REPORT ON ALTERNATIVE TECHNOLOGIES
POTENTIALLY APPLICABLE TO
BOSTON HARBOR WASTEWATER TREATMENT FACILITIES
TO REDUCE FACILITY SIZE
for the U.S. ENVIRONMENTAL PROTECTION AGENCY, REGION I
JUNE 1985
THIBAULT/BUBLY ASSOCIATES
Environmental Planners, Scientists and Engineers
235 Promenade Street, Providence, RI 02908
-------
REPORT ON ALTERNATIVE TECHNOLOGiES
POTENTiALLY APPLICABLE TO
BOSTON HARBOR WASTEWATER TREATMENT FACILITIES
TO REDUCE FACILITY SIZE
June, 1985
THIBAULT/BUBLY ASSOCiATES
Environmental Planners, Scientists and Engineers
235 Promenade Street
Providence, Rhode Island 02908
-------
TABLE OF CONTENTS
Page
SCOPE 1
FINDINGS 2
METHODOLOGY 6
RISKS OF INNOVATION 12
APPENDIX A: PRIMARY TREATMENT A - 1
APPENDIX B: SECONDARY TREATMENT B - 1
APPENDIX C: PURE OXYGEN/ACTIVATED SLUDGE (PURE 02) C -
APPENDIX D: ROTATING BIOLOGICAL CONTACTORS D - 1
APPENDIX E: POWDERED ACTIVATED CARBON/ACTIVATED SLUDGE E - 1
-------
LIST OF TABLES
Table 2:
Table 3:
Table 4:
Table 5:
Table 6:
Table A-I:
Table A-2:
Table B-i:
Table C-i:
Table C-2:
Table C-3:
Table C-4:
Table C-5:
Table C-6:
Table C-7:
Table C-a:
Table 0-1:
Table D-2:
Table 0-3:
Table E-l:
Table E-2:
Table E-3:
4
5
8
9
10
15
A-3
A-4
5-3
C-3
C-4
C-,
C-6
C-7
C-?
C-9
C -i D
D-5
0-7
0-9
E-6
E- 9
E-9
Table 1: Comparison of Space Requirements of Alternative Technologies
(in Acres)
Comparison of Costs of Alternative Technologies (in $1,000,000)
Applications of Microscreens
Applications of Pure Oxygen Systems
Applications of Powdered Activated Carbon Wastewater
Treatment System
Risks of Operational Failure and/or Adverse Environmental Impacts
Influent Wastewater Characterizations
Space and Power Requirements -- Primary Microscreens
Influent Characteristics
Design Parameter: Secondary Sedimentation Alternatives
for Use with Pure Oxygen Activated Sludge Systems
Space Requirements: Pure Oxygen Activated Sludge --
South System
Space Requirements: Pure Oxygen Activated Sludge --
North System
Space Requirements: Pure Oxygen Activated Sludge --
Combined Systems
Power Requirements: Pure Oxygen Activated Sludge
Space Requirement Summary: Pure Oxygen Activated Sludge
Pure Oxygen Process Design
Design Equation for Flotation
Aerated Biological Contactor Installation
ABC/Bioscreen System
Space and Energy Requirements: Rotating Biological Contactors
Space Requirements: Powdered Activated Carbon/Activated Sludge
PAC/AS System
PAC/AS System Design Criteria
-------
LIST OF FIGURES
b a t
FIgure 1: Pin Oxygen Proce. Flow Schematic C -3
FIg u re 2: TypIcal PAC/AS System E a 3
-------
REPORT ON ALTERNATIVE TECHNOLOGIES
POTENTiALLY APPLICABLE TO
BOSTON HARBOR WASTEWATER TREATMENT FACILITIES TO
REDUCE FACILITY SIZE
A. SCOPE
This report summarizes the findings of a study to facilitate the mitigation
of adverse environmental impacts of the various alternative wastewater
treatment facilities being considered for Boston Harbor by:
I. Identifying alternative treatment technologies that would require less
space than the technologies that had been hitherto considered.
2. Calculating, for use in subsequent site impact mitigation studies, the
facility sizes that would be required by these alternative technologies.
In general, alternatives considered were limited to those using off-the-
shelf technologies.
Report on Alternative Technologies - 1 2896f
-------
B. FINDlNc
The principal findings of the study included:
I. That there appear to be several independent technologies that could
each reduce the size of the facility by a significant amount (20% or
more).
2. That there are several combinations of alternative technologies that
could reduce the overall size of a secondary treatment plant by about
50%.
3. That the alternative technologies are not more costly, that the costs
of their more expensive equipment is more than offset by economies
inherent in smaller overall size including reductions in excavation,
foundations, concrete work, piping and sitework.
Specific facility substitutions that could be made include:
1. For primary treatment, microscreens in place of sedimentation for a
component space reduction from about 14 acres to about 2 acres.
2. For secondary treatment, in place of conventional aerated activated
sludge and conventional sedimentation:
a. pure oxygen activated sludge and tube settlers for a reduction
from about 36 acres to about 17 acres.
b. air driven rotating biological contactors and secondary
microscreens for a reduction from about 36 acres to about 15
acres.
c. activated sludge mixed with powdered activated carbon
combined with conventional sedimentation and carbon recovery
for an overall spatial reduction of about 16 acres.
Report on Alternative Technologies - 2 2896f
-------
Adding to each of these specific facility reductions, its concomitant
reductions in grading, roadways, buffer zones, etc., the total space savings
would be likely to be increased by a factor of two so that, if any one of
these technologies does prove to be applicable, the total facility size might
well be reduced by about 1/3.
And finally, note that the changes in environmental impacts that might
result from these reduced space requirements could be significant.
At any site, the smaller plant size would greatly enhance the feasibility of
roofing-over, or other wise covering, wastewater processing devices,
making complete odor, pathogen, VOC and noise control far easier to
achieve.
On Deer Island, the reduced plant would allow development of a consoli-
dated secondary treatment plant with better buffering toward Winthrop
and less adverse impact on the island itself.
On Long Island, the reduced plant would allow development of a full
consolidated secondary treatment plant with no need to disturb the Parade
Ground to the northeast, the wetlands to the southwest, the cemetery area,
or the edges of the bluffs.
Specific space requirements of the various alternative technologies (and of
the conventional activated sludge alternative) are listed in Table 1.
Estimated construction costs of the various alternatives are listed in
Table 2.
Report on Alternative Technologies - 3 2896f
-------
Table I COMPARISON OF SPACE REQUIREMENTS OF
ALTERNATIVE TECHNOLOGIES (in Acres)
Alternatives
1 2 3 4 5 6 7 8 9 Ta
Sed. Sed. Sed. MS MS MS MS Sed. MS Sed.
AS 02 PAC AS 02 PAC RBC - - - - RBC
Sed. TS Sed. Sed. TS Sed. MS - - - - MS
Primary
Solids
Removal 14 14 14 2 2 2 2 14 2 14
Aeration 12 4 25’ 12 4 25” II —— — II
Secondary
Solids
Removal 24 13 24 13 4 — — 4
Sludge
Processing” 7 4 2 7 4 2 6 2 2 6
Other 2112212121
Subtotal 64 42 48 52 30 36 30 23 Il 42
Grading,
Roadways,
Bu ffers,etc. 42 48 52 30 36 30 23 II 42
Total 128 84 96 104 60 72 60 46 22 84
M lternati ye I. Sedimen ta tion/Actj vated Sludge/Sedimentation
2. Sedimentation/Pure Oxygen/Tube Settlers
3. Sedimentation/Powdered Activated Carbon
4. Microscreen/Activated Sludge/Sedimentation
5. Microscreenf Pure Oxygen/Tube Settlers
6. M icroscreenfPowdered Activated Carbon
7. MicroscreenfRotating Biological Contactors/Microscreen
8. Sedimentation
9. Microscreen
10. Sedimentation/Rotating Biological Contactors/Microscreen
‘lncludes sedimentation and carbon regeneration.
“Includes thickening and digestion.
Report on Alternative Technologies - 4
-------
Table 2 COMP RlSON OF CONSTRUCTION COSTS OF
ALTER NATIVE TECHNOLOGIES (in $I 000,0OO)
Alternatives’
I 2 3 4 5 6 7 8 9 10
Sed. Sed. Sed. MS MS MS MS Sed. MS Sed.
