TM 5-814-3/AFM 88-11, Volume III
(3) Determine detention time:
13,773 cu ft 7.48 gal/hr
' 2.06 hr, use 2.1 hr;
Detention time =
1,200,000 gal/day 1 day/24 hr
(4) Set diffused air supply at 1 scf/gal wastewater treated.
(5) Determine clarifier volume, using an overflow rate of 800 gpd/sq ft and a tank depth of 12 ft:
Surface area = 1,200,000 gpd ' 1,500 sq ft;
800 gpd/sq ft
Volume = (12 ft)(1,500 sq ft) = 18,000 cu ft;
- 1 tank, 20 ft wide by 80 ft long, would be suitable.
(6) Assuming 90 percent NH3-N reduction in the nitrification stage, determine NO3-N and loading applied
to the denitrification stage.
(0.90)(200 lb/day NH3-N) = 180 lb/day NO3-N
(7) Determine methanol dosage rate, assuming 3 lb methanol per pound nitrate nitrogen removed.
3 lb methanol
Methanol dose = (180 lb/day NH3-N).
' 540 lb methanol/day
&N
lb
NO3
(8) Determine tank volume, using detention time:
Volume = (1,200,000 gal/day 1 day/24 hr)(2.1 hr)(1 cu ft/7.48 gal) = 14,037 cu ft, use 14,040.
C-14. Anaerobic sludge digestion. (Refer to para 16-6b.)
a. Design requirements and criteria. Determine the digester volume, and gas yield and heat requirement
for the anaerobic digestion of combined activated sludge and primary sludge. Assume the following
conditions apply:
Sludge amount = 1,200 lb/day;
Sludge solids after thickening = 3%;
Detention time = 15 days;
Volatile matter reduction = 60%;
Temperature = 80EF (in digester);
Gas yield rate = 15 cu ft/lb VSS destructed;
Volatile sludge content = 75%.
b. Calculation and results.
(1) Determine digester volume:
1,200 lb/day
Sludge volume '
' 4,796, use 4,800 gal/day;
8.34 (0.03)
1
' 4,800
' 642 cu ft/day;
7.48
Digester volume = 642 cu ft/day 15 days = 9,630 cu ft.
(2) Determine gas yield:
cu ft
Gas yield = (15
1,200 lb/day 0.75 0.60) ' 8,100 cu ft/day ' 5.6 cfm.
lb VSS destroyed
C-37
Previous Page
