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ASSESSMENT OF DESIGN TRADEOFFS
WHEN USING
INTRACHANNEL CLARIFIERS
H
IS
Jon H. Bender
Wastewater Research Division
Water Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
0
Presented at:
Water Pollution Control Federation, 59th Annual
Conference, Los Angeles, California. October 6-9, 1986
WATER ENGINEERING RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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CORP Author
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Report
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! Stock Number
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j Assessment of design tradeoffs when using intrachannel clarifiers
j Bender, Jon H.
, Environmental Protection Agency, Cincinnati, OH. Water Engineering
Research Lab.
[ U.S. Environmental Protection Agency, Water Engineering Research
I Laboratory
1986
j EPA/6oo/J-87/286
j PB88-i8s2io
127885114
j Clarification; Sewage treatment; Activated sludge process; Oxidation
reduction reactions; Design; Operations; Aerators; Sludge; Maintenance;
1 Cost effectiveness; Reprints; Oxidation ditches; Trade offs
Subject Added
Ent
Collation
Holdings
Sewage—Purification— Filtration
j 23 p. : ill. ; 28 cm.
j LIBRARY CALL NUMBER
' EMAD EPA/6oo/ J-87/286
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INTRODUCTION
A conventional oxidation ditch system, shown in figure 1, is a type
of activated sludge process where the mixed liquor continuously circulates
around a channel used as the aeration basin. Achieving adequate perform-
ance from this system as with any activated sludge wastewater treatment
system requires the effective separation of the activated sludge from the
treated wastewater. After separation, the activated sludge must return
to the aeration basin. Secondary clarifiers, usually located adjacent to
the oxidation ditch, allow for the gravity separation of the solids.
These clarifiers then mechanically collect and remove the separated
sludge sending it to another system that pumps the sludge back to the
oxidation ditch.
Intrachannel clarifiers, also shown in figure 1, represent a rela-
tively new alternative to conventional secondary clarifiers for oxidation
ditch processes. These devices allow the solids/liquids separation and
sludge return to occur within- the aeration channel. This eliminates the
need for an external secondary clarifier, its associated equipment and a
sludge return system. Using intrachannel clarifiers, therefore, could
reduce the capital and operation costs over a conventional oxidation
ditch system.
Eight different manufacturers currently market intrachannel clari-
fiers, though others may have entered the market during preparation of
this paper. Each of these proprietary devices operates based upon a
different concept to achieve solids/liquids separation in the aeration
channel. Some may argue that all of these devices are not truly intra-
channel clarifiers. For this paper, however, the author has chosen to
include all of the devices in the market w'ithout making such distinctions.
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SLUDGE RETURN SYSTEM
INFLUENT
1
SECONDARY
CLARIFIER
OXIDATION DITCH
EFFLUENT
CONVENTIONAL OXIDATION DITCH SYSTEM
INFLUENT
OXIDATION DITCH
INTRACHANNEL
CLARIFIER
L
EFFLUENT
OXIDATION DITCH WITH
INTRACHANNEL CLARIFIER
Figure 1. Comparison of a Conventional Oxidation Ditch
System With One With an Intrachannel Clarifier.
-2-
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All of these devices, however, have not reached the same stage of
development. Some are operating in full-scale facilities, others are
included in facilities being designed or under construction, while others
are concepts with or without pilot testing. Currently, 80 municipal
wastewater treatment facilities throughout the United States are using or
will be using intrachannel clarifiers (1).
A complete independent assessment of all these intrachannel clari-
fiers or the process in general has not been completed. Data on the design,
performance capabilities, energy requirements and costs of these systems
have been collected only by the manufacturers for their respective devices.
These data show that intrachannel clarifiers are a valid concept and can
achieve acceptable levels of solids/liquids separation. Zirschky (1)
summarizes these data and indicates that one can expect an effluent of
20 or 30 mg/L of biochemical oxygen demand (BOD) and total suspended
solids (TSS). He also reports that these systems have produced higher
effluent qualities but does not believe that sufficient data are avail-
able to show that they can consistently achieve these levels.
This paper contains no new data on these systems and, therefore,
falls short of being the complete independent assessment needed. Instead
it presents the various intrachannel clarification concepts and discusses
the different tradeoffs a designer must consider in selecting any of
these devices.
