Two common desalination processes for reverse osmosis equipment

Reverse osmosis equipment, also known as water purification equipment, is used in many industries with extremely high desalination rate requirements. Today, we will introduce two common desalination water treatment equipment processes, hoping to be helpful to you.

I. In reverse osmosis equipment, electrodialysis units are combined with other water treatment equipment for desalination systems.

　　Electrodialysis is generally used for partial desalination of high-salinity, high-hardness brackish water and for deep treatment in deep desalination.

　　Due to the application range of electrodialysis desalination, in application, the requirements of raw water quality and desalted water quality should be considered, combined with ion exchange water treatment technology, to give full play to their respective advantages in the water treatment process, so as to achieve reasonable technical requirements, economic benefits and stable operation. Common reverse osmosis equipment systems are as follows.

　　1. Pretreatment electrodialysis ion exchange

　　This system combines electrodialysis units and ion exchangers, and has been widely used at home and abroad in its early stages.

　　Its combination principle is that when the water resistivity is above 20*104_ucm, the electrodialysis unit is prone to polarization and cannot continue to adapt; conversely, ion exchange can adapt to the treatment of low-salinity water and can produce high-purity water. Therefore, in this combined water treatment system, electrodialysis is used as a pretreatment for ion exchange water treatment to remove most (60%-90%) of the salt in the raw water, and the remaining small part can be further removed by ion exchange to produce desalted water.

　　According to the desalination water quality requirements, ion exchange can adopt single-bed, double-bed, mixed-bed or other different combinations. This system has good water quality, stable operation, low regenerant consumption, and strong adaptability to changes in raw water salinity. It is suitable for brackish water or coastal areas affected by seawater backflow.

　　This combined desalination water treatment system has been widely used in the fields of power, chemical industry, light industry, and electronics.

　　2. Pretreatment ion exchange electrodialysis

　　3. Pretreatment ion exchange (softening), electrodialysis ion exchange (softening)

　　In this reverse osmosis equipment combined system, ion exchange softening treatment is carried out before and after electrodialysis, because pre-softening can prevent scaling and blockage of the electrodialysis unit and improve the desalination efficiency of electrodialysis. Ion exchange softening treatment after electrodialysis can further reduce the hardness and relative alkalinity of water, ensuring the water quality of medium and low pressure boiler feed water.

　　Application of electrodialysis in water treatment

　　Slightly brackish water and seawater desalination, seawater concentration and salt making, pure water preparation, industrial wastewater (electroplating wastewater, papermaking wastewater, heavy metal wastewater), radioactive wastewater, reverse osmosis equipment, ion membrane electrolysis, etc.

II. Electrodialysis unit process system in reverse osmosis equipment

　　Selection of economical and reasonable electrodialysis process system for reverse osmosis equipment (i.e., desalination method) is an important part of the electrodialysis desalination process design. Generally, it should be determined through technical and economic comparison according to the raw water quality, water quantity and water quality requirements.

　　Common desalination methods used in reverse osmosis equipment include direct current method, circulation method and partial circulation method.

　　1. Reverse osmosis equipment direct current desalination: After the raw water passes through one or more electrodialysis units in series, the required water quality can be achieved. It is suitable for situations with constant water volume and raw water concentration. The advantages of this method are continuous water supply and simple pipeline. The disadvantage of this method is that the water quality of the fixed-type equipment changes with the change of raw water salinity.

　　2. Reverse osmosis equipment circulation desalination:

　　The raw water is circulated multiple times in the electrodialysis unit and the water tank to achieve the ideal effluent water quality. Its advantages are that regardless of the change in raw water concentration, the raw water can be treated to any required level, the flow rate is high, the desalination speed is fast, and the electrodialysis unit is small in size. Its disadvantages are that it needs to set up a circulation pump and water tank, can only supply water intermittently, and consumes a lot of electricity. It is suitable for small equipment with small production water volume, high raw water salinity, and high effluent water quality requirements.

　　3. Reverse osmosis equipment partial circulation desalination:

　　It is a combination of direct current seawater desalination and circulating seawater desalination. In the partial circulation desalination process system, the desalted water from the electrodialysis unit is divided into two ways: one is continuous water output for user use, and the other is returned to the electrodialysis unit and mixed with the water in the water phase to continue desalination. Its characteristics are that it uses fixed-type equipment and can meet the requirements of different water quality and water volume. When the raw water salinity changes, the circulation amount can be adjusted to ensure the stability of the effluent water quality, but the system is complex and the energy consumption is high. It is suitable for large-scale water treatment systems.