Post Treatment

Post treatment for high quality drinking or process water

Depending on the treated water application, the Reverse Osmosis permeate should be conditioned prior to end usage. Permeate from RO system is characterized by its ionic imbalance. This is due to the selectivity of the membranes to reject more divalent ions than monovalent, resulting in disproportioned concentrations of calcium, magnesium and bicarbonates compared to sodium and chlorides, as well as an unstable.


One of the most popular solutions adopted to balance the ions in the product water is the dosing of carbon dioxide (CO2) and hydrated lime (Ca(OH)2); these chemicals are added after both permeates from first pass and second pass have been blended together before the intermediate fresh water reservoir in an alternative sequence. Different technologies options for pH adjustment of the RO permeate are available these are summarized in below:

Technology options for pH adjustment.

Ø  Limestone dissolution Adsorption of CO2 dissolution of dolomite in contact filters

Ø  Lime Water Injection Adsorption of CO2 and injection of lime water

Ø  Chemical Dosage Injection of Calcium Chloride and Sodium bicarbonate

Each technology has different features and application differs on the location and on size of plants. Table below shows the typical advantages and disadvantages of each technology and the prevailing application in the industry.

Typical advantages and disadvantages of each technology




Typical Application

Limestone dissolution

High reliability

Low maintenance need

High investment Cost

-    Large desalination

-    project both thermal and SWRO

Lime Water injection

Medium investment Costs

Possible high water Turbidity Dependence on lime quality

-    Large desalination

-    project both thermal and SWRO

Chemical Dosage

Low investment costs

High operational Cost

-    Small desalination Project


FARAN’s Remineralization and Neutralization prefabricated packages are included CO2 neutralization system which provides automated pH neutralization of alkaline water/wastewater or CO2 addition for remineralization of drinking water or industrial process water that has been treated by reverse osmosis. The system consists of CO2 contacting equipment and process controls.