SKF 3413 POLLUTION CONTROL

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Primary Wastewater Treatment

Introduction

Primary treatment Initial phase of wastewater treatment

It uses physical treatment methods

Removes settleable or floating solids only Goal : 60% of suspended solids in raw sewage

35% of BOD5

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Primary treatment Initial phase of wastewater treatment

It uses physical treatment methods

Removes settleable or floating solids only Goal : 60% of suspended solids in raw sewage

35% of BOD5

Raw Sewage

Screening

Grit Removal

Pretreatment Primary Treatment

Scope

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Grit Removal

Equalization Basin

Primary Settling

Pump

Figure 1 : Degrees of treatment

WasteWater

Primary Treatment

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Screening Grit ChamberSedimentation tank

WasteWater

Physical Unit OperationTreatmentProcess

Physical Unit Operation Design

Screening Bar Racks i) Manualii) Mechanical

Fine Screen

Comminutors

Grit Removal Grit Chamber i) Velocity Controlledii) Aerated

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Grit Removal Grit Chamber i) Velocity Controlledii) Aerated

Equalization Flow equalization i) In-line equalizationii) Side-line equalization

Sedimentation(Solid-Liquidseparation)

Clarifier i) Circular Solid Contactii) Parallel Inclined Plateiii) Tube settlers

Flotation Dissolved-Air Flotation (DAF)

Definition:The process to remove large solids from the flow. unit operation that removes suspended matter from water.These may include natural and man-made trash (leaves,branches, roots, rocks, rags, and cans).

Purpose of screening:To remove gross pollutants from the waste water stream

Types of screening: Screens may be classified as course and fine screens,depending on the size of material removed

SCREENING PROCESS

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Definition:The process to remove large solids from the flow. unit operation that removes suspended matter from water.These may include natural and man-made trash (leaves,branches, roots, rocks, rags, and cans).

Purpose of screening:To remove gross pollutants from the waste water stream

Types of screening: Screens may be classified as course and fine screens,depending on the size of material removed

Physical Unit Operation

Bar Racks-Coarse Screening

2 types : Manual Racks , Mechanical Racks

Manual Racks Opening : 25mm 50 mm Channel Approach Velocity : 0.3-0.6 m/s

Mechanical RacksOpening : 5 40 mm Channel Approach Velocity: 0.6-1.2 m/s

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Bar Racks-Coarse Screening

2 types : Manual Racks , Mechanical Racks

Manual Racks Opening : 25mm 50 mm Channel Approach Velocity : 0.3-0.6 m/s

Mechanical RacksOpening : 5 40 mm Channel Approach Velocity: 0.6-1.2 m/s

Physical Unit Operation

Fine Screen

Used after the coarse screeningprocess Remove material that may createoperation and maintenance problems indownstream processes Consist of wedge-wire, perforated plateor closely a space bars with opening 1.5to 6.4 mmVelocity through the effective area : 0.4to 0.8 m/s.

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Fine Screen

Used after the coarse screeningprocess Remove material that may createoperation and maintenance problems indownstream processes Consist of wedge-wire, perforated plateor closely a space bars with opening 1.5to 6.4 mmVelocity through the effective area : 0.4to 0.8 m/s.

Physical Unit Operation

Comminutors

Break up wastewater solid byrevolving cutting bars

Placed downstream of grit chambers

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Comminutors

Break up wastewater solid byrevolving cutting bars

Placed downstream of grit chambers

Grit Chamber

Grit : Inert Dense material such as sand, broken glass

Purpose of Grit ChamberSlows down the flow to allow grit to fall out

Consists of 2 basic types : Velocity controlled Aerated

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Grit : Inert Dense material such as sand, broken glass

Purpose of Grit ChamberSlows down the flow to allow grit to fall out

Consists of 2 basic types : Velocity controlled Aerated

Physical Unit Operation

Velocity Controlled Grit Chambers(horizontal flow)

Classical laws of sedimentationfor discrete, nonflocculatingparticles. (Type 1 sedimentation)

Liquid velocity : 0.3 m/s

Liquid velocity controlled byspecially designed weir.

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Velocity Controlled Grit Chambers(horizontal flow)

Classical laws of sedimentationfor discrete, nonflocculatingparticles. (Type 1 sedimentation)

Liquid velocity : 0.3 m/s

Liquid velocity controlled byspecially designed weir.

Physical Unit OperationAerated Grit Chambers

useful for the rapid separation of these inertparticles.

Small, total volume based on 3-min retentionat maximum flow

Diffused air create the mixing pattern withthe heavy, inert particles removed bycentrifugal action and friction against thetank walls.

Floatable solids are removed in the aeratedgrit chamber.

The settled grit is normally removed with acontinuous screw and buried in a landfill.

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useful for the rapid separation of these inertparticles.

Small, total volume based on 3-min retentionat maximum flow

Diffused air create the mixing pattern withthe heavy, inert particles removed bycentrifugal action and friction against thetank walls.

Floatable solids are removed in the aeratedgrit chamber.

The settled grit is normally removed with acontinuous screw and buried in a landfill.

