Environmental Engineering Reference
In-Depth Information
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It maximizes tank use.
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It allows a higher organic loading.
Note:
During the complete mix, activated sludge process organisms are
in the declining phase on the growth curve.
Pure oxygen
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Pure oxygen requires primary treatment.
It permits higher organic loading.
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Higher solids levels are required.
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It operates at higher
F/M ratios.
It uses covered tanks.
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The use of pure oxygen poses potential safety hazards.
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Oxygen production is expensive.
Contact stabilization
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Contact stabilization does not require primary treatment.
During operation, organisms collect
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organic matter (during contact).
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Solids and
activated sludge are separated from flow via settling.
Activated sludge and solids are aerated for 3 to 6 hr (stabilization).
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Note:
Return sludge is aerated before it is mixed with influent flow.
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The activated sludge oxidizes available organic matter.
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Although the process is complicated to control, it requires less
tank volume than other modifications and can be prefabricated as a
package
unit for flows of 0.05 to 1.0 million gallons per day (MGD).
A disadvantage is that common process control calculations do not
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provide usable information.
extended aeration
Extended aeration does not require primary treatment.
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It is frequently used for small flows such as schools and housing
subdivisions.
It uses 24-hour aeration.
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It produces the least amount of
waste activated sludge.
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The effluent is low in
BOD (the process is capable of achieving 95%
or greater removal of BOD).
The
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effluent is low in organic and ammonia nitrogen.
oxidation ditch
The
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oxidation ditch does not require primary treatment.
It is similar to the extended aeration process.
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