TM 5-814-3/AFM 88-11, Volume III
C-19. Chlorinator. (Refer to para 17-3.)
a. Design requirements and criteria. Determine the capacity of a chlorinator for an activated sludge
wastewater treatment plant with an average flow of 2 mgd. The peaking factor for the treatment plant is 2.5.
The average required chlorine dosage is 8 mg/L and the maximum required chlorine dosage is 20 mg/L. EPA
regulations require 30 min contact time at peak hour conditions.
b. Calculations and results.
(1) Determine capacity of the chlorinator at peak flow:
lb Cl2/day = 20 mg/L 8.34 lb/gal 2 mgd 2.5 = 834.
Use four 250 lb/day units.
(2) Estimate the daily consumption of chlorine:
Average dose = 8 mg/I (see table in chap 16) lb Cl2/day 8 8.34 2.0 = 133.4.
Use 140.
It should be noted that the total unit capacity is about 6 times the average needed chlorine. This is to cover
the peak hydraulic flow of wastewater and to cover a wider range of dosage of chlorine that might be needed
under unfavorable conditions. Space requirements for the 4 units and for storage of chlorine tanks is
estimated to be about 400 sq ft.
(3) Chlorine contact tank. Required volume for 30 min contact time:
Vol = Q T;
where
Q = peak flow rate, gpm;
T = detention time, min.
Vol = 2.0 106 gal/day (2.5)(30 min) ' 104,170 gal ' 13,930, use 14,000 cu ft.
1,440 min/day
Assume 6 ft SWD + 2 ft freeboard.
L
' 10 for plug flow tank; therefore,
Let
W
L W D = Vol.
Since L = 10W; therefore,
Vol
10 W2=
D
Vol
14,000
'
' 15.3 ft
W=.
10 D
10 6
L = 10W = 153 ft in length.
Therefore, the basic chlorine contact tank dimensions are:
153 ft 15.3ft 8 ft (6 ft SWD).
Baffling is used to construct a more regular tank shape and to prevent short circuiting. (Refer to EPA Process
Design Manual for Upgrading Existing Wastewater Treatment Plants for layout of tank baffles.) Using
a flow channel width of 15.3 ft and 4 side-by-side plug flow compartments, the overall tank width is:
153 ft
' 38.3 ft.
4
The length is:
4 15.3 ft = 61.2.
The tank dimensions are therefore:
61.2 ft 38.3 ft 8 ft (6 ft SWD).
C-41
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