Basic Units of Measurement and Conversions - Basic Mathematics for Water and Wastewater Operators - page 13

TABLE 2.4
Weight, Volume, and Concentration Calculations

To Calculate Formula

Pounds

Concentration (mg/L) × Tank volume (MG) × 8.34 lb/MG/mg/L

Pounds/day

Concentration (mg/L) × Flow (MGD) × 8.34 lb/MG/mg/L

Quantity (lb/day)
Concentration(mg/L)

Million gallons/day

8.3× lb/MG/mg/L

Quantity (lb)
Tank volume(MG)

Milligrams/liter

× 8.34 lb/MG/mg /L

Kilograms/liter

Concentration (mg/L) × Volume (MG) × 3.785 L/gal

Kilograms/day

Concentration (mg/L) × Flow (MGD) × 3.785 L/gal

Pounds/dry ton

Concentration (mg/kg) × 0.002 lb/dry ton/mg/kg

• 454 grams = 1 pound (lb)

• 1000 milliliters = 1 liter (L)

• 1000 milligrams = 1 gram (g)

• 1 ft 3 /sec (cfs) = 0.6465 million gallons per day (MGD)

Note: Density (also called specific weight ) is mass per unit volume and may be
written as lb/ft 3 , lb/gal, g/mL, or g/m 3 . If we take a fixed-volume container, fill it
with a fluid, and weigh it, we can determine the density of the fluid (after subtract-
ing the weight of the container).

• 1 gallon of water weighs 8.34 pounds; the density is 8.34 lb/gal

• 1 milliliter of water weighs 1 gram; the density is 1 g/mL

• 1 cubic foot of water weighs 62.4 pounds; the density is 62.4 lb/ft 3

• 8.34 lb/gal = milligrams per liter, which is used to convert dosage in mg/L

into lb/day/MGD (e.g., 1 mg/L × 10 MGD × 8.34 lb/gal = 83.4 lb/day)

• 1 psi = 2.31 feet of water (head)

• 1 foot head = 0.433 psi

• °F = 9/5(°C + 32)

• °C = 5/9(°F - 32)

• Average water usage, 100 gallons/capita/day (gpcd)

• Persons per single family residence, 3.7

CONVERSIONS
Use Tables 2.3 and 2.4 to make the conversions that are necessary in the following
example problems. Other conversions are presented in appropriate sections of the
chapter.