Common Formulas

Question 1

Pounds formula: Daily loading (lbs/day)

Answer 1

(Concentration, mg/l)(Flow, MGD)(8.34,lbs/gal)

Question 2

Population Equivalent (P.E.)

Answer 2

Daily Loading, lbs/ (PE factor, daily lbs/ person)

Question 3

Daily loading (lbs/ day)

Answer 3

(PE)(PE factor, daily lbs/ person)

Question 4

Volume of rectangular tank (gal)

Answer 4

(L, ft)(w, ft)(h, ft)(7.48 gal/ft^3)

Question 5

Volume circular tank (gal)

Answer 5

(Pi)(r^2, ft)(7.48 gal/ft^3)
Or
(.785)(d^2, ft)(h,ft)(7.48, gal/ft^3)

Question 6

Return sludge rate, mgd

Answer 6

(Total flow, mgs)(settleable solids, %)/100%

Question 7

Percent removal efficiency

Answer 7

[(In-out)/in]*100

Question 8

Detention time, hrs

Answer 8

[(Tank volume, ft^3)(7.48 gal/ft^3)(24 hrs/day)]/ flow, gal/ day

Question 9

Pipe slope (grade)

Answer 9

Rise or drop/ run =
diff in height/diff in length

Question 10

Chlorine dose, mg/l

Answer 10

(Chlorine demand, mg/l) +(chlorine residual, mg/l)

Question 11

Dosage,mg/l

Answer 11

(Chemical feed, lbs/ day)/(flow, mgd)(8.34lbs/gal)