tL

Reactor

Holter Perfusion
Roller Feed Pump

Mixer

Feed Tank

5-1/2 liters

Air Supply

Moisture
Trap

FIGURE 2

CONE REACTORS*
SCHEMATIC OF APPARATUS

*As manufactured by Pope Scientific

Effluent
Holding
Tank

Concentric Cones

Flow
Meter


PAGE NOT

AVAILABLE

DIGITALLY


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

Kg BOD Feed
Kg MLVSS Day

Clarifier Overflow
rate Liter/m¢min
(gal/ft* min)

TABLE 2

DATA SUMMARY

6.5°C Cone Reactor
Feed: Primary Plant Effluent

VW 15 13
139 132 153
2346 1885 1880
1915 1563 1587

51.3 16.3 13.3

63 88 91

u 69 96

53 36 31

62 73 80

0.10 0.14 0.18

3.7 4 4.9

(0.091) (0.10) (0.12)

28

155

2285

1801

11.7
92

45
33
79


solids to build up to a good operating level of about 3,000 mg/1 as shown
in Figure 14. It took a longer time for the up side biomass to reach that
level, Figure 15.

The upflow clarifier did not appear to perform as well as the horizontal
flow clarifier in period III and was sporadically passing solids causing
effluent suspended solids levels to vary from 20 to 100 mg/1. For the
horizontal flow side, Figure 14, the effluent suspended solids were gener-
ally below 40 mg/1.

In late April, the effect of autoinduced sludge wastage is apparent in the
up side, Figure 15. This wastage may have been triggered by the Rhodamine-
B dye which was injected on April 6 and April 16. Both units were shut
down on May 1, 1972.

OXIDATION DITCHES

Grube and Murphy (9) reported consistent removal efficiencies exceeding 90
percent at liquid temperatures of 2°C and air temperatures ranging down to
-49°C (-58°F) for the College oxidation ditch. Detention time in the clari-
fier was established at 5 hours through a dye study. Retention times in
the ditch averaged 2.3 days. No ice cover was reported at any time except
during mid-January and early February when transient skim ice formed ahead
of the rotor. Ice formation on the rotors did become a problem but was
eliminated by hanging rubber mats from the rotor housing to 5 cm (2 in.)
above the liquid surface. Influent temperatures averaged 16.6°C with a
minimum of 7.5°C.

Monthly autoinduced sludge wasting was reported with the MLSS of the ditch
increasing gradually for 3-4 weeks with the effluent suspended solids re-
maining low. At an undefined maximum mixed liquor concentration, a large
mass of solids was discharged for 1 to 2 days and the cycle repeated. Dis-
charged solids showed good settleability and produced no odor. The cause
of the discharge was not known.

All reported information for this ditch is summarized in Table 5. Apparent-
ly sampling from 1967 through 1969 and 1972 did not catch the effluent when
solids were being passed due to autoinduced wastage or operational upsets.
The 1969 data are unpublished and supplied by the Institute of Water Re-
sources, University of Alaska. They are from grab samples that were collec-
ted from one to six times per month, but in most cases, weekly. The 1972
data was unpublished data supplied by College Utilities Corporation and are
from grab samples that were collected, generally once every other week.

For the January through March 1971 data, 2 of the 23 sampling dates have ef-
fluent BOD's greater than feed (raw sewage) BOD's. Three of the 17 effluent
BOD's are greater than corresponding feed BOD's for the May through July
1971 data.

All the sample sets except two were grab. Sludge return line plugging and
anaerobic activity in the ditch may have been responsible for the poor May

37


SOLIDS SEPARATION

Solids separation is dependent upon both the biological and physical aspects

of the system. Sludge, although it may bulk and Jead to separation problems,
can be developed which will perform efficiently and produce non-turbid effluent
at temperatures <1°C. A turbid effluent at cold temperatures, as at higher
temperatures, is caused by an unacclimated sludge or an organic loading rate
which is too high. Under these conditions, a less stabilized sludge develops
with a corresponding relative decrease in numbers of stalked ciliates and an in-
crease of free swimming organisms which contributes to turbidity. High loading
at low temperatures affects the separation process resulting in poor performance.

Tube settlers can provide effective solids separation for sludges with sludge
volume index (SVI) ranging up to 250 at temperatures above 10°C. They can also
be considered as a device for improving effluent quality during upsets in the
biological process or during peak flow rates. Cleaning of the tubes is neces-
sary on a routine basis during normal operation with high MLSS concentration or
bulking sludges. If a regular turnover of sludge in the tubes is not main-
tained by frequent cleaning, denitrification at temperatures greater than 8°C
can cause sludge to rise in the tubes and overflow in the effluent. Tube
settlers also make it difficult to determine sludge blanket depth.

The performance of the upflow clarifier with tubes was comparable to the hori-
zontal flow clarifier at the EAFB pilot units. Clarifier overflow rates should
be held below 12 lit/sq m/min (0.3 gal./sq ft/min) at low operating tempera-
tures on an average daily flow basis and 20 lit/sq m/min (0.5 gal./sq ft/min)
at peak flows.

SLUDGE WASTING

Careful attention to sludge wasting and disposal in cold climates for the exten-
ded aeration process is a necessity. As the process temperature decreases,
the excess sludge production increases and may reach 0.6 Kg SS/Kg BOD applied
below 7°C. The standard wastage criteria of 0.5 Kg SS/Kg BOD applied is ade-
quate if 0.1 Kg SS/Kg BOD applied can be tolerated in the effluent. MLSS
levels appear to be cyclic, thereby causing widely fluctuating effluent sus-
pended solids levels. At low temperatures, this auto-induced sludge wastage
in the effluent can be expected to be more severe. Sludge wasting and dis-
posal facilities or a polishing lagoon for effluent discharge should be
provided where necessary to protect receiving waters. Larger extended aera-
tion units lacking wastage facilities should have a sand filter or micro-
screen for effluent filtration

NUTRIENTS AND COLIFORM REMOVAL

At low temperatures, 6°C or less, there was no significant nitrogen removal
in the pilot extended aeration units. Phosphorus removal was also insigni-
ficant, but appeared to be independent of temperature. Total coliform
reduction at low temperatures, 10°C or less, was from 90-98 percent; similar
to warmer temperature expectations.


SECTION VIT
MINOR FACTORS AFFECTING PERFORMANCE

MIXING

Results from the qualitative dye study at EAFB indicated that there was com-
plete mixing in the aeration basin but that the minimum system flow-through
time was very short. For instance, the horizontal side, Rhodamine-B dye
(v1 liter 40% solution) was injected into the feed and in less than 5 min-
utes, the aeration basin was completely colored. A colored upwelling under
the clarifier effluent trough was noted at 35 minutes. The liquid ] meter
down in the center of the horizontal flow clarifier had not developed any
color by the time the dye was beginning to pass out with the effluent at
about 45 minutes. This indicates that it would be most wise to locate

the effluent weir away from any wall or baffle when density currents could
cause upwelling. Mixing time to color the up side aeration basin was also
less than 5 minutes, but the dye appeared above the tubes (settler) in 25
minutes and was passing into the effluent at 1/2 hour.

The velocity profile for the EAFB extended aeration basins was determined
using a vertical vane, magnetic head, velocity meter. This instrument in-
dicated only the horizontal component of the velocity. Surface velocities
were measured by timing a floating wood block. The velocities at various
depths are listed in Table 11.

All velocities except those near the surface were consistently less than
the generally recommended 0.3 meters (1 ft) per second but there was no
excessive sludge accumulation in the bottom of either basin. It should be
remembered, however, that both units were fed with primary effluent. Opera-
tion with air inputs as low as 5 cmm/10® liters (0.7 SCFM/1000 gal.) had
caused some MLSS to settle in the aeration basin.

For weaker sewage, mixing may require more air than does oxygen transfer.
For adequate mixing in vertical wall tanks with 3.4 m (11 ft) aerator

submergence, the air requirement is 7 to 14 cmm/10© liters (1 to 2.0
SCFM/1000 gal.).

Grube (9) reported surface velocities on the College Utilities oxidation
ditch to be about 0.3 m per second. Murphy (10) later reported excessive
sludge deposition and said, "...it thus appears that the rectangular con-
figuration and the aerators used in this plant are unsuitable for keeping
the floc in suspension.”