Specific advantages claimed by the manufacturers, discussions of
their stage of development or other information that would possibly lead
a designer to choose one device over another have been purposely excluded
from this paper. The author believes that,-g^l'!,lltlii;.MWj^liUB»i3H6^ftetr:S:^
For any specific application, the designer may find any of the devices
-3-
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more appropriate. For this reason, this paper will discuss intrachannel
clarifiers in generic terms expecting that the designer will select the
best device for his or her particular application after discussions with the
different manufacturers.
DIFFERENT TYPES OF INTRACHANNEL CLARIFIERS
The following discussions present only the basic concepts of operation
for the different intrachannel clarification devices. Detailed design
information regarding structural requirements, scum handling, piping and
appurtenances will have to be obtained from the respective manufacturers.
Each device is presented below in alphabetical order by manufacturer's name.
Advanced Environmental Enterprises BMTS (2)
Figure 2 shows a schematic of the BMTS. AEE locates the dividing
wall of the aeration channel off-center making the aeration channel wider
on the side with the clarifier than on the side where aeration occurs.
The clarifier spans the entire width of the aeration channel with the end
walls forcing the circulating mixed liquor flow beneath it. Baffles form
the bottom of the clarifier. Spaces between the baffles allow the mixed
liquor displaced by the raw wastewater flow to enter the clarifier and
the separated sludge to return to the aeration channel. Submerged orifice
pipes collect the clarified effluent and remove it from the system.
EIMCO Process Equipment Co. Carrousel Intraclarifier (3)
Figure 3 shows a schematic of the EIMCO Carrousel Intraclarifer.
EIMCO uses its intrachannel clarifier in conjunction with its Carrousel
oxidation ditch system. The clarifier spans the entire width of one side
of the aeration channel. It uses a sloped solid floor as a bottom with
the circulating mixed liquor flow forced beneath it. Mixed liquor
displaced by the raw wastewater flow enters the front of the clarifier
through inlet control gates. Inlet baffles reduce the effects of turbu-
lence at the inlet on clarifier performance. Effluent launders located
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AERATION ZONE
EFFLUENT
UPSTREAM END WALL
SUBMERGED ORF1CE
DISCHARGE PIPES
DOWNSTREAM
END WALL
CLARIFIER
BOTTOM BAFFLES
AERATION
CHANNEL
Figure 2. Advanced Environmental Enterprises BMTS (2).
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AERATOR
EFFLUENT LAUNDERS
INLET
.BAFFLES
TRAVELING BRIDGE &
SCRAPER MECHANISM
INLET CONTROL GATES
TRAVELING BRIDGE AND SCRAPER
EFFLUENT
LAUNDER
AERATION
CHANNEL
CLARIF1ER FLOOR
SLUDGE
RETURN
PORT
Figure 3. EIMCO Process Equipment Co. ^Carrousel Intraclarifier (3),
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at the back of the clarifier collect and remove treated wastewater from
the system. Separated sludge returns to the aeration channel through
ports located at the side of the sloped bottom. A traveling bridge and
scraper mechanism provides positive sludge removal. If necessary, multiple
clarifiers are typically located adjacent to each other so that they can
use a common traveling bridge and scraper mechanism.
Envirex, Inc. Side-Channel Clarifier (4)
Figure 4 shows a schematic of the Side-Channel Clarifier that Envirex
markets along with their Vertical Loop Reactor system. A Vertical Loop
Reactor consists of a rectangular aeration basin with a horizontal divider
baffle that creates two compartments in the basin. Mixed liquor contin-
uously circulates similar to that in an oxidation ditch, but between the
upper and lower compartments of the aeration basin. Aeration consists of
diffusers in the bottom compartment and a mixer/aeration device that
circulates the mixed liquor. The Side-Channel Clarifiers are built into
the sides of the Vertical Loop Reactor. Mixed liquor displaced by the
wastewater flow enters the slots at the bottom of the clarifiers. Recir-
culation ports provide for separated sludge return to the aeration basin.
Clarified effluent is withdrawn at the top of the clarifier.
INNOVA-TECH, Inc. Pumpless Integral Clarifier (5)
Figure 5 shows a schematic of the Pumpless Integral Clarifier that
INNOVA-TECH markets along with its Total .Barrier oxidation ditch system.
The Total Barrier oxidation ditch uses a draft tube aeration system.
