The main causes of increased pressure drop in reverse osmosis:
1. The pressure drop increases in the front section:
(1) Water bypass around the filter cartridge. The main function of the micron-level filter cartridge in the RO system's front section is to intercept impurities and protect the RO membrane. However, if the filter cartridge becomes loose or the connection parts between filter cartridges are not installed, it may cause water bypass. When water bypasses, the first thing to cause an increase in pressure drop in the front membrane element.
Sometimes the filter cartridge may run well for several months without obvious pressure drop increase or slow pressure drop increase, which may be caused by water bypass. Generally, the filter cartridge should be replaced every 2-5 months to prevent microbial growth or when the pressure drop reaches 15psi. Sometimes, it may also cause degradation of the filter cartridge due to hydraulic shock or incompatible substances.
(2) Penetration of the media filter. Impurities may penetrate the filter and some impurities may also penetrate or bypass the filter cartridge filter, causing an increase in pressure drop in the front membrane element of the system.
(3) Wear of the pump impeller. In practice, high-pressure pump impellers have worn out, releasing stainless steel impurities and contaminating the membrane element. Proper use of high-pressure pumps is very important.
(4) Membrane element expansion phenomenon. Hydraulic imbalance, water hammer phenomenon, or improper use of heat exchangers may cause this phenomenon.
2. The pressure drop increases in the rear section:
(1) Insufficient scale inhibitor. If the composition of the feedwater changes, such as an increase in silicon content, the system recovery rate may need to be lowered or the dosage of scale inhibitors adjusted.
Scale inhibitors can delay the deposition of silicates, and some can also act as dispersants, keeping colloidal compounds suspended in the water without depositing. When the feedwater does not have sufficient scale inhibitors, due to the highest concentration of concentrate in the system's final section, sedimentation first occurs in the final section, causing an increase in pressure drop.
(2) System recovery rate is too high. When the system recovery rate is too high, it will increase the concentration of concentrate in the final section, thereby increasing the tendency to scale. When these parts (membrane elements) scale, they will increase their pressure drop.
3. Pressure drop increases in a random section
(1) Damage to the concentrate seal. The concentrate seal may be damaged due to improper installation in reverse or hydraulic damage, causing part of the feedwater to bypass the membrane element, reducing the water flow rate through the membrane element. When this occurs, the membrane element surface is prone to scaling and contamination, causing an increase in pressure drop in that section.
(2) Cleaning contaminants that block the membrane elements. During cleaning of the RO system, if the micron filter fails or is not used, it is possible to introduce larger particle impurities into the RO system, contaminating the membrane elements and increasing their pressure drop.
(3) Microbiological contamination.
4. Pressure drop generally increases in each section
(1) The inlet water valve is not tight. During shutdown, if the inlet water valve is not tight, water will seep through the membrane continuously, causing salt to accumulate on the membrane surface, increasing the concentration polarization during operation and potentially causing pollution. This will also increase the pressure differential.
(2) The membrane surface is contaminated during operating the RO system. In this case, the pressure differential of each section will increase, and the membrane needs to be cleaned when the pressure differential reaches a certain value.
Therefore, to ensure the normal operation of the RO system and extend its service life, it is crucial to regularly clean and maintain the membrane components to ensure the normal operation of the membrane and avoid excessive pressure differential that may damage the system. By adopting scientific management and effective maintenance, the RO system can maintain a stable operating state and provide people with more pure drinking water resources.
