Environmental Engineering Reference
In-Depth Information
Example 8.3
Problem: The SSV 30 is 365 mL/L and the MLSS is 2365 mg/L. What is
the SVI?
Solution:
365 mL/L 1000
2365 mg/L
×
Sludge Volume Index
=
=154.3
The SVI equals 154.3. What does this mean? It means that the sys-
tem is operating normally with good settling and low effluent turbidity.
How do we know this? Another good question. We know this because we
compare the 154.3 result with the parameters listed below to obtain the
expected condition (the result):
svi value
expected Condition (indicates)
Less than 100
Old sludge; possible pin floc; increasing effluent turbidity
100 to 200
Normal operation; good settling; low effluent turbidity
Greater than 250
Bulking sludge; poor settling; high effluent turbidity
The SVI is best used as a trend indicator to evaluate what is occur-
ring compared to previous SVI values. Based on this evaluation, the
operator may determine if the SVI trend is increasing or decreasing
(refer to the following chart):
svi value
result
adjustment
Increasing
Sludge is becoming less dense.
Decrease waste.
Sludge is either younger or bulking.
Increase return rate.
Sludge will settle more slowly.
Sludge will compact less.
Decreasing
Sludge is becoming more dense.
Increase waste rate.
Sludge is becoming older.
Sludge will settle more rapidly.
Decrease return rate.
Sludge will compact more with no
other process changes.
Holding
constant
Sludge should continue to have its
current characteristics.
No changes are indicated.
8.14.4 Waste activated sludge
The quantity of solids removed from the process as waste activated
sludge is an important process control parameter that operators need to
be familiar with and, more importantly, should know how to calculate:
Waste(lb/day)
=
×
WASConcentration(mg/L)
WAS
(8.9)
Flow (MGD)
×
8.34lb/MG/mg/L
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