EPA-670/2-75-045
May 1975
Environmental Protection Technology Series
REPLACEMENT OF ACTIVATED SLUDGE
SECONDARY CLARIFIERS BY DYNAMIC STRAINING
National Environmental Research Center
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
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EPA-670/2-75-045
May 1975
REPLACEMENT OF ACTIVATED SLUDGE SECONDARY CLARIFIERS
BY DYNAMIC STRAINING
By
Michael Joyce
William Schultz
Arvid Strom
FMC Corporation
Environmental Equipment Division
Itasca, Illinois 60143
Contract No. 68-03-0102
Program Element No. 1BB043
Project Officer
Richard C. Brenner
Advanced Waste Treatment Research Laboratory
National Environmental Research Center
Cincinnati, Ohio 45268
NATIONAL ENVIRONMENTAL RESEARCH CENTER
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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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 commercial products constitute endorsement or recommendation
for use.
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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 multi-
disciplinary focus through programs engaged in
• studies on the effects of environmental contami-
nants on man and the biosphere, and
• a search for ways to prevent contamination and
to recycle valuable resources.
As part of these activities, the study described herein presents a
pilot-scale evaluation of the feasibility of replacing conventional
secondary gravity clarifiers in the activated sludge process with
dynamic strainers equipped with ultrasonic transducers.
A. W. Breidenbach, Ph.D.
Di rector
National Environmental
Research Center, Cincinnati
m
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ABSTRACT
Pilot plant studies were conducted on domestic wastewater to deter-
mine the feasibility of replacing conventional activated sludge
gravitational clarifiers by dynamic straining. The dynamic strainers
consisted of a rotating cylinder cleaned by an internal ultrasonic
transducer. A primary strainer was placed and operated directly in
the mixed liquor in the aeration tank. A secondary strainer was
installed and operated in a separate tank to further clarify the
effluent from the primary strainer.
This work indicated that dynamic straining is a technically feasible
process for replacing conventional activated sludge gravitational
clarifiers. Suspended solids removals of well over 99 percent were
achieved with a single primary strainer operating in the pilot plant
aerator with a mixed liquor suspended solids concentration of over
6,500 mg/1. When operated at lower specific flow rates, primary
straining appears to be capable of consistently producing an effluent
suspended solids in the 15-30 mg/1 range.
Present economic predictions indicate that plants equipped with
primary and secondary dynamic strainers would cost more than plants
utilizing conventional secondary gravity clarifiers. This factor
can be tempered by several projected dynamic straining advantages.
Two-stage dynamic straining has excellent application where space
limitations exist. Secondary gravity clarifiers could be eliminated
under the right conditions and aeration tank sizes could be appreci-
ably smaller with the higher MLVSS concentrations achievable with
dynamic straining. An existing overloaded activated sludge plant
could be upgraded with primary straining only without expanding the
facilities. In locations or applications where filamentous growth
is prevalent, primary straining could be used to effectively control
bulking. During the testing program, dynamic straining revealed
itself to be resistant to shock loading.
This report was submitted in fulfillment of Contract No. 68-03-0102,
by the FMC Corporation, Environmental Engineering Laboratories,
under the sponsorship of the U. S. Environmental Protection Agency.
iv
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CONTENTS
PAGE
REVIEW NOTICE ii
FOREWORD ill
ABSTRACT iv
LIST OF FIGURES vi
LIST OF TABLES vii
SECTION
I CONCLUSIONS 1
II RECOMMENDATIONS 4
III INTRODUCTION 6
IV DESCRIPTION OF EQUIPMENT 8
V DESCRIPTION OF OPERATION 16
VI DISCUSSION 22
SPECIFIC FLOW RATES 22
SUSPENDED SOLIDS REMOVALS 32
DAILY OPERATION 34
VII ECONOMIC ANALYSIS 37
VIII ACKNOWLEDGEMENTS 48
IX REFERENCES 49
X APPENDICES 50
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FIGURES
NUMBER PAGE
1 DYNAMIC STRAINER UNIT 9
2 PRIMARY STRAINER 10
3 SECONDARY STRAINER 11
4 EQUIPMENT PHOTOGRAPHS 12
5 DYNAMIC STRAINING FLOW DIAGRAM 14
6 A COMPARISON OF INCREASING AND DECREASING .... 20
HEAD TESTS
7 PRIMARY STRAINER INTERNAL PUMPING HEAD 24
8 SECONDARY STRAINER INTERNAL PUMPING HEAD .... 25
9 SECONDARY TANK WATER VELOCITY PROFILES 26
AT DIFFERENT FLOW RATES
10 TOTAL HYDRAULIC HEAD CURVES AS A FUNCTION .... 28
OF ROTATIONAL SPEED
11 NET HYDRAULIC HEAD CURVES AS A FUNCTION 29
OF ROTATIONAL SPEED
12 CLEAN WATER TEST OF MICRO-FABRICS 31
13 SETTLING VELOCITIES OF PARTICLES IN 36
PRIMARY STRAINER EFFLUENT
vi
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TABLES
NUMBER PAGE
1 MICRO-MESH FABRIC SPECIFICATIONS 13
2 SAMPLING AND ANALYSES SUMMARY 17
3 OPERATIONAL DATA OUTLINE 18
4 OUTLINE OF STRAINER CHARACTERIZATION PROGRAM 19
5 ESTIMATED TOTAL CONSTRUCTION COSTS 41
6 ESTIMATED ANNUAL OPERATION AND MAINTENANCE COSTS - ... 43
3,785 M3/DAY (1 MGD) PLANT
7 ESTIMATED ANNUAL OPERATION AND MAINTENANCE COSTS - ... 44
37,850 M3/DAY (10 MGD) PLANT
8 TOTAL ANNUAL COST COMPARISONS BETWEEN DYNAMIC 45
STRAINING AND CONVENTIONAL ACTIVATED SLUDGE
TREATMENT PLANTS
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SECTION I
CONCLUSIONS
Dynamic straining, wherein solids are removed by a rotating drum
utilizing a stainless steel micro-mesh fabric, cleaned by ultra-
sonics and the rotational effect, is a technically feasible process
for replacement of conventional activated sludge gravitational
clarifiers. Suspended solids removals of well over 99 percent can
be achieved with primary strainers operating in mixed liquor with
a suspended solids concentration of over 6,500 mg/1. When operated
at lower specific flow rates of 1.35-2.70 1/sec/m2 (2-4 gpm/ft2),
primary straining appears capable of consistently producing an effluent
which equals or betters the Federal Secondary Treatment Standards for
suspended solids of 30 mg/1 or 85 percent overall plant removal,
whichever results in the lowest residual.
Further improvement in suspended solids removal is effected by using
a secondary strainer in series with the primary strainer. Suspended
solids removed during secondary straining are returned to the mixed
liquor aeration system.
Commercially acceptable specific flow rates of up to 8 1/sec/m2 of
filtering surface (12 gpm/ft2) have been demonstrated at a mixed
liquor suspended solids (MLSS) concentration of 6,500 mg/1. Specific
flow rates approximately twice those stated above can be achieved at
the lower suspended solids operation for the secondary strainer.
A 10-micron nominal rating stainless steel Robusta weave is the
recommended cloth for both the primary and secondary strainers. Cloths
with smaller nominal openings inhibit flow rate without any signifi-
cant reduction in effluent suspended solids. Cloths with larger
openings do not exhibit sufficiently higher specific flow rates to
warrant the decrease in effluent quality.
Specific flow rate performance is affected by nominal opening size of
the fabric, suspended solids concentration, rotational speed, and
hydraulic head. Suspended solids removals are affected by nominal
pore size, concentration of suspended solids in the liquid surrounding
the strainer, and the peripheral speed of the strainer. In general,
maximum specific flow rates occurred at net hydraulic heads of 25 to
75 mm (1 to 3 in) over the range of interrelated variables studied
during this pilot plant program. Solids removal efficiencies decrease
and specific flow rates increase rapidly as the rotational speed of the
drum is increased.
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A predominantly filamentous biomass,. which was encouraged to prolif-
erate throughout the experimental program, appears to be the most
desirable mixed liquor culture for the application of dynamic strain-
ing, combining the attributes of high specific flow rates and
suspended solids removals.
Preliminary economic comparisons for plants with conventional
gravitational clarification and plants with two-stage dynamic strain-
ing clarification with capacities of 3,785 and 37,850 ntf/day (1 and
10 mgd) indicate that dynamic straining plants would have a total
construction cost approximately 8.2 percent higher than conventional
plants at the 3,785 m3/day (1 mgd) level, and approximately 21.5
percent higher at the 37,850 m3/day (10 mgd) level. These estimates
were based on the current FMC standard strainer production model. From
a process applications standpoint,this basic model was sized for
relatively low solids concentrations such as found in wastewater
treatment lagoons. No effort was made to redesign equipment to
optimize costs for high solids concentrations which would prevail in
mixed liquor applications.
Annual operating costs for dynamic straining are also indicated to be
higher than those for conventional operations, substantially so at
the higher plant capacity of 37,850 m3/day (10 mgd). However, these
operating cost estimates were based on very preliminary conservative
assumptions concerning labor, maintenance, and power requirements
for the strainers. Amortization has a significant effect because of
the differences in total construction costs.
The economics of dynamic straining can be significantly improved by
replacing the secondary strainer with a sand filter or gravitational
clarifier operating at high overflow rates. It was indicated during
this study that simple gravitational clarification of the fine
colloidal solids in the primary strainer effluent would be difficult,
suggesting that chemical addition may be necessary to obtain satis-
factory coagulation and flocculation.
Upgrading of existing organically and/or hydraulically overloaded
treatment plants appears to be a viable application for primary
straining. Higher MLSS levels could be maintained (provided the
necessary additional oxygen transfer capability existed or could be
acquired) while concomitantly decreasing solids loadings on existing
secondary clarifiers to very low levels. A significant improvement
in both biological and secondary clarifier performance would be
expected by such a modification of operating conditions. This could
be accomplished with little, if any, increase in land requirements
for the treatment plant.
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Many activated sludge treatment plants experience prolonged periods
of uncontrolled bulking due to filamentous growth. Installation of
a primary strainer directly in the mixed liquor would eliminate the
adverse effects of bulking on secondary clarlfier operation and on
effluent quality.
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SECTION II
RECOMMENDATIONS
Although day-to-day strainer operating and performance data were
taken and independent characterization data for the important oper-
ating variables of the strainer were confirmed and appeared repro-
ducible, additional work is recommended to evaluate the steady-state
performance of the strainer and the response to diurnal flow vari-
ations. This is especially important to establish methodology for
automatic control of strainer peripheral speed under varying flow
conditions.
Suspended solids concentrations in the primary strainer effluent were
low enough to warrant testing of granular-media filtration to provide
a polished final effluent without use of the relatively expensive
secondary strainer. Improvement of effluent quality, reduction of
costs , and reduction of return flow to the aeration tank are indicated
by such a substitution.
The nature of the biological solids was shown to be a very important
consideration in the performance of the strainer. Further work
should be undertaken to establish primary strainer performance with
different activated sludge biomass characteristics. For instance,
comparison of performance on a nitrifying sludge versus the predomi-
nantly heterotrophic sludge grown under the highly loaded carbon
removal conditions used for this study would provide valuable design
information. Microscopic studies and evaluation of performance with
respect to different load factors, cell retention times, and other
biological processing parameters would aid in defining the range of
feasible strainer applications.
The very cursory work performed on this project on settleability of
the fine solids contained in the primary strainer effluent should be
expanded and coagulation and flocculation of these solids studied using
conventional chemical techniques. This would be of importance in
determining design data for utilization of the primary strainer in
conjunction with an existing overloaded secondary clarifier. Also,
coagulation and flocculation of these solids should prove beneficial
to the performance of a secondary strainer, if applied, in the
production of a more polished effluent and the minimization of return
f1ows.
When operated at lower specific flow rates of 1.3 to 2.6 1/sec/m2
(2 to 4 gpm/ft2), preliminary results indicated that a primary strainer
-------
was capable of producing an effluent that without further clarifi-
cation, filtration, or straining would meet the Federal Secondary
Treatment Standards for suspended solids, i.e.less than or equal to
30 mg/1. With sufficient standby strainers and with a 100 percent
reliable back-up power supply source, this raises the possibility
of completely eliminating secondary clarifiers and downstream
polishing devices in certain situations. This potential application
of primary straining should be more thoroughly evaluated via a
series of longer-term pilot runs.
Another potential application of primary straining which merits
evaluation is as an independent first-stage clarification device in
a two-stage activated sludge system. This type of system is used
where year-round nitrification is required. The optimum residual
8005 and suspended solids concentrations in the first-stage effluent
are 35-50 mg/1 each. Bleed through of these two constituents in
these amounts enhances flocculation and settling of the second-stage
nitrifying sludge. It appears primary strainers installed in the
first-stage reactor could readily be tailored to produce the optimum
desired first-stage effluent quality.
One variable not studied in the program reported herein was the power
supply to the sonic transducer. In concurrent studies with FMC
field units, this variable has had an appreciable effect on attain-
able specific flow rates and suspended solids removal efficiencies in
low suspended solids applications. The impact of this variable in
high suspended solids mixed liquor applications should be investi-
gated.
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SECTION III
INTRODUCTION
The treatment capacity of an activated sludge plant is most often
limited by the secondary clarifier. As the volumetric BOD loading
increases, the MLSS concentration under aeration must be gradually
increased to maintain the organic (F/M) loading within the desired
operating range. However, an increase in MLSS concentration leads to
a proportional increase in mass (solids) loading on the secondary
clarifier. At some point, the solids loading on the secondary clarifier
will begin to exceed the sludge thickening capability of that unit,
necessitating a reduction in MLSS level and resulting in a higher than
desired F/M loading. This in turn may result in decreased soluble
organics removals and poor biomass settling characteristics. Poor
sludge settling characteristics can also result from a predominantly
filamentous sludge, even though this type of sludge yields efficient
BOD removal.
The problems mentioned above suggest that a better method of liquid/
solids separation would result in greater treatment plant capacity
and reliability. Straining is a method of liquid/solids separation
which is not dependent on the settleability of the solids involved.
This contract was concerned with the investigation of separating
activated sludge solids using the process of straining as an alternative
to gravitational settling.
An experimental study was undertaken to evaluate the technical
performance of dynamic straining. Using the data obtained, a preliminary
economic evaluation has been completed comparing secondary clarifiers
and dynamic strainers. The dynamic strainers consist of rotating drums
covered with micro-mesh fabric. The fabric is cleaned by ultrasonic
energy and the rotational effect.
FMC Corporation has been investigating the process of straining for
about five years. The dynamic strainer itself has been used for several
different applications. For low suspended solids conditions, it was
tested on municipal treatment plant and aerated lagoon effluents. This
strainer has also been used to strain the mixed liquor resulting from
the treatment of cheese whey.
As an offshoot from this previous work, the dynamic strainer was then
evaluated on domestic wastewater generated mixed liquor in a package
plant at the Environmental Engineering Laboratories in Santa Clara,
California. The results of this limited experiment indicated that the
strainer could remove at least 90 percent of the MLSS at a specific
flow rate of 4.8 l/sec/m^ (7 gpm/ft^). This work along with the
operational problems of secondary clarifiers led to the proposal of this
project.
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The project was broken down into three phases; Phase I - equipment
manufacture, Phase II - equipment installation and process shakedown,
and Phase III - pilot plant operation and evaluation. The entire
project was scheduled for completion over a 9 to 10 month period.
The dynamic strainers were designed and constructed during the first
phase. The design was completed at the FMC Environmental Engineering
Laboratories, and the strainers were fabricated at the FMC Central
Engineering Laboratories. The package plant used in this study was
already in place at Environmental Engineering Laboratories.