AS 02 PAC AS 02 PAC RBC -- -- RBC
Sed. IS Sed. Sed. T5 Sed. MS — -- MS
Primary
Solids
Removal 58 58 58 17 17 17 17 58 17 58
Aeration 130 83 105 130 83 105 45 —— — 45
Secondary
Solids
Removal 212 75 212 212 73 212 53 —- — 53
Subtotal 400 216 375 359 175 334 115 58 17 156
Other 368 368 368 368 368 368 368 722 722 368
Total 768 584 743 727 543 702 483 780 739 524
‘Alternative 1. Sedimentation/Activated Sludge/Sedimentation
2. Sedimentation/Pure Oxygen/Tube Settlers
3. Sedimentation/Powdered Activated Carbon
4. MicroscreenlActivaled Sludge/Seth mentation
5. Mic roscreen/Pure Oxygen/Tube Settlers
6. M icroscreen/Powdered Activated Carbon
7. Microscreen/Rotating io1ogicaI ContactorsfMicroscreen
8. Sedimentation
9. Microscreen
10. Sedimentation/Rota ling Biological Contactors/Microscreen
Report on Alternative Technologies - 5 2896f
-------
C. METHODOLOGY
A study team was assembled for the specific task. It consisted of:
I. Robert F. Ferrari, P.E., Chief Engineer of Thibault & Associates, Inc.
2. Kris Keshavan, PE., Ph.D., Chairman of the Department of Civil
Engineering at Worcester Polytechnic Institute.
3. Fred Hart, P.E., Ph.D., Professor of Sanitary Engineering, Worcester
Polytechnic Institute.
The team reviewed the designs and assumptions used in the site location
study and in the 301(b) waiver application and examined the key space
requiring components of the conventional activated sludge technology to
identify possible alternatives that might significantly reduce the space
requirements of the facility.
Key findings at this stage were that: 1) sedimentation was the principal
space demanding component of the system, and 2) that there was a
possibility that simple sedimentation might not be consistently effective on
the harbor islands because of the high wind exposure at the sites and the
storm flow peaks characteristic of combined systems; these effects might
be particularly significant for secondary sedimentation.
The next step of the study was to identify alternatives that would reduce
the space required for solids removal. These alternatives fell into two
categories:
1. Direct alternatives to simple sedimentation, i.e., microscreening,
tube settlers, chemically assisted settling, etc.
Report on Alternative Technologies - 6 2896t
-------
2. Alternatives that would produce sludges that would settle more
rapidly than the sludge generated by the conventional activated
sludge process. These included pure oxygen/activated sludge and
powdered activated carbon/activated sludge.
These alternatives are briefly described below:
The microscreening alternative for solids removal appears to be generally
applicable to primary solids removal regardless of whether it is followed by
secondary treatment and regardless of the process used for secondary
treatment. It is well-suited to the irregular flows of combined sewers, is
insensitive to wind effects, and requires less space than simple sedimen-
tation.
Microscreening’s use for secondary solids removal is, however, limited to
fixed film secondary treatment processes (i.e., trickling filters, rotating
biological contactors, etc.) and as a backup for clarifiers used in waste
activated sludge systems since it is considered to be unacceptable for
processes that recirculate waste sludge.
Table 3 shows the range of applications of the microscreening equipment.
Note that the applications include both primary and secondary treatment
processes.
Report on Alternative Technologies - 7 2896f
-------
Table 3 APPLICTIONS OF MICROSCRrENS
Date of
Location Flow Description Operation
Primary Applications
Mann City, CA 10.0 MCD 2 @ 8’ dia x 6’ L; 60 mesh 1977
Kailua, HI 15.5 MCD 2 @ 10’ dia x 4’ L; 20 mesh 1978
Kaenohe, HI 15.5 MCD 2 @ 10’ dia x 4’ L; 20 mesh 1978
Superior, WI 6.5 MGD-CSO 2 @ 6’ dia x 8’ L; 50 mesh 1978
Golden, CO
(Coors Brewery) 10.0 MGD I @ 10’ dia x 10’ L; 30 mesh 1980
Lewiston, ID
(Potlatch Corp.) 43.2 MCD I @ ID’ dia x 16’ L; 20 mesh 1980
Secondary Applications
South Lyon, MI 2.0 MCD 2 @ 10’ dia x 14’ L; 21 micron 1981
Sherman, NY 0.5 MCD 2 @ 4’ dia x 4’ L; 21 micron 1981
Washington Court-
house, OH 2.2 MCD 4 10’ dia x 16’ L; 21 micron 1983
Lincoln City, OR 4.5 MCD 2 @ 10’ dia x 14’ L; 21 micron 1982
Ambler, PA 2.2 MCD 4 @ 20’ dia x 16’ 1; 21 micron 1982
Latrobe, PA 1.3 MCD 5 @ 10’ dia x I)’ L; 22 micron 1982
Medina, OH 2.0 MCD 2 @ 10’ dia x 16’ L; 22 micron 2980
Mountaintop, PA 2.5 MCD 3 @ 10’ dia x 16’ L; 21 micron 1981
Pleasant Unity, PA 1.5 MCD 2 @ 8’ dia x 8’ L; 74 micron 1981
West Westmoreland, PA 3.6 MCD 3 @ 10’ dia x 16’ L; 74 micron 1981
New Shoreham, RI 1.0 MCD I @ 8’ dia x 4’ L; 21 micron 1980
Mt. Olive, NC 2.5 MCD 2 @ 6’ dia x 8’ L; 21 micron 1980
Sparks, NV (water
treatment) 25.0 MCD I @ 10’ dia x 10’ L; 60 micron 1979
Harris County, TX 6.0 MGD I @ 10’ dia x 16’ L; 21 micron 1981
Harris, TX 27.0 MCD I @ 6’ dia x 4’ L; 21 micron 1981
Chnistianburg, VA 2.5 MCD 3 @ 8’ dia x 8’ L; 22 micron 1980
The tube settler alternative for solids removal has much more limited
applicability, i.e., it is believed suitable (in this case) only for the removal
of secondary solids following the pure oxygen/activated sludge process. In
this application, however, it is a substantial space saving alternative,
completely independent of microscreening, i.e., it represents an indepen-
dent second alternative to significant space savings, even if microscreens
are found to be unacceptable for reasons not yet identified.
The tube settler is a geometric variant of simple sedimentation achieving
the effect of a multi-level sedimentation system without the structural and
mechanical problems of a multi-level system. It reduces the space
Report on Alternative Technologies - 8
-------
required for secondary sedimentation by about 50% and is not sensitive to
wind induced disruptions.
The pure ox genfactivated siudge alternative was selected for preliminary
development in part because it permits use of tube settlers and in part
because it aflows significant space savings in the activated sludge process
itself. lts use has been limited, for the most part, to large systems where
land space has been a problem. it is more sophisticated than some other
processes but it has been widely applied. Table 4 shows some of its
applications.
Table 4 APPLICATIONS OF PURE OXYGEN SYSTEMS
Design Flow 02 Capacity 0 Supply
Location mgØ Ton s/day ixar system
Denver (/2, CO tO 7.5 MAROX LLQ
Detroit 0 1 , Ml 300 I SO NOX CRYO
Hollywood, FL 36 50 OASES CRYC
Newton creek, NY 20 14 UNOX PSA
Wayandotte, M i 100 60 UNOX PSA
Cedar Rapids, 1k 33 120 UNOX CRY O
Dade County, FL 60 100 OASES CRYO
Danville, VA 24 33 UNOX PSA
Denver, CO 72 80 UNOX CRYO
Detroit, Ml 600 450 OASES CRYO
Duluth, MN 43.6 80 UNOX CRYO
#1, Oakland, CA 120 250 UNOX CRYO
Harrisburg, PA 35.4 50 UNOX CRVO
Hopewell, VA 57.6 100 UNOX PSA
Louisville, KY 1 05 lO G UNOX CRYO
Miami, FL 55 80 UNOX CRYO
Middlesex, NJ 120 450 UNOX CRYO
Ne Orleans, LA 122 140 OASES CRYO
Pensacola, FL 24 40 OASES CRYO
Pliilade lphia,PA 2 10 90 UNOX CRYO
Pima County, AZ 25 22 UNOX PSA
Tona anda, NY 30 32 UNOX CRYO
‘ UNOX Union Carbide Corp. (covered’l
OASES Air Products & chemicals Inc. (covered)
MAROX r FMC Corp. (open)
CRYO r On-Site Cryogenic Oxygen Gas Generation
L IQ On-Site Liquid 02 Storage & vaporization
PSA On-Site Pressure Swing Absorption 02 Gac Generation
Report on Alternative Technologies - 9
-------
The powdered activated carbon/activated sludge alternative , like pure
oxygen/activated sludge, does allow for a significant reduction in the space
required for the activated sludge process itself, but it is not known to be
acceptable for use with tube settlers. However, it does generate sludge
that settles rapidly in a simple sedimentation tank, reducing that space
need, and, when used with a carbon recovery process, producing no
secondary sludge, saving space that would otherwise be used in several
sludge processing steps. Table 5 shows some of its applications.
