Environmental Protection Technology Series
SURGE FACILITY FOR
WET AND DRY WEATHER FLOW CONTROL
National Environmental Research Center
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
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EPA-670/2-74-075
November 1974
SURGE FACILITY FOR WET
AND DRY WEATHER FLOW CONTROL
By
Harold L. Welborn
Y-T-0 & Associates
Walnut Creek, California 9^596
For
City of Rohnert Park
Rohnert Park, California 94928
Demonstration Project No. S800769
Program Element 1BB034
Project Officer
Wi11iam D. Bi shop
U.S. Environmental Protection Agency
Region IX
San Francisco, California 94111
NATIONAL ENVIRONMENTAL RESEARCH CENTER
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
For sale by the Superintendent of Documents, U.S. Government
Printing Office, Washington, D.C. 20402
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REVIEW NOTICE
The National Environmental Research Center -
Cincinnati has reviewed this report and approved
its publication. Approval does not signify that
the contents necessarily reflect the views and
policies of the U. S. Environmental Protection
Agency, nor does mention of trade names or com-
mercjal products constitute endorsement or recom-
mendation for use.
ii
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FOREWORD
Man and his environment must be protected from the adverse
effects of pesticides, radiation, noise and other forms of
pollution, and the unwise management of solid waste. Efforts
to protect the environment require a focus that recognizes the
interplay between the components of our physical environment
air, water, and land. The National Environmental Research
Centers provide this multidisciplinary focus through programs
engaged in
o studies on the effects of environmental
contaminants on man and the biosphere, and
o a search for ways to prevent contamination
and to recycle valuable resources.
This particular effort demonstrated how one facility can
be optimally utilized to provide flow equalization for wet and
dry-weather wastewater flows as well as some degree of treat-
ment to storm flows.
A. W. Breidenbach, Ph.D.
Di rector
National Environmental
Research Center, Cincinnati
l l l
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ABSTRACT
This report represents the culmination of a three-year project which encompassed
the design, construction, operation, testing and evaluation of a surge facility
designed to provide flow equalization and some degree of treatment to all storm
flows and to provide rate control of wet weather and dry weather wastewater flows
to interceptor sewers.
The Rohnert Park Demonstration Project was designed to test a method whereby
solids could be prevented from accumulating on the bottom of an inexpensive
earthen, lined basin without the use of conventional mechanical sludge collection
equipment.
The overall costs for the demonstration facilities included: $32,400 for design;
$370,000 for construction; and $14,000 for construction inspection. The major
mechanical equipment costs are estimated at approximately $80,000.
An economic evaluation showed that it was advantageous to use a surge facility
at Rohnert Park as part of a regional plan to transport its wastewater to the
Regional Plant rather than pump the entire wet weather peak flows.
The principal features of the surge facility were a 2,841 cubic meter (0.75 million
gallon) Sedimentation-Equalization Basin, variable underflow pumps, a surface
aerator and Pool Sweeps. The Pool Sweeps were used to continuously "sweep" the
bottom and sides of the earthen, lined basin to move and temporarily resuspend the
settled sewage solids and thereby maintain the flow of solids in the absence of
mechanical collection mechanism, steep bottom slopes or a completely mixed
basin.
The full size facility was tested under actual field conditions with influent flows
varying from a low of 25 to a high of 243 liters per second (400 to 3,850 gallons
per minute).
The ability of the surge facility to provide adequate hydraulic control to eliminate
diurnal flow variations was documented early in the Demonstration Period.
Under storm flow conditions, at which time the Sedimentation-Equalization Basin
was operating at over 90 percent of its design capacity of 6.0 mgd, the surge
facility was able to remove approximately 45 percent of the influent Suspended
Solids and over 90 percent of the influent Settleable Solids. BOD removal under
storm flow conditions was not significant.
Although a significant portion of the solids flow through the surge basin could be
attributed to the operation of the Pool Sweeps, their overall performance could
not justify their use in other similar facilities.
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CONTENTS
Page
Abstract I v
List of Figures vi
List of Tables vi'
Acknowledgments
Section
I Conclusions 1
II Recommendations 3
III Introduction 4
IV Project Facilities 8
V Testing and Evaluation 22
VI Discussion 64
VII Glossary 80
VIM Abbreviations and Symbols 83
IX Metric Units and English
Equivalents 85
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FIGURES
No. Page
1 Laguna de Santa Rosa 5
2 Demonstration Project Flow Sheet 9
3 Sedimentation-Equalization Basin 11
4 Basin Cross Section 11
5 Floating Aerator 12
6 Pool Sweep Schematic Diagram 14
7 Pool Sweep in Operation 15
8 Pool Sweep with Hoses 15
9 Pool Sweep Water Supply Suction Screen 16
10 Overflow Structure 16
11 Skimming Structure 17
12 Dry Weather Flow Diagram 20
13 Wet Weather Flow Diagram 20
14 Test No. 1 Concentration Curves 30
15 Test No. 2 Concentration Curves 36
16 Test No. 3 Concentration Curves 40
17 Test No. 4 Concentration Curves 44
18 Rainfall and Daily Flows 47
19 Test No. 5 Concentration Curves 48
20 Test No. 6 Concentration Curves 51
21 Test No. 7 Concentration Curves 54
22 Test No. 8 Concentration Curves 55
23 Test No. 9 Concentration Curves 56
24 Pool Sweep Hose Wear 72
25 Regional Wastewater System Schematic 76
v i
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TABLES
No. Page
1 Summary - Basic Test Parameters 23
2 Test A - Average Waste Strength of Various Flows 24
3 Test D. - Average Waste Strength of Various Flows 27
4 Test E>2 ~ Average Waste Strengths of Various Flows 28
5 Test No. 1 . Suspended Sol ids Mass Balance 32
6 Test No. 1. BOD Mass Balance 33
7 Test No. 2. Suspended Solids Mass Balance 38
8 Test No. 2. BOD Mass Balance 39
9 Test No. 3. Suspended Solids Mass Balance 41
10 Test No. 3. BOD Mass Balance 42
11 Test No. 4. Underflow Mass 45
12 Test No. 5. Suspended Solids Mass Balance 49
13 Test No. 5. BOD Mass Balance 49
14 Test No. 6. Underflow Mass 52
15 Test No. 7. Suspended Solids Mass Balance 57
16 Test No. 7. BOD Mass Balance 58
17 Test No. 8. Suspended Solids Mass Balance 59
18 Test No. 9. Suspended Solids Mass Balance 60
19 Test No. 9. BOD Mass Balance 61
20 Summary of Suspended Solids Mass Balances 63
21 Summary of BOD Mass Balances 63
22 Average Overflow Quality 66
23 Cost Summary - Alternate 1 - Regionalization Without
Surge Facilities 77
24 Cost Summary - Alternate II - Regionalization With
Surge Facilities 78
VI I
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ACKNOWLEDGMENTS
The support of the Mayor and Council of the City of Rohnert Park, California, is
gratefully acknowledged. The valuable assistance of the City of Rohnert Park
City Manager, Mr. Peter M. Callinan, the Superintendent of Public Works,
Mr. C.A. (Bill) Wiggins, and the treatment plant operator, Mr. Douglas Pro-
vencher, is also gratefully acknowledged.
The cooperation of the City of Santa Rosa and, in particular, Mr. Frank Poulsen,
the Superintendent of Utilities, and Mr. Larry Pringle, the Plant Supervisor at
the Laguna Wastewater Treatment Plant, is acknowledged with sincere thanks.
Special thanks are extended to Dr. William D. Bishop, EPA Project Officer,
whose guidance throughout the project was invaluable.
VI I I
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SECTION I
CONCLUSIONS
Design and operation of surge facilities is dependent on control of hydraulics
and sol ids flow.
By metering the influent and underflow and continuously monitoring the water
surface, it was relatively easy to produce a uniform underflow rate during normal
dry weather flow periods while maintaining the variation in water surface within
desired limits.
The quality of overflow to the storage pond is not nearly as dependent on
hydraulic loading as it is with a conventional sedimentation basin (clarifier).
With normal clarifiers, the removal of BOD is directly related to the hydraulic
detention time, that is, the lower the detention time the lower the percent
removal. BOD removals through the Sedimentation-Equalization Basin, however,
did not follow the same direct relationship. For example, at a relatively long
detention time of 13.9 hours, the BOD concentration in the overflow was 12 per-
cent higher than the influent BOD concentration. In another test, when the
hydraulic detention time was 8.8 hours, there was a 79 percent removal of BOD,
overflow to influent , and during a storm flow period when the hydraulic deten-
tion time was only 3.6 hours, there was no removal of BOD. The unpredictable
nature of the BOD concentration through the Sedimentation-Equalization Basin
appears to be the result of the production of soluble BOD from the anaerobic
decomposition of settled sewage solids on the bottom of the basin. Suspended
Solids and Settleable Solids removals varied from about 55 to 45 percent and
about 98 to 90 percent, respectively, as the hydraulic detention time varied
from 13.9 to 3.6 hours.
The basin configuration, including size, shape and flow pattern, the underflow
pumping, the aerator, the Pool Sweeps and the hydraulic loading were all
found to have an effect on the solids movement through the Sedimentation-
Equalization Basin.
The Pool Sweep units did have an observable beneficial effect on the movement
of solids through the Sedimentation-Equalization Basin but their performance,
as used and modified in this Demonstration Project, did not warrant their selection
as a primary sludge mover in a similar surge facility.
Operating experience with the demonstration surge facility indicated that solids
which had accumulated on the bottom of the basin could be removed easily by
simply drawing down the basin with the underflow pumps. After most of the
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liquid wastewater was removed from the basin, the remaining sludge blanket
"flowed" toward the center sump where it could be pumped out.
The "tethering" effect of the Pool Sweeps being restrained by the supply hose
had a noticeable adverse effect on the mobility of the units and probably had
a similar adverse effect on its overall performance.
It appears that surge facilities in the Rohnert Park and Santa Rosa area are justi-
fied on the basis of dry and wet weather flow equalization even if wet weather
flows are reduced substantially by collection system rehabilitation.
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SECTION II
RECOMMENDATIONS
More study is warranted on the solids flow-through mechanisms which exist in
this type of facility.
Future surge facilities of the type used for this project should be designed with
multiple basins to add more flexibility for handling the wide range of flows.
Alternative methods of removing settled solids from the bottom of the Sedimenta-
tion-Equalization Basin should be investigated. Most likely solutions include
periodic lowering of the basin contents and periodic complete mixing of the
basin contents.
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SECTION III
INTRODUCTION
The City of Rohnert Park is located in the south-central portion of Sonoma
County, California, approximately 60 miles north of San Francisco. The drain-
age area surrounding Rohnert Park is tributary to the Russian River. The city
is a relatively new addition to the Santa Rosa Plain, started in 1957 and incor-
porated in 1962. It is primarily a residential community that is presently
supported by industry outside the city, and by local industry and commerce
generated from the nearby California State College in Sonoma. The Santa Rosa
Plains area is shown in Figure 1 .
The climate of the Rohnert Park area is characterized by warm, dry summers and
mild, wet winters. The mean daily maximum temperature in the summer is 80°F
and the mean daily minimum temperature in the winter is 40°F . Average annual
rainfall is 30 inches and average annual evaporation is 60 inches.
The original Rohnert Park Wastewater Treatment Plant was constructed in 1957.
It was a primary treatment plant designed for an average flow of 21 .9 liters
per seconds (l/s) (0 .5 mgd). The principal features of the plant included
influent pumping, primary sedimentation and oxidation ponding. Sludge was
treated with anaerobic digesters and drying beds.
As part of the long-range plan for sewerage facilities in the Santa Rosa Plain,
construction of the Laguna Treatment Plant was recommended in a 1962 engineer-
ing report for the County of Sonoma entitled, "Collection, Treatment, and
Disposal of Sewage and Industrial Wastes Within the Santa Rosa Plain" by
M. Carleton Yoder, Consulting Engineer. It was also recommended that
Rohnert Park and Cotati tie in with the proposed facility. In the regional plan,
all wastewater south of Mark West Creek (see Figure 1) would go to the Laguna
Regional Plant. This would cover the existing area presently sewered to the
cities of Sebastopol, Santa Rosa, Rohnert Park and Cotati. In 1967, Stage 1
Construction of the Laguna Regional Wastewater Treatment Plant was completed
by the city of Santa Rosa. It had an initial capacity of 110 l/s (2.5 mgd).
By 1966, increased growth and the addition of the newly constructed California
State College Sonoma to the Rohnert Park Sewerage System was causing the
original Rohnert Park treatment facilities to be overloaded. A study made for
the City of Rohnert Park in 1966 entitled "Wastewater Collection, Treatment
and Disposal" by M. Carleton Yoder Associates, Consulting Engineers, indicated
that it was not economically feasible to transport Rohnert Park wastewater to
the Laguna Regional Treatment Plant at that time. However, the report
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Figure 1. Laguna de Santa Rosa Area
BMV3
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recommended that a re-evaluation of the feasibility of connecting to the Laguna
Plant be made at the time that the next expansion of the city's treatment facili-
ties was required.
One of the main factors of concern to the design of treatment and disposal
facilities at Rohnert Park was the high wet weather wastewater flows encountered
during the rainy season. Although detailed data were not available, it was
estimated that peak wet weather flows exceeded average dry weather flows by
as much as eight to ten times.
At this point in time, the idea of the unique surge facility was presented to the
Federal Water Pollution Control Administration (now EPA) in the form of a grant
request. The surge facility would be used for two principal functions. The first
would be to provide flow equalization and some degree of treatment to all storm
flows regardless of flow rate. The second would be to provide rate control of
all dry weather flows to the interceptor sewer. The initial request was for a
project which covered both the surge facility and the transmission line to the
regional treatment plant. As a result of discussions and correspondence with
FWPCA, the original grant request was revised. The Demonstration Project,
as revised, included the surge facility but not the transmission lines. It was felt
that the knowledge gained through operation of the surge facility would be used
to design the optimum system for transporting the wastewater to the Regional
Plant, thus resulting in a considerable savings in costs of regionalization.
The uniqueness of the Rohnert Park Surge Facility was in the method of sludge
removal from the surge basin. For this particular facility, an attempt was made
to show that Pool Sweeps, an item normally used for cleaning the bottom of
swimming pools, could be adapted to a small surge facility in order to maintain
the flow of solids through the basin.
The primary objectives, or areas of investigation, of the demonstration period
as originally outlined in the Demonstration Project proposal included: 1) research
and development on the sludge collection and removal system; 2) studies of
primary sedimentation tank (clarifier) efficiencies comparing variable versus
uniform flow conditions; 3) economic evaluation of the proposed surge facility
as compared to conventional alternatives for transporting and treating local
wastewater including capital and O&M costs; and 4) evaluation of possible
application of the Rohnert Park system to other regional wastewater collection
plans.
In order to make the most meaningful evaluation of relative costs for transporting
and treating regulated or controlled flows versus normal variable flows, and to
show the potential use of this type of facility for an entire regional wastewater
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facility, it was decided to make the economic comparison of alternatives specifi-
cally for the Santa Rosa Plains regional area of which Rohnert Park is a part.
Implementation of the Demonstration Project by the City of Rohnert Park covered
the following periods. The design was accomplished during the period from
January 1970 through May 1970. The construction took approximately twelve
months and was completed in May 1971. The actual demonstration period began
in July 1971 and ended in February 1973.
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SECTION IV
PROJECT FACILITIES
DESIGN OBJECTIVES
The design objective for the Demonstration Project was to provide a surge facility
which would remove the normal dry weather peaks which occur in wastewater
flows and the peaks which occur due to wet weather infiltration/inflow, and
thus, provide a uniform flow to a regional treatment plant system. As is the
case with all surge facilities, one of the major problems encountered is the
settlement of sewage solids on the bottom of the storage facility. The Rohnert
Park Demonstration Project was designed to test a method whereby these solids
can be prevented from accumulating on the bottom of an inexpensive earthen,
lined basin without the use of conventional mechanical sludge collection
equipment.