During the second phase, the primary strainer was mounted in the
aeration tank. The secondary strainer was placed in another smaller
auxiliary tank. The remainder of the shakedown phase consisted of
building solids in the aeration tank, installing the composite
samplers, and adjusting the hydraulics of the system.
The third phase consisted of two different methods of evaluating the
strainers. The system was operated continuously with daily monitoring
and sample collection. Also, specific tests were performed during this
period to determine specific flow rates and suspended solids removals
for several different sets of operating conditions.
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SECTION IV
DESCRIPTION OF EQUIPMENT
Each dynamic strainer unit consists basically of five parts as shown
in Figure 1; the supporting drum basket, the micro-mesh fabric, the
ultrasonic cleaning transducer, the drive unit, and the outer
protective expanded metal cover. Sketches of the primary and second-
ary dynamic strainer installations utilized on this project are shown,
respectively, in Figures 2 and 3. Photographs of the strainer instal-
lations are presented in Figure 4.
The 0.61-m (2-ft) diameter by 0.61-m (2-ft) high inner expanded metal
drum basket supports the strainer fabric while allowing the liquid to
pass through to the inside. The micro-mesh strainer fabric is wrapped
around the periphery of the basket and sealed against leaks by a
silicone rubber based adhesive. Only stainless steel fabric was used
in this study. The specifications of the four cloths that were tested
are listed in Table 1, Kressilk Products, Incorporated, (1).
The ultrasonic transducer is located inside the basket and mounted on
the stationary axle. The power for this unit is supplied by an
ultrasonic generator located remotely in a control cabinet.
The ultrasonic transducer is exposed to the full vertical length of
the cloth. The ultrasonic energy excites the fabric and sheds the
solids back into the liquid reservoir. The complete cloth is cleaned
each revolution as the basket rotates past the stationary transducer.
This cleansing method is very simple, economical, and reliable. Also,
it should be noted that conventional microscreen spray cleaning
systems are not nearly as efficient at the high MLSS concentrations of
interest in this project.
The basket and strainer fabric are rotated by a 3-hp electric motor
attached to a variable speed drive unit. This unit provides a maximum
rpm of 180 and a minimum rpm of 30. The rotational effect of the
strainer also helps to keep the fabric free of solids buildup.
The strainer units are supported by brackets made of angle iron
mounted on the top of the tanks. The strainer itself and the effluent
piping are connected with the use of a WECO Air-0-Union seal. This
allows the strainer to be lowered through the liquid and connected
without draining the tank. Then the seal is inflated to 60-80 psig
to secure the strainer outlet pipe. The wastewater flow coming in
through the fabric discharges through the outlet pipe to a standpipe
outside the tank. The standpipe maintains an adequate water level in
the strainer to keep the ultrasonic unit submerged so that it can
clean the fabric effectively.
8
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DRIVE
UNIT
STATIONARY
ULTRASONIC
CLEANING
TRANSDUCER
OUTER PROTECTIVE
EXPANDED METAL
COVER
MICRO-MESH FABRIC
ROTATING SUPPORTING
DRUM BASKET
FIGURE 1
DYNAMIC STRAINER UNIT
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TOTAL
HYDRAULIC f
HEAD
MEASUREMENT
VARIABLE
SPEED
DRIVE
STANDPIPE-
RAW WASTEWATER OR
PRIMARY EFFLUENT
BAFFLE AND-v
TRANSDUCER
SUPPORT
STATIONARY
AXLE
TO
SECONDARY
STRAINER
^AERATION
TANK
BAFFLE
"STATIONARY
- BACKING
-MICRO-FABRIC
- COVER
PRESSURIZED
AIR SEAL
TEST MEASUREMENTS
' AND SAMPLES
FIGURE 2
PRIMARY STRAINER
10
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TOTAL
HYDRAULIC
HEAD
MEASUREMENTS
VARIABLE
SPEED
DRIVE
STANDPIPE
SECONDARY
STRAINER
EFFLUENT
PRIMARY STRAINER
EFFLUENT
-SECONDARY
STRAINER
HOLDING TANK
EXPANDED
METAL COVER
AND FASTENER
BAFFLE
RETURN FLOW TO
AERATION TANK
PRESSURIZED
AIR SEAL
TEST MEASUREMENTS
AND SAMPLES
FIGURE 3
SECONDARY STRAINER
11
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Primary strainer in place
in aeration tank.
Secondary strainer minus micro-
mesh fabric and outer cover.
Standpipe on the left is on the side
of the aeration tank. A sampler is
next to it. The secondary strainer
tank is on the far right.
FIGURE 4
EQUIPMENT PHOTOGRAPHS
12
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TABLE 1
MICRO-MESH FABRIC SPECIFICATIONS
Nominal
Micron
Rating
Absolute
Micron
Rating
Nominal
Mesh Count
(Openings/inch)
(Warp x shoot)
Wire Diameter
Inches
(Warp x shoot)
Twilled Dutch Weave
5 (4-6) 12-14 200 x 1400 .0028/.0016
10 (10-13)
20 (18-22)
40 (35-45)
Robusta Reverse Dutch Weave
15-18 850 x 155
25-27 600 x 125
48-54 280 x 70
.0012/.004
.0016/.005
.0035/.008
An FMC SL-144 modified complete mix activated sludge package treatment
plant was used for this study. The package plant was supplied with
municipal wastewater obtained in continuous supply from an interceptor
sewer. The wastewater was screened and comminuted prior to entering
the primary clarifier. The primary clarifier has a volume of 9.8 ITH
(347 ft3 or 2,600 gal) and a surface area of 5.9 m2 (63.6 ft2). The
clarified influent was then pumped into a 15.2 m3 (535 ft3 or 4,000 gal)
aeration tank. The primary strainer was placed directly in the mixed
liquor at one end of the aeration tank opposite the influent port. The
effluent from the primary strainer was fed by gravity into a secondary
holding tank with a volume of 4.5 m3 (158 ft3 or 1,180 gal). The
secondary strainer was mounted in this tank. The final effluent was
obtained from the secondary strainer. To keep the solids concentration
constant in the secondary tank, a return flow was pumped from the bottom
of the cone shaped secondary holding tank back into the mixed liquor.
Sludge wasting was accomplished by pumping directly from the aeration
tank.
In the secondary holding tank, a cylinder, 0.61 m (2-ft) in diameter and
0.71 m (2.33 ft) high, was connected to the rotating shaft above the
basket strainer to minimize radial mixing.
Three FMC samplers were used on the project. Daily composite samples
were taken on the primary effluent, the primary strainer effluent, and
the final or secondary strainer effluent. The samplers were set to take
a sample every 15 minutes. Samples collected on Monday were a composite
sample of the weekend. A complete flow diagram for the experimental
system is sh^wn in Figure 5.
13
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RAW
WASTEWATER
PRIMARY
CLARIFIER
PRIMARY SLUDGE
TO SEWER
90° NOTCH WEIR
VARIABLE SPEED DRIVE
SAMPLER
VARIABLE SPEED PUMP
AERATION
TANK
WASTE ACTIVATED SLUDGE
TO SEWER
PRIMARY
*Y
IER
V
)
\
7 '
!
L
V
1
J
, x
^
SE
"ST
/
\
RETURN
PUMP
FIGURE 5
DYNAMIC STRAINING FLOW DIAGRAM
SECONDARY
STRAINER
FINAL
EFFLUENT
SECONDARY
HOLDING
TANK
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Most of the installation work involved mounting the strainers and
providing the necessary pumps and piping. The package plant was in
place prior to this project. Two-and three-inch PVC pipe was used for
the additional piping required by the strainers.
Variable speed pumps were used for both the influent and return flows.
These pumps provided the flow adjustment required for evaluation of
the strainers.
15
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SECTION V
DESCRIPTION OF OPERATION
Equipment manufacture (Phase I of the project schedule) was completed
in September 1972. Installation of equipment (Phase II) was initiated
in October 1972. The plant was put in operation the first week in
November 1972. One hundred and ninety liters (50 gal) of mixed liquor
seed were introduced into the aeration tank along with primary effluent
and batch aerated. On November 30, the MLSS concentration reached
340 mg/1. The plant was then fed primary effluent on a continuous
basis. Samples were taken daily and some analyses performed. By
December 20, the MLSS concentration had reached 4,000 mg/1. The remain-
der of Phase II was accomplished between December 21, 1972 and
February 7, 1973, and consisted of process shakedown and optimization
of system hydraulics. Operation and evaluation of the pilot plant test
facility (Phase III) began on February 8 and lasted for approximately
12 weeks. Plant operation, system monitoring, and data collection were
continuous during this period. Additionally, for the first 10 weeks of
Phase III, a series of batch experiments in which system influent flow
was temporarily stopped were undertaken to characterize strainer perform-
ance as a function of several variables.
Five samples were taken each day during the 12-week operation and
evaluation phase. Samples collected on Monday mornings represented 72
hours of continuous weekend sampling. As previously mentioned,
composite samples were obtained for the primary effluent, primary
strainer effluent, and secondary strainer effluent. Also, grab samples
of the secondary return flow and the mixed liquor were taken. A list
of the analyses performed on each sample is shown in Table 2. All
analytical work was performed in accordance with procedures and methods
detailed in "Standard Methods for the Examination of Water and
Wastewater," Thirteenth Edition, Washington, D. C. (1971).
Mechanical and operational data were also recorded daily, as indicated
in Table 3.
Following process shakedown, the experimental program to characterize
the dynamic strainers was initiated on February 8, 1973. The variables
evaluated during this 10-week segment of Phase III included nominal
pore size of the strainer fabrics, suspended solids concentrations in
the aeration and secondary holding tanks, rotational speed of the
strainers, and hydraulic head in both tanks.
An outline of the experimental characterization program is given in
Table 4. Initially, a 20-nricron fabric was put on the primary strainer
and a 10-micron fabric on the secondary strainer. For the first
characterization tests on the primary strainer, the MLSS concentration
was adjusted to about 2,500 mg/1. The drum speed was set and the
16
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TABLE 2
SAMPLING AND ANALYSES SUMMARY
SAMPLE NUMBER
1
2
3
4
5
TYPE
Composite
Grab
Composite
Grab
Composite
LOCATION
Primary Effluent
Mixed Liquor
Primary Strainer Effluent
Secondary Strainer Return
Secondary Strainer Effluent
SAMPLE
TSS VSS TOC SOC COD BOD5 Total N NH3-N pH DO
1
2
3
4
5
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Z
Z
Y
Y
Z
Z
Z
Z
Z
X
X
X
Z
X - Daily, Monday through Friday
Y - Monday, Wednesday, and Friday
Z - Occasionally
liquid level raised to achieve the maximum head allowed by the tank.
Then the effluent butterfly valve was opened and the influent flow was
stopped. As the liquid level dropped, the flow and corresponding head
were recorded. This flow was measured with the use of a 20 1 (5.3 gal)
container and stop watch. Head was recorded as the difference in the
liquid levels of the tank and the standpipe. Suspended solids samples
were taken at several different head measurements. When the liquid
level dropped enough so that the flow stopped, the strainer was set at
a new rotational speed and the aforementioned procedure repeated. This
testing method was changed slightly to accommodate the higher specific
flow rates obtained at higher drum speeds.
The head versus flow curves had an optimum flow at a head slightly
larger than the head at which the flow stopped. At the higher flows,
the level in the tank dropped too fast to allow the screen to suffi-
ciently clean itself before the head dropped past the optimum point.
To eliminate this problem, the tests were started with a low head that
produced no flow for a given strainer peripheral velocity. Then the
head was slowly increased by introducing influent in controlled amounts.
This procedure was followed throughout the remainder of the testing
program. A comparison in Figure 6 of the head versus flow curves for
the increasing head test procedure and the decreasing head test pro-
cedure shows the marked contrast.
17
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TABLE 3
OPERATIONAL DATA OUTLINE
PARAMETERS MEASURED
LIQUID FLOW
AIR FLOW
STRAINER SPEED
HYDRAULIC HEAD
SONIC GENERATOR AMPS
TURBIDITY
DISSOLVED OXYGEN
LOCATION
Primary Effluent
Secondary Strainer Return
To Aeration Tank
Primary Strainer
Secondary Strainer
Primary Strainer
Secondary Strainer
Primary Strainer
Secondary Strainer
Primary Strainer Effluent
Secondary Strainer Effluent
Aeration Tank
During the first segment of the characterization program, head versus
flow curves were obtained with the primary strainer for several drum
speeds at a MLSS level of 2,500 mg/1. Similar curves were also
recorded for a MLSS concentration of 1,800 mg/1. The same procedure
(recording flow as head increased) was used to obtain head versus flow
curves for the secondary strainer at three different suspended solids
levels and several different drum speeds. During this phase of high
flow rates, the fabric area was reduced by 74 percent to eliminate back
pressure effects in the effluent piping. Plastic sheet was wound around
the drum and taped in place to blind the fabric.
For the second segment of the characterization program, a 40-micron
fabric was placed on the primary strainer. The 10-micron fabric
remained on the secondary strainer. Data were obtained for the primary
strainer at MLSS levels of 2,500, 3,500, and 6,000 mg/1. The secondary
strainer was again characterized at three different suspended solids
levels.
18
-------
TABLE 4
OUTLINE OF STRAINER CHARACTERIZATION PROGRAM
I. Fabric Combination - 20-m1cron, I0-m1cron (Feb. 8)
A. Primary 20-«1cron
1. MLSS - 2,570 rag/1 - Obtained head (H) versus flow (Q)
curves for tip speeds of 188, 376, 564, 752 ft/Bin
2. MLSS - 1,830 mg/1 - Changed procedure to Increasing head -
Obtained head (H) versus flow (Q) curves for speeds of
376 and 752 ft/mln
B. Secondary 10-micron
1. Tank SS - 130 mg/1 - H versus Q curves - 188, 376, 564
ft/mln
2. Tank SS - 40 mg/1 - Changed procedure to Increasing head.
H versus Q curves - 564 and 752 ft/mln
3. Tank SS - 90 mg/1 - H versus Q curves - 564 and 752 ft/«1n
II. Fabric Combination - 40-m1cron, I0-m1cron (March 8)
A. PrlmarJ 40-«1cron
1. MLSS - 2,370 mg/1 - H versus Q curves - 376, 564, 752
ft/m1n
2. MLSS - 3,700 mg/1 - H versus Q curves - 188, 376, 564,
752 ft/mln
3. MLSS - 6,140 mg/1 - H versus Q curves - 188, 376, 564,
752 ft/mln
B. Secondary
1. Tank SS - 245 mg/1 - H versus Q curves - 564, 752, 1,128
ft/m1n
2. Tank SS - 166 mg/1 - H versus Q curves - 376, 564, 752,
1.128 ft/mln
3. Tank SS - 112 mg/1 - H versus Q curves - 376 ft/mln
III. Fabric Combination - 10-mlcron, 5-m1cron (April 1)
A. Primary 10-mlcron
1. MLSS - 6,630 mg/1 - H versus Q curves - 188, 376, 564,
752 ft/mln
2. MLSS - 9.100 mg/1 - H versus Q curves - 188, 376. 564.
752 ft/mln
3. MLSS - 12.200 mg/1 - H versus Q curves - 188, 376. 564,
752 ft/mln
B. Secondary 5-m1cron
1. Tank SS - 48 n*
ft/m1n
2. Tank SS - 300 mg/1 - H versus Q curves - 564 ft/mln
1. Tank SS - 48 mg/1 - H versus Q curves - 232, 376, 564, 752
ft/m1n
19
-------
8
NOTE: I IN= 2.54 CM I GPM/FT2 =0.679 L/SEC/M2
~ 7
LJ
z
OT
>-
or
34
a:
o.
