membrane component must be replaced;

(4) Reduce the operating temperature and operate according to the design temperature of 25 degrees Celsius;

(5) Operating at a higher recovery rate will increase the TDS of the average influent  concentrated water, thus increasing the Osmotic pressure. When operating at a recovery rate of more than 75%, the amount of concentrated water will decrease, so that the concentration ratio of water in the membrane module will increase, resulting in a serious decline in the quality of feedwater. As the Osmotic pressure of this feedwater increases, the amount of permeable water will decrease. In serious cases, salt scale will be separated from the membrane surface, and water must be produced according to the design recovery rate;

(6) Membrane fouling occurs. Metal oxides or impurities adhere to the membrane surface, causing blockage of the reverse osmosis membrane (primary).

(7) During operation, the pressure difference of reverse osmosis increases, the operation management of pretreatment is improved, the water quality of reverse osmosis is improved, and the reverse osmosis components are cleaned with drugs;

(8) When mixing oil, be careful not to allow oil to enter the feedwater as it can contaminate the reverse osmosis membrane;

(9) Ensure that the filter element inside the filter is regularly replaced. If not replaced for a long time, it may cause the filter element to become clogged, thereby affecting the water inflow of reverse osmosis;

(10) The increase of inlet water conductivity will increase the Osmotic pressure that must be overcome when the produced water passes through the membrane.

Solution to conductivity increase

(1) Firstly, it is necessary to confirm whether the opening of each valve is correct and whether the ratio of pure water to concentrated water is correct;

(2) Is the conductivity of the incoming water increasing, that is, is the conductivity of the incoming water higher than before (such as during the Humen salt tide, the conductivity increases to 1000 μ Cm);

(3) Whether the reverse osmosis membrane is contaminated, such as inorganic scaling CaSO4, MgSO4, BaSO4, organic pollution, metal oxide pollution, etc;

(4) Is the reverse osmosis membrane in contact with strong oxidizing agents (such as Cl2), which can degrade it? Any contact with oxidizing substances can damage the membrane components;

(5) The O-ring is damaged or leaking, which can cause a rapid increase in the conductivity of the reverse osmosis effluent;

(6) Reverse osmosis membranes come into contact with highly oxidizing substances such as Cl2, O3, etc., and are oxidized and degraded by highly oxidizing substances.

Reasons and solutions for the decrease in water production

(1) Whether the RO reverse osmosis membrane is contaminated or blocked;

(2) The conductivity of the inlet water increases;

(3) It was found that membrane component compaction occurs when the reverse osmosis membrane operates under conditions that greatly exceed the reference pressure, and the membrane component must be replaced.

(4) Does the working pressure reach the rated working pressure of the reverse osmosis membrane. Determine the rated working pressure based on the model of the reverse osmosis membrane, and increase the inlet pressure appropriately to increase water production.

(5) The raw water contains a certain concentration of suspended solids and soluble substances.

Suspended solids mainly consist of inorganic salts, colloids, and biological particles such as microorganisms and algae. Soluble substances mainly include easily soluble and insoluble salts, metal oxides, acids and bases, etc. During the reverse osmosis process, the volume of influent water decreases and the concentration of suspended particles and dissolved substances increases. Suspended particles will deposit on the membrane, blocking the water channel and increasing frictional resistance (pressure drop). When insoluble salts exceed their saturation limit, they will precipitate from concentrated water and form scale on the membrane surface, reducing the flux of RO membrane, increasing operating pressure and pressure drop, and leading to a decrease in product water quality.

(6) The impact of water temperature.

The rated water yield of the reverse osmosis membrane is designed based on 25 ℃, and for every 1 ℃ decrease in temperature, the water yield decreases by 2-3%.

All of the above factors cause a gradual decrease in the water production of the reverse osmosis membrane, an increase in salt permeability, and a decrease in the quality of pure water. In general, the service life of reverse osmosis membranes is 2-3 years. After the reverse osmosis membrane is damaged, it should be replaced in a timely manner, otherwise it not only affects the water yield but also deteriorates the water quality.