Cleaning method used to clean membrane system

How do I know which cleaning method to use to clean my membrane system?

In order to get the best cleaning results, it is important to choose the right cleaning agent and cleaning procedure, as incorrect cleaning can actually deteriorate the system performance.

Why is the pH of the RO produced water lower than the pH of the feed water?

In a closed system, the relative content of CO2, HCO3- and CO32- varies with pH. Under low pH conditions, CO2 accounts for the major part, in the medium pH range, it is mainly HCO3- and in the high pH range, it is mainly CO32-.

As the RO membrane can remove dissolved ions but not dissolved gases, the CO2 content of RO produced water is basically the same as the CO2 content of RO feed water, but HCO3- and CO32- can often be reduced by 1 to 2 orders of magnitude, which will break the balance between CO2, HCO3- and CO32- in the feed water. In a series of reactions, CO2 will combine with H2O in the following reaction equilibrium shift until a new equilibrium is established.

CO2 + H2O --- HCO3- + H+

If the feed water contains CO2, the pH of the produced water from the RO membrane element will always decrease. For most RO systems the pH of the produced water will have a pH drop of 1 to 2 pH, and when the feed water alkalinity and HCO3- are high, the pH drop of the produced water will be even greater. A very small number of feed waters, containing less CO2, HCO3- or CO32- will see less change in the pH of the produced water.

If the pH of the RO effluent is low, add a metering pump to adjust the pH to alkaline by adding NaOH, because when the pH is between 7.5 and 8, the desalination effect of RO can reach the best.

How can I reduce the energy consumption of the membrane system?

Low energy consumption membrane elements can be used, but it should be noted that their desalination rate is slightly lower than that of standard membrane elements.