I3
ui
< 2
a: *•
u.
o
UJ
Q.
PRIMARY STRAINER CONDITIONS ~-
60 RPM
2,000 mg/7 MLSS
INCREASING HEAD
DECREASING HEAD
2345
TOTAL HYDRAULIC HEAD (IN )
FIGURE 6
A COMPARISON OF INCREASING
AND DECREASING HEAD TESTS
20
-------
A 10-micron fabric was used on the primary strainer and a 5-micron
fabric on the secondary strainer for the last segment of the
characterization program. Head versus flow curves were compiled for
the primary strainer at MLSS levels of 6,500, 9,000, and 12,000 mg/1.
The 5-micron fabric on the secondary strainer was characterized at
two different suspended solids levels.
Following the characterization of the individual strainer variables,
the entire system was operated continuously for about two weeks,
beginning April 18. During the strainer characterization testing
program, the 10-micron fabric yielded the best results on the primary
strainer. Therefore, the 10-micron primary/5-micron secondary fabric
combination was used on the strainers during the uninterrupted
continuous flow segment of Phase III. The MLSS level was held around
8,000 mg/1. The system was monitored in the same manner as during the
process shakedown and strainer characterization work.
21
-------
SECTION VI
DISCUSSION
The ultimate feasibility of dynamic straining is dependent on two
performance parameters; specific flow rate and suspended solids
removal. Both of these will be discussed in terms of the variables
analyzed during the testing period and day-to-day continuous
performance.
SPECIFIC FLOW RATES
Specific flow rates were affected by four variables; nominal opening
size of the micro-fabric, unstrained suspended solids concentration,
strainer rotational speed, and hydraulic head.
The rotation of the drum causes a centrifugal pumping head. Differ-
ential heads were measured as the difference between the liquid level
at the tank wall and the standpipe overflow as shown in Figures 2 and
3. When no influent is entering the system, this difference is the
pumping head. If the liquid head in the tank outside the drum is
increased and influent flow is introduced to the system causing a
discharge from the standpipe, some friction head loss occurs. These
friction losses can be assumed to take place across the micro-fabric,
as the losses through the piping are minimal at normal flows. The net
head or driving head across the micro-fabric is the total head
measured during experimentation minus the centrifugal pumping head at
zero flow, which is composed of internal and external pumping heads.
Net head is a more meaningful parameter in determining straining
characteristics. Different sizes and configurations of strainers and
tanks will have unique centrifugal pumping heads. Similar results
should be expected when performances of different strainers with
the same fabric covering are compared at the same net heads.
The theoretical pumping heads can be approximated by using the Navier-
Stokes equations in cylindrical coordinates for the steady flow of an
incompressible fluid around a vertical axis. The radial variation of
pressure head due to rotation is given by Equation 1, which represents
the elevation of the liquid surface at increasing distance from the
axis of rotation, Daily and Harleman, (2).
dH = V? (1)
dr gr
Integration over the radial distance from the internal baffle to the
drum provides an equation for the internal pumping head by making the
assumption that the internal layer of water between the internal
baffling and the drum has the same velocity as the drum.
22
-------
p
(2)
Where,
Hp-j = Internal pumping head in feet
V = Tangential velocity of water in ft/sec
r = Radial distance from rotational -axis in inches
g = Gravitational constant =32.2 ft/sec2 (9.8 m/sec2)
r2 = Radius of drum in inches
r] = Radius of exterior edges of internal baffling in inches
Plots of theoretical Hp.j versus the velocity of the drum for the
primary and secondary strainer are shown in Figures 7 and 8,
respectively.
To calculate the external pumping head the velocity profile of the
water outside the drum had to be obtained. Water velocities in the
secondary tank were measured with a current meter at different distances
from the drum. Velocity profiles at zero flow and with a specific flow
rate of 1.2 1/sec/m2 (1.8 gpm/ft2) are shown in Figure 9 for a drum
peripheral velocity of 1.83 m/sec (6 ft/sec). These velocity measure-
ments are averages of measurements taken at several different depths.
Ignoring wall effects, the following linear equation represents a fair
approximation of the water velocity profile outside the drum at zero
flow:
V = 3(ft/sec) - 0.06 / ft Ir (3)
j see-in/
Where,
V = Water velocity in ft/sec
r = Radial distance from vertical axis of drum in inches
This equation, shown graphically in Figure 9, can be used to calculate
the theoretical external pumping head. When this value was added to
the theoretical internal pumping head, the sum was within 10 percent of
the value of the actual pumping head obtained by experimentation.
Substituting the velocity function (Equation 3) in Equation 1 and
integrating for the values of r from the outer edge of the drum to the
tank wall, yields a value for external pumping head for the secondary
23
-------
o
LU
X
o
2
Q.
NOTE:
I IN = 2.54 CM
I FT/SEC-0.305 M/SEC
ACTUAL
PUMPING
HEAD
(I NTERNAL
PLUS EXTERNAL]
THEORETICAL
PUMPING HEAD
[INTERNAL)
0 3 6 9 12 15
DRUM PERIPHERAL VELOCITY ( FT/SEC )
FIGURE 7
PRIMARY STRAINER INTERNAL
PUMPING HEAD
24
-------
16
12
8
o
UJ
X
o
z
CL
NOTE:
I IN - 2.54 CM
I FT/SEC-0.305 M/SEC
ACTUAL
PUMPING
HEAD
(INTERNAL
PLUS
EXTERNAL)
THEORETICAL
PUMPING HEAD
(INTERNAL)
0 3 6 9 12 15
DRUM PERIPHERAL VELOCITY ( FT/SEC )
FIGURE 8
SECONDARY STRAINER INTERNAL
PUMPING HEAD
25
-------
o
LU
cn
o 4
3
UJ
o: 3
UJ
i
NOTE:
I IN=2.54 CM
I FT/SEC = 0.305 M/SEC
I GPM/FT2 • O.679 L/SEC/M2
2 -
A
30 IN
0 GPM/FT2
V=3-O.O6 R
L8 GPM/FT2
20 IN
I
IO IN
TANK WALL
OUTER EDGE
OF DRUM
DISTANCE FROM VERTICAL AXIS OF DRUM (IN)
FIGURE 9
SECONDARY TANK WATER VELOCITY
PROFILES AT DIFFERENT FLOW RATES
26
-------
strainer of 2.97 cm (1.17 in) at a drum peripheral velocity of
1.83 m/sec (6 ft/sec).
Hn« = i In 30 . CL36 (30-12)+ °-Q036 (900-144)
pe 32.2 TT 32.2 64.4
Hpe =0.09712 ft = 1.17 in
Utilizing Equation 2 or Figure 8, a value of the internal pumping head
of 2.97 cm (1.17 in) is obtained at a drum peripheral velocity of
1.83 m/sec (6 ft/sec). Therefore, the total pumping head for this
drum velocity is:
HT = 2.97 + 2.97 = 5.94 cm (2.34 in)
The external pumping head is more pronounced in the secondary strainer
than in the primary strainer, particularly at higher drum velocities,
because of the circular holding tank and the absence of aeration. The
velocity profile on the outside of the drum changes as flow through the
strainer increases and so the pumping head also changes. The actual
pumping head curves in Figures 7 and 8 are based on averages from all
the data taken when there was no flow through the respective strainers.
The effect of head on specific flow rate was consistent throughout the
program. As previously shown in Figure 6, the specific flow rate
increased as the measured head increased until a peak specific flow rate
was attained. Then, as the head continued to increase, the specific
flow rate dropped off gradually. An explanation of these observations,
based on the data obtained, is that this phenomenon is a result of the
opposing forces acting on the suspended solids being strained. The
combined effects of the strainer rotation and ultrasonics force the
solids away from the fabric, while the hydraulic head forces the solids
toward the screen. On the low-head side of the peak, the combined
forces of rotation and ultrasonics are larger than the force due to the
head. Therefore, the specific flow rate through the strainer continues
to increase with increasing liquid head. Then* when these opposing
forces along with other head losses and viscous effects balance, the
maximum specific flow rate is reached. The viscous effects include the
force exerted on the solids by the flowing liquids. On the high-head
side of the peak, the force due to hydraulic head exceeds the cleaning
effect of the other two forces and the specific flow rate decreases.
The data show that as rotational speed increases, the hydraulic head
required for maximum specific flow rate also increases. The shape of a
set of total head versus specific flow rate curves, at different
rotational velocities, is similar for both strainers and is illustrated
in Figure 10. Figuce 11 shows a set of net head versus specific flow
rate curves. The shape of the curves is again characteristic of both
strainers.
27
-------
30
T-20
u.
UJ
I
10
o
u.
o
NOTE;
IN=2.54 CM
I GPM/FT2" 0.679 L/SEC/M2
SECONDARY STRAINER
10 -M FABRIC
120 RPM
I
10 20
TOTAL HEAD (IN )
30
FIGURE 10
TOTAL HYDRAULIC HEAD CURVES
AS A FUNCTION OF ROTATIONAL SPEED
28
-------
NOTE:
I IN * 2.54 CM
I GPM/FT* » 0.679 L/SEC/M*
176 RPM
PRIMARY STRAINER
20J4 FABRIC
«i
Q.
O
UJ
I 2
o
u.
p
3 -
I -
2345
NET HEAD (IN)
FIGURE 11
NET HYDRAULIC HEAD CURVES AS
A FUNCTION OF ROTATIONAL SPEED
29
-------
The effect of rotational speed (peripheral velocity) on specific
flow rate was also quite consistent during the test program. The
specific flow rate increased as the velocity increased. This result
can be explained on the basis of the theory proposed in the previous
paragraphs. The greater speed provides a larger hydraulic and
ultrasonic rotational cleaning due to a smaller and more energetic
boundary layer around the drum and more frequent ultrasonic cleaning.
Therefore, greater liquid head can be applied before the hydraulic
head force on the solids exceeds the opposing cleaning forces.
Another factor in the character of the boundary layer is the flow
into the drum. As the flow increases, the water with slower
velocities relative to the drum is swept into the drum bringing water
with higher velocities relative to the drum closer to the drum with
more cleaning energy.
This phenomenon can explain why peak specific flow rates were signifi-
cantly lower when the liquid head was quickly lowered past the peak
point in early testing. Starting at higher heads caused the screens
to become immediately partially blinded with solids. The head in the
tank would drop quickly as the peak specific flow rate was approached,
not allowing sufficient time for the fabric to clean itself to obtain
satisfactory specific flow rates, which would have in turn further
increased the cleaning efficiency.
The effect of MLSS concentration on primary strainer specific flow rate
was predictable in most cases. As the level of MLSS increased, the
specific flow rate decreased. This was attributed to greater clogging
of the micro-fabric with solids. The same effect was experienced for
all three mesh sizes used. However, the solids levels used with the
secondary strainer were not high enough to yield a similar conclusive
result.
The effect of micro-fabric nominal opening size on specific flow rate
was unexpected, although static, clean water straining tests proceeded
as anticipated. Clean water total hydraulic head versus specific flow
rate curves for four different micro-fabric sizes are shown in Figure 12,
The 40-micron and 10-micron fabrics were also evaluated on the primary
strainer under similar conditions at a MLSS level of about 6,000 mg/1.
The 10-micron fabric yielded a maximum specific flow rate of 8.1
1/sec/m2 (12 gpm/ft2}. The maximum specific flow rate of the 40-micron
fabric was only 2.3 1/sec/m2 (3.36 gpm/ft2). The 20-micron fabric was
never evaluated at the same MLSS concentration as the 10-micron fabric.
However, the maximum specific flow Kate achieved with the 20-micron
fabric was 10 1/sec/m2 (14.8 gpm/ft^)at a MLSS level of about 1,800
mg/1. Based on previously mentioned.results on the effect of MLSS
level on primary strainer specific flow rate, the 10-micron fabric was
judged to have exhibited the best overall performance. All three
micro-fabrics tested on the primary strainer were of the same Robusta
weave.
30
-------
400
.NOTE'-
I IN» 2.54 CM
I GPM/FT2- 0.679 L/SEC/M2
300
CM
CL
UJ
S 200
o
o
u_
o
It!
100 —
2345
TOTAL HEAD (IN)
FIGURE 12
CLEAN WATER TEST OF MICRO-FABRICS
31
-------
One possible explanation for the anomalous performance of the fabrics
is that this phenomenon is associated with the nature of the biomass.
Possibly, the 10-micron fabric allows less entanglement of filamentous
microorganisms and, therefore, is more easily cleaned. Also, the
more rigid and porous fabrics may not be cleaned as effectively by the
ultrasonic energy. Obviously, work in this area is not conclusive.
Used with the secondary strainer, the 10-micron fabric provided a
maximum specific flow rate of 17 1/sec/m2 (25 gpm/ft2). For similar
suspended solids levels, the 5-micron fabric yielded only 1.9 1/sec/m
(2.8 gpm/ft2). This 5-micron fabric was a Dutch-Twill weave which has
inferior specific flow rate capacities.
SUSPENDED SOLIDS REMOVALS
During the testing program, suspended solids removals were affected
by three of the test variables; nominal pore size, suspended solids
concentration, and the peripheral velocity of the strainer.
The effect of peripheral velocity on suspended solids removal was
quite consistent throughout the testing program. For both the primary
and secondary strainers and for all four fabrics tested, the effluent
quality decreased with an increase in peripheral velocity.
Two possible explanations for this observation have been proposed. As
the velocity increases, more of the floe particles near the fabric are
broken down and pass through the fabric. Also, at lower speeds, a
solids blanket may accumulate due to reduced frequency of ultrasonic
cleaning and reduced hydraulic cleaning. This would help to filter
out the smaller particles. For an increase in peripheral velocity
from 1.9 m/sec (376 ft/min) to 3.8 m/sec (752 ft/min), the effluent
suspended solids increased 200 to 400 percent.
The suspended solids levels in the respective tanks affected suspended
solids removals. As the suspended solids concentrations in the tanks
increased, effluent suspended solids also increased. However, the
percent solids removed by the strainer also increased. Similar results
were obtained with both strainers for all fabric sizes.
The effect of fabric nominal pore size on suspended solids removal was
predictable. The larger pore sizes allowed more suspended solids to
pass through. For the most part, head did not significantly affect
suspended solids removal.
All graphs and data tabulations obtained during the strainer character-
ization test program are presented in Appendices A and B. The infor-
mation contained in these graphs and tabulations is summarized below.
32
-------
On the primary strainer, the 10-micron fabric was more effective in
removing MLSS than either the 20-or 40-micron fabrics tested. In the
MLSS range of 6,240-6,840 mg/1, residual suspended solids were less
than 15 mg/1 at a rotational speed of 30 rpm and less than 30 mg/1
at 60 rpm on the 10-micron fabric. This yielded?peak specific flow
rates, respectively, of 1.2 1/sec/m2 (1.7 gpm/ft^) at a total head of
4.6 cm (1.8 in) and 3.3 1/sec/m2 (4.8 gpm/ft2) at a total head of
9.7 cm (3.8 in). Increasing the rotational speed to 90, then to 120
rpm increased the peak throughout rate to 4.5 1/sec/m2 (6.7 gpm/ft2)
at a total head of 16.8 cm (6.6 in) and 8.1 1/sec/m2 (12.0 gpm/ft2)
at a total head of 30.5 cm (12.0 in), respectively. However, residual
suspended solids increased at the higher throughput rates to 40-80
mg/1 at 90 rpm and 90-120 mg/1 at 120 rpm. Increasing the rotational
speed further to 150 rpm resulted in excessive solids breakthrough
and a substantial drop in peak specific flow rate.