INNOVA-TECH markets two clarifier configurations; the in-channel and side-
channel. The in-channel configuration forms the barrier in the oxidation
ditch with an extended draft tube running underneath it. In the side-
channel configuration, the clarifier is located adjacent to the aeration
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AERATION/MIXER
DIFFUSERS
HORIZONTAL DIVIDER
BAFFLE
SIDE-CHANNEL CLARIF1ERS
EFFLUENT LAUNDER
HORIZONTAL DIVIDER
BAFFLE
i
RETURN SLUDGE PORTS
INLETS .
Figure 4. Envirex, Inc. Side-Channel Clarifier
in a Vertical Loop Reactor (4).
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EFFLUENT
LAUNDERS
TRAVELING BRIDGE
SLUDGE
RETURN SIPHON
BARRIER WALL
DRAFT TUBE
AERATOR
1N-CHANNEL
CONF1GURATJON
SIDE-CHANNEL
CONFIGURATION
EFFLUENT
LAUNDERS
TRAVELING BRIDGE
SLUDGE
RETURN SIPHON
BARRIER WALL
DRAFT TUBE
AERATOR
INLET
TRAVELING BRIDGE
SLUDGE RETURN SIPHON
/
DRAFT TUBE
AERATOR
EFFLUENT
LAUNDERS
Figure 5. INNOVA-TECH, Inc. Pumpless Integral Clarifier (5),
-9-
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channel and uses a standard draft tube aerator. Both configurations rely
on the draft tube aerator to create a head differential between the
clarifier and the aeration channel. This head differential permits a
traveling bridge sludge siphon mechanism to return separated sludge to the
aeration channel. Effluent launders collect and remove the treated
wastewater from the system.
Lakeside Equipment Corporation - Sidewall Separator (6)
Figure 6 shows a schematic of a Sidewall Separator which Lakeside
uses in conjunction with their oxidation ditch equipment. The divider
wall in the aeration channel is located off center. Each Sidewall
Separator projects out from the wall of the aeration channel and extends
its full depth. Most of the circulating mixed liquor flows between the
separators while a portion of it enters the inlet. Inside the separator
mixed liquor, displaced by the raw wastewater flow, moves through inclined
baffles. A submerged orifice pipe collects and removes the clarified
liquid. Separated sludge moves down through the baffles and is returned
to the mixed liquor flowing underneath the baffles before it flows out the
back end of the separator.
Mixing Equipment Company Lightnin Integral Clarifier (7)
Figure 7 shows a schematic of the Lightnin Integral Clarifier that
Mixing Equipment Company uses in conjunction with its barrier oxidation
ditch system and draft tube aerator. The clarifier is located adjacent
to the oxidation ditch. Mixed liquor displaced by the raw wastewater
flow enters the clarifier through inlet slots in the common wall between
the aeration channel and the clarifier. Once in the clarifier, the flow
encounters a "chimney baffle" intended to minimize short circuiting in the
clarifier. Effluent launders at the far Side of the clarifier collect
and remove treated wastewater from the system. Separated sludge returns
-10-
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AERATION ZONE
SIDEWALL SEPARATORS
SIDEWALL
SEPARATORS
EFFLUENT
SUBMERGED
ORF1CE
DISCHARGE
PIPE
BAFFLES
INLET
0
AERATION CHANNEL
Figure 6. Lakeside Equipment Corp. Sidewall Separator (6),
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CLARIF1ERS
CHANNEL
BARRIER
AERATION CHANNEL
.^DRAFT
//TUBE
AERATORS
^DUCTWORK
SUPPORT BEAMS
EFFLUENT
LAUNDER
UPPER
DUCTWORK
CHIMNEY
BAFFLE
SLUDGE SCRAPER
MECHANISM
LOWER
DUCTWORK
AERATION CHANNEL'
Figure 7. Mixing Equipment Co. Lightnin Integral Clarifier (7)
-12-
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to the aeration basin through bottom slots in the common wall. A sludge
scraper mechanism assists in positive sludge removal from the clarifier.
Structures called "ductwork", located at the inlet and sludge return
slots, protrude into the aeration channel.
SYDLO, Inc. Integral Clarifier/Oxidation Ditch System (8)
Figure 8 shows a schematic of the Integral Clarifier which SYDLO
incorporates into a standard oxidation ditch. The clarifier spans the
entire side of the oxidation ditch with standard tube settler modules
located across the entire width. Mixed liquor displaced by the influent
wastewater flow proceeds upward through the tube settler modules.