GENERAL FLOW SHEET DESCRIPTION
The general flow pattern is shown in Figure 2 and is described below. All
wastewater enters the plant from the east into the pump station which contains
the treatment plant headworks and raw sewage pumping facilities. From there
the raw sewage is pumped to the influent metering and sampling station from
which it flows by gravity to the center of the Sedimentation-Equalization Basin.
The underflow from the basin is pumped by the underflow pumps located in
the basement of the control building to the clarifier. The underflow from the
clarifier goes to the digester and the effluent from the clarifier goes to the
storage pond. The overflow from the Sedimentation-Equalization Basin goes by
gravity directly to the storage pond, and by opening a gate in the overflow
structure, the overflow can be returned to the basin from the storage pond.
All flows which overflow the storage pond go through the effluent metering and
sampling station and chlorination facilities prior to discharge.
As used in this report, the term "surge facility" represents the total facility in-
cluding raw sewage pump, Sedimentation-Equalization Basin, underflow pumping,
storage pond and overflow chlorination, whereas the term "Sedimentation-Equal-
ization Basin" refers only to the basin itself along with the associated influent
pipe, Pool Sweeps, aerator, overflow structure and skimming structure.
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Figure 2. Demonstration Project Flow Sheet
RAW SEWAGE
PUMPS
COMMINUTORS
PLANT
INFLUENT
SEDIMENTATION
EQUALIZATION
BASIN
STORAGE
POND
(OXIDATION)
EFFLUENT
CHLORINATION
HINEBAUGH CREEK
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DESIGN AND OPERATIONAL PARAMETERS
To acquaint the reader with the Rohnert Park facilities, this section discusses
the design and operational parameters of the major components of the facilities.
The major components of the system include: 1) influent pump station; 2) influent
metering and sampling; 3) Sedimentation-Equalization Basin; 4) control building;
5) underflow pumping facilities; 6) clarifier; 7) storage pond; 8) effluent meter-
ing and sampling; and 9) chlorination facilities.
Influent Pump Station
The influent pump station contains two comminutors, an eight-inch pump with a
25 hp fixed speed motor and two six-inch pumps with 20 hp variable speed motors,
The total pumping capacity of the raw sewage pumps is 263 liters per second
(l/s) (6 mgd).
Influent Metering and Sampling
The influent metering structure is a Parshall flume with a one-foot throat width
having a maximum capacity of approximately 350 l/s (8 mgd). The influent
sampler is a flow proportional sampler controlled by either a hand-set electric
timer or by a signal from the influent flow transmitter. The sample is contin-
uously pumped through the sampler from immediately ahead of the Parshall flume.
Sedimentation-Equalization Basin
This basin is the principal component of the Demonstration Project. The major
components of the basin, some of which are shown in Figures 3 and 4, include:
1) basic configuration; 2) influent pipe; 3) aerator; 4) Pool Sweeps; 5) overflow
structure; and 6) skimming structure.
Basic Configuration -
The basin shown in Figures 3 and 4 is an earthen structure lined with gunite.
Gunite was chosen because it is relatively inexpensive and is quite durable
from the application tested. The use of the "rigid" liner did cause some
initial problems during construction, however. The native soils used for the
embankments were quited expensive and were not thoroughly wetted prior to
installation of the gunite. When the basin was filled for the first time, the
expanding soil buckled the lining. Once repaired, no further movement was
observed. When full, it has a capacity of 2,841 cubic meters (cu m) (0.75 mil-
lion gallons) and a minimum detention time of three hours based on the design
maximum flow of 263 l/s (6 mgd). The side slopes are 2:1, and the bottom
slope is approximately 12:1 toward the center. The center sump is cone-shaped
10
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Figure 3. Sedimenfation-Equalizafion Basin
Figure 4. Basin Cross Section
22-0"
INFLUEN
/?TRUC1
[rjL^ 97.00"
20'-0"
T METERING
URE
101 00
v^ 2
50-0"
91.00
r 12
13.5'
50-0"
DIA ±
OVERFLOW WS 9900
9100
12 \
20-0"
101 00
2 .x^"
8750
18 INFLUENT,
8100
GUNITE LINING
10" UNDERFLOW.
11
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and is 13-1/2 feet in diameter at the top and 6-1/2 feet deep. The overall
diameter of the basin to the centerline of the levees is 152 feet. The approxi-
mate diameter of the water surface at elevation 99.0 is 132 feet.
Influent Pipe -
The influent to the basin discharges vertically upward in the center of the basin
immediately under the floating aerator at approximate elevation 87.5.
Aerator -
This unit is a floating surface aerator which is held in position by the two verti-
cal pipes. The aerator is shown in Figure 5. For this application, the aerator
was designed just to maintain a residual dissolved oxygen (DO) in the
Sedimentation-Equalization Basin during the normal or dry weather flow periods.
The objective of the aeration was to prevent septicity and the resulting odors.
The 15 hp aerator in the 2,841 cu m (0.75 mg) basin provides 0.15 hp per
1,000 cu. ft. of tank volume whereas a range of 0.5 to 1 .0 hp per 1 ,000 cu. ft,
is generally required to maintain a completely mixed basin. The exact ratio
will depend on basin design parameters such as surface area, depth, waste
strength, etc.
FigureS. Floating Aerator
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Pool Sweeps -
The Pool Sweeps are shown in Figures 6, 7 and 8. Figure 6 is a schematic diagram
showing all of the major components of the unit. Figure 7 shows a unit operating
in the Sedimentation-Equalization Basin. Note the "tethering" effect of the main
supply hose which is attached to the water supply outlet at the periphery of the
basin. Figure 8 shows the unit out of water and indicates the relative length of the
normal sweep hoses and the modified single hose, with "wye" assembly, which was
used during a portion of the demonstration period. For the Demonstration Project,
the Pool Sweeps were used in an attempt to maintain the flow of solids through the
basin. The water supply outlets for the three Pool Sweeps used during the major
portion of the testing period were evenly spaced around the periphery of the
Sedimentation-Equalization Basin. The major components of the Pool Sweep are:
1) the main body which contains all of the water pressure operated valves and
gears; 2) the thrusters (back and front) which give it mobility in open water;
3) the bottom rotating ring which gives it mobility when it comes in contact with
a vertical or sloped wall; 4) the water supply line which delivers approximately
1 .25 l/s (20 gpm) at 3.5 kgf/cm (50 psi) to the main body; 5) the side wall hose
(shorter) and the bottom hose (longer) which provide the agitation to the solids
which settle to the bottom and sides of the basin; 6) the top spray jet which,
when used in a swimming pool, washes the vertical side walls; and 7) the main
jets in the extreme ends of the side wall and bottom hoses.
The water supply intake for the Pool Sweeps was obtained from the effluent end
of the clarifier just under the water surface. The primary effluent was then
pumped into a loop supply system in the top of the basin levee. When first
placed in service, frequent plugging of the main valving of the Pool Sweep body,
by small pieces of plastic, primarily, required that a cleaner water supply be
found.
Because we felt it would yield useful information to operate the units on a waste-
water supply, we devised a PVC pipe suction screen to remove all material which
could plug the units. The suction screen, shown in Figure 9, was made from a
one meter (approximately 3 feet) length of PVC pipe which was perforated along
its entire length with one-inch diameter holes and wrapped with a fine screen.
The screen could be raised and cleaned easily and put back in service quickly.
With the quality of primary effluent being used, the Pool Sweeps could be
operated continuously for approximately 48 hours before the screen required
cleaning.
Overflow Structure -
The overflow structure shown at the far corner of Figure 3 and in Figure 10 has
four sharp-crested rectangular weirs, totaling 1 .42 meters (8 feet, 4 inches), set at
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Figure 6. Pool Sweep Schematic Diagram
MAIN BODY
TOP SPRAY
MAIN THRUSTER
ROTATING TIRES
SUPPLY HOSE
MAIN FLOAT
SIDE WALL HOSE
BOTTOM HOSE
HOSE JET
REVERSING THRUSTER
(Not Shown)
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Figure 7. Pool Sweep in Operation
TETHER POINT
POOL SWEEP
Figure 8. Pool Sweep with Hoses
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Figure 9. Pool Sweep Water Supply Suction Screen
Figure 10. Overflow Structure
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elevation 99.0. Each weir is independently adjustable over a 0. 1 1 meter
(4-inch) vertical range. The overflow structure was designed to bypass all flows
in excess of the underflow up to a maximum of 263 l/s (6.0 mgd) directly to the
storage pond.
To monitor the water surface fluctuations in the Sedimentation-Equalization
Basin, a float-operated, portable stage recording device was added to the over-
flow structure. The recorder was a Stevens type "F" with interchangeable stage
and time gears. For this project, we selected time gears which gave an 8-day
chart and stage gears which gave an indication of 0.5 foot per inch of chart or
0.1 foot per inch of chart depending on the depth variation expected during any
particular testing period.
Skimming Structure -
The skimming structure shown in Figure 11 and previously shown in Figure 7 was
designed to facilitate the removal of floating scum and grease in the Sedimentation-
Equalization Basin. The underflow pumps were valved so that they could draw from
the skimming structure. Stop logs were used to control the amount of overflow
into the box while skimming. The skimming structure could also be used as a
side drawoff for the basin underflow, if needed.
Figure 11. Skimming Structure
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Control Building
The control building houses the operator's desk, the underflow pump controls, all
of the plant metering and recording instruments, the chlorination equipment, and
the laboratory. The laboratory was equipped to do all of the tests necessary for
the Demonstration Project and for operating the treatment plant with the exception
of the bacteriological tests.
Underflow Pumping Facilities
The flow out of the bottom of the Sedimentation-Equalization Basin is pumped by
the underflow pumps located in the basement of the control building. The under-
flow pumping facilities consist of two 4-inch pumps with belt-driven variable
speed drives. The suction for the underflow pumps draws from the bottom of the
center sump of the Sedimentation-Equalization Basin. The pumps discharge into
a single manifold and a 6-inch magnetic flowmeter. The underflow can be set
at any desired rate up to 100 l/s (2.3 mgd). When the surge facility becomes
part of a regional sewerage system the underflow pumps will discharge into an
interceptor to the regional treatment plant. During the Demonstration Project,
however, the underflow, which contained the raw sludge from the incoming flow,
went to the clarifier.
Clarifier
The clarifier used during the Demonstration Project was a typical primary clarifier
operated in the normal manner. The clarifier had a design capacity of 22 l/s
(0.5 mgd) based on the conventional design criteria of a 2-hour detention time
and a 32.61 cu m per square meter per day (m^/m /day) (800 gallons per day per
square foot, gpdsf) overflow or rise rate. The clarifier influent came from the
underflow pumps and the effluent normally went to the northeast corner of the
storage pond. The bottom sludge went to the 10.37 meter (34-foot) diameter
digester and ultimately to sand drying beds.
Storage Pond
The existing 4.86 hectare (12-acre) by 1 meter (3-foot) deep oxidation pond,
which was part of the original treatment plant, was intended in the demonstra-
tion to be a storage pond which would collect and store all of the winter peak
flows which overflowed the Sedimentation-Equalization Basin. During the
normal dry weather periods, the original plan was to bypass the storage pond and
keep it empty until it was needed for winter storm flow storage. The effluent from
the clarifier would go directly to chlorination facilities and then be discharged.
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jEffluent Metering and Sampling
The effluent metering structure contains a 0.16 meter (6-inch) Parshall flume
and a 1 .48 meter (4-foot, 6-inch) sharp-crested rectangular weir. The two flow
measuring devices are set to give a combined capacity of 263 l/s (6 mgd) at a
pond elevation of 98.05; i.e., when the Parshall flume has 0.43 meters (l.Sfoot)
of head on it and when the resulting head on the weir is 0.18 meters (0.55 foot).
The effluent sampler is a flow proportional sampler controlled by either a hand-
set electric timer or by a signal from the effluent flow transmitter. The sample is
taken from a waste stream which is continuously pumped through the sampler from
immediately ahead of the Parshall flume.
Chlorination Facilities
The chlorination facilities consist of two flow paced chlorinators which normally
work in parallel, one for prechlorination and one for post-chlorination. They
are interconnected through a manifold assembly so that each is a backup for
the other. The post-chlorination facilities at the effluent metering location
consist of a solution distribution manifold, a baffled concrete mixing chamber
and an earthen contact pond which provides approximately 20 minutes' contact
time at the design maximum flow before the effluent enters the 305 m (1,000 ft.)
of outfall line. All flows which leave the plant are measured and chlorinated
prior to discharge.
PRINCIPAL MODES OF OPERATION
As originally envisioned, there would be two principal modes of operation for
the surge facility. There would be the dry weather flow plan of operation and
the wet weather flow plan of operation. Both modes of operation are represented
in their respective flow diagrams shown in Figures 12 and 13. The principal
objectives of the dry weather flow program were to determine the hydraulic control
available to the system for the daily flow variations; to determine the partial
treatment obtained with this type of facility during the detention process; to
determine the effect of the basin on subsequent treatment processes; and to
determine the effectiveness of the Pool Sweep mode of operation in the control
of solids movement through the surge facility. The principal objectives of the
wet weather flow operation were to determine the hydraulic control characteris-
tics at the higher peak flow rates encountered in. the winter; to determine the
quality of overflow from the Sedimentation-Equalization Basin to the larger stor-
age facility; to determine the effectiveness of the Pool Sweep mode of operation
during the periods of peak flow through the Sedimentation-Equalization Basin,
and to determine the probable storage requirements, both in size and configura-
tion .
19
-------
Figure 12. Dry Weather Flow Diagram
*%££%&- VAR1ES-POOL SWEEP
LEGEND
PUMPING
STATION
O Metering, Recording ft Sampling
Sampling Only
Liquid Level Recording
Normal Flow
Figure 13. Wet Weather Flow Diagram
SEDIMENTATION-
EQUALIZATION STORAGE
BASIN POND
"POOL SWEEP"
LEGEND
O Metering, Recording ft Sampling
I I Sampling Only
Liquid Level Recording
Flow
CONTROLLED FLOW
TO CLARIFIER
(INTERCEPTOR
SEWER- FUTURE)
20
-------
Just prior to the completion of construction of the Demonstration Project facilities,
Rohnert Park's waste discharge requirements were revised and upgraded by the
State of California Regional Water Quality Control Board. The new requirements
precluded the discharge of primary effluent, and therefore, did not allow the
diversions of flow around the 4.86 hectare (12-acre) storage pond. To obtain
the wastewater quality required, all flows had to be given an additional level of
treatment by operating the storage pond as a conventional oxidation pond. The
determination of potential operational problems due to the intermittent filling and
drying of the storage pond was, therefore, not possible.
21
-------
SECTION V
TESTING AND EVALUATION
The Demonstration Project testing covered the period from July 1971 to February
1973. The first two tests, listed as A and B, were begun soon after construction
was completed. The major objectives of these tests were to evaluate the hydraulic
control capability and flexibility of the surge facility and to evaluate the relative
efficiency of the primary clarifier when used in the normal way or when used
following a surge basin. Tests A and B were made under dry weather mode of
operation as discussed in Section IV.
The second set of tests, listed as C and D, were made during the first winter of
the demonstration period (1971-72). They were made using the wet weather mode
of operation, also discussed in Section IV. The very dry winter and subsequent
very low flows during this winter resulted in almost no overflow. For this reason
these two tests are discussed under the heading "Dry Weather Testing."
The third set of tests, numbered 1 through 4, were used to study the overall opera-
tion of the surge facility and, in particular, the solids flow through the basin and
the Pool Sweep operation. These four tests were also made using the wet weather
mode of operation. The tests were run during a "dry weather" period, however,
and an overflow was produced by lowering the underflow rate to approximately
75 percent of the average dry weather flow. For this reason, tests 1 through 4
are discussed under the heading "Dry Weather Testing."
The last set of tests, numbered 5 through 9, represent the testing performed under
wet weather flow conditions. They were used to study the overall operational
characteristics of the surge facility under heavy or peak flow conditions and,
in particular, the solids flow through the basin.
