United Stales September
Environmental Protection 1986
Agency
Intrachannel
Clarification
An Update
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Intrachannel Clarification - An Update
Introduction
Intrachannel clarifiers have now been funded almost
seventy times through the construction grants program,
and twelve of these systems were operational as of
June 1986. The geographical distribution of these
facilities is shown in Table 1. The operational
experiences at these facilities have shown that while
construction, O&M, and energy savings can be
achieved using an intrachannel clarifier, problems may
also be experienced especially if proper design criteria
are not utilized. An evaluation of several of the
operating systems was conducted in early 1986. The
evaluation identified several advantages and common
problems which are highlighted herein. Many of the
systems were in start-up; thus, the problems reported
may not be typical of the long-term performance of the
systems.
The Process
The intrachannel clarifier originated as a modification of
the oxidation ditch process in which aeration and
clarification are conducted in the same basin. A
subsequent modification by several manufacturers was
to place the clarifier adjacent to the oxidation ditch
using common wall construction. Due to the unique
means of wastewater flow into and sludge return from
these common wall clarifiers, these systems are also
included in the assessment of intrachannel clarifiers.
The systems funded the most to date have been the
United Industries BOAT CLARIFIERS™ and the Armco
Environmental Enterprises-Burns and McDonnell
Treatment System (BMTS™).
The BOAT CLARIFIER™ is constructed of stainless
steel and requires little to no modification in design for
installation into a conventional oxidation ditch. The
clarifier is fabricated independent of the ditch structure
and can be placed directly into the channel.
Independent construction also allows for surface flow
around the unit which eliminates the possibility of
floating debris accumulating in the channel. The mixed
liquor enters through the stern of the BOAT™ where
quiescent conditions exist. As the wastewater flows
toward the bow of the BOAT'" the solids settle and
EPA
Region State
II New York
New Jersey
III Delaware
Maryland
Virginia
West Virginia
IV Alabama
Florida
Kentucky
Mississippi
South Carolina
Tennessee
V Illinois
Minnesota
Ohio
VI Arkansas
Louisiana
Oklahoma
Texas
VII Iowa
Kansas
Missouri
VIII South Dakota
IX Arizona
X Idaho
Total
Manufacturer
1
2
3
4
5
6
7
- Armco Environmental
Enterprises
- United Industries
- EIMCO
- Lakeside
Equipment Corp.
- Lightnin
- Innova-Tech
- Envirex
Manufacturer
1234567 Total
1 1
1
1
1
1 2
3 1
1 6
1 8
4121
3
1
2
2
2
7
1 2
12
2 2
2
2
2
5 2
2
1
1
38 46 2 1 2
Location
Kansas City, MO
Baton Rouge, LA
Salt Lake City, UT
Bartlett, IL
Rochester, NY
Valley Forge, PA
Waukesha. Wl
2 4
1 2
1
1
3
4
7
9
8
3
1
2
2
2
7
3
12
4
2
2
2
7
2
1
1
2 1 92
System
BMTS1"
(Burns & McDonnell
Treatment System)
BOAT CLARIFIER"
Carrousel
Intraclarifier
Sidewall Separator
Draft Tube Channel
Pumpless Integral
Clarifier
Side-Channel
Clarifier
Table 1. Location of Intrachannel Clarifier Systems in
Design, Construction or Operation.
