AS Process Description (cont'd)
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• Primary feeders ⟶ bacteria
• Secondary feeders ⟶ protozoa, rotifers
• "Bug growth" in the mixed-liquor is usually
maintained in the declining or endogenous growth phase, for a variety of
reasons, including good settling properties of sludge.
• Continued "synthesis" of organics leads to a large buildup of microbial
mass; thus, "excess"
activated sludge must be "wasted" from the
system to maintain proper F/M ratio and growth
phase.
Combined Sewer Overflow (CSO)
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, During major storm events, combined volumes may exceed the capacity of
the treatment plant, requiring bypass directly to the receiving water
The primary effluent from the clarifier still contains:
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- ∼ 30-40% residual suspended organics from the raw sewage;
- high colloidal and dissolved organics, i.e., 60-70% of BOD in raw sewage;
- high concentrations of BOD and nutrients (N & P).
Unit operations of pre-treatment
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• Several devices are placed upstream of the primary treatment to provide
protection of the WWTP equipment; ensure proper operations of
downstream processes.
• These devices are classified as pre-treatment and they have little effect in
reducing BOD5
Primary Treatment
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Physical operations are used to remove the
floating and settleable solids
, Grit Chambers
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Long narrow tanks that are designed to slow down the flow so that grit will
settle out of the water.
Rectangular clarifiers
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For rectangular clarifiers, inboard box weirs are used to provide the
necessary weir length to meet the weir loading rate.
Thermophilic
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(heat-loving): 50 - 65 degC
Aerated grit chamber
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• Primary feeders ⟶ bacteria
• Secondary feeders ⟶ protozoa, rotifers
• "Bug growth" in the mixed-liquor is usually
maintained in the declining or endogenous growth phase, for a variety of
reasons, including good settling properties of sludge.
• Continued "synthesis" of organics leads to a large buildup of microbial
mass; thus, "excess"
activated sludge must be "wasted" from the
system to maintain proper F/M ratio and growth
phase.
Combined Sewer Overflow (CSO)
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, During major storm events, combined volumes may exceed the capacity of
the treatment plant, requiring bypass directly to the receiving water
The primary effluent from the clarifier still contains:
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- ∼ 30-40% residual suspended organics from the raw sewage;
- high colloidal and dissolved organics, i.e., 60-70% of BOD in raw sewage;
- high concentrations of BOD and nutrients (N & P).
Unit operations of pre-treatment
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• Several devices are placed upstream of the primary treatment to provide
protection of the WWTP equipment; ensure proper operations of
downstream processes.
• These devices are classified as pre-treatment and they have little effect in
reducing BOD5
Primary Treatment
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Physical operations are used to remove the
floating and settleable solids
, Grit Chambers
Give this one a try later!
Long narrow tanks that are designed to slow down the flow so that grit will
settle out of the water.
Rectangular clarifiers
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For rectangular clarifiers, inboard box weirs are used to provide the
necessary weir length to meet the weir loading rate.
Thermophilic
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(heat-loving): 50 - 65 degC
Aerated grit chamber
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