DESIGN CONSIDERATIONS FOR
EXTENDED AERATION IN ALASKA
FEDERAL WATER QUALITY ADMINISTRATION
NORTHWEST REGION
ALASKA WATER LABORATORY
College, Alaska
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DESIGN CONSIDERATIONS FOR EXTENDED AERATION IN ALASKA*
by
Sidney E. Clark
Harold J. Coutts
Conrad Christiansen
FEDERAL WATER QUALITY ADMINISTRATION
ALASKA WATER LABORATORY
College, Alaska
*Paper presented at the International Symposium for Cold Regions
Water Pollution Control, University of Alaska, Institute of
Water Resources, July 22 to 24, 1970.
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A Working Paper presents results of investigations
which are to some extent .limited or incomplete.
Therefore, conclusions or recommendations-.-expressed
or implied—are tentative.
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CONCLUSIONS
The feasibility of the extended aeration activated sludge process
as a relatively economical and effective means of secondary waste
treatment has been demonstrated in the laboratory and in the field.
\
The process requires more consistent operation and maintenance than
aerated lagoons and this is a disadvantage where costs are high and
skilled operators are extremely scarce.
The Utilization of exposed aeration chambers for the extended aeration
process is feasible. Earthen basins are also feasible for use where
economic and construction conditions warrant. When utilizing exposed
basins, heat loss effects must be evaluated in conjunction with deten-
tion time determinations to avoid potential freezing problems. Solids
entrainment in ice can cause failure of an activated sludge process.
Environmental protection in varying degrees should be provided for
the remaining equipment, such as heated enclosures for pumps and flow
measurement devices. Housing must be provided for secondary sedimenta-
tion basins and should include a minimum of an unheated structure with
panels which can be removed for warm weather operation.
Effective solids separation is the key to successful operation of
extended aeration facilities and is dependent on both the biological
and physical aspects of the system. It has been demonstrated that a
sludge can be developed which will perform very efficiently at tem-
peratures <1°C. A turbid effluent will result at cold temperatures
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with an unacclimated sludge or loading rates that are too high. Under
these conditions, a less stabilized sludge develops with a corresponding
relative decrease in numbers of stalked ciliates and an increase of dis-
persed bacteria which appears to contribute to turbidity (22).
A bulking sludge may develop at cold operating temperatures. This
type of sludge can lead to separation problems but will provide a very-
clear effluent at temperatures ranging down to less than 1°C.
Properly designed tube settlers will provide effective cold (0 to 4°C)
temperature solid separation. This is true for sludges with SVI's
ranging up to 250. A backwash cycle should be provided for reliable
operation and is mandatory for operation with high MLSS concentration
(4000 mg/1) and bulking sludges.,. Some effort should be directed
toward developing upflow clarifier configurations for cold temperature
application since the method has advantages (27). The tube settler
does provide an upflow cVarifier type action in high MLSS activated
sludge solid separation applications. Providing consistent solids
separation with tube settlers at warmer temperatures (greater than 4°C)
appears to be the most demanding and yet insufficiently defined area
•of need in their application.
Cold climate sludge wasting and disposal for the extended aeration
process must be given consideration for the following reasons:
(1) Excess solids production increases with decreasing temperature.
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(2) Shorter detention times to prevent freezing will also increase
X, '-i.
solids production at a given MLSS level.
(3) Auto induced sludge wasting may be expected to be more severe,
placing greater potential stress on the receiving water.
(4) Retarded assimilative capabilities of the receiving water at
cold temperatures.
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RECOMMENDATIONS
Facility Design
The following design recommendations are based on laboratory studies,
experience with the Eielson Air Force Base pilot facility, and experience
reported by others:
I
!
(1) Exposed aeration basins should be considered for reducing con-
struction costs of waste treatment facilities. Raw sewage temperatures
and heat loss effects must be considered to prevent freezing which can
cause process failure by entrainment of solids from the system.
(2) Housing should be provided for pretreatment units such as bar racks,
pumps and flow measuring equipment.
(3) Some minimum protection should be provided for aeration equipment
such as strip heaters or minimum heat enclosures for compressors and
unheated housing for oxidation ditch rotors.
(4) Housing should be provided for secondary sedimentation basins.
Minimum housing would include a structure with panels which may be
removed for warm weather operation.
(5) Where economic and construction considerations warrant, earthen
basin designs should be considered for aeration chamber construction.
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Otherwise, sidewalls that are vertical or near the angle of repose
should be utilized to promote better mixing.
(6) Submerged settling units should be situated in the center of
basins with low sidewall construction with aeration on at least two
sides to promote adequate mixing. Several questions require answers
before submerged settling units are practical.
(7) When basins with low sidewall slope construction are utilized
f
without submerged settling units, the aeration devices should be clus-
tered in the center of the basin for best mixing.
(8) Flexible membranes should not be used where the danger of heavy
icing exists.
(9) Concrete block and concrete grout should be considered as econom-
ical liner materials where the design permits.
(10) Tube settlers with backwashing of tubes should be given consid-
eration for both submerged settling units and sedimentation basin
installations, however, more information is necessary before their
reliability is predictable. Effective methods must be provided for
removal of settled solids from the unit for recirculation. Lack of this
capability will result in poor tube settler performance. Considerable
thought must be given to maintenance, both routine and emergency, prior
to and during the design phase for tubesettlers to be useful.
Process Design
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The following preliminary recommendations for. low temperature extended
aeration systems are. based on laboratory studies and experience re-
ported by other investigators. Attempts will be made to verify these
findings on a pilot plant scale.
(1) Organic loadings should be maintained below ^ 0.20 #BOD/#MLVSS-
Day. More studies are necessary at higher F/M values, especially up
to 0.4 #BOD/#MLVSS.
(2) Provision should be made for sludge wasting of ^ 0.5 #MLSS/#BOD
removed, particularly at shorter detention times such as a 12 hour
detention time system. Further studies are necessary to determine
temperature and detention time influences.
p
(3) Tube settler overflow rates-should be held below 0.5 gpm/ft with
high MLSS concentrations (^ 4000 mg/1).
(4) Sludge wasting and disposal facilities or a polishing lagoon for
effluent discharge should be provided where heavy discharges of sus-
pended solids may place excessive stress on receiving waters.
Research and Development Needs
The following list of suggested research and development needs is not
intended to be all inclusive but includes areas which have come to
the attention of the authors through laboratory and pilot plant ex-
perience and a review of experience reported by other investigators:
(1) Sludge bulking conditions at lower temperatures (^ 8°C and below)
must be defined so the condition can be predicted in actual application,
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(2) Further develop low temperature bio-kinetic parameters at detention
-times ranging from 4 to 36 hours and varying MLSS levels.
