How to measure the desalination rate of a single membrane
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During the operation of the reverse osmosis membranes, a sudden drop in the desalination rate can occur. After analysis, it was found that one set of membranes (six membranes) had high conductivity. Upon inspection, no damage was detected in the connectors or the membranes themselves. It was only by checking each membrane individually that it was possible to determine which one was defective. How can we quickly and accurately detect online which membrane is causing the drop in desalination rate?
If a pressure vessel exhibits a higher water production concentration than other vessels in the same series, it is necessary to examine the performance of the membrane elements inside that vessel. The method described in this section allows for the identification of the location of the fault within the pressure vessel, online and without the need to remove the membrane elements. The detection method involves inserting a plastic tube with a diameter of about 1/4 inch into the water production center tube of the entire membrane module, as shown in Figure 9-2. This requires disconnecting the pipe connecting the water production tube of the unit under test to the main water production tube, or removing the plug at the water output end on the other side of the pressure vessel. If the connection to the main product water pipe has not been disconnected, it should be ensured that the product water from other pressure vessels does not affect the detection process. When the RO/NF system is operating under normal conditions, the water sample taken initially from the central tube of the pressure vessel where the water is produced is not representative. It is necessary to wait a few minutes for the sampling tubes to be flushed and for the system to reach equilibrium; only then can the TDS value of the produced water flowing out of these sampling tubes be measured using a handheld instrument, with the data being recorded. This value reflects the TDS level of the water produced by the membrane element at that location. The sampling tube should be pulled out 6 inches from the deepest point (depending on the brand of the housing) in order to measure the conductivity of the water produced at the adapter between the pressure vessel end plate and the membrane element; it should then be pulled out another 8 inches to measure the conductivity at that location. By taking samples at such intervals, a distribution pattern of the water conductivity can be obtained, as shown in Figure 9-2. The interval between sampling points must be 8 inches (200 mm), so that the fifth sample taken in each group corresponds to the internal joint between two components. This measurement method can collect data from multiple locations of each component, while simultaneously checking the “O”-rings of all internal joints and adapters. Therefore, markings should be made on the sampling tube during measurement to quickly locate the desired sampling position. For more detailed information, you can refer to Dow’s instructions, which provide a fairly thorough explanation
The detection method can be used to measure the desalination rate of a single membrane
Thank you for your reply; the results of my test were very good