Tablei APPLICATIONS OF POWDERED ACTIVATED CARBON
WASTEWATER TREATMENT SYSTEMS
WA Wet Air Regeneration
MH = Multiple Hearth Regeneration
WA Night soil/Organic removal
WA Night soil/Organic removal
MH Chemicals/Organic removal
WA Domestic, textile/Organic
removal
WA Night soil/Organic removal
‘J A Night soil/Organic removal
WA Domestic, textilelNitrifi—
cation
WA Domestic/Nitrification
WA Domestic/Nitrification
WA Night soil/Organic removal
WA Groundwater/Organic re-
moval
WA DomesticfNitrification
V. A Domestic/Nit ru ication
WA Domestic, industrial/Nun—
fication
WA Domestic/Reuse
WA Chemicals/Organic removal
W Domestic/Nitrification
Regeneration
Method
Waste/Treatment
Location
Design
Flow/mgd
Startup
Kimitsu, japan
Oga City, Japan
DuPont, Deepwater, N)
Vernon, CT, U5A
.13
.32
40.0
6.5
1975
1977
1977
1979
Senroku, Japan
Oizumi, )apan
E. Burlington, NC, USA
.37
.21
12.0
1979
1980
1981
Medina, OH, USA
Mt. Holly, NJ, USA
Ibaragi, Japan
ESC, Muskegon, Ml, USA
10.0
5.0
.4
1.5
1981
1982
1982
1983
S. Burlington, NC, USA
Bedford Heights, OH, USA
Kalamazoo, Ml, USA
9.5
3.1
53.5
1984
1984
1985
El Paso, TX, USA
Sauget, IL, USA
N. Olrnsied, OH, US
53.5
27.0
7.0
1985
1986
1986
Report on Alternative Technologies - 10
-------
And finally, to identify a fixed film secondary oxidation process that could
be used with secondary microscreening, preliminary calculations were
made for two alternatives, a packed media trickling filter and rotating
biological contactors. The trickling filter size required to meet secondary
effluent standards was too large to be useful, but the rotating contactors
appeared possible in a somewhat smaller space than would be required by
conventional activated sludge.
To determine the facility sizes that could be achieved by these techno-
logies, preliminary calculations were made of their major components.
These are appended.
Report on Alternative Technologies - I 1 2896f
-------
0. RISKS OF INNOVATION
The construction of any facility that is not EXACTLY like some other,
completely successful facility will, of necessity, contain an element of
risk. Indeed, the history of civil engineering is a litany of disaster, from
the Firth of Tyne Bridge to the windows of the John Hancock Building.
Every attempt to build larger, or better, or on a more difficult site poses
this risk. On every project, the engineers must find the appropriate point
between doing it better, making more efficient use of society’s limited
resources, and avoiding risk, building it stronger, larger, and more
conservatively.
Over the years, engineering technologies have improved, structurally,
chemically, mechanically, electrically, etc.; but progress has been slow.
Common sense usually argues for conservatism wherever the resources are
available, and progress is usually made only where goals cannot otherwise
be attained. Such cases become opportunities for benefiting from the
errors of the past. It can be done rationally, sorting through the experi-
ence of the past for the best elements that can be applied to the subject
problem, or it can be done by failing back to “the way it’s always been done
before,” avoiding exposure to criticism, and, possibly, throwing out the
most reliable systems, the least environmentally harmful systems, and the
least costly systems.
The key point is that the standard method, “the tried and true,” is not
necessarily the most reliable, or the most responsible environmentally, or
the least costly. In fact, with the non-domestic sewage loads on the
system, it is possible that conventional activated sludge coupled with
simple sedimentation may not be.
In comparing alternatives, prior to selecting (or discarding) any possibility,
the following questions should be evaluated:
Report on Alternative Technologies - 12 2896f
-------
On reliability:
a. How does the alternative handle storm peaks? What effect do
they have on the stability of the process? on the effectiveness
of the treatment?
b. Will slug loads of chemicals disrupt the treatment process? For
how long?
c. Will road salt, washed in following winter ice storms upset the
process? Kill, or stunt, the biota? Interfere with settling?
d. Will salt water inflow on very high tides interfere with settling?
e. Will winds, common to the shoreline, interfere with settling?
f. Does it require sophisticated operators? How much monitoring
is required for its operation and control? How many para-
meters? How often should they be measured? How many
adjustments have to be made to keep the process stable and
effective? How often do they require adjustment? Can the key
parameters be measured automatically? Can the adjustments
be made automatically? etc.
g. Are the components modular? i.e. can all parts be taken off line
(one or a few at a time) without impairing the effectiveness of
the balance of the system?
2. On environmental impacts:
a. How much land does the process require?
b. Does the process facilitate the emission of odor and/or noise to
the atmosphere?
Report on Alternative Technologies - 13 2896f
-------
c. Is the process suited to enclosure for odor and noise control?
d. How much excavation (and excavation related effects such as
noise, traffic and vibration) will the alternative require?
e. How much field construction (and field construction related
effects) will the alternative require?
f. Will effluent from the plant meet discharge standards in a
consistent manner?
g. Will the process absolutely intercept offensive, neutral
buoyancy personal plastic products?
3. On costs:
a. What will the initial construction cost be?
b. How much energy will be required?
c. How large a staff will be needed to operate the facility (to
adjust for variations in flow and effluent quality)?
d. How large a staff will be needed to maintain the facility?
Answers to these questions will require a detailed assessment of the state
of the art in each technology, a task beyond the scope of this report.
Table 6, however, does present a preliminary comparison of the conven-
tional activated sludge/sedimentation process with the RBC/microscreen
process.
Report on Alternative Technologies - 14 2896f
-------
Table 6 RiSKS OF OPER iTIONAL FAILURE
AND/OR ADVERSE ENVIRONMENTAL IMPACTS
Activated Sludge Rotating Contactors
With Sedimentation With Microscreeris
I. Storm Flows Washout of biota Physical destruction of
Poor sedimentation screens
2. Chemicals Fast, complete kill of biota Slow, gradual kill of biota
Slow recovery Quick recovery
3. Road Salt/High Loss of biota Little impact
Tides Poor sedimentation
Li. Winds Poor sedimentation No impact
5. Operator Sophisti- Careful monitoring Relatively simple
cation and control
6. Odor Control Large areas to contain Relatively small areas
to contain (can produce
extreme odors)
7. Land Use and Con-
struction Impacts Large plant Small plant
8. Plastics Removal Requires effective pre- Absolute (should be removed
treatment in preliminary processing)
9. Effluent Quality Variable Unknown
ID. Mechanical Relia- Well developed Poor (new technology with
bility limited debugging)
II. History Extensive Limited
Report on Alternative Technologies - 15
-------
APPENDiX A
PRIMARY TREATMENT
Two alternatives to conventional primary clarification were considered.
- High rate microscreens
- Chemically assisted primary clarification
The microscreens were found to be an attractive alternative to conven-
tional sedimentation for the subject applications; chemically assisted
primary clarification was not.
Microscreening is a physical straining process used for separation of solids
from a liquid suspension by passage of the liquid through a porous
membrane, e.g., the screening or filtering medium. Separation occurs
through the retention of solids, either by direct capture on the screening
medium or by indirect capture on the “biomat” formed on the screening
medium from the previous capture of solids.
A microscreen consists of a screening medium attached to the periphery
of a rotating horizontal drum. Flow enters through the open inlet of the
rotating drum and is forced radially through the screen by the differential
static head inside and outside the drum. Solids are temporarily retained
on the screen, for removal at the top of the drum’s rotation by spray
water from nozzles located above the rotating drum. Typically, the
backwash spray operates constantly, generating a continuously renewed
screening medium. Screened solids wash into a backwash trough, located
inside the screening drum, and are discharged to solids handling processes.
Factors affecting the hydraulic capacity of a microscreen include the
concentration and type of solids applied, degree of mineral precipitation
in process streams, size of media aperture openings, effectiveness of the
backwash system, available hydraulic gradient across microscreen, and
Primary Treatment - I 2 93f A -
-------
the net efficiency or net effectiveness of a screen media mounting
design. All of the aforementioned factors must be considered in the
selection of the proper media size and in the determination of the
quantity and size of units required. The design analysis shou ld also
include consideration of the desired reduction in waste constituents, the
waste backwash concentration, and what if any provisions will be needed
to control slime and mineral deposition.
