2.Fault causes, identification methods, and prevention measures for the decrease in desalination rate of the RO system

The reasons for the decrease in desalination rate and normal water production after standardization are:

2.1 Leakage of O-ring

When the O-ring is damaged due to the use of incompatible chemicals or mechanical stress (such as the movement of membrane elements caused by water hammer) during lubrication, leakage may occur. Sometimes, there may also be situations where the O-ring is not installed or installed incorrectly, which can lead to leakage.

The method to prevent leakage of the "O" ring: When lubricating, use the designated lubricant "glycerin"; Install a thrust ring during installation to prevent the membrane elements from bouncing back and forth.

2.2 Membrane surface damage

The damage to the membrane surface is mostly caused by the combined action of sharp particles, crystals, and water hammer on the front-end elements of the system.

Measures to prevent surface damage to the membrane:

a) Timely replace the security filter element to prevent sharp, hard particles or activated carbon particles from entering the membrane element in the water;

b) Before starting the high-pressure pump, first exhaust the membrane system, or install an electric slow door or variable frequency start of the high-pressure pump to prevent water hammer;

c) When cleaning fouling membrane elements, the initial flow rate should be as small as possible to prevent damage caused by excessive flow erosion.

2.3 Back pressure

At any time, if the water production pressure is 0.3 bar higher than the inlet or concentrated water pressure, the composite membrane may experience delamination between the composite layers, thereby damaging the membrane elements.

The reason for the decrease in desalination rate and increase in water production after standardization is membrane oxidation

When the membrane comes into contact with oxidizing substances in water, it is oxidized and destroyed, which is irreversible chemical damage. Once this happens, all membrane elements can only be replaced.

Possible reasons for membrane oxidation:

a) Excessive residual chlorine or other oxidizing substances in the inflow of the membrane system;

b) When cleaning and disinfecting, if appropriate disinfectants are not selected or the cleaning and disinfection requirements are not strictly followed, the cleaning time or temperature may exceed the standard, resulting in membrane oxidation.

c) The oxidation of membrane elements can be determined by pressure staining test.