EPA-600/2-75-039
September 1975
Environmental Protection Technology Series
IMPROVED LIQUID-SOLIDS SEPARATION BY
AN ALUMINUM COMPOUND IN
ACTIVATED SLUDGE TREATMENT
Municipal Environmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development,
U.S. Environmental Protection Agency, have been grouped into
five series. These five broad categories were established to
facilitate further development and application of environmental
technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in
related fields. The five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the ENVIRONMENTAL PROTECTION
TECHNOLOGY series. This series describes research performed
to develop and demonstrate instrumentation, equipment and
methodology to repair or prevent environmental degradation
from point and non-point sources of pollution. This work
provides the new or improved technology required for the
control and treatment of pollution sources to meet environ-
mental quality standards.
This document is available to the public through the National
Technical Information Service, Springfield, Virginia 22161.
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EPA-600/2-75-039
September 1975
IMPROVED LIQUID-SOLIDS SEPARATION BY AN
ALUMINUM COMPOUND IN ACTIVATED SLUDGE TREATMENT
by
Charles F. Lenhart
Greene County, Ohio 45385
Joe W. Cagle
Nalco Chemical Company
Oak Brook, Illinois 60521
for the
Board of Greene County Commissioners
Greene County, Ohio
Project No. 17030 EBH
Project Officer
Edwin F. Earth
Wastewater Research Division
Municipal Environmental Research Laboratory
Cincinnati, Ohio 45268
MUNICIPAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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DISCLAIMER
This report has been reviewed by the Municipal Environ-
mental Research Laboratory, U.S. Environmental Protection
Agency, and approved for 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.
11
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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 Municipal Environmental Research
Laboratory contributes to this multidisciplinary focus through
programs engaged in
studies on the effects of environmental con-
taminants on the biosphere, and
a search for ways to prevent contamination and
to recycle valuable resources.
This report describes more efficient wastewater treatment
obtained by addition of aluminum compounds to the process.
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ABSTRACT
This study demonstrates that feeding liquid alkaline
alumina, identified as sodium aluminate, to a small
to medium (2.5 million gal per day) activated sludge
wastewater treatment plant is a practical method of
gaining several operational benefits. Specific
benefits were found in the areas of solids handling
and ease of sludge volume index control. Additional
benefit was noted in the concentration of aerobically
digested solids, particularly in cold weather. Reduc-
tion of suspended solids carryout of secondary clari-
fiers resulted from the sodium aluminate feed, reducing
the loading to the tertiary treatment unit. The in-
creased sludge density from the inorganic chemical
introduced into the plant permitted the plant to pro-
tect itself against solids washout during spot flows
(periods of infiltration/in-flow) at greater than
164% of designed plant capacity. Phosphorus removal
in amounts approaching 80% were achieved with feed
rates of 10 mg/liter as Al to the aeration basins.
The cost of alkaline alumina addition was 2.6C per
1000 gallons of raw wastewater flow.
This report was submitted by the Greene County Sanitary
Engineering Department, (T. E. Troutman, Sanitary
Engineer), 651 Dayton-Xenia Road, Xenia, Ohio, 45383
in fulfillment of Grant Number 17030 EBH under the
sponsorship of the U. S. Environmental Protection Agency
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TABLE OP CONTENTS
SECTION PAGE
I Introduction 1
II Conclusions and Comments 2
III Recommendations 5
IV Project Development and Schedule 7
V Detailed Data on Treatment Units and
Description of Treatment Facilities ... 13
VI Chemical Feeding System 23
VII General Description 25
VIII Effect of Sodium Aluminate Feed on
Solids and Solids Handling 28
IX Bibliography 59
v
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TABLES
NO. PAGE
1 Sodium Aluminate Dosing Schedule 7
2 Analytical Data Summary 8
3 Digested Sludge Analytical Data Summary .... 55
FIGURES
NO. PAGE
1 Chemical Feed Schematic 9
2 Chemical Application Point, Primary Tank
Weir Trough 10
3 Phosphorus Variations with Sodium
Aluminate Additions 11
4 Beavercreek Wastewater Treatment Plant
Schematic Flow Diagram 21
5 Chemical Feed Pump . 24
6 Bulk Chemical Storage Tanks . 24
7 Secondary Clarifier 25
8 Aeration Tank Overflow Weir 26
9 Aeration Tank 26
10 Sludge Volume Index 30
11 Percent MLSS One Half Hour Sedimentation .... 32
12 Solids in Mixed Liquor mg/1 33
VI
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FIGURES (continued)
NO. PAGE
13 Return Sludge SS mg/1 34
14 Mixed Liquor Dissolved Oxygen 36
15 Plant Flow million gal/day 37
16 Temperature of Raw Sewage 40
17 Secondary Clarifier, Suspended Solids mg/1 .... 41
18 Microstrainers 41
19 Secondary Clarifier BOD5 43
20 Raw and Final Wastewater pH 44
21 Raw Wastewater BOD5 45
22 Raw Wastewater BODg Average Characteristics ... 46
23 Percent BOD Removal 47
24 Analysis of Ammonia Nitrogen - Raw & Final .... 47
25 Analysis of Nitrate Nitrogen - NO3-N 48
26 Aerobic Digestion in Service 49
27 Supernatant Volume (gallons) 49
28 Supernatant SS mg/1 50
29 Supernatant BOD mg/1 50
30 Trucks for Hauling Sludge 51
31 Digested Sludge pH 52
32 Digested Sludge - Percent Dry Solids 53
33 Digested Sludge - Percent Volatile Solids .... 54
34 Digested Sludge - Percent Volatile Reduction ... 54
Vll
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ACKNOWLEDGEMENTS
We wish to thank the EPA for the funding that made this
study possible and the following individuals for their
technical and manuscript review assistance.
Mr. Edwin F. Earth
U. S. Environmental Protection Agency
Municipal Environmental Research Laboratory
Cincinnati, Ohio 46268
Mr. Morgan W. Cochran
Plant Manager
Jackson Pike WWTP
City of Columbus
Columbus, Ohio
Mr. John G. Conway, M.P.H., Ph.D
Department of Environmental Health
Biological Sciences
Wright State University
Dayton, Ohio
Mr. John E. Richards
State of Ohio
Assistant Director of Ohio EPA
Columbus, Ohio
Mr. Timothy E. Troutman, P.E.
Sanitary Engineer
Greene County Department of Sanitary Engineering
Xenia, Ohio
Vlll
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SECTION I
INTRODUCTION
This study was undertaken to determine the effects of
sodium aluminate additions on the activated sludge
waste treatment process. It was postulated that con-
siderable benefit could be obtained by adding the
chemical to the primary and aeration basins. Improve-
ments were expected in the areas of sludge volume index
control, waste sludge handling and concentration through
dewatering of the digester solids. The benefits of
sodium aluminate usage for phosphate removal are well
documented in the literature. This benefit, although
important in helping the plant reach discharge require-
ments, was secondary to the study.
Also of primary interest was the feasibility of chemical
dosing in small wastewater treatment plants as a normal
part of daily operation.
It also appeared reasonable that improved solids handling
could have major impact on hydraulic size requirements,
power consumption and tertiary treatment design. A
thorough study was needed to measure the long-term impact
of sodium aluminate dosing and the treatability with
disposal of the resultant solids. It is entirely pro-
bable that future wastewater treatment plant design will
call for chemical flocculation of organic colloidal
solids prior to final treatment. This study should pro-
vide background on the use of sodium aluminate for this
purpose.
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SECTION II
CONCLUSION AND COMMENTS
The conclusions drawn by the authors of this report are
based on the analytical and operations data summaries
from Greene County - Beavercreek Wastewater Treatment
Plant, as well as from opinions of operating personnel
resulting from actual plant experiences.
1. Waste water throughout the study was typical of
the normal, domestic sewage treated at the plant,
2. No attempt was made to adjust plant flow or
treatment conditions other than as necessary
to maintain good, efficient wastewater treat-
ment operations.
3. The plant is designed for treatment of 2.5
million gal per day average on an annual basis.
During the study, flow rates from a weekly
average low of 1.715 million gal per day to
a high of 4.098 million gal per day, from 69
to 164% of design, were treated.
4. Various injection points throughout the primary
and aeration basins were evaluated. it was
found that the most efficient point to treat
the mixed liquor stream was at the outlet of
the primary.
5. Chemical cost during the project, exclusive
of freight charges, was computed to be 2.6
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7. The addition of sodium aluminate permitted
maintenance of a sludge blanket in the secondary
clarifier, even at flow rates as high as 164%
of plant design. A case history documenting
flow conditions where a washout of solids in
the secondary clarifier was expected but did
not occur while on sodium aluminate feed is
included.
8. With sodium aluminate in the flow stream, Sludge
Volume Index (SVI) was greatly improved. Control
of Mixed Liquor Suspended Solids (MLSS) was
easier because of improved settling characteris-
tics. Thicker return sludge resulted from the
feed of sodium aluminate and this permitted a
substantial reduction in waste activated sludge
volumes to be handled.
9. Higher levels of MLSS could be retained in the
secondary clarifier during aluminate application.
10. Return sludge volume rate was lower because the
plant could deliver the same amount of micro-
organisms with less total flow volume. This
resulted in less power needed to pump the sludge
plus less liquor volume hydraulically added
ahead of the aeration basin.
11. Improved solids removal with sodium aluminate
reduced the loading on the microstrainers used
for tertiary treatment. This improved the
efficiency of the tertiary treatment.