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re-enter the ditch through sludge ports (Figure 1) The
clarified effluent then ftows over a weir m the bow and
is removed Irom the ditch Semi-concentrated solids
are wasted Irom (he stem of the BOAT"
>_
a Location of the BOAT in an Oxidation Ditch
• vje Hoped •
rS^Oge Return
'ON
b Details of the BOAT "
Figure 1 BOAT CLARlFIER'"
In the BMTS '. the clanfier is constructed as pan of the
ditch (Figure 2) The mixed liquor enters the clanfier
through baffles in the bottom of the dander As the
wastewater flows upward toward submerged orifice
launderers. solids settle back down through the baffles
and re-enter the ditch Solids wasting is accomplished
by wasting the mixed liquor from the ditch
Advantages
The advantages of intrachannel clanfiers can include
reduced construction and O&M costs and a reduction
in land area requirements Common wall construction
reduces concrete requirements Hydraulic head
differences and gravity are used to force wastewater
into the clanfier and return sludge back into the ditch
Pumping requirements are fhereoy reduced Control
over sludge return is eliminated, and sludge age ts
easily controlled by wasting mixed liquor from the ditch
or from the mtrachannel clanfier
Figure 2 BMTS" intracharwei Barrier
Start-up Operational Difficulties
As of March 1986, many of the systems listed n Table
1 had only recently begun operation The operational
problems reported may thus be more representative of
start-up problems rather than tang-term design
deficiencies At several systems, problems have been
encountered with obtaining adequate (low velocity in
the oxidation ditch Proper operation o» the danfier is
dependent upon adequate wastewater flow velocity
around the ditch Several faaktes have reported thai
inadequate velocity has caused solids settling in the
ditch, resulting in sludge bulking and excess scum
accumulation Changes m mixer design or mixing
systems have smce corrected velocity problems at
some facilities
nsuffoent aeration has also occurred n several
systems in general, aerator systems when have
performed well in conventional oxidation ditch systems
provide adequate aeration m mtracnanne* clanfier
systems
Structura'. prob'ems with submerged propeler mocers
have also occurred The ongmal support masts were
not strong enough to withstand the vexation of the
mixer and masi failure resulted The use of
masts has corrected this problem
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Undersizing of the sludge handling facilities is the final
common problem reported. Several systems are
experiencing difficulty in wasting sufficient solids to
keep the mixed liquor suspended solids (MLSS)
concentration and the sludge age at desirable levels.
The design of the solids dewatering and removal
facilities should take into account the consistency and
settleability of the sludge associated with the specific
intrachannel system being considered.
Design Keys
Based upon the operational problems discussed above,
it is important to provide:
• Adequate mixing and aeration capacity
• Scum removal systems where flow barriers occur
• Adequate sludge handling capacity
• Adequate structural support for the mixing and
aeration systems
In addition, one manufacturer recommends not using
an intrachannel clarifier if the peak-to-average flow ratio
exceeds 2.5. Finally before selecting or designing a
system, it is recommended that operating systems be
contacted.
Effluent Quality
When adequate flow velocity, aeration, and sludge
handling facilities are available, secondary effluent
quality is achieved. An effluent quality of 20 to 30 mg/L
of BOD and TSS is reasonable to expect. Better
effluent qualities have been attained at some systems;
however, sufficient data are not available to determine
if such treatment levels can be maintained
continuously.
References
A brief review of the systems currently available is
presented in the following references:
1, Intrachannel Clarification - State of the Art, by
John Zirschky. Presented at the Field Evaluations of
I/A Technologies, Technology Transfer Seminar
Available from EPA-OMPC.
2. U.S.EPA. 1983. Intrachannel Clarification - A Project
Assessment. DMPC-WH595; 401 M Street, SW;
Washington, DC 20460,2 page brochure.
3. Anon. 1986. Emerging Technologies with Roots in
the Past. Water Engineering and Management.
March, 1986. pp.28-31.
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Mention of trade names or commercial products does not constitute
endorsement
Prepared by Environmental Resources Management, Inc
For additional information on intrachannel clarifiers, the
manufacturers listed in Table 1 or EPA regional offices,
listed below, may be contacted.
EPA-OMP«WH-SM) EPA-WEHL («9|
401 M Shunt SW 26 Wnsl SI Clan Sireat
Washington DC 20460 Cincinnati. OH 45268
|3CZt382 736fr7369 (513)569-7931
EPA Region f EPA Region 6
John F Kennedy Fedeisl Baiting 1201 Elm Streel
Boston. MA 02203 Daias IK 75270
EPA R«glon 2 EPA Region 7
26 Federal Puza 726 Minnesota Avcnoo
New York. NY 10278 Kansas City KS 66101
EPA Roglon J EPA Roglon 8
641 ChWBW. Sb«ot 999 teih Stj«gt
Ph,iadftip*wi PA 19107 Denver CO B0202
EPA Region 4 EPA Hogton 9
345 Coixltand Si/cot. NE 21S Frenvxn Sl'egl
Ailantii. GA 30365 San Francisco, CA 9410S
EPA Xeglon 5 EPA Roglon 10
230 Sculh Oeaitnm Strmt 1200 Wi Avenue
Cheapo. 'L £0604 Soattle WA 98101
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