Wastewater Math Review Questions

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Wastewater Treatment Math

  1. Concentration (milligrams/liter or parts/million) to quantity (pounds or kilograms)

  2. *Concentration to Pounds:

    The solids concentration in the aeration tank is 2580 mg/L.  The tank volume is 0.90 MG.  How many pounds of solids are in the tank?


    *Concentration to Kilograms:

  3. Concentration  (milligrams/liter or parts/million) to quantity (pounds or kilograms)/Day

  4. *Concentration to Pounds/Day:

    How many pounds of solids are discharged per day when the plant effluent flow rate is 4.85 MGD and the effluent solids concentration is 23 mg/L?


    *Concentration to Kilograms/Day:

    The effluent contains 27 mg/L of BOD5.  How many kilograms per day of BOD5 are discharged when the effluent flow rate is 11.5 MGD?


  5. Quantity (Pounds or Kilograms) to Concentration (milligrams/liter or parts/million)
  6. The process control calculation indicates that the aeration tank should contain 12,168 pounds of suspended solids.  The tank has a volume of 0.61 MG.  What should the suspended solids concentration be in the aeration tank?



  1. Quantity (Pounds or Kilograms)/Day to Concentration (milligrams/liter or parts/million)

  2. The scales indicates that 190 pounds per day of chlorine are currently being used to treat a flow of 2.5 MGD.  What is the chlorine dose in milligrams per liter.



  3. Volume in Cubic Feet to Volume in Gallons: Volume in Gallons = Volume in Cubic Feet  x  7.5 Gallons/Cubic Feet

  4. How many gallons of sludge can be pumped to a digester which 3,240 cubic feet of volume available?


  5. Volume in Gallons to Volume in Cubic Feet:

  6. How many cubic feet of sludge are removed when 15,500 gallons are withdrawn from a digester?

  7. Gallons to Pounds:

  8. If 1,235 gallons of solids are removed from the primary settling tank, how many pounds of solids are removed?


  9. Pounds to Gallons:

  10. How many gallons of water are required to fill a tank which holds 6,458 pounds of water?

Wastewater Treatment Plant Performance, Percent Removal Or Efficiency:

Preliminary Treatment:
Grit Channel Velocity Using a Float:

Grit Channel Velocity Using Flow and Water Area:

Settling Tank:
Surface Settling Rate in Gallons/Square Foot/Day:


Weir Overflow Rate in Gallons/Foot/Day: