Secondary Treatment Configurations SOP Pretreatment Workshop August 2011

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Pretreatment components  Section objectives Describe various engineered systems that maintain high-rate aerobic digestion of organic compounds found in domestic wastewater Describe various engineered systems that maintain high-rate aerobic digestion of organic compounds found in domestic wastewater Provide an understanding of the typical issues associated with these components Provide an understanding of the typical issues associated with these components Describe basic operation and maintenance procedures required to keep these systems functional Describe basic operation and maintenance procedures required to keep these systems functional

Basic aerobic treatment environments  Saturated Suspended growth Suspended growth Fixed/attached growth Fixed/attached growth Integrated fixed/activated sludge (IFAS) Integrated fixed/activated sludge (IFAS)  Unsaturated Media filters Media filters Trickling filters Trickling filters

Saturated treatment  Suspended growth  Fixed/attached growth  Integrated fixed/activated sludge (IFAS)

Saturated aerobic units: Primary distinctions  Packaging  Flow of effluent  Aeration method  Biomass management

Suspended growth reactors  Activated sludge process  Biomass is thoroughly mixed with nutrients and biodegradable compounds  Organisms flocculate and form active mass of microbes - biological floc  Extended aeration to limit biomass wasting Endogenous respiration Endogenous respiration

Suspended Growth

Suspended growth

USEPA Manual, 1980 USEPA Manual, 1980

Sequencing Batch Reactor  Suspended growth treatment process  Utilize a single chamber for achieving aeration, clarification and anoxic conditions  Flow equalization chamber for dosing effluent into the treatment chamber

Sequencing batch reactors

Fixed/attached growth reactors  Fixed-film process  Inert medium is submerged in the aeration chamber  Effluent circulated through media and attached microbes  Colloidal and dissolved organics compounds absorbed by biological film  Extended aeration to limit biomass wasting  Food brought to bugs

Fixed-film reactors

Rotating Biological Contactor (RBC)

Membrane bioreactors Wikipedia

Flow schemes  Continuous inflow  Batch processes

Aeration  Air supply and delivery component  Distribution device  Venting device

Air supply delivery  Methods Aspirator/Aerator Aspirator/Aerator Compressor Compressor Blower Blower Free Air Free Air

Aerator/Aspirator

Aerator/Aspirator  Spinning shaft or impeller creates a vacuum (venturi)  Vacuum pulls air into the water

Compressor  Two distinct types of compressors Rotary Rotary Linear Linear  Both types fitted with filters  Relative to blowers: Greater pressure Greater pressure Lower air flow Lower air flow Rotary Linear

Blowers  Fitted with inlet screens/filters  Relative to compressors: Lower pressure Lower pressure Greater air flow Greater air flow

Air distribution device  Introduces air into the water  Includes any supply line(s)  Various methods

Aspirator/aerator  Shaft piping delivers the air supply  Distribution relative to pressure

Diffused air distribution Diffused air distribution  Compressor or blower delivers air  Mode of distribution is manufacturer specific Solid pipe Perforated pipe Holes Slots Porous material

Diffused air distribution Diffused air distribution Perforated Pipe

Diffused air distribution Diffused air distribution Porous ceramic diffuser

Diffused air distribution  Spargers small interconnected passageways inside a ceramic matrix small interconnected passageways inside a ceramic matrix

Oxygen transfer into solution  Small diameter bubbles More surface area per unit volume More surface area per unit volume Oxygen transfer takes place across interface between air and water Oxygen transfer takes place across interface between air and water

Point of injection  Usually near bottom of tank more time for oxygen to go into solution more time for oxygen to go into solution more hydrostatic pressure on bubble more hydrostatic pressure on bubble more mixing of contents more mixing of contents

“Free” air  Alternately rotates media through air space in top of unit and down into effluent in basin  Water accepts oxygen from air

Aeration and Mixing  Aeration system also encourages also encourages mixing mixing displacement of water as air is introduced causes turbulence displacement of water as air is introduced causes turbulence

Air supply operation  Continuous  Timed

Venting  Air entering system  Air must exit somewhere Unit Unit House vent House vent Biofilter Biofilter

Biomass management  Returning sludge to a previous point in treatment system  Keeps the biological processes working  At some point, accumulated solids will have to be removed

Passive sludge return system  Settled material automatically returns to the aeration chamber  No moving parts  Limited flexibility for including anoxic treatment process

Active sludge return system  Pump on bottom of settling chamber  Control panel with timer Timing of return Timing of return Volume returned Volume returned Location for returned material Location for returned material

Proprietary configurations  Modular units with complete configuration  Subcomponents installed in prefab tanks  Specific to proprietary products

Basic aerobic treatment environments  Saturated Suspended growth Suspended growth Fixed/attached growth Fixed/attached growth Integrated fixed/activated sludge (IFAS) Integrated fixed/activated sludge (IFAS)  Unsaturated Media filters Media filters Trickling filters Trickling filters

Unsaturated treatment  Media filters  Trickling filters

Media filters  A container or lined excavation containing a specific media through which wastewater flows  Treatment occurs in unsaturated conditions  Designed to follow primary treatment

Flow regimes for media filters  Single pass  Recirculating

Single-pass media filter NSFC

Recirculating media filter schematic

Typical configuration  24 – 36 inches of media  Methods of distribution Pressure distribution - most common Pressure distribution - most common Spray nozzlesSpray nozzles DriplinesDriplines Gravity Gravity

 Increasingly, timer-controlled dosing is being used  Usually lined to collect filtrate for external dispersal  May be configured to drain into rock pad beneath unit in certain soil/site conditions Typical configuration

 Single-pass: 1 – 2 gal / ft 2 /day  Multiple-pass filters: up to 5 gal / ft 2 /day  Increased loadings may be allowed for certain proprietary designs Typical hydraulic loading

 Single-pass filters: Historically - 4 times/day Historically - 4 times/day Current recommendations - as high as times/day Current recommendations - as high as times/day  Multiple-pass: times/day Dosing frequency

Treatment process  Wastewater applied in small doses  Percolates over media in thin film  Organisms on media contact wastewater  Air is maintained in media pores  Oxygen is transferred into the thin film and to organisms  Aeration typically passive

Treatment occurs by:  Filtration and trapping  Adsorption  Biological decomposition  Biochemical transformation Nitrification Nitrification Denitrification (especially if recirculated) Denitrification (especially if recirculated)

Types of media  Washed, graded sand  Gravel  Foam chips and cubes  Expanded polystyrene  Peat  Synthetic textile materials  Bottom ash from coal-fired plants  Crushed glass  Other

Sand and gravel filters  Single pass or recirculating mode  Sand/Gravel media specifications Must (generally) be processed to provide the right gradation Must (generally) be processed to provide the right gradation Screened for proper gradation Screened for proper gradation Washed Washed  Must be handled carefully after processing to maintain the specification and remain free of fines

Cutaway demo

Single pass sand filter with pump basin

Questions?