12. Chlorine demand was reduced while on sodium
aluminate because of less solids and BOD
entering the chlorine contact tank.
13. The man-hours required for operation of the
chlorine contact tank were also reduced because
less time was required for routine cleaning and
maintenance.
14. The addition of sodium aluminate resulted in a
greater ability to concentrate solids in the
aerobic digesters. Previous to the use of
sodium aluminate, it was difficult to supernate
the digester, particularly in cold weather.
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15. In this plant it became a practice to build the
solids in the final clarifiers to a depth of 4 ft
before wasting sludge while feeding the sodium
aluminate. Using this process of solids concen-
tration, a discharge to the digesters of Waste
Activated Sludge (WAS) as high as 1 1/2% by
weight dry solids became possible. By pumping
thicker sludge to the digesters/ the flow
volume was reduced, which increased digester
capacity.
16. It was found that BOD and Suspended Solids (SS)
loadings to the aeration tanks were reduced and
increased concentrations of primary tank solids
(raw sludge) resulted when alumina (contained in
the solids on the microstrainer) was recycled.
17. With greater solids concentration in the digester
(due to more concentrated feed and the ability to
decant), the resulting effect of less sludge to
be disposed of meant less hauling time and lower
total hauling cost to the plant.
18. Chemical feed of this type has its place in small
to medium-size plant operations. Chemical addition/
as a normal part of daily operations, proved to be
a relatively simple operator's function. Once the
sodium aluminate feed was under way, it was quick-
ly found that, rather than being a time-consuming
liability to the daily operation, the sodium
aluminate enhanced several areas of the operation.
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SECTION III
RECOMMENDATIONS
1. Adequate bulk storage of sodium aluminate or coagu-
lants must be designed into the plant to insure
sufficient product availability at all times, plus
additional capacity to take advantage of minimum
freight charges at maximum bulk shipment pricing.
We suggest, for a 2 million gallon per day plant,
that storage for a minimum of 5,000 gallons bulk
liquid be provided.
2. Best results were obtained by feeding the product
neat. No advantage was noted by the addition of
dilution water. All lines and valves that are
installed should be compatible with the chemicals
used. In this plant, best results were obtained
with ductile iron valves and polyvinyl chloride
valves and lines.
3. Standby or dual pumping capability should be pro-
vided .
4. Chemical feed rates should be measurable at any
time and the chemical feed rate should be totalized.
Sight glasses on the bulk tanks were provided and
found to be a reliable gauge of tank inventory.
5. Bulk unloading lines to the tanks should be
readily accessible to a delivery truck. This line
should be a 2-inch fill line with either a 2-inch
quick-release coupling or a threaded 2-inch nipple.
6. Train operators to respond to changes that require
adjustments in process control and chemical feed
rate. Plant flow rates, color, odor, turbidity,
settling characteristics, quality of digester
supernatant, and clarity of secondary and clarifier
effluent should be observed and adjusted as required,
Waste water temperature, pH, dissolved oxygen, and
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settled solids are also important operations criteria,
Periodic and routine checks of the feeding equipment,
with measurement of chemical dosage, are required to
ensure that the correct amount of chemical is being
fed.
7. Results depend on continuous and proportionate
chemical feed. Personnel should be provided for
as many hours a day as is feasible; 24-hour-per-day
coverage is ideal, but not mandatory.
8. Equalize the flow through the plant by every
available means to keep conditions as near con-
stant as possible.
9. Provide flexibility to allow optimization of
chemical feed for each individual plant. We recom-
mend feed points ahead of the primary and at the
end of the primary basins as well as to at least
three points in the aeration system, i.e. inlet,
midway and outlet.
10. Plant records should be maintained to monitor the
results of chemical feed. We recommend the follow-
ing basic operating criteria be monitored.
a. Suspended solids throughout the plant.
b. Incoming and effluent BOD.
c. Turbidity out of secondary .clarifier and plant
effluent.
d. Dry solids basis of the -sludge handling system.
e. Phosphorus levels.
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SECTION IV
PROJECT DEVELOPMENT AND SCHEDULE
The project was fully under way by October 1, 1973 and was
completed by August 1, 1974. Table 1 shows the actual dosing
schedule.
TABLE 1 - SODIUM ALUMINATE DOSING SCHEDULE
Time Period
10-1-73 thru 10-24-73
10-25-73 thru 11-25-73
11-26-73 thru 12-22-73
12-23-73 thru 1-13-74
1-14-74 thru 2-11-74
2-11-74 thru 3-10-74
3-10-74 thru 5-5-74
5-5-74 thru 7-28-74
Dosinq
10 mg/1 additions of aluminum
to the aeration tanks
no aluminum additions
10 mg/1 additions of aluminum
to the aeration tanks
no aluminum additions
10 mg/1 additions of aluminum
to the aeration tanks
no aluminum additions
10 mg/1 additions of aluminum
to the aeration tanks
no aluminum additions
Samples of raw water and settled wastes, and final plant
effluent were collected every two weeks and submitted for
outside-plant laboratory analysis. These data are shown
in Table 2.
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TABLE 2 - ANALYTICAL DATA SUMMARY*
oo
Sample
10/15
11/12
12/10
1/28
2/27
3/25
4/22
5/10
5/20
Sample
Location
Raw
Settled
Final
Raw
Settled
Final
Raw
Settled
Final
Raw
Settled
Final
Raw
Settled
Final
Raw
Settled
Final
Raw
Settled
Final
Raw
Settled
Final
Raw
Settled
Final
Ammonia
NH3
27
27
12.0
30
27
19.0
26
25
15.0
11
9.7
5.2
25
8.9
24
23
7.8
23
21
8.1
25
28
13.0
31
27
6o5
Nitrate
NO3
1.0
1.0
51.0
1.0
1.0
23.0
4.0
4.0
18.0
4.0
2.0
1.0
2,0
17.0
3.0
4oO
43.0
1.0
6.0
31.0
1.0
1.0
9.0
1.0
1.0
40.0
Nitrite
NO2
.01
.01
1.4
.01
.01
.67
.09
.10
.30
.10
.01
14.0
.01
.82
.01
.01
.99
.01
.01
.30
.01
.01
.43
.01
.05
.99
Total P
Phosphorus
10.0
10.0
2.0
12.0
10.0
7.9
8.8
8.5
2.7
5ol
5.9
1.0
9.5
4.4
8.8
9.8
1.7
23.0
7.0
2.8
7,8
7.0
5.1
8.8
8.1
4.9
Kjeldahl
Nitrogen
33
-
-
43
31
21.0
38
37
15.0
19
32
6.5
37
-
14.0
160
29
7.8
42
43
12
40
34
15
37
30
7.9
Total P
Soluble
Phosphorus
9.4
10.0
1.7
11.0
10.0
7.8
8.8
7.4
2.2
4.7
5.4
0.8
9.1
3.9
8.8
8.2
1.5
7.9
5.9
1.7
7.2
6.6
5.0
8.8
7.5
4.9
*Results in mg/1
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Routine plant operations analytical work sheets were used
to provide the basic data on sludge volume index, solids
control/ etc. Dosing of the liquid sodium aluminate was
set and maintained at 10 milligrams per liter as Al. The
original time sequence for dosing was four weeks on and
four weeks off. This permitted comparison of plant data
under a wide range of operating conditions. The only
exception to this dosing schedule was near the end of the
study when we extended one dosing period to a full eight
weeks from March 11 to May 5. This was done to minimize
the apparent alumina overlap and to obtain data on longer
operations.
The sodium aluminate was delivered bulk into three 1000-
gallon storage tanks. Details of the chemical feed system
are shown in Figures 1, 2, 5 and 6.
AERATION TANKS
PRIMARY
SETTLING
NORMAL
FEED POINT
FLOW
SIGNAL
7
SECONDARY
CLARIFIERS
Q
-o
MICRO-
STRAINERS
CHLORINE CONTACT
CONTROLLER
ALTERNATE
FEED POINT
MOOOl BULK CHEMICAL
U3AL7 STORAGE TANKS
O BULK DELIVERY
QUICK DISCONNECT
FIGURE 1 - CHEMICAL FEED SCHEMATIC
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FIGURE 2 - CHEMICAL APPLICATION POINT, PRIMARY TANK WEIR TROUGH
The aluminum does not interfere with biological nitrification
or carbon and solids removal. The compounds of alumina are
usually colored white, which accounted for the lighter tan
appearance of the activated sludge observed when dosing with
sodium aluminate.
Because sodium aluminate is an alkaline aluminum salt, its
usage does not contribute sulfates, chlorides, or other
dissolved solids except for a small amount of sodium to the
wastewater treatment plant effluent. Sodium aluminate does
not reduce alkalinity in the waste stream; consequently, it
will not depress the pH (See Figure 20). It is noted that
acid metal salts (such as alum, ferric chloride or ferric
sulfate) use up alkalinity and can depress the pH in a
waste stream that is not sufficiently buffered to absorb
the alkalinity reduction.
Sodium aluminate reduces phosphorus in a wastewater treatment
plant by chemically precipitating soluble phosphorus and
"floe sweeping" this insoluble phosphate down with the floc-
culated colloidal matter and settleable suspended solids. The
chemical reaction of sodium aluminate in phosphorus removal
is as follows:
Na
2 A1204 + 2 P0~3 + 4 H20 = 2 A1P04 + 2 NaOH + 6 OH
_ i
10
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The precipitated aluminum phosphate retains its identity
through aerobic and anaerobic sludge digestion and is not
resolubilized. This will result in a reduction in superna-
tant phosphorus recycle and insure removal of phosphorus
with the digested sludge.
