1. Mixed liquor suspended solids: 3,000 mg/L, Aeration tank: 70 ft long, 42 feet wide, 10 feet deep
Find pounds of solids contained in the aeration tank

2. Mixed liquor suspended solids: 5,000 mg/L, Aeration tank: 70 ft long, 42 ft wide, 10 ft deep
Find pounds of solids under aeration

3. An activated sludge facility is wasting 500,000 gpd with a concentration of 2,500 mg/L, how many pounds are wasted per day?

4. An activated sludge facility is wasting 400,000 gpd with a concentration of 2,500 mg/L, how many pounds per day of sludge would be wasted?

5. Wet Well Diameter = 8 ft, Drawdown Time = 225 seconds, Drawdown Distance = 1.26 feet, Refill Time = 410 seconds, Refill Distance = 1.19 feet
Find the pumping rate, in gallons per minute of this lift station pump

Answers:

1. 5504 lbs
(Davidson Pie Chart or) Loading formula: Flow, MGD X Conc, mgl/L X 8.34 lbs/gal
Find Flow or this time Volume in MGD = L, ft X W, ft X H, ft = 70 ft X 42 ft X 10 ft = 29,400 cuft
Convert cuft to gallons = 29,400 cuft X 7.48 gal/cuft = 219,912 gal
Convert gallons to million gallons (shuffle) = 0.22 MG
Work problem, 0.22 MG X 3,000 mg/L X 8.34 lbs/gal =

2. 9,174 lbs
(Davidson Pie Chart or) Loading formula: Flow, MGD X Conc, mg/L X 8.34 lbs/gal
Find Flow or this time Volume in MGD = L, ft X W, ft X H, ft = 70 ft X 42 ft X 10 ft = 29,400 cuft
Convert cuft to gallons = 29,400 cuft X 7.48 gal/cuft = 219,912 gal
Convert gallons to million gallons (shuffle) = 0.22 MG
Work problem, 0.22 MG X 5,000 mg/L X 8.34 lbs/gal =

3. 10,425 lbs/day
(Davidson Pie Chart or) Loading formula: Flow, MGD X Conc, mg/L X 8.34 lbs/gal
Convert flow from GPD to MGD = 0.50 MGD
Work the problem, 0.50 MGD X 2,500 mg/L X 8.34 lbs/gal =

4. 8,340 lbs/gal
(Davidson Pie Chart or) Loading formula: Flow, MGD X Conc, mg/L X 8.34 lbs/gal
Convert flow from GPD to MGD = 0.40 MGD
Work the problem, 0.40 MGD X 2,500 mg/L X 8.34 lbs/gal =

5. 191.74 gal/min
Pumping Rate, gpm = [(Drawdown Volume)/(Drawdown Time)] + [(Refill Volume) / (Refill Time)] Find Drawdown Volume = (draw your circle and name your parts):(8 ft diam)/(2) = 4 ft Radius
Volume = 3.14 X R, ft X R, ft X H, ft = 3.14 X 4 ft X 4 ft X 1.26 ft = 63.3 cuft
(NOTE: Height in this case is the Drawdown Distance)
(NOTE: Could have used 0.785 X D, ft X D, ft X H, ft or 0.785 X 8 ft X 8 ft X 1.26 ft)
Convert cubic feet to gallons: 63.3 cuft X 7.48 gal/cuft = 473.5 gal Drawdown Volume
Convert Drawdown Time from Seconds to Minutes = (225 sec) / (60 sec/min) = 3.75 Drawdown Time, min
Next find Refill Volume = 3.14 X 4 ft X 4 ft X 1.19 ft = 59.79 cuft
(NOTE: Could have used 0.785 X 8 ft X 8 ft X 1.19 ft)
Convert cuft to gal: 59.79 cuft X 7.48 gal/cuft = 447.23 gal
Convert Refill Time from Sec to Min = (410 sec) / (60 sec/min) = 6.83 min
Work problem, [(473.5 gal) / (3.75 min)] + [(447.2 gal) / (6.83 min)] =