BIOLOGICAL CHARACTERISTICS

Poor settling sludges were developed during the operation of the cold room
bench scale reactors with the Sludge Volume Index (SVI) consistently ran-
ging above 200. The sludge produced appeared to be of a zoogeal type

65


mg/1 suspended solids under present biological conditions and 5-20 mg/1
under normal conditions. They stated that material will collect on top of
the tubes and that routine cleaning is required to maintain effluent qual-
ity. Pohl (21) investigated tube settlers in the laboratory and found his
best results at room temperature; however, he felt the tubes occasionally
passed excessive colloidal solids.

Tube settlers were evaluated as a possible alternate means of providing
solids separation and return. Initial data were obtained from the 33.7-
liter reactor with 5 cm x 5 cm (2 x 2 in.) settling tubes. These results
are summarized in Table 7 and are based on continuous flow without an on-
off or backwash cycle. A plot of effluent suspended solids vs. overflow
rates is shown in Figure 18.

Effluent overflow rates were varied by utilizing two pumps, one to provide
recycle and one for effluent, as shown in Figure 5. A desired overflow
rate (less than the feed rate) was set with the effluent pump on one of
the tubes while the remaining feed was forced to flow through the second
tube to the overflow Tine. The desired flow rate through the second tube
could then be obtained by utilizing a recycle pump.

During operation, sludge rose in the tubes until it reached a level at
which it was in equilibrium with the effluent flow. Action in the tube
consisted of a rolling motion in which solids were being carried up along
the top side of the tube in a mass with the effluent, as shown in Figure
19. The mass gradually settled toward the bottom side of the tube where
it entered 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). This fact was confirmed by placing
Rhodamine-B dye in one of the 33.7-liter reactor tubes while the sludge
was at a high level of approximately 1.3 m (50 in.) and timing the rate of
descent along the bottom of the tube. Figure 20 shows a plot of sludge
level in the 5 cm x 5 cm (2 x 2 in.) tubes at various continuous overflow
rates.

As an illustration of the tendency of the sludge to reach a certain level
in the tubes in equilibrium with the effluent flow, a plot of sludge rate
of ascent vs. sludge height at a given overflow rate is presented in Figure
21. This curve was obtained by shutting off the effluent flow until the
sludge settled to a low height in the tube. The overflow rate was then
set and the sludge height recorded at specific time intervals. As can be
seen, the rate of sludge rise markedly decreases as the sludge height in-
creases.

During this period of operation, the SVI's of the mixed liquor ranged
around 230 without hindering operation of the reactor. During the pre-
viously described erratic cold room operation, while trying to reach an
8°C reactor temperature, the mixed liquor SVI increased to around 260 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, even-
tually spilling out with the effluent. Cutting the effluent flow rates
back to less than 8 lit/sq m/min (0.2 gal./sq ft/min) resulted in lowering
the DO in the effluent tubes to zero, further complicating the problem.

47


PERCENT BOD REMAINING

PERFORMANCE VS. SOLIDS DETENTION
EIELSON AIR FORCE BASE EXTENDED AERATION UNITS

LEGEND: SIDE PERIOD TEMPERATURE °C
( oI 7-17
100 +- A Horizontal( Il 2-9
904+ A (II) (III 1-8
80 + ( 1 7-19
© Up II 2-7
70 (III 1-8

30 4
O (III)
20 74
A (1)
NSF Package Plant
Startup Data (T3)
10 4
9 4 NSF Theoretical
4 Effluent SSO
8 Mature Plant (13)
7+
6+
5 +
4 t t 4
500 1500 2500 3500

MLSS x DETENTION (mg/1-days)

FIGURE 17
45


SLUDGE HT (cent.)

L 40
1007 b A
Q
S (0)
L 30
Ls ©. a | emetactures
&A Tube Length
50 20
°
ran Legend: © <1°C
L A4C
0 (gpm/ft?) MLSS: 4000 mg/1
0.3 0.5 0.7
it } L
T T T
10 20 30

Overflow Rates Lit/sq m/min

FIGURE 20
33.7-LITER REACTOR
SLUDGE HEIGHTS IN EFFLUENT TUBES

VS.
EFFLUENT OVERFLOW RATES WITH CONTINUOUS FLOW THROUGH TUBES

5]


TABLE 9

47.1-LITER REACTOR
SLUDGE LEVELS IN TUBES AT
VARIOUS EFFLUENT OVERFLOW RATES

Overflow Rate! Reactor 10 x 8.9 cm Tube(2) | 5 x 8.9 cm Tubes (2)
Liter Susp. Sludge Hts cm (in.) | Sludge Hts cm (in.)
m min Solids
(gpm/ft2) Temp (°C) | (mg/1) | SVI High Low High Low

1.2 (.3)

[on 1/2 hr

off 1/2 hr] 4 4407 | 185 | 86 (34) §8 (23) | 61 (24) 28 (11)

2.0 (.5)

[on 1/2 hr

off 1/2 hr] 4 4253 | 223 1119 (47) | 58 (23) | 76 (30) 20 (8)

2.0 (.5)

[on 2-1/2 hr

off 1/2 with

backwash] 8 4023 | 232 | 58 (23) 0 38 (15) 0

[1] Notes in brackets indicate the type cycle
of effluent flow through the tubes

(2) High and low points represent the maximum heights
which the sludge reached in the tubes during
effluent flow and the minimum levels reached
during the off cycle or backwash cycle

55


PERCENT BOD REMOVAL

TEMPERATURE EFFECTS OF LOADING ON PERFORMANCE
EFFLUENT SS LIMITED TO LESS THAN 100 mg/1
DATA FROM EIELSON AIR FORCE BASE AND REFERENCES (10 & 12)

LEGEND:
O 1-7°c--AERL & EAFB
9 Period III Horizontal Side ), ..
V_ Period III Up Side 18°C
O 7-12°C (10) & EAFB
@ 12-25°C (12) & EAFB
100 +-
| e
g fo)
o e
o to © @ © 2 Warm
~_~--@---0_ 0 TEMP TREND
% T~ Le >
6 “~~
vv ~.lo
“Swe 6
80 -+- oO ~2O
O~ Shp a)
e “\A% a
e VX,
8 a <%
70 + _
N
N
~
oO06U0d~C~wNN
Oo
a]
50 -+-
oO
40 |
0 0.04 0.08 0.12 0.16 0.20
ORGANIC LOAD Kg BOD
Kg MLSS DAY
FIGURE 16

43


St

Feed
Tank

Refrigera-
tion Unit

Feed Pump
(Hol ter)

QU
VITTTHT

Effluent
Tank

10 cm

Tube

Mixing Pump

Reactor

Air Supply Plexiglas

Moisture
Trap

FIGURE 6

47. 1-LITER (12.5 GALLON) REACTOR
SCHEMATIC OF APPARATUS

|-hr timer

r4accc O

Solenoid Valves

Effluent
Pump
(Holter)

4 24-hr

Recycle
Pump (Holter)

Effluent Tank
5 cm Tubes


PAGE NOT

AVAILABLE

DIGITALLY


UPSETS

The EAFB extended aeration units were relatively insensitive to starvation
or temporary lack of oxygen. As noted on Figures 12 and 13, the feed was
off for.as long as 3 consecutive days in October with very little effect
upon performance. A white surface foam formed on the aeration basin indi-
cating the starvation condition. Due to temporary unbalance in the aeration
system, the air to one side or the other was off for many hours (overnight
in a few cases) with no noticable effect upon performance.

The effect of Rhodamine-B dye poisoning is noted on Figure 12 for period

III. Dye strength was estimated to be from 2 to 7 mg/] in the aeration ba-
sins. The high concentration was used to qualitatively define the basin's
flow patterns without the use of a fluorometer. The dye-induced wastage

did not occur until 4 to 6 days after injection into the low temperature
mixed liquor. Apparently, the inhibitory effects took 3 to 5 days to develop.

64


SECTION
I
Il

It

Iv

\

VI

VII

VIII

CONTENTS

RECOMMENDATIONS
SUMMARY AND CONCLUSIONS

Facility Design

Organic Loading

Solids Separation

Sludge Wasting

Nutrients and Coliform Removal
INTRODUCTION

General
Scope and Purpose
Basic Process Description

FACILITIES AND METHODS
Cold Room Bench Scale Reactors
Eielson Air Force Base Pilot Plants
Oxidation Ditches

OPERATION AND PERFORMANCE
Cold Room Reactors
Eielson Air Force Base Units
Oxidation Ditches

MAJOR FACTORS AFFECTING PERFORMANCE
Organic Loading Effects
Solids Levels and Separation
Solids Accumulation and Wastage
Dissolved Oxygen Levels
Upsets

MINOR FACTORS AFFECTING PERFORMANCE
Mixing

Biological Characteristics
Equipment Housing and Process Exposure

OTHER PERFORMANCE CRITERIA

Nutrients
Total Coliforms

REFERECES

GLOSSARY

Vii

PAGE

Aadwn

a

NAD

10

10
17
23

26
26
29
37
40
40
44
57
63
64
65
65
65
68
70

70
74

81


similar to that reported by Heukelekian and Wiesburg (35) who found a direct
correlation between increasing SVI and increasing bound water for this type
of bulking. Very little evidence of Sphaerotilus was noted during microscopic
examination. Ludzack (18) also reported a poor settling sludge at low tem-
peratures (5°C) with very poor drainability.