(3) Further develop low temperature tube settler design criteria and
backwashing techniques at various MLSS levels.
(4) Investigate upflow clarifier designs for low temperature appli-
cation.
(5) Investigate methods of sludge digestion .and disposal under low
temperature conditions; particularly the use of the freeze-thaw cycle
as an aid to promoting better drainability.
(6) Develop reliable methods for positive recirculation of settled
solids from submerged settling units.
(7) Further investigate criteria for predicting heat loss from ex-
posed basins.
(8) Continue evaluation of cold temperature bio-kinetic design para-
meters on pilot plants and existing facilities.
(9) Develop design and operation criteria for low temperature hori-
zontal flow clarifiers.
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(10) Investigate power requirements and mixing characteristics of
various earthen basin configurations.
(11) Further investigate the effects of heavy ice cover on solids
entrainment in aeration basins, particularly where flow patterns are
parallel to the surface as in the oxidation ditch.
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INTRODUCTION
Alaska is the largest state of the United States, sparsely populated
and with a variety of climates, including arctic, subarctic, marine sub-
arctic and temperate. The population is small and widespread with
294,417 people (preliminary 1970 census figure) inhabiting 586,000
square miles of land area. Settled areas requiring domestic sewage
treatment include large municipalities, military installations, remote
sites and villages, each of these having different requirements and
presenting different problems.
Construction and power costs in Alaska are very high in general, and
excessively so in remote areas (1.5 to 5 times Seattle construction cost
index). Skilled personnel for operation of treatment plants are scarce
and, in most cases, nonexistent.
The effect of man's waste on Arctic and Subarctic ecosystems has re-
ceived little attention in the past and is not well understood. Because
of recent increased interest in the Arctic region, some information is
now becoming available on man's possible influence. For example, during
the winter, dissolved oxygen (DO) of ice-covered Alaska rivers may reach
extremely low levels of 3 mg/1 or less under natural conditions (10, 12,
28). Because of the retarded ability of Alaska streams to replenish DO
under total or nearly total ice cover, it becomes essential that the
natural balance not be upset by man. Under these conditions, high level
secondary sewage treatment will be required to assure adequate stream
protection.
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One of the major advantages of biological processes for provision of
'secondary treatment is their ability to oxidize waste without large in-
puts of energy, thus reducing shipping costs, etc., associated with
materials required for chemical treatment. All factors considered,
extended aeration systems have considerable potential for reliable
and economical secondary treatment at larger governmental installations
and larger communities in Alaska (populations greater than 250).
Current extended aeration research is being conducted by several groups:
1. Corps of Engineers
Cold Regions Research and Engineering Laboratory
Alaska District
2. University of Alaska
Institute of Water Resources
3. Federal Water Quality Administration, Alaska Water Laboratory
Cold Climate Research Program
Waste treatment research at the Alaska Water Laboratory is concerned
primarily with adapting methods developed in the contiguous United
States to the extreme cold climates found in Alaska. The scope of the
present work, on activated sludge is. in general, limited to extended
aeration, and includes investigations in the following areas:
1. Low temperature bio-kinetics
2. Low temperature solids removal
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3. Degree of environmental protection required for equipment and
processes.
4. Aeration requirements
5. Aeration chamber mixing
6. Waste sludge characteristics and disposal
The above investigations are being conducted on a laboratory and pilot
plant scale. Monitoring of existing facilities is also taking place.
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LITERATURE AND EXPERIENCE REVIEW
Low Temperature Biological Treatment Feasibility
Although the activated sludge process is affected by temperature,
operation at temperatures approaching freezing is feasible. A number
of investigators have reported a considerable amount of biological
activity taking place at freezing temperatures and below (3, 15).
Miller (23) has reviewed the information available on microorganisms
indigenous to cold environments and found that research on psychro-
philic organisms is still in the initial stage, but concluded that
"truly psychrophilic microorganisms do exist and are distinguished by
their ability to grow at very, low temperatures and to do so at rates
comparable to those of mesophiles at higher temperatures." The feasi-
bility of effective biological treatment by full-scale extended
aeration facilities at operating temperatures as low as 2°C has been
demonstrated (2, 13, 30).
Temperature Effects
Pasveer (24) conducted laboratory scale temperature studies with
activated sludge and reported that the process goes on almost as well
at 3-5°C as it does at 20°C. Wuhrmann (34), found in his studies of
the activated sludge process that "the BOD removal-seems to be only
slightly influenced by temperature, whereas nitrification is markedly
higher in summer than in winter." Ludzack (21) conducted bench scale
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studies using a continuous apparatus with a detention time of 24
"hours and a loading of 35# COD/1000 ft3 and demonstrated COD re-
moval efficiencies of <90% at 21-25°C, 90% at 10°C and 84% at 5°C.
Hunter et al . (19) conducted batch operated laboratory scale studies
on the effect of temperature and retention times on the activated
sludge process. At temperatures between 4°C and 45°C, they found
little change of BOD or suspended solids removal efficiencies. As
the temperatures increased, they found less filamentous growth and
increased protozoa and rotifer populations. Grube and Murphy (13)
evaluated an oxidation ditch and found BOD removal efficiencies
greater than 90% with liquid temperatures of 2°C, air temperatures
ranging down to -40°C, and average detention times of 2.3 days.
Influent temperatures averaged 16.6°C with a minimum of 7.5°C.
Gustaffson and Westbury (14) evaluated the activated sludge process
for application at Kiruna, Sweden, and obtained 75% BOD reduction
with a 3 1/2 hour detention time system at 2.8-4.8°C and 2700-3500
mg/1 MLSS.
Temperature Coefficient
The temperature coefficient, e, is used in the relationship
k1/k2 = e (t] - t2)
to define the effect of temperature on biological activity. The
values k-j and V.% refer to velocity constants at temperatures t-j and
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respectively. The value of e indicates the extent of the temperature
effect on the biological activity. Use of this equation, known as
the Arrhenius relationship, to define the effect of temperature on
wastewater and reaction rates, dates back to Streeter and Phelps (1925)
and Theriault (1927), who reported e values of 1.047 for domestic waste-
water and river water (35). Pohl (25) concluded that 0 was dependent
on the mixed liquor concentrations: e = 1.038 at low MLSS and 1.000
at high MLSS. Benedict (4) conducted studies in the temperature range
of 4-32°C and concluded e (e = 1.078 @ 4°C) was independent of loading
when the loading rate did not exceed 0.53 Ibs BOD/day/lb/MLSS, but e
increased as loadings above .0.53 were imposed. Eckenfelder (8)
suggested that e, based on overall treatment efficiencies, was a
function of the organic loading and reported e values for activated
sludge of 1.00 at low loadings and 1.02 at high loadings.