Clarified liquid is removed at the surface while separated sludge flows
downward through the tube settler modules returning to the mixed liquor
flowing beneath the clarifier. Aeration channel flow beneath the
clarifier is increased by the raised section on the floor of the aeration
channel.
United Industries Boat Clarifier (9)
Figure 9 shows a schematic of the Boat Clarifier that United Industries
uses in conjunction with standard oxidation ditch systems. The Boat
Clarifier is placed in one side of the aeration channel where the circulat-
ing mixed liquor flows around and underneath it. Mixed liquor, displaced
by the influent wastewater flow, enters at the downstream end or back of
the clarifier. Clarified effluent enters the front of the clarifier over
a weir before its removal from the system. Separated sludge returns to
the aeration channels through a large number of sludge return ports that
cover the entire bottom of the clarifier. Each port has its own separate
hopper. By design, the Boat Clarifier restricts the flow in the aeration
channel creating a head differential betwe'en the clarifier and aeration
channel that assists sludge removal through the ports.
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AERATION ZONE
EFFLUENT LAUNDERS
SETTLER MODULES
Figure 8. SYDLO, Inc. Integral Clarifier/Oxidation Ditch System (8),
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AERATION ZONE
BOAT CLAR1F1ER
AERATION CHANNEL
BOAT CLAR1F1ER
SLUDGE HOPPERS
INLET
T
WE1R
^* ^ ^-SLUDGE RETURN POR
Figure 9. United Industries Boat Clarifier (9).
-15-
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DESIGN TRADEOFFS WHEN CONSIDERING INTRACHANNEL CLARIFIERS
Elimination of the separate secondary clarifier and sludge return
system by using an intrachannel clarifier in an oxidation ditch at first
appears to offer many advantages. Using any of these devices, however,
has several implications relative to the design and operation of the
facility that the designer must consider. The following sections discuss
these various design tradeoffs.
Thickening Capabilities and Impact on Size of Sludge Handling Facilities
Conventional oxidation ditch systems with separate secondary clari-
fiers usually waste the required excess sludge from the underflow of the
secondary clarifier. A properly designed and operated secondary clarifier
will typically concentrate the separated sludge to 2-4 times the concentr-
ation of the mixed liquor depending on the recycle rate and operating
strategy.
Oxidation ditch systems with intrachannel clarifiers, however, must
waste sludge from either the aeration channel or the intrachannel clarifier.
Wasting mixed liquor directly from the aeration channel means that the
plant's sludge handling facilities will have to handle higher volumes of
a more diluted waste sludge than a conventional oxidation ditch system.
Some concentration of the sludge, however, may be possible within the
intrachannel clarifier depending on the particular configuration chosen.
This would lower the volume of sludge wasted.
When a wastewater treatment plant designer chooses an intrachannel
*
clarifier the anticipated waste sludge concentration from the system must
be estimated and its impact on the size of the plant's sludge handling
facilities considered. Any cost savings associated with the intrachannel
clarifier must be weighed against any increased sludge handling costs over
those of a conventional oxidation ditch plant.
-16-
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Wastewater treatment plant designers have numerous alternatives
available for sludge handling systems. They must select the most cost-
effective alternative based on the particular conditions at their plant.
Examining the impact of feed sludge concentration on each of these alter-
natives is definitely beyond the scope of this paper. The following
example shows the effect that wasting a thinner, sludge could have on the
size of the sludge handling system at a plant using an intrachannel
clarifier.
In this example the plant will use a gravity thickener for the waste
activated sludge, to concentrate the feed sludge to the sludge handling
facilities. Gravity thickeners are sized based on the minimum surface
area that meets both hydraulic surface leading and solids loading require
ments (10,11).
Figure 10 shows the impact of feed sludge concentrations on the
required thickener surface area for a hypothetical 18,900 m3/d (5.0 mgd)
treatment facility at the hydraulic and solids loading indicated (11).
The mass of sludge wasted would control the thickener solids loading and
this loading would not change with lower waste sludge concentrations.
Hydraulic loadings, however, increase with lower waste sludge concentra-
tions. In this analysis when the waste sludge concentration drops below
about 5000 mg/L, additional thickener size is required to meet the surface
hydraulic loading requirements.
Other sludge handling alternatives may be affected to a greater or
lesser degree by having to waste a more dilute sludge from a facility
with an intrachannel clarifier. Generalizations regarding appropriate
technologies for sludge handling or their cost-effectiveness for various
sizes of facilites using intrachannel clarifiers, however, can not be made.
