State of California-Department of Public Health

Drinking Water Field Operations Branch, Santa Rosa

Daily Calculation of Chemical Dosages(For solutions made with LIQUID CHEMICALS)

The calculation of chemical dosages is important in order to track the effectiveness of the chemical feed processes. To calculate a chemical dosage on a given day, you need to know the following:

1. Quantity of water produced that day (gallons)…………… Equation 1OR

Plant flow rate (gpm)..........................................……… .Equation 2

2. Amount of chemical solution injected that day (gallons)…Equation 1OR

Chemical feed rate (mL/min)………………………………..Equation 2

3. Percent strength of the chemical. An example is 48.5% aluminum sulfate by weight. The percent strength of sodium hypochlorite (NaOCl) is by volume (Trade %) and not by weight; examples are 5.25% and 12.5% sodium hypochlorite by volume.

4. Specific gravity (Sp. G.) of the chemical. Sp. G. is the weight of the chemical in relation to the weight of an equal volume of water. An example is 1.335 for aluminum sulfate. For NaOCl, the Sp. G. is incorporated into the Trade %. Hence, use 1 for the Sp. G. of NaOCl for calculating dose.

5. A.If the chemical is diluted prior to use: The number of gallons of chemical and the number of gallons of water used to make the solution are needed. For example, if one gallon of chemical is added to 24 gallons of water, the final mixture would contain 25 gallons of solution;

The percent strength and Sp. G. of the solution must be calculated using the following formulas:

Percent strength of the solution = [(gallons of chemical added) * (Sp.G.) * (percent strength of the chemical)]

[gallons of water added + gallons of chemical added * Sp. G.]where Sp. G. = specific gravity of chemical

Specific gravity of the solution =[gallons of water added] + [(gallons of chemical added) * (Sp. G. of the chemical)][gallons of water added + gallons of chemical added]

B.If the chemical is not diluted prior to use : The percent strength and specific gravity of the solution is simply the percent strength and specific gravity of the chemical.

Chemical dosage is calculated using either of the following equations:Equation 1

Dosage, mg/L = 9,991 * (gallons of solution injected) * (percent strength of solution) * (specific gravity of solution)

(gallons of water produced)

Equation 2

Dosage, mg/L = (chemical feed rate, mL/min) * (percent strength of solution) * (specific gravity of solution)(0.3785) * (plant flow rate, gpm)

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