Solids Separation
Solids removal plays a very important part in the efficiency of the
activated sludge treatment process. The degree of sludge separation
directly influences the quality of effluent from wastewater treatment
plants with higher concentrations of effluent solids contributing to
high effluent BOD. Reed and Murphy (27) conducted an investigation
on settling characteristics of activated sludge at temperatures ranging
from 1.1 to 23.4°C and found that the influence of temperature on
settling velocity decreased as the concentration increased. They de-
veloped an equation for zone settling based on experimental data. They
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also suggested upflow sludge blanket clarifiers as having greater
potential for cold regions application. Benedict (4) suggested that
the effect of sludge settleability on gross COD removal was magnified
at low temperatures and as the-loading rate was increased.
Hansen (16) reported on a method of solids separation which success-
fully employed shallow depth sedimentation theory. The settling units
consisted of small diameter tubes (1-inch) inclined at 5° and 2-4 feet
in length. Detention times were very short and backwashing was
necessary for removal of accumulated solids. Hansen (17) also reported
on the use of steeply inclined tubes (60°) which permit solids deposit-
ed in the tubes to continuously slide down by gravity. A secondary
clarifier of a trickling filter plant was converted to a biological
reactor and the steeply inclined tubes utilized for solids separation
which increased plant efficiency from 85 percent to more than 95 per-
cent. The effluent suspended solids averaged 70 mg/1 varying from a
low of 7 mg/1 to a high of 190 mg/1 which was comparable to those
produced by a conventional clarifier of an extended aeration plant of
the same capacity (3000 gallons per day at 12-hour detention). Other
reports are available which descirbe the use of tube settlers in
water treatment and waste treatment solids separation (6, 29).
Pohl (26) investigated tube settlers in the laboratory and obtained the
best results at room temperature but found the tubes passing excessive
collodial solids occasionally.
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Design Parameters
Little imformation is available on biological treatment process design
for temperatures less than 5°C. Ludzack (21) and Hunter, e_t a]_. (19)
observed that excess MLSS accumulation increased with decreasing temper-
ature. The cell yield (c) increases with increasing temperature
because it is believed a larger portion of BOD removed is utilized for
energy at low temperatures than at high temperatures (32). Since the
rate of endogenous respiration is depressed at low temperatures, the
quantity of excess sludge produced is increased. Benedict (4) reports
values for c and k (endogenous rate) at 4°C of 0.42 mg/mgCOD and 1.32
percent respectively.
Aeration
Eckenfelder and O'Connor (9) stated that the temperature coefficient
9, when applied to oxygen transfer efficiencies, has been reported to
vary from 1.016 to 1.047 and that studies on bubble aeration indicated
a temperature coefficient of 1.02 applied. The effects of temperature
on stream reaeration has been studied under controlled experiments in
the laboratory (1). A value for 9 of 1.0241 for the temperature range
of 5 to 30°C was found. Black (5) described a procedure for evalua-
tion of aeration devices and stated that a 9 value of 1.030 or higher
should be used for cold water.
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ALASKA WATER LABORATORY PILOT PLANT AND LABORATORY STUDIES
Laboratory Studies
During the past two years, three bench scale activated sludge reactors
have been utilized for kinetics and solids separation studies. The
three units are illustrated in Figures 1, 2, and 3. The systems have
been operated as continuous flow through systems with the feed being
primary effluent brought to the laboratory from the Eielson primary
sewage treatment plant. Routine analysis included influent and
effluent BOD and COD, mixed liquor and effluent suspended solids (SS)
and volatile suspended solids (VSS). Nutrient analysis of the influent
and effluent samples were made weekly and included ammonia, nitrite,
nitrate, organic nitrogen, total phosphates and orthophosphates. A
limited number of coliform counts were made on the influent and
effluent. Microscopic examinations of the reactor contents were made
on an irregular basis at times when apparent or suspected changes in
the mixed liquor had taken place. The examinations consisted of
general observations on the relative quantities of protozoa present
and the degree of activity. BOD, COD, and solids analyses were done
in accordance with Standard Methods procedures (31). Coliform counts
were made by the membrance filter method as described in Standard
Methods and nutrient analyses were made in accordance with Federal
Water Quality Administration Standards (11).
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The cone reactors (Figure 1), when operated at 1.3°C and 6.5°C for
long periods of time, showed some interesting characteristics which
are summarized in Tables 1 and 2. Both biological sludges were rel-
atively easy to establish.
The reactor runs started with the longest detention time first and
the times decreased in chronological order. The 1.3°C reactor took
a considerable amount of time to establish a stable system (more
than 3 months). However, a good removal rate was obtained before
the MLSS stabilized. There was apparently little difference in the
biological activity at the two temperatures, but, operation of the
reactor at 6.5°C was more erratic.
Both reactors generally showed "auto induced slude wasting" in the
same manner as the College Utilities oxidation ditch described by
Grube and Murphy (13). The MLSS would build up to a point and begin
to pass solids for 1 or 2 days and then repeat the cycle. The cycle
was repeated within 2 to 3 weeks as opposed to the monthly occurrence
reported by Grube and Murphy.
The reactors differed in their manner of passing solids, with the
1.3°C reactor generally having a much more turbid effluent and the
6.5°C reactor having a relatively clear effluent. Heavy solids
passed from the 6.5°C reactor by rising in the settling tube as a
solid mass. As the concentrations of solids in the mixed liquor
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increased, the level of solids in the settling tabe would rise until
spilling over into the effluent tank. After passing an undetermined
amount of solids, the cycle would be repeated. A gradual drop in pH
was noted in the 6.5°C unit as the suspended solids began to build
before discharging. The pH dropped from slightly above 7 to values
of 6.6 to 6.7. pH of the 1.3°C unit consistently remained around
7.4. The 6.5°C effluent solids settled to the bottom of the effluent
tank leaving a clear liquid above, whereas, the 1.3°C effluent solids
did not settle out to any degree. As the 1.3°C reactor became more
stabilized, the effluent became less turbid and the MLSS began to
increase. The 6.5°C reactor operation was less stable, with the
maximum level of MLSS generally not rising above 2300 as opposed to
3000 for the 1.3°C MLSS. Results of nutrient analysis are presented
in Table 3. There was a significant change in nitrate and total
nitrogen at 6.5°C when going from 9 to 13 hours detention time. This
was also true at 1.3°C to a lesser degree. There was a greater
reduction in ammonia nitrogen and a greater increase in nitrate
nitrogen at 6.5°C. Ammonia was essentially not affected at 1.3°C.
Total nitrogen removals were much higher at 6.5°C than at 1.3°C with
little detention time effects.
Overall results of operation of the 8.9 gal and 12.45 gal reactors
are presented in Tables 4 and 5. Temperature changes were accomplished
by a gradual increase or decrease in the constant temperature room
temperature. These reactors were operated at 12-hour hydraulic detention
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times with daily sludge wasting to maintain the MLSS at 4000 mg/1.
