The basic neutralizing treatments fail to confer optimal characteristics to all water.
This is the case of fresh water containing little or no carbon dioxide, and moreover that supersaturated water at pH greater than 8.3.
To achieve the desired result, it is necessary to apply to these waters a remineralization treatment that will give them a mineralization higher than would be obtained by an elementary neutralization treatment (carbonated or not)..
Remineralization per CO2 injection and neutralization per neutralizing reagent.
In general, it is carried out the injection of carbon dioxide (CO2) in water, prior to introduction or reagent neutralizing by filtration.
This is made in the base of columns or vessels specially designed : CO2 is injected by simple pipes or by better calibrated porous diffusers or nozzles.
Neutralizing filters based calcium carbonate:
Note: a consumption of filter media will be carried out depending
on the amount of CO2 present in aggressive water, and the CaCO3 rate
of the media.
NOTE - Solubility of CO2:
The solubility of carbon dioxide (carbonic gas) in water depends the temperature and the partial pressure of this gas over water.
Take, for example below, the amount dioxide dissolved in pure water (mg/liter CO2 vs T°C) - pressure = atmospheric pressure.
Note the following maximum values:
<Note: link CO2>
Re-mineralization by chemical addition (injection of sodium bicarbonat and calcium salt).
This treatment relates soft waters and still supersaturated with CO2 free.
The injection of sodium bicarbonate "transformed" aggressive CO2 free CO2.
It is possible that only the action of the bicarbonate will achieve the desired equilibrium zone.
Treatment should be supplemented (or preceded) by adding with strong calcium salts, calcium sulfate or calcium chloride, which is usefu :
Conclusion concerning remineralization treatments.
Note: trade ferric chloride introduced into the water 40% of its
weight of anhydrous calcium chloride.
POSSIBLE ALTERNATIVE TREATMENT:
CO2 injection is always associated with neutralization, except of course, if it is a supersaturated water.
In addition, this treatment must often be part of a comprehensive treatment of coagulation / flocculation (the process of agglomeration and precipitation of particles).
In this case, there are several possibilities:
This latter approach is only possible on the waters of which the
TAC is low enough that there is virtually no decarbonation.
Its interest is twofold:
Note also that if CO2 injection is made before the entry of a filtration must avoid falling to entry on these to avoid degassing.
Concluding remarks .
Difficulties are sometimes encountered in bringing the water to the perfect balance :
* If this balance is achieved by the injection of a reagent , the dosage thereof must be very precise , after having been determined according to the characteristics of the water after treatment . Any error due to faulty dosage or change the characteristics of the water, can lead to aggressive water or scale-forming .
* Water that is too soft , even balanced vis-à -vis the limestone , do not produce a desired protective deposit of calcium carbonate , unless treatment of carbonation is sometimes reluctant to adopt .
* It is , in practice, difficult to maintain the balance, water would be from the treatment plant . Indeed , any change in temperature will make the water in the network or in the subscriber or aggressive , or encrusting .
* A water even perfectly balanced , can remain corrosive towards metals and disadvantages that result last as a protective deposit will not bear all the metal surfaces in contact with water.
For these reasons, it is sometimes the complete equilibrated previously exposed by an inhibition processing paralyzing , aggressive or scale-forming water capacity