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.

(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**

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).

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