Application data from other activated sludge treatment
plants show the Al:P ratio when using sodium aluminate
for phosphorus removal has varied from 0.5:1 to 2.0:1.
Most applications require an A1:P ratio of about 1.4:1.
In this study, the controlled removal of phosphorus was
of secondary importance. For this reason, no attempt was
made to maintain a specific ratio of sodium aluminate feed
to incoming raw inlet phosphorus levels. Figure 3 demon-
strates, however, that the average phosphorus (as P) removal
while feeding sodium aluminate (S.A.) at Greene County -
Beavercreek Wastewater Treatment Plant was 79.6$. This
compares to removal levels of 41.7$ without sodium aluminate
feed.
_ 15
N.
o>
E 12.5
10
CO
7.5
CO
S 5
o
Si 2>S
o
I 0
lA
§
ON
SA
O
§
05
DATE < MONTH AND DAY
OFF
SA
ON
SA
OFF
SA
OFF
SA
ON
SA
CM
ON
SA
o
§
OFF
SA
o
S
OFF
SA
ON SA - PERIODS OF DOSING
OFFSA - PERIODS OF NO CHEMICAL ADDITIONS
FIGURE 3 - PHOSPHORUS VARIATIONS WITH SODIUM ALUMINATE ADDITIONS
11
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Figure 3 shows a direct comparison of incoming phosphorus
levels to final phosphorus content of the plant effluent.
Incoming raw waste phosphorus levels (as P) range from a
high of 11.0 mg/1 to a low of 4.5 mg/1. Phosphorus levels
in the final range from a high of 7.7 to a low of 3.5
without sodium aluminate feed. Phosphorus levels in the
final plant effluent while feeding sodium aluminate range
from a high of 2.2 mg/1 to a low of 0.8 mg/1.
This activated sludge wastewater treatment plant benefited
greatly from metallic ion addition. The chemical-biological
floe, produced by alumina ion addition/ provided a readily
settleable mixed liquor with the important side benefit of
phosphorus removal. There was also residual benefit
because the mixed liquor stream contained recycled alumina
for some time after the aluminate feed was discontinued.
For purposes of this study, the time period where benefit
was noted following discontinued sodium aluminate feed is
called "alumina overlap."
It is generally accepted that the use of high molecular
weight polymer flocculants can even further increase
the efficiency of metal salts. For the purpose of this
study, though, it was decided to investigate the role of
an aluminum compound alone. In any final design, polymer
flocculant capabilities should be included.
12
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SECTION V
DETAILED DATA ON TREATMENT UNITS
AND DESCRIPTION OF TREATMENT FACILITIES
Detailed plant data and brief descriptions of the treatment
facilities are outlined below. Plant schematic shown on
Figure 4.
The plant is rated to have a nominal capacity of 2.5 million
gal per day (average design flow for a 24-hour period on an
annual basis) and is capable of biologically treating the
wastes from a population equivalent of 25,000 people. It
will hydraulically take peak flows of approximately 2 1/2
times the average flow or 6 million gal per day.
Efficiencies Expected
The treatment plant with all equipment on line will normally
operate at 95% efficiency in the reduction of BOD and sus-
pended solids. Based upon raw wastes of approximately
200 mg/1 of BOD and suspended solids of 240 mg/1 the effluent
will average approximately 10 mg/1 of BOD and 12 mg/1 of
suspended solids.
Utilities
Electric power for the Beavercreek Wastewater Treatment Plant
is furnished by the Dayton Power & Light Company and services
are reliable.
Grit Chamber
Grit removal also provides protection for plant equipment by
removing abrasive material such as sand, stones, cinders or
other heavy inorganic materials. These materials can cause:
(1) wear by abrasion of the mechanical equipment that the
flow comes in contact with, (2) clogging of pipe lines, tanks
and hoppers and, (3) problems with sludge handling and dis-
posal.
These materials, once removed, can be disposed of by using
them as fill or by burying them.
13
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Comminutor
The purpose of a comminutor is to shred debris and rags that,
if not altered, could cause line stoppages, pump clogging
and interference with proper operation of valves.
Screening
Screening in the Beavercreek Wastewater Treatment Plant is
provided as an alternative to comminuting in the event of
mechanical difficulties encountered with the comminutor.
Primary Sedimentation
The purpose of the primary settling tank is to remove the
settleable solids as well as a portion of the BOD. The
settled solids are then pumped as raw sludge to the
aerobic digestion process.
Floatable material in the wastewater flow is also removed
at the outlet end of the primary tanks by hand operated
skimmers. Grease removal is an important step in the
treatment process. These skimmings are disposed of by
burial.
Chemical Additions
As the requirements for removal of nutrients from the waste-
water stream are becoming more stringent, provisions to dose
the waste stream with one of many available chemical coagu-
lants have been added to many wastewater treatment plants.
The Beavercreek plant has the necessary equipment to dose
aluminum salts to the waste stream. This is accomplished
by pumping sodium aluminate into the effluent weir trough
at the primary settling tank. The entire contents of the
aeration tanks then become entrained with the aluminum
coagulants so that, along with removing phosphorus, there
are the additional benefits of improved settling characteris-
tics of the mixed liquor.
Activated Sludge Process
In the activated sludge system, flocculated microbiological
growths are continuously circulated and mixed with organic
wastes in the presence of oxygen. Oxidation and diminution
in the size of the waste particles is accomplished in the
aeration step which is followed by solids/liquid separation.
A portion of the separated solids is returned to the in-
coming waste during the aeration phase to maintain proper
mixed-liquor/suspended-solids concentration. The remainder
of the solids is washed from the system.
14
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The Beavercreek plant also has the flexibility to permit
operation as a reaeration process or a contact stabilization
process, which are modifications of the activated sludge
process.
Secondary Clarification
Like primary clarification, the purpose of secondary clarifi-
cation is to remove solids. The secondary tanks should remove
the flocculent biological solids produced by an aeration
process. These solids are then returned to the point of the
process where it mixes with the settled sewage. This is
bacteria-enriched sludge that becomes excellent "seed"
material when mixed with the settled sewage.
Return Sludge Pumps
Return sludge is the material that settles to the bottom of
the secondary clarifiers. The purpose of return sludge
facilities is to return this sludge to the primary effluent
as well as to "waste" excesses of this material out of the
activated sludge (aeration) system.
Microstrainers (Effluent Screens)
These are drums covered with wire mesh used to retain and
remove suspended or floating solids that can be present in
the effluent from the secondary clarifiers.
Chlorination
The purpose of chlorination at the Beavercreek plant is to
disinfect the effluent. This destroys bacteria which might
be harmful to water supplies, bathing beaches and other
recreational areas. The chlorine contact tank also serves
as an additional tank that provides space to remove any
solids that will settle. A skimming area is also provided
with the chlorine contact tank.
Aerobic Digestion of Sj.udgej3
This process involves the digestion of suspended organic
matter by means of aeration. Aerobic digestion takes place
in the presence of dissolved oxygen. This method alters
organic solids to: (1) effectively control or destroy
agents of disease and infection, (2) decompose organic matter
to relatively stable organic or inorganic compounds, and
(3) reduce the volume of material to be handled.
Land Application of Liquid Sludge
Once the raw and waste activated sludges are fully digested
and stabilized, the -ultimate disposal of the liquid sludge
15
-------
is to apply it to the land. This acceptable and highly
recommended procedure is accomplished by trucking the liquid
sludge to various farm sites where the sludge is applied to
the land. The valuable nutrients and soil conditioning
properties improve the productivity of the land.
Basic Design Data
The following design data is for the total plant; this includes
the original plant as well as recent additions and expansion:
(1) Design Conditions
Design year (originally projected)
Actual design population
Design capacity BOD @ 0.17
Ibs per capita
Design capacity SS @ 0.20
Ibs per capita
Present Population
Design flow per capita
Average design
Maximum design
Wastewater characteristics:
Biochemical Oxygen Demand
- BOD 200 mg/1 =
Suspended Solids - SS 240 mg/1 =
Degree of treatment required:
BOD removal
SS removal
Average Flow
(2) Grit Removal
Type
Physical Removal
Number
Size (@ design flow)
Volume
Capacity
Displacement velocity @ avg flow
Detention time @ avg flow
to 1985
25,000 people
22,500 "
100 gal per capita/day
2.5 million gal/day
6.0 " ««
4170 Ibs per day
5004 Ibs per day
85 - 95%
85 - 95%
2,500,000 gpd
104,167 gph
1736 gpm
28.93 gps
3.86 cfs
constant velocity
buckets with chain drive
one
25.25 x 4.5 x 1.33 ft SWD
(side wall depth)
151 cu ft
1132 gal
.64 fps
39 sec
16
-------
Grit removal bypass:
Type
Physical removal
Number
Size (@ design flow)
Displacement velocity @ avg flow
Detention time @ avg flow
(3) Screening
Type
Number & nominal capacity
Maximum capacity
Alternate:
Type
Physical removal
Size
Construction
Size of openings
Slope
Displacement velocity @ avg flow
@ 1.3 ft SWD
(4) Pumping Raw Wastewater
Type
Number
Driver horsepower
Size
Capacity
(5) Primary Clarification
Number
Size
Volume of the tank
Capacity
Detention time @ design flow
Surface settling rate
Weir length
Weir overflow rate
Surface area weir length ratio
Solids loading (disregarding recycle)
Expected removals from design flow:
Suspended solids
BOD
constant velocity
hand cleaned
1
25.25 x 4.5 x 1.33 ft SWD
0.64 fps
39 sec
comminutor
1 @ 2.5 million gal/day
7.5 million gal/day
bar screen
hand cleaned
3.5 ft wide x 6.25 ft high
1-1/2 x 1/2 inch steel bars
1-1/2 inches
45° angle
0.83 fps
centrifugal
2
125 HP each
14 x 14 x 14-3/4 inches
6250 gpm @ 53 ft of head
54 ft long x 25 ft wide x
13 ft SWD
17,550 cu ft
131,625 gal
1.3 hours
1852 gpd/sq ft
96 ft
36,042 gpd/lin ft
14 sq ft/ft
3.7 Ib/day/sq ft
46%
25%
17
-------
(6) Aeration Tanks
Number
Size
Volume each
Volume total
Capacity each
Capacity total
BOD to aeration
BOD loading
Detention time (@ design)
(7) Air Requirements - Activated Sludge
Aeration tanks
Air required
Blower capacity (7 centrifugal @ 600
cfm ea. - 2 positive displacement
@ 900 cfm ea.)
