Environmental Engineering Reference
In-Depth Information
Raw sludge volatile matter = 74%
Digested sludge volatile matter = 55%
Solution:
(0.740.55)
-
×
100
%VMReduction
=
=
57%
0.74
-
(0.740.5
×
5)
10.6.2.9.6 Percent moisture reduction in digested Sludge
(
)
×
%Moisture%Moisture
in
-
100
%Moisture
Reduction
out
=
(10.26)
(
)
%Moisture%Moisture
-
×
%Moist
ure
out
in
in
Example 10.26
Problem:
Using the digester data provide below, determine the per-
cent moisture reduction and percent volatile matter reduction for the
digester:
Raw sludge percent solids = 6%
Digested sludge percent solids = 14%
Note:
% Moisture = 100% - percent solids.
Solution:
(0.940.86)
-
-
×
100
%MoistureReduction
=
=
61%
0.94
(0
.940.86)
×
10.6.3 Composting
The purpose of composting sludge is to stabilize the organic mat-
ter, reduce volume, and eliminate pathogenic organisms. In a composting
operation, dewatered solids are usually mixed with a bulking agent (e.g.,
hardwood chips) and stored until biological stabilization occurs. The com-
posting mixture is ventilated during storage to provide sufficient oxygen
for oxidation and to prevent odors. After the solids are stabilized, they are
separated from the bulking agent. The composted solids are then stored
for curing and applied to farmlands or other beneficial uses. Expected
performance of the composting operation for both percent volatile matter
reduction and percent moisture reduction ranges from 40 to 60%.
10.6.4 lime stabilization
In the lime stabilization process, residuals are mixed with lime to
achieve a pH of 12. This pH is maintained for at least 2 hr. The treated
solids can then be dewatered for disposal or directly land applied.