In the MLSS range of 8,760-9,540 mg/1, the primary strainer 10-micron
fabric produced residual suspended solids of 20-25 mg/1 at 30 rpm,
30-35 mg/1 at 60 rpm, 50-80 mg/1 at 90 rpm, and 85-95 mg/1 at 120 rpm.
Peak specific flow rates were very similar to those observed in the
MLSS range of 6,240-6,840 mg/1 for rotational speeds up to 90 rpm.
At 120 rpm, however, the peak throughout rate was only 5.4 1/sec/m2
(7.9 gpm/ft2) compared to 8.1 1/sec/m2 (12.0 gpm/ft2) at the lower
MLSS level.
As the MLSS concentration was further increased to 11,520^12,720 mg/1,
both throughput rates and residual suspended solids deteriorated
significantly. For example, at 60 rpm, residual suspended solids
were in the 65-75 mg/1 range and the peak specific flow rate attained
was 1.2 1/sec/m2 (1.8 gpm/ft2). At 90 rpm, the corresponding values
were 90-100 mg/1 and 2.2 1/sec/m2 (3.2 gpm/ft2).
On the secondary strainer, the 5-micron and 10-micron fabrics exhibited
approximately the same capability for removing residual suspended
solids contained in the primary strainer effluent. However, the attain-
able throughput rates on the 5-micron fabric were only 1/5 to 1/10
those achieved with the 10-micron fabric. Percentage suspended solids
removal on the 10-micron fabric increased with increasing concentration
of solids in the secondary holding tank up to 260 mg/1. Concentrations
above 260 mg/1 were not evaluated.
Suspended solids removals on the secondary strainer 10-micron fabric
were as follows:
1. For a rotational speed of 90 rpm, suspended solids
removals averaged 50-65 percent at a holding tank
suspended solids concentration of 30-50 mg/1, 85-90
percent at 90-100 mg/1, 85-90 percent at 160-170 mg/1,
and 90 percent at 225-230 mg/l%
33
-------
2. For 120 rpm, suspended solids removals averaged 50-65
percent at a holding tank suspended solIds concert*
tratlon of 30-35 mg/1, 80-85 percent at 80-100 mg/1,
80-85 percent at 165-170 mg/1, and 90 percent at
250-260 mg/1.
3. For 180 rpm, suspended solids removals averaged about
75 percent at a holding tank suspended solids concen-
tration of 160-170 mg/1 and 85 percent at 250-260 mg/1.
Peak specific flow rates for the secondary strainer 10-micron fabric
ranged from 6 to 10 1/sec/m2 (9 to 14 gpm/ft2.) at 90 rpm and from
8 to 17 1/sec/m2 (12 to 25 gpm/ft2) at 120 rpm. In both cases, the
higher throughput rates corresponded to the lower holding tank
suspended solids concentrations. For the two holding tank suspended
solids concentrations tested at 180 rom, the peak throughput rate
averaged 14-15 1/sec/m2 (21-22 gpm/ft2). Peak specific flow rates
occurred at total heads of 20-23 cm (8-9 in) at 90 rpm, 36-41 cm
(14-16 in) at 120 rpm, and 64-69 cm (25-27 in) at 180 rpm.
DAILY OPERATION
After process shakedown, the entire experimental system was operated
continuously, whenever possible. Minor interruptions occurred
periodically including mechanical failures and operational upsets.
However, daily samples and operating data were obtained on a near-
continuous basis.
The hydraulics of the package treatment plant were inadequate to
handle the large flows utilized during the strainer characterization
testing program. The influent pump could supply only about 1.3
I/sec (20 gom) which was equivalent to a specific flow rate of about
2.7 1/sec/m2 (4 gpm/ft2). During the characterization programs, an
additional high-rate pump was used to help fill the tanks.
A second hydraulic problem was the primary effluent piping. As influent
flows became very large, the head loss through this section became
limiting. During specific evaluation tests on the primary strainer,
this line was bypassed. Despite these hydraulic limitations, daily
monitoring and operation permitted observation of several very
important operational parameters.
One area of special interest was the shape of the head versus specific
flow rate curves. Daily operation supplied an opportunity to check
the validity of these curve's over a longer period than possible with
each specific test. Because of the hydraulic limitations, the
strainers could be evaluated continuously only at the lower rotational
speeds. Under these conditions, it was found that daily operation did
closely parallel the experimentally obtained head versus specific
flow rate curves.
34
-------
A peripheral velocity of 1.9 m/sec (376 ft/min) was frequently used
for day-to-day operation. At this velocity* the liquid level could
be dropped to equal the pumping head. The tnfluent flow was then
usually set at a rate slightly below the maximum indicated for those
conditions. The liquid level would thereafter rise until the necessary
head on the strainer was achieved. Balancing of flows was easily
maintained. If the influent flow exceeded the peak strainer through-
put capability for a specific rotational speed, the liquid head would
continue to increase until the tank under investigation overflowed.
The most obvious remedy to this problem was to increase the strainer
rotational speed to accommodate the increased flow. However, since
automatic control of rotational speed was not available, a float switch
was used to shut off the influent pump if the liquid level rose too
high. The pump would start again when the head had fallen beneath a
predetermined point.
The nature of the biomass was another area of special interest. For
this particular project, there was not sufficient time to adequately
document the effect of biomass on strainer operation. However, some
work was done and observations made based on that work. Filamentous
growth prevailed in the mixed liquor. Previous pilot plant work at
this site also experienced similar mixed liquor cultures. This type
of biomass proved"to be very strainable.
The dynamic strainer system also appeared to be selective for the
filamentous microorganisms. Twice during the experimental program
the primary strainer had to be removed from the system to make repairs
on the drive unit. During the repair period, the system was operated
conventionally with a secondary clarifier for a few days. When the
primary strainer was returned to the system, suspended solids removals
were quite poor initially. Then, after several days, the biomass
would readjust, become more filamentous, and suspended solids removals
would improve.
The strainability of the biomass was also affected by the organic
(F/M) loading. During the third phase of the characterization testing
program, the MLSS concentration was raised to about 12,000 mg/1 by
supplementing the primary effluent feed with beet molasses. Following
these tests, addition of beet molasses was stopped. The system
continued to operate effectively for about three days. Then, both
the specific flow rates and suspended solids removals started to
deteriorate. During this period, the organic loading dropped below
0.05 kg BOD5/day/kg MLVSS (0.05 Ib BOD5/day/lb MLVSS). Several differ-
ent mechanical adjustments were made in an attempt to improve strainer
performance, but were unsuccessful. Beet molasses was then added
again, and after two days the specific flow rate improved.
Limited studies were undertaken to define the settling characteristics
of the primary strainer effluent. Figure 13 is a graph showing the
percentage of solids with settling velocities equal to or less than
prescribed values. The procedure for obtaining settling velocities
35
-------
for unhindered settling was obtained from the Link-Belt Division of
FMC Corporation, (3). These settling results are predictably poor due
to the very fine nature of the discrete particles which pass through
a 10-micron fabric. Additional studies should be undertaken to deter-
mine settleability of varying primary strainer effluents. Chemical
addition may be necessary to enhance flocculation of these fine solids.
These studies would be important in determining the capability of
dynamic straining to upgrade existing activated sludge treatment plants,
Dynamic straining could decrease the solids loading on an existing
secondary clarifier where solids thickening capacity had been exceeded.
At the same time, it would permit maintenance of a higher MLVSS concen-
tration in the aeration tank, thereby lowering the organic (F/M)
loading without increasing the size of the aeration facilities.
The results of day-to-day continuous operation during the process
shakedown and experimental
Appendix C.
study phases are summarized in detail in
120
100
UJ
CO J-
co <
UJ O
-«o
x z
^™
i£
CO o
O o
_l _l
QUJ
CO >
H O
z z
UJ _)
o »-
DC »-
Ul UJ
Q. CO
80
60
40
20
NOTE:
I FT/MIN
0.305 M/MIN
40mg// SS INITIALLY
24% COLLOIDAL SOLIDS
.01
.05 .1
SETTLING VELOCITY (FT/MIN)
.5
FIGURE 13
SETTLING VELOCITIES OF PARTICLES
IN PRIMARY STRAINER EFFLUENT
36
-------
SECTION VII
ECONOMIC ANALYSIS
An economic comparison between activated sludge plants utilizing
dynamic straining clarification versus gravitational clarification
would not be sufficient without comparing the economic changes in
other processes which dynamic straining can alter. Aeration tank
volumes and sludge handling facility requirements are both altered
by dynamic straining. An economic comparison of 3,785 and 37,850 m3/
day (1 and 10 mgd) plants has been calculated using Patterson, et al,
(4), as a basis for estimating costs on every unit process except
dynamic straining.
The cost estimate for dynamic straining has been evaluated using FMC's
current basic production model for which the process specifications
principally cover lagoon effluent applications. The production model
has approximately 6.5 m2 (70 ft ) of screening area. A cost of $58,600 per
strainer has been established for estimating purposes in this report.
Tanks for secondary strainers would add about $5,000 to the cost of
each strainer. Larger units, design improvements, and combined tankage
for secondary straining should bring the cost down considerably.
For estimating annual costs, a conservative fabric life of one year was
used. The fabric will cost approximately $161/m2 ($15/ft2) to replace.
Power requirements are approximately 1.6 kw/m2 (0.2 hp/ft2) to rotate
the drum and 0.37 kw/m2 (0.04 hp/ft2) for ultrasonic cleaning. The cost
of electrical power was assumed at 1.5^/kw-hr. Other annual mainten-
ance1 material costs for the strainer were estimated at one percent of
the capital cost per year.
Manpower requirements for dynamic straining in an integrated facility
were difficult to estimate. Without automation, to optimize effluent
quality, the strainer rotational speed would have to be manually
changed in response to variations in flow. For this reason, manpower
requirements for dynamic straining were conservatively estimated to be
50 percent greater than the manpower requirements for secondary gravity
clarifiers in a conventional plant with the same flow rate.
Peak daily flow rates of 6,435 m3/day (1.7 mgd) and 56,775 m3/day
(15 mgd) were, assumed for the 3,785 nwday (1 mgd) and 37,850 m3/day
(10 mgd) plants, respectively. For a peak daily flow rate of 6,435 m3/
day (T.7 mgd), fabric area requirements are 13.0 m2 (140 ft2, i.e.
two strainers) for primary straining and 6.5 m2 (70 ft2, i.e. one
strainer) for secondary straining* The fabric area requirements for a
peak daily flow rate of 56,775 m3/day (15 mgd) are 117 m2 (1260 ft2,
i.e. 18 strainers) for primary straining and 58.5 m2 (630 ft2 i. e.
nine strainers) for secondary straining. These area requirements are
equivalent to throughput rates of roughly 7.1 l/sec/m^ do. 5 gpm/ft*)
for primary straining (includes 25 percent recycle flow from the second-
ary strainer holding tank) and 11.4 1/sec/m2 (16.8 gpm/ft2) for secondary
37
-------
straining at the peak daily flow rates. To prevent deterioration of
effluent quality in the event of strainer breakdown or during
maintenance periods, for estimating purposes, one standby strainer
was provided for the smaller plant (yielding a total of four strainers)
and four standby strainers were provided for the larger plant (yielding
a total of 31 strainers). This design requires a return flow rate of
25 percent from the secondary strainer holding tank to the aeration
tank.
For the conventional systems using secondary gravity clarification, a
design surface loading at average daily flow of 26.5 m3/day/m2
(650 god/ft2) was utilized for the 3,785 m3/day (1 mgd) plant and
28.5 m3/day/m2 (700 gpd/ft2) was used for the 37,850 m3/day (10 mgd)
plant. The slightly higher average surface loading for the larger
plant was allowed because of its smaller peak daily/average daily flow
ratio. In addition, for estimating purposes, an excess capacity
factor (ECF) of 1.5 was used for secondary clarification for the smaller
plant and 1.17 for the larger plant.
A design surface loading for primary clarification at average daily
flow of 36.7 m3/day/m2 (gpo gpd/ft2) was utilized for the 3,785 m3/day
(1 mgd) plants and 40.7 m3/day/m2 (1,000 gpd/ft2) was used for the
37,850 m3/day (10 mgd) plants. Again, the higher average surface load-
ing for the larger plant was selected because of its smaller peak daily/
average daily flow ratio.. Identical ECF's were used for estimating
primary clarification construction costs as were used for secondary
clarification.
Raw wastewater characteristics were assumed to be 200 mg/1 of BODs and
250 mg/1 of suspended solids, Removals during primary clarification
were projected to be 35 percent for BODs and 50 percent for suspended
solids. Final effluent quality was based on assumed overall removals
of 90 percent for both constituents, yielding a BODs of 20 mg/1 and a
suspended solids of 25 mg/1.
MLSS design levels were established at 2,600 mg/1 for the conventional
process and 5,500 mg/1 for dynamic straining, permitting a 60 percent
reduction in aeration tank volume requirements for the dynamic strain-
ing plants. For the smaller plants, nominal aeration detention times
based on raw wastewater flow of 6.75 and 2.7 hr were selected, respect-
ively, for the conventional and dynamic straining systems. For the
larger plants, slightly lower aeration detention times of 6.0 and
2.4 hr, respectively, were used. This resulted in organic loadings
of 0.25 kg BODs applied/day/kg MLVSS (0.25 lb BOD5/day/lb MLVSS) for
the smaller plants, and 0.29 kg BODc applied/day/kg MLVSS (0.29 lb
BODs/day/lb MLVSS) for the larger plants, assuming a 70 percent mixed
liquor VSS content. Because the organic loadings were the same for the
conventional and dynamic straining plants, waste activated sludge pro-
duction was assumed to be equal for both systems. For the smaller plants,
with a slightly lower organic loading than the larger plants, a waste
38
-------
activated sludge yield of 0.50 kg VSS/kg BOD removed (0.50 Ib VSS/lb
BODc removed)was used. A waste activated sltidge yield of 0.56 kg
VSS/kg BOD5 removed (0.56 Ib VSS/lb BOD5 removed) was used for the
larger plants. In all cases, the VSS content of the waste activated
sludge was assumed to be 70 percent.
For estimating aeration tank construction costs, an ECF of 1.5 was
used for the 3,785 m3/day (1 mgd) plants and 1.14 was used for the
37,850 m3/day (10 mgd) plants. The installed aeration requirements
for both processes were assumed to be 110 m3 air/kg BODc removed
(1,770 ft3 air/lb BOD5 removed).
The sludge handling and disposal schemes for the two different size
plants are discussed below. For both size plants, it was assumed that
excess activated sludge was returned to the primary clarifier for
joint settling and partial thickening with the primary sludge. The
conventional plant excess activated sludge was wasted from the second-
ary clarifier underflow at a concentration of 13,000 mg/1. The dynamic
straining process requires wasting of excess sludge directly from the
aeration tank at the assumed MLSS concentration of 6,500 mg/1. Because
of the difference in these concentrations, it was assumed that the
combined primary and waste activated sludges would thicken to 3.5
percent solids in the primary clarification system of the conventional
plants, but only to 3.0 percent solids in the primary clarifiers of the
dynamic straining plants.
The combined sludges were further thickened in gravity thickeners. An
output of 6.0 percent solids was set as the thickened sludge objective
for both types of plants. To achieve this, a solids loading of
39 kg/mvday (8 Ib/fWday) was utilized to calculate required thicken-
er surface area for the conventional plants with their input combined
sludge concentration of 3.5 percent solids. For the thinner 3.0
percent solids input combined sludges produced by the dynamic strainer
plants, the thickener design solids loadings were decreased to 31.7
kg/m2/day (6.5 lb/ftvday). ECF's of 2.0 and 1.5 were used, respectively,
for estimating thickener construction costs for the smaller and larger
plants. The percentage differential in the thickener costs due to the
difference in required thickener sizes was much more significant for
the 37,850 m3/day (10 mgd) plants than the 3,785 m3/day (1 mgd) plants.