Because of the differences noted in operation of the cone reactors at 1.3°C
and 6.5°C, it was decided to raise the 33.7-liter reactor temperature gra-
dually, first to 4°C and then to 8°C, letting the reactor stabilize at each
temperature. This was done in an attempt to determine the changing sludge
characteristics with temperature changes from 4° to 8°C.

Reactor temperature was first raised to 4°C from less than 1°C over a period
of 2 days with no noticeable effects. After stabilizing at 4°C, reactor
temperature was again raised. However, at the same time, the coils of the
cold room refrigeration unit began to freeze due to excessive mositure con-
densation and the cold room operation became very erratic. Reactor tempera-
ture went from 4°C to 10°C, back to 6.5°C, and finally stabilized at around
8°C within about 5 days. The SVI jumped from around 230 to 260 with the
sludge changing from a granular matrix to a fluffy, snowflake appearance.
The reactor began to pass heavy solids concentrations in the effluent 3

days after the erratic cold room operation began. Noticeable microscopic
changes during this period were an obvious reduction in quantity and activity
of protozoa.

Reactor operation was maintained at 8°C for approximately 10 days during which
time it did not return to its normal state. It was subsequently returned to
the colder operating temperatures and the feed cut off for 12 days in an at-
tempt tc improve the settling qualities of the sludge. The SVI's returned

to around 230 but few other changes took place with negligible decrease in
suspended solids or percent volatile suspended solids. The quantity and
activity of protozoa did begin returning to their former state at about the
time the reactor temperature was returned to the lower level.

The significance of protozoa in an efficiently operating activated sludge
process, as reported by McKinney (17), was observed during operation of

the reactors even at the coldest temperatures. The 47.1-liter reactor

was started at temperatures <2°C with return sludge seed 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, 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
states that the presence of stalked ciliates indicated an activated sludge
system with a low BOD effluent. Vorticella was present in both reactors

after initial startup except for one period in the 47.1-liter reactor as
described below.

After stable operations at temperatures of <2°C and 14°C, the 47.1-liter
reactor temperature was increased to 8°C over a period of 6 days. Effluent

67


Table 11. EIELSON AIR FORCE BASE EXTENDED AERATION BASINS
HORIZONTAL VELOCITY COMPONENTS

Velocities in Meters/second (ft/second)

Location in Aeration Basins

Horizontal Flow Up Flow
Depth m (ft) Cc D A B
Surface ee-- n= 10.37 (1.2) | 0.30 (1,0) | ----  ---
0.3 (1) 0.15 (0.5) |0.30 ( 1.0) | 0.27 ( 9.9) 0.12 (0.4)
1.0 ( 3) 0.06 (0.2) |0.09 (0.3) }0.18 ( 0.6) 0.12 (0.4)
1.5 ( 5) 0.09 (0.3) }0.06 ( 0.2) }0.03 ( 0.1) 0.09 (0.3)
2.1 ( 7) 0.06 (0.2) |0.09 ( 0.3) | 0.06 ( 0.2) 0.09 (0.3)
2.7 (9) 0.03 (0.1) |0.06 ( 0.2) }0.09 ( 0.3) 0.12 (0.4)
3.4 (11) 0.06 (0.2) |0.06 ( 0.2) }0.12 ( 0.4) } 0.18 (0.6)
Liquid Depth wen nee | 307 (12ft) | 3.7 (12ft) wrote
Air lifts off; using 3.4 cubic meter/min (cmm) compressor;
bleeding approximately 1.4 cmm
2.3m (7 1/2') 2.3m (7 1/2!)
0.9m 0.9m
3") —
( | A (3')
x x x
c 1) A B
Horizontal Flow Up Flow ~
ro)
—_— &
—— Aerators Aerators
a
Pian
Front 2/3 of Aeration Basins

66


Clark, et al. (8) have stated "When utilizing exposed basins, heat loss
effects must be evaluated in conjunction with detention time determinations
to avoid potential freezing problems. Solids entrainment in ice can cause
failures of an activated sludge process." Concentrating waste sludge by

this method was discussed in Section VI.

During March of 1972, the sewage feed temperature for the EAFB units was
less than 4°C. With a hydraulic detention of 1 day, a thin sheet of ice
formed on all basins except directly over aerators and air lift sludge
returns. Based upon the author's experience, the following maximum ex-
posed aeration basin (housed clarifiers) detentions should not be exceeded
where the average January temperature is less than -23°C (-10°F):

Detention, Days Sewage Temperature, °C
1 5
2 10
4 20

It is possible to operate with longer detentions at lower temperatures
but operating problems will increase exponentially.

69


SECTION V
OPERATION AND PERFORMANCE

COLD ROOM REACTORS

Results of operation of the bench scale cone reactors are summarized in
Tables 1 and 2. Filtered effluent represents the effluent sample run
through a filter pad (used in separation of membrane filter pads in pack-
aging) which was coarse enough to leave bacteria for seed in BOD determi-
nations yet reduce the suspended solids to essentially zero. BOD deter-
minations on the filtered effluent samples were performed to obtain a
rough determination of the amount of dissolved organic material removed.

Both biological sludges were relatively easy to establish. The 6.5°C
reactor had been operating for approximately 6 months before this series
of sampling was begun. The reactor, operating at 1.3°C, was placed in
operation approximately 6 weeks before sampling began and seeded with
material that had been aerated in the cold room in a 19-liter (5-gal.)
container which was batch fed periodically with domestic sewage. The reac-
tor runs were started with the longest detention time first and the times
decreased in chronological order. The 1.3°C reactor did not become stabi-
lized until the shorter detention times were reached, as evidenced by the
MLSS buildup as time progressed.

There was apparently little difference in the biological activity at the
two temperatures; however, operation of the reactor at 6.5°C was more
erratic. These reactors were operated with a clarifier overflow rate

less than 7.1 lit/sq m/min (0.17 gal./sq ft/min). Both reactors generally
practiced "autoinduced sludge wasting" in the same manner as the College
Utilities oxidation ditch as described by Grube and Murphy (1). 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 with 2 to 3 weeks as op-
posed to the monthly occurrences 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 concentra-
tion of solids in the mixed liquor increased, the level of solids in the
settling tube 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 be-
gan to build before discharging. The pH dropped from slightly above 7 to
values of 6.6 to 6.7. The 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,

26


10

[cm
4 5cm
T
—~—yJ-——} — -—
Effluent | Effluent
|
|
|
|
145cm
|
/ / a
° ( Influent ——q
O° 60° Air —>- 1" =
! } —
<— ‘ocn—>4 |

FIGURE 3

33.7-LITER (8.9-GALLON) REACTOR DETAILS

12


4.6 1 (15') 3.4 m (11')

re _ -
Horizontal M.L. Feed Slot
q | y 1 Horizontal Clarifier
| nO Aerators i el tE- & Hoppers
7 " a 7, HORIZONTAL
10 ca (4") i ho AERATION L A

Airlifts (2)

A

BASIN

4m

‘|

[+> 10 cm (4") ® Sludge
Collector

i

1

\

\ =
\

A >t r
i

Horizontal Effluent Box

f 5 cm (2") ® Feed Pipes (2)
- -

=

i aires il i qe M.-L. Down Flow Channel
N

te
tr

i it
tp f=

— f {Of
Fm (14") \ NAY TL. Feed Troughs (3)

Effluent

“ 1 Pi
10 cm (4") 9 siudbe 15 om (6") Collector Pipes (3)
Collection and Return

i
i
® Bo |__uUp Effluent Box
= | : :
~ ! =
a 8 k i | H wd \ |
| | T >a 4 UPTAILOW K ore :
i i . ! ttl uent Line
i | /airliftd (2) -jtonr dice Vv
CLARIFIER | | 4
Le}
net

Air ‘Pipe
and Valves

FIGURE 7. CEIELSON AIR FORCE BASE EXTENDED AERATION PILOT PLANTS


Bypass channel for circulation through
back channel and under tubes

102 , 25 cm
> | Y
Return Fe
——d 20 on
Effluent | ___
157 cm
. 1°
Air ————
rr 8.94

cm

Figure 5

47.1-LITER (12.5-GALLON) REACTOR DETAILS


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

Kg BOD Feed
Kg MLVSS-DAY

Clarifier Overflow
rate liger/m min
(gal/ft° min)

TABLE 1

DATA SUMMARY

1.3°C Cone Reactor
Feed: Primary Plant Effluent

21 15
WwW 170
1074 1561
890 1324
37 i
66 93
29 43
40 62
64 64
0.74 0.21
3.0 4.1
(0.074) (0.10)

27

201

2657

2212

20
90

38
28
86

184

2926
2402

14
92

82
44
76

0.20


a

Kg excess volatile sludge = c(Kg BOD removed) - k(Kg volatile sludge)
day day

Net Growth = New Growth - Endogenous Increase

The cell yield (c) represents the ratio of new cells produced per unit weight
of biochemical oxygen demand (BOD) removed from the wastewater. The endo-
genous respiration rate (k) represents the decrease in cell tissue in the
process due to self-destruction of cellular material. The volatile sludge

present in a system is generally measured by the weight of volatile sus-
pended solids (VSS).

