Course TEN-702
Industrial waste management
unit-2
• Lecture -11
Pretreatment
• Every plant needs some pretreatment
• Minimum pretreatment is coarse
screening
• As plants become larger, mechanical
screening and grit removal are standard
• Odor control and flow equalization are
common
Primary Clarification
• Primary clarification is reported to be the
“oldest and most widely used unit operation
in wastewater treatment.”
• Developments in the technology of
wastewater treatment in chronological
order:
–
–
–
–
Outhouses
Sewage flowing in gutters
Convey raw sewage via pipe to discharge
Primary clarifiers added as treatment step
before conveying wastewater to discharge
Primary Clarification
• Goal of primary clarification is to produce
effluent that leads to economical wastewater
treatment
• Primary clarification provides some measure of
flow equalization
• Primary clarifiers remove floating material and
scum
• Prevalence of primary clarifiers
– Essential at larger wastewater plants
– Not necessary at small plants for most activated
sludge processes
Circular Clarifiers
Primary Clarification
• Circular
primary
clarifier can
be round or
rectangular
Primary Clarification
Primary Clarification
Primary Clarification
• Primary clarifiers are similar to
final clarifiers
– Designed to settle solids
– Includes scum removal
– Quiescent (non-turbulent)
conditions are important
– Weirs and baffles
Primary Clarification
• Differences between primary and final
clarifiers
– Primary clarifiers can receive larger hydraulic
loadings
– Primary clarifiers typically more shallow in
depth
– Primary sludge has more difficult pumping
requirements because it has higher percent
solids
– Reliability and redundancy of primary
clarifiers not so critical as with final clarifiers
Primary Clarification
• Solids and organics removal in
primary clarifiers
– 50% TSS removal
– 25% BOD removal
Primary Clarification
• Primary clarifiers
– Except at larger plants, not common given
desire to control cost
– Beneficial to the treatment process due to
buffering of influent loading and flow to
downstream secondary processes
– Can impact biological nutrient removal
processes because of the removal of BOD
In next lecture we will discuss mixing, coagulation, and flocculation
Thanks!