Single-Stage Reverse Osmosis Equipment

The system desalination rate of reverse osmosis equipment is generally 98%—99%. Such desalination rate can meet the requirements in most cases. In the electronics industry, ultra-high pressure boiler feed water, and individual pharmaceutical industries, the requirements for pure water may be higher. At this time, single-stage reverse osmosis equipment cannot meet the requirements.

Osmosis is a common phenomenon in nature. For example, if a cucumber is put into salt water, it will shrink due to water loss. The process of water molecules in the cucumber entering the salt water solution is the osmosis process. If a water tank is divided into two parts by a membrane that only allows water molecules to pass through, and pure water and salt water are injected into both sides of the membrane to the same height. After a period of time, it can be found that the liquid level of pure water has dropped, while the liquid level of salt water has risen. We call the phenomenon of water molecules migrating through this membrane to the salt water osmosis. The rise of the salt water level is not endless, and it will reach a balance point at a certain height. At this time, the pressure represented by the liquid level difference between the two ends of the membrane is called osmotic pressure. The magnitude of osmotic pressure is directly related to the concentration of salt water.

After the above device reaches equilibrium, if a certain pressure is applied to the liquid surface at the salt water end, at this time, water molecules will migrate from the salt water end to the pure water end. The process of solvent molecules migrating from a dilute solution to a concentrated solution under pressure is called reverse osmosis. If salt water is added to one end of the above facility and a pressure exceeding the osmotic pressure of the salt water is applied to that end, we can obtain pure water at the other end. This is the principle of reverse osmosis water purification.

There are two keys to producing pure water with reverse osmosis facilities: one is a selective membrane, which we call a semi-permeable membrane, and the other is a certain pressure. Simply put, there are many pores on the reverse osmosis semi-permeable membrane, and the size of these pores is equivalent to that of water molecules. Since bacteria, viruses, most organic pollutants and hydrated ions are much larger than water molecules, they cannot pass through the reverse osmosis semi-permeable membrane and are separated from the water passing through the reverse osmosis membrane.