Pounds Formula

Prepared ByMichigan Department of Environmental Quality

Operator Training and Certification Unit

1. Loading on treatment system.

CALCULATION OF POUNDSCALCULATION OF POUNDS

We often need to know how many pounds of material we are dealing with.

2. Calculating pounds of a chemical to add.

3. Calculating pounds of a material being discharged.

Pounds Pounds FormulaPounds Pounds Formula

mg/L (Metric)mg/L (Metric)ToTo

Pounds (English)Pounds (English)

CALCULATION OF POUNDSCALCULATION OF POUNDS

1. The Quantity of water must be known.(The flow of the water stream or the volume

of the tank containing the water.)

Three things must be known to calculate the POUNDS of material in a quantity of water.

2. The Concentration of material in water must be known. (Lab analysis)

3. The Weight of a gallon of water

The Weight of a gallon of water is a constant.

1 gallon of water weighs 8.34 pounds

Pounds =

CALCULATION OF POUNDSCALCULATION OF POUNDS

ConcentrationOf STUFF

In theWater

Conc. x Flow (or Volume) x 8.34 Lbs/gallon

XQuantityOf Water

The STUFFIs In

WeightOf TheWater

X

Flow (volume) and concentration must be expressed in specific units.

Flow or Volume must be expressed as millions of gallons:

= MG

i.e.) A tank contains 1,125,000 gallons of water. How many million gallons are there?

1,125,000 gal = 1.125 MG 1,000,000 gal/MG

1,000,000 gal/MGgallons

Concentration must be expressed as parts per million parts.

Concentration usually reported as milligrams per liter. This unit is equivalent to ppm.

1 mg = 1 mg = 1 mg = ppm liter 1000 grams 1,000,000 mg

ppm = PartsMil Parts

=Lbs.

Mil Lbs.mg/L =

Lbs. =

When Flow (volume) is expressed as MGand Concentration is in ppm,

the units cancel to leave only pounds.

Concentration x Flow (or Volume) x 8.34 Lbs/gallon

Lbs.M Lbs. X X M gal Lbs.

gal

= Lbs.

If we enter flow rate in M gal per day (MGD), the answer will be in Lbs/day.

Lbs.M Lbs. X X

M gal Lbs.gal

Lbs./Day =

Concentration (mg/L) x Flow (MGD) x 8.34 Lbs/gal.

Day

= Lbs./Day

EXAMPLE POUNDS CALCULATIONS

= 150 Lbs./day Suspended Solids

Calculate the POUNDS of suspended solids discharged to the receiving stream if the suspended solids concentration was 15 mg/L and the plant flow was 1.2 MGD.

1.

POUNDS/day =

15 mg/L X 1.2 MGD X 8.34 #/gal

POUNDS/day =Conc. (mg/L) X Flow (MGD) X 8.34 pounds/gallon

= 3.1 Lbs./day Phosphorus

Calculate the POUNDS of Phosphorus discharged from a system if the Phosphorus concentration was 0.75 mg/L and the flow was 500,000 gallons/day.

2.

POUNDS/day =

0.75 mg/L X500,000 gal/day

X 8.34 #/gal

POUNDS/day =Conc. (mg/L) X Flow (MGD) X 8.34 pounds/gallon

1,000,000

= 0.75 mg/L X 0.50 MGD X 8.34 #/gallon

Calculate the POUNDS of Mixed Liquor Volatile Suspended Solids, (MLVSS) in a 250,000 gallon aeration tank if the MLVSS concentration is 2500 mg/L.

3.

POUNDS =Conc. (mg/L) X Flow (MG) X 8.34 pounds/gallon

= 5200 Lbs MLVSS

Calculate the POUNDS of Mixed Liquor Volatile Suspended Solids, (MLVSS) in a 250,000 gallon aeration tank if the MLVSS concentration is 2500 mg/L.

3.

POUNDS =

2500 mg/L X250,000 gallons

X 8.34 #/gal

POUNDS =Conc. (mg/L) X Q (MG) X 8.34 pounds/gallon

1,000,000

= 2500 mg/L X 0.25 MG X 8.34 #/gallon

The Pounds formula can be rearranged to calculate flow or concentration:

a. M gal = Lbs _ 8.34 Lbs/gal x conc. (mg/L)

b. conc. (mg/L) = Lbs _

8.34 Lbs/gal x M gal.

What volume may be discharged to meet a pounds limit?

What is the concentration if this amount of chemical was added?

Pounds =

CALCULATION OF POUNDSCALCULATION OF POUNDS

ConcentrationOf STUFF

In theWater

Conc. x Flow (or Volume) x 8.34 Lbs/gallon

XQuantityOf Water

The STUFFIs In

WeightOf TheWater

X

1. Calculate the POUNDS of suspended solids discharged to the receiving stream if the suspended solids concentration was 18 mg/L and the plant

flow was 0.20 MGD.

Practice Problems

2. Calculate the POUNDS of BOD going to a treatment system if the influent BOD concentration was 195 mg/L and the flow was

86,000 gallons/day.

3. Calculate the CONCENTRATION of Alum added if 43 pounds were fed into a flow of 0.125 MGD.

4. Calculate the number of GALLONS that may be discharged per day from a lagoon if the permit limit is 30 pounds of BOD per day

and the BOD concentration is 20 mg/L.

Work Calculations on Separate PaperAnswers Given on Next Slides

POUNDS CALCULATIONS

= 30 Lbs./day Suspended Solids

POUNDS/day = Conc. (mg/L) X Flow (MGD) X 8.34 pounds/gallon

Calculate the POUNDS of suspended solids discharged to the receiving stream if the suspended solids concentration was 18 mg/L and the plant flow was 0.20 MGD.

1.

POUNDS/day =

POUNDS/day = 18 mg/L X 0.20 MGD X 8.34 #/gal

Conc. (mg/L) X Flow (MGD) X 8.34 pounds/gallon

= 140 Lbs./day BOD

Calculate the POUNDS of BOD going to a treatment system if the influent BOD concentration was 195 mg/L and the flow was 86,000 gallons/day.

2.

POUNDS/day =

POUNDS/day = 195 mg/L X 86,000 gal/dayX 8.34 #/gal

Conc. (mg/L) X Flow (MGD) X 8.34 pounds/gallon

1,000,000

= 195 mg/L X 0.086 MGD X 8.34 #/gallon

= 41.25 mg/L Alum

Calculate the CONCENTRATION of Alum added if 43 pounds were fed into a flow of 0.125 MGD.

3.

43 #/day = Conc. (mg/L) X 0.125 MGD X 8.34 #/gal

POUNDS/day = Conc. (mg/L) X Flow (MGD) X 8.34 pounds/gallon

0.125 X 8.34 0.125 X 8.34

430.1325 X 8.34

= Conc. (mg/L)

0.18 = Flow

Calculate the number of GALLONS that may be discharged per day from a lagoon if the permit limit is 30 pounds of BOD per dayand the BOD concentration is 20 mg/L.

4.

POUNDS/day =

30 #/day = 20 mg/L X Flow MGD X 8.34 #/gal

Conc. (mg/L) X Flow (MGD) X 8.34 pounds/gallon

20 mg/L X 8.34 #/gal 20 X 8.34

3020 X 8.34 Flow MGD

0.18 MGD X 1,000,000 = 180,000 gallons/day

MGD

=

Pounds Formula

Prepared ByMichigan Department of Environmental Quality

Operator Training and Certification Unit