-17-
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IMPACT OF WASTE SLUDGE CONCENTRATION ON REQUIRED THICKENER SURFACE AREA
CSJ
o
01
01
o
a
L
0)
01
u
•w-4
-C
200 r
150
100
50
\Area Based on Hydraulic Loading
vof 5870 L/m2. d (144 gpd/ft2)
Area Based on Solids Loading
of 30 kg/m2. d C6 Ib/ft2- d)
5000
10000
15000
20000
Waste Sludge Concentration Cmg/L)
Figure 10. Impact of Waste Sludge Concentration on Size of
Sludge Handling Facilities for Example Plant.
-18-
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Restriction of Aeration Channel Flow by Intrachannel Clarifiers
Conventional oxidation ditch systems are designed to maintain the
mixed liquor in the aeration basin at a velocity of 0.30 m/s (1.0 fps)
to prevent solids deposition. This value represents an industry standard
that has been used for decades in the design of oxidation ditch systems
(12). Aeration devices specially designed for these systems provide
sufficient energy to maintain this velocity and meet process oxygen
requirements.
To a certain degree, all intrachannel clarifiers restrict the circu-
lating flow of the mixed liquor in the aeration channel. The aeration
equipment must overcome these restrictions to maintain adequate velocities
throughout the aeration channel. Zirschky (1) reports that inadequate
aeration and mixing are the most predominant and significant problems of
the intrachannel clarification systems in operation.
Designers of systems using any of the intrachannel clarifiers must
make sure that the aeration device they provide adequately mixes and
aerates the oxidation ditch. The capability of the aeration device to
overcome the increased headl-oss in the channel because of the intra-
channel clarifier must also be considered.
Aeration Channel and Clarifier Maintenance
Conventional oxidation ditch systems with separate secondary clari-
fiers typically have multiple units with provisions that allow the plant
to continue treating wastewater with a unit out of service for maintenance.
For instance, in a plant with two aeration channels and two separate
secondary clarifiers, shutting down one of the aeration channels will
allow the two clarifiers to continue to operate at the same hydraulic and
solids loadings as before. The operational aeration channel, however,
will receive an increased hydraulic and organic loading which may affect
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its performance. Removing one of the clarifiers from service would not
affect aeration capacity, but the increased hydraulic and solids loading
to the operational clarifier may affect its performance.
When the same oxidation ditch plant, provided with two aeration
channels and intrachannel clarifiers, must remove either an aeration
channel or clarifier from service for maintenance, both processes must be
removed together. Neither of the processes, though potentially operational,
could work in conjunction with the others to provide additional treatment
capacity. Severe performance problems could exist during maintenance.
Designers must consider how the oxidation ditch facility using an
intrachannel clarifier will maintain adequate treatment performance when
either the aeration channel or clarifier must be taken out of service.
Ope ra t i on a 1 F1 ex i b i1i ty
One of the claimed advantages of using an intrachannel clarifier is
the elimination of the sludge return system. Elimination of the sludge
return system saves its capital cost and the need to operate and maintain
the system but also eliminates the capability to monitor or adjust return
sludge flows.
In a conventional oxidation ditch system the operations staff must
periodically monitor and adjust the. return sludge flows. When problems
with sludge settling characteristics begin to affect performance, one
strategy calls for reducing return sludge flows to lower the solids
loading to the clarifier (13). A second strategy temporarily treats the
return sludges chemically, to oxidize and remove the problem organisms
from the sludge.
None of the options would be available to an operator of a facility
with an intrachannel clarifier. At this time, however, there has not
«
been sufficient operational experience with these systems to determine
-20-
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whether giving up control of the return sludge will impact the long term
performance capabilities of these systems.
SUMMARY
Intrachannel clarifiers represent a relatively new alternative to
conventional separate secondary clarifiers for the oxidation ditch process
by providing solids/liquids separation and sludge return within the aera-
tion channel. Eight different manufacturers supply intrachannel clarifiers
each having a different principle of operation. Eighty different waste-
water treatment facilities throughout the United States are using or will
be using intrachannel clarifiers.
Intrachannel clarification appears to be a valid concept and units
have produced effluents that have met secondary treatment standards. At
this time, however, no one has completed an independent assessment of the
long term performance capabilities, energy requirements and costs of
these systems. Virtually all of the data on these systems has been
collected by tlfe manufacturers for their respective devices. This paper
has not provided any additional data on these systems.
