Page 389 - Fair, Geyer, and Okun's Water and wastewater engineering : water supply and wastewater removal

JWCL344_ch10_333-356.qxd 8/2/10 9:02 PM Page 349

10.7 Treatment and Disposal or Reuse of Wastewater 349

2
b. Effective area 1 8,000>4 2,000 ft .
c. Dimensions such as 20 ft 100 ft.
4. Trickling filters, one in number:
a. Assumed loading 3 MG/acre/d.
2
b. Effective area 0.8>3 0.27 acre 43,560 0.27 10,500 ft .
c. Diameter (10,500 4> ) 1>2 116 ft.

Solution 2 (SI System):
1. Primary settling in two tanks, averaging 3.1 m in depth.
a. Assumed detention period 2 h.
b. Effective volume/tank flow time 8,000 378 (2>24)>2 126,000 L
3
126 m .
2
3
c. Surface area 126 m >3.1 m 40.6 m .
d. Dimensions such as 3 m 13.6 m.
3
e. Surface hydraulic loading [(8,000 378>2)>1,000 m ]>(3 m 13.6 m)
2
3
37.1 m /d/m .
2. Sludge digestion in two tanks:
3
a. Assumed storage requirement 0.057 m /capita.
3
b. Effective volume 0.057 8,000>2 228 m each.
c. Assuming an area equal to settling tanks, depth below settling compartment
3
228 m /3 m 13.6 5.6 m (plus 0.6 m to keep sludge clear of slots).
3. Sludge-drying beds, four in number:
2
a. Assumed area requirement 0.093 m /capita.
2
b. Effective area 0.093 8,000>4 186 m .
c. Dimensions such as 6 m 31 m.
4. Trickling filters, one in number:
2
a. Assumed loading 0.0028 ML/m /d.
6
2
2
b. Effective area [8,000 378>10 ]MLD>[0.0028 MLD>m ] 1,080 m .
c. Diameter (1,080 4> ) 1>2 37 m.

10.7.4 Disposal into Receiving Waters
Outfalls into receiving waters should terminate well below low-water mark. Wastewater or
effluent is dispersed effectively when a number of outlets, called diffusers, are (a) spaced
sufficiently far apart to prevent interference and (b) situated at or near the bottom of the re-
ceiving water to keep the generally warmer and lighter wastewater from spreading over the
receiving water in a persistent layer (Fig. 10.11). Density differences make themselves felt
especially in marine outfalls. Strength, direction, and dimension of prevailing currents and
the likelihood of their reaching water works intakes, bathing places, shellfish laying beds,
and other important spots are matters for study.
Whatever the relative dilution, the forces of natural purification, or self-purification,
inherent in natural bodies of water can, in the course of time and distance, ultimately return