To simplify the identification of each of the tests, Table 1 gives a summary of
the pertinent data for each test.
DRY WEATHER TESTING
Test A
The primary objective of Test A was to provide a trial period of operation to test
the capability and flexibility of the hydraulic control of the surge facility.
Principally, we wanted to achieve the operation of the Sedimentation-Equalization
Basin at a constant underflow rate 24 hours per day accommodating the normal
22
-------
Table 1 . SUMMARY - BASIC TEST PARAMETERS
CO
Test
No.
Dry We
A
B
C
Dl
D2
1
2
3
4
Maximum flow rates
Influent,
l/s°
ather Testing
52. 5C
69.4
84.5
52. 5C
54. 7C
82.0
82.0
75.7
-
Storm Flow Testing
5
6
7
8
9
126
-
170.3
242.9
239.7
Underflow,13
l/s
52.5
-
51.7
36.3
41.6
35.0
35.0
35.0
32.8
37.8
39.4
39.7
37.8
37.8
Overflow,
l/s
0
-
32.8
16. 2C
13. lc
47.0
47.0
40.7
-
88.2
-
130,6
205.1
201.9
Ae rator
On
On
Off
Off
On & Off
Off
Off
Off
Off
Off
Off
Off
Off
Off
Pool
Sweeps
On
On
On
On
On
On
On
Off
On
On
On
On
On
On
Average influent characteristics
Settleable
Solids
ml/l/hr
9.2
8.6
10.8
6.0
9.8
7.87
13.25
11.77
-
7.50
-
4.46
3.25
3.71
Suspended
Solids
mg/l
264
250
305
194
227
167
130
159
-
82
-
79
133
104
BOD,
mg/l
274
224
-
193
202
149
270
238
-
258
-
134
-
70
°0.063 liters per second (l/s) = 1 gallon per minute (gpm).
Underflow remained constant during tests.
cAverage values are given instead of maximums.
Averages shown are for 6 to 22 data points for Tests A through
7 to 12 data points for Tests 5 through 9.
10 to 24 data points for Tests 1 through 4; and
-------
daily influent variation while maintaining the water surface elevation within
acceptable limits. Acceptable limits were considered not high enough to cause
an overflow and not low enough to affect the operation of the aerator.
By observing the influent and underflow flowmeters in conjunction with the
Sedimentation-Equalization Basin stage recorder, it was possible to adjust the
underflow pumps to provide a constant underflow rate out of the basin while
accommodating the daily flow variations. It was found that a total daily water
surface fluctuation of less than two feet at approximate elevations 96 to 98 (one
to two feet below overflow) was required to produce the desired result.
Table 2 shows the results of tests performed on 22 days during the months of
August and September 1971 .
Table 2. TEST A - AVERAGE WASTE STRENGTH OF VARIOUS FLOWS
Characteristics
a
Q avg., l/s
DO, mg/l
Settleable Solids, ml/l/hr
Suspended Solids, mg/l
BOD, mg/l
Influent
52.5
0.0
9.2
264
274
Underflow
0.3
7.4
244
228
Clarifier
effluent
0.1
0.4
120
128
Storage
pond
effluent
5.4
0.1
76
59
0.063 liters per second (l/s) = 1 gallon per minute (gpm)
Test A evaluated: 1) the average characteristics of the raw wastewater (BOD,
DO, flow, Suspended Solids, and Settleable Solids); 2) the change in waste-
water characteristics through the Sedimentation-Equalization Basin; 3) the
treatment efficiency of the primary clarifier under conditions of constant flow
from the bottom of the Sedimentation-Equalization Basin; and 4) the observable
effects of the Pool Sweep operation.
24
-------
During this testing period, the detention time in the Sedimentation-Equalization
Basin was about 10 to 12 hours and the aerator was operated the major portion of
the time. The underflow rate was set to eliminate any overflow from the basin.
The test results shown in Table 2 indicate the following average changes in the
wastewater characteristics as a result of flowing through the Sedimentation-
Equalization Basin: 1) 17% BOD reduction; 2) 15% Suspended Solids reduction;
and 3) 20% Settleable Solids reduction.
Under the condition of uniform flow, the clarifier was able to remove an average
of 44% of the BOD, 50% of the Suspended Solids, and 94% of the Settleable
Solids. The hydraulic loading on the clarifier at a flow rate of 52.5 l/s (1 .2 mgd)
was 75.42 mvmVday (1,850 gpdsf), more than twice the design rate of 32.61
m3/m2/day (800 gpdsf).
The total removal through the Sedimentation-Equalization Basin and the clarifier
was, therefore, 53% BOD, 55% Suspended Solids, and 95% Settleable Solids.
During the initial testing period, the Pool Sweeps went through a trial period in
which the nozzle jet size was varied to obtain the optimum combination of water
volume, pressure and velocity at the end of the floor and wall hoses.
Preliminary observation of the Pool Sweep operation without the aerator indicated
that the action of the hoses "sweeping" the bottom of the basin was helping to
prevent the buildup of solids. The floating portion of the Pool Sweep unit,
however, did not appear to cover as wide an area or follow as arbitrary a path
as did the same units in a swimming pool . The main reason for this appeared to
be the fact that in a swimming pool the Pool Sweep supply hose is long enough to
allow the floating head to hit and run along the vertical sides, but, in our
application, the floating head is "tethered," that is, restrained by the supply
hose rather than the vertical walls. Subsequent to these tests, several modifica-
tions were made to the internal valving of the drive jets. None of the modifica-
tions proved to better the operation of the sweeps, however. Recurring plugging
of the internal valves in the floating head of the Pool Sweep proved to be one
of the major problems associated with the use of a primary effluent for the water
supply.
Our experience would indicate that a water of secondary effluent quality or
better is required to operate the sweeps without plugging. It was later found
that the high concentration of grease in a primary effluent also caused a buildup
within the main body of the Pool Sweep which was detrimental to their operation
and required frequent maintenance.
25
-------
Test B
Test B included the development of background data for future evaluation of the
Sedimentation-Equalization Basin. A specific objective was to establish the
treatment efficiency of the primary clarifier under the normal conditions of
variable hydraulic and solids loading rates. To accomplish this, the raw sewage
was bypassed around the Sedimentation-Equalization Basin directly to the clarifier.
During the testing period, the flow rate through the clarifier varied from 18.9 to
69.4 l/s (300 to 1, TOO gpm) representing surface loading rates of 27.92 to
101 .92 nrVm^/day (685 to 2,500 gpdsf). In general, the flow remained above
50.5 l/s (800 gpm) between the hours of 10:00 a.m. and 10:00 p.m.
Based on the results of six tests made in October 1971, under the above condi-
tions, Test B gave the following results in terms of removal efficiencies through
the clarifier: BOD65%; Suspended Solids61%; and Settleable Solids93%.
The removal efficiences for BOD and Suspended Solids were higher than expected
based on the results of previous tests of clarifier performance when the flow first
passed through the Sedimentation-Equalization Basin. A possible explanation for
this was the action of the aerator and the resulting attrition of the solids as they
passed through the Sedimentation-Equalization Basin. The agitation the waste
receives from the surface aerator probably changes the form of the solids from
larger to smaller and to more soluble forms, also. These would cause the lower
values for Settleable Solids measured in previous tests. The difference is small,
however.
Throughout Test B, we continued to have a plugging problem with the Pool
Sweep units which was attributed ro the supply water. Prior to Test C, a
special screening device for the Pool Sweep water supply was placed in
operation. Using this device, we were able to operate all the Pool Sweeps
continuously for approximately 48 hours. Less than ten minutes was required
for one man to clean the device and place it back in service.
TestC
For Test C, the Demonstration Project facilities were operated according to the
wet weather mode of operation previously shown in Figure 13. However, due to
the unusually dry winter and subsequent low storm flows in the wastewater
collection system, the Sedimentation-Equalization Basin overflowed only twice
and then only a small amount. Under the above conditions of practically no
overflow, additional tests were made to evaluate the changes in the character-
istics of the sewage as it passed through the Sedimentation-Equalization Basin.
During a testing period in late December 1971 when: 1) 2.6 inches of rain fell;
2) the aerator remained off except for very short periods; 3) the inflow varied
from 42.9 to 84.5 l/s (0.98 to 1 .93 mgd) and averaged 48.2 i/s (1.10 mgd); and
26
-------
5) the Pool Sweeps remained on continuously, the following average changes were
documented.
Based on the average results of seven tests made on December 20 through
December 27, 1971, the Settleable Solids were reduced by 24% as the flow
passed through the Sedimentation-Equalization Basin and the remaining Settleable
Solids in the underflow were reduced by 97% in the clarifier. The Suspended
Solids were reduced by 7.4% as the flow passed through the Sedimentation-
Equalization Basin and the remaining Suspended Solids were reduced by 59% in
the clarifier. The BOD was not measured for Test C. These results indicate that
either there was an accumulation of solids in the basin or there was an attrition
of solids taking place in the basin or both.
Tests D! and D2
Prior to Tests D] and D2, in mid-January 1972, the operational procedures of the
surge facility were modified slightly. By reducing the underflow rate to 35.0 l/s
(0.8 mgd) an average overflow rate of approximately 13.1 l/s (0.3 mgd) was pro-
duced. The remainder of the operational schedule remained the same, as did the
sampling and testing program. During two separate periods in the last part of
January and in February, tests were conducted to provide information on the
operational characteristics of the Sedimentation-Equalization Basin under overflow
conditions. The primary objectives of these two tests were the evaluation of
overflow quality in relation to influent quality and the evaluation of the quantity
of solids remaining in the basin. Table 3 summarizes the results of eight tests
made between January 22 and January 31, 1972.
Table 3. TEST D] - AVERAGE WASTE STRENGTHS OF VARIOUS FLOWS
Characteristics
Q avg . , l/sa
BOD, mg/l
Suspended Solids, mg/l
Settleable Solids, ml/l/hr
Influent
52.5
193
194
6.0
Underflow
36.3
167
159
5.5
Overflow
16.2
110
84
0.3
a0.063 liters per second (l/s) = 1 gallon per minute (gpm)
27
-------
The data summarized above are for those days when the aerator was off. In terms
of quality (mg/l), the overflow contained only 57% of the influent BOD, 43% of
the influent Suspended Solids, and 5% of the influent Settleable Solids.
In Test D], a mass balance of BOD and Suspended Solids through the Sedimentation-
Equalization Basin made by multiplying the flow rate times the waste strength,
gives a clear indication of the buildup of solids in the basin. Using the data
presented in Table 3, the mass balances indicate that 60% of the influent BOD and
57% of the influent Suspended Solids were removed in the underflow. At the same
time, 18% of the influent BOD and 13% of the influent Suspended Solids were
removed in the overflow. This means that 22% of the BOD and 30% of the Sus-
pended Solids remained in the basin during the test period , and/or there were
sampling/analytical inaccuracies.
Table 4 summarizes the results of seven tests with the aerator on and seven tests
with the aerator off during the period from February 14 through February 28, 1972.
Table 4. TEST D2 -AVERAGE WASTE STRENGTHS OF VARIOUS FLOWS
Characteristics
Qavg., l/sa
BOD, mg/i
Suspended Solids,
mg/l
Settleable Solids,
ml/l/hr
Influent
Aer. off
54.7
202
227
9.8
Aer. on
54.7
198
219
6.8
Underflow
Aer. off
41 .6
Aer. on
41 .6
Overflow
Aer. off
13.1
96
113
0.4
Aer. on
13.1
176 b
199 b
3.9b
a 0.063 liters per second (l/s) = 1 gallon per minute (gpm)
b
The operator fears that high grease concentrations were interfering with
these test results.
As can be seen from Table 4, the test results with the aerator offwere fairly
consistent with the results of Test Di . That is, the overflow contained 47% of
the influent BOD concentration (mg/l), 50% of the influent Suspended Solids
concentration, and 4% of the influent Settleable Solids concentration.
28
-------
The effects of leaving the aerator on during the periods when the Sedimentation-
Equalization Basin is overflowing to the storage pond are shown in the second set
of data in Table 4. The mixing action of the surface aerator reduced the effective-
ness of the Sedimentation-Equalization Basin to remove solids prior to overflow.
Under these conditions, the overflow contained 57% of the influent BOD concen-
tration (mg/l) as compared to 47% with the aerator off; the overflow contained
89% of the influent Suspended Solids concentration as compared to 50% with
the aerator off; and the overflow contained 57% of the influent Settleable Solids
concentration as compared to 4% with the aerator off. These data clearly show
that the aerator must be left off to allow the basin to remove the greatest amount
of solids prior to overflow to the overflow storage pond.
Test No. 1
Test No. 1 was the first comprehensive test which involved the sampling of all
flows into and out of the Sedimentation-Equalization Basin on an hourly basis
for a complete 24-hour period. During the testing period, the aerator was not
operated at all and the Pool Sweeps were operated continuously. Samples were
taken at the basin influent metering channel, the clarifier influent channel (basin
underflow), and the basin overflow structure. Each sample was analyzed for DO,
BOD, Settleable Solids, and Suspended Solids. A graphical presentation of the
results are shown in Figure 14.
The relationship of the Settleable Solids with time at the three sampling points
shows that there was a marked decrease in the Settleable Solids concentration
between influent and underflow. The two most probable explanations for this
are an attrition of solids, and a net accumulation of large or heavy solids in
the basin. The curves show that during the low flow period from about 2:00 a.m.
to 7:00 a.m., the solids concentration in the underflow remained below those
in the influent. This indicates that the solids which accumulated on the basin
floor during the higher flow period were not being removed as we had anticipated.
The overflow Settleable Solids concentrations were quite low throughout the time
that overflow occurred.
The relationship of the Suspended Solids with time at the three sampling points
shows that during the higher flow periods the underflow contained a lower solids
concentration than the influent, but during the lower flow -period, the underflow
concentration was higher than the influent. The overflow remained considerably
lower in solids than the influent or underflow.
Comparing Settleable and Suspended Solids data it appears that the heavier,
larger Settleable Solids are accumulating in the basin while the lighter, smaller
solids are more effectively being removed by the action of the Pool Sweeps or
the flow patterns set up by the basin underflow or both,
29
-------
Figure 14. Test No. 1 Concentration Curves
\ 20
-N,
5
16
12
I
300
240
ISO
120
60
\
a
350
300
250
200
\50
100
50
T
-^t
. V
V
^AZ
\
LEGE HD : 'LOW
T
\T
\
\
\_.>
JNDEIIFLOW
i)VERirOW
NFLU-NT
s^
^v
\
80
70
60
50
40
30
- 20
0800
1200
1600
2000
TIME
2400
0400
0800
fc
5!
I
30
-------
Figure 14 also shows the relationship of the BOD with time at the three sampling
points. Due to the volume of analytical equipment required for these tests and
the space requirement for the incubation period, we were forced to limit the
number of dilutions for each test. For this reason, these results are probably less
definitive than those for Settleable and Suspended Solids previously given.
Figure 14 does indicate that the BOD concentration in the underflow is not
significantly less than in the influent.
Evaluating these results with those just discussed regarding Suspended and Settle-
able Solids, it is evident that the concentration of soluble and finely suspended
organic matter which is measured as BOD must be increasing in the basin at the
same time that the larger, heavier solids are accumulating in the basin. The most
apparent explanation for this is the anaerobic decomposition of the sludge blanket
which had accumulated on the bottom of the basin prior to and during the test.
This decomposition breaks down solids and converts them to soluble forms of BOD
in the same manner as they are broken down in a digester. Evidence of this is
found in the production of gases which caused large amounts of sludge to rise to
the surface of the basin and the presence of odors which are associated with the
anaerobic decomposition. The mass balances made with the Suspended Solids
and BOD data are presented in Tables 5 and 6. They indicate that on the day
tested there was not an accumulation of total solids in the basin even though
there appears to be a distinct accumulation of large solids as shown in Figure 14,
Settleable Solids.
During the course of the first 24-hour testing period, Test 1, the following
observations were made of the Pool Sweeps and their performance:
1 . All the Pool Sweep units were operating properly at the beginning of the
24-hour testing period.