An important parameter in biological treatment of wastewater is the food to
microorganism ratio (Kg BOD/Kg MLVSS Day) which varies considerably for the
different variations in the activated sludge process. The conventional
activated sludge process operates at an organic loading factor varying

from 0.2 to 0.5 Kg BOD/Kg MLVSS Day, with a volumetric loading factor of
about 0.56 Kg BOD/Day cubic meter (35 1b BOD/Day 1000 cubic feet) of aeration
tank capacity. Excess sludge disposal for normal domestic sewage is about

1.5 percent of influent flow and BOD removal efficiencies are 80 percent or
better.

The extended aeration process operates at loading factors ranging from 0.05
to 0.2 Kg BOD/Kg MLVSS Day, or about 0.32 Kg BOD/Day cu m (20 1b

BOD/Day 1000 cu ft) of aeration tank capacity. Extended aeration BOD
removal efficiencies approach those of conventional activated sludge when
sludge wasting is practiced. When excess volatile sludge, produced in the
extended aeration system, is allowed to go out with (wasted in) the process
effluent, percentage BOD removals are lower, ranging upward from 50 percent.


SECTION X

GLOSSARY

BOD - Biochemical Oxygen Demand, 5 day - 20°C

cium - cubic meters per minute

coD - Chemical Oxygen Demand, dichromate oxidation
DO - Dissolved Oxygen

EAFB - Eielson Air Force Base

gpm ft? - gallons per minute per square foot

K cal - kilogram calories

Tb - pound mass

Lit liter(s)

ne sq m - square meter(s)
i - cum - cubic meter(s)
ng - milligram mass

MG - million gallon(s)

MGD - million gallons per day

MLSS - mixed liquor suspended solids

MLVSS - mixed liquor volatile suspended solids
0-P - orthophosphate

SCF - standard cubic feet

‘SCFM - standard cubic feet per minute

ss - suspended solids

SVI - sludge volume index

T-P total phosphate

S - total solids

TVS - total volatile solids

VSS - volatile suspended solids

81


suspended solids increased from approximately 5 mg/1 before the temperature
change to approximately 18 mg/1 during the change and to a maximum of 46
mg/1 3 days after reaching 8°C. During this period, the effluent became
very turbid with very few solids settling out in the effluent tank. Pro-
tozoa became very reduced in numbers and very inactive. Again, the return
to normal operation corresponded to an increase in the number of Vorticella
and Paramecium present in the sludge. Coliform removals also directly cor-
respond to the numbers of protozoa present, dropping from 99.8 percent re-
movals before the upset to less than 80 percent during the period of reduced
protozoa.

Aside from temperature change, the only other parameter measured, which
could explah the sudden change in reactor performance, was an increase in
dissolved solids for over a one day period. Dissolved solids ranged from
250 to 360 mg/1 prior to the sharp increase to 450 for one day and a sub-
sequent decrease to .360 mg/1. This could be evidence of toxic material

in the feed. Ten days after returning to stable operation at 8°C, the
sludge was exhibiting the same characteristics as with the 33.7-liter reac-
tor. That is, the SVI's were ranging around 250 and the floc exhibited a
fluffy snowflake appearance. Reactor operation was not impaired under these
conditions because of the backwash cycle added to the settling apparatus.

EQUIPMENT HOUSING AND PROCESS EXPOSURE

At EAFB the unheated A-frame clarifier provided sufficient protection even
though it was not totally sealed at the clarifier surface or around a poly-
ethylene film curtain door. During low liquid temperature operation, thin
ice formed on the surfaces of the clarifiers but did not affect the opera-
tion other than to make manual removal of floatables difficult. During cold
weather, 40°C and colder, a 38,000 K cal/hr space heater (150,000 BTU/hr)
was set at about 4°C and aimed at the sampling equipment to assure operation
and liquid samples. It is obvious that freeze protection is necessary any-
where aqueous fluids are exposed.

Grube and Murphy (9) indicated a thick ice formation on the concrete block
oxidation ditch-clarifier building interior due to condensation. The ice
did not create any problems, however. They reported the building tempera-
ture remained relatively constant at 1.7°C.

At the Glenwood, Minnesota oxidation ditch (11) only the rotors had any
climatic protection. They were covered with a structure similar to that
at the College oxidation ditch.

In subarctic climates, if sufficient care is used in the design of extended
aeration units, there is no reason to house the aeration basin. Ranganathan
and Murphy (10) reported that the College oxidation ditch accumulated a sheet
of surface ice approximately 6 m (20 ft) wide, 30 cm (1 ft) thick and 21 m
(70 ft) long by mid-April of 1971. Solids concentration in the ice was
probably much higher than in the mixed liquor. They reported that when the
ice melted it released large quantities of solids.

68


At a later date, the 47.1-liter reactor was placed in operation. This
reactor was constructed with two tube sides, one 10 cm deep by 8.9 cm
wide, and two 5 cm deep by 8.9 cm wide, as shown in Figure 5. This reac-
tor also had a channel running down behind the tubes to permit circulation
of mixed liquor under the tubes for removal of settled sludge.

This reactor was operated for a period of time with a very low continuous
overflow rate and then increased to an average rate of 20 lit/sq m/min
(0.5 gal./sq ft/min) with an alternate on-off cycle. In other words, with
overflow for 1/2 hour and no overflow for 1/2 hour as a cycle, the actual
flow then was 40 lit/sq m/min (1 gal./sq ft/min) for 1/2 hour.

A summary of results for this reactor is shown in Table 8 and the corres-
ponding maximum and minimum sludge heights in the tubes presented in Table
9. As indicated, the SVI's again ranged above 200 with very consistent
solids removals. Effluent solids concentrations are very low for the whole
range of studies. The longer on-times for the on-off cycle (2-1/2 hours as
opposed to 1/2 hour) did indicate that longer cycles may result in higher
effluent solids concentration. The data were inconclusive, however, because
of the few sets of data and the fact that the change in temperature may have
been a contributing factor in the higher effluent solids at 7.8°C.

Neither the 5 cm x 8.9 cm tubes or the 10 cm x 8.9 cm tube appeared to have
an advantage as far as solids removal are concerned. There was a significant
difference between the maximum sludge heights reached within the tubes, how-
ever, which is a very important consideration. Lengths of the tubes will

be limited in actual application because of space requirements and economic
reasons.

As indicated in Table 9, the maximum sludge heights reached in the smaller
cross-section tubes were considerably less than those reached in the lar-
ger tube. This may be attributed to the fact that the two smaller tubes
provided twice the surface area at the top side of the tubes which signifi-
cantly reduced the effluent flow along these surfaces. Consequently. the
upward force on the sludge in the tubes was reduced resulting in lower sludge
heights.

An observation of sludge heights in the tubes during backwash operations
was also recorded. Introduction of the backwash cycle did significantly
reduce the maximum sludge heights by forcing the sludge blanket back down
the tubes. Backwashing provides a definite advantage in that it prevents
a bulky sludge from becoming stagnant in the tubes as occurred when the
33.7-liter reactor operation failed at 8°C. Cold room experience indica-
ted that clarifier backwashing in conjunction with low overflow rates was
successful in overcoming problems associated with bulking sludge.

Organic loading rates also affected sludge settleability as shown in Fig-
ure 22, which is a graph of settling rate--0 to 5 min rate in a 2-liter

settlometer vs. MLSS for different detention times and temperatures for

the horizontal side, EAFB pilot units. Generally, the settling velocity
decreased with decreasing temperature and increasing MLSS concentration.

