shows, thermal desorption treats volatile and semivolatile organics and volatile metals;
cost is medium to high. Alternatively, incineration handles organic wastes and metals
with an ash residue; cost is high. Nonhazardous solid wastes can be landfilled at low cost.
But the future cost may be much higher because landfill costs are rising as available land
becomes scarcer.
Polluted water can be treated with chemicals, aeration, or air stripping—all at low
cost. None of these methods can be combined with the earlier tentative choices. Hence,
the polluted water will have to be treated separately.
- Determine the landfill dimensions and other parameters
Annual landfill space requirements can be determined from VA = Wl 1100, where VA -
landfill volume required, per year, yd
3
(m
3
); W= annual weight, Ib (kg) of waste generat-
ed for the landfill; 1100 lb/yd
3
(650 kg/m
3
) = solid waste compaction per yd
3
or m
3
. Sub-
stituting for this site, VA = 1,500,000/1100 = 1363.6 yd
3
(1043.2 m
3
).
The minimum recommended depth for landfills is 20 ft (6 m); minimum recommend-
ed life is 10 years. If this landfill were designed for the minimum depth of 20 ft (6 m), it
would have an annual required area of 1363.6 x 27 fVVyd^3 •= 36,817.2 ft^3 /20 ft high -
1840.8 ft^2 (171.0 m^2 ), or 1840.9 ft^2 /43,560 ft^2 /acre = 0.042 acre (169.9 m^2 0.017 ha) per
year. With a 10-year life the landfill area required to handle solid wastes generated for
this site would be 10 x 0.042 = 0.42 acre (1699.7 m^2 , 0.17 ha); with a 20-year life the area
required would be 20 x 0.042 = 0.84 acre (3399.3 m^2 ; 0.34 ha).
As these calculations show, the area required for this landfill is relatively modest—
less than an acre with a 20-year life. However, in heavily populated areas the waste gen-
eration could be significantly larger. Thus, when planning a sanitary landfill, the usual as-
sumption is that each person generates 5 Ib (2.26 kg) per day of solid waste. This number
is based on an assumption of half the waste (2.5 Ib; 1.13 kg) being from residential
sources and the other half being from commercial and industrial sources. Hence, in a city
having a population of !-million people, the annual solid-waste generation would be
1,000,000 people x 5 lb/day per person x 355 days per year = 1,825,000,000 Ib
(828,550,000 kg).
Following the same method of calculation as above, the annual landfill space require-
ment would be VA = 1,825,000,000/1100 = 1,659,091 yd^3 (1,269,205 m^3 ). With a 20-ft
(6-m) height for the landfill, the annual area required would be 1,659,091 x 27/20 x
43,560 = 51.4 acres (208,002 m^2 ; 20.8 ha). Increasing the landfill height to 40 ft (12 m)
would reduce the required area to 25.7 acres (104,037 m^2 ; 10.4 ha). A 60-ft high landfill
would reduce the required area to 17.1 acres (69,334 m^2 ; 6.9 ha). In densely populated ar-
eas, landfills sometimes reach heights of 100 ft (30.5 m) to conserve horizontal space.
This example graphically shows why landfills are becoming so much more expensive.
Further, with the possibility of air and stream pollution from a landfill, there is greater
regulation of landfills every year. This example also shows why incineration of solid
waste to reduce its volume while generating useful heat is so attractive to communities
and industries. Further advantages of incineration include reduction of the possibility of
groundwater pollution from the landfill and the chance to recover valuable minerals
which can be sold or reused. Residue from incineration can be used in road and highway
construction or for fill in areas needing it.
Related Calculations. Use this general procedure for tentative choices of treat-
ment technologies for cleaning up contaminated waste sites. The greatest risks faced by
industry are where human life is at stake. Penalties are severe where human health is en-
dangered by contaminated wastes. Hence, any expenditures for treatment equipment can
usually be justified by the savings obtained by eliminating lawsuits, judgments, and years
of protracted legal wrangling. A good example is the asbestos lawsuits which have been
in the courts for years.