2. The Sedimentation-Equalization Basin had operated under the test
condition for a period in excess of one week prior to the 24-hour test.
This was done to insure the stability of the basin operation.
3. As the sweeps passed over the bottom of the basin, they would dislodge
large clumps of anaerobic sludge which would rise to the surface where
it would stay and accumulate. The rising clumps of sludge would appear
adjacent to the floating Pool Sweep head and would be accompanied
by released bubbles of gas produced by the anaerobic sludge blanket.
4. The upper sprays on the Pool Sweep floating head which are conven-
tionally used for spraying down the sides of a swimming pool were
not effective in breaking up the floating sludge.
31
-------
Table5. TEST NO . 1. SUSPENDED SOLIDS MASS BALANCE
Time
800
900
1000
1100
1200
1300
1400
1500
1600
1700
1800
1900
2000
2100
2200
2300
2400
0100
0200
0300
0400
0500
0600
0700
0800
Influent
flow rate
l/sQ
63.0
66.2
66.2
68.1
68.1
66.2
63.0
63.0
63.0
69.4
75.7
78.9
82.0
69.4
69.4
63.0
44.2
32.8
34.1
34.1
31.6
31.6
33.4
44.2
Accumulative mass in kilograms
Influent
kg
68.2
122.1
184.6
233.3
298.6
341.5
379.2
432.9
478.3
516.1
582.1
642.6
689.8
741.8
789.8
826.8
865.0
881.5
885.8
893.2
897.7
900.4
905.7
931.2
Underflow
kg
31.8
71.5
103.4
138.3
189.9
239.0
287.2
326.3
354.9
401.7
450.8
477.5
540.6
587.8
635.3
694.3
753.5
774.8
792.8
801.6
810.2
822.3
838.4
867.4
Overflow
kg
3.4
6.9
13.0
20.4
29.1
36.0
42.5
48.8
57.1
65.4
74.3
85.2
93.2
103.1
116.9
125.2
128.8
129.3
129.3
Underflow &
Overflow kg
35.2
78.3
116.4
158.7
218.9
275.1
329.7
375.1
412.0
467.1
525.1
562.7
633.7
690.9
752.2
819.5
882.2
904.1
922.1
931.0
939.6
951.6
967.8
996.8
0.063 liters per second (1/s ) = 1 gallon per minute (gpm)
0.454 kilograms (kg) = 1 pound (Ib)
32
-------
Table 6. TEST NO . 1. BOD MASS BALANCE
Time
1000
1200
1400
1600
1800
2000
2200
2400
0200
0400
0600
0800
Influent
flow rate
l/s a
63.0
66.2
66.2
68.1
68.1
66.2
63.0
63.0
63.0
63.0
69.4
75.7
78.9
82.0
69.4
69.4
63.0
44.2
32.8
34.1
31.6
33.4
44.2
Accumulative mass in kilograms
Influent
L ,
Ky
75.0
182.4
261.0
320.2
433.8
516.4
564.7
652.2
724.9
746.7
766.5
807.5
Underflow
kg
90.9
150.5
224.2
306.0
408.2
480.8
585.9
688.4
756.6
800.4
817.5
854.8
Overflow
kg
11.9
45.0
86.1
111.5
129.7
160.2
192.2
227.1
243.9
245.6
Underflow &
Overflow kg
102.8
195.6
310.3
417.5
537.8
641.0
778.2
915.5
1000.5
1046.0
1063.1
1100.4
b
0.063 liters per second (l/s) = 1 gallon per minute (gpm)
0.454 kilograms (kg) = 1 pound (Ib)
33
-------
5. One of the Pool Sweep units repeatedly looped back over its supply
hose and became entangled and inoperative. This unit was freed and
placed back in service as soon as the problem was observed.
Following Test 1, the Sedimentation-Equalization Basin was drawn down in order
to make a visual inspection of the bottom of the basin. There were large deposits
of sewage solids on the bottom. It is estimated that there was approximately
20,000 gallons of sludge in the basin. The fluid nature of the deposited sludge
made it impossible to determine its spacial arrangement in the basin. There was,
however, evidence of Pool Sweep action In a semicircular pattern in front of
each Pool Sweep supply line connection point. This pattern was indicative of
the lack of mobility previously mentioned which was attributed to the "tethering"
of the Pool Sweeps on the supply hose.
The solids which had accumulated on the bottom of the basin could be removed by
simply drawing down the basin with the underflow pumps. An investigation of
the removal of the solids revealed that it would cost approximately $25 per 1,000
gallons to have the solids trucked away. For the approximate 20,000 gallons
estimated to be hauled away, the cost would be approximately $500. It is feasible
that this method could be used in the future to handle the accumulated solids in
the basin. The operational problems associated with the long detention time of
the sludge, namely the production of odors, would exist, however, and would
detract from the feasibility of using this as a normal mode of operation.
Following the removal of the deposited sludge, the basin was put back in service
with the underflow rate increased to match the average daily influent flow.
The higher flow rate was used in an attempt to minimize the deposition of solids
until the remaining tests could be run.
A preliminary evaluation of the data was made to identify problems and operational
parameters of the Sedimentation-Equalization Basin and the Pool Sweeps. The
results of the evaluation were discussed with the Pool Sweep representatives and
with the EPA Project Officer. As a result of the preliminary evaluation, it was
concluded that the sweep hoses did not have sufficient motion or force to main-
tain the movement of solids along the bottom of the basin. Since the Pool Sweeps
were already operating at the manufacturer's recommended maximum working
pressure of 4.22 to 4.92 kgf/cm2 (60-70 psi), this method of producing the in-
creased motion could not be used. The Pool Sweep representatives experimented
with a "wye" assembly which allowed a single longer bottom hose to be operated
with the combined water of the original two hoses. When operated in a swimming
pool, where its performance could be observed, the change in sweep hose con-
figuration showed improved force and mobility according to the manufacturer.
The "wye" assembly is shown in Figure 8, in the right forefront.
34
-------
Test No. 2
Test No. 2 was used to study solid flow through the basin and its overall operation,
This test was similar to Test No. 1, the only difference being in the amount of
time prior to the test at which the pond was operated under the test conditions.
That is, with the aerator off, the Pool Sweeps on and the underflow at a contin-
uous rate of approximately 35.0 l/s (0.8 mgd). Seven days prior to Test No. 2,
the aerator was turned off and remained off. The Pool Sweeps were operated con-
tinuously for seven days prior to the test and during the test. All flows into and
out of the Sedimentation-Equalization Basin were monitored every hour and one-
half, for a complete 24-hour period. Samples were taken at the basin influent
metering channel, clarifier influent channel (basin underflow) and the basin
overflow structure. Each sample was analyzed for Settleable Solids, Suspended
Solids and BOD. A graphical presentation of the results is shown in Figure 15
which shows that there was a marked decrease in the Settleable Solids concen-
tration between the influent and underflow. It also indicates that a decrease in
the Settleable Solids concentration of the influent is not always paralleled by
a decrease in the Settleable Solids concentration in the underflow. These
results indicate that there is a buildup or a net accumulation of large or heavy
Settleable Solids in the basin. It should be noted, however, that the irregular
pattern of the concentration of Settleable Solids in the underflow could be an
indication that the Pool Sweeps were active and dislodging solids which got into
the underflow. The overflow Settleable Solids were quite low throughout the
time that the overflow occurred.
Figure 15 shows that the underflow contains less total solids than the influent.
Unlike Test No. 1, however, during the low flow period at late night and early
morning, the underflow Suspended Solids concentration did not become greater
than the influent. This is an indication that during this test there was not a
continuing removal of solids from the basin when the influent flow and Suspended
Solids concentration dropped off. The overflow Suspended Solids remained
considerably lower than the influent or underflow throughout the test.
Figure 15 also shows the relationship of the BOD with time at the three sampling
points. The significant things which are shown in this figure is' the somewhat
parallel strengths of the influent and underflow as measured by the BOD and the
fact that the BOD in the underflow is not significantly less than in the influent.
This means that if there is an accumulation of the heavier Settleable Solids in
the basin, there must also be an increase in the other forms of organic loading,
mainly soluble BOD and finer Suspended Solids, that are leaving the basin in
the underflow.
35
-------
Figure 15. Test No. 2 Concentration Curves
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80
70
60
50
40
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0800
1200
1600
2000
TIME
2400
0400
0800
I
I
I
36
-------
The mass balances made with the Suspended Solids and BOD data are presented
in Tables 7 and 8. Table 7 indicates that there was a net accumulation of 333 kg
(733 Ibs) or 50 percent of the total influent Suspended Solids. The BOD mass
balance shows that the total BOD leaving the basin, including both the underflow
and overflow, was approximately 318 kg (700 Ibs) less than the total influent BOD.
Of the total leaving the basin, 69% was in the underflow and 31% was in the
overflow. The only significant difference between the operation of the Sedimenta-
tion-Equalization Basin during Test Nos. 1 and 2 was the amount of time previous
to the test that the basin was operated in the mode tested, that is, with the Pool
Sweeps on and the aerator off. Under these conditions, it has been shown that there
is an accumulation of Settleable Solids in the basin. Prior to Test No. 1, the
amount of solids which accumulated in the basin was quite high. In Test No. 2,
however, the amount was less because of a much shorter period of accumulation.
Test No. 3
Test No. 3 was performed to evaluate the effectiveness of the Pool Sweeps,
specifically. For this test, the aerator was turned off six days prior to the test.
The Pool Sweeps were turned off six days prior to the test and remained off through-
out the test. The underflow pumps ran continuously at a rate of approximately 35.0
l/s (0.8 mgd) throughout the test. The sampling points and the analyses made of
the samples were the same as those used for Test Nos. 1 and 2. A summary of the
significant results of this test are shown graphically in Figure 16 and in tabular
form in Tables 9 and 10.
Figure 16 clearly shows that there was a marked decrease in the amount of Settle-
able Solids which were being removed from the basin in the underflow when the
Pool Sweeps were turned off. As before, the overflow Settleable Solids remained
quite low throughout the test. The curves showing the variation in Suspended
Solids with time indicates that when the Pool Sweeps were not operating, the
Suspended Solids concentrations in the underflow remained fairly constant at
approximately 40 to 80 milligrams per liter (mg/l) with the exception of the first
data point at 0830. The uniformity or variability of these Suspended Solids con-
centrations in the underflow is felt to be a direct indication of the influence of
the Pool Sweeps.
The curves showing the BOD concentration with time generally show that the
underflow and overflow concentration remained similar throughout the period
when overflow occurred. The significance of this, when compared to the same
evaluation made during Test Nos. 1 and 2 indicates that when the Pool Sweeps
are not operating, the consistency of the underflow represents that of a fairly
homogenous mixture of wastewater in the basin. It could be reasoned, therefore,
that the Pool Sweeps, as shown in Test Nos. 1 and 2, were changing the BOD con-
centration in the underflow as a result of their operation and that the lack of varia-
bility of underflow BOD concentration is a direct result of the lack of Pool Sweep
operation.
37
-------
Table 7. TEST NO. 2. SUSPENDED SOLIDS MASS BALANCE
Time
0830
1000
1130
1300
1430
1600
1730
1900
2030
2200
2330
0100
0230
0400
0530
0700
Influent
flow rate
l/s°
31.6
63.1
63.1
63.1
63.1
56.8
56.8
75.7
82.0
75.7
63.1
44.2
28.4
28.4
25.2
25.2
Accumulative mass in kilograms
Influent
kg
24.8
135.3
193.4
254.6
312.9
357.6
416.6
523.3
579.5
608.7
626.4
649.8
659.8
663.0
673.5
675.1
Underflow
kg
10.8
30.1
43.9
62.5
79.6
97.5
114.5
163.9
170.8
180.8
188.9
206.1
215.8
223.2
229.2
236.5
Overflow
kg
8.7
19.6
30.0
38.1
44.4
55.7
73.3
80.5
92.0
95 03
96.4
Underflow &
overflow kg
10.8
30.1
52.6
82.1
109.6
135.6
158.9
219.6
244.2
261.2
280.9
301.5
312.2
319.6
325.6
332.9
0.063 liters per second (l/s) = I gallon per minute (gpm)
0.454 kilograms (kg) = 1 pound (Ib)
38
-------
Table 8. TEST NO. 2. BOD MASS BALANCE
Time
0830
1000
1130
1300
1430
1600
1730
1900
2030
2200
2330
0100
0230
0400
0530
0700
Influent
flow rate
l/s°
31.6
63.1
63.1
63.1
63.1
56.8
56.8
75.7
82.0
75.7
63.1
44.2
28.4
28.4
25.2
25.2
Accumulative mass in kilograms
Influent
kg
156.6
357.5
501.6
812.6
1032.8
1189.8
1246.5
1301.0
Underflow
kg
69.3
168.5
249.1
342.7
427.0
531.9
606.8
681.7
Overflow
kg
73.5
118.9
196.3
284.8
307.3
310.3
Underflow &
Overflow kg
69.3
242.1
367.9
539.0
711.8
839.1
917.0
991.9
0.063 liters per second (1/s) = 1 gallon per minute (gpm)
b
0.454 kilograms (kg) = 1 pound (Ib)
39
-------
Figure 16. Test No. 3 Concentration Curves
24
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70
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0800 1200 1600 2000 2400 0400 0800
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40
-------
Table 9. TEST NO. 3. SUSPENDED SOLIDS MASS BALANCE
Time
0830
1000
1130
1300
1430
1600
1730
1900
2030
2200
2330
0100
0230
0400
0530
0700
Influent
flow rate
1/3°
56.8
62.1
69.4
69.4
63.1
63.1
63.1
69.4
75.7
69.4
56.8
44.2
31.6
31.6
25.2
25.2
Accumulative mass in kilograms
Influent
kg
23.0
92.1
152.4
238.8
289.5
336.8
385.5
452.2
444.9
644.8
662.7
681.0
692 00
702.7
712.0
716.0
Underflow
kg
40.6
50.6
58.5
68.1
81.0
90.3
102.3
110.0
123.6
140.3
153.7
166.6
179.7
189.4
197.1
206.8
Overflow
kg
6.0
13.5
22.0
31.7
40.3
44.8
53.0
62.4
76.0
86.4
92.9
95.9
Underflow &
overflow kg
46.6
64.1
80.5
99.8
121.3
135.1
155.4
172.4
199.6
226.6
246.6
262.4
275.6
285.3
293.0
302.7
0.063 liters per second (1/s) = 1 gallon per minute (gpm)
'0.454 kilograms (kg) = 1 pound (Ib)
41
-------
Table 10. TEST NO. 3. BOD MASS BALANCE
Time
0830
1000
1130
1300
1430
1600
1730
1900
2030
2200
2330
0100
0230
0400
0530
0700
Influent
flow rate
l/s°
56.8
63.1
69.4
69.4
63.1
63.1
63.1
69.4
75.7
69.4
56.8
44.2
31.6
31.6
25.2
25.2
Accumulative mass in kilograms
Influent
kg
122.6
309.8
473.3
645.6
915,3
993.9
1072.3
1088.6
Underflow
kg
41.2
99.3
148.0
202.3
286.6
354.0
440.2
503.8
Overflow
kg
32.2
101.5
139.8
199.7
289.6
307.5
Underflow &
Overflow kg
73.4
200.8
287.8
402.0
576.2
661.5
747.6
811.3
0.063 liters per second (1/s) = 1 gallon per minute (gpm)
L
0.454 kilograms (kg) = 1 pound (Ib)
42
-------
The mass balances for Suspended Solids and BOD through the Sedimentation-
Equalization Basin are presented in Tables 9 and 10. Comparing the Suspended
Solids mass balance from this test with that of Test No. 2 indicates that without
the Pool Sweeps in operation there was only a slight decrease in the amount of
Suspended Solids removed in the underflow. This result indicates that while the
Pool Sweeps did have a positive effect on the removal of Suspended Solids, the
net effect was not as substantial as had been anticipated. The BOD mass balance,
shown in Table 10, shows that 46% of the influent BOD was removed in the
underflow. This compares to a 60% removal obtained in Test No. 2 when the
Pool Sweeps were in operation. This again documents the fact that although there
was an increase in the amount of BOD being removed in the underflow with the
Pool Sweeps in operation, that increase was not substantial .
