Environmental Engineering Reference
In-Depth Information
Table 10.6 volaTile aCids-To-alKaliniTy raTios
volatile acids-to-
alkalinity ratio
operating Condition
Optimum
≤
0.1
Acceptable range
0.1-0.3
Increase in % carbon dioxide in gas
≥
0.5
Decrease in pH
≥
0.8
Solution:
525,000 gal
12,250 gpd
SRT
=
=
42.9days
10.6.2.9.4 estimated gas Production in Cubic feet per day
The rate of gas production is normally expressed as the volume of
gas (ft
3
) produced per pound of volatile matter destroyed. The total cubic
feet of gas a digester will produce per day can be calculated by:
GasProduction (ft )VM lb/day)
3
=
×
%VMRedu
ction
in
(10.24)
3
×
Production Rate (ft /lb)
Example 10.24
Problem:
A digester receives 11,450 lb of volatile matter per day. Currently,
the volatile matter reduction achieved by the digester is 52%. The rate
of gas production is 11.2 cubic feet of gas per pound of volatile matter
destroyed. What is the estimated gas production in cubic feet per day?
Solution:
Est. Gas Production = 11,450 lb/day × 0.52 × 11.2 ft
3
/lb = 66,685 ft
3
/day
10.6.2.9.5 Percent volatile matter reduction
Because of the changes occurring during sludge digestion, the cal-
culation used to determine percent volatile matter reduction is more
complicated:
=
(
)
×
%VM
-
VM
100
in
out
%VMReduction
(10.25)
(
)
%VM
-
VM
×
%VM
out
in
in
Example 10.25
Problem:
Using the data provided below, determine the percent volatile
matter reduction for the digester:
