1. There is residual gas in the equipment running under high pressure, forming an air hammer that will damage the membrane
There are two common situations: A. After the equipment is emptied and restarted, the pressure is increased quickly without exhausting the gas. The remaining air should be exhausted at a pressure of 2 to 4 bar before gradually increasing the pressure. B. When the joint between the pretreatment equipment and the high-pressure pump is not well sealed or leaking (especially the microfilter and the subsequent pipeline leaking), when the pretreatment water supply is not sufficient, such as microfiltration blockage, some air will be sucked in due to vacuum in the poorly sealed area. The microfilter should be cleaned or replaced to ensure that the pipeline does not leak. In short, the pressure should be gradually increased when there are no bubbles in the flow meter. If bubbles are found during operation, the pressure should be gradually reduced to check the cause.
2. Incorrect shutdown method
A. Rapid pressure reduction during shutdown does not perform thorough flushing. Since the concentration of inorganic salts on the concentrated water side of the membrane is higher than that of the raw water, it is easy to scale and contaminate the membrane. B. Rinse with pretreated water with chemical reagents added. Water containing chemical reagents may cause membrane contamination during equipment shutdown.
When preparing to shut down, stop adding chemical reagents, gradually reduce the pressure to about 3 bar, and rinse with pretreated water for 10 minutes until the TDS of the concentrated water is very close to the TDS of the raw water.
3. Poor disinfection and maintenance lead to microbial contamination
This is a common problem in the use of composite polyamide membranes. Because polyamide membranes have poor residual chlorine resistance, chlorine and other disinfectants are not properly added during use, and users do not pay enough attention to microbial prevention, which can easily lead to microbial contamination. The excessive microorganisms in pure water produced by many manufacturers are caused by poor disinfection and maintenance.
The main manifestations are: when leaving the factory, the reverse osmosis equipment is not maintained with disinfectant; the entire pipeline and pretreatment equipment are not disinfected after the equipment is installed; no disinfection and maintenance measures are taken during intermittent operation; the pretreatment equipment and reverse osmosis equipment are not disinfected regularly; the maintenance fluid is invalid or the concentration is not enough.