Total capacity
Air available at design
(8) Return Sludge Pumps
Type
Number
Size
it
Capacity
H
Total capacity (average flow)
(9) Secondary Clarification Tanks
Type
Number
Size
it
Surface area
ii H
Total surface area
Volume
ii
Total volume
Capacity
ii
Total capacity
93 ft long x 24 ft wide x
12.7 ft SWD
28,346 cu ft
113,384 cu ft
212,595 gal
850,380 gal
3127 Ibs/day
27.6 lbs/day/1000 cu ft
8.2 hours
1600 cu ft/lb BOD
3475 cfm
6000 cfm
8,640,000 cu ft/day
2763 cu ft air/lb BOD
centrifugal
2
6 x 11 x 10-1/4 inches
4x3x3 inches
2000 gpm @ 24 ft of head
150 gpm @ 36 ft of head
10% to 175% of 2.5 million
gal per day
circular
2
1 § 90 ft dia x 10 ft SWD
1 @ 50 ft dia x 10 ft SWD
1 @ 6,359 sq ft
1 @ 1,962 sq ft
8,321 sq ft
1 6 63,590 cu ft
1 @ 19,620 cu ft
83,210 cu ft
1 § 476,925 gal
1 <§ 147,150 gal
624,075 gal
18
-------
Detention time (total)
Surface settling rate (@2.5 mgd)
Solids loading - MLSS @ 2500 mg/1
(10) Microstrainers
Type - Drum - continuously cleaned
Number
Size
Surface area
Total surface area
Effective surface area
Total effective surface area
Loading - 1 unit on line @ avg flow
Loading - 2 units on line @ avg flow
(11) Chlorination
Number
Contract chamber size
Volume less baffles
Capacity
Detention time @ design flow
Chlorination capacity
(12) Centrifuges
Number
Type
Mountings
Maximum rpm
Maximum G1s
Bowl capacity
Nominal capacity
Production (@ feed of 50 gpm
with 1% DS)
Thickened sludge
(13) Sludge Digestion
Number
Type
Size (each)
Volume (each)
Volume (total)
Capacity (each)
Capacity (total)
6.0 hr @ 2.5 million gal
per day
300 gal/day/sq ft
6.3 Ib/day/sq ft
10 ft dia x 10 ft long
314 sq ft each
628 sq ft
235 sq ft each
470 sq ft
7.4 gal/sq ft/min
3.7 gal/sq ft/min
41 x 36 ft
9,333 cu ft
70,000 gal
40 min
50 to 1000 Ib/day
solid bowl
vertical
1400
1300
16.0 cu ft
50 gpm
250 dry Ib solids/hr
to digestion
2
aerobic
50 ft dia; 20 ft SWD
39,200 cu ft
78,400 cu ft
294,000 gal
788,000 gal
19
-------
Capacity (cu ft/capita)
Detention time @ 4% sludge
Volatile solids loading
(14) Air Requirements Sludge Digestion
Aerobic Digesters (600 cu ft/lb
volatile solids)
Air required
Blower capacity (positive displacement)
Air capacity
Total air capacity
Air available/capita @ design
Air available @ design
(15) Sludge Pumping
Raw sludge, transfer and digested
sludge (piston type)
Digested sludge, transfer and raw
sludge (975 rpm centrifugal)
Waste activated sludge (vari-speed
centrifugal)
Chlorine contact tank (submersible,
centrifugal)
3.1
74 days
0.03 Ib/cu ft/day
1,605,000 cu ft/day
1115 cfm
5 @ 790 cfm
3950 cfm
5,688,000 cfd
227
2127 cu ft/lb volatile
solids added/day
1 @ 0 to 150 gpm @ 41 ft
head
1 @ 150 gpm @ 36 ft head
2 @ 100 to 400 gpm @ 24 ft
head
1 @ 525 gpm @ 20 ft
head
(16) Chemical Storage
Mild steel tanks
Number
Capacity (each)
Total capacity
(17) Chemical Feed Pump
Positive displacement, vari-speed
Number
Capacity
Land Application of Liquid Sludges
Method
Capacity
1000 gal
3000 gal
0 to 7.5 gph
Tank truck
1 @ 6000 gal
1 @ 1500 gal
20
-------
FIGURE 4 - BEAVERCREEK PLANT WASTEWATER TREATMENT SCHEMATIC FLOW DIAGRAM
-------
Sodium Aluminate Properties
Some shelf life stability difficulties were found in the 26.4%
aluminate product originally fed and the product was changed
to 19.9% midway through the study. Adjustment in chemical feed
rate was made to maintain the same ratio of A1203 to plant
influent.
Technical description of products used are as follows . Product
A was the first material used. It was followed by Product B
halfway through the study.
Product A
Color ............................... clear
Specific gravity at 120° F .......... 1.56
Weight per gallon ................... 13.0 Ibs
C>4 weight percent ............. 42.5
0 weight percent ............... 26.4
Product B
Color ............................... water white to straw
Na20 to A1203 ratio ................. 1.5 to 1.0
Specific gravity at 100° F .......... 1.45 to 1.46
A1203 weight percent ................ 19.9
The product used is supplied commercially and is an alkaline
solution of alumina. It is chemically identified as sodium
aluminate. The viscosity of Product B at 0° F was 14,000 cp,
at 20° F, 2,000 cp; and at 40° F, 280 cp. The pH of the 5%
solution of this liquid sodium aluminate was 12.7.
Principles of Flocculation, Coagulation and Phosphorus Removal
with Sodium Aluminate
Sodium Aluminate is an alkaline metal salt with the chemical
formula Na^A^O/. A common trade name is soda alum. When
dissolved in water, sodium aluminate releases hydroxide
alkalinity and aluminum hydroxide.
Na2Al204 + 4 H2O = 2 A1(OH)3 + 2 NaOH
In wastewater clarification, sodium aluminate functions as
both a flocculant and a coagulant. Its reaction in activated
sludge treatment produces a chemical-biological floe with large
surface area. This permits coagulation of colloidal material
and flocculation of the fine percipitated particles. The
aluminum hydroxide precipitate is tied up in the floe structure
of the biomass.
22
-------
SECTION VI
CHEMICAL FEEDING SYSTEM
The chemical handling and feeding system (Figure 1) has
become an important link in the treatment process at the
Beavercreek Wastewater Treatment Plant. The chemical
system at one time was a major maintenance problem. With
the availability of improved Sodium Aluminate Product B
and much rehabilitation, the chemical feed system has
become a reliable asset to the treatment process. (Figures
1, 5 and 6 graphically indicate vital portions of the
chemical feed system.)
Bulk chemical is delivered to the plant by tank trucks and
is easily unloaded after attaching the hose on the truck to
a 2-inch quick-disconnect coupling. To prevent aeration,
which can cause CO2 absorption and possible destabilization
of NaoAl^C^, chemical is unloaded by a bottom-fill procedure.
Tank inventory is controlled by watching glass sight tubes
mounted on the tanks. Feeding is done by pumping the sodium
aluminate through 2-inch PVC lines to the point of discharge.
The pumping is done by a Milton-Roy diaphragm pump that is
proportioned to the incoming wastewater flow by a flow meter
signal from a Foxboro magnetic flow meter through a Foxboro
transmitting signal converter.
Experience 'has shown that at the Beavercreek plant the most
reliable feeding point is at the discharge of the primary
sedimentation tank. The product is dosed undiluted (neat).
Since the ultimate objective is to dose the mixed liquor
inventory, there is no significant benefit in adding dilution
water to the chemical. The chemical feed pump is a positive
displacement type with capacities from 0 to 7.5 GPH.
23
-------
FIGURE 5 - CHEMICAL FEED PUMP
FIGURE 6 - BULK CHEMICAL STORAGE TANKS
24
-------
SECTION VII
GENERAL DESCRIPTION - ACTIVATED SLUDGE PROCESS
Activated Sludge
The activated sludge process is used to convert nonsettleable
substances and the finely divided, colloidal and dissolved
solids into settleable sludge and to remove this newly formed
sludge. The first phase is accomplished in the aeration tanks
(Figures 8 and 9), the second in the secondary clarifier
(Figure 7).
