How Often Do You Flush Reverse Osmosis Membrane?

How Often Do You Flush Reverse Osmosis Membrane?

More and more people are becoming aware of the benefits of purifying their drinking water, and many are now choosing to install Reverse Osmosis (RO) systems in their homes. The RO membrane is a vital and expensive part of the system and must be flushed to stay clean and functional. This article will help you explore the appropriate schedule to flush out your reverse osmosis membrane and other tips to keep your system in top shape.

You should flush your reverse osmosis membrane at the end of every day. This procedure will keep your RO membrane clean and elongate the lifespan of your system. An even better approach is to flush it out after every use to ensure there is no buildup of mold or contaminants.

An RO membrane is at the core of your entire reverse osmosis system. It is where most contaminants are filtered and rejected. A typical reverse osmosis membrane can last from three to five years. However, the actual lifespan of your system will depend on how often you flush it and how well it is maintained. Let’s take a look at how you can keep your RO membrane in great condition.

Read my comprehensive article about reverse osmosis.

Two Main Ways to Flush Your RO Membrane

The RO membrane is definitely the most vital part of your system. It blocks 99% of contaminants and provides you with clean drinking water. Flushing your membrane is important to ensure the system is running well and extending its lifespan. There are two main ways you can flush your RO membrane:

1. Flushing with a flush kit

Almost all the new RO systems come with a manual flush valve built in to make the process easier. Here is how you use this flush kit:

  1. Locate the back waste line that is connected to your canister
  2. A flush kit with a ball valve will be installed on this waste line
  3. When the ball valve is in line with the waste line, the system will be in flushing mode
  4. When the system is in this position, you can run it for about 20-30 minutes

2. Flushing without a flush kit

In this case, the flow restrictor will not be installed separately or be apparent on the outside of the waste line. Here is how you flush your membrane using this process:

  1. Remove the waste line from the canister
  2. Locate the flow restrictor inside the waste line
  3. Remove the flow restrictor
  4. Connect the waste line back to the RO system
  5. Run the system for 30 minutes
  6. Once the flushing is done, turn the system off
  7. Remove the waste line from the system
  8. Put the flow restrictor back in and connect the waste line to run the system normally

Check out this video on how to flush a reverse osmosis system.

Signs That Your RO Membrane Needs Flushing More Often

If you don’t clean out your membrane or flush it often, there will be some clear signs that will indicate a need for a flush or cleaning:

  • Salt permeability levels experience an increase of 10% to 15%
  • The permeate flow of pressure drops by 10%-15% under normal water pressure conditions
  • The overall difference between the pressures of the raw water inlet and the water increases by 10%-15%
  • Temperature correction is done to maintain the pressure, and it increases by 10%-15%

Advanced Cleaning Methods for RO Membrane

If routine flushing does not remove scaling or contamination, you need to perform a thorough cleaning of the membrane to prevent it from becoming damaged. Let’s look at the different advanced methods of cleaning a contaminated reverse osmosis membrane:

Physical cleaning

Certain processes such as vibrations, ultrasonic waves, and turbulence are used to remove pollutants and contaminants attached to the membrane. This method should rarely be used because it can decrease overall water permeability and it can damage the membrane in the long term.

Chemical cleaning

Chemicals are used to clean away and dissolve the pollutants on the membrane. These are harsh chemicals, so this method should also be used only when necessary. Here are the different types of chemical cleaning methods:

High-pH cleaning chemicals

Chemicals that have a high pH are used to break down organic and biological pollutants. These chemicals break the bond of calcium that binds these biological elements together. This dissolves these compounds and cleans the membrane.

Low-pH cleaning chemicals

Low-pH chemicals are usually used before high-pH chemicals to dissolve the contaminants in stages. However, they actually remove the anionic charge of the organic compounds, which may cause them to stick further into the membrane and damage it.

How to Use Chemicals to Clean Your RO Membrane

By now, we have established that chemical cleaning is used when the contamination is no longer removable by regularly flushing out your RO membrane. Here are the essential steps in this process:

1. Mixing the chemical cleaning solution

The composition of the cleaning solution is the core of this entire cleaning process and depends on the kind of contaminants that must be cleared out. Use the following formula to determine which chemicals need to be used:

Quantity of chemical agent = Amount of freshwater x percentage concentration of contaminants.

2. Adding the solution to the RO unit

The first step is opening the clean water injection valve while the unit is running a normal cycle and add the RO product water into the cleaning tank. When the product water fills up half the chemical cleaning tank, add the cleaning solution until it reaches the full mark on the tank. Close the injection valve and startup the cleaning pump,

Now, open the cleaning fluid’s circulation valve and stir the solution every 5 minutes. Also, keep checking the pH level of the solution. You can use the pH paper method or a pH meter to determine the pH level. A change in the pH level will indicate the cleaning process’s status.

3. Rinsing the membrane

There are two types of rinsing processes required: The first type is prior to adding the cleaning agent, this will ensure that all the sediments will come to the surface of the membrane; the other is when the cleaning is done and flushing the membrane will remove all the chemical agents from the system.

4. Soaking the membrane

Soaking is done to ensure that the chemical works its magic and dissolves the pollutants. At the same time, it can ensure that all the contaminants fall away from the membrane’s surface.

5. Circulating the membrane

The cycling process ensures that the pollution molecules stuck in the membrane collide through friction and shearing to complete the chemical cleaning process.

Frequently Asked Questions

1.   Can RO membranes be reused if they are contaminated?

Contaminated RO membranes can be reused only if they are properly cleaned using physical or chemical cleaning and are free of all contamination before being re-inserted into a healthy RO unit.

2.   Can fungus grow in RO systems?

Fungus and other microorganisms can find a home in a reverse osmosis system if it is not cleaned out properly. Regular flushing of the membrane can prevent the build up of organic and inorganic sediments and keep the system clean.

3.   Can you backwash RO systems?

Backwashing is used commonly to clean media filters, but RO membranes can get permanently damaged if they are backwashed for cleaning purposes.

Final Thoughts

RO membranes are the heart and soul of an RO system, and they need constant flushing to stay in good shape and free from contaminants. As mentioned previously, more advanced cleaning methods may be required to clean the reverse osmosis membrane if it is seriously contaminated.

Boch Richard

Richard Boch is a chemical engineer responsible for designing water filtration systems for industrial and residential customers. He has more than 20 years of experience with ion exchange, activated carbon, and reverse osmosis. Richard's expertise has made him a go-to source for municipalities and businesses looking to improve their water quality. When he's not working, Richard enjoys spending time with his wife and two young children.

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