Common Contaminants in Membrane Elements and Their Removal Methods

Membrane elements may be contaminated

After a period of normal operation, reverse osmosis (RO) membrane elements may be contaminated by suspended substances or insoluble substances in the feed water, which may include calcium carbonate scale, calcium sulfate scale, metal oxide scale, silicon sedimentation, organic or biological sedimentation. The nature and speed of contamination depend on the feed water conditions, and the contamination develops gradually. If measures are not taken in the early stages, the performance of the membrane elements will be damaged in a relatively short period of time.

Common contaminants of membrane elements and their removal methods

Calcium carbonate scale

When the pH of the feed water is raised due to the failure of the scale inhibitor or acid adding system, calcium carbonate may deposit. It is necessary to detect the occurrence of calcium carbonate scale precipitation as early as possible to prevent growing crystals from damaging the membrane surface. If calcium carbonate scale is detected early, it can be removed by running the system for 1 to 2 hours with the feed water pH reduced to between 3.0 and 5.0. For calcium carbonate scale with longer precipitation times, citric acid cleaning solution can be used for circulating cleaning or overnight soaking. Note: Ensure that the pH of any cleaning solution is not lower than 2.0, otherwise it may damage the RO membrane elements, especially at higher temperatures, and the pH should not exceed 11.0. Use ammonia to raise the pH and sulfuric acid or hydrochloric acid to lower the pH.

Calcium sulfate scale

The cleaning solution is an excellent way to remove calcium sulfate scale from the membrane surface.

Metal oxide scale

The method of removing carbonates described above can be used to easily remove deposited hydroxides (such as iron hydroxide).

Silicon scale

Typically, only professional water treatment cleaning methods can remove silicon scale that does not coexist with metal or organic matter.

Organic sediment

Organic sediment (such as microbial slime or mold) can be removed with cleaning solution 3. To prevent re-infection, approved sterilization solutions can be circulated and soaked in the system for a long period of time. If the RO device is stopped for three days, disinfection treatment should be used, and consultation with a professional water treatment company is required to determine the appropriate sterilizing agent.

Cleaning solution

It is recommended to use a dedicated cleaning solution for water treatment when cleaning membrane elements. It is very important to chemically analyze the contaminants before cleaning. The detailed analysis of the analysis results can ensure the selection of the best cleaning agent and cleaning method. The cleaning method and the obtained cleaning effect should be recorded for each cleaning, providing a basis for finding the best cleaning method under specific feed water conditions.