On the topic of water purification, I think many people have heard a more foreign word, RO reverse osmosis, which generally refers to the terminal water purifier. The water coming out of the RO reverse osmosis purifier is directly drinkable, very clean. It filters out the harmful substances in the water and retains the beneficial mineral substances. Drinking such water for a long time is very helpful to our health.

Why is it called "reverse osmosis" filtration?

When the same volume of dilute solution (such as fresh water) and concentrated solution (such as brine) are placed on both sides of the semi permeable membrane, the solvent in the dilute solution will naturally pass through the semi permeable membrane and spontaneously flow to the side of the concentrated solution. This phenomenon is called permeation.

When the permeation reaches equilibrium, the liquid level of the concentrated solution side will be higher than that of the dilute solution by a certain height, which forms a pressure difference, which is called osmotic pressure. If a pressure greater than the osmotic pressure is applied on the side of the concentrated solution, the flow direction of the solvent will be opposite to that of the original one, and it will start to flow from the concentrated solution to the side of the dilute solution. This process is called reverse osmosis.

In short, it is to apply pressure on the concentrated solution through power on, change the original penetration direction, and realize the countercurrent of concentrated solution, so as to purify the concentrated solution and produce pure water.

Why waste water is produced?

The working process of reverse osmosis membrane, the core component of water purifier, is actually a process of liquid concentration. The salt content of water increases with the water passing through the surface of reverse osmosis membrane, and the osmotic pressure of water also increases. When the osmotic pressure increases to the pressure of booster pump, water cannot flow into the purified water end through reverse osmosis membrane. This part of the water that fails to pass is the waste water produced during water production.