As the thickeners were designed to discharge combined primary and
waste activated sludges with the same solids content, and since the
activated sludge systems were designed to yield identical sludge pro-
duction, both unit mass and unit volume of the sludges leaving the
thickeners were the same for the conventional and dynamic strainer
plants. Assuming that the characteristics of these sludges would be
very similar, all subsequent sludge handling units were equally sized
for the two types of plants.
The thickened sludges were stabilized in each plant in a two-stage
39
-------
anaerobic digester. A total hydraulic retention time (HRT) of 30 days
was assumed, divided equally between the completely mixed first-stage
digester and the stratified secondary digester. For estimating digester
construction costs, ECF's of 1.5 and 1.33 were used, respectively, for
the smaller and larger plants. A VSS reduction of 50 percent during
digestion was assumed for all cases.
Dewatering of digested sludge in the smaller plants was accomplished
on sludge drying beds. For the larger plants, vacuum filtration of
digested sludge was assumed as the dewatering step. Sludge drying bed
area was calculated using a digested sludge solids loading of
73 kg/m2/month (15 lb/ftz/month). Vacuum filter design was based on a
digested sludge solids loading of 19.5 kg/m2/hr (4 Ib/ft2/hr). ECF's
of 1.0 and 1.06 were selected, respectively, for the drying beds and
vacuum filters.
Tables 5, 6, and 7 show the estimated total construction costs and the
annual operation and maintenance costs for the four plants. Table 8
summarizes these results into total annual costs based on an amortiz-
ation rate of 7 percent over 20 years. The construction cost for the
3,785 m3/day (1 mgd) dynamic straining plant was estimated to be
8.2 percent higher than for the conventional plant, while the 37,850 m3/
day (10 mgd) dynamic straining plant would cost about 21.5 percent
more initially. Comparing total annual costs, the dynamic straining
plants were estimated to cost approximately 8.6 and 23.4 percent more,
respectively, than their conventional counterparts. The biggest
influence on the larger percent difference in the total annual costs
for the 37,850 m3/day (10 mgd) plants is that the same strainer unit
cost was assumed for both size plants, while the cost per ft2 of surface
area for secondary gravity clarification decreased by 50 percent as the
size of the plant increased from 3,785 to 37,850 m3/day (1 to 10 mgd).
As stated earlier, larger strainer production units and equipment
designed for the process application should substantially decrease cost.
However, it would be difficult to assume that a reduction of 50 percent
in the cost of straining equipment could be accomplished. For this
reason, dynamic straining is more economically feasible for smaller
plants.
Safety factors in case of power failure or strainer breakdown are
important operational considerations. An emergency auxiliary power
source would be one solution to power failure. Flow through the
strainers would stop in a very short time during a power failure. This
would result in loss of mixed liquor solids to the receiving water
unless emergency power was started almost immediately.
If standby strainers were not provided, in the event of strainer break-
down or fabric failure, that unit would have to be shut down, and the
specific flow rate through the other strainers would have to be
increased by increasing the rotational speed. The 3,785 m3/day (1 mgd)
plant would, as stated previously, require three operating strainers,
two primary strainers in the aeration tank and one secondary strainer.
40
-------
TABLE 5
ESTIMATED TOTAL CONSTRUCTION COSTS
*
Cost Component
Raw Wastewater Pumping
Grit Removal, Flow Measurement, Screening
Primary Sedimentation
Primary Sludge Pumping
Aeration Basin Structure
Aeration Diffused Air System
Final Sedimentation
Recirculation or Intermediate Pumping
Chi or 1 nation Feed Systems
Chlorination Contact Basins
Gravity Sludge Thickener
Anaerobic Sludge Digestion
Sludge Drying Beds
Administration and Lab Facilities
Garage and Shop Facilities
Subtotal
Yardwork
Total Construction Cost
Land
Engineering
Subtotal
Legal, Fiscal and Administrative
Subtotal
Interest During Construction
Conventional
$ 93,700
45,900
65,000
37,300
95.900
86,500
76,400
41,200
32,500
15,400
39,500
181,200
44,500
43,000
12,500
$ 910.500
127,500
$1,038,000
11,100
121,300
$1,170,400
16.200
$1.186.600
72,700
3,785 m3/day (1 MGD)
Plant Dynamic Straining Plant
$ *
*
*
*
51,500
*
(Straining) 239,400
20,600
*
*
41,100
*
*
*
*
$1,010,100
*
1,137,600
8,900
*
$1,267,800
*
$1,284,000
78,700
Total Initial Investment Cost
$1,259,300
$1,362,700
*Same Cost as Conventional Plant.
Note: Estimated Costs Based on National Average EPA-STP Construction Cost Index as of March, 1974 = 190.97.
-------
ro
TABLE 5 (CONTINUED)
ESTIMATED TOTAL CONSTRUCTION COSTS
Cost Component
Raw Uastewater Pumping
Grit Removal, Flow Measurement, Screening
Primary Sedimentation
Primary Sludge Pumping
Aeration Basin Structure
Aeration Diffused A1r System
Final Sedimentation
Redrculatlon or Intermediate Pumping
ChloH nation Feed Systems
ChloHnation Contact Basins
Gravity Sludge Thickener
Anaerobic Sludge Digestion
Sludge Holding Tanks
Vacuum Filtration
Administration and Lab Facilities
Garage and Shop Facilities
Yardwork
Total Construction Cost
Land
Engineering
Legal, Fiscal and Administrative
Interest During Construction
Conventional
$ 456.500
176,600
211,500
76,600
458,800
433.000
275,100
149,500
86,800
52,700
94,500
464.000
77,700
573,700
140,600
41,600
Subtotal $ 3,769,200
527,700
$ 4,296.900
20,000
371,900
Subtotal $ 4,688.800
34.500
Subtotal $ 4,723,300
428,300
37,850 m3/day (10 MGD)
Plant Dynamic Straining Plant
$ *
*
*
*
207,900
*
(Straining) 1,627,200
59,800
10 ,500
$4,790,700
*
$5,318,400
16,000
*
$5,706,300
*
$5,740,800
520,600
Total Initial Investment Cost
*Same Cost as Conventional Plant.
$ 5.151,600
$6,261.400
Note: Estimated Costs Based on National Average EPA-STP Construction Cost Index as of March, 1974 - 190.97.
-------
TABLE 6
ESTIMATED ANNUAL OPERATION AND MAINTENANCE COSTS
u>
3,785 m3/day (1 MGD) Plant
Cost Component
Raw Wastewater Pumping
Grit Removal, Flow Measurement, Screening
Primary Sedimentation
Primary Sludge Pumping
Aeration Diffused Air System
Final Sedimentation
Recirculation or Intermediate Pumping
Chi on nation Feed Systems
Gravity Sludge Thickener
Anaerobic Sludge Digestion
Sludge Drying Beds
Administration and Lab Facilities
Laboratory Operation
Yardwork
Conventional
Labor
$ 4.300
4,700
2.800
4.800
7,700
3,100
4,100
2,100
2,700
6,100
4,900
2,300
13.900
3,500
Materials
$ 1,600
1,800
400
1,200
9,700
500
1,600
4,000
300
1,900
400
1.800
500
500
Plant
Total
$ 5,900
6,500
3,200
6,000
17.400
3,600
5,700
6,100
3,000
8,000
5,300
4,100
14,400
4,000
Dynamic Straining
Labor
$ *
*
*
*
*
(Straining) 4,700
2,100
*
2,900
*
*.
*
*
*
Materials
$ * $
*
*
*
*
9,900
800
*
400
*
*
*
*
*
Plant
Total
t
*
*
*
*
14,600
2,900
*
3,300
*
*
it
*
*
Totals $ 67,000 $ 26.200 $ 93.200
$66.800 $34.900 $101.700
*Same Cost as Conventional Plant.
Note: Materials Costs include Supplies and Power. Costs based on National Average Wholesale Price
Index for Industrial Commodities, March, 1974 = 146.6.
Labor Costs based on Average Labor Cost of $10,400/man-year(U. S. Department of Labor Cost
Index of $4.35/hr for March, 1974 plus 15% for Indirect Costs).
-------
TABLE 7
ESTIMATED ANNUAL OPERATION AND MAINTENANCE COSTS
37,850 m3/day (10 MGD) Plant
Cost Component
Raw Wastewater Pumping $
Grit Removal, Flow Measurement, Screening
Primary Sedimentation
Primary Sludge Pumping
Aeration Diffused Air System
Final Sedimentation
Recirculation or Intermediate Pumping
Chi or i nation Feed Systems
Gravity Sludge Thickener
Anaerobic Sludge Digestion
Sludge Holding Tanks
Vacuum Filtration
Administration and Lab Facilities
Laboratory Operation
Yardwork
Conventional Plant
Labor
6,700
15,000
7,700
9,500
23,000
9,600
5,800
7.800
3,500
10,700
4,500
23,300
13.100
19,500
9,400
Materials
$ 8,700 $
3,900
2,100
3,400
51,500
2,800
8,700
20.400
700
4,400
1,500
26,500
5.800
2.100
2,300
Total
15.400
18,900
9,800
12,900
74,500
12,400
14,500
28,200
4,200
15,100
6,000
49,800
18.900
21.600
11,700
Dynamic Straining Plant
Labor
$ *
*
*
*
*
(Straining)$ 14,400
2,300
*
3,800
*
*
*
*
*
*
Materials
$ *
*
*
*
*
$ 88,600
3,500
*
800
*
*
*
*
*
*
Total
$ *
*
*
*
*
$ 103,000
5,800
*
4,600
*
*
*
*
*
*
Totals $ 169,100 $ 144,800 $ 313,900
$ 170,700 $ 225,500 $ 396,200
*Same Cost as Conventional Plant.
Refer to Table 6 for Costing Basis.
-------
TABLE 8
TOTAL ANNUAL COST COMPARISONS BETWEEN
DYNAMIC STRAINING AND CONVENTIONAL ACTIVATED
SLUDGE TREATMENT PLANTS
3,785 m3/day (1 MGD) 37,850 m3/day (10 MGD)
Conventional Straining Conventional Straining
01 Amortization (7 percent over 20 years) $ 118,900 $ 128,600 $ 486,300 $ 591,000
Operation and Maintenance 93,200 101.700 313,900 396,200
Totals $ 212,100 $ 230,300 $ 800,200 $ 987,200
Cost/1000 gal. Treated 58$ 63$ 22$ 27$
Cost/m3 Treated 15.3$ 16.6$ 5.8$ 7.1$
-------
If the secondary strainer failed, the final effluent would temporarily
come from the primary strainers. In this case, the suspended solids in
the effluent would rise to 30 to 80 mg/1, depending on the momentary
specific flow rate while the secondary strainer was not in operation.
If a primary strainer failed, a portion of the mixed liquor could be
temporarily pumped to the secondary stratning tank. This would, in
effect, convert the secondary strainer to a primary strainer for the
period one of the primary strainers was not operating. The final
effluent in this situation would again come from primary strainers.
Larger plants with more strainers could handle this transition more
successfully and achieve a cleaner final effluent. However, to avoid
the situation where effluent quality deteriorates temporarily while
one or more of the operating strainers are out of service, the above
operational mode was rejected for estimating purposes in favor of
providing standby strainer units.
The economics of dynamic straining could be changed by replacing the
secondary strainer with a granular-media filter or a gravitational
clarifier. Addition of chemicals may be necessary to enhance solids
flocculation for gravitational clarification of primary strainer
effluent.
A 3,785 m3/day (1 mgd) sand filter would cost slightly less than a
secondary strainer, and the return flow requirements would be about
1/5 as much as secondary straining return flow requirements. The sand
filter would, however, not be able to operate as a standby clarifi-
cation unit in case of a primary strainer breakdown.
Plant upgrading is also a viable application for primary straining.
Higher MLVSS levels and reduced solids loadings on existing secondary
clarifiers could provide for increased organic and/or hydraulic
capacities at minimum investment for plants whose alternative is to
expand to treat projected increases in flow. For existing activated
sludge plants that are experiencing substantial overloading, primary
straining may offer a method of substantially improving overall
performance during the interim period before the next planned expansion.
In these instances, pure oxygen gas could be used to satisfy the higher
oxygen demand created by the higher MLVSS concentrations.
The cost disadvantages of dynamic straining can be offset by several
factors. These include positive solids control, especially in locations
or applications where filamentous growth is prevalent. Also, total
plant land requirements are 20 to 30 percent less with dynamic strain-
ing than conventional systems. In urban areas or for expansion purposes,
this may be a very important factor. For estimating purposes, a 20 per-
cent reduction in land requirements was used for the dynamic straining
plants.
Another potential application for the strainer is as an independent
first-stage clarification device in a two-stage activated sludge system.
46
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Two-stage activated sludge systems are being used increasingly where
year-round nitrification is required. In these types of systems, it
is not necessary for the first-stage clarification unit to achieve
very low effluent suspended solids. Rather, it has been found desir-
able to bleed 35-50 mg/1 of BODc and suspended solids into the
second-stage nitrification reactor to enhance agglomeration and settling
of this essentially autotrophic sludge culture. Primary strainers
operating in the first-stage reactor could be tailored to produce an
effluent with the desired suspended solids level, and would obviate
the need for constructing intermediate first-stage gravity clarifiers.
This could be particularly advantageous in converting existing single-
stage activated sludge systems to two-stage processes.
47
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SECTION VIII
ACKNOWLEDGEMENTS
The support of the project by the National Environmental Research
Center, Office of Research and Development, U. S. Environmental
Protection Agency, Cincinnati, Ohio, and the assistance of the
Project Officer, Mr. Richard C. Brenner, especially in compilation
of the economics data, is acknowledged with sincere thanks.
-------
SECTION IX
REFERENCES
1. Kressilk Products, Inc., "Metal Filter Cloth Technical and
Performance Data," Monterey Park, California (1969).
2. Daily, J. W., and Harleman, Donald R. F., "Fluid Dynamics,"
Addison-Wesley Publishing Company, Inc., Reading,
Massachusetts (1966).
3. Pentz, H., "Gravity Separation or Settling of Solids from
a Liquid," FMC Corporation, Link-Belt Division, Colmar ,
Pennsylvania (1965).
4. Patterson, W. L., and Banken, R. F., "Estimating Costs and
Manpower Requirements for Conventional Wastewater Treat-
ment Facilities," U. S. Environmental Protection Agency,
Water Pollution Control Research Series, Project No. 17090
DAN, Contract No. 14-12-462 (October 1971).