Microscreens are typically designed to hydraulic loading criteria that have
been established for various applications. Hydraulic loadings are defined
in terms of fprn/ft 2 net effective submerged surface area (or the
instantaneous submerged fabric area; this negates any areas related to the
drum frame or media supports which are impervious to flow). The
hydraulic loading criteria are based on the influent suspended solids
loading, nature of solids, selected media size, and available hydraulic
gradient across microscreen. Operational parameters that impact
rnicroscreen hydraulic capadty are drum speed, backwash application
rate, and operating headloss range. 11 biological slime or mineral deposits
are expected to occur then a routine for scheduling cleansing should also
be developed. Generally, I to 5 percent of the feed flow will be used for
backwashing. The exact percentage is dependent on the specific
application.
In general, microscreens are well suited to applications with high
peak-to-average flow variation. Important features of the microscreen
process are:
- simple operation
- low energy requirements
- low installation cost
- reliable effluent quality
- modularity
- ease of maintenance
Primary Treatment — 2 2893f A — 2
-------
A range of pilot and full scale application studies indicate that micro-
screens applied for primary treatment can achieve a consistent 60% total
suspended solids removal and up to 40% BOD 5 removal from this influent
waste stream.
To test the input of microscreens on facility size, several preliminary
design studies were made. These studies assumed that the full wet
weather discharge would undergo complete treatment, using reasonabIe”
assumptions regarding net effective screening area, screen materials,
mesh size (maximum 60 mesh), headloss across the screen and backwash
f lowra te.
The options considered were:
Option 1. A separate facility for the South System.
Option 2. A separate facility for the North System.
Option 3. A combined facility to treat all wastewater.
The influent waste characteristics for each of the options are indicated in
Table A-I.
Table A-I INFLUENT WASTEW TER CI-IARACTERIZATION
Influent South System North System Combined
Design Flow I S O mgd 353 mgd 500 mgd
Peak Flow 310 mgd 930 mgd 1240 mgd
Design/Peak Ratio 2.06/1.0 2.6511.0 2. 1 4/ 1 .0
OD 5 150 mg/I 165 mg/I 161 mg/I
TS S 200 mg/I 165 mg/I 176 mg/i
A-3
-------
Table A-2 summarizes space and power requirements for each of the
options.
Table A-2 SPACE AND POWER REQUIREMENTS
PRIMARY MICROSCREENS
Option I
South System
Equipment
23 units @ 12 ft dia. x 16 ft L
Effluent Quality:
BOO 5 : 98 mg/I @ 35% removal
TSS: 80 mgI! @ 60% removal
Power Requirement: 150 hp
Area required for primary microscreens: (including all facilities) 11,900 ft 2
(0.3 acres)
Option 2
North System
Equipment
100 units @ 12 ft dia. x 16 ft I
Area required for primary microscreens: 117,500 ft 2 (1.10 acres)
Effluent Quality
BOO ,: 108 mg/I @ 35% removal
TS5: 66 mg I @ 60% removal
Power Requirement: 600 hp
Option 3
Combined Treatment Facility
Eq ipment
125 units @ 12 ft dia. 16 ft 1
Effluent Quality:
BOD 5 : 105 mg/I @ 33% removal
TSS: 70 mg/I @ 60% removal
Power Requirements: 7% hp
Area required for primary microscreens: 59,400 ft 2 (1.4 acres)
A-4
-------
APPENDIX B
SECONDARY TREATMENT
In evaluating alternative secondary treatment processes the following
factors were given at least genera! consideration:
- spatial requirements
- overall process complexity and level of operator skill
- ability to treat the incoming waste stream and handle hydraulic,
organic and possible toxic shock loads
- cost of capital equipment
- long term operating and maintenance costs
- interrelation with existing facilities
A number of secondary treatment processes were given initial consider-
ation but these were culled down to the three most attractive alternatives
for in-depth study. These included:
I. Pure Oxygen Activated Sludge for use with tube settlers
2. Rotating Biological Contactors for use with secondary
microscreening
3. Powdered Activated Carbon/Activated Sludge
At an intermediate level, the review also included some quantitative
analysis of packed tower trickling filters, deep shaft biological reactors
and several variations of the conventional activated sludge process. All
of these were found, for one reason or another, to be less attractive and
they were not explored further.
Note that each of the three alternatives selected for in-depth study has a
number of closely related primary and secondary clarification consider-
ations as well as a specific impact upon sludge thickening, treatment and
disposal requirements. For this reason each of the secondary treatment
Secondary Treatrrient - I B -
-------
processes is presented along with related processes for other necessary
facilities.
The basic secondary treatment processes of each of the three alternatives
all have extensive, full scale general operating experience, but not
necessarily in combination with the solids removal technologies proposal.
As a result, it must be recognized that all these combinations would
require extensive field pilot scale testing before their application.
In determining the spatial and other requirements of the three alter-
natives, the same influent characterization was used for each. This
characterization, as detailed in Table B-I, is essentially the same as that
used in previous studies of the Deer Island/Nut Island system.
Table B-i INFLIJENT CHARACTERISTICS
Raw Plant Iniluent Nut Island Deer island Combined
Design Flow 150 MCD 350 MCD 500 MCD
Peak Flow 310 MCD 930 MCD 1240 MCD
Peak/Design Ratio 2.06/1.0 2.65/1.0 2.48/1.0
SODs i5 1 mg/i 165 mg/I 161 mg/I
TSS 200 mg/I 165 mg/i 176 mg/i
Primary Effluent to
Secondary Treatment
SOD 5 (35% removal) 98 mg/I 108 mg/i 105 mg/I
T53 (60% removal) 80 mg/i 66 mg/I 70 mg/I
B-2
-------
APPENDIX C
PURE OXYGEN/ACTIVATED SLUDGE (PURE 02)
I. Introduction
In recent years, pure oxygen/activated sludge systems have become more
common in locations where land availability for the construction of
conventional air-activated sludge systems is severely limited. The
reported advantages of the pure-0 2 system include:
I. Smaller sized based on:
Capability of operating at higher MLVSS, typically 5000
mg/i to 8000 mg/i. This is possible because much higher
dissolved oxygen concentrations in the mixed liquor can be
maintained in such reactors as compared to air-activated
sludge systems.
Higher food-to-microorganism ratio (F/M) can be
maintained as compared to conventional activated sludge
systems. Typical values vary from 0. i to 1.0 pound of
BOD 5 per pound of MLVSS.
Lower detention time for the reactor, I to 3 hours
Much higher BOD loadings per unit volume of reactor can
be handled, 150 to 225 lbs. BOD per day per 1000 ft 3
2. Better settling sludge with good thickening characteristics
3. Lower net sludge production per unit of BOD removed
4. Higher 02 transfer per unit horsepower
5. More stable treatment
6. Capability to meet higher oxygen demands
To test the suitability of pure-oxygen activated sludge to the subject
problem, preliminary designs for such systems were developed for the
following options:
Pure Oxygen/Activated Sludge - C -
-------
OPTION I: A separate plant f or the South System
OPTION 2: A separate plant for the North System
OPTION 3: A combined plant for flows from both plants.
2. Pure-Oxygen Reactor Design
The pure-0 2 activated sludge reactors were designed as continuous-flow
complete mix reactors. The flow pattern, the equations governing the
design and assumed values of the biological and other constants are given
in Appendix A. It should be emphasized that actual design values should
be obtained after making laboratory and pilot plant studies for the waste
flows at Deer Island and Nut Island.
Assuming that high efficiency “Rotating Active Diffusers” (RAD) will be
used in the reactor, an 02 transfer efficiency of 90% can be used. An
additional 25% of 02 production capacity is recommended for the oxygen
generators in case there is nitrification in the reactors and also for other
possible unforeseen higher 02 demands. Also, a liquid oxygen storage
facility should be provided in case there is a breakdown of oxygen
generators. For example, at the Detroit Plant No. 1, a storage facility
with a capacity equal to 5 days of 02 requirement is provided. It is
recommended that a similar capacity of liquid °2 storage facility be
provided at these plants also.
3. Secondary Settling Tanks
As an alternative to conventional settling tanks, inclined tube settling
tanks were considered in this study. Table C-i describes the two
methods. Inclined tube settlers have been successfully used for activated
sludge plants, with overflow rates as high as 4,000 gpd/ft 2 based on the
tube covered area have been used, which is nearly 5 times that of the
conventional types. The problem of slime build up inside the tubes has
been overcome by installing a permanent air grid under the tube modules
to periodically air—scrub and clean the tubes. The frequency of cleaning
Pure Oxygen/Activated Sludge - 2 C - 2
-------
would range from one week to several months. The tube covered area of
the settling tank varies from 67 to 80 percent of the total tank area.
Inclination of the tubes would vary from 45° to 60° to the horizontal.