The data should be interpreted with caution for they do not suggest that
one would not be able to hold a MLSS concentration greater than 3000 mg/1
at an overflow greater than 12 lit/sq m/min (0.30 gal./sq ft/min).

53


SECTION I

RECOMMENDATIONS

The conventional extended aeration sewage treatment process can provide
secondary treatment with low temperature sewage under subarctic conditions
if the two following recommendations are followed:

1. Facility Design: The required degree of protection against freezing
must be determined b) proper heat transfer calculations.

2. Process Design: (a) Organic loading should not exceed 0.08 Kg BOD/
Kg MLSS/Day at MLSS temperatures below 7°C. (b) An effluent polishing
system, such as a lagoon, sand filter, or microscreen, should be used if
separate sludge wastage facilities are not installed.


DIMENSIONS
1.3-2 m (4.3-6 ft)

I Water Depth
(9) Ditch Volume 1260 m> (333,000 gat.)

Clarifier Volume - 205 m> (54,000 gal.)
Rotors (2) 0.7 m (27.5 in.) dia x 4 m (13 ft)
89 RPM @ 22 KW (30 HP)

9 Rotors hanging below housing

9 m (30 ft)
ty | Circular clarifier
e
Lo vA
8
; IN
a a
» + influent
b---4

1
i
effluent

Capacity: 1/2 MGD

Location: College, Alaska

Start Up: Summer 1965

wo, FIGURE 11

COLLEGE UTILITIES OXIDATION DITCH

12 m (40 ft)

24


Cell vield (c) increases with increasing temperature because it is believed
a larger portion of BOD removal is utilized for energy at low temperatures
than at high temperatures (26). The rate of endogenous respiration is de-
pressed at low temperatures (more so than cell yield); therefore, the quantity
of excess sludge produced is increased. Benedict (16) reports values for c
and k (endogenous rate) at 4°C of 0.42 mg/mg COD and 0.0132/day respectively.

In discussing small extended aeration treatment plants, an Alaskan Depart-
ment of Health and Welfare report (27) indicates that, since the effluent
will usually be discharged into a small stream, it must be well treated.
The report also states that, in most cases, to produce a good effluent,
sludge wasting must be practiced.

Morris (28) studied the effects of effluent discharges to streams by two
extended aeration plants having no provision for intentional sludge wasting,
and stated that plant efficiency is directly related to the amount of solids
lost in the effluent. He indicated sludge discharges occur similar to those
described by Grube and Murphy (1) with solids depositing on the stream bed,
creating nuisance potential.

Statements such as the above should be considered along with the fact that
excess solids production increases with decreasing treatment plant tem-
peratures. In view of this observation, sludge wasting and disposal in
cold climates must be given special consideration. Based on cold room data,
Tables 3 and 4, it would appear that provision should be made for wasting
0.5 Kg solids per Kg of BOD removed at colder operating temperatures (<5°C)
and at organic loadings of 0.1 Kg influent BOD/Day/Kg MLVSS.

Different results were obtained at EAFB extended aeration units where the
solids accumulation is defined as:

Solids accumulation (SA) = AMLSS + Solids Lost (EFFLUENT + WASTAGE)

Solids accumulation is calculated as a ratio of SS to input BOD. The following
formula is used to calculate the solids accumulation from a computer printout
of data from the EAFB pilot plant:

SA = (AMLSS) (DETENTION TIME) + TOTAL SS LOST
(Avg Feed Bod) (Data Per- Avg Feed BOD
iod) (Days )

Where: AMLSS = MLSS at end of data period - MLSS at start of
data period.

The EAFB data points for the six periods are plotted in Figure 24, Solids
Accumulations, along with the NSF package plant data (13). Some of the
EAFB data indicates that excess solids were accumulating at rates greater
than 0.6 Kg SS/Kg BOD applied. Excess solids are suspended solids above
those required to-maintain a constant MLSS level. Under normal operations,
some SS is wasted into the effluent. Assuming an SA of 0.6, applied (feed)
BOD equal to 200 mg/1 and an effluent SS of 20 mg/1, then the separate
(exclusive of effluent) wastage requirement would be reduced by 0.1 Kg SS/
Kg BOD; yielding 0.5 Kg SS/Ka BOD to be wasted. The 0.5 figure then seems

60


adequate for low temperatures at low organic loadings <0.08 Kg BOD/Kg MLSS/
Day. High loadings at low temperatures is of course impracticable as shown
earlier. The EAFB influent SS to BOD ratio varied from 0.6 to 0.9. If one
is designing for a higher feed ratio, then the wastage facility capacity
might have to be increased.

Under normal conditions without intentional wastage, the MLSS will build

up to a certain high level (limited by settling characteristics and system
operation), then considerable SS will pass into the effluent in a short time,
reducing the MLSS to a more optimum level. This self-wastage has been called
"autoinduced wastage" (9). Between the wastage periods, the effluent SS has
always been less than 100 mg/1 for extended aeration units in stable equili-
brium. Intentional wastage should also always keep the effluent SS less than
100 mg/1.

At EAFB, intentional wastage was practiced only in period I. In period II
both sides were losing MLSS. During period II], it was attempted to find
the maximum MLSS the system would hold before autoinduced wastage occurred.
The horizontal side reached ~4100 mg/1 and the up side 13300 mg/1 before
autoinduced wastage was triggered at the low mixed liquor temperatures.

Separate intentional wastage has not been practiced at the College oxida-
tion ditch which caused some of the poor 1971 performance (Table 5). The
1972 performance appears much better, because autoinduced wastage periods
and recovery probably occurred between the every-other-week sampling periods.
Observation of the ditch effluent between some of the September and October
sampling periods showed it to be very rich in SS. The MLSS concentration,
as sampled, was observed to slowly drop from 5820 mg/1 on August 2, 1972,

to 2570 mg/1 on October 25, 1972.

The above discussion points out the necessity of obtaining 24-hour flow
proportioned composite samples for characterizing any short detention
(less than 10 days) biological waste treating system. In the opinion of
the author, separate intentional wastage would prevent sludge banks from
forming downstream of any secondary sewage treatment plant.

When separate wastage is practiced, disposing of the wasted sludge then
becomes a problem. Sludge digestion and disposal methods present a problem
at colder temperatures due to added heat requirements and poor drainability.
Ludzack (18) indicates that sludge development at cold temperatures may re-
quire digestion at higher temperatures before disposal. Thomas (26) indi-
cates the freeze-thaw cycle may be taken advantage of in cold climates to
increase drainability. Clark, et al. (8), have shown that sludge can

be concentrated in ice forming on an exposed aeration (digestion) basin.
The Sewage Commission of the City of Milwaukee (29) reports that freezing
is an excellent method of activated sludge conditioning. But they also
reported that capital and operating costs (refrigeration) were appreciably
higher for .the freeze method than for the chemical method. In the lower

49 states, freezing sludge is expensive, but in cold climates, it does not
require refrigeration facilities. Space to store wasted sludge during

the short summers is not usually expensive unless land values are high.

62


DISSOLVED OXYGEN LEVELS

The major winter difference between the oxidation ditch and the EAFB units
was in the activated sludge characteristics. The oxidation ditch MLSS
reached 5800 mg/1 with SVI less than 100, while the EAFB units limited
themselves to about 4100 mg/1 with SVI's usually greater than 100. A major
cause for this difference may have been the mixed liquor DO levels. The
oxidation ditch subsurface DO was usually less than 1 mg/1, while the DO
of the EAFB pilot units was usually greater than 1.5 mg/1 with no gradient
due to depth. At EAFB, lower DO activated sludges appeared to settle fas-
ter. Murphy (10) indicated that the cage rotors at the College utilities
oxidation ditch were not capable of transferring sufficient oxygen under
prevailing conditions.

For extended aeration, the oxygen requirements are much higher than for
conventional activated sludge due to the endogenous respiration and nitri-
fication requirements. For temperate climates, air requirement values of
100-130 cubic meters/Kg BOD (1500-2000 SCF/1b BOD) have been quoted (30,
31). Oxygen requirement is lower for low temperature operation because of
less nitrification and a lower wet oxidation (endogenous respiration) rate.

The following equation has been used to define the temperature effect of
oxygen transfer rates:

= wel) > Ty)
Ky = Kyo 1 2

where:

K = rate at TY)

@ = temperature coefficient

Eckenfelder and O'Connor (32) state that the temperature coefficient 0,
when applied to oxygen transfer efficiencies, has been reported to vary
from 1.016 to 1.047 and that studies on bubble aeration indicate a tempera-
ture coefficient of 1.02 applies. Effects of temperature on stream reaera-
tion have been studied under controlled experiments in the laboratory and
a @ value of 1.0241 found for the temperature range of 5 to 30°C (33).

