What are the reasons for the rapid decline in desalination efficiency of reverse osmosis membranes in water purification equipment?

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This post was last edited by hesonchang214 on 2020-4-10 at 13:34. 1. An increase in pressure difference leads to a decline in desalination efficiency. An increase in pressure difference is often accompanied by a rapid drop in desalination efficiency. Under normal flow conditions, an increase in pressure difference is usually caused by the accumulation of impurities, contaminants, and scale in the mesh screens of the water flow channels of the membrane elements, which leads to a decrease in the output water flow rate. When the set water supply flow rate is exceeded, an excessive pressure difference can also occur. When the water supply pressure rises too quickly during startup, a large water hammer pressure difference is generated. If the membrane is contaminated, especially by microorganisms, the pressure difference will also increase. The pressure difference between the feed water and the concentrated water represents the hydraulic resistance, which is related to the flow rate and temperature of the feed water; it is necessary to maintain a certain flow rate for both the product water and the concentrated water. Possible causes of a high pressure difference include scale, microbial contamination, precipitation of scale inhibitors, leakage in the filter media, and damaged seals for feedwater/concentrate water. 　　2. Unreasonable online chemical cleaning: Ultra-pure water equipment is inevitably contaminated during operation. Pre-treatment and the addition of various chemicals can only minimize the likelihood of reverse osmosis being contaminated, but cannot completely eliminate it. Therefore, for reverse osmosis systems that are in operation for a long time, it is necessary to thoroughly investigate and determine which type of contaminant is present after a certain period of operation. 　　3. Poor control of residual chlorine Sodium hypochlorite is widely used as a disinfectant in the pretreatment of pure water systems. In reverse osmosis systems, chlorination is applied to the feed water to prevent microbial contamination in the reverse osmosis process. Residual chlorine is measured using a colorimeter, with the target quality concentration at the inlet of the sand filter being generally 0.5 mg/L, not less than 0.3 mg/L; it should be less than 0.1 mg/L at the safety filter before reverse osmosis. The main problem with polyamide membranes is preventing them from oxidizing. Both residual chlorine in the incoming water and strong oxidation have adverse effects on it, and strict control is necessary. Therefore, it is extremely important to regularly test the residual chlorine level in the reverse osmosis feed water.