Test No. 4
To investigate the effects of the influent configuration of the Sedimentation-
Equalization Basin as it applies to the solids flow characteristics of the basin,
Test No. 4 was devised. For this test, the aerator was turned off five days prior
to and during the test. The Pool Sweeps ran continuously for five days prior to
and during the test. The underflow pumps ran continously at an average rate of
32.8 l/s (0.75 mgd) throughout the test. On the day of the test, as soon as
the Sedimentation-Equalization Basin began to overflow, the influent was diverted
around the basin directly to the primary clarifier. After the diversion had been
made, the only things operating within the basin were the underflow pump and
the Pool Sweeps. The objective of this test was to determine if the influent
configuration, as previously shown in Figure 4, had a discernible effect on the
ability of the Pool Sweeps or the bottom currents produced by the underflow to
aid in the removal of Settleable Solids and Suspended Solids and BOD from the
basin.
When the test began and the influent was diverted, the influent BOD and
Suspended and Settleable Solids obviously stopped also. The measurements of
the underflow concentration from that point on were measurements of the basin
contents and any contribution of solids which were dislodged from the bottom by
either the Pool Sweeps or the underflow current. Comparing the results shown
in Figure 17 for Test No. 4 and Figure 15 for Test No. 2, it is obvious that a
major portion of the solids in the underflow come directly from the influent flow.
Figure 17 clearly shows that when the influent flow was diverted, the underflow
Settleable Solids dropped immediately to the level associated with the minimum
flows at night during Test No. 2. The Settleable Solids tests indicated that the
influent configuration and any resulting flow circulation patterns did not have a
significant effect on the concentration of Settleable Solids in the underflow.
Comparing Suspended Solids concentration curves also indicates.that any turbulence
or circulation patterns in the area of the center sump caused by the incoming flow
43
-------
Figure 17. Test No. 4 Concentration Curves
12
\ 10
ki
\
fen
250
200
150
100
50
\
03
350
300
250
200
150
100
50
\
IO-30
z
UNDERFLOW
UNDERFLOW
Dl\
\JJ_NDEKFLOW
'ERTED
N
\
0800
1000
1200
1400
TIME
1600
1800
2000
44
-------
did not significantly affect the concentration of Suspended Solids removed in the
underflow. The fact that the Settleable Solids, Suspended Solids and BOD remained
fairly stable and similar to those values experienced in Test No. 2 is due to the
fact that without the influent waste we are drawing off the fairly homogeneous
basin contents which have a relatively high strength due to the accumulation of
solids in the basin.
Table 11 indicates the accumulative total pounds of both BOD and Suspended
Solids in the underflow during the testing period. During the time from 10:00 a.m.
until 7:00 p.m., 247 kg (545 Ibs) of BOD and 67 kg (148 Ibs) of Suspended Solids
were contained in the underflow. During the same period of time in Test No. 2,
where the only significant difference was the presence of the influent flow to the
basin, 211 kg (465 Ibs) of BOD and 79 kg (174 Ibs) of Suspended Solids were con-
tained in the underflow. In general, the mass balance information indicates that
the configuration of the basin center sump and the physical arrangement of the
influent pipe only slightly affected the overall Suspended Solid and BOD removal
in the basin.
Table 11. TEST NO. 4. UNDERFLOW MASS
Time
0830
0930
1030
1130
1230
1330
1430
1530
1630
1730
Underflow
rate
l/sa
136.1
136.1
133.7
132.5
128.9
127,7
119.4
18-H5
lOteS
10K5
Accumulative mass in kilograms'*
Suspended solids
kg
6.4
21.9
36.4
44.8
53.9
64.8
71.5
80.6
89.3
97.8
BOD
kg
36.2
63.4
109.1
134.3
160.7
202.0
245.1
279.8
310.7
335.8
°0.063 liters per second (1/s) = 1 gallon per minute (gpm)
0.454 kilograms (kg) = 1 pound (Ib)
45
-------
STORM FLOW TESTING
Tests Nos. 5 through 9 were conducted in the winter of 1972-1973 and were
tests of the hydraulic surge facility under wet weather flow conditions. All of
the tests, with the exception of No. 6, were carried out with the aerator off, the
Pool Sweeps on and a constant underflow rate. Figure 18 graphically shows the
daily rainfall for the winter of 1971-1972 and 1972-1973 and the resuling average
daily flow into the demonstration facilities. It should be noted that the winter of
1971-1972 was very dry with only thirteen total inches of rainfall compared to a
normal of about thirty inches. Because of the lack of any significant storm flows
into the demonstration facilities, we were not able to generate any meaningful
data on the performance of the surge facility under stormflow conditions during
the 1971-72 winter. For this reason, the Demonstration Project was extended to
include the winter of 1972-73. The days on which the major tests were made are
shown in Figure 18. The major storms in January, 1973, were not tested because
of equipment failure affecting the Pool Sweep operation.
Test No. 5
The test conditions for Test No. 5 were moderate stormflows and normal Sedimenta-
tion-Equalization Basin operation. The influent flow for this test ranged from
75.7 l/s (1,200 gpm) to 126 l/s (2,000 gpm). The underflow rate was a constant
37.8 l/s (600 gpm). For this test, the aerator was turned off and the Pool Sweeps
were turned on at 8:00 a.m. in the morning just prior to the beginning of the test.
A graphical presentation of the test results for Settleable Solids, Suspended Solids,
and BOD concentrations are shown in Figure 19. Comparing the Settleable
Solids curves and the Suspended Solids curves, it can be seen that most of the
larger heavier Settleable Solids were accumulating in the basin rather than
being carried out with the underflow. And at the same time, the remaining
Suspended Solids were being removed in the underflow almost as fast as they
were coming into the basin. The curve showing the BOD concentration versus
time indicates that the underflow BOD remained above the influent BOD con-
centration during most of the testing period. This would indicate that during
the higher stormflow periods, there is a flushing out of the higher concentrations
of BOD in the basin by the less concentrated stormflows. Observation of the
overflow quality characteristics of the surge facility indicates that almost all
Settleable Solids were removed before overflow, that a significant amount (34%)
of the Suspended Solids were removed before overflow and that a large amount
(79%) of BOO was removed before overflow.
To more precisely document the total flow of BOD and Suspended Solids through
the basin, mass balances shown in Tables 12 and 13 were prepared. The Sus-
pended Solids mass balance shown in Table 12 indicates that 33% of the influent
Suspended Solids was removed in the underflow. The overflow contained
46
-------
Figure 18. Rainfall and Daily Flows
(T) DENOTES TEST NUMBER
T WINTER 1971-1972
OCT. NOV. DEC. JAN.
FEB.
MAR.
5
4
o
D>
E
I
a>
OCT.
WINTER 1972-1973
NOV. DF,C. JAN.
FEB.
MAR.
47
-------
Figure 19. Test No. 5 Concentration Curves
I
5
§
§
ki
I
Ui
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K
Uj
$
PENDED SOLIDS -mg/
\
10
8
6
250
200
150
100
50
350
300
250
200
150
100
50
O
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\
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4
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NT
ki nw
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^~ ^^
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-
-
"
-
-
130
120
no
100
90
80
70
60
I
0800
1000
1200
1400
TIME
1600
1800
2OOO
48
-------
Table 12. TEST NO. 5. SUSPENDED SOLIDS MASS BALANCE
Time
0830
0930
1030
1130
1230
1330
1430
1530
1630
Influent
flow rate
l/s
75.7
82.0
126.2
126.2
126.2
123.0
116.7
75.7
75.7
b
Accumulative mass in kilograms
Influent
kg
22.6
45.0
85.9
121.8
156.3
201.4
231.7
253.5
275.3
Underflow
kg
15.5
24.4
32.7
42.3
52.9
62.2
70.7
80.9
90.0
Overflow
kg
6.5
15.1
28.9
49.0
65.6
83.5
98.7
106.9
113.9
Underflow &
overflow kg
22.0
39.5
62.5
91.3
118.5
145.7
169.4
187.8
203.7
a0.063 liters per second (l/s) = 1 gallon per minute (gpm)
b0.454 kilograms (kg) = 1 pound (Ib)
Table 13. TEST NO. 5. BOD MASS BALANCE
Time
0830
0930
1030
1130
1230
1330
1430
1530
1630
Influent
flow rate
l/s0
75.7
82.0
126.2
126.2
126.2
123.0
116.7
75.7
75.7
Accumulative mass in kilograms
Influent
kg
102.2
320.1
513.0
654.7
Underflow
kg
46.8
118.9
193.8
231.5
Overflow
kg
25.0
63.6
96.7
114.0
Underflow &
overflow kg
71.8
182.5
290.6
345.5
a0.063 liters per second (l/s) = 1 gallon per minute (gpm)
"0.454 kilograms (kg) = 1 pound (Ib)
49
-------
approximately 41% of the mass of Suspended Solids due to the high overflow rate
even though the concentration remained below that of the influent and underflow.
This left approximately 26% of the influent Suspended Solids which accumulated
in the basin. The BOD mass balance shown in Table 13 indicates that approximately
35% of the influent BOD was removed in the underflow while only 17% remained
in the overflow. This left approximately 48% which accumulated in the basin
during the testing period.
Test No. 6
Test No. 6 was conducted to duplicate the operational parameters of Test No. 4,
that is, try and determine if the basin influent configuration could be influencing
the flow of solids through the basin. For this test, the aerator was turned off two
days prior to the beginning of the test. The Pool Sweeps ran continuously for two
days prior to the test and during the test. The underflow rate varied from 39.4 l/s
(625 gpm) at the beginning of the test to 30.6 l/s (485 gpm) at the end of the
test. The influent flow was diverted around the surge facility to the clarifier just
prior to the beginning of the testing period. The underflow test results are shown
in Figure 20. In general, the strength of the underflow, as measured by the
Settleable Solids, Suspended Solids and BOD, was less during this test than it was
for Te^st No. 4. Settleable Solids, Suspended Solids, and BOD were approximately
1 .5 ml/l/hr., 80 mg/l and 300 mg/l, respectively, during Test No. 4 compared to
0.2 ml/l/hr., 50 mg/l and 90 mg/l, respectively, during Test No. 6. This was
due to the fact that this test was conducted during the winter when the overall
flow through the basin was greater than during the previous testing period. The
average' influent concentrations for both tests which should be used when compar-
ing the underflow concentrations were previously shown in Table 1. The con-
sistent low values and lack of variation shown in Figure 20 again indicates that
the action of the Pool Sweeps was not dislodging or moving solids so that they
could be removed in the underflow. Table 14 shows the accumulative total pounds
of Suspended Solids and BOD which were removed in the underflow. The decrease
in the total kilograms of BOD in the underflow for this test as compared to Test
No. 4 is due primarily to the weaker waste as mentioned in the discussion of
Test No. 5.
Test Nos. 7, 8 and 9
Tests 7, Sand 9 conducted in the month of February, 1973, were the principal
tests of the storm flow operation of the Sedimentation-Equalization Basin. For
each of these tests, the aerator was turned off and the Pool Sweeps turned on in
the morning prior to the beginning of the tests. The underflow rate remained
at approximately 37.8 l/s (600 gpm) during each of the three tests. In Test
No. 7, the influent flow rate varied between 118.2 l/s (1,874 gpm) and
170.3 l/s (2,706 gpm). This represents a detention time in the Sedimentation-
50
-------
Figure 20. Test No. 6 Concentration Curves
10
§ s
\
o.
250
200
\50
5 I0°
I
50
350
300
250
200
150
100
50
oeoo
e-oo
FLOW
DIVERTED
7
UVDER,
UNDERFLOW
z
1000
1200
1400
TIME
1600
1800
2000
5]
-------
Table 14. TEST NO. 6. UNDERFLOW MASS
Time
0800
0900
1000
1100
1200
1300
1400
1500
1600
1700
1800
1900
Underflow
rate
l/sa
149.2
149.2
149.2
146.9
140.9
140.9
132.5
132.5
131.3
125.3
119.4
115.8
Accumulative mass in kilograms
Suspended solids
kg
7.2
15.8
20.1
28.2
36.2
41.4
46.1
52.3
57.5
64.4
79.1
89.4
BOD
kg
36.9
57.6
81.3
113.9
131 .8
145.0
0.063 liters per second (1/s) = I gallon per minute (gpm)
0.454 kilograms (kg) = 1 pound (Ib)
52
-------
Equalization Basin of approximately 4-1/2 to 5-1/2 hours. In both Test Nos.
8 and 9, the influent flow rate varied between approximately 183.9 l/s
(2,915 gpm) and 240.8 l/s (3,817 gpm). This represents a detention time in the
Sedimentation-Equalization Basin of between 3-1/2 and 4-1/2 hours. The flows
during Test Nos. 8 and 9 were very close to the design peak flow for the surge
facility of 263 l/s (6 mgd) and the design detention time of three hours. A
graphical presentation of the storm flow testing data is given in Figures 21, 22,
and 23. In addition, the data are tabulated in terms of the mass balances for
both Suspended Solids and BOD in Tables 15 through 19.
Comparing the Settleable Solids curves for each of the tests, it can be seen that
when the storm flows became a very large percentage of the total flow, the
Settleable Solids became less concentrated and less variable, primarily between
three and five milliliters per liter per hour (ml/l/hr). The higher storm flows
did not significantly increase the concentration of Settleable Solids in the over-
flow over the values occurring during earlier tests with much lower overflow
rates. Even when the detention time in the Sedimentation-Equalization Basin
was reduced to less than four hours there was an accumulation of larger and/or
heavier solids in the basin. This is apparent when the Settleable Solids concen-
trations for the influent and underflow are compared.
The overflow Suspended Solids concentrations increased only marginally over what
they were in earlier tests. As in previous tests with lower influent flow rates,
the underflow Suspended Solids concentration is about the same as or slightly
less than the influent concentration.
The Suspended Solids mass balances through the Sedimentation-Equalization
Basin for the three major storm flow tests indicate that when the storm flow rate
became quite high, near 241 l/s (3,816 gpm), the percentage of influent Sus-
pended Solids being removed in the underflow was reduced. However, the total
amount of Suspended Solids being removed from the basin including the over-
flow was approximately the same for all three tests. In the three tests, the per-
centage of Suspended Solids which was not removed and, therefore, must have
accumulated in the basin during the seven-hour period from 10:00 a.m. to
5:00 p.m., amounted to 43%, 42% and 38% for Test Nos. 7, 8 and 9,
respectively.
In the case of the BOD mass balance through the Sedimentation-Equalization
Basin, there was a marked difference in the manner in which the mass passed
through the basin. Comparing Test Nos. 7 and 9, when the influent flow rate
varied from 171 l/s (2,706 gpm) to 241 l/s (3,817 gpm), respectively, the
percentage of the influent BOD being removed in the underflow was fairly
constant at about 15%. The percentage of influent BOD removed in the over-
flow, however, varied considerably from 44% in Test No. 7 to 76% in Test No. 9.
53
-------
Figure 21 . Test No. 7 Concentration Curves
*
-X.
\
5
«0
5
§
Uj
5!
3
d
^
^
<0
\
I
CO
5
§
1
s
§
^
12
10
250
200
150
100
50
\
ci
Ci
Hi
350
300
250
20O
150
100
50
0800
-V
\.
LEGEND; F
_ow
fltFttJENT
UNDER! 3.0
py/ERFLQW
\
\
1000
1200
1400
TIME
1600
1800
180
170
160
150
140
130
120
110
100
90
80
70
2000
Q
k.
54
-------
Figure 22. Test No. 8 Concentration Curves
C:
V ,2
\
S ,o
1 .
^1
SJ
6
U
vl
J .
J
*^
U 2
0
S 250
3>
200
2
J 150
1
i 100
I
? 50
i
0
350
300
* 250
s 20°
i
3
150
100
50
v^
/'
X
^--
y
/
/
/
/
[^ ^s.
