Course info

General

            All chemical dose in water plant operations are computed by weight.  The pound is the common unit of weight used in U.S. water and wastewater plants.

 The Pounds Formula

 The Pounds Formula is written mathematically, as follows:

Dose, Lbs = (Volume, MG) (Concentration, mg/L) (8.34 lbs/gallon)

 It is often necessary to convert gallons to million gallons per day in order to utilize the Pounds Formula.  This is accomplished by dividing any quantity of "gallons" by 1,000,000 gallons.  If the quantity being converted is less than 1.0 million gallons, the answer will be in the form of a decimal fraction, like, 0.750 MG for 750,000 gallons.  For quantities which exceed 1.0 million gallons, the answer will take on the form of a whole number, plus a decimal fraction, such as, 1.75 MG for 1,750,000 gallons.

 The Davidson Pie Chart

             There are four parts to the Pounds Formula.  Given any three of the knowns, the fourth unknown can be calculated.  The Davidson Pie Chart shown on the following page can help operators keep terms in their proper place and quickly solve for the fourth unknown.