Breaking Down Reverse Osmosis
What is Reverse Osmosis? Reverse osmosis removes contaminants from unfiltered water, or feed water, when pressure forces it through a membrane. Water flows from the more concentrated side (more contaminants) of the RO membrane to the less concentrated side (fewer contaminants) to provide clean, pure water. The fresh water produced is called the permeate. The waste water produced is called concentrate.
What is an RO Membrane? A membrane that has small pores that block contaminants but allow water molecules to flow through. The RO membrane is an important component and regular maintenance is required to ensure maximum efficiency. Membrane fouling is a normal occurrence in RO units, but it is important to know that it is reversible when chemical cleaning is done correctly.
When is it time for a membrane clean?
· when the permeate flow decreases by 10 – 15%
· when the pressure differential increases by 10-15%.
· When the quality of permeate decreases.
How frequently these signs occur can depend on:
· the quality of the feed water
· proper pre-treatment
· the percentage of rejection with which the unit is operated.
As per AWC (American Water Chemicals), the chemical cleaning consists of both high pH and low pH chemicals. The process is performed by a combination of circulating through the system, and then stopping the circulation and “soaking”. It is recommended the high pH cleaning be performed first to penetrate and disperse biological and organic foulants. Water mixed with high pH cleaner is circulated carefully throughout the unit, while monitoring pH every 15-30 minutes to maintain a pH between 11-12. Every 30-60 minutes, the circulation can be stopped to allow the membranes to “soak” for about 30-60 minutes. Circulation should then be started again to flush off foulants and to bring fresh cleaning chemical to the membrane surface. This process should be repeated for 4 hours. Once a high pH cleaning is complete, the system is flushed, and then circulated with a mixture of water and low pH cleaner. A low pH cleaning should be performed at a pH of 2-3 for 3 hours.
Overall, understanding how to clean membranes and why it is important is essential in getting the most out of an RO unit. By properly and periodically performing membrane cleans, the benefits include:
· reduce operating pressures
· improve water quality
· increase output
· lower operating costs.
· extend the life of membranes
Any further questions please contact your Jutzi Water Technologies representative.