The 8.9 gal reactor was later converted to a 24 hour operation.
Sludge was wasted by drawing off the required amount of mixed
liquor. A portion was used for a solids analysis to determine the
exact amount of solids removed. The effluent BOD and COD figures
of 9 to 21 mg/1 and 46 to 96 mg/1 indicate that a considerable
amount of biological activity takes place at low operating temper-
atures.
Effluent BOD/COD ratios varied from 0.13 to 0.27 indicating that
effluent organics were well oxidized. These were in comparison
with the influent BOD/COD ratios of 0.55 to 0.66.
The amounts of sludge wasted varied from 0.42 m9 -»usp. solids at
mg BOD removed
the low temperatures to 0.14 at 10.5°C and 24 hour detention time.
The pH of both reactors ranged from 7.2-to 7.6 during the sample
periods reported.
Poor settling sludges were developed during operation of these
reactors with the Sludge Volume Index (SVI) consistently ranging
above 200. The sludge produced appeared to be of a zoogeal type
similar to that reported by Heukelekian and Wiesburg (18) who found
a direct correlation between increasing SVI and increasing bound
water for this type of bulking. Very little evidence of Sphaerotilus
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was noted during microscopic examination. Ludzack (21) also re-
ported a poor settling sludge at low temperatures (5°C) with very
poor drainability.
The significance of protozoa in an efficiently operating activated
sludge process as reported by McKinney (22), was observed during
operation of the reactors even at the coldest temperatures. The
12.45 gal reactor was started at temperatures <2°C with return
sludge from an oxidation ditch treating domestic sewage. Initially,
the effluent was very turbid as the sludge was acclimating itself
to the new conditions. The decreasing turbidity of the sludge as
acclimation progressed corresponded to increasing numbers of
protozoa, generally Paramecium and Vorticella. As reported by
McKinney (22), a very well stabilized activated sludge system will
have few stalked ciliates and no other protozoa because of relatively
few bacteria, whereas, a somewhat less stabilized system will have
greater numbers of free swimming ciliates because of greater numbers
of free swimming bacteria. He stated that the presence of stalked
ciliates indicates an activated sludge system with a low BOD effluent.
Vorticella was present in both reactors after initial startup except
for one period in the 12.45 gal reactor as described below.
After stable operation at temperatures <2°C and ^°C the 12.45 gal
reactor temperature was increased to 8°C over a period of 6 days.
The effluent suspended solids increased from approximately 5 mg/1
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before the temperature increase to approximately 18 nig/1 during
the increase and reached a maximum of 46 mg/1 after 3 days at 8°C.
During this period, the effluent became turbid with few solids set-
tling out in the effluent tank.' The protozoa became very reduced
in numbers and inactive. Again, the return to normal operation
corresponded to an increase in the number of Vorticella and Parame-
cium present in the sludge. Coliform removal also corresponded
directly to the numbers of protozoa present, dropping from 99.8
percent removal before the upset to less than 80 percent during
the protozoa number reduction. Ten days after returning to stable
operation at 8°C, the sludge was exhibiting the same characteristics
as with the 8.9 gal reactor. That is, the SVI was ranging around
250 and the floe exhibited a fluffy snowflake appearance. Operation
of the reactor was not impaired under these conditions because a
backwash cycle was added to the settling apparatus. Protozoa in-
creased in numbers when the systems stabilized at 12°C.
Sludge wasting and disposal in cold climates should be given attention.
Based on data presented earlier, it would appear that provision should
be made for wasting 0.5 Ib solids per Ib or BOD removed at colder
operating temperatures (<5°C) and at organic loadings of 0.1 Ib influent
BOD per Ib MLVSS-Day. Sludge digestion and disposal methods present a
problem at colder temperatures due to added heat requirements and poor
drainability. Ludzack (21) indicated that sludge development at cold
temperatures may require digestion at higher temperatures before
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disposal. Thomas (33) indicated the freeze-thaw cycle may be taken
"advantage of in cold climates'to increase drainability.
Tube settlers have been evaluated as a possible alternate means of
providing solids separation and return. During operation, sludge
rises in the tubes until it reaches a level at which it is in equi-
librium with the effluent flow. Action in the tube consists of a
rolling motion in which solids are being carried up along the top
side of the tube in a mass with the effluent, as shown in Figure 4.
The mass gradually settles toward the bottom side of the tube where
it enters a current moving downward caused by the weight of the
solids. During normal operation, solids in the tube are constantly
being replaced at a relatively high rate (<3 hrs). In the temp-
erature range of 0° through 4°C the SVI of the mixed liquor ranged
around 230 and did not hinder the operation of the reactor. At 8°C
and above, the SVI increased to values of 260 and greater and the
sludge took on a fluffy snowflake appearance. The rolling action
of the sludge in the tubes stopped and the sludge height began to
rise eventually spilling out with the effluent. Cutting the effluent
flow rates, back to less than 0.2 gpm/ft2 resulted in lowering the
DO in the effluent tubes to zero, which further complicated the
problem. The studies indicate that some means for backflushing tube
settler controlled upflow clarifiers must be provided if mixed
liquor concentrations greater than 2000 mg/1 are to be achieved with
reliable operation.
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The 12.45 gal reactor was operated for a period of time with a very
low continuous overflow rate and then increased to an average rate
of 0.5 gpm/ft2 with an alternating on-off cycle. In other words,
with the on 1/2 hour—off 1/2 hour cycle, the actual flow was 1 gpm/
ft2 for 1/2 hour. The SVI again ranged above 200 with very consistent
solids removal. The effluent solids concentrations were very low for
the whole range of studies. The longer on times for the on-off cycle
(2-1/2 hours on as opposed to 1/2 hour) did indicate that longer cycles
may result in higher effluent solids concentration. Summaries of the
results obtained at various temperatures and overflow rates are pre-
sented in Tables 6 and 7, and Figures 5 and 6. Adding a backwash cycle
provided a definite advantage in that it prevented a bulky sludge from
becoming stagnant in the tubes.
Indications are that sludge bulking probably is a general problem in
the activated sludge process at colder operating temperatures and special
precautions in design will be necessary to assure effective solids con-
trol. This problem was reported by Ludzack (21). Bulking sludges have
not been reported in cold temperature oxidation ditch studies (2,13);
however, these ditches were operated at much longer detention times (1.6
'to 2.3 days) which may be a factor. Downing (7) showed that settle-
ability is improved by longer detention time (>10 hrs) and very short
detention time (<5 hrs) when operating an activated sludge plant at
warm temperatures. At any rate, indications are that backwashing in
conjunction with lower overflow rates will overcome this problem.
