Principle of pH Control in Reverse Osmosis Operation - 3

Post-processing Stage: Water Stability and Pipeline Protection

If RO water passes through acidification and/or contains a large amount of permeated CO.₂The produced water typically has an acidic pH (5-6.5), which can be corrosive to metal pipes and equipment (such as pumps, tanks, and valves), potentially leading to the leaching of heavy metals (e.g., copper, lead). This does not meet the sensory and sanitation requirements for drinking water.

Adjust the pH of the RO permeate water to an appropriate range (usually near neutral or slightly alkaline) to ensure stability, compliance with standards (such as drinking water standards), and reduce its corrosiveness to subsequent equipment and transmission pipelines.

Neutralizing low pH water output

De-gassing (Carbon Dioxide Removal) Through aeration (baffled vent tower) or vacuum degassing, the physical stripping of dissolved CO₂Remove CO₂Afterward, the pH of the water will naturally rise to approximately 8.0-8.5 (with only a trace amount of CO remaining).₂With HCO₃-Balance).

Add Alkali: Directly add alkali (commonly NaOH) to the product water to neutralize H+. Effect: Rapidly increase pH to the target value (e.g., 7.0-8.5).

2. Stabilization (Re-mineralization):

RO water is "hungry water," with its low ion concentration and alkalinity making it corrosive. It can dissolve the protective layer on the inner walls of pipes (such as calcium carbonate scale), leading to corrosion and the "red water" phenomenon.

During or after adjusting the pH with alkali, an appropriate amount of calcium (such as Ca(OH)2) may be added.₂, CaCO₃Filters) and bicarbonates (such as NaHCO3)₃The principle is to moderately increase the hardness and alkalinity of water, making it slightly prone to calcium carbonate precipitation (mild positive LSI), forming an extremely thin protective layer of calcium carbonate on the inner wall of the pipes, thus inhibiting corrosion (referred to as "mild scaling corrosion inhibition").