Table C-I DESIGN PARAMETERS SECONDARY SEDIMENTATION ALTERNATIVES
FOR USE WITH PURE OXYGEN ACTIVATED SLUDGE SYSTEMS
A. Conventional Settling Tanks
Overflow rates based on average flow without including recirculation: 600 gpd ft 2
Overflow rate based on peak flow without including recirculation 1200 gpd/ft
Solids loading at average flow 3 lb/ft 2 /day
Depth of water in settling tank = 12’
Width of settling tank = go’
Maximum horizontal velocity at peak flow = 100 ft/hr.
B. Inclined Tube Settlers
Depth: 12’
Width = 40’
Tube Covered Area = 70% of total tank area
Overflow rate based on Qav + - Q’ applied to covered area of tank = 2000 gpd/ft 2
4. Air Flotation to Thicken Activated Sludge
To thicken excess activated sludge pressure air-flotation units were
assumed. Pressure flotation has been extensively used for this purpose
with good results. Typically, 4% to 6% float solids concentrations can be
obtained with a recovery in the range of 90% to 99%. The subnatant of
the flotation unit can be returned to the primary tank without significant
adverse effect on its efficiency.
En this preliminary design, typical design parameters were used. in actual
design, these values should be determined by running laboratory tests
using a bench scale flotation cell, in conjunction with the p Iot plant study
of the pure oxygen activated sludge system. The use of polyelectrolytes
would substantially increase the solids loading capacity of the flotation
units and it is recommended they be used. In this design, waste activated
sludge drawn directly from the reactor would be thickened.
Pure Oxygen/Activated Sludge - 3 C - 3
-------
Solids loading rate with polyelectrolytes would be 30 lb/ft 2 /day.
Standard flotation units of 16’ width and 70’ length would be used in these
plants.
Table C-2 SPACE REQUIREMENTS
PURE OXYGEN ACTIVAJED SLUDGE
OPTION I SOUTH SYSTEM
Pure-oxygen Reactors
0, nominal detention time 1.02 hours
Number of reactors, 120w x 185’l x 20’d 2
Volume of reactors = 880,000 ft 3 6.64 x i06 gal.
Area of reactors = 44,000 ft 2 : 1.02 acres
%taste sludge produced = 31.8 tons/day as TSS
Volumetric BOD loading = 169 lb BOD5/l000 ft 3
Okygen Requirement = 79 Tons/day including 25% reserve
Oxygen Storage Capacity = 5 x 79 = 395 Tons
- Vol. flow rate of waste activated - 0 41 m d
- sludge withdrawn from setthng tanks -
Q’ Vol. flow rate of waste activated
w . = 1.22 mgd
sludge withdrawn from reactors
Secondary Settling Tanks
Conventional Tanks:
Peak OR 1200 gpd/ft 2 18 tanks (80’ x 182’ x 12’) 6.02 acres
@ 35 lb solids/ft 2 /day 18 tanks (80’ x 240’ x 12’) = 7.93 acres
Tube Settlers:
@ OR = 2000 gpd/ft 2 for Qav Qr 36 tanks (40’ x 116’ x 12’)
= 3.83 acres
Pressure Air-Flotation Units
Q’ . * R 3.226 mgd
Number of units (l6’w x 7O’l) 2
Surface Loading 1458 gpd/ft 2
Area required: 2,500 ft’ = (0.1 acres)
Overall BOD 5 Removal Efficiency r 72%
Soluble BOD Removal Efficiency 90%
C-4
-------
Table C- ) SPACE REQUIREMENTS
PURE OXYGEN ACTIVATED SLUDGE
OPTION 2 NORTH SYSTEM
Pure-oxygen Reactors
Number of Reactors (120’w x 183’I x 2O’d) = 6
0, Nominal Hydraulic Detention Time based on Qav 1.31 hours
Q’, True Detention Time based on Qay + Qr: 0.87 hours
V Volume of Reactors = 19.93 million gallons
= 2,665,000 ft 3
Area of Reactors I 33,200 ft 2 3.06 acres
Waste Sludge Produced 81.3 Tonsiday as TSS
Volumetric SOD Loading 141 lb BOD /l000 ft 3 for 6 reactors
Oxygen Storage Capacity 3 x 204 = 1020 Tons
Q - Vol. fLow rate of waste activated - 0 04 m d
- sludge withdrawn from settling tanks - g
- Vol. flow rate of waste activated - 3 12 m d
- sludge withdrawn from reactors - g
Secondary Settlin& Tanks
Conventioral Tanks:
Peak OR= l2 1 0gpd/ft 2 =54tanks{S0’x lI0’x l2 t d)= 1723 acres
0 35 lb solidsfft /day = 54 tanks (20’ x 190’ x 12’) = 18.84 acres
Tube Settlers:
@ OR = 2000 gpd/ft 2 for Qav • Or a 108 tanks (40’ x 90’ x 12’)
= 8.93 acres
Pressure Air-Flotation Units
• R 8.36 mgd
Number of units ( 16’w x 70’I) = 6
Surface Loading a 1244 fPdIft 2
Area required: 6,800 ft 0.2 acres
Overall SOD 5 Removal Efficiency = 73%
Soluble BOO Removal Efficiency 91%
C-5
-------
Table C-4 SPACE REQUIREMENTS
PURE OXYGEN ACTIV;TED SLUDGE
OPTION 3 COMBINED SYSTEMS
Pure-oxygen Reactors
Number of Reactors (120’w x 185’l x 20’d) S
0, Nominal Detention Tine : 1.22 hours
Volume of Reactors 3,552,000 ft 3 : 26.56 x to6 gal
Area of Reactors: 177,600 It 2 : 4.08 acres
Waste Sludge Produced : 113 Tons/day as TSS
Volumetric BOD Loading: 148 lb 600 ,11000 ft 3
Oxygen Requirement 283 Tons/day including 25% Reserve
Oxygen Storage Capacity: S x 283: 1415 Tons
Vo l. flow rate of waste sludge - 45 mgd
withdrawn from settling tanks —
- Vol. flow rate of waste sludge - 4 34 m d
- withdrawn from reactors — g
Secondary Set l lanR Tanks
Conventional Tanks:
Peak OR : 1200 gpd/ft 2 : 72 tanks (80’ x 380’ x 12’d) s 23.8 acres
@ 35 lb solids/1t 2 /day : 72 tanks (80’ x 202’ x 12’) : 26.71 acres
Tube Settlers1
@ OR : 2000 gpd/ft 2 for Qav + Qr : 144 tanks (40’ x IOU’ x 12’)
33.22 acres
Pressure Air—Flotation Units
‘w’ 1t 11.62 mgd
Number of units (16’w x 70’l) : S
Surface Loading : 1300 pd/ft 2
Area required: 9,000 ft : 0.2 acres
Overall SOD 5 Removal Efficiency : 72%
So iuble SOD Removal Efficiency = 90%
C-6
-------
Table C-i POWER REQUIREMENT5
PURE OXYGEN ACTIVATED SLUDGE
South North Combined
System System System
Primary Microscreens I SO hp 750 tip 900 hp
eration Tanks 2250 tip (4500 tip 6750 hp
Secondary Clarifiers 18 hp 54 hp 72 tip
Gravity Thickeners 60 tip J80 hp i SO tip
Daft Units 80 tip 240 tip 640 hp
Dtnaerobic Digestion Gas Mixing 50 tip 120 tip ISO hp
TOTAL 2608 hp 5844 hp 8642 hp
Energy Recovery
Digester Gas
(31 Tonsof Sludge/Day) C 900 tip) ( 2250 tip) ( 3200hp )
Net Energy Requirement 1708 hp 3594 tip 5492 hp
Table C -6 SPACE REQUIREMENT SUMMARY
PURE OXYGEN ACTIVATED SLUDGE
South North Combined
System System System
Primary Microscreens .3 A 1.1 A 1.4 A
02 Reactors 1.1 A 3.2 A 4.3 A
Tube Settlers 3.8 A 8.9 A 13.2 A
Flotation Thickeners .1 A .2 A .2 A
Primary Digesters 1.0 A 1.0 A 1.7 A
Secondary Digesters I. IA 1.0 A 2.0 A
7.4 A 15.4 A 22.8 A
C-7
-------
Figure I PURE OXYGEN PROCESS FLOW SCHEMATIC
Q ,mgd
I Alternate
Waste as
Withdrawal
From
Primary Q+Q V
Treatment
Qmgd
S =BOD 5
mg/I
Final
Effluent
S
Q-Q
or
S = Soluble BOD mg/i
conc. mg/I of return sludge
BOD 5 mg/I
Q mgd
as waste flow
Pure Oxygen/Activated Sludge - 8
C-8
-------
Table C-7 PURE OXYGEN PROCESS DESIGN
O, Y(S 0 -S )
-. x 11 10
Where X Mixed Liquor Volatile Suspended Solids Concentration or MLVSS in the
reactor in mg/I
5,000 mg/i (assumed for this design)
Xr VSS Concentration of Return Sludge
= 15,000 mg/i (assumed for this design)
Y Sludge Yield Coefficient
0.6 lb cells produced/lb of BOD 5 removed (assumed for this design)
Endogenous decay coefficient
= 0.1 per day (assumed for this design)
5oIu Ie SOD, in the primary effluent, mg/I
S Soluble BOD 5 in the effluent of the secondary clarifier, mg/I
0 c = Mean cell residence time, days
YU-kd = 5 days for an assumed U value of 0.5
U = Food-Microorganisms Ratio
0.5 lb BOD 5 /lb MLVSS (assumed for this design)
O Nominal hydraulic detention lime, days
= V/Q
V Volume of the liquid in the reactor, million gallons
Q = Flow rate of primary effluent, mgd
Flow rate of return sludge, mgd
Flow rate of settled waste activated sludge, mgd, ii withdrawn from
the settling tank
Flow rate of waste activated sludge, mgd, if withdrawn directly from
the reactor
MLVSS
MLSS 0.S (assumed for this design)
Overall BOD 5 of the effluent 30 mg/I
Effluent suspended solids concentration = 30 mg/I
Assuming thai 65% of suspended solids are biodegradable and the deoxygenation
coefficient to be 0.1 per day (base JO), the soluble BOD 5 of effluent, S 11.2 mg/I
Waste Activated Sludge Production
lb of VSS produced/day (2)
VSS
TSS - 0.