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Unless a polishing lagoon is employed, provision should be made for
sludge wasting. These studies" indicate a probably maximum wasting
rate of around 0.5 #SS/#BOD removal.
Pilot Plant
In cooperation with the Alaskan Air Command, the Alaska Water Laboratory
constructed and operated a pilot waste treatment facility at Eielson Air
Force Base (EAFB). The facility included an aerated lagoon and an
extended aeration basin. The purpose of the facility was to increase
the knowledge of biological waste treatment at cold temperatures and to
develop design criteria.
Eielson Air Force Base is located 22 miles southeast of Fairbanks and
has a similar subarctic climate. The mean annual temperature at
Fairbanks is approximately 25°F with minimum and maximum recorded
temperatures of -66°F and +99°F respectively (20). The area has
approximately 150 degree days below 0°F.
Originally intended to serve as a facultative lagoon, the extended
aeration unit consisted of an earthen basin lined with 20 mil polyvinyl
chloride film (PVC) and tube settler modules as shown in Figures 7 and
8. The PVC film at the bottom of the basin was covered with 6 inches
of sand and a concrete pad poured in the center for support of aerators.
Aeration and mixing were provided by eight Hydroshear aerators, manu-
factured by the Chicago Pump Company. Air supply was by a 120 SCFM
Sutorbilt blower, manufactured by the Fuller Company.
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Solids separation was provided by two tube settler modules. The tube
"settlers were developed by Neptune Microfloc Company for use in water
treatment. The manufacturer has recently initiated studies to adapt
them for use in activated sludge separation (17). This type of
settler was felt to provide optimum design for submerged operation
which was desired to overcome icing problems. The basin was fed by a
Marlow centrigal pump, manufactured by ITT Marlow Company. Pumping
rate was approximately 180 gpm with the feed drawn from a manhole on
the influent line just before entry to the EAFB primary treatment plant.
Temperature of the sewage averages about 20°C with the sewer lines
enclosed in a utiliddr, which is heated during the winter months.
The extended aeration facility as described was built to provide the
very simplest operation with a minimum of environmental protection for
evaluation under cold climate conditions. Construction of the extended
aeration facility was completed in December 1968 and the unit placed in
operation later that month. The unit was operated at a 2-day detention
time, which corresponded to an average overflow loading rate on the
tube settler of 1.3 gpm/ft^. A problem was encountered with breakage
of pumps, due to entrained solids entering the pumping chamber. The
feed line also filled with solid material and plugged. As a result,
the basin was not fed for a week, during which time 3 feet of ice
formed over the pond and frozen foam built up to 8 feet abover.the aer-
ator.
-------
Beginning in January 1969 and lasting approximately 6 weeks, a period
.of extremely cold weather occurred with ambient air temperatures dropping
as low as -60°F. A detention time of 1 day was maintained during this
period with no ice forming. The loading on the tube settlers was approx-
o
imately 2.5 gpm/ft . The gear housing of a compressor was broken and
teeth stripped from the gears while attempting to start it at a low
temperature. Apparently, metal contraction had reduced clearances which
caused internal rotating parts to make contact with and break the pump
housing.
During February, the feed pumps were moved inside the Eielson primary
treatment plant and feed taken from the grit chamber. For the remaining
of the winter and the following spring, while operating at a detention
time of 2 days, the MLVSS of the system generally did not rise above
500 mg/1.
Inadequate mixing was suspected as the cause of poor performance, and
velocity measurements were made with an ice current meter obtained from
the M. S. Geological Survey which measured the horizontal component only.
Velocities were generally lower than the 1.0 ft per second recommended
for complete mixing, except within 2 feet of the surface. The aeration
rate was 120 cfm, depth of the basin 11 feet and with approximately 4
horsepower input. Velocities were measured again at a later date with
300 cfm being delivered and 9 horsepower input with generally the same
-------
results except the surface velocities were higher. The velocities
•found were not considered low; enough to cause the extremely poor basin
performance.
The possibility of excessive turbulence being carried into the tubes
was also considered because of the close proximity of the settler
modules to the aerators (2-3 feet). To check the possibility, a new
aerator was fashioned of a short length of 3-inch pipe attached to
flexible hose and placed in the basin approximately 10 feet from the
settler modules. The MLSS of the basin increased to 1000 mg/1 during
operation of this aerator which did indicate that basin turbulence or
entrained air bubbles was effecting the settler operation.
The basin was then taken out of operation to permit modifications in
preparation for the next winter's operation. The modifications are
illustrated in Figures 9 and 10. The system was placed in operation
in December 1969. It was recogniized that at a detention time of 24
hours and with low winter operating temperatures, the hydraulic load
on the tube settlers would be too great. An attempt was made to
reduce the hydraulic load on the system while maintained a BOD load
equivalent to a 24-hour detention time system by supplementing the
feed with primary sludge from the Eielson tratment plant. Basin ve-
locity proved to be restricted around and beneath the separator hoppers
because of the low clearance and resistence offered by the settler
support. As a result, a heavy sludge deposit blocked the separator
hoppers, accumlated in the tubes and passed into the effluent.
-------
During a cold period in January 1 97G, the surface of the basin began
to freeze due to low heat energy being supplied. The sludge accu-
mulated in the ice, reducing the suspended solids level in the pond
from approximately 2500 mg/1 to less than 200 mg/1. During this
period, the mean ambient temperatures averaged -23°F, with a range of
-8 to -35°F. Wind velocity ranged from 10 knots to calm and averaged
3 knots.
A block was cut from the ice and a sample taken of the unfrozen sludge
beneath the ice. A cross section is shown in Figure 11. The ice had
reached a thickness of 14 inches with a sl.udge layer of 17 inches
beneath the sampling point. The sludge was not moving under the ice
and apparently had attached itself, building up a thicker and thicker
layer which eventually froze into the ice layer.
The long sloping side walls associated with earthen basins present
two very important problems in activated sludge aeration chamber ap-
plications. The relatively high surface area to volume ratio will
result in high heat energy losses from the system which may be very
critical with low temperature influent. Greater heat losses will
promote ice formation which will entrain MLSS from the system, de-
stroying the effectiveness of the process.
The second problem is the difficulty in obtaining adequate basin velo-
cities at lower depths without excessively high horsepower for mixing.
-------
Even at high aeration, rates, the minimum recommended velocities of
1.0 fps were generally not present in the pilot facility extended
aeration basin at Eielson Air Force Base.
Another effect observed during operation in the second winter was
that, with the aerators off center, a circular flow was induced in
the basin in the horizontal plane around the aerators. The flow
was similar to the Coriolis effect which may be observed when drain-
ing a bathtub, etc., and seemed to be promoted by the earthen basin
shape of a large surface area to bottom area ratio. This effect will
only become a problem in situations in which flow directions in the
basin are important as in the Eielson AFB pilot facility, where the
circular flow pattern did have an effect in hindering sludge removal
from bneath the hoppers.