49
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SECTION X
APPENDICES
PAGE
A. PEAK SPECIFIC FLOW RATES AND SUSPENDED SOLIDS
REMOVALS VERSUS DRUM PERIPHERAL VELOCITY
FIGURE 1 PRIMARY STRAINER, 10-MICRON 52
FIGURE 2 PRIMARY STRAINER, 20-MICRON 53
FIGURE 3 PRIMARY STRAINER, 40-MICRON 54
FIGURE 4 SECONDARY STRAINER, 5-MICRON 55
FIGURE 5 SECONDARY STRAINER, 10-MICRON 56
B. STRAINER CHARACTERIZATION TEST DATA
TABLE 1 PRIMARY STRAINER, 10-MICRON 57
MLSS 6,500 MG/L
TABLE 2 PRIMARY STRAINER, 10-MICRON 58
MLSS 9,000 MG/L
TABLE 3 PRIMARY STRAINER, 10-MICRON 59
MLSS 12,000 MG/L
TABLE 4 PRIMARY STRAINER, 20-MICRON 60
MLSS 1,800 MG/L; 40-MICRON, MLSS 2300 MG/L
TABLE 5 PRIMARY STRAINER, 40-MICRON 61
MLSS 2,400 MG/L
TABLE 6 PRIMARY STRAINER, 40-MICRON, 62
MLSS 6,200 MG/L
TABLE 7 PRIMARY STRAINER, 40-MICRON 63
MLSS 3,600 MG/L
TABLE 8 SECONDARY STRAINER, 5-MICRON 64
TANK SS 50 MG/L
TABLE 9 SECONDARY STRAINER, 10-MICRON, 65
TANK SS 40 MG/L
50
-------
SECTION X
APPENDICES (CONTINUED)
PAGE
B. STRAINER CHARACTERIZATION TEST DATA (Cont.)
TABLE 10 SECONDARY STRAINER, 10-MICRON 66
TANK SS 150 MG/L
TABLE 11 SECONDARY STRAINER, 10-MICRON, 67
TANK SS 200 MG/L
C. MONTHLY SONIC STRAINING PLANT PERFORMANCE
AND OPERATING DATA
TABLE 1 JANUARY 1973 PERFORMANCE DATA 68
TABLE 2 JANUARY 1973 OPERATING DATA 69
TABLE 3 FEBRUARY 1973 PERFORMANCE DATA 70
TABLE 4 FEBRUARY 1973 OPERATING DATA 71
TABLE 5 MARCH 1973 PERFORMANCE DATA 72
TABLE 6 MARCH 1973 OPERATING DATA 73
TABLE 7 APRIL 1973 PERFORMANCE DATA 74
TABLE 8 APRIL 1973 OPERATING DATA 75
51
-------
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FIGURE A-2
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53.
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DRUM PERIPHERAL VELOCITY ( FT/SEC )
FIGURE A-3
PRIMARY STRAINER, 40-MICRON
54
-------
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DRUM PERIPHERAL VELOCITY ( FT/SEC )
FISURE A-4
SECONDARY STRAINER, 5-MICRON
55
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3 6 9 12 15
DRUM PERIPHERAL VELOCITY ( FT/SEC)
FIGURE A-5
SECONDARY STRAINER, 10-MICRON
56
-------
TABLE B-l
PRIMARY STRAINER
10-MICRON, MLSS 6,500 MG/L
30 RPH
Total Hat Spac. Iff.
Haad Haad Flow , SS
In In GPM/Ft' MG/L
0.6 0.0 0.0
1.0 0.4 0.6
1.1 O.S 1.2
1.2 0.6 1.3
l.S 0.9 1.5 12
1.6 1.0 1.6
1.8 1.1 1.6
1.8 1.1 1.7 13
1.9 1.2 1.6
2.0 1.4 1.6
2.1 1.5 1.6
2.it 1.8 l.S
60 WH
Total Net Spac. Gff.
H«ad Head • Flou , SS
In In GPM/Ft' HC/L
1.9 0.0 0.0
2.0 0.1 0.8
2.1 0.2 1.5 25
2.4 0.5 2.4
2.6 0.8 2.8 25
2.8 0.9 2.7
2.8 0.9 2.9
2.9 1.0 3.0 28
2.9 1.0 3.1
3.0 1.1 3.3 25
3.0 1.1 3.7
3.0 1.1 4.2 17
3.1 1.2 M.I*
3.1 1.2
-------
TABLE B-2
PRIMARY STRAINER
10-MICRON, MLSS 9,000 MG/L
30 RPH
Total Nat Spac. Eff.
Head Head Flow , SS
In In GPM/Ft NG/L
0.6 0.0 0.0
0.8 0.1 O.S
0.9 0.2 1.2 24
1.0 O.U 1.5
1.2 0.6 1.7 20
1.4 0.8 1.7
1.5 0.9 1.9
1.5 0.9 1.8
1.6 1.0 1.8
1.8 1.1 1.8
2.0 1.4 1.7
2.2 1.6 1.7
60 RPH
Total Nat Spac. Eff.
Haad Haad Flow 88.
In In GPM/Ft* MG/L
2.0 0.0 0.0
2.2 0.2 1.0
2.6 0.6 1.6 35
2.8 0.8 2.1
2.8 0.6 2.3 28
2.8 0.8 2.4
2.9 0.9 2.7
2.9 0.9 2.9 31
2.9 0.9 3.0
3.0 1.0 3.2
3.2 1.2 3.5 32
3.U 1.4 3.9
3.5 1.5 3.9
3.6 1.6 3.9
4.0 2.0 3.9 36
4.2 2.2 4.0
4.2 2.2 4.0
4.2 2.2 3.8
4.2 2.5 3.5
90 RPM
Total Nat Spac. Eff.
Haad Haad Flow SS
In In OPM/Ft* MG/L
4.0 0.0 0.0
4.1 0.1 1.0
4.5 0.5 1.7 51
4.9 0.9 2.6 51
5.0 1.0 3.0
5.1 1.1 3.5 51
5.6 1.6 4.5 53
5.9 1.9 4.8 53
6.0 2.0 4.9
6.0 2.0 5.1
6.2 2.2 5.3 66
6.4 2.4 5.6
6.4 2.4 5.7
5.8 2.8 6.1
6.8 2.8 6.3 79
6.9 2.9 6.1
7.0 3.0 6.3
7.0 3.0 6.3
7.1 3.1 6.1
7.8 3.8 6.1
8.2 4.2 5.5
8.5 4.5 5.1
6.4 4.8 4.7
120 HPM
Total Nat Spac. Eff.
Haad Haad Flow SS
In In GPM/Ft' MG/L
7.4 0.0 0.0
7.6 0.2 0.9
7.9 0.5 1.8 91
8.0 0.6 2.5
8.1 0.8 2.8 81
8.4 1.0 3.5
8.5 1.1 3.9 92
8.5 1.1 4.4
8.9 1.5 5.1 86
9.2 1.9 5.6
9.6 2.2 6.7 96
10.1 2.8 7.4
10.4 3.0 7.4
10.8 3.4 7.9
11.0 3.6 7.9
11.2 3.9 7.4
11.8 4.4 7.9 88
12.5 5.1 6.7
12.8 5.4 6.1
12.9 5.5 5.8
Ul
00
MLSS 8,760-9,540 nig/1
Effective Straining Area-4.8 ft2
-------
TABLE B-3
PRIMARY STRAINER
10-MICRON, MLSS 12,000 MG/L
ao m
Total Net Spec. Eff.
Head Head Flow - 8t
In In GPM/Ft N8/L
1.1 0.0 0.0
1.5 0.4 O.i*
1.6 0.6 0.5 53
2.4 1.2 0.5
3.1 2.0 0.5
60 KM
Total Net Spec. Eff.
Head Head Flow - 88
In In GPM/Ft N6/L
2.9 0.0 0.0
3.0 0.1 0.5
3.2 0.4 1.0
3.4 0.5 1.1 65
3.6 0.8 1.2
3.8 0.9 1.4
3.9 1.0 1.6 72
«».0 1.1 1.7
1.1 1.2 1.8
i».2 1.4 1.8
4.2 1.4 1.8
4.5 1.6 1.8
4.6 1.8 1.8
4.9 2.0 1.7
5.0 2.1 1.7
5.1 2.2 1.7
5.2 2.4 1.7
90 KPN
Total Net Spec. Eff.
Head Head Flow _ SS
In In GPM/Ft MC/L
5.0 0.0 0.0
5.5 0.5 0.7
5.9 0.9 1.4
6.0 1.0 1.7 99
6.1 1.1 2.1
6.4 1.4 2.1
6.6 1.6 2.3 92
6.8 1.8 2.5
6.9 1.9 2.6
6.9 1.9 2.7
6.9 1.9 2.7
6.9 1.9 2.8
7.0 2.0 2.9 88
7.1 2.1 2.9
7.2 2.2 3.0
7.2 2.2 3.0
7.5 2.5 3.2
7.8 2.8 3.2
8.0 3.0 3.2
8.1 3.1 3.0
8.2 3.2 2.9
8.5 3.5 2.9
120 RPM
Total Net Spec. Eff.
Head Head Flow , «.
In In GPM/Ft' MO/L
8.2 0.0 0.0
i.6 0.4 0.7
9.1 0.9 1.4
9.2 1.0 1.9 154
9.4 1.1 2.1
9.6 1.4 2.3
9.8 1.5 2.5
10.0 1.0 2.6
10.0 1.8 2.7
10.1 1.9 2.8 124
10.1 1.9 3.0
10.2 2.0 3.2
10.4 2.1 3.0
10.6 2.4 2.9
10.8 2.5 2.8
11.0 2.4 2.8
cn
10
MLSS 11,520-12,720 mg/1
Effective Straining Area-4.8 ft2
-------
TABLE B-4
PRIMARY STRAINER
20-MICRON, MLSS 1,800 MG/L; 40-MICRON, MLSS 2,300 MG/L
60 RPM
Total Nat Sp«c. Eff.
Head Head Flow , SS
In In GPM/Ft N6/L
2.0 0.0 l.i* 49
2.4 0.4 2.5
2.6 0.6 3.4 45
2.9 0.9 «4.2
3.2 1.2 5.1
3.4 !.>» 6.0
3.6 1.6 6.6 36
4.0 2.0 6.0
4.4 2.4 5.1 42
5.0 3.0 4.0
5.6 3.4 3.4 37
•
120 RPM
Total Net Spec. Eff.
Head Head Flow - SS
In In GPM/Ft MG/L
7.4 0.0 1.2 86
7.9 0.5 2.2
8.2 0.9 2.8
8.2 0.9 3.2
8.4 1.0 4.1
8.6 1.2 5.3
8.9 1.5 5.9 78
9.1 1.8 7.0
9.1 1.8 7.8
9.4 2.0 8.9 78
9.8 2.4 9.5
10.2 2.9 11.0 88
10.5 3.1 12.3
11.6 4.2 14.7 86
11.8 4.4 13.2
12.4 5.0 14.7 76
13.1 5.8 13.2
13.4 6.0 12.3
13.5 6.1 11.0
90 RPM
To.tal Net Spec. Eff.
Head Head Flow , SS
In In GPM/Ft MG/L
4.9 0.4 0.9
5.1 0.6 1.8 68
5.1 0.6 2.0
5.4 0.9 2.3
5.5 1.0 2.4
5.6 1.1 2.6
5.8 1.2 2.7
5.8 1.2 2.8 96
5.8 1.2 2.8
5.8 1.2 3.0
5.9 1.4 3.3
6.1 1.6 3.6
6.2 1.8 3.7
6.4 1.9 3.8
6.6 2.1 3.8
6.8 2.2 3.7
6.9 2.4 3.6 84
7.1 2.6 3.5
7.4 2.9 3.3
7.5 3.0 3.2
.
120 'RPM
Total Net Spec. Eff.
Head Head Flow SS
In In GPM/Ft MG/L
8.9 2.4 119
9.0 3.0 124
9.1 3.7
9.4 4.2 128
9.8 5.0 136
10.1 5.5
10.9 6.5
11.2 6.9
11.4 6.9
11.9 6.5
12.2 6.9
12.9 6.5
13.0 6.1
13.5 5.8
13.6 5.5
13.9 5.2
_ ,
MLSS 1,725-1,935 mg/1
Effective Straining Area-4.8 ft'
MLSS 2,180-2,480 mg/1
Effective Straining Area-2.9 ft
-------
TABLE B-5
PRIMARY STRAINER
40-MICRON, MLSS 2,400 MG/L
60 RPM
Total Net Spec. Eff.
Head Head Flow . SS
In In GPM/Pt MG/L
2.6 0.1 2.8
2.8 0.6 3.1 78
2.9 0.7 3.1
2.9 0.7 3.6
2.9 0.7 3.6
2.9 0.7 3.5
2.9 0.7 3.8
3.0 0.8 3.9 79
3.1 0.9 4.2
3.1 0.9 4.3
3.2 1.0 4.4 76
3.4 1.2 4.6
3.5 1.3 4.6
3.6 I*1* U.6
3.8 1*6 4.4
3.9 I-7 U.U
4.0 I-8 U.3
U.I 1.9 U.2 120
60 RPM
Total Net Spec. Eff.
Head Head Flow SS
In In CPU/Ft' MG/L
2.4 0.1 1.3 59
2.5 0.2 1.8 67
2.6 O.U 2.1
2.9 0.6 2.5
3.0 0.6 3.0 71
3.1 0.9 3.3
3.1 0.9 3.U 82
3.U 1.1 3.7
3.8 1.5 3.i* 67
U.I 1.9 3.3
4.9 2.6 3.2 •
5.2 3.0 3.1 53
90 RPM
Total Net Spec. Eff.
Head Head Flow , SS.
In In GPM/Ft MG/L
4.4 0.1 1.2 172
4.9 0.6 2.7 150
5.0 0.8 3.1
5.1 0.9 3.3
5.1 0.9 3.7 135
5.2 1.0 U.O
5.6 l.i* U.U 139
5.9 1.6 >».6
5.9 1.6 4.6
6.1 1.9 U.9 101
6.1 .1.9 5.2
6.2 2.0 5.5 109
6.4 2.1 6.0
6.5 2.2 6.0 97
6.8 2.5 6.1
6.9 2.6 6.0
7.1 2.9 5.8
7.1 2.9 6.0
7.2 3.0 5.5 91
7.5 3.2 5.0
7.8 3.5 4.8
8.0 3.8 U.U
120 RPH
Total Net Spec- Eff.
Head Head Flow . SS
In In GPM/Ft MO/L
10.6 0.1 1.1 85
10.9 O.U 2.0
10.9 O.U 2.U 108
U.4 0.9 3.1 109
11.6 1.1 3.7
11.9 l.U U.I 125 v,
12.0 1.5 U.6
12. U 1.9 U.8 11U
12.8 2.2 U.9
12.9 2.U 5.2
13.1 2.6 5.5
13.8 3.2 5.5 113
1U.1 3.6 5.7
1U.U 3.9 5.2
1U.5 H.O U.8 105
1U.6 4.1 4.6
MLSS 2,260-2,520 mg/1
Effective Straining Area-2.9 ft'
-------
TABLE B-6
PRIMARY STRAINER
40-MICRON, MLSS 6,200 MG/L
30 9SH
Total Nat Spec. Eff.
Haad Head Plow . »
In In GPM/Ft MO/L
1.0 0.0 0.0
1.2 0.2 0.8 420
1.5 0.5 1.2
1.8 0.8 1.2
2.1 1.1 1.2 320
2.4 1.4 1.1
2.6 1.6 1.1
60 RPM
Total .Nat Spac. Eff.
Haad Haad Flow , 49
In In GPM/Ft' MG/L
2.5 0.0 0.0
2.6 0.1 0.9 186
2.8 0.2 1.5 152
3.0 0.5 1.8
3.2 0.8 1.9
3.4 0.9 2.1 146
3.4 0.9 2.1
3.5 1.0 2.2
3.5 1.0 2.2
3.6 1.1 2.3
3.8 1.2 2.4 126
3.8 1.2 2.3
3.8 1.2 2.4
3.9 1.1 2.4
3.9 1.4 2.1
U.I 1.6 2.3
4.4 1.9 2.1
4.6 2.1 2.0
90 Mff
Total Nat Spac. Eff.
Haad Haad Flow . SS
In In GPM/Ft MG/L
5.6 0.0 0.0
6.1 0.5 0.8 168
6.4 0.8 1.3 17"*
6.6 1.0 1.5
7.0 1.4 1.5
7.5 1.9 1.4
7.9 2.2 1.2
120 KPN
Total Nat Spac. Eff.
