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Misuse Of Membrane Method In Water Treatment Equipment
- Jun 25, 2018 -

Misuse of membrane method in water treatment equipment



Misconception 1: Membrane water treatment equipment is a difficult operating system


In fact, the membrane water treatment system operation is highly automated. Start-stop, dosing and online flushing operations can be programmed and executed by the PLC system. This can be done unattended, requiring only manual scheduled inspections and periodic maintenance. No additional operating staff is required.


Misunderstanding 2: The membrane is delicate and easily damaged


Due to lack of experience, some companies have encountered problems such as broken film and discarded film in the membrane system designed and constructed. The user mistakenly believes that the membrane product is difficult to maintain. In fact, the main problem lies in two aspects: process design and membrane itself.


Misconception 3: Brand and RO quantity is more important than membrane area and system design


According to different reverse osmosis manufacturers, the types of common reverse osmosis membranes on the market are: low pressure reverse osmosis membranes, ultra low pressure reverse osmosis membranes, brackish water reverse osmosis membranes, anti-pollution reverse osmosis membranes, ultrapure water reverse osmosis membranes, Seawater desalination film and so on.


Many users pay more attention to the number of RO membranes in the membrane reuse system and decide which series of reverse osmosis membranes should be used according to the requirements of the end user on the desalination rate, the requirements on the operating pressure, the requirements on the contamination speed and the cleaning frequency, and the Water quality is determined.


Theoretically speaking, the minimum water yield of a single 8040 membrane element is 0.46T/h (using surface water as the influent water source), 0.80T/h (using groundwater as the influent water source), and 1.15T/h (one-step inverse The infiltration system produces water as a secondary reverse osmosis system. The 8040 membrane element can theoretically be used when the system produces more water than the above values. However, whether to use the 8040 membrane element also needs to consider the system's recovery rate requirements, whether to allow the return of concentrated water, system footprint, pressure vessel cost and the overall economics of the system and many other factors. In addition, the reverse osmosis water production is also affected by other factors such as temperature.


Misconception 4: The more membranes, the better


Within a certain range, increasing the number of membranes can increase the water safety of membrane systems and reduce operating costs. However, after the number of membranes increases to a certain extent, the amount of water evenly distributed to the unit membrane decreases, and the flow velocity of the cross-flow filtration membrane surface is lower than the critical value, and the deposited debris on the membrane surface cannot be taken away, resulting in increased fouling of the membrane. Water production performance decreased. Moreover, after the increase in the number of membranes, the amount of flushing water required increases, and if the flushing pump and the compressed air amount do not meet the flushing volume requirement per unit membrane area, it is difficult to thoroughly flush the membranes, which will increase the membrane fouling and affect the water production performance.


According to the comprehensive balance of various factors, it is generally believed that the reverse osmosis system above 5T/h adopts the 8040 membrane element, and the reverse osmosis system below 3T/h adopts the 4040 membrane element. The reverse osmosis system of 3~5T/h is adopted. 8040 or 4040 membrane elements are available.


Misconception 5: RO membrane must use anti-pollution membrane


Anti-pollution RO membrane is divided into two types: one is that the membrane has a wider circulation channel, which is not easy to block and resist pollution, and this membrane is generally applicable; the other is through the surface modification of the RO membrane, making the RO membrane negatively charged and positively charged. Sex or electricity neutrality, based on the principle of repulsion of electrical homogeneity, makes it difficult for specific properties of pollutants to be deposited on the surface of the membrane so as to achieve anti-pollution characteristics. The latter's anti-pollution performance depends largely on the characteristics of water quality.