Key Management Points for Shutdown of NF Nanofiltration / RO Reverse Osmosis Systems
2026-07-20
I. Routine System Shutdown
Frequent start-stop cycles cause pressure shocks that damage membrane elements; minimize start-stop operations as much as possible. Pressure ramping, flow regulation and flow reduction shall be performed gently throughout the process, and the startup sequence shall be identical to that during initial commissioning.
Standard Shutdown Procedures
- Open the permeate drain valve and the high-pressure pump bypass valve to reduce feed water flow.
- Gradually open the concentrate control valve to lower system pressure to 30~40 psi.
- Maintain low-pressure flushing for 10–20 minutes (the flushing flow rate shall not exceed the maximum allowable feed flow of a single membrane element, and differential pressure shall stay within the limit).
- Shut down the chemical dosing system to complete the shutdown process.
Automatic Control Instructions
The full start-stop logic can be fully automated via PLC; regular patrol inspection shall be conducted on the operating status of electrical components including water pumps, valves and sensors.
II. System Shutdown Management
1. Short-term Shutdown (Less Than 48 Hours)
① Complete the full standard shutdown procedure and perform low-pressure flushing on the entire pipeline and pressure vessels.
② Conduct another full low-pressure flushing every 24 hours to inhibit bacterial and microbial proliferation inside the membranes.
2. Long-term Shutdown (More Than 48 Hours)
Two preservation schemes are available: periodic fresh water maintenance and chemical preservation solution immersion storage.
Scheme A: Scenarios with Access to Periodic Flushing
① Fill the entire system with qualified RO permeate water, fully purge air from pipelines and pressure vessels, then close all valves to isolate air ingress.
② Ambient temperature ＞20℃: perform one full low-pressure flushing per day.
③ Ambient temperature ＜20℃: perform one full low-pressure flushing every two days.
Scheme B: Standard Immersion Storage (No Access to Periodic Flushing)
① Prepare 1~1.5 wt% sodium bisulfite preservation solution; circulate the solution through the CIP cleaning system to fully fill all membrane elements and thoroughly expel trapped air.
② Close all feed, concentrate and permeate valves completely to block air entry, which would otherwise degrade the preservation solution.
③ Test the pH value of the preservation solution weekly; replace with fresh solution immediately if pH drops below 3.
④ Control storage temperature within 5~45℃: low temperature benefits membrane storage, while anti-freezing measures shall be implemented for pipelines to avoid freezing at all costs.
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