Terashima, et al. (34), indicated the mass of oxygen transferred is more
affected by increasing the saturated dissolved oxygen concentration than
by decreasing the overall oxygen transfer coefficient and concluded low
water temperatures are not detrimental to oxygen transfer. In other words,
the increase in driving force (higher saturation) at lower temperatures
more than compensates for the increase in diffusion resistance. They
found @ equal to 1.017 in the temperature range of 5-25°C.

For oxygen transfer, the minimum air rate (to maintain 1/2 mg/1 DO) into
5°C, 2000 mg/1 MLSS was found to be 63 cubic meters/Kg BOD (1000 SCF/1b
BOD) at the EAFB units. The transfer efficiency (including surface effects)
with the open-type aerators (monospargers and shearboxes, both underloaded)
was approximately 4 percent at 3.4 m (11 ft) depth and 1/2 mg/1 DO.

63


Feed rates were held constant. To create an artificially high overflow rate,
effluent was taken from the clarifiers and pumped back into the aeration
basin. The artificial overflow rate plus the effluent rate equalled the
total overflow rate.

Initially. raw sewage was used as feed to the extended aeration units. Two
5-cm (2-in.) trash pumps pumped from the aerated grid chamber of the Air
Base's existing primary plant to a flow equalizer cooling pond. From the
cooling pond, the sewage was pumped at a constant rate with variable speed
pumps to the extended aeration units. A cooling pond level control acti-
vated the 5-cm trash pumps in the sewage plant. In late October 1971,

due to considerable trash pump clogging and down time caused by the raw
sewage feed, it was decided to use primary effluent as feed. The trash
pumps were then moved to the end of the primary plant's clarifiers. In
late December 1971, it was realized that the cold air did not have enough
heat absorption capacity to cool the sewage down to 5°C at flow rates
through the feed equalizer cooling pond. A spray system was added to this
pond which caused considerable ice masses but kept the feed temperature at
5°C or below. Feed (cooled primary effluent in this case) was introduced
into the complete mix aeration basins (Figure 7) near the common corner of
the basins and clarifiers. Flow rates to the units were varied from 76 to
150 cu m/day (20,000 to 40,000 gal./day). Flow splitting, control and moni-
toring were accomplished with valves and venturi meters.

In the horizontal flow side mixed liquor was circulated by the aerators and
flowed into the horizontal flow clarifier (Figures 7, 8 and 10) through

the horizontal mixed-liquor feed hole and slot. Sludge was collected by a
10-cm (4-in.) manifold in the bottom of each of the two hoppers and re-
turned to the aeration basin by 10-cm airlifts. Effluent and artificial
overflow was collected near the surface at the end of the horizontal flow
clarifier. Artificial overflow was created in the same manner as for the
upflow section. Aeration in the horizontal side aeration section was ac-
complished by means of 30 Chicago Pump (C.P.) shearfuser aeration boxes
which were divided into 2/3 and 1/3 sections such that the air rate would
be varied over a wide range. As can be seen in Figures 7 and 10, the aera-
tion basins and clarifiers shared common walls. The basin walls were
reinforced concrete. All air lift sludge returns were mounted in the
aeration basins, the end of their discharge pipes terminated just at

water level. Air lines were steel pipes while sludge and airlift pipes
were plastic. The 60° sludge hoppers were sheet metal. Dead volume
between hopper and concrete walls was filled with sand. The horizontal
flow clarifier feed slot, as shown in Figure 8, is about 3.05 decimeters

(1 ft) high and consists of vertical 2.5 x 15 cm (1 x 6 in.) wood slats
placed 5 cm (2 in.) on center.

The aeration basins of both units were exposed to the environment. The
clarifier sections were housed in an insulated, unheated A-frame building.
During extreme cold periods (<-40°C or °F), limited heat was applied to
prevent freezing of the sampling systems. The A-frame was an equilaterial
triangle covering both clarifiers, approximately 3.7 x 9.2 m long (12 x

30 ft). The A's were 5 x 15 cm x 3.7 m, 0.6 mon centers (2 x 6 in. x

12 ft, 24 in. on centers). Roof panels were of sandwich construction with

21


Suspended Solids (mg/1)

5000

4000

3000

2000

1000

10

(oo)

fon

=~

he

°

Susrended
Solids

Dissolved
Oxygen

q
Station

Total

Na ;
LS /

NSN
“.

Effluent

180

+160
+140
+120

7100

T 80

40

+ +
14 16
Station

Influent Reactor

FIGURE 26

DENITRIFICATION STUDY, TUBE SETTLER NITROGEN PROFILE

73

Effluent

Dissolved Oxygen (mg/1)

Total Nitrogen (mg/1)


NUMBER
20

21

22

23

24
25
26

LIST OF FIGURES CONTINUED

33.7-Liter Reactor Sludge Heights in Effluent
Tubes vs. Effluent Overflow Rates with
Continuous Flow Through Tubes

Rate of Sludge Rise in Tubes vs. Sludge Height

2-Liter Settlometer Test, 0-5 Minute Rate EAFB
Pilot Extended Aeration blant

Volume Percent of Activated Sludge vs. Detention
Time--EAFB Pilot Extended Aeration Plant

Solids Accumulation EAFB Extended Aeration Units
Denitrification Study Sample Stations

Denitrification Study, Tube Settler Nitrogen
Profile

PAGE

51

52

56

58
61
72

73


NUMBER
1
2
3

10
|
12

13

16
7

18

LIST OF FIGURES

Basic Activated Sludge Treatment Process
Cone Reactors Schematic of Apparatus
33.7-Liter Reactor Details

33.7-Liter Reactor Schematic of Apparatus
47.1-Liter Reactor Details

47.1-Liter Reactor Schematic of Apparatus

Eielson Air Force Base Extended Aeration Pilot
Plants

Eielson Air Force Base Extended Aeration Pilot
Plant Sections

Upside Extended Aeration Pilot Unit

Horizontal Flow Extended Aeration Pilot Unit
College Utilities Oxidation Ditch

EAFB Pilot Extended Aeration Units Horizontal
Flow Clarifier Percent BOD Removal and Aeration

Basin Temperature

EAFB Pilot Extended Aeration Units Upflow Clarifier
Percent BOD Removal and Aeration Basin Temperature

EAFB Pilot Extended Aeration Units Horizontal

Flow Clarifier Mixed Liquor Suspended Solids and
Effluent Suspended Solids

EAFB Pilot Extended Aeration Units Upflow Clarifier
Mixed Liquor Suspended Solids and Effluent Suspended
Solids

Temperature Effects of Loading on Performance

Performance vs. Solids Detention EAFB Extended
Aeration Units

33.7-Liter and 47.1-Liter Reactors Effluent Suspended
Solids vs. Overflow Rates at Various Temperatures

Sludge Action in Settling Tubes

iv

PAGE

12
13
14
15

19

20

22

24

32

33

35

36

43

45

49
50


SECTION IV
FACILITIES AND METHODS

COLD ROOM BENCH SCALE REACTORS

Controlled temperature laboratory studies, using bench scale activated
sludge units were conducted at the Arctic Environmental Research Labora-
tory from 1969 to 1971.

Initial activated sludge studies were carried out on a laboratory scale
using two cone reactors, manufactured by the Pope Scientific Company. The
5 1/2-liter units consisted of two concentric cones and a center tube as
shown in Figure 2. Aeration and mixing were supplied by porous ceramic dif~-
fusers which caused the mixed liquor to circulate around the inner cone.
Effluent rose through the center tube, 25 cm (10 in.) in length, where
solids separation took place. The reactors were modified slightly to re-
place the original vacuum effluent drawoff design with an overflow device

as shown. Effluent was collected in plastic containers. Holter Perfusion
Roller Pumps were used for feeding. The feed rate of these pumps could be
varied from 0.33 to 1600 ml/min with a full scale accuracy within + 1 per-
cent. These units had two pumping tubes which permitted simultaneous pumping
from two sources.

The reactors were fed from 76-liter (20-gal.) plastic containers as shown
and the feed kept uniformly mixed with a paddle-type mixer. The desired
mixed liquor temepratures were maintained by placing the equipment in
refrigerated, walk-in, constant temperature rooms.

