Parts Per Million 2
Parts Per Million 3
Parts Per Million 4
Milligrams Per Liter
(Parts Per Million)
A part per million is equal to a milligram per liter. Parts per million (abbreviated ppm) is one part in a million parts. Parts per million refers to a ratio of weights. One part per million is one pound in a million pounds, one ounce in a million ounces, one gram in a million grams, etc. Therefore:
To visualize a part per million, locate and look at
75,000; 100,000; 125,000; 150,000; 500,000; or a
million gallon tank. A 125,000 gallon tank would contain a million
pounds of water. If one pound of sugar is dissolved in 125,000
gallons of water, this would be one part per million. A ten
pound bag of sugar in a million gallon tank of water would be a little
over one part per million, 1.2 ppm.
Milligrams Per Liter
Milligrams per liter also refers to a weight ratio. One milligram per liter is the same as one part per million when the reference volume is water because,
The constant, 120,000, is always used in the ppm formula when the chemicals used are weighed in pounds and the water measured in gallons since 120,000 gallons weighs 1 million pounds.
Examples of the use of the formula are given below:
Y = amount of chlorine needed (pounds)
120,000 = constant
The HTH is only 70% chlorine. Therefore,
If the weight of chemicals is measured in ounces, parts per million can be determined by:
If the weight of chemicals is measured in grams, parts per million can be determined by:
After making jar tests, suppose that the operator knows how many ppm have been added to the water. How would he determine how much chemical the machine should feed? Either of the three formulas given may be used and need only to be changed to find the amount of chemical needed:
Suppose the operator wishes to add 1 ppm of fluoride
to the water and the plant operates at a rate of 1.5 mgd. Sodium
silicofluoride is used, and contains 60 percent fluoride. Note
that the strength or purity of the chemicals must be taken into consideration
Using formula "C" above:
This indicates 3.9 grams per minute would be needed if the chemical were 100 percent pure fluoride. Since it is only 60 percent fluoride, the amount needed may be found by:
Thus 6.5 grams per minute of sodium silicofluoride is necessary to get 1 ppm of fluoride in the water which is being filtered at the rate of 1.5 mgd.
Grains per gallons is refered to frequently in literature and therefore, for reference there are 7,000 grains in one pound. One grain per gallon is the same dosage rate as 1,000,000 grains in 1,000,000 gallons of water.