Page 340 - Materials Chemistry, Second Edition

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The Sanitary Landfill 311

FIGURE 10.11 The stages of decom-
position in a sanitary landfill (U.S. EPA,
1994).

TABLE 10.11
Rapidly and Slowly Biodegradable Organic Constituents
in MSW
Organic Waste Rapidly Slowly
Component Biodegradable Biodegradable
Food wastes x
Newspaper x
Office paper x
Cardboard x
Yard wastes x x a
Textiles x
Rubber x
Leather x
Wood x
a
Branches, twigs, and other woody portions of yard wastes.

Phase I: The aerobic phase. During Phase I, the biodegradable components of MSW undergo
microbial decomposition immediately after placement in a landfill cell. Initially, oxygen occurs in suf-
ficient quantities in the interstices (voids) to allow for aerobic decomposition of the organic waste frac-
tion. The sources of the heterotrophic microbial populations responsible for waste decomposition, both
aerobic and anaerobic, are the waste itself and the soil material used as a daily cover. Wastewater treat-
ment plant sludge, disposed of in many MSWLFs, and recycled leachate are other sources of organisms.
The reaction for the aerobic oxidation of a glucose molecule was shown in Equation 8.1.

Common products of Phase I include CO ,H O, NO , and other oxygenated compounds. Oxygen
2 2 3
is rapidly depleted in the covered landfill cell by the action of the heterotrophic aerobic microor-
ganisms. Diffusion of oxygen into the void spaces is negligible; once the O level drops below 10
2
to 15% (v/v), anaerobic microorganisms are activated (Phase II).
Phase II: First anaerobic phase. By the onset of Phase II, anaerobic conditions have already
begun to develop. Nitrate and sulfate ions serve as electron acceptors for anaerobic heterotrophs and