Oxygen Requirement
lb 02 required/day lb First Stage BOD removed/day - l. i2 P, (3)
C-9
-------
Table C-8 DESIGN EQUATION FOR FLOTATiON
l.3a (fP-)R
Aft S
S fl’
S W
where A/s Solid ratio, lb/lb
= 0.02 for this design
a 5 = Air Solubility, mi/I = 18.7 mI/I @ 20°C
f Fraction of dissolved air at a given pressure 0.8 for this
design
Total Suspended solids concentration, mg/I
R Recycle flow rate, mgd
Waste activated sludge flow rate, mgd, drawn directly
from the reactor
P Absolute pressure in atmospheres.
Pressure used in this design is 60 psig
604 147
= = 5.082 atmospheres
c-b
-------
APPENDIX D
ROTATING BiOLOGICAL CONTACTORS (RBC)
1. Introduction
The RBC process has had widespread application in both municipal and
industrial wastewater treatment. The process consists of vertical,
deformed plastic disks mounted on a horizontal shaft that is rotated
slowly to immerse the disks in the wastewater. The surface of the disks
become covered with a thin layer of biomass which removes organic
pollutants from the waste stream. Shearing forces from the rotational
passage through the water remove excess biomass (sloughing) from the
disks. The sloughed off biomass remains in suspension in the waste
stream, until removed by secondary solids separation processes.
The rotating disks perform the following functions:
- Provide a surface media for growth of a waste stable oxidizing
biomass.
- Provide continuous contact with the wastestream.
- Provide continuous contact with the air.
- Continuously slough off excess biomass to control the creation of
anaerobic biomass.
- Provide sufficient agitation to maintain sloughed solids in
suspension until the separation phase.
Rotating Biological Contactors -
-------
Historically, however, RBC units have been plagued by both mechanical
and process control problems. Principal among these have been the
following:
- structural failure of shafts and/or support frames due to
underesti ma lion of sha ft loads.
- bearing failure due to corrosion or Lack of maintenance.
- organic overloading causing excessive anaerobic layer growth.
This increases the structural loads on the shafts and may also
inhibit the organic waste removal.
- lack of operational control including
• oxygen transfer
• rotational speed
• flow control and unit staging flexibility
temperature control
In the last 5 to 7 years, a number of advances in the process technology
have improved performance and equipment reliability. For the purposes
of this study, a recent modification of the RBC process, the Aerated
Biological Contactor system (ABC) was assumed.
The ABC unit is installed in a flat bottom tank in a similar manner to the
conventional RBC unit. An air header is installed in the lower portion of
the tank, designed to provide between 50 to 200 cfm @ 3 psi to the tank.
The corrugated, high-density polyethylene media disk is especially
designed to capture the upward flowing air and convert this airflow
(buoyancy) into a rotational force, to operate the contactor. Several
advantages are gained from this procedure.
Rotating Biological Con tactors - 2 D - 2
-------
The ABC unit maintains a thinner, predominantly aerobic
biomass, due to the stripping action of the airflow across the
media. This also serves to reduce the shaft loads, increasing the
effective life of the equipment.
The reduced biomass layer thickness allows the use of more
closely spaced disks, allowing a reduction in the total number of
units required and/or higher organic loading to each unit.
Existing ABC units have demonstrated a superior dissolved
oxygen (D.O.) profile, allowing the acceptance of higher organic
loading, or peak loading capacity, while maintaining aerobic
conditions.
Improved D.O. profiles associated with higher oxygen transfer
capability can result in higher organic removal rates for a given
waste stream.
Operational flexibility is provided in the following:
• Air flow can be adjusted seasonally or over the life cycle of
the facility to match the influent waste loads.
• Air flow can be reduced or adjusted to optimize energy
consumption.
Rotational speed can be adjusted for each contactor unit via
control of the air supply valve at each unit. This allows
maximum flexibility of unit staging and operations.
• Standby blower capacity provides the standby drive capability
for the ABC units, simplifying maintenance and improving
operator safety.
Rotating Biological Con tactors - 3 D - 3
-------
- Recent improvements in the RBC/ABC mechanical technology
include:
• factory sealed bearing to minimize failure or maintenance
problems
• lightweight FRP enclosures or buildings to house the
ABCIRBC units
• load bearing cells for each rotational shaft to monitor shaft
loads
• upgraded design standards for manufacture of shafts, frames,
and related structural items, as well as the plastic media.
2. Process Reliability
The Government Accounting Office (GAO) 1980 study titled, “Costly
Wastewater Treatment Plants Fail to Perform as Expected,” noted that
50% to 75% of all treatment plants were in violation of their permits at a
given time, and that greater than 87% of all the plants surveyed had
experienced at least minor permit violations. In constrast, a 1981 survey
by RBC/ABC manufacturers indicated that 60% of all RBC units were
continuously meeting permit requirements.
Overall there are approximately 100 ABC plants in operation throughout
the world, with approximately 70 in the United States. A partial listing is
provided in Table D-l.
Rotating Biological Contactors - 4 D - 4
-------
Table b-I ERA TED BiOLOGiCAL CONTACTOR INSTALLATION
Location Design Flow Date Operating
Union City, CA 20 mgd 1980
Lancaster, WI 0.74 mgd 1980
Glenwood Springs, CO 2.3 mgd 1979
Guelph, Ontario, Canada 12 mgd 1979
Canadaiqua, N Y 7.3 mgd 1980
3eddah, (airport) Saudi Arabia 4.8 mgd N/A
Orlando, FL 24 mgd 1980
Clermont Co , OH 7 mgd 1979
Philadelphia, PA (Northeast)’ 240 mgd 1981
‘Modified aeration tanks.
In addition, it should be noted that RBC/ABC units are particularly
amenable to retrofit of existing aeration or clarification tanks, as has
been demonstrated repeatedly in facility upgrades. A noteworthy
application of RBC/ABC technology occurred in 1981 at the North East
Wastewater Treatment Facility in Philadelphia, Pennsylvania. RBC units
were installed into the existing aeration tanks, providing a combination
RBC/AS treatment system (which essentially matches the proposed ABC
process) for the 240 mgd flowrate.
3. Combined RBC and Microscreen Process
To maximize the space efficiency of the process, the ABC units were
assumed to be combined with fine mesh microscreens (bio-screens) to
separate the secondary solids. This combination is described in is several
publications, including the Microscreen Technology Transfer Seminar to
U.S.E.P.A. Office, Region V “Direct Polishing of Fixed Film Reactor
Effluents.”
Extensive bench, pilot and full scale testing has demonstrated that the
microscreening process can effectively reduce secondary biological
treatment effluent to well within the conventional 30/30 standards used
for this study. A finer media mesh than that reviewed in the primary
Rotating Biological Contactors - 5 D - 5
-------
treatment option would be used (27 to 44 micron media). A grid design
permitting a headloss up to 24 inches and automatic self-cleaning spray
nozzles allows high solids loading.
As noted in primary treatment, advantages include the ability to accept
variable flows with sudden hydraulic peaking, slug solids loading and
extreme weather conditions without loss of efficiency. Maintenance is
relatively simple and operational flexibility is optimized.
This combined ABC/bio-screen process has been field evaluated and is
currently being installed at the Buncornbe Co. MSD-Ashville, NC, 40 MGD
facility.
