RO System Shutdown: How to Manage Four Different Downtime Scenarios

A reverse osmosis system can’t run 365 days a year without stopping. Maintenance, holidays, off-peak production seasons… there will always be times when it needs to be shut down (RO system shutdown).

But what many people don’t know is this: how well you manage the membrane system during shutdown directly determines how many years the membranes will last.

If you leave the membranes unattended during shutdown, they may dry out, develop bacteria, or even crack from freezing, causing irreversible damage. Today, we’ll explain the management key points for four shutdown scenarios all at once.

Routine shutdown refers to short-term system downtime, such as 0 to 48 hours.

At this stage, management can simply follow the normal shutdown procedure. But there is one key action that must be done: low-pressure flushing must be carried out at shutdown, and to prevent microbial growth, flush once every 24 hours.

Key points:

• Low-pressure flushing is mandatory and cannot be skipped.
• Flushing once every 24 hours is to prevent bacteria from multiplying on the membrane surface.

If the downtime is longer, such as 2 to 25 days, the management requirements are higher.

For membrane system shutdown, follow the shutdown steps described in Vontron’s “Daily Use and Maintenance of Reverse Osmosis Systems.” After shutdown, the following points must be achieved:

First, ensure the pressure vessels are filled with RO-produced pure water, then close all feed water valves, concentrate valves, and permeate valves. The purpose is to prevent membrane elements from drying out and to prevent microbial growth.

Second, flush regularly.

Third, add protective solution for special water sources.

For surface water or water sources with high microbial contamination, the reverse osmosis system needs to be flushed with a solution prepared from RO permeate water containing 1.0% sodium bisulfite.

If the membrane elements are also soaked in this solution, the effect is even better, and the interval between repeated flushes can be extended accordingly.

Fourth, pay attention to the temperature range.

During system shutdown, the temperature should be maintained between 5°C and 45°C. Low temperatures are beneficial for preserving membrane elements, but the system must be protected from freezing.

If the downtime exceeds 25 days, it is considered long-term shutdown. At this point, the management requirements are the highest.

Step One: Follow the normal shutdown procedure and flush the system with low-pressure product water.

Step Two: It is best to perform a chemical cleaning and sterilization treatment.

After cleaning, flush the system with low-pressure RO permeate water until the concentrate conductivity matches the feed water conductivity.

Step Three: Prepare a protective solution and soak the membrane elements. Prepare a protective solution containing 1.0% sodium bisulfite using reverse osmosis permeate pure water. Use the chemical cleaning system to circulate and flush the membrane elements, expel the air in the pressure vessels, and fully immerse the membrane elements in the protective solution to prevent them from drying out. Then close all feed water valves, concentrate valves, and permeate valves to prevent air from entering and causing the protective solution to fail.

Step Four: Check the pH value of the protective solution weekly. When the pH is less than 3, replace the protective solution promptly.

Step Five: Pay attention to the temperature range. During system shutdown, the temperature should be maintained between 5°C and 45°C. Low temperatures are beneficial for preserving membrane elements, but the system should be protected from freezing.

If, after the system is shut down, you plan to remove the membrane elements, then the removed membrane elements need special preservation treatment.

For specific operations, please follow the preservation and storage requirements for wet-type membrane elements.

Simply put: removed membrane elements cannot be stored just anywhere. They must be kept moist, avoiding drying out and freeze damage. For specific parameters, refer to the technical documents for the preservation and storage of wet-type membrane elements.

The four shutdown scenarios have different management key points:

Two Red Lines That Run Throughout:

The temperature must be maintained between 5°C and 45°C —too low will freeze, too high will damage. The membrane must not be allowed to dry out—moisture retention is the basic principle for preserving membrane elements.

If you encounter specific problems in RO system shutdown management, or are unsure whether a certain operation is compliant, please feel free to contact us anytime. We can help you develop the most suitable shutdown protection plan based on your actual situation.