FIGURE 7 - SECONDARY CLARIFIER
25
-------
FIGURE 8 - AERATION TANK OVERFLOW WEIR
FIGURE 9 - AERATION TANK
26
-------
The process depends on groups of microorganisms, i.e. bacteria
and protozoa, that are nourished by the organic portion of
wastewater solids. These microorganisms are provided with
the proper environment in which they not only live, but also
reproduce. The environment must be aerobic. After this, the
activated sludge must be separated from the treated wastewater
by sedimentation.
Secondary Clarification
Sedimentation efficiency depends on the weight and density
of the sludge developed and the flocculent nature of the
biomass. Absorption of oxygen and food by the microorganisms
is an important function in the removal of organic material
from the wastewater.
Basic requirements for a successful system are: (a) the
activated sludge must contain sufficient numbers of purifying
organisms; (b) dissolved oxygen must be present in sufficient
amounts in the aeration tanks at all times; (c) the activated
sludge (mixed liquor) must separate readily from the treated
wastewater in the secondary clarifier; (d) the loading and
sludge age should be controlled to maintain a well settled.
biomass.
Return Sludge
In the activated sludge process, untreated wastewater flows
into an aeration tank where it is immediately mixed with
activated sludge (return sludge). The mixing must be complete.
The retention time in the aeration basin must be adequate to
effect purification. Dissolved oxygen must always be present.
The activated sludge is withdrawn from the secondary clarifier
and a portion of the settled activated sludge (returned sludge)
is pumped back to the start of the process. This supplies
necessary microorganisms to aid in the treatment of additional
wastewater flow.
Waste Activated Sludge
The activated sludge is constantly increasing in quantity as
it removes organic material from the waste water and as the
microorganisms continue to grow. It is vital that excess
quantities of mixed liquor suspended solids be removed
from the system. The sludge so removed is termed "waste
activated sludge."
27
-------
SECTION VIII
EFFECT OF SODIUM ALUMINATE FEED ON SOLIDS AND SOLIDS HANDLING
The overall goal of this study was to demonstrate the effect
of alumina chemical dosing on wastewater solids and control
of the resultant solids. To demonstrate the changes that
took place in the plant, we selected three indicators normally
monitored in waste activated sludge operations. These process
barometers are as follows:
Percent Volume Mixed Liquor - 1/2 Hour Settling
This test method is described fully in standard methods.
An abbreviated description of the test is the filling of
a 1000-ml graduated cylinder with mixed liquor. This is
allowed to settle for 30 minutes and the amount of sludge
settled in this time is reported as percent volume mixed
liquor.
This test defines how fast the mixed liquor solids settle-,
as well as the compaction rate. The plant personnel also
visually observe the sample as it is drawn into the cylinder
for the size of the floe. Experience has shown that the con-
ditioning of the floe, and floe size, are important in sweeping
down smaller particles as the floe settles. This test result
provides not only a number but an observable condition of
settleability. With chemical feed, you can easily see if
you have the floe correctly conditioned for settling, with
alumina conditioning, you will notice a slight color change
from the conventional brown to a lighter tan.
The cross section of the cylinder stimulates the cross
sectional area of the secondary clarifier. If the sludge
does not settle in the cylinder test, you know it will not
settle in the secondary clarifier and you can expect solids
to carry over the clarifier weir.
Mixed Liquor Suspended Solids
This test method measures the amount of suspended solids
in the mixed liquor. The sample is filtered through a
weighed Gooch crucible - or filter paper, oven dried at
103° C and the gain in weight reported as mixed liquor
suspended solids.
28
-------
This sample is collected at the end of the aeration basin
(Figures 8 and 9), ahead of the secondary clarifier (Figure
7), and determines the amount of suspended matter to be
settled in the secondary clarifier. This plant attempts
to control the MLSS at 2200 - 2600 mg/1. Increased wasting
of secondary sludge will reduce the MLSS. The MLSS is
basically composed of biological floe. A control range of
2200 - 2600 for this plant provides optimum solids for
aeration and makes available the desired sludge age. This
concentraction of MLSS leaving the aeration basin must then
settle in the secondary clarifier. The control range of
2200 - 2600 mg/1, based on plant operating experiences,
provides the best solids concentration for settling and
clarifier effluent quality.
Sludge Volume Index (SVI)
The sludge volume index is a relationship calculated from
data obtained in the test for settled mixed liquor solids
and milligrams per liter of suspended solids to mixed
liquor.
Efficient activated sludge operation generally depends
on maintenance of the sludge volume index at a number of
100 or less, for a good settling sludge. A high SVI value
indicates poor settling characteristics.
We use the SVI as another indicator of how well the volume
of sludge produced in the plant would settle in the secondary
clarifier. For example, a condition of MLSS at 2400 mg/1 could
produce the following percent volume mixed liquor 1/2-hour
settleability: 60%, 30%, 15%. The sludge volume index in
these cases would be 272, 136, and 68, respectively. The
better and faster the sludge settling in the secondary
clarifier, the less chance you will have of solids carryout
over the weir. Also, the more concentrated the sludge in
the secondary clarifier, the less volume needed to recycle
back as return activated sludge.
Results on SVI, percent MLSS volume 1/2-hour sedimentation
and solids in mixed liquor are shown in Figures 11, 12
and 13.
29
-------
Figure 10 is a plot of time (43 weeks) against the SVI. The
plot point in each case for the SVI is the composite average
of the readings for that particular week. The times when
sodium aluminate was fed are identified on the horizontal
axis by the words "on SA."
You can see in this curve the effect of sodium aluminate feed
on the SVI. Starting from the first plot point, the SVI
remained low. Stopping the feed of SA at the 4th week resulted
in an upward increase of SVI. Starting the sodium aluminate
feed again at the 8th week resulted in a downward trend of a
rising curve index. This desirable index was lost again when
sodium aluminate feed was stopped at the 12th week. The upward
curve increased until the SVI reached 230. On their own
initiative, the operators started the sodium aluminate chemical
feed into the system to reestablish SVI control.
300
50
10
15
20 * 25 * * 30
TIME IN WEEKS
35
40
. ON SA
ONSA
, ON SA
ON SA
FIGURE 10 - SLUDGE VOLUME INDEX
30
-------
This cycle repeats again with each starting and stopping of
the aluminate feed. Control throughout the full 8-week
sodium aluminate injection time period (between the 23rd week
and 31st week of the study) was excellent. The curve trend
again starts upward at the conclusion of this last feeding
period on sodium aluminate. During the 8-week period without
dosing the sodium aluminate, the SVI reached intolerable levels
on the 160 to 250 SVI range. Note on the curve a time after
sodium aluminate feed is stopped but before the upward SVI
trend starts. We call this time period "alumina overlap."
It is a condition we describe where alumina is still present
in the system because of residual in the mixed liquor.
Mathematically/ the average difference between the sodium
aluminate addition periods was a 25% lower SVI during sodium
aluminate feed. More typically, however, allowing for
alumina overlap, the median SVI while on sodium aluminate
would be 86. Not feeding the sodium aluminate, the median
SVI would be 146. Figure 11 is a part of the 43-week time
period, as in Figure 10, against the percent volume mixed
liquor 1/2 hour settling.
You can see this curve closely parallels the Figure 10 curve
on SVI. Again, the impact on the settleable solids is readily
noted during the chemical dosing periods on sodium aluminate.
The "alumina overlap" is noted at the end of each sodium
aluminate chemical feed period.
Typically, (Figure 11, as related to Figure 10) when sodium
aluminate was being fed the 1/2-hour percent volume mixed
liquor settling rates were in the 10 to 20% range. Most
"alumina overlap" periods were in the 20 to 30% range and
extended no-feed periods resulted in a poor quality, 40 to
60% 1/2-hour settleability.
31
-------
o
z
tu
O
X
60
50
O
< 40
Z.
O
bJ
2
tn
tn
30
20
s '°
o
LJ
Q.
e
o
o
-I 1 1 1 1 1 1 1 1
' 5 * ' * ' 10 '
» tf * rt/\
15
' '20' ' ' '25*
TIME IN WEEKS
'30* ' '35' * ' '40' ' ' '45
1 QNSA | I ON SA I I ON SA I \ ON SA I
FIGURE 11 - PERCENT MLSS VOLUME ONE HALF
HOUR SEDIMENTATION
32
-------
Settleable Solids
Figure 12 is added to show the solids in mixed liquor, weekly
averages, plotted against the 43-week study period.
E
i
CC
o
o
UJ
x
O
CO
UJ
Ul
Q.
CO
CO
3200
3000
2800
2600
2400
2200
2000
1600
1600
1400
1200
1000
800
O
O
o
o
o
e
10
in
20 * 25 30
TIME IN WEEKS
35
40* -45
I ON SA l
1 ON SA
I ON SA I
1 ON SA I
FIGURE 12 - SOLIDS IN MIXED LIQUOR mg/1
It is noted that the solids in the mixed liquor remain
fairly constant between 2000 and 2400 throughout the test
program. This indicates that the solids in the mixed liquor
were not a significant variable on the SVI. it demonstrates
that the major impact on the settleability of the mixed
liquor solids came from sodium aluminate feed.
33
-------
Return Sludge
Figure 13, return sludge suspended solids in milligrams per
liter, points out that the daily return sludge suspended solids
were kept at a median level in the 5500 to 7500 mg/1 range.
This indicates a consistent ability to waste sufficient mixed
liquor solids for smooth operation. It is also noted that
during the 7th and 8th weeks, without sodium aluminate feed,
mixed liquor suspended solids were difficult to thicken.