4. Anaerobic Digestion of Secondary Sludge
This alternative will generate relatively large volumes of sludge,
suggesting the desirability of including a system for anaerobic digestion
and recovery of methane for power generation. If the system is properly
designed, sufficient energy should be available to operate all major unit
processes. Critical considerations for such design include:
- low energy secondary treatment process.
- digesters fed at a relatively uniform rate and consistent solids
concentration.
The low sludge volume is important in keeping the digester heating
requirements at a minimum.
Rotating Biological Contactors - 6 13 - 6
-------
To test the suitability of the ABC/Bioscreen process, three options were
developed:
Option 1. A separate plant for South System Flows.
Option 2. A separate plant for North System Flows.
Option 3. A combined plant for all flows.
The wastewater would be similar to that used in the analysis of the pure
oxygen system alternatives. All the options assume the use of the coarse
microscreen technology for primary treatment of the influent waste
stream. Table D-2 summarizes the area requirements of each of the
options reviewed.
The three options are described in Table D-3.
Table D.2 ABC/BlO-SCREEN SYSTEM
Area Requirement
Item Option I Option 2 Option 3
Primary Microscreens 0.3 acres 1.1 acres 1.4 acres
ABC Units 2.1 acres 9.2 acres 11.3 acres
Bio-Screen Units 0.9 acres 3.1 acres 4.0 acres
DAFT Units 0.4 acres 1.3 acres 1.6 acres
Secondary Digesters 1.0 acres 1.7 acres 2.6 acres
Primary Digesters 1.0 acres 1.0 acres 2.0 acres
TOTAL 5.7 acres 17.4 acres 22.9 acres
As proposed, the ABC/Bio-screen process for secondary treatment has
several significant advantages over other types of systems.
D-7
-------
- simplicity of mechanical operation.
- similar mechanical system for both the ABC and Bio-screen
equipment.
- simplified process control largely related to control of the main
plant aeration blowers.
- minimal adverse impact from hydraulic, organic, or solids
loading.
- process flexibility.
- low operational and power costs.
D-g
-------
Table 0-3 SPACE AND ENERGY REQUiREMENTS
ROTATING BIOLOGICAL CONTACTORS
OPTION I SOUTH SYSTEM
Equipment
Aerated BLological Contactors
136 units @ 16’ diam x 25’ L
Area required: 89,700 ft 2 (2.1 acres)
Secondary Bioscreen
80 units @ 12 ft dia x 16 ft L
Area required: 38,000 ft 2 (0.90 acres)
DAFT Units
8 units @ 25 ft W x 90 ft L
Area required: 16,000 ft 2 (0.40 acres)
Anaerobic Digestion
Utilize four (4) existing digesters with process equipment improvements, floating
covers, heat exchangers, etc., or construct new units with similar capacity.
Area required: 1 acre
Process Summary
Overall SOD removal efficiency: 72%
Soluble SOD removal efficiency; 90%
Energy Usag
Primary rnicroscreens 150 hp
ABC units 2,025 hp
Bioscreens 480 hp
Gravity Thickeners 60 hp
DAFT Units 320 hp
Anaerobic Digestion Gas Mixing IOU hp
TOTAL 3,135 hp required
Energy recovery: Digester Gas (based upon ( 4300 hp )
a sludge production of 150 tons/day)
NET BALANCE 1,165 hp in excess of
anticipated power needs
0-9
-------
OPTION 2 NORTHSYSTEM
Equipment
Aerated Biological Contactors
700 units @ 16’ tham x 25’ L
rea required: 402,500 ft 2 (9.2 acres)
Secondary Bioscreens
285 units @ 12 ft dia x 16 ft L
rea required: 135,400 ft 2 (3.1 acres)
DAFT Units
28 units @ 20 ft W x 90 ft L
Area required: 55,400 ft 2 (1.3 acres)
Anaerobic Digestion
Provide capacity equal to that existing pius 4 additional 100 ft dia units.
Area required: 75,000 ft 2 (1.7 acres)
Process Summary
Overall f3OD removal ci 1 iciency: 72%
Soluble OD removal efficiency: 90%
Energy Usage
Primary microscreens 600 hp
ABC units 7,000 hp
Bioscreens 1,710 hp
Gravity Thickeners 120 hp
DAFT Units 1,120 hp
0 tnaerobic Digestion Gas Mixing 225 tip
TOTAL I0,ll Shp
Energy recovery: Digester Gas ( 14,000 tip )
(based upon a sludge production
of 500 tons/day)
NET BALANCE 3,225 hp in excess of
anticipated power needs
D-IO
-------
OPTION 3 COMBINED TREATMENT FACILITY
Equipment
Aerated Biological Contactors
856 units @ 16’ diam x 25’ L
rea required: *93,000 ft 2 (11.3 acres)
Secondary Bioscreens
365 units @ 12 It dia x 16 ft L
Area required: 173,400 ft 2 (4.0 acres)
DAFT Units
36un its@ 2OftWx9OftL
Area required: 71,300 it 2 (1.6 acres)
Anaerobic Digestion
Provide capacity equal to that existing plus 4 additional 140 ft dia digesters.
Additional area required: 112,000 ft 2 (2.6 acres)
Process Summary
Overall BOD removal efficiency: 72%
Soluble BOD removal efficiency: 90%
Energy Usage
Primary microscreens 750 hp
ABC units 9,025 hp
Bioscreens 2,190 hp
Gravity Thickeners (existing) 180 hp
DAFT Units 2,560 hp
Anaerobic Digestion Gas Mixing 325 hp
TOTAL 15,030 hp
Energy recovery: Digester Gas ( 18,300 hp )
(based upon a sludge production
01 650 tons/day)
NET BALANCE 3,20 hp in excess of
antidpated power needs
-------
APPENDIX E
POWDERED ACTI VATED CARBON/ACTiVATED SLUDGE
I. introduction
Activated carbon treatment has conventionally been used as a tertiary
process following activated sludge treatment. Advances in dual sludge
digestion and activated carbon regeneration, however, have made the use
of powdered activated carbon (PAC) and activated sludge (AS) in a single
aeration unit feasible.
The advantage of adding PAC to biological solids in an aeration unit
include both improved toxic and difficult-to-degrade-organics removal
and increased BOD and COD removal efficiency. The waste activated
sludge (WAS) resulting from this process is thicker and requires smaller
sludge sedimentation facilities. From an operations standpoint, PAC
addition lessens aerator foam, prevents bulking and has a better oxygen
transfer efficiency.
More uniform plant operation and effluent quality result, especially during
periods of varying organic and hydraulic loads and during occasional toxic
shocks. These advantages are particularly relevant to the Deer island and
Nut Island wastewaters because of the effects of combined sewers area
and the potential problems from industrial discharges. A flow-chart of a
typical PAC/AS treatment system is shown in Figure 2.
PAC improves activated sludge plant performance in the following
manner: First, pollutants are removed from the wastewater by adsorption
onto the carbon. Since bio-oxidation is a concentration dependent
process, this sorption increases the rate of bio-oxidation. Second, the
carbon holds onto soluble (and possible harder-to-degrade) organics that
are in the mixed-liquor and places these organics in contact with the
biomass organisms for a time that is equal to the sludge age rather than
Powdered Activated Carbon/Activated Sludge - I E -
-------
the hydraulic detention period of the aeration unit. Such an extended
residence time allows refractory organics a greater opportunity for
degradation. Third, because the bio-degradation reaction on sorbed
organics results in a partial regeneration of the PAC solid, the combined
use of PAC and an active blo-mass yields a more effective adsorption
process as well as an increased bio-degradation reaction.
Finally, the PAC particles (with their high density relative to typical
MLSS) acts as a weighting agent and seed for flocculation of the biomass.
This process results in a better settling sludge for subsequent sludge
treatment and secondary setting units. If the wet-oxidation carbon
regeneration method is employed, the need for additional secondary
sludge disposal is eliminated.
Although the concentration of activated carbon needed in the MLSS to
adsorb incoming wastewater organics is less than 1,000 mg/I; experience
has shown that a high PAC slurry in the MLSS (around 10,000 mg/i) is
more desirable because this residual PAC will accommodate shock organic
loadings and unexpected toxic inputs. This type of operating charac-
teristic should be considered highly advantageous for the type of
wastewater received at both Nut Island and Deer island.
Typical design specifications for a PAC/AS system are provided in Table
E-3.