The cross sectional shape of a basin and the temperature to which it
is exposed will, in general, determine the type of liner which should
be provided. Material must be used which will prevent erosion and
scouring by velocities in the basin. Side slopes of less than 1
vertical to 2 horizontal permit use of flexible liners, whereas,
vertical sides will require bearing wall construction of impermeable
concrete or wood crib design with an impermeable liner.
Experience with the PVC liner indicates it is not feasible for use
in permanent installations for cold temperature applications. The
liner becomes very susceptible to damage at low temperatures because
-------
of brittleness, and ice formation can cause extensive breaks in the
lining. Aging and exposure to sunlight also increase its susceptibility
to damage.
Impermeable liners such as low temperature butyl rubber membranes are
feasible for use in earthen basins when the danger of major freezing
does not exist. Care must be taken to insure that the liner is resist-
ant to hydrocarbons which may be present in the sewage as softening or
dissolution may result.
Concrete provides a reliable material for cold temperature application.
However, construction is expensive in Alaska and particularly so in
remote areas. Examples of the successful application of cheaper methods
of concrete construction are the College Utilities oxidation ditch in
Fairbanks, Alaska, and the oxidation ditch at Glenwood, Minnesota (2).
Concrete block was used for the construction of vertical sides for the
College Utilities ditch. Concrete silo staves were originally used
for the sloping sidewall construction of the Glenwood ditch but were
not sealed and soil behind the staves washed out. The problem was
successfully alleviated by placing steel mesh and 4 inches of concrete
grout over the staves to provide a smoother waterproof lining.
-------
REFERENCES
1. Anonymous, "Effect of Water Temperature on Stream Reaeration,"
Thirty-First Progress Report, Committee on Sanitary Engineering
Research, Journal of the Sanitary Engineering Division, Proceed
ings of the American Society of Civil Engineers, 87, No. SA6
TNovember, 1961).
2. Anonymous, "Report on Operation of Oxidation Ditch Sewage Treat-
ment Plant, Glenwood, Minnesota," Department of Health, Divison
of Environmental Health, Section of Water Pollution Control
(July 8, 1965).
3. Ayres, John C., "Temperature and Moisture Requirements," Low
Temperature Microbiology Symposium Proceedings (Camden), Campbell
Soup Company (1962).
4. Benedict, Arthur Howe, "Organic Loading and Temperature in Bio-
Oxidation," Doctor of Philosophy Thesis, University of Washington
(1968). .
5. Black, S.A., "How to Evaluate Aeration Devices," Water and Pollution
.Control, 106, No. 10 (October 1968).
6. Culp, Gordon, "A Better Settling Basin," The American City (January
1969).
7. Downing, A.L., "Factors to be Considered in the Design of Activated
Sludge Plants," Advances in Water Quality Improvement, University of
• Texas Press, pp..190-202, (1968).
8. Eckenfelder, Wesley, Jr., "Theory of Biological Treatment of Trade
Wastes," Journal Water Pollution Control Federation, 39, No. 2
(1967).
9. Eckenfedler, W.W., and O'Connor, D.J., Biological Waste Treatment,
Pergamon Press, Inc., 44-01 21st Street, Long Island, New York
(1961).
10. Frey, Paul J.", "Significance of Winter Dissolved Oxygen in Alaska,"
presented at the Alaska Water Management Association Annual Meeting
(May 1969).
11. FWPCA Methods for Chemical Analysis of Water and Wastes, Federal
Water Pollution Control Administration, Division of Water Quality
Research, Analytical Quality Control Laboratory, Cincinnati, Ohio
(November 1969). .
-------
12. Gordon, Ronald C., Research Microbiologist, Alaska Water Laboratory,
College, ^Alaska, Unpublished data (April 1970).
13. Grube, Gareth A. and Murphy, R. Sage, "Oxidation Ditch Works Well
in Sub-Arctic Climate," Water and Sewage Works, 116, No. 7 (July
1968).
14. Gustaffson, Bengt and Westberg, Nils, "Experiment with Treatment of
Sewage from the Town of Kiruna by the Activated Sludge Method,"
Royal Institute of Technology, Stockholm, Sweden, Institute of
Water Supply and Sewage Technology, Institute of Water Chemistry,
65., No. 4 (1965).
15. Halvorson, H.O., Wolf, J., and Srinivasan, V.L., "Initiation of
Growth at Low Temperatures," Low Temperature Microbiology Symposium
Proceedings (Camden), Campbell Soup Co. (1962).
16. Hansen, Sigurd P. and Gulp, Gordon L., "Applying Shallow Depth
Sedimentation Theory," Journal American Water Works Association,
59., No. 9 (September 1967~T
17. Hansen, Sigurd P., Gulp, Gordon L., and Stukenberg, John R.,
"Practical Application of Idealized Sedimentation Theory," Pre-
sented at the 1967 Water Pollution Control Federation Conference,
New York City (October 10, 1967).
18. Heukelekian, H. and Wiesburg, D., "Bound Water and Activated Sludge
Bulking," Sewage and Industrial Wastes, 28. No. 4, p. 558 (April
1965).
19. Hunter, T.V. , Genetelli, E.J., and Gilwood, M.E., "Temperature and
Retention Time Relationships in the Activated Sludge Process,"
Proceedings of 21st Industrial Waste Conference, Purdue University
(1966).
20. Johnson, Philip R.," and Hartman, Charles W., "Environmental Atlas of
Alaska," Institute of Arctic Environmental Engineering, Institute of
Water Resources, University of Alaska, College, Alaska (1969).
21. Ludzack, F.J., "Observations on Bench Scale Extended Aeration Sewage
Treatment," Journal Water Pollution Control Federation, 37, No. 8
(August, 1965J;
22. McKinney, Ross E. and Gram, Andrew, "Protozoa and Activated Sludge,"
Sewage and Industrial Wastes, 28, No. 10 (October 1956).
23. Miller, Ann P., "The Biochemical Basis of Psychrophily in Micro-
organisms," Institute of Water Resources, University of Alaska,
College, Alaska (1967).
-------
24. Pasveer, A., "Research on Activated Sludge, V: Rate of Biochemical
Oxidation," Sewage and Industrial Wastes, 27, No. 7 (July 1955).
25. Pohl, E.F., "The Effect of Low Temperatures on Aerobic Haste Treat-
ment Processes," M.S. Thesis, University of Washington, Seattle,
Washington (1967).
26. Pohl, E.F., Chief, Sanitary Engineering Section, District Engineers
Office, U.S. Army Corps of Engineers, Anchorage, Alaska, Personal
Communications (April 22, 1970).