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V
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^
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INF
UN
(JV
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ow
LUEN
DERF
tKhL
^.^'"
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t-::-- _
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\
A
\
N
-
-
.
-
-
250
240
ti
230 i
220
fc
2,0 5
200 C
5
190 k
8
180 ^
|
170
0800 1000 1200 1400 1600 1800 2000
TIME
55
-------
Figure 23. Test No. 9 Concentration Curves
^ 12
\
S 10
5 8
0 '
\ 250
?
200
1
5
J 150
0
i 100
3
jj 50
1
r>
o
350
300
a, 250
i 20°
i
a
150
100
50
0
I
\
\
\
/
/
/
^~
\^~~
LEC
\
\
\
\
W^_
\
\
\
/
1
1
1
i
i
~~~'
i
END:
x-''
*=--^
/
/
/
(
^'.U
FLOW
INFLI
UNDE
OVER
K"\.
1 .
^s.
V.
1^-..
JENT
RFLOV
FLOW
^/x
^
V
X
\
\
\
(r. r=
1
-
-
~
-1
-
-
250
240
230 ^
220
U
k
210 Q
^
200 <;
x
U
190 .
P"
X
U
180 -
U
ITO
0800 1000 1200 1400 1600 1800 2000
TIME
56
-------
Table 15. TEST NO. 7. SUSPENDED SOLIDS MASS BALANCE
Time
0800
0900
1000
1100
1200
1300
1400
1500
1600
1700
1800
1900
Influent
flow rate
l/s°
145.1
160.9
170.3
170.3
164.0
157.7
151.4
148.3
145.1
141.9
141.9
116.7
Accumulative mass in kilograms
Influent
kg
21.4
75.8
128.5
178.8
237.8
294.0
337.6
381.4
417.9
441.4
486.9
520.4
Underflow
kg
9.7
19.9
36.5
49.2
58.3
66.1
74.9
82.9
90.3
99.8
109.5
117.8
Overflow
kg
15.4
35.8
52.9
72.0
93.8
111.9
127.4
148.9
162.8
177.4
198.4
211.7
Underflow &
overflow kg
25.1
55.7
89.4
121.2
152.1
178.0
202.3
231.8
253.1
277.2
307.9
329.5
0.063 liters per second (1 /s) - 1 gallon per minute (gpm)
0.454 kilograms (kg) = 1 pound (Ib)
57
-------
Table 16. TEST NO. 7. BOD MASS BALANCE
Time
0800
0900
1000
1100
1200
1300
1400
1500
1600
1700
1800
1900
Influent
flow rate
l/s0
145.1
160.9
170.3
170.3
164.0
157.7
151.4
148.3
145.1
141.9
141.9
116.7
Accumulative mass in kilograms
Influent
kg
91.4
297.3
524.3
647.0
821.9
880.7
Underflow
kg
21.4
50.0
77.2
101.5
133.0
151.6
Overflow
kg
167.1
241.1
343.0
413.2
487.6
526.3
Underflow &
overflow, kg
188.5
291.1
420.1
514.7
620.5
678.0
a0.063 liters per second (1/s) - 1 gallon per minute (gpm)
0.454 kilograms (kg) = 1 pound (Ib)
58
-------
Table 17. TEST NO. 8. SUSPENDED SOLIDS MASS BALANCE
Time
0800
0900
1000
1100
1200
1300
1400
1500
1600
1700
Influent
flow rate
l/sa
233.4
242.9
242.9
239.7
236.6
230.3
227.1
217.6
208.2
195.6
Accumulative mass in kilograms
Influent
kg
125.1
280.7
438.0
560.5
669.4
752.3
840.6
936.1
1039.4
1097.1
Underflow
kg
11.3
25.1
36.8
48.2
67.0
80.1
91.2
104.6
120.7
134.6
Overflow
kg
47.8
83.3
126.8
180.6
232.8
284.0
335.0
384.2
425.9
467.9
Underflow &
overflow kg
59.2
108.3
163.6
228.8
299.8
364.1
426.3
488.8
546.6
602.5
0.063 liters per second (1/s) - I gallon per minute (gpm)
0.454 kilograms (kg) = I pound (Ib)
59
-------
Table 18. TEST NO. 9. SUSPENDED SOLIDS MASS BALANCE
Time
0800
0900
1000
1100
1200
1300
1400
1500
1600
Influent
flow rate
1/3°
183.0
195.6
220.8
239.7
233.4
227.1
227.1
Accumulative mass in kilograms
Influent
kg
55.9
177.7
268.3
354.5
441.1
504.8
567.7
Underflow
kg
8.7
18.2
33.4
48.4
61.2
71.6
82.7
Overflow
kg
20.9
41.9
93.9
134.6
179.6
227.3
266.1
Underflow &
overflow kg
29.6
60.1
127.3
183.0
240.8
298.9
348.8
0.063 liters per second (1/s) - I gallon per minute (gpm)
0.454 kilograms (kg) = 1 pound (Ib)
60
-------
Table 19. TEST NO. 9. BOD MASS BALANCE
Time
0800
0900
1000
1100
1200
1300
1400
1500
1600
Influent
flow rate
l/s°
183.0
195.6
220.8
239.7
233.4
227.1
227.1
Accumulative mass in kilograms
Influent
kg
112.4
324.6
496.2
Underflow
kg
22.5
38.8
65.4
Overflow
kg
188.0
317.4
409.4
Underflow &
overflow kg
210.4
356.2
474.8
30.063 liters per second (1/s) = 1 gallon per minute (gpm)
0.454 kilograms (kg) = 1 pound (Ib.)
61
-------
This brought the total BOD removed from the basin both in the underflow and in the
overflow to 59% for Test No. 7 and 89% for Test No. 9. This means that approxi-
mately 41% of the influent BOD remained in the basin or was accumulated during
the lower storm flow period of Test No. 7 as compared to only 11% contained in
the basin during Test No. 9.
In order to compare the mass balance data for Tests 1 through 9, Tables 20 and 21
were prepared. Table 20 summarizes the total mass of Suspended Solids entering
the basin in the influent and leaving the basin in both the underflow and over-
flow during the same seven-hour period of each test. Table 21 summarizes the
total mass of BOD entering and leaving the basin during the same seven-hour
period. To aid in the evaluation of the mass balance data in Tables 20 and 21,
the following information Is pertinent to the individual test conditions.
Test Nos. 1 and 2 were parallel tests with the only difference being
in the amount of time prior to the actual test that solids were allowed
to accumulate in the basin.
Test Nos. 2 and 3 were run consecutively with the Pool Sweeps re-
moved from the service during Test No. 3.
Test Nos. 2 and 4 were parallel tests with the influent flow diverted
away from the Sedimentation-Equalization Basin during Test No. 4.
Test Nos. 4 and 6 were parallel tests except that Test No. 6 was
run during the winter when the normal flow rate was higher and the
resulting waste strengths were less.
Test No. 5 was normal winter operation with minor storm flows of
75.7 to 126 l/s (I,200to2,000gpm).
Test No. 7 was normal winter operation with moderate storm flows of
145 to 170 l/s (2,300 to 2,700 gpm).
Test No. 8 was normal winter operation with heavy storm flows of
196 to 243 l/s (3,100 to 3,850 gpm).
Test No. 9 was normal winter operation with heavy storm flows of
183 to 240 l/s (2,900 to 3,800 gpm).
62
-------
Table 20. SUMMARY OF SUSPENDED SOLIDS MASS BALANCES
Test
No.
1
2
3
4
5
6
7
8
9
Mass in 7 hours , kgb
Influent
356
262
277
230
342
759
568
Underflow
283
79
48
67
65
42
70
96
83
Overflow
50
42
37
99
127
343
266
Percent of influent
Underflow
80%
30%
17%
28%
20%
13%
15%
Overflow
14%
16%
13%
43%
37%
45%
47%
Remained
1 n RcLsln
6%
54%
70%
29%
43%
42%
38%
aTo enable a comparison of all tests, the mass data is for the seven-hour
period from 10:00 to 17:00.
i '
0.454 kilograms (kg) = 1 pound (Ib)
Table 21. SUMMARY OF BOD MASS BALANCES
Test
No.
1
2
3
4
5
6
7
8
9
Mass in 7 hours , kg
Influent
408
613
643
440
Underflow
266
211
125
247
206
86
96
54
Overflow
109
145
128
100
283
315
Percentof influent
Underflow
88%
47%
31%
34%
15%
13%
Overflow
36%
32%
31%
16%
44%
72%
Remained
In Basin
-24%
21%
38%
50%
41%
15%
°To enable a comparison of all tests, the mass data is for the seven-hour
period from 10:00 to 17:00.
0.454 kilograms (kg) = 1 pound (Ib)
63
-------
SECTION VI
DISCUSSION
GENERAL
As used in this report, the term surge facility represents the total facility, in-
cluding raw sewage pumps, Sedimentation-Equalization Basin, underflow
pumping, storage pond and overflow chlorination, whereas the term Sedimenta-
tion-Equalization Basin refers only to the basin itself along with the associated
influent pipe, Pool Sweeps, aerator, overflow structure and skimming structure.
In the development of a surge facility, there are two main items of concern.
The first is the control of the hydraulics of the system; that is, the control of
the volume and rates of flow of the wastewater through the facility. The
second is the control of the solid portion of the wastewater.
The control of the hydraulics is only dependent on the inflow and outflow rates
including average, minimum, maximum and duration. The sizing of all storage,
pumping and control facilities can be based on these parameters using sound
theoretical approaches.
The control of the solids movement through surge facilities is not nearly so cut
and dried. Since a surge facility practically by definition is a settling basin,
there will be some separation of solids in its normal operation. The size, shape
and flow pattern of a surge facility will govern the amounts of solids separation
that will take place. The deposition of solids can be desirable in cases where
partial treatment is desired or if the operation of the basin is set up to remove
accumulated solids periodically and perhaps truck the concentrated sludge to
the treatment plant directly. In most cases, however, the surge facility is used
only to store excess wastewaters until they can be placed back into the waste
stream or treatment process. In these cases, the objective or goal is to be able
to return all of the solids. Any solids remaining in a surge facility become a
handling problem at the least; and in the case of domestic waste solids, can
also become a nuisance or even a health hazard.
At the present time, the three generally accepted methods of preventing the
accumulation of sewage solids in a surge or storage facility is with mechanical
collection equipment installed in a specially designed concrete structure , by
providing very steep side slopes to a central draw-off point, or by providing
mixing with sufficient power to keep the wastewater contents completely mixed.
In the first case, the mechanical sludge collection equipment and necessary
structure(s) are expensive. In the second case, the restriction on structural
64
-------
shape, primarily the depth of sumps, eliminates this alternative except for per-
haps the very smallest facilities. In the third case, the power cost to provide
sufficient mixing is also expensive; and with the contents of a surge facility
completely mixed, any overflow would contain an excessive amount of solids
which would then accumulate in a storage facility if one exists or be discharged
as effluent.
HYDRAULIC CONTROL
The ability to control the Sedimentation-Equalization Basin to produce the de-
sired uniform flow rate was documented early in the Demonstration Period.
With the influent and underflow metered and the water surface monitored con-
tinuously, it was relatively easy to produce a uniform underflow rate during
normal dry weather flow periods while maintaining a desired variation in water
surface and preventing overflow to the storage pond. The Sedimentation-
Equalization Basin volume of approximately 3/4 of the average daily flow appears
to be adequate for this purpose. The design of the Sedimentation-Equalization
Basin provides for a volume of approximately 378.8 m^ (100,000 gallons) in the
top 0.3 m (1.0 ft) when the water surface is at elevation 99.0.
OVERFLOW QUALITY
One of the principal objectives of the Sedimentation-Equalization Basin is to
minimize the strength of the waste which overflows into the storage pond. To
minimize potential operation problems, such as nuisance from odors or flies or
ultimate removal requirements, associated with the deposition of solids and the
intermittent filling and drying of an overflow storage pond, it is important that
all wastes discharged to the pond be as low in solids, and particularly Settleable
Solids, as possible. To show the quality improvement which was gained through
the basin during the testing periods, Table 22 was prepared. This table indicates
the percent removal of BOD, Suspended Solids and Settleable Solids through
the Sedimentation-Equalization Basin during the portion of each major test in
which there was a significant overflow to the storage pond. Tests C, Di, and
Do were not included because test procedures and low storm flows resulted in
almost no overflow. Comparing the various tests, it can be seen that the in-
fluent flow rate varied from 56.8 to 227.1 l/s (900 to 3,600 gpm), and the
resulting theoretical hydraulic detention time varied from 13.9 to 3.6 hours.
The first thing which can be seen is that the operation of the Sedimentation-
Equalization Basin and its configuration and flow characteristics cause it to
operate less efficiently than a conventional clarifier. At the relatively long
hydraulic detention times, 3.6 to 13.9 hours, the removal efficiency for
Settleable Solids, Suspended Solids and BOD were all significantly lower than
you could expect from a conventional clarifier. The principal reasons for this
are the short-circuiting which is likely to occur due to the relative position
65
-------
of the influent and overflow in the basin and the effects of the accumulation of
solids in the basin. The short-circuiting is thought to be the major cause of the
lower Settleable and Suspended Solids removals while the accumulation of solids
in the basin is almost certainly the-cause of the erratic and generally low values
of BOD removal.
The BOD removals are most unpredictable and seem not directly dependent on
hydraulic loadings. There is a trend in the removals of Suspended Solids which
indicates that when the hydraulic loading approached a 3-hour detention time,
the removals were reduced to approximately 45% from approximately 55% at the
longer detention times. The Settleable Solids removals remained high in all the
tests and did not show signs of decreased quality until the theoretical detention
time dropped below five hours.
Table 22. AVERAGE OVERFLOW QUALITY
Test
No.
1
2
3
5
7
8
9
Influent
Rate
1/s*
56.8
58.0
63.7
89.6
151.4
227.1
. 218.3
Detention
Time
Hours
13.9
13.6
12.4
8.8
5.2
3.5
3.6
Overflow
Rate
l/s
22.1
23.3
29.0
51.7
111.7
189.3
180.4
Percent Removal
Settleable
Solids
99
98
97
99
98
94
90
Suspended
Solids
54
53
68
34
44
48
44
BOD
-12
26
31
79
31
0
Percent of influent removed in basin prior to overflow to storage pond. Based
average concenfration in mg/l over the test period.
0.063 liters per second (l/s) = 1 gallon per minute (gpm)
on
SOLIDS MOVEMENT
One of the primary functions of the Sedimentation-Equalization Basin is to
maintain the flow of solids through the surge facility while damping out the
hydraulic peaks. The following section discusses the pertinent factors affecting
the flow of solids through the Demonstration Project facilities. The discussion
66
-------
is based on the evaluation of test results described in Section V and on the
practical experience gained through operation of the surge facility.
Parameters Affecting Solids Movement
Those components of the design which were expected or found to have an effect
on the solids movement through the surge facility included: 1) basin configuration;
2) underflow pumping; 3) aerator; 4) Pool Sweeps; and 5) the hydraulic loading.
Basin Configuration -
The following elements of the basin configuration were found to have an effect
on the movement of solids through the Sedimentation-Equalization Basin:
1) side slopes; 2) bottom slope; 3) influent configuration; and 4) depth of water
in the basin.
Although the slope of the sides of the basin were designed as steep as the soil
conditions would allow (two horizontal to one vertical) it was not steep enough
to prevent the deposition of solids. The bottom slope was purposely designed
flatter to simulate the probable conditions which would exist if this facility were
larger and the bottom slope could not be made steeper. The flatter slopes were
also the testing grounds for the Pool Sweep units. There is no doubt that under
the conditions tested, the solids movement through the basin is directly affected
by the slope of the sides and bottom.
The configuration of the influent pipe in relation to the center sump and under-
flow draw-off point has an effect on the movement of solids through the basin.
When designed, the decision was made to introduce the waste into the basin in
a vertical direction in order to direct the influent upward into the aerator.