Equalization

Flow EqualizationIs used to overcome the operational problems caused by flow variations, toimprove the performance of the down stream processes and to reduce the sizeand cost of downstream treatment facilities

Is the damping of flowrate variations so that a constant or nearly constantflowrate is achieved

Achieved by constructing large basins that collect and store wastewater flowand from which waste water is pumped to treatment plant at a constant rate

2 layouts of equalization : In-line equalization (ILE) ; Side-line equalization(SLE)

Benefits biological treatment by providing steady flow and load

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Flow EqualizationIs used to overcome the operational problems caused by flow variations, toimprove the performance of the down stream processes and to reduce the sizeand cost of downstream treatment facilities

Is the damping of flowrate variations so that a constant or nearly constantflowrate is achieved

Achieved by constructing large basins that collect and store wastewater flowand from which waste water is pumped to treatment plant at a constant rate

2 layouts of equalization : In-line equalization (ILE) ; Side-line equalization(SLE)

Benefits biological treatment by providing steady flow and load

Rawwaste water

1 2 3PrimarySedimentation4

Screens Grit Removal

EqualizationFlow control

Figure 3 : In-line Equalization

Flow Diagrams

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Rawwaste water

1 2 3A

3B

PrimarySedimentation

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Figure 4 : Side-line Equalization

A B

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CD

Sedimentation Tank

Application: Removal of settleable solids Thickening of solids and biosolids

Process: Allowing large amounts of suspended solids to settle

at the bottom in the form of sludge Heavier solids settle by gravity Sludge are removed along with floating scum and

grease Remove 25 to 50% of BOD5 ; 50 to 70% of

suspended solids; 65% oil and grease

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Application: Removal of settleable solids Thickening of solids and biosolids

Process: Allowing large amounts of suspended solids to settle

at the bottom in the form of sludge Heavier solids settle by gravity Sludge are removed along with floating scum and

grease Remove 25 to 50% of BOD5 ; 50 to 70% of

suspended solids; 65% oil and grease

Physical Unit OperationA B

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C

D

Physical Unit Operation

Circular solid contact clarifierConfiguration:

Used in larger tanks than was previously thecase particularly when the sedimentation tankis covered to facilitate odor removal

Long sludge-holding times

Efficiently used in chemical flocculantsuspensions

Not suitable for biological suldges

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Circular solid contact clarifierConfiguration:

Used in larger tanks than was previously thecase particularly when the sedimentation tankis covered to facilitate odor removal

Long sludge-holding times

Efficiently used in chemical flocculantsuspensions

Not suitable for biological suldges

Physical Unit Operation

Parallel inclined Plate CircularClarifierConfiguration:

Large Surface AreaNo wind effectLaminar Flow

Drawbacks :Long periods of Sludge deposits cause septiccondition

Clogging of inner tube and channels

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Parallel inclined Plate CircularClarifierConfiguration:

Large Surface AreaNo wind effectLaminar Flow

Drawbacks :Long periods of Sludge deposits cause septiccondition

Clogging of inner tube and channels

Physical Unit Operation

Tube Settler RectangularClarifier

Operation principle:

Incoming flow enter tubes andflow upwardSolids settle inside the tubes andslide down into the hopper.

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Tube Settler RectangularClarifier

Operation principle:

Incoming flow enter tubes andflow upwardSolids settle inside the tubes andslide down into the hopper.

FlotationUnit operation used to separate solid or liquid particles from aliquid phase.

Advantage : Flotation vs Sedimentation>>very small or light particles that settle slowly can be removedmore completely and in a shorter time

Removal of finely divided suspended solids, particles withdensities close to that of water and also thickens biosolids.

Chemicals are commonly used to aid the flotation process wherethe function is to create a surface or a structure that can easilyabsorb or entrap air bubbles (i.e aluminium and ferric salts,activated silica)

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Unit operation used to separate solid or liquid particles from aliquid phase.

Advantage : Flotation vs Sedimentation>>very small or light particles that settle slowly can be removedmore completely and in a shorter time

Removal of finely divided suspended solids, particles withdensities close to that of water and also thickens biosolids.

Chemicals are commonly used to aid the flotation process wherethe function is to create a surface or a structure that can easilyabsorb or entrap air bubbles (i.e aluminium and ferric salts,activated silica)

Physical Unit Operation

Dissolved Air Flotation (DAF)

Operation Principle:

Dissolving air in the water or wastewaterunder pressure and then releasing the airat atmospheric pressure in a flotation tankor basin.

The released air forms tiny bubbles whichadhere to the suspended matter causingthe suspended matter to float to thesurface of the water where it may then beremoved by a skimming device

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Dissolved Air Flotation (DAF)

Operation Principle:

Dissolving air in the water or wastewaterunder pressure and then releasing the airat atmospheric pressure in a flotation tankor basin.

The released air forms tiny bubbles whichadhere to the suspended matter causingthe suspended matter to float to thesurface of the water where it may then beremoved by a skimming device

Conclusion

Primary treatment is generally understood as theset of operations performed to remove floatableand settling solids

Other benefits of primary settling includeequalization of side stream flows and removalof the biochemical oxygen demand (BOD)associated with settleable solids.

In primary treatment only physical operationssuch as screening, sedimentation and flotationare used.

Primary treatment is generally understood as theset of operations performed to remove floatableand settling solids

Other benefits of primary settling includeequalization of side stream flows and removalof the biochemical oxygen demand (BOD)associated with settleable solids.

In primary treatment only physical operationssuch as screening, sedimentation and flotationare used.