27. Reed, Sherwood C., and Murphy, R. Sage, "Low Temperature Activated
Sludge Settling," Journal of the Sanitary Engineering Division,
Proceedings of American Socity of Civil Engineers, 95, No. SA4
(August 1969).
28. Roguski, Eugene, Biologist, Alaska Department of Fish & Game,
Fairbanks, Alaska-, Personal Communications.
29. Schlecta, Alfred F. and Hsiung, Kou-Ying, "High Rate Processes in
Advanced Waste Water Treatment," Presented at the 1969 Water Control
Association of Pennsylvania (1969).
30. Schmidtke, N.W., "Low Temperature Oxidation Ditch Field Study,"
Thesis submitted to Department of Civil Engineering, University of
Alberta, Edmonton, Alberta, Canada (April 1967).
31. Standard Methods for the Examination of Water and Wastewater, 12th
Edition, American Public Health Association, New York (1965).
32. Stewart, Marvin J., "Activated Sludge Process Variations--The
Complete Spectrum," Water and Sewage Works, pp. R2-41 - R2-62
(December 1964).
33. Thomas, Harold Allen, Jr. ,.•;•"Report" of Investigation of Sewage
Treatment in Low Temperature Areas," for the Sub-Committee on
Waste Disposal, Committee on Sanitary Engineering and Environment,
National Research Council (May 22, 1950).
34. Wuhrmann, K., "Factors Affecting Efficiency and Solids Production
in the Activated Sludge Process," Biological Treatment of Sewage
and Industrial Wastes, B.J. McCabe and W.W. Eckenfelder (ed),
Reinhold Publishing Company, New York, New York '(1956).
35. Zanoi, A.E., "Secondary Effluent Deoxygenation at Different Temp-
eratures," Journal Water Pollution Control Federation, 41, No. 4
(April 19697!
-------
TABLE 1
DATA SUMMARY
1.3°C Cone Reactor
Feed: Primary Plant Effluent
Detention
Time (hrs)
Influent
BOD (mg/1)
Reactor
Susp. Solids (mg/1)
Volatile
Susp. Solids (mg/1)
Filtered Effluent
BOD (mg/1)
% BOD Removal
Unfiltered Effluent
Susp. Solids (mg/1)
BOD (mg/1)
% BOD Removal
Loading Factor
# BOD Feed
#MLVSS-Day
Product of
MLVSS and Det. Time
21
111
1,074
890
37
66
29
40
64
15
170
1,561
1,324
11
93
43
62
64
13
201
2,657
2,212
20
90
38
28
86
9
184
2,926
2,402
14
92
82
44
76
.19
14,700
.21
.17
19,500 28,000
.20
21,600
-------
TABLE 2
DATA SUMMARY
6.5°C Cone Reactor
Feed: Primary Plant Effluent
Detention
Time (hrs) 17 15 13 9
Influent
BOD (mg/1) 139 132 153 155
Reactor
Susp. Solids (mg/1) 2,346 1,885 1,880 2,285
Volatile
Susp. Solids (mg/1) 1,915 1,563 1,587 . 1,801
Filtered Effluent
BOD (mg/1) 51.3 16.3 13.3 11.7
% BOD Removal 63 88 91 92
Unfiltered Effluent
Susp. Solids (mg/i) 11 69 96 45
BOD (mg/1) 53 36 31 33
% BOD Removal 62 73 80 79
Loading Factor
# BOD Feed .08 .106 .18 .23
#MLVSS-Day
Product of
MLVSS and Det. Time 31,600 . 23,000 23,300 20,600
-------
TABLE 3
CONE REACTORS
RESULTS OF NUTRIENT ANALYSIS
13 Hour Detention Time
Nhh-N (Ammonia)
N02-N (Nitrite)
NOs-N (Nitrate)
Kjeldahl-N (Nitrogen)
Total (Nitrogen)
Total Nitrogen
Removals (%)
0-P04 (Otho-Phosphate)
1.3°C REACTOR.
Influent
22
.13
.13
41
41.26
--
20
Fi 1 tered
Effluent
19
.09
2.13
28
30.22
27
18
Unfil tered
Effluent
18
.05
2.02
29
31.07
25
18
6.5°C REACTOR
Influent
19
.11
.21
37
37.32
--
19
Fi 1 tered
Effluent
1
.13
9.17
3
12.30
67
18
Unfil tered
Effluent
1
.15
12.13
3
15.28
59
18
9 Hour Detention Time
NH3-N (Ammonia)
N02-N (Nitrite)
N03-N (Nitrate)
Kjeldahl-N (Nitrogen)
lotal (Nitrogen)
Total Nitrogen
Removals (%)
0-P04 (Otho-Phosphate)
Influent
21
.06
.11
36
36.17
—
17
.3°C REACTOR
Fi 1 tered
Effluent
19
.03
.68
26
26.71
26
14
Unfil tered
Effluent
19
.03
.54
27
27.57
24
15
6.
Influent
21
.06
.07
35
JD. IJ
•--
19
5°C REACTOR
Filtered
Effluent
1
.14
8.03
3
11.17
68
18
Unfil tered
Effluent
1
.12
14.45
3
17.57
50
16
(1) Total nitrogen results reported are the
nitrogen analysis
sum of the nitrite, nitrate and Kjeldahl
-------
TABLE 4
SUMMARY OF RESULTS OF 8.9 GALLON REACTOR AND
12.45 GALLON REACTOR AT 12-HR DETENTION
Feed: Primary Plant Effluent
Reactor MLSS (mg/1)
% VSS
BOD
COD
. ,. Ib Infl. BOD
Loadin9: Ib MLVSS-Day
c, . ,. . .
Sludge Wasted:
mg/MLSS
BOD Removed
Unf i 1 tered
Effluent
Suspended
Solids (mg/1)
BOD (mg/1)
BOD Removal (%)
COD (mg/1)
COD Removal (%)
BOD/ COD Ratio
Influent
Effluent
Reactor
REACTOR TEMPERATURE (AVG°C)
.6
4160
80
2489
5648
2.9
4097
80
2503
5788
3.8
4076
81
1477
5260
8.0
3737
80
1299
4705
0.12
0.42
18
21
89
78
76
0.60
0.24
0.44
0.10
0.33
3
13
92
46
73
0.60
0.23
0.43
0.10
0.32
12
17
90
67
78
0.55
0.25
0.28
0.14
0.33
5
9
96
96
83
0.66
0.16
0.28
-------
TABLE 5
SUMMARY OF RESULTS OF 8.9 GALLON REACTOR
AT. 24-HR DETENTION
Feed: Primary Plant Effluent
Reactor MLSS
% vss
BOD
COD
(mg/1)
Loading:
1b Infl. BOD
Ib MLVSS-Day
Sludge Wasted:
3
-
mg BOD Removed
Unf i 1 tered
Effluent
Suspended
Solids (mg/1)
BOD (mg/1)
BOD Removal (%)
COD (mg/1)
COD Removal (%)
BOD/COD Ratio
Influent
Effluent
Reactor
REACTOR
'1.9
2595
83
1693
3712
TEMPERATURE
6.8
3872
83
2105
5019
(AVG°C)
10.5
3896
82
1808
5178
0.07
0.42
3
14
93
51
83
0.66
0.27
0.46
0.07
0.16
4
10
95
53
84
0.66
0.19
0.42
0.07
0.14
6
10
95
69
80
0.62
0.13
0.35
-------
TABLE 6
8.9 GALLON REACTOR
RESULTS OF OPERATION WITH VARYING EFFLUENT
OVERFLOW RATES ON THE SETTLING TUBES
Reactor^
Temp
(°C)
.35
(.3-. 5)
.7
(.4-. 9)
4.2
(2.8-6.4)
3.8
(3.5-4.1)
INFLUENT
Susp.
