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352 Chapter 10 Introduction to Wastewater Systems

EXAMPLE 10.5 WASTEWATER APPLICATION ON LAND FOR IRRIGATION
Estimate the daily volume of wastewater that can be applied on an acre of land and the land area re-
quired to dispose of the domestic wastewater from a community of 10,000 people by irrigation and
through stabilization ponds 4 ft (1.22 m) deep. Assume that the annual depth of water employed in
the irrigation of crops is 10 in. (254 mm) and that the wastewater flow is 80 gpcd (303 Lpcd).

Solution 1 (U.S. Customary System):
1. Rate of irrigation [(10>12) 7.5 43,560]>365 750 gal/acre/d.
2
2. Irrigation area 10,000 80>750 1,100 acres 1.7 mile .
3. Stabilization-pond area 10,000>500 20 acres.
4. Detention period in ponds 20 43,560 4 7.48>(l0,000 80) 33 days.
Solution 2 (SI System:
2
2
1. Rate of irrigation (254 mm/yr) (1 yr/365 d) (1 m/1,000 mm) (m /1 m )
3
3
2
3
2
0.000696 m /m /d 696 m /km /d 6.96 m /ha/d.
2
2
2. Irrigation area (10,000 303) L/d/696,000 L/km /d 4.35 km .
3. Stabilization-pond area 10,000 persons>(1,235 persons/ha) 8.1 ha.
2
2
4. Detention period in ponds [(8.1 ha 10,000 m /ha) 1.22 m 1,000 L/m ]>[10,000
303] L/d 33 days.
10.8 DISPOSAL OF INDUSTRIAL WASTEWATER
Most water-carried industrial wastes can safely be added to municipal wastewater for treat-
ment and disposal. Some wastes, however, are so strong that they damage collection sys-
tems and interfere with or overload treatment facilities; pretreatment or separation from the
collection system then becomes mandatory. The requisite degree of preparatory treatment
depends on the composition, concentration, and condition of the wastes, the nature and ca-
pacity of the treatment works, and the nature and capacity of the receiving waters. Shock
loads, through sudden release of batches of wastes, are especially objectionable. Holding
or storage basins will dampen shocks if they apportion waste discharge to available treat-
ment plant and receiving water capacities.
Wastes rich in carbohydrates, proteins, and fats and not unlike domestic wastewater in
their degradability have a valid population equivalent. For example, the putrescible matter
in the combined wastes from a distillery that processes 1,000 bushels of grain a day is
equivalent to the wastewater from 3,500 people. By contrast, other industrial wastes may
persist in water without much change. Some may even interfere with wastewater treatment
and natural purification in receiving waters. Copper and other metal wastes are examples.
At high concentrations, copper inhibits the anaerobic digestion of settled solids and de-
stroys the biomass in trickling filters and activated sludge units. New synthetic organics
may also be quite destructive. Yet it is possible to acclimatize biological slimes to many
otherwise toxic organic chemicals, such as phenols and formaldehyde, which are degraded
in treatment plants and receiving waters.
Guiding principles in the solution of industrial wastes problems are, in order of
preference, (a) recovery of useful materials, (b) waste minimization by improvement of
manufacturing processes whereby waste matters and waste waters are reduced in amount,