The capacity of a deionization system (SDI) can be measured in several ways. It can be calculated using milliequivalents (MEQ) per liter, per cubic foot of resin or in grains. Generally speaking, 1 MEQ is equal to 1 mg of total dissolved solids (TDS) in CaCO3. In terms of grains, they represent 1 mg of TDS = 0.0584 grains.
Estimating the treatment capacity of a deionization system allows you to calculate the quantity of resin required to meet your water treatment needs in terms of both flow rate and quality. It is important to note that the treatment capacity of a deionization system is intimately linked to the quality of the water to be treated. The higher the total dissolved solids, the more quickly the resin is exhausted.
Calculate the treatment capacity of a deionization system
To begin, convert the number of milligrams of total dissolved solids (TDS) present in the water to grains per gallon (GPG). Once the conversion is complete you can then use the following data to estimate the treatment capacity of a cubic foot of resin
- New mixed bed resin: 10,000 grains/ft3
- Regenerated mixed bed resin: 9000 grains/ft³
To put things in perspective, let's imagine that the inlet water has a concentration of 25 grains per gallon. With a 20 cubic foot capacity tank of new resin, you could treat about 8000 gallons of water. Here is the calculation:
- 10,000grains|ft3 x 20ft3 / 25gpg = 8000 gallons of water
Example of the City of Montreal
Utilisons l’exemple de la ville de Montréal afin de mieux mettre en lumière l’importance de bien calculer la capacité SDI. L’eau montréalaise possède une concentration de 15 grains/gallon en matières dissoutes totale (CaCO3). Avec ce genre de concentration, un cylindre « 520 PG » d’une capacité de 3.6 pi³ de résine aurait une capacité de traitement approximative de 2400 gallons d’eau. Si ce cylindre était utilisé pour un débit de 5gpm, ce qui est très peu, la résine devrait être changée toutes les 8 heures.