Secondary Treatment
Configurations
SOP Pretreatment Workshop
August 2011
NDWRCDP Disclaimer
This work was supported by the National Decentralized Water
Resources Capacity Development Project (NDWRCDP) with
funding provided by the U.S. Environmental Protection Agency
through a Cooperative Agreement (EPA No. CR827881-01-0)
with Washington University in St. Louis. These materials have
not been reviewed by the U.S. Environmental Protection
Agency. These materials have been reviewed by
representatives of the NDWRCDP. The contents
of these materials do not necessarily reflect the views and
policies of the NDWRCDP, Washington University, or the U.S.
Environmental Protection Agency, nor does the mention of trade
names or commercial products constitute their endorsement or
recommendation for use.
CIDWT/University Disclaimer
These materials are the collective effort of individuals from
academic, regulatory, and private sectors of the
onsite/decentralized wastewater industry. These materials have
been peer-reviewed and represent the current state of
knowledge/science in this field. They were developed through a
series of writing and review meetings with the goal of formulating
a consensus on the materials presented. These materials do not
necessarily reflect the views and policies of University of
Arkansas, and/or the Consortium of Institutes for Decentralized
Wastewater Treatment (CIDWT). The mention of trade names or
commercial products does not constitute an endorsement or
recommendation for use from these individuals or entities, nor
does it constitute criticism for similar ones not mentioned.
Pretreatment components
 Section



objectives
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
Describe basic operation and maintenance
procedures required to keep these systems
functional
Basic aerobic treatment
environments
 Saturated



Suspended growth
Fixed/attached growth
Integrated fixed/activated sludge (IFAS)
 Unsaturated


Media 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
Suspended Growth
Suspended growth
Suspended growth
Suspended growth
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
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
Compressor
Blower
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
Linear

Both types fitted with
filters
 Relative to blowers:


Rotary
Greater pressure
Lower air flow
Linear
Blowers

Fitted with inlet
screens/filters
 Relative to compressors:


Lower pressure
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

Compressor or
blower delivers air
 Mode of distribution
is manufacturer
specific


Solid pipe
Perforated pipe
• Holes
• Slots

Porous material
Diffused air distribution
Perforated Pipe
Diffused air distribution
Porous ceramic diffuser
Diffused air distribution

Spargers

small interconnected passageways inside a ceramic
matrix
Oxygen transfer into solution

Small diameter
bubbles


More surface area per
unit volume
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 hydrostatic
pressure on bubble
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
mixing

displacement of
water as air is
introduced causes
turbulence
Air supply operation
 Continuous
 Timed
Venting

Air entering system
Air must exit
somewhere




Unit
House vent
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
Volume returned
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
Fixed/attached growth
Integrated fixed/activated sludge (IFAS)
 Unsaturated


Media 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
Recirculating Media Filter
Filter
Drainage
From
House
Septic Tank
Final Effluent Tank
Recirculation Tank
To Soil
Effluent Filter
Float Valve
in Tank
Dosing Pump
Effluent Pump
Typical configuration
– 36 inches of media
 Methods of distribution
 24

Pressure distribution - most common
• Spray nozzles
• Driplines

Gravity
Typical configuration

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 hydraulic loading
1 – 2 gal / ft2 /day
 Multiple-pass filters: up to 5 gal / ft2 /day
 Increased loadings may be allowed for
certain proprietary designs
 Single-pass:
Dosing frequency
 Single-pass


filters:
Historically - 4 times/day
Current recommendations - as high as 12-24
times/day
 Multiple-pass:
12-72+ times/day
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
PRO CE SSE S A T W OR K
LI Q U I D W A S T E S
O R G A N IC S
A IR
M E D IA
B IO L O G IC A L
M ASS
P A T HO G E N S
E X CE SS
CE L L M A SS
E N D PR O D U C T S
B.O .D .
SS
N U TR IE N T S
Treatment occurs by:
 Filtration
and trapping
 Adsorption
 Biological decomposition
 Biochemical transformation


Nitrification
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
Screened for proper gradation
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?