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Wastewater Treatment Basic Operations > Solids Handling > Flashcards

Solids Handling Flashcards

1
Q

Why do we handle solids?

A

To remove noxious raw solids from the waste stream

To remove excess biological solids from the process

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2
Q

What are the properties of primary sludge?

A

Course and fibrous
Much more dense than water
40-80% volatile organic matter

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3
Q

What are the properties of secondary sludge?

A

Less fibrous
More flocculant
Specific gravities close to water
75-80% volatile organic matter

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4
Q

What are the types of thickening?

A

Gravity
Flotation
Centrifugation
Filtration

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5
Q

What are the types of stabilization?

A

Digestion
Thermal
Chemical

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6
Q

What is stabilization?

A

Lowering the volatile organica and pathogens in sludge

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7
Q

What are the types of conditioning?

A

Chemical
Thermal
Elutriation (sludge rinsing)

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8
Q

What are the types of dewatering?

A

Filtration
Centrifugation
Drying beds

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9
Q

What are the types of volume reduction?

A

Drying
Incineration
Composting

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10
Q

What is the purpose of thickening?

A

Increase solids content from 0.5% to 4% or greater

To decrease the size of downstream equipment and the weight of solids being hauled offsite

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11
Q

What is gravity thickening?

A

Solids compaction by the overlying weight of settling solids

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12
Q

What is floatation thickening?

A

Solids driven to the surface by air bubbles where the overlying weight of solids compacts

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13
Q

What is mechanical thickening?

A

Free water is separated by gravity on a moving belt or by centrifugal force in a cetrifuge

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14
Q

What are the different types of gravity thickening?

A

Continuous loading

Non-Continuous loading

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15
Q

What is an appropriate ratio of WAS to primary sludge in a gravity thickener?

A

4:1 - 6:1

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16
Q

What is an appropriate blanket depth for a gravity thickener?

A

5-8 feet depending on equipment

17
Q

What is the solid retention time of a gravity thickener?

A

Primary sludge only: 1-2 days

Mixed sludge: 18-30 hours

18
Q

What is the appropriate air to solids ratio for dissolved air filtration?

A

0.02 : 0.04

19
Q

What are appropriate process control parameters for dissolved air filtration?

A 
Consistent feed rate
.4-1.0lb/ft2/hr
SVI of feed solids <200
Blanket thickness of 8-24”
Buoyancy of 1 ft3 of air = 0.075#

Wastewater Treatment Basic Operations (16 decks)

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