Haad Haad Flow . SB
In In GPM/Ft MG/L
9.1 0.0 0.0
9.4 0.2 0.8 316
9.8 0.6 1.7 327
10.0 0.9 2.1
10.0 0.9 2.0 290
10.0 0.9 2.1
10.0 0.9 2.3
10.2 1.1 2.5 278
10. U 1.2 2.6
10.4 1.2 2.6
10.4 1.2 2.8
10.4 1.2 2.8
10.5 1.4 2.9
10.6 1.5 3.0 240
10.6 1.5 3.0
10. 8 1.6 3.0
11.0 1.9 3.3 215
11.5 2.4 3.2
11.6 2.5 2.9
11.8 2.6 2.8
ro
MLSS 5,900-6,480 mg/1
Effective Straining Area-4.8 ft'
-------
TABLE B-7
PRIMARY STRAINER
40-MICRON, MLSS 3,600 MG/L
ao m
Total Nat Spac. Eff.
Haad Haad Flow - SS
In la GPM/Ft M6/L
0.9 0.0 0.0
1.1 0.2 1.0 31
1.2 0.4 1.8
1.4 0.5 2.0 47
1.4 0.5 2.2
l.i* 0.5 2.4
1.4 0.5 2.3
1.4 0.5 2.4 31
l.it 0.5 2.
-------
TABLE B-8
SECONDARY STRAINER
5-MICRON, TANK SS 50 MG/L
37 RFH
Total Nat Spec. Eff. Tank
Held Hud Flaw o SS S8
IB In GPN/rt MG/L MG/L
1.0 0.0 0.0
1.5 0.5 1.0 16 59
2.0 1.0 1.2 19
2.6 1.6 1.3 21
3.8 2.6 1.3
0.8 3.8 1.3 2U
5.8 0.8 1.3
7.2 6.2 1.5 27
8.5 7.S 1.9
9.5 8.5 2.1
11.0 10.0 2.3 29
13.2 12.2 2.»
15.8 14.8 2.6
17.5 16.5 2.7
18.5 17.5 2.9
20.5 19.5 2.9
22.5 21.S 3.0
2U.2 23.2 2.8 H3 61
26.0 25.0 2.5
60 MW
Total Nat Spac. Eff. Tank
Haad Haad Flow *» SS
In In CPU/Ft NG/L MG/L
2.6 0.0 0.0
3.2 0.6 1.0 20 SU
3.U 0.6 1.6
«.2 1.6 2.6 1«
6.0 3.U 2.6
8.2 5.6 2.6
11.0 8.1 2.6 17
M.O 11. » 2.6
15.8 13.1 2.7
17.8 15.1 2.9
19.0 16. H 3.0
21.2 18.6 3.0 30 51
22.2 19.6 2.9
2U.2 21.6 2.7
25.5 22.9 2.7
26.5 23.9 2.6
90 RPM
Total Met Spac. Eff. Tank
H«ad Haad Flat . SS SS
In In GPM/Ft MG/L M6/L
6.8 0.0 0.0
7.1 0.1* 0.9
7.6 0.9 1.7 16 39
6.0 1.2 1.7
8.8 1.6 2.0
9.1 2.1* 0.0
10.2 3.5 2.U
10.8 1.0 2.1 18
11.5 1.8 2.1
12.5 5.8 2.1
13.5 6.8 2.0
120 RPH
Total Nat Spac. Eff. Tank
Haad Head Flow 88 SS
In In GPH/Ft MG/L MG/L
10. S 0.0 0.0
12.0 1.2 1.3 10 39
12.5 1.8 1.7
12.8 2.0 1.8
13.1 2.<« 2.0
13.5 2.8 2.0
lt.0 3.2 2.6
1K.8 U.O 2.8 12
15.5 U.8 2.6
16.6 6.0 2.4
18.0 7.2 2.1
Effective Straining Area-4.8 ft'
-------
TABLE B-9
SECONDARY STRAINER
10-MICRON, TANK SS 40 MG/L
90 *»
Total Mat Sp«c. Eff. Tank
Hnd Haad Flan . SS SS
In In GPH/Ft HG/L HG/L
6.S 0.0 0.0
7.0 O.S 6.7 IS 28
7.9 1. 11.0
.0 1. 11.0 14 i«6
.0 1. 10. S
.1 1. 11.5 11 35
.4 1. 13.3
.6 2. 13.7
.0 2. 14.1
.1 2. 13.0
10.0 3. 11.0
11. S S.O 9.4
13.5 7.0 9.4
16.0 9.5 8.9
18.2 11.8 8.2
It.* 12.9 7.9
22.0 15.5 7.3 22 52
25.2 19.6 6.4
28.0 21.1 6.0
90 RPM
Total Mat Spac. Eff. Tank
Haad Haad Flo», SS SS
In In GP«/Ft NG/L HG/L
6.8 0.0 0.0
7.1 0.4 3.5 11 99
7.5 0.8 7.3
7.9 1.1 9.1 13 97
9.0 2.2 12.1
9.6 2.9 10.2
11.8 5.0 7.9 10 89
12.2 5.5 7.4
13.2 6.5 7.1
120 mm
Total Mat Spac. Eff. Tank
Haad Haad Flow , SS- SS
In In GPH/Ft HG/L HG/L
12.S O.S 6.1 11 31
13.0 1.0 8.9
13.4 1.4 11.0 14 29
14.0 2.0 17.S
14.2 2.2 20.3 13 31
14.6 2.6 22.1
15.1 3.1 25.4 11 36
16.5 4.5 25.4
17.6 5.6 23.0
18.1 6.1 21.1
16.8 6.8 16.9
19.6 7.6 13.3
22.0 10.0 9.2 9 32
23.6 11.6 6.6
25.2 13.2 5.9
120 RPH
Total Mat Spac. *** Tank
Haad Haad Flow , SS SS
In In GPH/Ft HG/L HC/I.
12.0 0.0 0.0
12. S 0.5 3.7 19 95
12.9 0.9 7.6
13.4 1.4 9.S
13.6 1.6 13.3
14.2 2.2 17.5 18 91
14.9 2.9 20.2
IS. 2 3.2 21.9
16.0 4.0 25.2
16.6 4.6 23.9 16 85
17.8 5.8 21.0
19.0 7.0 17.9 13 87
21.0 9.0 16.2
21.8 9.8 15.6
23.6 11.6 14.6 11 75
25.4 13.4 14.2
26.4 14.4 13.5
01
en
Effective Straining Area-1.26 ft2
-------
TABLE B-10
SECONDARY STRAINER
10-MICRON, TANK SS 150 MG/L
eo m
Total tat Spae. Eff. Tank
Haad Haad Flow , SS SS
In In CPU/Ft 116/1 NG/L
2.5 0.0 0.0
3.0 O.S 2.3
3.2 O.a 3.W
3.2 O.I 3.6 27 167
3.1* 0.9 ».l
3. it 0.9 5.1
3.6 l.'l 5.6
3.8 1.2 5.8
».0 l.S 5.5 21 165
H.S 2.0 1.1
90 KPN
Total Hat Spae. Eff. T«nk
Haad Haad Flo* , SS SS
In In ePH/Ft N3/L NG/L
.0 0.0 0.0
O.S .3
0.6 .9 27 169
0.9 ."•
1.0 .8
7. l.S .2 22 166
7. l.H .2
7. 1.5 .2
7. 1.6 .2
7. 1.6 .5
7. 1.8 .7
8. 2.0 .7 19 16*
1. 2.5 .7
6. 2.H .9
8.6 2.6 7.1
120 W*
Total Nat Spae. Eff. Tank
Haad Haad Flan , SS SS
In In GPU/Ft' NG/L NG/L
11.2 0.0 0.0
.11.5 0.2 .3
11.6 O.S .5 28 165
12.0 0.8 .2
12.0 0.6 .6
12. .1 .5 30 167
12. .2 .5
12. .» .7
12. .5 .7
12. .6 9.1
13.0 .8 9.8
13.0 1.8 10.2 28 166
13.1 1.9 10.2
13.2 2.0 10.6
13.5 2.2 10.6
13.6 2»» 10.6
13.6 2.5 11.0
U».0 2.8 11.0
W.I 2.9 11.0
W.2 3.0 11.6
1».S 3.2 11.6 25 171
15.0 3.8 11.0
15.2 4.0 9.8
15.8 U.S 7.9
180 *PN
Total Mat Spae. Eff. Tank
Haad Haad Flow , tS SS
In In CPU/Ft HG/L NG/L
22.9 3.3
23.it S.6 HO 163
23.5 7.5
23.9 8.7
2H.1 10.2 03 170
2«.S 11.5
24.6 12.7
2H.9 13. S3 162
25.2 H».
25.2 m.
2S.it 1U.
25. H IS.
25. 5 15.
25.8 17.0
26.0 16.1 31
26.K 17.0
26.5 18.1
27.0 19.5
27. W 21.1
26.0 21.1
28.2 21.1
Effective Straining Area-1.26 ft2
-------
TABLE B-ll
SECONDARY STRAINER
10-MICRON, TANK SS 200 MG/L
CTl
60 KPN
Total Hat Spec. BR. Tadc
Haad Mad Flo* , SS SS
I* H GP«/ft * HS/L KG/L
2.9 0.0 .0.0
3.0 0.1 2.9
3.1 0.5 3.8
3.5 0.6 U.O
3.5 0.6 4.1 9 118
3.5 0.6 «.«
3.6 0.6 S.I
3.9 1.0, 5.6
1.1 1.2 5.6 11 110
U.«t 1.5 5.2
1.6 1.6 it. 8
5.0 2.1 U.5 9 108
90 m
Total Nat Spa$. Eff. Tank
Haad Haad Flow , 88 SS
In In GPH/Ft HG/L HG/L
6.0 0.0 0.0
7.8 1.8 8.2
1.9 1.9 8.3 21 228
8.1 2.5 8.7
8.2 2.2 9.5
8.1 2.1 10.2
8.5 2.5 10.2 22 226
8.6 2.6 10.2
.2 3.2 9.5
.0 3.0 9.1
.1 3.1 8.7
.2 3.2 8.9
.U 3.1 8.5
.5 3.5 8.2
120 RTK
Total Hat Spec. Eff. Tank
Haad Kaad Flow . SS SS
In In GPH/Ft HG/L HG/L
11.5 6.7 23 256
11.5 5.8
11.6 7.7
11.9 »,0 30 2U9
11.9 9.U
11.9 10. U
12.1 10.8
12.1 11.0
12.2 11.5
12.2 11.8
12. U 12.1
12.5 12.7
12.6 13.3
12.8 lit.l
12.8 lit. 5 62 256
13.0 1«.9
13.1 IS.O
13.5 17.0
13.9 17.0
1U.2 16.3 26 2SU
lit. 5 15.9
It. 9 15. H
1S.U 1U.1
15.8 13.0
180 IPIt
Total Nat Spac. Eff. Tank
Haad Haad Flow , SS SS
In In GPM/rt HG/L HG/L
21.0 0.0 0.0
21.8 0.8 3.2
22.0 1.0 5.1 HI 252
22.5 1.5 8.1 250
22.8 1.8 8.1
23.2 2.2 10.8 19 260
23.5 2.S 11.5
23.8 2.8 13.7
2H.O 3.0 15.0
2H.6 3.6 18.1 38 251
21.9 3.9 19.5
25.1 1.1 20.0
25.5 M.5 21.1
25.6 >t. 6 21.1
25.8 U.B 22.0
26.1 5.1 21.1
26. U S.it 21.1
26.6 5.6 21.1
27.0 6.0 21.1
27.8 6.8 21.1
28. U 7. it 20. H
28.8 7.8 19.5
29.0 8.0 19.5
Effective Straining Area-1.26 ft2
-------
TABLE C-l
JANUARY 1973 PERFORMANCE DATA
Date
1
2
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
22
23
24
25
26
27
28
29
30
31
PRIMARY EFFLUENT
Q TOC/SOC BOD/COD SS/VSS NH3-N pH
gpd x 103 mg/1 mg/1 mg/1 mg/1
10 128/73 96/83 21.5 8.1
10 103/63 117/197 69/58 10.8 7.5
10 116/75 159/- 125/105 10.8 7.6
10
10
10 120/56 168/- 118/100 15.0 7.5
12 59/39 23/23 7.9 7.3
15 99/37 145/- 167/132 10.2 7.5
17 95/52 -/355 95/70 8.5 7.6
15 116/60 145/- 38/36 11.9 7.3
11
11
10 62/42 63/- 46/44 18.7 7.7
15 89/52 128/113 11.9 7.8
18 99/44 80/- 99/82 7.4 7.3
9
10 184/- 100/-
10
10
10 59/-
10
10
10
0 120/- 94/-
5 60/- 63/-
3
MIXED
LIQUOR
SS VSS
mg/1 mg/1
3360 3050
3760 3250
4230 3630
5030 4500
4420 4000
4620 3970
3210 2630
3710 3350
4340 3820
3560 3260
3780 3290
2230
1710
1890
1920
1900
1925
1300
PRIMARY STRAINER EFFLUENT
BOD/COD TOC/SOC SS/VSS NH3-N
mg/1 mg/1 mg/1 mg/1
21/8 43/37 11.3
23/- 23/9 45/34 7.1
30/- 29/12 49/36 9.9
36/- 39/12 71/62 12.5
21/9 -/24 8.8
51/- 28/10 85/67 6.5
19/7 42/27 5.7
50/- 34/19 50/46 9.6
17/- 33/11 62/54
22/5 64/64 ND(*
34/- 30/10 69/58 ND
SECONDARY STRAINER EFFLUENT
BOD/COD TOC/SOC SS/VSS NH,-N
mg/1 mg/1 mg/1 mg/1
23/9 41/37 10.7
22/- 26/11 37/27 7.1
13/- 26/12 40/32 9.9
33/- 37/13 53/46 12.5
18/8 -/24 8.1
27/- 23/12 37/29 5.7
-/62 15/8 27/17 4.5
48/- 32/17 44/40 9.9
ll/- 33/11 62/54 2.0
21/6 50/40 ND
31 /- 34/10 56/49 ND
9/- 4/-
8/- 3/-
8/- 4/-
8/- 4/-
00
(*) ND = Non Detectable
-------
TABLE C-2
JANUARY 1973 OPERATING DATA
Date
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
NIXED LIQUOR
Load
Factor
Lbs BOD
Lb MLVSS
0.10
0.12
0.11
0.15
0.12
0.19
0.47
0.12
Wasted
Solids
Lbs/day
24.7
37.5
17.5
32.1
8.8
6.2
PRIMARY STRAINER
Head
In H?0
£
1.5
1.5
2.0
1.5
1.5
2.0
2.0
2.0
1.5
1.3
1.3
1.5
1.5
Velocity
Ft/M1n
330
330
330
330
330
330
330
330
330
330
330
330
330
SECONDARY STRAINER
Head
1n H,0
£
10
10
10
10
10
10
9.5
10
10
10
10
10.3
Velocity
Ft/Ml n
766
760
760
760
760
760
760
760
760
700
685
685
685
AERATION TANK
Return
Flow
gpm
8
8
8
8
8
8
8
8
9
9
8
7
7
7
7
3
4
Return
SS
mg/1
190
79
Air Flow
Lbs/hr
70
70
70
70
70
70
69
70
75
71
156
156
161
01
Primary Strainer: 20 micron fabric, ultrasonic current 5.7-6.0 amps
Secondary Strainer: 10 micron fabric, ultrasonic current 2.4-3.7 amps
-------
TABLE C-3
FEBRUARY 1973 PERFORMANCE DATA
Date
1
2
3
4
5
6
7
8
9
10
11
12
14
15
16
21
22
23
24
26
27
28
PRIMARY EFFLUENT
Q i TOC/SOC BOD/COD SS/VSS NHa-N pH
gpd x 103 mg/1 mg/1 mg/1 mi/1
8 144/65 /500 166/166 26.6 7.3
11 100/56 116/85 8.5 7.3
8
8
9 85/42 52/46 9.9 7.3
7 81/33 123/95
8 81/39 107/- 97/62 6.8
0 78/-
6.5
6.5
6
6
61/38 70/- 48/35 8.5 7.3
7.5 -/401 143/121 7.4 7.5
6 88/- 65/65 7.9 7.4
5.5
89/33 -/328 232/127 7.9
56/29 70/- 63/57 8.5 7.6
72/61
7
9 58/37 50/38 11*3 7.3
10 117/94 7.4
MIXED
LIQUOR
SS VSS
mg/1 mg/1
1365 1125
1920 1590
2765 2380
2155 1930
2026 1700
1082 944
1364 1166
1698 1574
1650 1540
2095 1805
2430 2090
1410 1190
910 780
PRIMARY STRAINER EFFLUENT
BOD/COD TOC/SOC SS/VSS NH,-N
mg/1 mg/1 mg/1 mg/1
18/11 13/10 ND (*)
15/8 8/6 2.3
19/18 19/14 ND
35/7 108/88 ND
48/- 46/8 98/76 ND
72/- 73/13 150/131 ND
54/- 66/58 ND
47/- 65/48 ND
38/26 54/40
32/15 41/30 ND
27/14 78/27
47/32 2.8
4/3
SECONDARY STRAINER EFFLUENT
BOD/COD TOC/SOC SS/VSS NHv-N
mg/1 mg/1 mg/1 ,mgVl
-/23 14/9 3/3 ND
14/9 2/2 1.5
19/10 7/7 ND
9/6 14/7 ND
8/- 15/8 17/2 ND
21/- 28/11 39/34 ND
-/1 24 20/- 23/22 ND
18/- 30/21 ND
-/1 14 36/21 55/41
5/- 15/11 11/10 ND
18/14 59/17
20/12 ND
4/4
(*) ND = Non Detectable
-------
TABLE C-4
FEBRUARY 1973 OPERATING DATA
Date
1
2
3
4
5
6
7
13
14
IS
16
22
23
24
27
28
MIXED LIQUOR
Load
Factor
Lbs BOD
Lb MLVSS
0.17
0.26
0.23