_ 12,500-
. ON SA j
. . IQ . . . . 15. . . . 20* 25 30 *35* *40* '45
TIME IN WEEKS
. ON SA . .ON SA . . ON SA i
FIGURE 13 - RETURN SLUDGE SS mg/1
During the 27th and 28th weeks of the trial, which was the
middle of the 8-week feed period, attempts were made to
reduce the volume of returned sludge pumped daily. This
resulted in ability to concentrate the returned sludge
solids to levels in the 10,000 to 12,600 mg/1 range.
34
-------
No detriment to the secondary clarifier effluent was
evidenced by increasing levels of solids in the secondary
clarifiers at that time. Without more process control
equipment to positively control return sludge thickness
and volume, it was difficult to control solids concentrations
as effectively as desired.
Waste Activated Sludge
It became operational practice, however, to allow a sludge
blanket to develop in the secondary clarifier at time of
wasting of activated sludge. This was accomplished by
shutting off the return sludge pump until the sludge blanket
increased to 3 - 4 feet. Waste activated sludge suspended
solids of 1% to 1.5% could always be expected when this
procedure was followed while dosing sodium aluminate to
the flow stream.
This procedure was also tried without sodium aluminate in
the system, and floe carryover was always evident before the
sludge blanket could be removed from the secondary clarifier,
once the blanket approached the 3 to 4 foot range.
Dissolved Oxygen
Dissolved oxygen control at the Beavercreek Wastewater Treat-
ment Plant is validated by Figure 14. Assurance of an
aerobic environment in the aeration tank is vital to the
activated sludge process. Figure 14 indicates that the
effluent of the aeration system always contained a minimum
of 1.5 mg/1 of dissolved oxygen. On two of the cumulative
weekly averages dissolved oxygen levels of 4.8 to 5.2 mg/1
were reached.
The important trend that Figure 14 establishes is that the
DO's were in the range of 1.5 to 4.0 mg/1. These guidelines
are a basic criteria to the Beavercreek Wastewater Treatment
Plant operation.
35
-------
E 6.0
a:
o
O
UJ
X
z
I
UJ
(9
>-
X
o
o
UJ
5.0
4.0
3.0
2.0
1.0
i ON SA i
10
i ON SA i
15* * * * 20 25 * * 30
TIME IN WEEKS
i ON SA t . ON SA i
35
40
45
FIGURE 14 - MIXED LIQUOR DISSOLVED OXYGEN
Plant Flow
The plant flow during the study is shown in Figure 15. Each
plot point on the graph represents the average for each week
of the study.
Plant flow ranged from a low weekly average of 1.715 million
gal/day to a high of 4.098 million gal/day. Short-term flow
exceeded 5.5 million gal/day. Figure 15 points out that the
flows were near the 2.5 million gal/day design capacity of the
Beavercreek plant. Higher flows than 2.5 million gal/day
were attributed to infiltration in the collection system
as a result of rainfall. It is noted that the peak flows
came by coincidence at the times sodium aluminate was being
fed. These times were during the 9th, 16th, 17th, 27th
and 28th weeks of the study. Of importance is that, with
these peak flows, the plant did not have the expected sludge
upset of "solids washout." The reason offered here is that
36
-------
the sodium aluminate increases floe density, thus keeping
the sludge down in the secondary clarifier. Sodium aluminate
demonstrated its ability to coagulate and flocculate solids,
thus adding weight to the MLSS. A more compact sludge in
the secondary clarifier resulted from sodium aluminate feed.
This treated sludge stayed down at much higher flows than
plant design.
o
e>
*
i
o
CL
4.0
3.0
2.0
t.O
i ON SAi
10
ON SA
15 * * ' * 20 * * * 25 30'
TIME IN WEEKS
35
40
45
i ON SA i
i ON SA i
FIGURE 15 - PLANT FLOW MILLION GAL/DAY
Case Histories
The following are two case histories of the advantages of
having a coagulant aid in the mixed liquor flow stream when
the Beavercreek Wastewater Treatment Plant or similar waste-
water treatment plants are surcharged with excessive wet
weather (storm) flows. Both cases occurred in the spring-
of 1974: April 1, 1974 and June 22, 1974.
37
-------
The following circumstances describe the events involved.
The Beavercreek Plant is operated in a mode so that the raw
wastewater influent control gate is set to allow a maximum
wet weather flow rate into the plant of 5.0 million gal/day
or twice the design flow of the plant. It has been determined
that this much flow can be handled although somewhat less
effectively than "normal" high flow rates of 3.0 to 3.5 million
gal/day. Previous to both dates involved, it had been
necessary to perform maintenance on the grit removal equipment
which altered the inlet ga,te position and the gate can only
be reset by trial and error adjustments at higher flows.
Other factors in the sequence of events that led to the
surcharge comparisons were:
1. Several days of mild rainfall preceding the surcharge.
2. A concentrated rainfall of one inch or more over a
short period of time (1-2 hours).
3. Both surcharges occurred at night when the treatment
plant is not manned.
On April 1, 1974 the plant was checked by the Wastewater
Superintendent at 11:45 P.M. after several lift station
problems were corrected. An intense storm caused power
outages and one inch of rain in less than two hours. The
flow meter indicated that excessive flows had occurred for
approximately five hours. The flow meter was pegged at a
5.5 million gal/day rate. Pumping rates were so high that
raw wastewater was overflowing the primary clarifier.
Flows were estimated to exceed 12 million gal/day rates.
Sodium aluminate was being dosed to the flow at that time.
The control gate was throttled back to an actual 5.0 million
gal/day rate. Although the secondary clarifiers were slightly
turbid in appearance at this time, there was no evidence of
loss of mixed liquor blankets. This observation was sub-
stantiated the following day when the plant laboratory
determined that the MLSS concentration had increased from
2098 mg/1 to 2847 mg/1. This indicated that not only had
the 15,231 Ibs of MLSS been retained but solids capture of
an additional 5394 Ibs of solids washed in with the storm
flow had been accomplished. It is believed that the pre-
ceding experience points out that much benefit was realized
by having the sodium aluminate in the flow stream.
38
-------
On June 22, 1974, after several previous days of rain, the
Beavercreek area was deluged with a one-inch rain storm.
Even though several adjustments of the inlet gate had been
made to control the quantity of influent to the Beavercreek
Plant, the flow once again increased to the point that the
flow meter was pegged at 5.5 million gal/day and it was
estimated at this time that the flow peaked at 7 to 8
million gal/day or three times the design flow. This
situation existed for approximately 4 hours before the
pumps overcame the surcharge and reduced the flow to the
4.5 million gal/day range. When the operator arrived the
following morning, it was noted that no mixed liquor solids
were visible in the aeration system. The laboratory analysis
showed that the MLSS had been reduced from 2400 mg/1 to 826
mg/1 due to the surcharge flows. This "wash out" represented
a mixed liquor solids loss of 11,427 pounds. Assuming that
an additional 5,300 pounds of suspended solids were contributed
by the high flows, it is easy to arrive at a total of 16,727
pounds of suspended solids that were lost.
The conclusion is therefore drawn that sodium aluminate
not only enhances normal operations but also protects
small and medium-sized operations from high flow wash-out
problems. In many cases wet weather by-passes can be
entirely avoided if a coagulant is being dosed to the
flow stream.
Temperature of Raw Sewage
Figure 16 shows the weekly averages of the temperature of
the plant influent. Raw sewage temperatures ranged from
a high of 63° F to a low of 51° F during the study.
Waste stream temperatures in a waste activated sludge
plant have an important effect on plant operations. With-
out provision for temperature adjustment, the efficiency
of plant operations typically is at the mercy of the
elements. Biological activity decreases as the temperature
falls. Referring to Figure 11, it is noted that when the
raw wastewater temperature was at its lowest point, the
1/2 hour mixed liquor settling test shows sludge compaction
above 80% while feeding sodium aluminate.
39
-------
u.
o
tlJ
o
70°
60°
tu
»
CL
U.
O
u 50°
oc
UJ
CL
2
ON SA
. 10 - 15 20 * 25 * * 30
TIME IN WEEKS
ON SA| i ON SA i t ON SA i
35
40-
'45
FIGURE 16 - TEMPERATURE OF RAW SEWAGE
Secondary Clarifier Suspended Solids
Figure 17 demonstrates the impact of sodium aluminate on
suspended solids in the effluent of the secondary clarifier.
It is noted that the lowest levels of suspended solids
present in the effluent are during, or immediately following,
sodium aluminate feed. Only during sodium aluminate feed
do the levels of suspended solids drop to 5 mg/1 or less in
the clarifier effluent. The resultant decrease of suspended
solids while feeding sodium aluminate improved the perfor-
mance of the tertiary microstrainers.
NOTE: On, or shortly after sodium aluminate feed,
is the only time the final suspended solids drop
to 5 mg/1 or below.
40
-------
01
fc
(0
a
a
L.
(J
a
n
to
40
30
10
, ON SA ,
10
, ON SA
H I
15 * ' ' '20'
TIME
,ON SA ,
25 ' * *
IN WEEKS
i ON SA
30*
35
40
FIGURE 17 SECONDARY CLARIFIER, SUSPENDED SOLIDS mg/1
Beavercreek Wastewater Treatment Plant utilizes microstrainers
(Figure 18) for polishing of the secondary clarifier effluent.
During the time of this study, the microstrainer operation was
intermittent due to start-up and mechanical difficulties. It
was observed that when the microstrainers were operational,
charging them with secondary clarifier effluent not treated
with sodium aluminate resulted in an overloaded solids condition.
