Environmental Engineering Reference
In-Depth Information
•
Weir condition
—Weirs are level, flow over the weir is uniform, and
the weir overflow rate is within design specifications.
•
Scum removal
—The surface is free of scum accumulations, and the
scum removal does not operate continuously.
•
Sludge removal
—No large clumps of sludge appear on the surface,
the system operates as designed, the pumping rate is controlled to
prevent coning or buildup, and the sludge blanket depth is within
desired levels.
Performance
•
—The unit is removing expected levels of BOD
5
, total
suspended solids, and settleable solids.
unit maintenance
•
—Mechanical equipment is maintained in accor-
dance with planned schedules, and equipment is available for ser-
vice as required.
To assist the operator in judging primary treatment operation, sev-
eral process control tests can be used for process evaluation and con-
trol. These tests include the following:
•
ph
—Normal, 6.5 to 9.0
•
dissolved oxygen
—Normal, <1.0 mg/L
•
Temperature
—Varies with climate and season
•
Settleable solids
—Inluent, 5 to 15 mL/L; effluent, 0.3 to 5 mL/L
Bod
•
5
5—Influent, 150 to 400 mg/L; effluent, 50 to 150 mg/L
Percent solids
•
—Normal, 4 to 8%
•
Percent volatile matter
—Normal, 40 to 70%
•
heavy metals
—As required
•
jar tests
—As required
Note:
Testing frequency should be determined on the basis of the pro-
cess influent and effluent variability and the available resources. All of
these tests should be performed periodically to provide reference infor-
mation for evaluation of performance.
6.3 ProCess ConTrol CalCulaTions
As with many other wastewater treatment plant unit processes,
process control calculations aid in determining the performance of the
sedimentation process. Process control calculations are used in the
sedimentation process to determine:
• Percent removal
• Hydraulic detention time
• Surface loading rate (surface settling rate)
• Weir overlow rate (weir loading rate)
• Sludge pumping
• Percent total solids (%TS)