0.26
Wasted
Solids
Lbs/day
20.2
PRIMARY STRAINER
Head
1n H20
13.0
1.5
1.5
9.0
0.5
8.4
2.9
3.1
2.9
2.9
1.3
1.8
15.8
Velocity
Ft/Ml n
245
345
377
377
345
685
358
358
342
345
345
342
342
SECONDARY STRAINER
Head
1n H2o
0.4
6.0
2.75
2.5
3.0
9.0
4.5
6.6
4.8
6.5
30.0
6.8
29.5
Velocity
Ft/MIn
257
257
377
377
358
502
446
565
446
565
565
565
565
AERATION TANK
Return
Flow
gpm
6
4
5
5
5
6
3.1
3.8
4.2
3.8
3.8
3.8
3.8
5.0
3.0
Return
SS
mg/1
24
40
43
251
420
280
178
190
135
45
25
26
10
A1r Flow
Lbs/hr
126
126
118
118
152
82
164
146
148
147
147
149
119
Primary Strainer:
Secondary Strainer:
20 micron fabric, ultrasonic current 4.3-6.1 amps
10 micron fabric, ultrasonic current 3.7-5.9 amps
-------
TABLE C-5
MARCH 1973 PERFORMANCE DATA
Date
1
2
3
4
5
6
7
8
9
10
11
12
13
14
IS
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
PRIMARY EFFLUENT
Q * TOC/SOC BOD/COO SS/VSS NH,-N pH
gpd x 10J mg/1 mg/1 mg/1 nig/1
12 49/24 -/216 82/65 8.4 7.7
15 61/44 95/- 68/57 9.9 7.4
7
6
46/29 51/38
203/201
7 63/51
3 79/66
6 91/37 1 IS/80 7.5
6
6
8 52/32 59/- 40/34 17.3 7.2
4 72/33 124/- 8.5 7.3
8 65/25 87/- 143/113 11.3 7.6
8 70/32 80/57 7.3
8 54/22 86/68 12.2 7.6
8
8
3 49/17 79/63 8.8 7.5
7 70/20 133/105 10.7 7.4
3 50/20 60/- 59/49 13.8 7.5
5 46/21 -/153 42/26 9.9 7.6
9 57/30 95/- 73/55 7.7 7.1
5
2
15 80/28 -/1 31 104/98 23.2 7.6
6 104/31 420/310 9.4 7.4
6 77/40 85/- 110/56 25.4 7.6
15 54/19 -/217 100/50 8.5 7.8
8 75/42 117/- 72/59 11.0 7.4
8
MIXED
LIQUOR
SS VSS
mg/1 mg/1
1680 1460
530 450
204 158
216 178
332 284
600 460
915 760
1472 1310
470 -
950 810
1255 1085
1915 1655
2310 1900
2550 2120
2370 2130
2420 2080
2750 2290
3130 2690
3730 3150
3220 2780
3300 2790
6240 5400
PRIMARY STRAINER EFFLUENT
BOD/COD TOC/SOC SS/VSS NH,-N
mg/1 mg/1 mg/1 mg/1
24/15 22/16
111/83
20/17 142/114
50/11 132/108 ND
58/8 154/- ND
52/8 124/100 1
28/6 50/35 ND
11/6 56/12 5
42/8 98/77 ND
36/7 76/59 ND
20/5 46/32 ND
11/6 20/16 1
24/5 58/30 1
19/17 22/13 ND
24/8 94/66 ND
46/9 89/70 ND
SECONDARY STRAINER EFFLUENT
BOD/COD TOC/SOC SS/VSS NH,-N
mg/1 mg/1 mg/1 mg/1
-/64 18/11 14/12 ND (*)
12/- 19/15 10/8 ND
20/11 24/19
6/4
64/17 148/111
7/- 22/13 29/21 ND
38/9 627- ND
38/9 100/66 ND
12/7 12/8
27/9 63/42 1
8/6 3/2 ND
20/6 33/23 ND
8/- 13/7 22/19 ND
-/45 14/6 19/15 ND
13/- 11/6 19/14 ND
3/- 8/6 9/4 ND
11/8 13/5 ND
13/- 15/6 19/14 ND
-788 15/7 40/26 ND
74/- 59/10 140/110 ND
•xl
ro
(*) ND = Non Detectable
-------
TABLE C-6
MARCH 1973 OPERATING DATA
Date
1
2
4
12
13
14
16
19
20
21
22
23
26
27
28
29
30
MIXED LIQUOR
Load
Factor
Lbs BOD
Lb MLVSS
0.18
0.07
0.17
0.06
0.03
0.04
0.07
Wasted
Solids
Lbs/day
PRIMARY STRAINER
Head
In H90
2
1.9
4.5
1.9
2.9
11.4
11.1
1.4
2.4
5.4
4.9
6.4
3.4
3.9
9.1
2.9
5.6
Velocity
Ft/Ml n
350
380
350
420
310
310
350
380
570
500
500
360
360
350
380
380
SECONDARY STRAINER
Head
In H20
12.5
17.0
11.0
6.8
12.8
0
8.8
27.5
3.2
15.7
7.1
7.3
9.5
20.4
21.5
9.3
Velocity
Ft/Mi n
750
580
750
450
750
580
620
380
380
760
580
570
600
650
840
720
AERATION TANK
Return
Flow
gpm
&r
0
5.2
3.8
3.8
3.8
1.7
3.8
3.8
3.8
2,1
2.1
1.7
3.8
3.8
0
0
Return
SS
mg/1
14
324
256
252
293
236
96
124
141
114
60
19
190
A1r Flow
Lbs/hr
176
132
130
135
142
150
142
152
86
141
136
135
139
132
160
156
GO
Primary Strainer:
Secondary Strainer:
20 micron fabric through 3/4/73
40 micron fabric 3/5/73, Ultrasonic current 5.6-6.0 amps
10 micron fabric, ultrasonic current 3.7-4.3 amps
-------
TABLE C-7
APRIL 1973 PERFORMANCE DATA
Date
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
PRIMARY EFFLUENT
, TOC/SOC BOO/COD SS/VSS NH3-N pH
gpd x 10-* mg/1 mg/1 mg/1 mg/1
8
8 93/52 137/- 73/61 19.9 7.3
10 103/54 158/132 10.5 7.2
12 69/39 108/- 85/72 31.07.5
14 67/32 -/263 80/73 9.6 7.4
14 76/50 143/- 83/73 20.0 7.0
14
14
16 54/19 98/- 56/46 7.7
20 73/27 110/110 11.0 7.5
16 81/26 148/- 90/80 14.0 7.8
16 65/24 -/163 46/35 8.5 7.5
14 146/28 -/173 168/160 14.0 7.5
10
10
14 96/25 188/- 240/195 16.0 7.4
10 76/32 130/110 11.0 7.0
6 67/21 133/- 91/55 14.0 6.7
10 98/48 -7296 122/108 27.0 7.8
10
10
10
12 81/23 96/- 113/83 13.0 7.1
12 124/24 326/274 7.1
9 145/55 2477- 144/138 7.0
16 92/41 -7311 116/98 8.0 7.6
18 91/51 189/- 214/178 7.6
12
8
10 212/19 464/373 7.6
MIXED
LIQUOR
SS VSS
mg/1 rag/1
5980 4940
6140 5220
6040 5130
6440 5510
6400 5620
5420 4740
5660 4700
5750 4670
5900 5020
7180 6040
9040 7680
1136010240
10080 8640
9320 7960
8200 7040
8320 7680
9480 8000
7990 6870
7410 6080
PRIMARY STRAINER EFFLUENT
BOD/COD TOC/SOC SS/VSS NH3-N
mg/1 mg/1 mg/1 mg/1
56/5 118/87 ND (*)
32/6 67/59 ND
27/6 55/45 ND
17/4 27/21 4
13/7 45/44 2
20/7 55/50
13/8 10/5 2
24/9 34/19 3
15/7 21/16 ND
23/12 21/14 ND
130/110 48/32 11
34/20 35/30 ND
93/64 76/54 ND
53/25 45/10 ND
19/8 16/10 2
21/8 37/24
22/8 18/25
35/11 39/16 2
30/25 43/34
48/12 109/64
SECONDARY STRAINER EFFLUENT
BOD/COD TOC/SOC SS/VSS NHj-N
mg/1 mg/1 mg/1 mg/1
3/- 8/2 8/4 ND
17/6 21/18 ND
32/- 32/7 56/47 ND
-744 10/4 11/10 ND
4/- 10/5 12/11 ND
7/- 15/9 21/18
12/8 6/4 2
10/- 15/8 12/6 3
-/29 23/12 21/14 ND
4/- 14/10 5/4 ND
6/- 22/18 9/8 ND
45/18 40/32 ND
827- 105/63 80/61 ND
-/I 27 48/26 42/9 ND
2/- 13/9 7/3 1
13/8 21/15
5/- 18/8 13/13
-/34 12/12 11/9 ND
22/- 24/15 44/36
16/6 23/17
(*) ND - Non Detectable
-------
TABLE C-8
APRIL 1973 OPERATING DATA
en
Date
1
2
3
4
5
6
9
10
11
12 (*)
13 I*
14
IS
16 (*)
17 (*)
18
19
20
21
22
23
24
25
26
27
28
29
30
NIXED LIQUOR
Load
Factor
Lbs BOD
Lb MLVSS
0.06
0.07
0.09
0.09
0.13
0.31
0.07
0.03
0.07
0.08
Wasted
Solids
Lbs/day
16
65
40
35
20
29
10
PRIMARY STRAINER
Head
1n H20
2.9
2.4
2.1
3.6
1.9
2.9
2.2
3.4
2.9
2.9
2.9
1.8
2.9
3.2
3.0
3.1
3.5
5.2
3.4
Velocity
Ft/M1n
360
360
380
380
400
400
400
400
400
380
380
460
350
380
380
380
380
570
570
SECONDARY STRAINER
Head
In H20
7.5
7.5
10.2
6.8
1.4
10.0
7.0
7.0
7.0
6.5
5.0
4.5
4.5
4.5
4.0
4.8
11.6
4.8
Velocity
Ft/Ml n
630
630
570
570
500
720
680
570
570
560
560
470
460
470
470
470
470
380
380
AERATION TANK
Return
Flow
gpm
3
3
3
3
3
1
1
1
1
2
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
Return
SS
mg/1
197
79
297
43
52
31
90
112
90
84
41
64
66
78
52
103
30
315
Air Flow
Lbs/hr
154
160
160
156
158
158
158
156
150
149
170
300
152
172
170
170
170
175
175
(*) Boot moVassei added (not recorded 1n influent sample)
Primary Strainer: 10 micron fabric, ultrasonic current 5.9-6.9 amps
Secondary Strainer: 5 micron fabric, ultrasonic current 3.3-4.2 amps
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-670/2-75-045
2.
3. RECIPIENT'S ACCESSIOP*NO.
4. TITLE AND SUBTITLE
REPLACEMENT OF ACTIVATED SLUDGE SECONDARY CLARIFIERS BY
DYNAMIC STRAINING
5. REPORT DATE
May 1975: Issuing Date
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Michael Joyce, William Schultz, and Arvid Strom
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
FMC Corporation
Environmental Equipment Division
1800 FMC Drive West
Itasca, Illinois 60143
10. PROGRAM ELEMENT NO. JBB043
ROAP 21-ASR, Task 039
11. CONTRACT/GRANT NO.
68-03-0102
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
Einal. 1972-1973
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
Pilot plant studies were conducted on domestic wastewater-to determine the feasibility of replacing conventional
activated sludge gravitational clariflers by dynamic straining. The dynamic strainers consisted of a rotating
cylinder cleaned by an internal ultrasonic transducer. A primary strainer was placed and operated directly in
the mixed liquor in the aeration tank. A secondary strainer was installed and operated in a separate tank to
further clarify the effluent from the primary strainer.
This work indicated that dynamic straining 1s a technically feasible process for replacing conventional activated
sludge gravitational clarifiers. Suspended solids removals of well over 99 percent were achieved with a single
primary strainer operating 1n the pilot plant aerator with a mixed liquor suspended solids concentration of over
6,500 mg/1. When operated at lower specific flow rates, primary straining appears to be capable of consistently
producing an effluent suspended solids in the 15-30 mg/1 range.
Present economic predictions indicate that plants equipped with primary and secondary dynamic strainers would
cost more than plants utilizing conventional secondary gravity clarifiers. This factor can be tempered by
several projected dynamic straining advantages. Two-stage dynamic straining has excellent application where
space limitations exist. Secondary gravity clarifiers could be eliminated under the right conditions and
aeration tank sizes could be appreciably smaller with the higher MLVSS concentrations achievable with dynamic
straining. An existing overloaded activated sludge plant could be upgraded with primary straining only without
expanding the facilities. In locations or applications where filamentous growth Is prevalent, primary straining
could be used to effectively control bulking. During the testing program, dynamic straining revealed Itself
to be resistant to shock loading.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COS AT I Field/Group
Sewage treatment, *Activated sludge process
Aeration tanks, *Clarification, *Strainer;
Upgrading
*Dynamic straining,
Ultrasonic transducer,
*Liquid-solids
separation, Mixed
liquor solids control
13B
13. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (ThisReport)
Unclassified
21. NO. OF PAGES
84
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
76
.S. GOVERNMENT PRINTING OFFICE: 1975-657-593/5383 Region No. 5-11
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