Page 249 - Materials Chemistry, Second Edition

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220 Waste Management Practices: Municipal, Hazardous, and Industrial

FIGURE 8.4 Portable O meter.
2

The oxygen level of the pile can be measured using a simple portable O meter (Figure 8.4).
2
Oxygen requirements during aerobic composting can also be determined based on the composition
of feed substrate and final product. This method can be applied when small pilot-scale composting
studies are conducted and the final product composition is determined. Degradability of the feed
substrate is thus assessed as well. Rich (1963) formulated the following stoichiometric equation:
C H O N 0.5(ny 2s r c)O nC H O N sCO rH O (d nz)NH 3 (8.3)
y
z
a
d
w
2
b
c
x
2
2
where r 0.5[b nx 3(d nz)]
s a nw
The formulae C H O N and C H O N represent the compositions of feed substrate and final prod-
d
w
x
y
z
c
a
b
uct, respectively. An elemental analysis is necessary in order to establish the subscripts.
EXAMPLE 8.1
Pilot-scale aerobic composting was conducted on 1000 kg (dry solids) of MSW feedstock determined
to have an initial composition C H O N. By completion of composting (60 days), the initial 1000
31
35
67
kg of feedstock was reduced to 180 kg dry solids. The final product composition was determined to
be C H O N. Calculate the stoichiometric oxygen requirement per 1000 kg of feedstock.
9
20
14
SOLUTION
1. The molecular weight of the substrate is
Carbon 35(12) 420
Hydrogen 67(1) 67
Oxygen 31(16) 496
Nitrogen 1(14) 14
Total 997
The kg-mol of organic feedstock at the start of the process is 1000/997 1.00.