Many companies' reverse osmosis (RO) equipment operates stably, but after a period of shutdown and inactivity, problems arise upon restarting, such as turbid effluent, a sharp drop in desalination rate, and a decrease in permeate flow. In most cases, this is not due to equipment failure, but rather to inadequate protection of the membrane elements after shutdown, leading to oxidation, microbial growth, and structural damage. RO membranes are precision filtration elements, extremely sensitive to oxidants, desiccation, and biological fouling. Proper shutdown protection is crucial to preventing membrane element failure and extending equipment lifespan.
Large-scale Reverse Osmosis Equipment
The core cause of oxidative damage to reverse osmosis membranes is clear. After equipment shutdown, stagnant water in the pipeline allows residual chlorine and dissolved oxygen to continuously erode the membrane surface, damaging the membrane's pore structure. Simultaneously, stagnant water breeds bacteria and algae, forming a stubborn biofilm that accelerates membrane oxidation and aging. Furthermore, membrane element drying, temperature fluctuations, and impurity deposition can all cause irreversible damage, ranging from reduced water purification efficiency to outright replacement, significantly increasing maintenance costs.
I. Short-Term Shutdown Protection (Within 24 Hours)
Short-term shutdowns do not require chemical maintenance; the key is to maintain moisture, prevent stagnant water, and prevent oxidation. Before shutdown, perform a low-pressure flush of the system, replacing the raw water in the equipment with reverse osmosis pure water, and draining high-salt, high-chlorine water from the pipelines to reduce residual oxidizing media. After flushing, close the inlet and outlet valves, keeping the membrane housings fully filled and sealed to prevent the membrane elements from drying out. In high-temperature environments, it is recommended to flush briefly every 12 hours to inhibit microbial growth and prevent minor oxidative contamination at the source.
II. Medium- to Long-Term Shutdown Protection (More Than 3 Days)
For equipment shutdowns exceeding 3 days, chemical protection must be used to completely prevent oxidation and biological contamination. A standard preparation involves 500-1000 ppm of food-grade sodium bisulfite protective solution, adjusting the pH to 3-6. This effectively neutralizes residual chlorine, isolates oxygen, and prevents membrane oxidation. After preparation, circulate and flush the system to ensure the protective solution fills all membrane housings and pipelines, completely replacing any accumulated water.
After flushing, close all valves, seal the system, and affix a shutdown maintenance sign. In low-temperature environments, ensure proper insulation to prevent the protective solution from freezing and damaging the membrane elements; in high-temperature environments, ensure adequate ventilation and avoid direct sunlight to prevent rapid chemical deactivation. If the system is shut down for more than 30 days, drain the old protective solution, re-prepare the solution, and circulate it to maintain the protective effect.
Single-stage reverse osmosis equipment
III. Key Taboos for Shutdown Membrane Protection and Key Points for Startup
During shutdown maintenance, it is strictly forbidden to directly drain water from the membrane housing, to allow the membrane elements to dry in direct sunlight, or to use chemicals with excessive concentrations to avoid secondary corrosion of the membrane layer. Before starting up, flush the system under low pressure to completely replace the internal protective solution. After testing the effluent quality and pH value to ensure they meet standards, gradually increase the pressure for normal operation, avoiding sudden high-pressure impacts that could damage the membrane elements.
In short, 80% of non-natural losses of reverse osmosis membranes stem from improper shutdown protection. By distinguishing the duration of downtime and standardizing the flushing, sealing, and chemical maintenance procedures, membrane oxidation damage can be effectively prevented, the water purification performance of the equipment can be stabilized, the cost of membrane replacement and maintenance for enterprises can be significantly reduced, and the long-term efficient and stable operation of the equipment can be guaranteed.