Powdered Activated Carbon/Activated Sludge - 2 E - 2
-------
Figure 2 Ti PICAL PAC/AS SYSTEM
Regenerated
and
Influent
The PAC/AS system, combined with wet air oxidation regeneration has
the following advantages:
- high removals at BOD and COD via biological
assimilation/oxidation and physical adsorption at organics
- improved oxygen transfer
- adsorption of toxic substances and priority pollutants
- carbon makeup is generally less than %
Effluent
Regeneration
P(,wrh rcd Artivaud Carhori/ rtiv-ttecl Sltadg - 3
E-3
-------
- secondary biological sludge handling and disposal is eliminated ,
due to the wet air oxidation process while restoring the
adsorptive capacity of the powdered activated carbon
- regeneration ash settles out as a fine grit material with a
concentration at approximately 50-60% solids by weight, and is
generally suitable for landfilling or other disposal methods
- wet oxidation is flameless, eliminating problems associated with
particulate matter in process off gas
Due to the interrelated nature of the processes, the PAC/AS and wet
oxidation regeneration processes should be considered as a single process
alternative.
2. Applied Process Description
The proposed PAC/Wet Air Regeneration system would operate in
accordance with the flow diagram as shown in Appendix C. Upon entering
the treatment facility, the wastewater flow would pass through primary
treatment facilities. Thereafter, the flow would proceed to the scrubbing
channel of the PAC system where the regenerated carbon from the Wet
Air Regeneration process would be added to the flow.
In the aeration tanks, the wastewater would be aerated in the presence of
up to 15,000 mg/I of powdered activated carbon, microorganisms
(biomass), and inert ash. A dissolved oxygen level exceeding 1.0 mg/I
should be maintained in order to achieve a high degree of organic removal
and nitrification. Following aeration, a polymer would be added and the
mixture allowed to settle in the final clarifiers. The clarifier overflow
would then proceed to chlorination and to subsequent discharge.
Powdered Activated Carbon/Activated Sludge - 4 E - 4
-------
Clarifier underf low in each stage is returned to the aeration tank on a
continuous basis to maintain high mixed liquor concentrations. Excess
spent carbon and biomass produced would be wasted to a gravity thickener
and pumped to the continuous Wet Air Regeneration Unit.
The Wet Air Regeneration Unit would operate as follows: The spent
carbon slurry is raised to a pressure of approximately 55 bar (800 psi),
mixed with compressed air and passed through a heat exchanger to raise
its temperature to approximately 205°C (400°F). The mixture then flows
to a reactor where the air oxidizes the adsorbed organics and restores the
adsorptive capacity of the carbon. The regenerated hot slurry passes
through the heat exchangers giving up its heat to the incoming slurry,
then to pressure control valves which release the cooled slurry to the
atmospheric separator. During regeneration, the suspended ash associated
with the carbon slurry accumulates at the bottom of the reactor. The ash
is periodically removed from the unit and disposed of as a grit.
Since powdered carbon losses within PAC will occur, makeup of virgin
carbon will be necessary arid will be accomplished by addition of virgin
carbon to the treatment system.
The entire system has the flexibility needed to produce a high quality
effluent, even in an emergency situation. Shutdown of the regeneration
facilities for a number of days will not cause a serious deterioration in
effluent quality. Also, virgin carbon addition can be halted for a lengthy
period of time without deterioration in effluent water quality.
Three (3) options have been considered for the PAC/AS system:
OPTiON 1: Separate plant for South System
OPTION II: Separate plant for North System
OPTION Ill: Combined plant for all wastewater flows
Powdered Activated Carbon/Activated Sludge -5 E - 5
-------
Table E-l summarizes the results of the options reviewed.
The wastewater characterization is similar to that used in the analysis of
the other secondary treatment alternatives, This system should be
carefully evaluated via field pilot scale testing prior to any design effort
proceeding.
Table E-1 SPACE REQUIREMENTS
POWDERED ACTIVATED CARBON/ACTiVATED SLUDGE
OPTION I SOUTH SYSTEM
Equipment/Facilities
PA C/AS System
I Scrubbing channel 30’L x 20’W
4 Contact aeration tanks 185’L x l20’W x 20’D (I standby)
Clarification area @ 200,000 ft 2
2 Carbon thickeners @ 100 ft diameter
Oxygen req’d.: 130,000 lb/day
Hydraulic detention: 1.5 hr
BOD loading (design): 77 lbs/l0O ft 3 /day (w/o standby)
(peak): 151 lbs/ 1000 1t 3 /day (w/o standby)
Recycle rate: 65 MGD
Make-up carbon: J0, i00 lbs/day
Liquid polymer; 1,250 b/day
Wet Air Regeneration
4units@ l30gpmeach
Virgin carbon storage: 16,000 ft 3
Operative flow: 370 gpm
Design pressure: 1,200 psig
Ash disposal: 23,000 lb/day
rea Requirements
PAC/AS
(all equipment): 335,000 ft 2 (7.7 acres)
Wet \ir Regeneration
Building 5 trea: 17,00 ft 2 (0.4 acres)
Process Summary
Overall BOD 5 removal efficiency: 83%
Overall Soluble BOO removal efficiency: 95%
Poa’er requirement: 7200 HP
Fuel: 1,250 MMBTU/yr
Area includes that required for ‘PAC sludge ” thickening. It does not include facilities
for primary sludge treatment or handling.
E-6
-------
OPTiON ii NORTH SYSTEM
Equipment/Facilities
PA C/AS System
2 Scrubbing channels @ 60’L x 20’IW
8 Contact aeration tanks @ 185’L x 120’W x 20’D ( I standby)
Clarification area 467,000 ft 2
i Carbon thickeners @ 110’ diameter
Oxygen req’d.: 336,000 lb/day
Hydraulic detention: 1.5 hrs
BOD 5 loading (design): 86 lbs/I0O 11 3 /day (wlo standby)
(peak): 220 lbs/i 00 ft 3 /day (w/o standby)
Recycle rate: 150 MGD
Make-up carbon: 26,000 lb/day
Liquid polymer: 3,000 lb/day
Wet Air Regeneration
9Units@ I SO gpm
Virgin carbon 5torage: 35,000 ft 3
Operating flow: 960 gpm
Design pressure: 1,300 psig
Ash disposal: 42,000 lb/day
Area Requirements
PAC/AS
(all equipment): 753,000 ft 2 (17.3 acres)
Wet Air Regeneration
Building area: 30,000 It 2 (0.7 acres)
Process Summary
Overall BOO 5 removal efficiency: 81%
Overall soluble BOO removal efficiency: 94%
Power requirement: 18,250 HP
Fuel: 3,200 MMBTUIyT
-------
OPTION III COMBINED TREATMENT FACILITY
Equipment
PAC/AS
2 scrubbing channels 80’L x 20’W
Ii Contact aeration tanks @ 185’L x 120’W x 30’D (I standby)
Clarification area @ 660,000 ft 2
4 Carbon thickeners @ 130’ diameter
Oxygen req’d.: 465,000 lb/day
Hydraulic detention: 1.5 hours
80D 5 loading (design): 84 lbs/bOO ft 3 /day (yb standby)
(peak): 200 Ibs/1000 1t 3 /day (w/o standby)
Recycle rate: 215 MGD
Make-up carbon: 36,000 lb/day
Liquid polymer: 4,250 lb/day
Wet Air Regeneration
12 Units @ I SO gpm
Virgin carbon storage: 50,000 ft 3
Operating flow: 1,350 gpm
Design pressure: 1,300 psig
Ash disposal: 86,000 lb/day
Area Requirements
PAC/AS
(all equipment): 1,055,000 ft 2 (24.2 acres)
Wet Air Regeneration: ‘45,000 ft 2 (1.1 acres)
Process Summary
Overall BOD 5 Removal Efficiency: 82%
Overall Soluble BOD REmoval Efficiency: 94%
Power Requirement: 25,000 HP
Fuel: 4,200 MMBTU/yr
E-8
-------
Table E-2 PA C/AS SYSTEM
Area Requirement
Item Option I ption II Option Ill
Primary Microscreen 0.3 acres 1.1 acres 1.4 acres
PA C/AS 7.7 acres 17.3 acres 24.2 acres
Wet Air Regen. 0.4 acres 0.7 acres 1.1 acres
Primary Sludge Digestion 1.0 acres 1.0 acres 2.0 acres
Total 9.4 acres 20.1 acres 28.7 acres
Table E-3 PAC/AS SYSTEM DESIGN CRITERIA
Aeration Design
SRT 5 days
HDT 2 hours
Biomass Yield 0.30 gm VSS/gm COD
MLSS 15,000 mg/I
Secondary Settling
Overflow Rate 800 gpdlft 2 average)
1,200 gpd/ft (maximum)
Solids Loading Rate 150-250 lb/ft 2 /d
Sludge Concentration 3%-5%
Chemical Addition
Polymer I mg/I
Powdered Carbon Makeup 75-ISO mg/I without wet air regeneration
5-12 mg/I with wet air regeneration
E-9
------- |