A 33.7-liter (8.9-gal.) activated sludge reactor, as shown in Figure 3,

was fabricated to study settling characteristics of settling tubes (clari-
fiers) at controlled temperatures. The Neptune Microfloc Company developed
tube settlers for use in water treatment and has conducted studies to evalu-
ate them for use in activated sludge separation (4). A schematic of the
reactor and associated equipment is shown in Figure 4. Two settling tubes
were provided, each 5 cm (2 in.) square and 1.2 m (48 in.) long and inclined
at an angle of 60 degrees. Each tube also had an effluent drawoff. The
reactor was designed to provide a circulation pattern sweeping down in front
of the tubes to carry the settled sludge away. A tank of approximately 230
liters (60 gal.) was constructed for feeding the reactor and the contents
kept completely mixed with a circulating pump, drawing from near the bottom
of the tank and returning to the bottom of the hopper, as shown. During
periods when the cold room temperatures were increased above 4°C, the feed
tank contents were kept cool with a Blue M refrigeration unit. Holter

pumps were used for feeding the reactor and for controlling the effluent
flow from the settling tubes.

A second reactor of 47.1 liters (12.5 gal.) was fabricated to further
study tube settler characteristics and is shown in Figures 5 and 6. The
settling portion of the reactor consists of one 10 cm x 8.9 cm x 1.8m
(4 in. x 5 in. x 70 in. long) tube with an individual drawoff and two

10


ACKNOWLEDGEMENTS

The foresight and initiative of the Arctic Environmental Research Laboratory's
first Waste Treatment Research Director, Mr. Sidney E. Clark, provided the
impetus for a viable waste treatment research program, of which this report
is a summary of the work on extended aeration. His contribution is acknow-
ledged with sincere thanks.

The Alaska Air Command. Headquarters, Civil Engineering Division, has pro-
vided most of the support in the initial construction of the Eielson Air
Force Base pilot plants. Their assistance is acknowledged with sincere thanks.

The 5010th Civil Engineers of Eielson Air Force Base, and especially Mr.
Jack Howard and the waste plant operators, have given their continued assis-
tance in maintaining, operating, and sampling the Eielson Air Force Base
pilot plants. Their contribution is acknowledged with sincere thanks.

The College Utilities Corporation has provided the unpublished data on their
oxidation ditch. Their contribution is acknowledged with sincere thanks.

vii


TECHNICAL REPORT DATA
(Please read Instructions an the reverse before completing)

TR PORT NO. 2. 3, RECIPIENT'S ACCESSIONNO,
-A-660/2-74-070 te. on
AP ee tir Is. REPORT DATE

Extended Aeration Sewage Treatment in Cold Climates f-2ecember 1974

66021000
7 AUTHOR(S) }. PERFORMING ORGANIZATION REPORT NO.
H. J. Coutts and C. D. Christianson
MING ORG NIZATION NAME AND AODAESS |70. PROGRAM ELEMENTNO, —————=&Y
U.S. Environmental Protection Agency 1BB044
Arctic Environmental Research Laboratory tte ANT NO.

National Environmental Research Center
ege, Alaska 99701

by. INSORING AGENCY NAME ANDO ADDRESS 13. TYPE OF REPORT AND PERIOD COVERED
U.S. Environmental Protection Agency

14, SPONSORING AGENCY CODE

16, SUPPLEMENTARY NOTES

[Te ABSTRACT

. In an effort to develop design criteria for biological treatment of low tempera-
| ture domestic sewages, the Arctic Environmental Research Laboratory has designed and
operated two parallel low temperature extended aeration units near Fairbanks, Alaska.
The two units had exposed aeration basins utilizing submerged aerators and were dif-
ferentiated by type of clarifier. One unit had conventional horizontal flow clari-
fier while the other had a modified upflow clarifier with tube settlers. The liquid
temperature varied from 0°C to 19°C. In addition, 0.5 MGD subarctic, oxidation ditch
and low temperature bench scale units were studied.

Organic loading was the parameter most seriously affected by low temperatures.
It was found that BOD removals above 80% at liquid temperatures below 7°C could gen-
erally be maintained at loadings of 0.08 Kg BOD/Kg MLSS/Day or less. As in warmer
climates, intentional sludge wastage was found to be required. Low temperature
solids accumulation rates indicated that standard wastage criteria of 0.5 Kg SS/Kg
BOD is usually adequate.

Other parameters investigated and reported were: (1) aeration for oxygen transfer
and mixings (2) comparative clarifier performance; (3) nutrient and total coliform
emovals

ia KEY WORDS AND DOCUMENT ANALYSIS

a * be PTORS, b.1OENTIFIERS/OPEN ENDED TERMS |c. COSATI Field/Group
waste treatment, sewage treatment, subarctic, activated

biological waste treatment, low tempera- | sludge, extended aera-

ture activated sludge, cold regions ex- tion, aeration, clarifi-

tended aeration, subarctic, Alaska, cation, organics,

domestic sewage coliforms, nutrients

Ta, DISTRIBUTION STATEMENT 18. SECURITY CLASS (This Report) ‘21, NO. OF PAGES +Y

‘20. SECURITY CLASS (This page) 22. PRICE

EPA Form 2220-1 (9-73)

# U.S, GOVERNMENT PRINTING OFFICE: 1975-697- 940/89 REGION 10


SL

TABLE 13

EIELSON AFB EXTENDED AERATION--NITROGEN CYCLE
Concentrations mg/liter as N

Feed Horizontal Effluent Upflow Effluent Horizontal Upflow
Mixed Liquor | Mixed Liquor
NOo* Age Age
Date | NO, NHy-N TKN-N} NO,  NOg  NHg-N TKN-N | NO, -NOz NHg-N TKN-N} T°C | Days} T°C | Days
10/13/71} 0.14 14 23 11.3 0.22 13 15 0.32 0.02 53 27 15 50 | 15 20
11/17/71 | 0.05 22 32 | 0.14 19 1.8 4.5 |1.2 1.4 V7 22 10 22 | 12 44
12/08/71} 0.31 24 26 | 0.05 17 J 2 0.04 0.01 20 22 8 80 8 13
01/12/72) 0.14 24 25 | 0.09 5.3 14 13 0.04 0.05 11 10 4 32 4 3
02/09/72} 0.02 25 27, | 0.03 0.17 21 22 0.03 0.24 22 21 3 7 3 21
02/23/72 | 0.02 24 26 | 0.01 0.01 23 24 0.01 0.01 23 27 5 24 5 7
03/01/72] 0.02 26 27 | 0.01 0.01 23 26 0.03 0.04 26 26 2 83 2 27
03/08/72} 0.03 21 29 | 0.07 0.02 19 22 0.01 0.13 20 23 0 167 0 25
03/15/72} 0.02 23 26 | 0.09 0.05 20 23 0.01 0.07 22 25 1 130 2 32
03/22/72 | 0.03 21 26 | 0.06 0.01 18 24 0.01 0.01) 21 25 1 132 1 35
03/29/72 | 0.02 21 27° | 0.10 0.05 25 28 0.01 0.01 23 24 3 => 3 ---
04/05/72 | 0.02 24 27: | 0.14 0.09 22 25 0.01 0.01 24 23 5 308 4 90
04/12/72 | 0.03 24 27} 0.02 0.10 21 25 0.01 0.03 21 24 =o 63 | -- 32
04/19/72 | 0.02 28 33. | 0.01 0.09 20 21 0.01 0.04 18 19 5 491 5 192
04/26/72 | 0.02 15 22; 0.03 0.11 18 23 0.02 0.01 30 31 3 778 4 5



10.

12.

SECTION IX
REFERENCES

Grube, Gareth Alden. "Evaluation of an Oxidation Ditch Activated Sludge
Plant in Subarctic Alaska." M.S. Thesis. College, Alaska. University
of Alaska. May 1968.

Alter, Amos J. "Sewerage and Sewage Disposal in Cold Climates." Cold
Regions Science and Engineering Monograph 111-C56. Corps of Engineers,
U.S. Army Cold Regions Research and Engineering Laboratory. DA Project
17062112A130. October 1969.

Stewart, Marvin J. "Activated Sludge Process Variations--the Complete
Spectrum." In: Water and Sewage Works. December 1964. pp. R2-41 -
R2-62.

Conley, Walter R. and Alfred F. Slechta. “Recent Experiences in Plant
Scale Application of the Settling Tube Concept." In: Proceedings
Water Pollution Control Federation's 43rd Annual Conference. Boston,
1970.

American Public Health Association. Standard Methods for the Examina-
tion of Water and Wastewater. 12th Edition. New York. 1965.

