Membrane Fouling in Ultrapure Water Equipment

With the development of various industries, the requirements for water quality have become increasingly stringent, leading to the widespread application of ultrapure water equipment. However, water still contains a large number of microorganisms, insoluble organic matter, and particulate matter, all of which are contaminants that the pretreatment process of ultrapure water equipment cannot completely remove. Over time, the accumulation of these substances on the membrane sheets will cause a decline in membrane element performance. So how do you determine the membrane fouling status of an ultrapure water system?

Visual Inspection: Visual inspection involves removing the two membrane elements (inlet and concentrate ends) from the membrane housing and examining their appearance to determine if the following conditions exist:

1. Check if the membrane element housing of the ultrapure water equipment is intact and undamaged. In some systems, water hammer or membrane element blockage can increase the pressure difference between the inlet and concentrate ends, causing the fiberglass housing of the membrane element to crack.

2. Check if there is sediment or other deposits on the inlet end membrane element housing and end cap. In some poorly designed reverse osmosis systems, suspended solids in the feed water are not completely removed, and these substances will flow into the membrane element with the water flow. The main reason for this is that the removal of particulate matter during pretreatment does not meet the feed water requirements.

3. Check the inlet face of the ultrapure water equipment membrane element for foreign objects, such as large particles or activated carbon particles. The presence of foreign objects at the inlet indicates that the pretreatment process is insufficient to remove particles to meet the reverse osmosis system's feed water requirements. In this case, the SDI value needs to be tested, and the security filter should be checked and its cartridge replaced.

4. Check if the filter screen on the concentrate end of the ultrapure water equipment membrane element has been flushed out. This indicates an excessive pressure difference between the inlet and outlet of the membrane element, which may cause a "telescope phenomenon," indicating severe membrane fouling and requiring immediate cleaning.

5. Check the concentrate end of the ultrapure water equipment membrane element for sediment. If there are obvious white granular sediments on the concentrate end of the membrane element, it can be determined to be inorganic salt structural fouling, indicating that the LSI index of the feed water is greater than 0, or that the amount of scale inhibitor added is insufficient to prevent inorganic salt scaling, posing a risk of scaling to the system.

Weight Comparison: After the disassembled membrane element is placed vertically to drain excess water, it is weighed and compared to the weight of the unused membrane element to determine the type of membrane fouling.

Cleaning Flow Rate: The cleaning flow rate refers to the flow rate of the cleaning solution into the pressure vessel during the cleaning process. The cleaning flow rate varies depending on the diameter of the pressure vessel.

Reverse osmosis membranes are a major consumable in ultrapure water equipment. Once fouled, they will inevitably affect the quality of the entire system's effluent. Therefore, to ensure stable effluent quality, regular checks on membrane element fouling are essential.

The above content is an introduction to how to determine the membrane fouling status of ultrapure water equipment. We hope this information is helpful. If membrane fouling is found in ultrapure water equipment, it must be addressed promptly.