FIGURE 18 - MICROSTRAINERS
41
-------
This overload could be a result of solids contributed
either as suspended or in a colloidal form. The net
result would be a greater differential across the screens
because the nature and quantity of the suspended solids
would blind the screen media. This caused the microstrainer
drum to speed up as a means of adjusting solids removal rate
When the drum reaches maximum speed and the differential
still exists, a portion of the flow to the microstrainers
is automatically by-passed.
It was not within the scope of this study to evaluate
tertiary devices with regard to removal of suspended solids.
However, we offer the idea that chemical coagulation is a
necessary prerequisite to efficient operation of physical
tertiary devices for reduction of suspended solids. In
our experience, chemical coagulation to resolve colloidal
solids prior to the microstrainer application is a necessity
at Beavercreek Wastewater Treatment Plant.
Secondary Clarifier BOD
The secondary clarifier BOD5 (Figure 19) indicates that
the BOD effluent from the secondary clarifier was generally
in a range of 8 to 18 mg/1. The Beavercreek Wastewater
Treatment Plant is no different from most other wastewater
treatment plants in that various upsets of the biological
process must be dealt with and sludge characteristics will
be uncertain. It is therefore desirable to make the
treatment process more reliable. It is felt that this is
accomplished at the Beavercreek Wastewater Treatment Plant
when dosing the flow stream with sodium aluminate.
Figure 19 points out the upward trend of the secondary
clarifier effluent BOD in the 22nd and 23rd weeks of the
study when sodium aluminate was not being dosed. The most
graphic example, however, was in the 41st, 42nd and 43rd
(Figure 19) weeks of the study when the sodium aluminate
dosing had been discontinued for 10 weeks and secondary
effluent BOD escalated to the high 20's and 30's.
42
-------
30 r
E
f
o
o
BD
20
15
ON SA
10
i ON SA
20 25 * * '
TIME IN WEEKS
30-
35
40-
, ON SA ,
ON SA
FIGURE 19 - SECONDARY CLARIFIER BOD5
The significant point that we wish to convey is that it
is possible to operate wastewater treatment plants efficiently
without coagulants a certain portion of the time. The long-
term operation of a secondary treatment plant with effluent
BOD and SS in the 10 - 20 mg/1 range, sludge volume indexes
always below 100 and stabilized mixed liquor masses is difficult
to ensure without some type of coagulant addition.
It is the desire of the authors of this study that the
information will be valuable to those entities that need
a practical alternative to meet the newly-applied National
Pollutant Discharge Elimination System regulations. Also we
wish to provide information that could be helpful in optimizing
existing tertiary operations.
43
-------
RAW
FINAL
to
H
Z
X
a.
8.0
7.8
7.6
7.4
7.2
7.0
I
i ON SAt
10 15 20 25
TIME IN WEEKS
i ON SA i i ON SA i t ON SA
30
35
FIGURE 20 - RAW AND FINAL WASTEWATER pH
Overall Plant Performance
Figure 20 indicates that pH values at the Beavercreek
Wastewater Treatment Plant are always in an acceptable range
for a treatable raw wastewater and a good quality effluent.
The raw wastewater and final effluent varied between the pH
values of 7.1 and 7.8; therefore, caustic or acid balancing
agents are not required.
The raw wastewater, other than having treatable temperature
and pH values, also possessed expected domestic wastewater
characteristics.
There are the normally expected changes in BOD^ as Figure
21 shows .
44
-------
300.
250 _
I
QN SA
10
QN SA I
15 20
TIME
i ON SAi
25 30
IN WEEKS
t ON SA
35
40
45
FIGURE 21 - RAW WASTEWATER BOD,
The curve drawn through Figure 22 indicates that the raw
wastewater BOD can be expected to be in a range of 160 to
180 mg/1. The only requirements necessary to adjust for
the peaks and valleys of Figure 22 are to make air adjustments
in the aeration tanks and waste excess activated sludge as
required.
45
-------
250
200
,150
o
o
CO
>- 100
-------
95 ,-£
090
ui
a:
LJ
S
8 5
8 0
666 66 6
6 66 6
. * 66
1
1
1
10
15 20 25 30
TIME IN WEEKS
35
40
FIGURE 23 - PERCENT BOD REMOVAL
Figures 24 and 25 trace the plant performance characteristics
through the nitrogen cycle. The average ammonia reductions
(Figure 24) were 61.6 percent during the study.
40
30
z
«9_
V)
20
< 10
O
ui CM o co £ tf>
I § § ^ S S
TIME, MONTH AND DATE
ON OFF ON ON OFF ON
SA SA SA SA SA SA
-------
Nitrification was always achieved as Figure 25 also points
out. Nitrate nitrogen (Figure 25) shows that the secondary
clarifier NO-.-N varied between 0.9 and 45 mg/1. Nitrification
could be accomplished at all times with the degree of nitri-
fication depending on length of aeration time as well as
dissolved oxygen available.
The sodium aluminate additions have no apparent effect on
either the ammonia reduction or nitrification.
6.
Kl
O
Z
CO
LJ
O
O
CC
|JU
a:
z
45_
40
35
30
25
20
15
10
5
* 1
5
i ON SA |
1
10
, ON SA f
\
15
J
20
TIME IN
1
25
WEEKS
ON SA
1
30
1
35
1
40
FINAL EFFLUENT
FIGURE 25 - ANALYSIS OF NITRATE NITROGEN,
Aerobic Sludge Digestion
The Beavercreek Wastewater Treatment Plant has two aerobic
sludge digesters (Figure 26). The addition of sodium aluminate
has been helpful in the aerobic digestion process.
Previous to alumina additions to the plant flow, it was impossible
to produce any quantity of low solids and low BOD supernatant.
It was found that once the mixed liquor became entrained with
the sodium aluminate the waste-activated sludge carried alumina
with it to the aerobic digesters and significant benefits to
the operation occurred.
48
-------
FIGURE 26 - AEROBIC DIGESTION IN SERVICE
The first observation was that high volumes of good quality
supernatant became available after initiating sodium
aluminate feed. Figures 27, 28 and 29 show that exceptional
quantities of low BOD, low suspended solids supernatant
were withdrawn from the sludge digestion tanks.
1C
UJ
fi
Z
o
d
5
H-
Z
<
<
Z
-------
90
^ 80
o>
E 70
m 60
o
"
o
LJ
o 30
S 20
in
% 10
I
1
I
10-73 11-73 12-73
1-74 2-74 3-74 474
TIME, MONTH AND YEAR
AEROBIC DIGESTION
5-74 6-74
7-74
o
CD
FIGURE 28 - SUPERNATANT SS mg/1
100
90
80
70
60
50
40
30
20
/\
J I L
2 N -
J-J
TIME, MONTH AND YEAR
AEROBIC DIGESTION
FIGURE 29 - SUPERNATANT BOD mg/1
50
-------
On a monthly basis, Figure 27 points out that supernatant
quantities of 230,000 to 870,000 gallons were drawn. Lower
volumes were drawn when carrying low liquid levels in the
digesters. Colder temperatures of the digester contents
resulted in poorer settling characteristics - and fewer
gallons of supernatant drawn. Figures 28 and 29 illustrate
that supernatant SS and BOD quality were exceptionally good.
Supernatant SS (Figure 28) ranged from 18 to 81 mg/1.
Supernatant BOD (Figure 29) ranged from 23 to 92 mg/1.
The limiting factor on the amount of supernatant to be drawn
soon became the physical depth draw-off limitations of the
digesters. The next benefit that followed the ability to
draw supernatant was the thickening of the digested sludge,
which ultimately resulted in fewer gallons of digested
sludge to be transported for disposal. Since it is within
the framework of the Beavercreek Wastewater Treatment Plant
and the Greene County Sanitary Engineering Department policy
to consider well-digested sludge as a resource, all digested
sludge is ultimately applied to the land (Figure 30) in
Greene County to be utilized for its soil conditioning
ability. Therefore, the ability to haul fewer gallons of
sludge becomes important to the plant process as well as
reducing the operating costs of the wastewater treatment
plant.
FIGURE 30 - TRUCK FOR HAULING SLUDGE
51
-------
Several alumina analyses were run on the digested sludge.
Concentrations of Al^C^ varied from 0.2 mg/1 to 650 mg/1.
The ability to compact the digested sludge remained as there
was always alumina available in the digested sludge even
though extended no-dose periods were involved. Having
digested sludges of 2% dry solids or greater, resulted in
lower overall hauling costs of the digested sludge because
of fewer gallons to haul to farm land.
Figures 31 through 34 show that the quality of the digested
sludge was excellent. The pH was in the range of 7.0 to 7.3,
volatile solids between 47 and 58%, and volatile reductions
between 47.3 and 65.3%. These are all considered excellent
guidelines for a good quality digested sludge.
9.0 _
8.0
in
2
7.0
X
a.
6.0
_L
_L
J_
10-73
11-73
12-73
1-74
2-74
3-74
4-74
5-74
6-74
7-74
TIME , MONTH AND YEAR
AEROBIC ALLY DIGESTED SLUDGE
FIGURE 31 - DIGESTED SLUDGE pH
52
-------
3.0_
2-0
O
en
DC
O
1.0
10-73 11-73 12-73
1-74 2-74 3-74 4-74
TIME , MONTH AND YEAR
5-74 6-74 7-74
FIGURE 32 - DIGESTED SLUDGE - PERCENT DRY SOLIDS
53
-------
70
Q
o
UJ
60
50
UJ
£40
ui
Q.
