What is the difference between two-stage reverse osmosis equipment and single-stage reverse osmosis equipment?

First of all, the concepts of "segment" and "level" should be clarified here. "Section" means that the concentrated water of the membrane module is treated by the next group of membrane modules and flows through N groups of membrane modules, which is called N section; "Grade" means that the produced water of the membrane module is treated again by the membrane module, and the produced water is treated by the membrane module for n times, which is called N grade. The secondary reverse osmosis equipment uses the water produced by the primary reverse osmosis as the inlet water of the secondary reverse osmosis, and the concentrated water of the secondary reverse osmosis is returned as a part of the inlet water of the primary reverse osmosis. Generally, the first-stage recovery rate of this design is 75%, and the second-stage recovery rate is 90%. For power plants, qualified desalted water can be obtained by adding a mixed bed or EDI after two-stage reverse osmosis treatment. The difference between two-stage reverse osmosis and single-stage reverse osmosis is mainly the quality of water produced. Take the influent conductivity of primary reverse osmosis as an example. The conductivity of primary reverse osmosis water is about 50uS/cm, while that of secondary reverse osmosis water is about 3uS/cm. As far as the total recovery rate is concerned, there is no difference between two-stage reverse osmosis and single-stage reverse osmosis, because the second-stage concentrated water is reused.