Eliminating the conventional secondary clarifier, its associated
equipment, and the sludge return system may appear to automatically improve
the cost-effectiveness of oxidation ditch systems. Designers considering
using intrachannel clarifiers, however, must make sure that they evaluate
the impact of the anticipated waste sludge concentrations on the size of
the sludge handling facilities. They must also determine if the aeration
equipment can provide adequate amounts of oxygen and maintain adequate
channel velocities when used in conjunction with a particular intrachannel
clarifier. Other considerations include the ability to maintain treatment
during maintenance and the impact of losing return sludge control. Each of
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these factors may reduce the cost-effectiveness of oxidation ditch systems
using intrachannel clarifiers.
DISCLAIMER
"This paper has been reviewed in accordance with the U.S. Environmental
Protection Agency's peer and administrative review policies and approved for
presentation and publication."
REFERENCES
1. Zirschky, J.H., "Intrachannel Clarification, State of the Art."
Presented at the Field Evaluations of I/A Technologies, Seminar Series
U.S. Environmental Protection Agency, 1986.
2. Advanced Environmental Enterprises, 5400 East 60th Street, Kansas
City, MO 64130.
3. EIMCO Process Equipment Company, P.O. Box 300, Salt Lake City, UT 84110.
4. Envirex Inc., A Rexnord Company, 1901 S. Prarie. Ave., Waukesha, WI 53185,
5. INNOVA-TECH, Inc., P.O. Box 920, Valley Forge, PA 19481.
6. Lakeside Equipment Corporation, 1022 E. Devon Avenue, Bartlett, IL 60103,
7. Mixing Equipment Co., Inc., 135 Mt. Read Blvd., Rochester, NY 14603.
8. SYDLO, Inc., 578 Minette Circle, Mississauga, Ontario L5A 3B8.
9. United Industries, Inc., P.O. Box 3838, Baton Rouge, LA 70821.
10. Metcalf and Eddy, Inc., Wastewater Engineering: Treatment, Disposal,
Reuse, 2nd Edition. McGraw-Hill Book Company, 1979.
11. Process Design Manual: Sludge Treatment and Disposal. EPA 625/1-79-
011, U.S. Environmental Protection Agency, Cincinnati, OH, 1979.
12. Ettlich, W.F., A Comparison of Oxidation Ditch Plants to Competing
Processes for Secondary and Advanced Treatment of Municipal Wastes.
EPA-600/2-78-051, U.S. Environmental Protection Agency, Cincinnati,
OH, 1978.
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13. Handbook: Improving POTW Performance Using the Composite Correction
Program Approach. EPA-625/6-84-008, U.S. Environmental Protection
Agency, Cincinnati, OH, 1984.
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TECHNICAL REPORT DATA
(Please rtad Instructions on the reverse be/ore completing)
. REPORT NO.
2.
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
5. REPORT DATE
Assessment of Design Tradeoffs When Using
Intrachannel CUrifiers
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Oon H. Bender
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
U.S. EPA, WERL, WRD
26 West St. Clair Street
Cincinnati, Ohio 45268
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
Water Engineering Research Laboratory, Cin., OH
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
13. TYPE OF REPORT AND PERIOD COVERED
Journal Article
14. SPONSORING AGENCY CODE
EPA/600/14
IS. SUPPLEMENTARY NOTES
Presented at WPCF 59th Annual Conference, Los Angeles, CA, October 6-9, 1986.
Submitted to Journal Water Pollution Control Federation.
16. ABSTRACT
Intrachannel clarifiers replace secondary clarifiers in the oxidation ditch
process by providing solids/liquids separation and sludge return within the aeration
channel. Eight different manufacturers supply intrachannel clarifiers each having
a different principle of operation. Intrachannel clarification appears to be a
valid concept based on data collected by the manufacturers. Sufficient data are
not available for a complete assessment of the long term performance capabilities,
energy requirements and costs of these systems. This paper presents the principles
of operation for the eight different intrachannel clarifiers and discusses design
tradeoffs that facility designers must consider when selecting any of these devices.
17.
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18. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (Tins Report/
UNCLASSIFIED
21. NO. OF PAGES
20. SECURITY CLASS < Tilts pagei
UNCLASSIFIED
22. PRICE
EPA Farm 2220-1 (R«v. 4-77) PREVIOUS EDITION is OBSOLETE
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