Basic Units of Measurement and Conversions - Basic Mathematics for Water and Wastewater Operators - page 43

Required Amount of Chemical (Inactive Ingredient)
Because industrial strength chemicals are normally less than 100% active ingredient,
the amount of chemical must be adjusted to compensate for the inactive components.

Activeingredient required(lb/day)

%Activeingredient

Requiredamount (lb/day) = (2.12)

■ Example 2.100
Problem : To achieve the desired phosphorus removal, 180 lb of ferric chloride must
be added to the daily flow. The feed solution is 66% ferric chloride. How many
pounds of feed solution will be needed?

Solution :

Active ingredient required (lb/day)

%Activeingredient

180 lb/day
0.66

Requiredamount = = = 273 lb/day

Dry Chemical Feed Rate
When chemical is to be added in dry (powder, granular, etc.) form, the chemical feed
rate can be expressed in units such as pounds per hour or grams per minute.

Requiredamount (lb/day)
2

Feed rate (lb/hr) = (2.13)

44hr/day

Requiredamount (lb/day) × 454 g/lb

Feed rate (g/min) = (2.14)

1440 min/day

■ Example 2.101
Problem : A plant must feed 255 lb/day of high-test hypochlorite (HTH) powder to
reduce odors. What is the required feed rate in pounds per hour? In grams per minute?

Solution :

255 lb/day
24 hr/day

Feed rate (lb/hr) = = 10.6 lb/hr

255 lb/day ×

1440 min/day

454 g/lb

Feed rate (g/min) = = 80 g/min

Liquid Chemical Feed Rate
If chemical is fed in liquid form, the required amount (pounds, grams, etc.) of pro-
cess chemical must be converted to an equivalent volume (gallons, milliliters, etc.).
This volume is then converted to the measurement system of the solution feeder (gal-
lons/day, milliliters/minute, etc.).