Environmental Engineering Reference
In-Depth Information
Table 8.3 Conversion faCTors ( K )
Process
lb solids /lb bod 5 removed
Primary
1.7
Activated sludge with primary
0.7
Activated sludge without primary
Conventional
0.85
Step feed
0.85
Extended aeration
0.65
Oxidation ditch
0.65
Contact stabilization
1.00
Trickling filter
1.00
Rotating biological contactor
1.00
Waste (lb/day) = Waste (mg/L) × Flow (MGD) × 8.34
Solids Removed (lb/day) = TSS out (lb/day) + Waste (lb/day)
(SolidsProduced
-
Solids Remo
ved)
×
100
%Mass Balance
=
(8.24)
Solids Produced
8.14.7.6 Explanation of Results
If the mass balance is ±15%, the process sampling and testing and
process control are within acceptable levels. If the balance is greater
than ±15%, investigate further to determine if the discrepancy repre-
sents a process control problem or is the result of nonrepresentative
sampling and inaccurate testing.
8.14.7.7 Sludge Waste Based on Mass Balance
The mass balance calculation predicts the amount of sludge that
will be produced by a treatment process. This information can then be
used to determine what the waste rate must be, under current operating
conditions, to maintain the current solids level:
SolidsProduced (lb/day)
Wa
(8.25)
WasteRate(MGD)
=
steConcentration8.34
×
Example 8.13
Problem: Given the following data, determine the mass balance of the
biological process and the appropriate waste rate to maintain current
operating conditions.
Process = extended aeration (no primary)
Influent flow = 1.1 MGD
Influent BOD 5 = 220 mg/L
Influent TSS = 240 mg/L
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