Reverse osmosis water treatment technology | what is back pressure, what adverse consequences will water back pressure have

Release Date:

2024-04-01

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In reverse osmosis water treatment technology, the performance evaluation and operation safety of membrane components are key considerations. Among them, the standard desalting rate, the actual desalting rate and the system desalting rate of the membrane element are the core indicators to measure its filtration efficiency, which is worthy of in-depth understanding and grasp.


First, the standard desalination rate of the membrane element is determined by the manufacturer under specific standard conditions. For example, the standard desalting rate of CPA2 and CPA3 membrane elements can reach 99.2% (average 99.5%) and 99.96% (average 99.7%), respectively, which mainly reflects the theoretical desalting capacity of the membrane element for sodium chloride solution. However, in practical applications, the actual desalting rate of membrane elements may be lower or higher than the standard value due to the complexity of water composition, temperature changes, average water flux selection, system recovery and other factors that differ from the standard test conditions.

Reverse osmosis membrane back pressure
The system desalting rate is an important parameter to evaluate the overall desalting effect of the whole reverse osmosis device, which is different from the standard or actual desalting rate of a single membrane element. Under normal circumstances, in the reverse osmosis system composed of multiple membrane elements in series, each membrane element is in different actual conditions, resulting in the system's desalination rate cannot be directly equivalent to the performance of a single membrane element. Only when the reverse osmosis device contains only one membrane element, the desalting rate of the system is consistent with the actual desalting rate of the membrane element. In order to accurately predict the desalting rate of the system, the designer and the user can perform the actual calculation with the help of the calculation software provided by the membrane component manufacturer.


In addition, it is worth noting that the back pressure of water production is an important consideration when it comes to the operational safety of reverse osmosis systems. The so-called back pressure refers to the situation where the pressure on the water side of the product is greater than the pressure on the water supply side. The reverse osmosis membrane element is uniquely constructed as a series of envelope shaped film pockets tightly wound around the product water center tube. Raw water penetrates from the outer surface of the membrane into the inside of the membrane bag and collects into the center tube to output fresh water.


In order to avoid adverse effects, a fabric support layer is installed inside the membrane pocket to guide the product water flow, while a mesh layer is used to ensure that the water flow is uniform and disturbs the membrane surface. However, if the pressure on the water-producing side is too high, exceeding the pressure on the feedwater side, it may lead to the rupture of the bonding wire, seriously affecting the desalination function of the membrane element, and even causing the loss or significant reduction of the desalination rate. Therefore, in the normal operation and maintenance of the reverse osmosis system, the occurrence of water production back pressure must be prevented.


In the normal state, the reverse osmosis membrane relies on pressure to drive filtration, and there is no back pressure problem. However, when the system stops, fails or the valve is not operated properly, back pressure may be generated, which needs to be effectively prevented and properly solved through scientific and reasonable valve Settings and rigorous operating processes to ensure the stable and efficient operation of the reverse osmosis system.

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