pH adjustment for RO purified water system

[lotus7312]

We are designing a purified water system with one stage RO. One article about RO system said the pH of the water inlet to RO has to be adjusted to above 8.3. The reason is there will be only HCO3- and CO32- ions in the water, and not CO2 gas since RO can not reject CO2 gas. Does anyone use RO system for the purified water? Do you need to add alkali solution to adjust pH?
Many thanks

 

[ileroy]

dear,

indeed the pH of the system is more acid when undergoing an RO operation. As a result the CO2 will present under ionic form. You can shift this equilibrium using a slight injection of an alkalic agent (as NaOH) to shift the pH slightly.

If not, pH and conductivity of the produced water might be not compliant to the requirements

regards

Ileroy