Reverse osmosis is a membrane separation technology that utilizes the function of selectively permeable (semi permeable) membranes with pressure as the driving force. When the pressure applied in the system is greater than the osmotic pressure of the inlet solution, water molecules continuously pass through the membrane, flow into the central pipe through the water production channel, and then impurities such as ions, organic matter, bacteria, viruses, etc. in the effluent flow out at one end, which are trapped on the inlet side of the membrane and then flow out at the outlet end of the concentrated water, thus achieving the purpose of separation and purification.

Different materials of purified water equipment membranes have different pH ranges, such as acetate fiber membranes with a pH range of 3-8, aromatic polyamide membranes with a pH range of 4-10, and DuPont nylon hollow fiber membranes with a pH range of 1.5-12. When the pH value of the feed solution exceeds the usage limit of the membrane, it will cause harmful effects such as hydrolysis and aging of the membrane, resulting in a decrease in water production and a sustained decrease in membrane performance, until the membrane is damaged. Usually, the pH value during the operation of acetate fiber membrane should be controlled between 4-7, while the pH value during the operation of directional polyamide membrane should be controlled between 3-11. The allowable pH range for composite membrane is about 2-11.