For some areas with poor water quality, two-stage reverse osmosis equipment is used to improve the water quality. Dual-stage reverse osmosis is suitable for water quality with conductivity greater than 500μs/cm, and the water resistivity can reach 0.5-0.2MΩ · cm (conductivity 2-5μs/cm).
In dual-stage reverse osmosis, the produced water of the first stage enters the second stage as raw water. There is also a continuous flow of concentrated water circulation.
Using this process, the effluent of the second stage fully meets the national pure water standard. The dual-stage system is commonly used in the pharmaceutical, medical, electronics, and purified water industries.
The concentrated water of the second-level reverse osmosis is recycled back to the original water tank of the first level. Because the water quality of the second-level concentrated water is better than that of the original water, it can reduce the salt content of the incoming water of the previous level, and also reduce the salt content of the produced water, improving the quality of the produced water.
The collection rate of the first stage reverse osmosis is equivalent to that of the ordinary reverse osmosis system, with a maximum of 75%. The inlet water of the second stage reverse osmosis is the production water of the first stage reverse osmosis,
which contains only a small amount of monovalent ions and gases, so a high collection rate (up to 75% -90%) can be used.
