Common problems in the use of industrial reverse osmosis membrane components

1.Water flux attenuation

Reason: Membrane fouling, organic matter, inorganic matter, suspended solids, microorganisms and other pollutants in the water source will gradually accumulate on the surface of the membrane, forming a membrane fouling layer; Scaling problem, where hardness ions in water react with other ions on the membrane surface to form deposits; Membrane aging, as the usage time increases, the membrane material will undergo a certain degree of aging; Improper operating conditions, such as excessively high inlet pressure, excessively low inlet flow rate, or excessively high inlet temperature; Incomplete cleaning may result in incomplete removal of pollutants, leading to the accumulation of pollutants on the membrane surface again.

Judgment method: Regularly monitor the water production and quality of the reverse osmosis system, compare the initial and current water flux during operation; When monitoring changes in system pressure and water flux attenuation occurs, the system may require higher pressure to maintain the original water production rate; The decrease in water flux of membrane elements is usually accompanied by a decrease in salt removal rate. If the salt removal rate is found to be lower than the design value during testing, it may be a signal of water flux attenuation.

Response measures: Regularly clean the membrane components and select appropriate cleaning agents for reverse cleaning according to the type of pollution; Ensure that the operating conditions of the membrane system are within the recommended range, avoid excessive inlet pressure and temperature, and ensure stable inlet flow rate; Adopting advanced pretreatment techniques such as sedimentation, filtration, softening, and iron removal to reduce the load of pollutants in water; If the water flux of the membrane has not been effectively restored after multiple cleaning cycles and there are signs of aging or damage to the membrane material, replacement of the membrane element may be considered.

2.Scaling phenomenon

Reason: The water quality was not fully analyzed, resulting in an unreasonable system design; Improper use or insufficient dosage of scale inhibitors; The water quality has changed, and the system operating parameters have not been adjusted in a timely manner.

Response guide: Conduct a comprehensive analysis of water quality before system design; Select effective scale inhibitors/dispersants for dosing; Adjust system operating parameters in a timely manner when water quality changes; Remove or reduce ions that cause scaling during pretreatment.

3.Oxidation phenomenon

Reason: Excessive residual chlorine or other oxidizing substances in the inlet water of the membrane system.

Response guide: Take measures such as adding reducing agents to ensure that the residual chlorine in the influent is less than 0.1ppm; Install ORP/residual chlorine instruments in the system for real-time monitoring to ensure that oxidizing substances do not enter the membrane element RO system.

4.Telescope phenomenon

Reason: Failure to follow the requirements during installation or disassembly resulted in relative misalignment between reverse osmosis membranes; Insufficient rigidity and strength of the membrane shell caused deformation during pressurized operation; When starting the high-pressure pump, the inlet pressure of the system rises too quickly.

Response guide: Strengthen the recording and analysis of operational data. After data standardization, when the pressure difference exceeds 15% of the initial value, chemical cleaning should be carried out in a timely manner, and attention should be paid to not exceeding the maximum allowable pressure difference. Once a serious telescope phenomenon occurs, it is necessary to replace the damaged membrane components and investigate the cause of the pressure difference exceeding the standard.

5.Concentration polarization phenomenon

Reason: During the reverse osmosis process, due to the continuous passage of water through the membrane, there is a concentration difference between the saltwater near the membrane surface and the inlet saltwater. The concentration of the solution on the membrane surface is relatively high, and as a large amount of water passes through the membrane surface, the concentration increases significantly, forming a supersaturated solution. Some salts will slowly precipitate crystals.

Response guide: Increase the flow rate of concentrated water and increase the shear force on the membrane surface; Control the recovery rate and system average flux.

6.Compaction phenomenon

Reason: High inlet pressure, high temperature, water hammer. When there is air in the reverse osmosis system, the high-pressure pump is started. The pressure of the high-pressure pump rises too quickly, which can cause a strong impact force on the RO membrane, resulting in water hammer effect and easy damage to the reverse osmosis membrane.

Response guide: After the membrane element is compressed, the damaged membrane element needs to be replaced; Control the operating pressure and temperature of the membrane element within the design requirements.

7.Membrane surface damage

Reason: Particulate matter in the incoming water enters the RO system, causing scratches on the membrane surface; Scratches caused by scaling substances; Water hammer; Chemical substances can cause damage to the membrane surface.

Response guide: Replace the security filter element in a timely manner to prevent hard particles in the water from entering the membrane element; When cleaning fouling membrane components, the initial flow rate should be minimized to prevent damage caused by excessive flow flushing; To prevent water hammer, low-pressure exhaust should be carried out before starting the high-pressure pump, and the rising pressure of the high-pressure pump should not be too fast. Variable frequency, soft start or electric slow opening valve should be used for starting the high-pressure pump; Prevent incompatible chemicals from entering the membrane system.