Solids
(mg/1)
95
112
94
77
BOD
(mg/1)
244
253
193
142
COD
(mg/1)
292
370
229
283
REACTOR
Susp. SVI
Solids
(mg/1)
3973 238
4237 238
4147 ™
4067 229
EFFLUENT
Overflow
Rate
(gpm/ft2)
.4
.3
.6
.3
.6
.5
.8
Susp.
Solids
(mg/1)
10
8
20
10
• 14
10
13
BOD
(mg/1)
12
22
29
17
20
14
20
% BOD
Removal
95
91
89
91
90
90
86
COD
(mg/1)
69
71
87
60
70
62
69
• % COD
Removal
76
79
77
74
69
78
76
(1) Values in parenthesis are minimum and maximum for that period
-------
TABLE 7
12.45 GALLON REACTOR
RESULTS OF OPERATION WITH VARYING EFFLUENT OVERFLOW
RATES ON THE SETTLING TUBES
Reactor
Temp
(°c)
2.4
(1.4-3.5)
2.9
, ? '
4.4
(4.0-4.7)
7.8
(6.8-8.4)
INFLUENT
Susp.
Solids
(mg/1)
77
86
93
87
BOD
(mg/1)
177
185
223
194
COD
(mg/1)
303
275
321
313
REACTOR
Susp. SVI
Solids
3957 —
-
4157 214
4095 235
4504 209
EFFLUENT
Overflow^
Rate
(gpm/ft2)
.2
(continuous)
.3
(on 1/2 hr
off 1/2 hr)
.5
(on 1/2 hr
off 1/2 hr)
.5
(on 2 hr
off 1 hr)
Tube
Size
2 x 3.5
4 x 3.5
2 x 3.5
4 x 3.5
2 x 3.5
4 x 3.5
2 x 3.5
4 x 3.5
Susp.
Solids
(mg/1 )
2
2
4
3
4
5
12
14
BOD
(mg/1)
19
19
12
10
12
12
20
23
% BOD
Removed
89
89
94
95
95
95
90
88
COD
(mg/1)
35
39
50
52
55
69
69
64
% COD
Removed
88
87
82
81
83
79
78
80
(1) Values in parenthesis are minimum and maximum for that period
(2) Notes in parenthesis indicate the time cycle of effluent flow through the tubes
-------
Mixer
Holter Perfusion
Roller Feed
Pump
Reactor
Effluent
Holding
Tank
Concentric Cones
Moisture
Trap
FIGURE 1
CONE REACTORS*
SCHEMATIC OF APPARATUS
•*J\s manufactured by Pope Scientific
-------
Mixing
Pump
f
To Aeration Chamber
Refriger-
ation
Unit
j
i
j
Feect
Tank^
Settling
Tubes
Holter :
Perfusic
Roller
Feed
k60 Gal
Pump
Air Supply
n
Effluent
Pump
(HoUer),
Moisture
Trap
Reactor
Plexiglas
Effluent
Recycle
Pump
(Holter)
Effluent
Overflow
Line
Reactor
Side View
Effluent
Tanks
FIGURE 2
AWL REACTOR
8.9 GALLON
SCHEMATIC OF APPARATUS
-------
1-hr timer
D
lenoid Valves
24-hr
Timer
Refrigera-
tion Unit
Recycle
* Pump (Holter)
Feed Pump (Holter
Moisture
Trap
Effluent Tank
2" Tubes
FIGURE 3
AWL REACTOR
12.45 GALLON
SCHEMATIC OF APPARATUS
-------
Beginning _
of clear effluent
and sludge
interface
Gear
Effluent
Particles
rising above
sludge blanket
Sludge circulation
pattern
FIGURE 4
SLUDGE ACTION IN UPFLOW CLARIFIER SETTLING TUBES
-------
50..
40 -.
-------
20._
l/l
3 15.
o
-a
0)
TD
QJ
Q-
3 10.
CO
OJ
3
4!
UJ
5 -
A
A
.0
A 0 A
o
v
B
Legend
Continuous Flow
O< 1°C
A^ 4°C
Intermittent Flow
on 1/2 hr
off 1/2 hr
Q% 3°C
V^ 4°C
Intermittent Flow
on 2 hr
off 1 hr
A^C
MLSS ^ 4000 mg/1 ,
III! f . 1 i
III! ' 1 I 1
.1 .2 .3 .4 .5 .6 .7 .8
Overflow Rates (gpm/ft2)
FIGURE 6
8.9 GALLON AND 12.45 GALLON REACTORS
EFFLUENT SUSPENDED SOLIDS vs
OVERFLOW RATES AT VARIOUS TEMPERATURES
-------
xA
\
.70"-
Aerators
Plan View
Tube Settler
Modules
\
70'
\
A
Maximum Working Liquid Depth
View A-A
FIGURE 7
EXTENDED AERATION PILOT FACILITY
EIELSON A.F.B. .
1968 Configuration
-------
4'
Settling
Tubes
Effluent
Header
!o O
O O O O O O
"l I ! I i~[lTiTiTr
• 11 n ['!!!!•!
1, I 11 ' I
I' I 11 I ,
I
i. M . iit
Ll_l_LLLJ_lLJ_LLL
5'
FIGURE 8
TUBE SETTLER MODULE
1968 Configuration
-------
Chicago Pump
Shearfusers
Monosparj
Diffuser
Header
} Tube Settler
Modules
Plan View
Elevation
FIGURE 9
EXTENDED AERATION PILOT FACILITY AFTER MODIFICATION
EIELSON A.F.B.
1969 Configuration
-------
\\
FIGURE 10
TUBE SETTLER MODULE DESIGN
.WITH FLOW BENEATH THE HOPPER
1969 Configuration
------- |