The most simple method to reduce alkalinity is to add a strong acid. There are other methods but not so simple.

In most cases people who complain about alkalinity in drinking water really have problems with the hardness (high calcium concentration) which causes calcium carbonate precipitation. This has other solutions.

Thank you Henrik Andersen for your reply. But can we add strong acid to drinking water?

Generally, there are three processes for alkalinity removal i,e. nanofiltration, lime softening, Cl- anion exchange

@Megha Tharayil: It is not problematic to add a strong acid to drinking water provided it is not contaminated (food grade). Sulfuric (H2SO4) and hydrochloric (HCl) are cheap and available in good quality. After they react with the alkalinity the residual is just the harmless ions sulfate or chloride.

@Robert Fairchild: Destillation requires a lot of equipment and continuous distillation of an entire drinking water supply requires a lot of energy. Should we think about the carbon footprint.

@Mohammed Bashir:

I agree that nanofiltration and Cl- anion exchange can reduce alkalinity but they are not really simple processes.

I disagree about the lime softening process. This process is addition of Ca(OH)2 which precipitates CaCO3 as the pH increases. The water is less hard after the process but alkalinity is increased.

I mentioned in my first post that alkalinity and hardness are often confused with each other. Nanofiltration and lime softening are some of the most established advanced treatments for water softening.

Thank you all

not in my skill. But in alkali aggregate reaction in conctrein civil work can use some criteria in ASCE standard.

no methods simpler than Henrik's.

You may use resin in a column.

The alkalinity of well water is due to dissolved salt. I suggest solar water desalination process to reduce alkalinity of well water

It is important to understand the meaning of the parameter alkalinity then one considers how to reduce it: Alkalinity is the sum of dissolved species that can react to neutralize strong acid and it is defined by the analytic procedure to titrate a water sample with acid until the pH is reduced to below the pKa of bicarbonate. At this point the alkalinity is calculated from the mole of acid used for titration per volume of sample. As this is not a concentration of any actual chemical in the water the unit is not written as mol/L but as equivalents per liter (eq/L).

The simple method is to add acid to reduce alkalinity. Although nanofiltration is effective for softening it is not very effective for removing alkalinity. Capital costs are substantial. In addition, you need to handle concentrate stream.

You can also consider using CO2 as a soft neutralising agent which can not lead to very low pHs even if added in excess...

Adding CO2 will reduce the pH but formally seen CO2 cannot change alkalinity.

Adding acetic acid or citric acid does remove alkalinity, but it leaves acetate or citrate in the water. This is not desirable in drinking water as it give a taste to the water.

Another problem is that these ions are reduced so they can be oxidised by chlorine which gives disinfection by-products if chlorination is used. If chlorine isn't maintained in the pipes it will give biofilm growth.

Aerate/degass the well water to allow CO2 to escape - this will reduce the alkalinity. Maybe also add a sulfuric acid to reduce any scaling risks

I suggest you look up a precipitation/coagulation/flocculation chapter in a water treatment book. There are multiple such methods for dealkylization using alum and ferric salts. If your budget is more, then I suggest using chloride based anion exchange.

Ali Farhat , Adding or removing CO2 doesn't change the alkalinity of water unless there is precipitation of carbonates. Please consider the definition of alkalinity. https://en.wikipedia.org/wiki/Alkalinity#Addition_of_CO2

Henrik Rasmus Andersen Aeration will not knock down the CO2 only but will also transform the bicarbonate to carbonate, and if followed by a precipitation stage for example using a clarifier, the carbonate will likely to precipitate (partially) with the calcium in the water, and thus alkalinity will decrease.

Dosing acid will further reduce the alkalinity afterwards.

Hello Dr Megha Tharayil

You can use either of these two methods to reduce high alkalinity from drinking water,

1-Lime softening. While reducing total alkalinity, lime softening does convert HCO3– to CO3--,

2-Hydrochloric acid, sulfuric acid or a combination of these can be used. This process converts the bicarbonates and carbonates present into carbonic acid.

Best regards

Fatah BOUTELDJAOUI