Environmental Engineering Reference
In-Depth Information
10.6.1.1.3 digester efficiency (Percent reduction)
To determine digester efficiency, or the percent reduction, a two-
step procedure is required. First the percent volatile matter reduction
must be calculated and then the percent moisture reduction. Because of
the changes occurring during sludge digestion, the calculation used to
determine percent volatile matter reduction is more complicated:
=
(
)
×
%VM
-
VM
100
in
out
%VMReduction
(10.18)
(
)
%VM
-
VM
×
%VM
out
in
in
Example 10.18
Problem:
Using the digester data provided below, determine the percent
volatile matter reduction for the digester:
Raw sludge volatile matter = 71%
Digested sludge volatile matter = 53%
Solution:
(0.710.53)
-
-
×
100
%VMReduction
=
=
53.9,or54%
0.71
(0.710.5
×
3)
Now we can determine the percent moisture reduction:
(
)
×
%Moisture%Moisture
in
-
100
%Moisture
Reduction
out
=
(10.19)
(
)
%Moisture%Moisture
-
×
%Moist
ure
out
in
in
Example 10.19
Problem:
Using the digester data provided below, determine the percent
moisture reduction for the digester.
Note:
% Moisture = 100% - percent solids.
Raw sludge
Percent solids = 6%
Percent moisture = 100% - 6% = 94%
Digested sludge
Percent solids = 15%
Percent moisture = 100% - 15% = 85%
Solution:
(0.940.85)
− ×
− .940.85)
100
%MoistureReduction
=
=
64%
0.94
(0
×