301I
I
I
I
I
10-73 11-73 12-73 1-74 2-74 3-74 4-74 5-74 6-74 7-74
TIME: MONTH AND YEAR
FIGURE 33 - DIGESTED SLUDGE - PERCENT VOLATILE SOLIDS
10-73 ttTZ 12-73
1-74 2-74 3-74 4-74 5-74
TIME , MONTH AND YEAR
6-74 7-7*
FIGURE 34 - DIGESTED SLUDGE - PERCENT VOLATILE REDUCTION
54
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TABLE 3 - SUMMARY OF DIGESTED SLUDGE DATA FROM
GREENE COUNTY BEAVERCREEK WASTEWATER TREATMENT PLANT*
Lab
TKN
NH3,N
N02,N
N03/N
K
P - Total
P - Sol.
Mg
Mn
Al - Sol. & insol.
Fe - Sol. & insol.
Na
Cl
SO3
Cu
Pb
% Dry Solids
% Volatile Solids
PH
BOD
Temp. - °C
* Results in mg/1
N.A. - Not Analyzed
10-25-73
N.A.
380
0.1
1.0
69
510
25
688
N.A.
400
180
NoA.
609
N.A.
N.A.
N.A.
1.43
52
7.3
3600
22
2-8-74
N.A.
530
N.A.
N.A.
290
840
63
1330
N.A.
650
100
N.A.
359
N.A.
N.A.
N.A.
2.69
54
7.4
5000
12
6-27-74
Primary
Diqester
1210
25.3
0.1
1.0
16.5
330
103
77
1.0
19
N.A.
190
N.A.
250
03
.5
1.63
58
6.8
N.A.
28
6-27-74
Secondary
Diqester
730
26.4
0.1
1.0
17.0
330
107
87
1.2
23
N.A.
190
N.A.
200
.4
.5
1.44
56
7.2
N= A.
29
55
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Table 3 indicates the many desirable characteristics of the
aerobically digested sludge at the Beavercreek Wastewater
Plant. The "big three," nitrogen, phosphorus and potassium
(potash), are in abundant supply. The rationale for
considering this digested sludge as a valuable resource for
land disposal is discussed briefly as follows:
Nitrogen - Without nitrogen, plants will be yellowish rather
than green. They will be unexpectedly small and sickly.
The plants will be yellow because the lack of nitrogen keeps
the chlorophyll from being formed. Nitrogen is a part of
the material in plant cells. Without nitrogen, plant cells
will not be healthy. They are unable to make chlorophyll
that will provide the food for the plant.
Phosphorus - Phosphorus plays an important part in the
younger, rapidly growing plant material. Without the
element phosphorus, a plant does not make the right food
chemicals for itself. Again the plant will be small. The
plant will/ however, be a very dark green. The supply of
nitrogen in the plant food builds up because it does not
get used as it should.
Potassj-um (Potash) - Potassium is needed in the root tips
and in the growing tip of the stem. Potassium, like
phosphorus, is needed for healthy growing plant material.
Plants without potassium have spotted leaves and the edges
of the leaves turn brown. The oldest leaves will turn
brown first. Potassium is also important in forming the
flower and, therefore, the fruit of the plant.
At the Beavercreek Wastewater Treatment Plant the final
operation in the solids-handling section of the plant is
the land application of liquid sludge. There is no other
single portion of the operation as important as the
liquid sludge hauling for land application.
Utilizing land application of the liquid sludge first
depends on the quality of the sludge. Correctly digested,
the sludge does not carry offensive odors, pathogens or other
negative characteristics. The next step in making privately-
owned land available for sludge utilization is selling the
fact that the sludge is a valuable resource to the land owner.
The last consideration is the proximity to the waste treat-
ment facility of land suitable for liquid sludge assimilation.
The application of sodium aluminate to the mixed liquor improved
the aerobic digestion process and enhanced Greene County's
approach to the consideration of digested sludge as a valuable
natural resource.
56
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Advantages Accompanying a. Chemical Feed System
Most advantages of a chemical feed system are to be found in
the net results of the efficiency of the wastewater treatment
plant. Encouraging operators to observe any changes due to
chemical additions, usually results in a keener awareness
of the fine points of the operation. MLSS concentrations
become more closely watched. Sludge volume index changes/
and controls over wasting activated sludge are closely
scrutinized by all concerned personnel. Reliability of the
operation is greatly improved. For treatment plants unable
to provide 24-hour a day seven day per week coverage, the
addition of sodium aluminate to the mixed liquor serves
an important purpose. The frequent adjustments of return
sludge rates are not as necessary with a "weighted" mixed
liquor mass. Manpower requirements for physical cleaning of
chlorine contact tanks are reduced when fewer solids escape
the secondary clarifier due to sodium aluminate additions.
Actual chlorine requirements were also reduced by 50% when
fewer biological solids escaped the secondary clarifier, making
the "kill" requirement for disinfection lower.
Plant. Personnel
In order to implement a new operational procedure or to
modify an existing operational procedure, total cooperation
from operating personnel must be developed, it becomes
difficult to make recommendations concerning personnel
without first knowing the organization. It was our experience
that implementing the improved liquid-solids separation with
an aluminum compound in an activated sludge wastewater treat-
ment plant study was possible.
Requirements Accompanying a_ Chemical Feed System
Adequate time must be devoted to assigning various respon-
sibilities of the operating procedure. Collection and
processing of data should be as expedient as possible.
Maintenance and operation of the chemical feeding system
in the case of a chemical feeding operation is essential.
It is believed that all factors must be considered as there
are definite liabilities and assets to a chemical feeding
system. Consideration must be given to capital costs of
the system. Chemicals and freight add expense to the
operation. Safety of personnel handling chemicals must be
considered, added personnel time to operate and maintain
the chemical feeding system is required and the need for
additional analysis will increase the load on the laboratory.
57
-------
Not to be overlooked also is additional administrative and
supervisory time for purchasing of chemicals, training
personnel and processing adequate records.
In summary we would conclude that adaptation of small
wastewater treatment plants to a chemical feed system is
feasible. The total situation should be thoroughly
evaluated. The benefit of having the ever-present
"operator" (sodium aluminate) to improve the operation
is considered a cost-effective investment at Greene County's
Beavercreek Wastewater Treatment Plant.
Since the sodium aluminate study has been completed,
Greene County has decided to dose sodium aluminate to the
flow stream on a regular, continuous basis without
interruptions in order to comply with NPDES requirements.
58
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SECTION IX
BIBLIOGRAPHY
Grant 17030 EBH
1. "Operation of Wastewater Treatment Plants," WPCF
Manual of Practice No. 11 (1970).
2. "Sewage Treatment Practices," Water and Sewage Works
Magazine, Scranton Gillette.
3. "Sewage Treatment," 2nd Edition, Imhoff and Fair
(1966), John Wiley & Sons, New York, N. Y.
4. "Applied Chemistry of Wastewater Treatment," Mancy,
McClelland, Pohland, Ann Arbor Science, Ann Arbor,
Michigan.
5. "Standard Methods for the Examination of Water and
Wastewater," Thirteenth Edition (1971), APHA, AWWA,
WPCF.
6. "Manual for Sewage Plant Operators," Texas Water
and Sewage Works Assoc., (1955) Austin, Texas.
7. Technifax 88, "Aerobic Biological Waste Treatment,"
Nalco Chemical Company.
8. "Sewage Treatment Basic Principles and Trends," 2nd
Edition by R. L. Bolton and L. Klein, Ann Arbor
Science Publishers, Inc., Ann Arbor, Michigan.
9. Technifax 71, "Removal of Phosphorus from Municipal
Wastewater," Nalco Chemical Company.
59
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/2-75-039
2.
4. TITLE AND SUBTITLE
IMPROVED LIQUID-SOLIDS SEPARATION BY AN
ALUMINUM COMPOUND IN ACTIVATED SLUDGE
TREATMENT
3. RECIPIENT'S >CCESSIOf*NO.
5. REPORT DATE
September 1975 (Issuing Date)
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
8. PERFORMING ORGANIZATION REPORT NO.
Charles F. Lenhart and Joe W. Cagle
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Board of Greene County Commissioners
Greene County, Ohio
10. PROGRAM ELEMENT NO.
1BC611
11.
NO.
17030 EBH
12. SPONSORING AGENCY NAME AND ADDRESS
Municipal Environmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
13. TYPE OF REPORT AND PERIOD COVERED
Final, Oct.1974-June 1975
14. SPONSORING AGENCY CODE
EPA-ORD
1G. SUPPLEMENTARY NOTES
16. ABSTRACT
Addition of sodium aluminate to a full scale (10,000 m3/day)
activated sludge facility greatly enhanced solids separation
processes.
Comparative data for periods with and without chemical dosing
are provided.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS C. COSATI Field/Group
Activated sludge process,
Phosphorus, Sludge digestion,
Settling, Chemical removal
(sewage treatment)
Sodium aluminate,
Aerobic digestion,
Mixed liquor solids,
Settleability, Sus-
pended solids, Chemi-
cal dosing system,
Microstrainer
13B
18. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (This Report)
UNCLASSIFIED
21. NO. OF PAGES
68
20. SECURITY CLASS (This page)
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (9-73)
60
IM. GOVERNMENT PRINTING OFFICE 1975-657-695/5325 Region No. 5-11
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