During the dry weather periods, this allowed the incoming raw waste, which
generally had no DO, to be aerated and mixed with the contents of the basin.
Without the aerator, the flow still wells up to the surface due to initial velocity
and convective currents produced by the difference in wastewater temperatures,
i.e., influent normally warmer.
If the influent pipe had been turned down, it is felt that two different conditions
would have existed depending on the relative rate of influent versus underflow.
If the influent was less than the underflow, it is likely that all influent would go
directly to the underflow with the difference being made up of basin contents
from adjacent to the center sump. Suspended Solids near the center sump would
probably be drawn into the underflow. If the influent was greater than the
underflow, however, the excess would be deflected back out of the center sump
creating a vertical velocity past the edge of the center sump which could hinder
or even stop the movement of Suspended Solids into the underflow. Test Nos.
4 and 6, which were both run without an influent flow, were designed to test
67
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the effects of the basin influent configuration on the movements of solids. The
tests and their results were discussed in Section V. The two tests did not provide
sufficient data to make a positive determination of the effects of the influent
configuration on the movement of solids through the basin. It did appear, how-
ever, that with the aerator off and at the flow rates tested, the influent configur-
ation had only a small effect on the overall movement of Suspended Solids through
the basin. For example, the absence of the influent flow did cause the Settleable
Solids concentration in the underflow to decrease slightly. It is believed that
this was caused by the absence of the heavier influent solids which were going
directly into the bottom sump and out with the underflow.
The depth of water, or more appropriately, the ratio of depth to surface area,
also has an effect on solids movement through the basin. A shallow basin has
the effect of damping out any flow patterns in the outer areas of the basin, thus
creating more "dead" areas. The flow patterns mentioned would be those
caused by convective or velocity currents from the influent pipe or by the aerator.
Underflow Pumping -
The underflow pumping rate appears to affect the movement of solids based on
two criteria. First the ratio of underflow to influent flow and second the ratio
of underflow to basin volume. As the ratio of underflow to influent flow in-
creases, there is a tendency for more of the Suspended Solids to be removed
before they have time to settle. The ratio must be quite high, approaching one,
before a significant increase in the amount of Settleable Solids is noticed in
the underflow, however. ~ As the ratio of underflow to basin volume increases,
there is the same tendency to capture more Suspended Solids before they settle;
but in addition, the higher" underflow rate causes the bottom currents moving
radially inward to increase and, thus, cause settled bottom deposits to be moved
inward. Based oh observed operations and on test results, it appears that the
inward radial currents are only able to move solids if they are quite close to the
rim of the center sump and if they have already been dislodged from the bottom.
Therefore, it is concluded that the influence of the bottom currents toward the
movement of deposited solids is slight.
Aerator -
The Sedimentation-Equalization Basin has two modes of operation depending on
the"aerator being on or off. The following discussion is relative to the condi-
tions which exist when the aerator is on, normally when flows are lower.
The surface type floating aerator has two principal functions, i.e., to supply
oxygen to the wastewater in the basin and to provide mixing of the basin
contents. The amount of mixing that takes place is a function of the size
68
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(horsepower) of the aerator. If sufficient power were provided, the basin could
be completely mixed and solids deposition would be all but eliminated. This,
however, could require as much as five times the size and horsepower of the exist-
ing unit. As designed for this project, the aerator was sized to provide oxygen
to maintain DO in the basin but not to provide complete mixing. The action of
the aerator is to draw the wastewater up from beneath the unit and then discharge
it radially outward from the center at the water surface. In the process, the
wastewater is aerated in an artificial hydraulic jump created by the revolving
rotor. The currents generated by the aerator are radially outward on the surface
and then roll under and are radially inward on or near the bottom. In the Sedimen-
tation-Equalization Basin, the visual observation of flow and current patterns indi-
cates that velocities in the outer edges of the basin are very small. The resulting
effects of the aerator on the movements of solids in the outer areas of the basin are
probably small. Near the center of the basin the solids tend to be resuspended by
the inward and upward currents, letting only the heaviest solids settle downward
into the center sump.
Pool Sweeps -
The function of the Pool Sweeps, which were described in Section IV, was to
continuously "sweep" the bottom and sides of the basin to move and temporarily
resuspend the settled sewage solids. Those operational parameters of the Pool
Sweeps which are felt to affect their performance when used for this application
include: 1) the mobility of the main body or floating portion of the unit;
2) the quantity and pressure of the supply water; 3) the quality of the supply
water; 4) the length and number of sweep hoses; and 5) the jet nozzle sizes at
the ends of the sweep hoses.
In a swimming pool, the Pool Sweep maintains its motion in two ways. First is
the thruster jets and second is the circular rotating ring which forms the base of
the unit (see Figure.6). In the Sedimentation-Equalization Basin, the Pool
Sweeps were "tethered" on the supply hoses from the distribution points around
the edge of the basin. This restraint did not allow the units to hit and run along
all four sides as they do in a swimming pool. Instead, they move outward toward
the center of the basin and when they reach the end of the line they slow down
and finally stop as the pull of the supply hose matches the force of the main
thruster. The lack of "random" motion significantly reduced the frequency of
coverage for any particular area on the basin floor.
The action of the thruster jets is regulated by an internal valve in the main body
which directs the water to the rear main thruster or to the front reversing thruster.
The cut of the valve was modified during the initial phases of the Demonstration
Project to improve its mobility. It was found that the modifications could not
significantly increase the mobility of the units.
69
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The water supply for the Pool Sweeps is from the primary clarifier effluent and is
pumped to the common supply line encircling the Sedimentation-Equalization
Basin. The amount of water and the pressure affect both the mobility of the main
body of the Pool Sweeps and the mobility of the underwater "sweep" hoses. The
normal operating pressure for the Pool Sweeps when used in a swimming pool is
about 2.81 to 3.52 kgf/cm (40 to 50 psig). The operating pressure for the
Demonstration Project system was increased from 4.22 to 4.92 kgf/cm^ (60 to
70 psig). This was the maximum pressure recommended by the Pool Sweep manu-
facturer. The increased pressure did increase the action and power of the sweep
hoses but no significant increases in the solids movement through the basin could
be determined. In conjunction with the increased pressure, the hose jet size was
varied to determine the optimum combination of pressure and volume from the
sweep hoses which would produce the most forceful action of the hoses. The ma-
jor portion of these tests were performed by the Pool Sweep manufacturer in a
swimming pool prior to placing them in the Sedimentation-Equalization Basin.
In this way, the bottom hoses could be observed as each change was made. When
placed in the wastewater of the Sedimentation-Equalization Basin, the only
observable feature of the Pool Sweep was the floating body and its movement.
The length and number of Pool Sweep hoses was anticipated to affect the move-
ment of solids through the basin. The normal design of the Pool Sweep system
includes two hoses, one called the bottom hose and the other called the wall
hose. The bottom hose is long enough so that when the Pool Sweep is in the
deepest part of the basin the bottom two feet of the hose rests on the floor. The
wall hose is generally several feet shorter and is not intended to sweep the bottom.
The initial Demonstration Project installation included both hoses as just described,
Following the first set of tests, including the first 24-hour Test No. 1, the Pool
Sweep representatives developed a "wye" assembly which allowed a single longer
bottom hose to be operated with the combined water of the original two hoses.
This change in configuration showed improved force and mobility in swimming
pool tests conducted by the manufacturer. The "wye" assembly was previously
shown in Figure 8. The "wye" assemblies were installed on all of the Demonstra-
tion Project Pool Sweeps, however, subsequent tests were not able to show a
significant improvement which could be attributed to the hose modification.
Hydraulic Loading -
High hydraulic loadings through the Sedimentation-Equalization Basin result in an
increase in the percentage of influent solids which are carried out in the overflow
and a'decrease in the percentage of influent solids which are removed in the
underflow. This was previously shown in Table 20. Even though the concentra-
tion of solids in the overflow remained lower than in the underflow, the high
volume of overflow caused the major increase in the mass of solids in the overflow.
70
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OPERATION AND MAINTENANCE
In addition to the normal operation and maintenance (O&M) of the standard
waste treatment equipment, the Demonstration Project had additional O&M
associated with the surge facility and related equipment; namely, Pool Sweeps.
The operation and maintenance of the Sedimentation-Equalization Basin, in
general, consisted of hosing down the sides and periodically removing the accumu-
lated floating grease. Grease removal could be accomplished by hand loading
into a dumpster to be hauled away or by controlling the surface drawoff at the
skimming structure. Its position in the basin allowed the prevailing winds to
collect the grease in front of the skimming structure and, consequently, no
mechanical skimming was required.
The use of the Pool Sweeps was accompanied by several special O&M problems
which were related to either the water supply or to the configuration of the
Sedimentation-Equalization Basin.
The water supply selected for operating the Pool Sweeps was primary clarifier
effluent. This was chosen rather than tap water, which was available, because
the anticipated future use of these units quite possibly would be where an adequate
supply of pure water would not exist or was uneconomical to use. The poorer
quality water caused two major problems. First, the internal valving of the Pool
Sweep has close tolerances and small pieces of plastic or similar material would
completely immobilize the units when they would become lodged inside the main
body of the Pool Sweep. The clarifier at the Rohnert Park facility was heavily
loaded and it is possible that a more efficient clarifier would help this problem.
The second O&M problem caused by the quality of the water supply was the
accumulation of grease in the interior of the main Pool Sweep body which would
eventually alter the operation of the unit or plug it completely. This phenomenon
can be expected with all primary effluents which contain a normal amount of
grease and oils.
The configuration of the basin caused problems with the operation of the Pool
Sweeps. First, the finish on the gunite lining (float finish) proved to be far too
abrasive for the wearing materials on the sweep hoses. Under continuous use,
the hoses would wear so severely that the ends of the hoses would wear completely
out in as short a time as two months. A picture of a new and worn hose end is
shown in Figure 24. The second problem associated with the basin configuration
was the presence of the overflow structure out in the basin. The Pool Sweep
covering that area of the basin would periodically get in behind the structure and
could not get out by itself. Another problem which could be avoided in most
cases was the tangling of the Pool Sweep units. The Pool Sweeps would not
71
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tangle as long as the supply hoses were short enough not to allow the main bodies
to overlap the same area. When just the bottom hoses overlapped, tangling did
not occur.
Figure 24. Pool Sweep Hose Wear
WORN
If solids were allowed to accumulate on the bottom of the basin as a routine method
of operation, most could be removed by simply drawing down the basin with the
underflow pumps. The operational problems associated with the long detention
time of the bottom sludge, primarily the production of nuisance odors, would
exist and would detract from the feasibility of using this as a normal mode of
operation. The approximate cost of removing the concentrated sludge would be in
the range of $25.00 to $30.00 per 1,000 gallons and would be additive to the nor-
mal costs of a surge facility since the other components are designed based on
hydraulic capacity which would not change.
MODIFICATIONS TO SURGE FACILITY
Based on the information gained through the evaluation of test results and the
actual operation of the surge facility, there appears to be several areas where a
design or operational change could benefit its operating characteristics.
72
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To prevent the problems caused by the poor quality of the water supply to the
Pool Sweeps, it is felt that a clarified secondary effluent or better is required.
If the required basin size is not much greater than the Rohnert Park facility, the
slope of the sides and bottom could be increased to improve the flow of solids
toward the center sump.
The structure for skimming and overflow should be set back into the levees so
that there is no obstructions within the basin which could hinder the operation of
Pool Sweeps or other sludge-moving equipment.
The lining of the basin should be as smooth as possible to prevent excessive wear.
If guhite is used, it should have a steep trowel finish and a durable coating of
cement sealer, e.g., epoxy. The use of a flexible lining such as a hypalon or
molded asphalt panels could be an acceptable material if the movement of the
bottom Pool Sweep hoses would not wear the lining. This would have to be in-
vestigated.
One of the principal shortcomings of the Pool Sweep mode of operation as used in
this Demonstration Project was that the sweeping action is random. Without a
stronger inward bottom current or steeper bottom slopes, it does not appear that
there could ever be a significant net movement of solids toward the center sump.
At this time, it does not appear that the Pool Sweeps can be modified to provide a
uni-directional sweeping action toward the center sump.
An alternative means of moving the settled sludge along the bottom and, in par-
ticular, toward the center sump, would include fixed underwater sprays or jets
directed toward the center sump. The spacing of the spray nozzles or ports would
be quite critical and would probably require considerable testing to establish
an efficient design.
Another alternative way would be a series of high pressure nozzles mounted on a
manifold pipe which would be fed through a pivot point in the center of the basin.
The manifold would extend radially outward from the center and would have inter-
mediate roller supports along its length. The drive for the manifold, which would
rotate around the basin approximately every hour, could be one or more water-
driven motors operating on the same water supply system as the manifold itself.
Special attention would have to be given to the positioning and operation of the
aerator since no supports or guide posts could be placed in the path of the rotating
manifold and the pond could not be lowered without first stopping the manifold in
the proper location to miss the aerator float supports.
During the dry weather flow periods when there is generally no overflow, there
are other alternatives for maintaining the flow of solids. The most obvious is to
provide enough horsepower for the aerator to keep all of the solids in suspension.
73
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The operating cosh of the larger aerator would be approximately five times as much
as the present one; and in addition, the physical dimension of the basin would
probably have to be altered somewhat to increase the depth to surface area ratio.
The present Rohnert Park facility has a water depth of 8 to 10 feet, and the average
distance across is about 130 feet. This fairly shallow basin would be quite in-
efficient if an attempt were made to keep it completely mixed. A completely
mixed basin would have an additional benefit of providing the possibility of some
treatment as well as flow control. The present facility was not able to provide
any significant treatment through aeration and recycle of solids from the clarifier
because the flow of solids could not be maintained through the basin.
Another possibility is to use a variable speed aerator and/or a variable pitch
turbine mixer to minimize the operating costs for a basin which need not be mixed
all of the time but does need to be completely mixed to suspend the settled sludge
for removal from the basin.
If solids are allowed to accumulate in the basin and then be removed periodically
as previously discussed, only minor modification to the existing facilities would
be required. Principally, the discharge pipe from the underflow pumps to the
clarifier would have to be modified to allow concentrated sludge to be.pumped
directly into trucks to be hauled to the regional treatment facility.
ECONOMIC EVALUATION
In order to illustrate the economics of surge facilities, a set of hypothetical
alternatives was assumed for the Laguna de Santa Rosa planning sub-area of which
Rohnert Park is a part. The long-range planning for this area calls for the
existing treatment facilities at Rohnert Park, Sebastopol and Santa Rosa's College
Avenue site to be abandoned and replaced with pumping and transmission facilities
to transport all wastes to the Laguna Regional Wastewafer Treatment Facility. In
addition, there is an area of the county which is presently sewered to the Regional
Plant 1 All of the present sewerage systems have high ratios of peak wet weather to
average dry weather flows and the possibility of excess infiltration/inflow. The
cost-effective evaluation of infiltration/inflow problems for all four areas should
include the use of surge facilities. For the purpose of comparison, the following
assumptions were made: 1) each of the four tributary areas would be served by a
separate pump station or surge facility; 2) the regional treatment plant will be an
activated sludge secondary facility using digesters for sludge treatment; and
3) the interceptors will be gravity sewers averaging ten to twelve feet deep.
Each surge facility will have influent and underflow pumping, a surge basin with
three hours' detention at peak flow, a storage basin approximately six feet deep
with two days' detention at maximum daily flow, a control building and a chlorina-
tion facility for emergency wet weather overflow.
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The formal design criteria for treatment' facilities takes into account daily peaks
which for this regional facility would be approximately 1.7 times average daily
flow- This means, for example, that a primary clarifier designed to handle 1 .0 mgd
at an overflow rate of 800 gpdsf would be expected to operate efficiently during
the daily peaks which would be approximately 1 .7 mgd or an overflow rate of
1,360 gpdsf. Applied to the idea of a constant flow 24-hour per day, this means
that a plant could logically be designed at these higher rates and that approximately
sixty percent of the plant size would be required for all those units where the hy-
draulics control. The solids handling facilities would not be affected, however.
