Environmental Engineering Reference
In-Depth Information
8.13.3 settling Tank influent
8.13.3.1 Dissolved Oxygen
The dissolved oxygen level of the activated sludge settling tank
should be 1 to 3 mg/L; lower levels may result in rising sludge.
8.13.3.2 pH
Normal pH range in an activated sludge settling tank should be
maintained between 6.5 and 9.0; decreases in pH may indicate alkalinity
deficiency.
8.13.3.3 Alkalinity
A lack of alkalinity in an activated sludge settling tank will prevent
nitrification.
8.13.3.4 Total Suspended Solids
Mixed liquor suspended solids sampling and testing are required
for determining solids loading, mass balance, and return rates.
8.13.3.5 Settled Sludge Volume (Settleability)
Settled sludge volume (SSV) is determined at specified times during
sample testing (e.g., 30- and 60-minute observations).
•
—When the process is operating properly, the
solids will settle as a blanket (a mass), with a crisp or sharp edge
between the solids and the liquor above. The liquid over the solids
will be clear, with little or no visible solids remaining in suspen-
sion. Settled sludge volume at the end of 30 to 60 minutes will be in
the range of 400 to 700 mL.
normal operation
•
old or overoxidized activated sludge
—When the activated sludge is
overoxidized, the solids will settle as discrete particles. The edge
between the solids and liquid will be fuzzy, with a large number
of visible solids (e.g., pin floc, ash floc) in the liquid. The settled
sludge volume at the end of 30 or 60 minutes will be greater than
700 mL.
•
young or underoxidized activated sludge
—When the activated
sludge is underoxidized, the solids settle as discrete particles, and
the boundary between the solids and the liquid is poorly defined.
Large amounts of small visible solids are suspended in the liquid.
The settled sludge volume after 30 to 60 minutes will usually be
less than 400 mL.
•
Bulking activated sludge
—When the activated sludge is experienc-
ing a bulking condition, very little or no settling is observed:
