Environmental Engineering Reference
In-Depth Information
Note:
In most instances, the amount of suspended solids leaving the
process as scum is so small that it is ignored in the calculation.
Total Suspended Solids In (lb) = TSS
in
× Flow(MGD) × 8.34
(8.20)
Total Suspended Solids Out (lb) = TSS
out
× Flow (MGD) × 8.34
(8.21)
Sludge Solids = Sludge Pumped (gal) × %Solids × 8.34
(8.22)
(
)
⎡
⎣
⎤
⎦
×
TSS
(lb)
−
TSS
(lb) + Slud
ge Sol. (lb)
100
% Mass
Balance
(8.23)
in
out
=
TSS
(lb)
in
8.14.7.2 Explanation of Results
1. If the mass balance is ±15%, the process is considered to be in bal-
ance. Sludge removal should be adequate, and the sludge blanket
depth should be remaining stable. Sampling is considered to be pro-
ducing representative samples that are being tested accurately.
2. If the mass balance is greater that ±15%, more solids are enter-
ing the settling tank than are being removed. The sludge blanket
depth should be increasing, effluent solids may also be increasing,
and effluent quality is decreasing. If the changes described are not
occurring, then the mass balance may indicate that sample type,
location, times, or procedures or the testing procedures are not
producing representative results.
3. If the mass balance is less than ±15%, fewer solids are entering the
settling tank than are being removed. The sludge blanket depth
should be decreasing, and the sludge solids concentration may
also be decreasing. This could adversely impact sludge treatment
processes. If the changes described are not occurring, the mass
balance may indicate that sample type, location, times, or proce-
dures or the testing procedures are not producing representative
results.
Example 8.12
Problem:
Given the following data, determine the solids mass balance
for the settling tank:
Influent flow = 2.6 MGD
Influent TSS = 2445 mg/L
Effluent flow = 2.6 MGD
Effluent TSS = 17 mg/L
Return flow = 0.5 MGD
Return TSS = 8470 mg/L