Those elements of a secondary activated sludge treatment plant which could be
reduced in size by having a constant influent flow include: 1) headworks;
2) metering; 3) all sewage pumping; 4) primary sedimentation tanks; 5) aeration
basins; 6) secondary sedimentation tanks; and 7) disinfection facilities.
Flow data for all areas were taken from the March 1973 report, "Subregional Waste-
water Management Plan for the Santa Rosa Plain," by Brown and Caldwell, Water
Resources Engineers, Inc. and Yoder-Trotter-Orlob & Associates.
The cost estimating data came from a set of unpublished preliminary cost estimating
curves and tables used by Yoder-Trotter-Orlob & Associates for work in the San
Francisco Bay Area. Although the cost estimates presented are as accurate as
possible they should not be used by others for similar work. Their value lies in
having a timely basis for a relative cost comparison.
Based on the construction and operation of the Rohnert Park Demonstration Project,
it is estimated that the construction cost of a surge facility will vary depending on
the size of the facility as follows: the larger, facility will cost approximately 1 .33
times the cost of a typical raw sewage pump station which will handle the same
peak wet weather flow; the smallest will cost approximately 2.0 times. It is also
estimated that the operation and maintenance cost for a surge facility will average
approximately 1 .5 times that for a similar sized pump station.
A schematic diagram indicating the regionalization scheme is shown in Figure 25.
This figure indicates the projected average dry weather flows (adwf) and peak wet
weather flows (pwwf) for 1985 for each separate area. Also indicated is the maxi-
mum or peak flow rate which would result if a surge facility were used instead of
a standard pumping station at each location. The respective interceptor sizes,
depending on whether or not a surge facility is used, are also indicated. Tables
23 and 24 summarize the estimated cost which would be associated with the two
alternatives. Both the estimated capital cost and estimated annual operation
and maintenance (O&M) costs are presented. The estimated O&M costs on the
interceptors did not differ significantly between alternatives and was, therefore,
left out of the economic comparison.
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Figure 25. Regional Wastewater System Schematic
SEBASTOPOL
COLLEGE AVE.
0.4
1.2
08
24" 54"
18"
42"
9.3
35.0
18.6
LEGEND
adwf (mgd)
60
48'
1 AfilJNA
REGIONAL
13.9
50.4
27.8
^ '
i
i
i
1.4
6.0
2.8
COUNTY
AREA
ROHNERT PARK
42"
36"
2.8
8.2
5.6
0.4
x
1.2-
0.8-
pwwf from pump station (mgd)
pwwf from surge facility (mgd)
interceptor size for pump station
interceptor size^
for surge facility
,18'
adwf = average dry weather flow
pwwf = peak wet weather flow
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Table 23. COST SUMMARY - ALTERNATE I
REGIONALIZATION WITHOUT SURGE FACILITIES
Item
Annual
O&M
Capital
cost
Regional Treatment Plant
Design adwf, 13.9mgd
Design pwwf, 50.4 mgd
Local Pumping Stations
College Avenue, 35.0 mgd
County Area, 6.0 mgd
Rohnert Park, 8.2 mgd
Sebastopol, 1 .2 mgd
Subtotal
Interceptors to Regional Plan
College Avenue -
18,000ft- 54 in. @$82.20/ft
Sebastopol -
10,000 ft - 24 in. @ $31 .90/ft
College Avenue and Sebastopol (combined)
18,000ft -60 in. @$90.40/ft
County Area -
(No interceptor required)
Rohnert Park -
22,000ft -42 in. @$60.85/ft
Subtotal
Total Annual O&M Cost
Total Capital Cost
$490,000
$ 25,500
5,850
10,000
2,250
$ 43,600
$533,600
$ 9,400,000
$ 1,000,000
310,000
380,000
108,000
$ 1,798,000
$ 1,480,000
319,000
1,627,000
1,340,000
$ 4,766,000
$15,964,000
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Table 24. COST SUMMARY - ALTERNATE II
REGIONALIZATION WITH SURGE FACILITIES
Item
Regional Treatment Plant
Design adwf, 8.4 mgd
Design pwwf, 27.8 mgd
Local Surge Facilities
College Avenue, 35.0 mgd
County Area, 6.0 mgd
Rohnert Park, 8.2 mgd
Sebastopol, 1 .2 mgd
Subtotal
Interceptors to Regional Plant
College Avenue -
18,000 ft -42 in. @ $60.85/ft
Sebastopol -
10,000ft - 18 in. @$24.65/ft
College Avenue and Sebastopol (combined) -
18,000ft - 48 in. @ $73.15/ft
County Area -
(No interceptor required)
Rohnert Park -
22,000ft - 36 in. @ $48.65/ft
Subtotal
Total Annual O&M Cost
Total Capital Cost
Annual
O&M
$385,000
$ 38,200
8,800
15,000
3,400
$ 65,400
$450,400
Capital
cost
$ 7,370,000
$ 1,333,000
558,000
647,000
216,000
$ 2,754,000
$ 1,095,000
246,500
1,318,000
-
1,071,000
$ 3,730,500
$13,854,500
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There are several benefits which would be gained if surge facilities were used
which are extremely valuable but do not show up in an economic analysis. All
these benefits are related primarily to the uniform flow delivered to the regional
plant and can be grouped into three main categories: performance, reliability,
and flexibility.
The performance of secondary treatment facilities, and in particular, a biological
system, is strongly affected by either hydraulic or concentration surges. Most
upsets which result in decreased effluent quality are caused by these surges or
slugs. The surge facility mode of operation allows the hydraulic surges to be
eliminated and the waste concentration (strength) variations to be dampened to
whatever level required by varying the design of the surge facility. The uniform
flow and strength allows each unit process to operate in a stable mode of operation
and at peak efficiency.
The reliability of the regional treatment plant is enhanced by the use of a surge
facility in the same way as performance is affected. For a treatment plant to be
reliable it should operate efficiently and not be easily upset. The use of a surge
facility removes hydraulic surges and dilutes slugs of high strength or even toxic
wastes, thereby minimizing the principal causes of upset processes.
The use of a central regional plant and several remote surge facilities has a large
degree of flexibility which would not exist if simple pump stations were used. The
large storage facilities which are used primarily for winter overflow could be
easily used as treatment units (ponds) during the dry weather flow. If lightly
loaded, the ponds could be used to treat a portion of the waste at any of the remote
locations for local reuse.
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SECTION VII
GLOSSARY
Anaerobic Digestion - The degradation of organic matter brought about through
the action of micro-organisms in the absence of molecular oxygen.
BOD - Abbreviation for biochemical oxygen demand. The quantity of oxygen
used in the biochemical oxidation of organic matter in a specified time, at a
specified temperature, and under specified conditions. Also, a standard test
used in assessing wastewater strength.
Chlorination - The application of chlorine to water or wastewater, generally
for the purpose of disinfection, but frequently for accomplishing other biological
or chemical results.
Digester - A tank in which sludge is placed to permit the biological decomposition
of the organic matter in the sludge and resulting in partial gasification, liquifi-
cation and mineralization.
Dissolved Oxygen - The oxygen dissolved in water, wastewater, or other liquid
usually expressed in milligrams per liter, parts per million, or percent of satura-
tion. Abbreviated DO.
Domestic Wastewater - Wastewater which includes all of the water-borne wastes
originating from residential, commercial, and recreational developments and the
water-borne wastes originating from the sanitary facilities of industrial develop-
ment.
Dry Weather Flows - Normal wastewater flow with little or no infiltration.
Effluent - Wastewater, partially or completely treated, flowing out of a treat-
ment plant.
Infiltration - The water entering a sewer system and service connections from the
ground through such means as, but not limited to, defective pipes, pipe joints,
connections, or manhole walls. Infiltration does not include, and is dTstmguTshed
from, inflow.
Inflow - The water discharged into a sewer system and service connections from
such sources as, but not limited to, roof leaders, cellar, yard, and area drains,
foundation drains, cooling water discharges, drains from springs and swampy areas
manhole covers, cross connections from storm sewers and combined sewers, catch
basins, stormwaters, surface runoff, street wash waters, or drainage. It does not
include, and is distinguished from, infiltration.
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Infiltration/Inflow - The total quantity of water from both infiltration and inflow
without distinguishing the source.
Influent - Water, wastewater, or other liquid flowing into a reservoir, basin, or
treatment plant, or any unit thereof.
Organic matter - Chemical substances of animal or vegetable origin, or more
correctly, of basically carbon structure, comprising compounds consisting of
hydrocarbons and their derivatives.
Outfall - A conduit leading from a treatment plant or wastewater collection sys-
tem to the point of final discharge.
pH - The reciprocal of the logarithm of the hydrogen-ion concentration. The con-
centration is the weight of hydrogen-ions, in moles, per liter of solution. Neutral
water, for example, has a pH value of 7 and a hydrogen-ion concentration of I0~'
moles per liter.
Present Worth - The present worth of a cost occurring at some future point in
time is the present amount of money, that when invested at a selected interest
rate, will be at that particular future time worth that amount.
Primary Treatment - The first major (sometimes the only) treatment in a waste-
water treatment plant, usually sedimentation. Primary treatment removes a sub-
stantial amount of suspended matter but little or no colloidal and dissolved matter.
Secondary Treatment - The treatment of wastewater by biological methods after
primary treatment by sedimentation.
Sedimentation - The process of subsidence and deposition of suspended matter
carried by water or wastewater, by gravity. It is usually accomplished by re-
ducing the velocity or wastewater below the point at which it can transport the
suspended matters.
Sewage- The spent water of a community. Term now being replaced in technical
usage by the more preferable term, wastewater. See Wastewater.
Sludge - The accumulated solids separated from liquids such as water or waste-
water, during processing, or the deposits on bottoms of streams or other bodies of
water. Also, the precipitate resulting from chemical treatment, coagulation or
sedimentation of water or wastewater.
-------
Sludge Digestion - The process by which organic or volatile matter in sludge
is gasified, liquified, mineralized, or converted into more stable organic matter
through the activities of either anaerobic or aerobic organisms.
Suspended Solids - Solids that either float on the surface or are in suspension
in water, wastewater, or other liquids, and which are largely removable by
laboratory filtering.
Tertiary Treatment - The treatment of wastewater beyond secondary treatment by
using various physical and chemical processes. Tertiary treatment can include
processes to remove additional suspended solids, BOD or algal nutrients like
nitrogen or phosphorus.
Turbidity - A condition in water or wastewater caused by the presence of suspen-
ded matter which results in the scattering and adsorption of light rays. Also, a
measure of fine suspended matter in liquids.
Wastewater - The spent water of a community. From the standpoint of source, it
may be a combination of the liquid and water-carried wastes from residences, com-
mercial buildings, industrial plants, and institutions, together with any ground-
water, surface water, and stormwater that may be present. In recent years, the
word "wastewater" has taken precedence over the word "sewage."
Wffstewater Reclamation - Treatment of wastewater for reuse, either for
irrigation of agricultural lands or landscape, for groundwater recharge, for
stream flow augmentation, for surface impoundments, or for industrial purposes.
Wastewater Treatment - Any process to which wastewater is subjected in order
to remove or alter its objectionable constituents and thus render it less offensive
or dangerous. See Primary Treatment, Secondary Treatment, Tertiary Treatment.
Wastewater Treatment Plant - An arrangement of devices and structures for
treating wastewater, industrial wastes, and sludge. Sometimes used as synony-
mous with waste treatment plant, water pollution control, or water reclamation
plant.
Wet Weather Flow - A combination of dry weather flows and infiltration/inflow
which occurs as a result of rainstorms. This flow, in older or poorly constructed
systems, can be many times the dry weather flow.
82
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SECTION VIII
ABBREVIATIONS AND SYMBOLS
adwf Average dry weather flow
BOD Biochemical oxygen demand
cu.ft. Cubic feet
cu.m. Cubic meter
ft. Feet (foot)
gal. gallon
gad gallons per acre per day
gpd gallons per day
gpdsf gallons per day per square foot
gpcd gallons per capita per day
gpm gallons per minute
hp horsepower
kg kilogram
I liter
Ibs/day pounds per day
Ips liters per second
m meter
mg million gallons
mgd million gallons per day
mg/l milligrams per liter
pad pounds per acre per day
pdwf peak dry weather flow (hourly rate)
ppcd pounds per capita per day
psi pounds per square inch
pwwf peak wet weather flow (hourly rate)
83
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sq. ft. square feet (foot)
sq . m . square meter
Set. S Settleable Solids
SS Suspended Solids
84
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SECTION IX
METRIC UNITS AND ENGLISH EQUIVALENTS
Recommended Units
Description
Length
Area
Volume
Mass
Time
Velocity
Flow
Pressure
Temperature
Hydraulic
Loading
Unit
meter
centimeter
square meter
square centimeter
Hectare o
(10,000m )
cubic meter
liter
kilogram
second
meter per second
cubic meter per second
liter per second
kilogram (force) per
square centimeter
degree Celsius
cubic meters per square
meter per day
Symbol
m
cm
2
m «
cm
ha
3
m
1
kg
s
m/s
3/
m/s
l/s
kgf/cm
C
3/ 2/j
m /m /day
English Equivalents
3.28ft.
0.3937 in.
10.744sq. ft.
0.155 sq. in.
2 .471 acres
35.314cu.ft.
0.264 gal.
2.205 Ib
S
3 .28fps
15,850 gpm or 35
314cfs
15.85 gpm
14.223 psi
c;
C=| (F-32)
24.58gpdsf
85
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-670/2-74-075
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
SURGE FACILITY FOR WET AND DRY WEATHER FLOW CONTROL
5. REPORT DATE
November 1974; Issuing Date
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Harold L. Welborn
(Y-T-0 & Associates,
8. PERFORMING ORGANIZATION REPORT NO.
Walnut Creek, California 94596)
9. PERFORMING ORGANIZATION NAME AND ADDRESS
City of Rohnert Park
6750 Commerce Boulevard
Rohnert Park, California 94928
10. PROGRAM ELEMENT NO.
1BB034; ROAP 21-ASY; Task 140
11. CONTRACT/GRANT NO.
S800769
12. SPONSORING AGENCY NAME AND ADDRESS
National Environmental Research Center
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati , Ohio 45268
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
The surge facility tested in this EPA Demonstration Project provided peak
flow equalization and some degree of treatment to all storm.flows and rate control
of all wet and dry weather wastewater flows. The Rohnert facility was designed to
test a method whereby solids could be prevented from accumulating on the bottom of
an inexpensive earthen, lined basin without the use of conventional mechanical sludge
collection equipment. The principal features of the surge facility were a 2,84l cubic
meter (0.75 million gallon) Sedimentation-Equalization Basin, variable underflow pumps,
a surface aeratoj.-and Pool Sweeps. The Pool Sweeps were used to continuously "sweep"
the bottom and sides of the earthen, lined basin to move and temporarily resuspend
the settled (sewage, sol ids and, thereby, maintain the flow of solids in the absence of
mechanical coMectTon; mechanism, steep' bottom slopes, or a completely mixed basin.
Under the storm'fUw'conditions, the surge facility removed approximately 45 percent of
the influent'Suspended Solids and 90 percent of influent Settleable Solids prior to
overflow to a storage pond. Although a significant portion of the solids flow through
the surge basin could be attributed to the operation of the Pool Sweeps, their overall
performance could >not'justify their use in other similar tfaci lit ies.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. ^COSATl Field/Group
Surge tanks, "Storm surges, Flood control
Flow control, Sewage, Sewage disposal,
Flow measurement, Flow distribution,
Sewage treatment, "Settling basins,
"Storage tanks, Underflow, Sedimentation
tanks, Water influx
Surge basin, "Flow
equalization, Sludge
removal, "Infiltration,
Pool sweep, "Sedimenta-
tion-equalization, "Peak
storm flow
13B
18. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (ThisReport)'
UNCLASSIFIED
21. NO. OF PAGES
94
20. SECURITY CLASS (Thispage)
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (9-73)
U.S. GOVERNMENT PRINTING OFFICE: 1974-657-588/5321 Region No. 5-M
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