FWPCA Methods for Chemical Analysis of Water and Wastes. Cincinnati.
Federal Water Pollution Control Administration, Division of Water
Quality Research. November 1969.

Johnson, Philip R. and Charles W. Hartmai. Environmental Atlas of
Alaska. College, Alaska. Institute of Arctic Environmental Engineering,
Institute of Water Resources, University of Alaska. 1969.

Clark, Sidney E., Harold J. Coutts, and Conrad D. Christianson. "Design
Considerations for Extended Aeration in Alaska." In: Proceedings of
the International Symposium on Water Pollution Control in Cold Climates.
College, Alaska, University of Alaska. July 1970.

Grube, Gareth Alden, and R. Sage Murphy. "Oxidation Ditch Works Well
in Subarctic Climates." In: Water and Sewage Works, 116, No. 7.
July 1969.

Ranganathan, K. R. and R. Sage Murphy. "Bio-Process of the Oxidation
Ditch when Subjected to a Subarctic Climate." Institute of Water

Resources, University of Alaska. College, Alaska. Report No. IWR-27.
May 1972.

Anonymous. "Report on Operation of Oxidation Ditch Sewage Treatment
Plant, Glenwood, Minnesota." Department of Health, Division of
Environmental Health, Section on Water Pollution Control. July 1965.

Porges, Ralph and Grover L. Morris. Extended Aeration Sewage Treat-
ment. U.S. Department of Health, Education and Welfare, Robert A. Taft
aanitary Engineering Center, Technical Services Branch. Cincinnati.
June 1960.

78


5 cm x 8.9 cm x 1.8m (2 in. x 3.5 in. x 70 in.) long tubes with a common
effluent drawoff. This reactor was fed in parallel with the other tube
settler reactor from the same feed tank. Holter pumps were used for feed
and to control the effluent rates. :

The cone reactors were monitored primarily for biokinetic information and
samples collected on Monday, Wednesday and Friday. Routine analyses in-
cluded influent and effluent BOD's, mixed liquor and effluent suspended
solids (SS), and volatile suspended solids (VSS). Nutrient analyses were
made on the influent and effluent samples on a weekly basis during the
second half of the study period and included ammonia, nitrite, nitrate,
and organic nitrogen, anc total and orthophosphates.

Feed consisted of effluent from the Eielson Air Force Base primary treatment
plant. The feed was brought to the Laboratory in 19-liter (5-gal.) con-
tainers and held in the constant temperature room overnight before feeding.
Samples were taken of the feed tank contents immediately after feeding, again
before the next feeding, and the two results averaged to provide influent
data for the sampling period. Effluent was collected in the plastic con-
tainers and samples taken at the end of the sampling period.

Essentially, the same procedures were followed with the tube settler reactors
as with the cone reactor units with the exception that sampling was done on
a daily basis. Feed consisted of effluent from the Eielson Air Force Base
primary plant which was brought to the laboratory in 57-liter (15-gal.) con-
tainers and held overnight in a cold room at 1°C before feeding. Samples
were collected 7 days per week at the beginning of the study and reduced

to 5 days per week later. BOD and COD analyses were run routinely on the
influent and effluent samples and Tuesdays and Thursdays on the reactor
mixed liquor samples. Suspended solids and volatile suspended solids were
performed daily on the influent and mixed liquor samples. Suspended solids
analyses only were performed on the effluent because of difficulty in ob-
taining reliable VSS figures at low concentrations. Total solids and total
volatile solids analyses were done on the mixed liquor only. Effluent for
each sample period was collected in 114-~liter (30-gal.) plastic containers.
After sampling, the effluent containers were emptied and collection for the
next sample period begun.

A limited number of nutrient and coliform determinations were made on the
influent and effluent samples at times consistent with the study schedules
of the reactors. Microscopic examinations of the reactor contents were
made on irregular basis at times when apparent or suspected changes in the
mixed liquor had occurred. The examinations consisted of general observa-
tions on the relative quantities of protozoa present and the degree of ac-
tivity. BOD, COD, and solids analyses were done in accordance with Standard
Methods procedures (5). Coliform counts were made by the membrane filter
method as described in Standard Methods and nutrient analyses made in accor-
dance with Federal Water Quality Administration Standards (6).

16


EPA-660/2-74-070
DECEMBER 1974

Environmental Protection Technology Series



13.

15.

16.

17.

20.

21.

22.

23.

24,

25.

National Sanitation Foundation. Package Sewage Treatment Plant
Criteria Development: Part 1. Extended Aeration. 1966.

Wuhrmann, K. "Research Development in Regard to Concept and Base
Values of the Activated Sludge System." In: Advances in Water Qualit

Improvement, Gloyna, E. F. and W. W. Eckenfelder (eds.). Austin,
Texas, University of Texas Press. 1968.

Reed, Sherwood C. and R. Sage Murphy. "Low Temperature Activated
Sludge Settling." In: Journal of the Sanitary Engineering Division
Proceedings of American Society of Civil Engineers, 95, No. SA4.
August 1969.

Benedict, Arthur H. "Organic Loading and Temperature in Bio-oxidation."
Ph.D. Thesis. University of Washington. 1968.

McKinney, Ross £. and Andrew Gram. "Protozoa and Activated Sludge."
In: Sewage and Industrial Wastes, Vol. 28, No. 10. October 1956.

Ludzack, F. J. "Observations on Bench Scale Extended Aeration Sewage
Treatment." In: Journal Water Pollution Control Federation, Vol. 3,
8:1092-1100. August 1965

Hansen, Sigurd P. and Gordon L. Culp. “Applying Shallow Depth Sedi-
mentation Theory." In: Journal American Water Works Association,
Vol. 59, No. 9. September 1967

Hansen, Sigurd P., Gordon L. Culp, and John R. Stukenberg. "Practical
Application of Idealized Sedimentation Theory." In: Proceedings of
1967 Water Pollution Control Federation Conference. New York

October 1967.

Pohl, E. F., Chief, Sanitary Engineering Section, U.S. Army Corps of
Engineers, Anchorage, Alaska. Personal communications. April 22, 1970.

Downing, A. L. "Factors to be Considered in the Design of Activated

Sludge Plants." In: Advances on Water Quality Improvement. University
of Texas Press, 1968. pp 190-202.

Reed, Sherwood C. and Allan W. Crouther. "Single Tank Secondary
Sewage Treatment for the Arctic." In: Proceedings of the ASCE Cold

Regions Engineering 2lst Alaskan Science Conference. College, Alaska.
University of Alaska. August 1970.

Reed, Sherwood C., Sanitary Engineer, Construction Engineering, U.S.
Army Cold Regions Research and Engineering Laboratory, Hanover, New
Hampshire. Personal communications. April 27, 1970, and March 1972.

Hunter, T. V., E. J. Gentelli, and M. E. Gilwood. "Temperature and
Retention Time Relationships in the Activated Sludge Process." In:
Proceedings of the 21st Industrial Waste Conference. Purdue University.
1966.

79


through July 1971 performance. Murphy and Rangathan (10) indicated excessive
sludge deposition (SS<20,000 mg/1) in quiescent sections of the ditch. A
sludge return pump was installed in June 1972. One period of autoinduced
sludge wastage into the effluent was noticed between two August 1972 sample
dates, but effluent samples were apparently not collected during the. sus-
pended solids loss.

The Glenwood, Minnesota oxidation ditch (11) was studied in late January
1965. At the time of the study, the ditch was operating at »40 hours de-
tention time with an actual loading of 1.0 Kg BOD/cu m/min (6 1b BOD/1000
cu ft/day) or about half the design loading. The settling tank overflow
rate was 15 lit/sq m/min (0.37 gal./sq ft/min), opposed to the design over-
flow rate of 23 lit/sq m/min (0.57 gal./sq ft/min). During the winter sam-
pling period, the air temperature ranged from -4°C (25°F) to -33°C (-27°F).
Mixed liquor temperature in the ditch ranged from 0.°C (32°F) to 2°C (36°F)
and averaged 1°C (34°F). Raw sewage temperature ranged from 4°C to 10°C
(40° to 50°F). The greatest ice formation occurred during windy weather
and covered approximately 75 percent of the ditch with 1.3 to 2 cm (1/2 to
3/4 in.) thick ice which gradually dissipated during calm weather. BOD
removals averaged 92 percent over a 4-day sampling period.

39


to avoid potential freezing problems. The detention time available
before icing occurs is a function of sewage temperature, ambient air
temperature, and aeration basin configuration. For interior Alaska, the
following maximum detention times at the corresponding sewage tempera-
tures should provide an adequate margin of safety:

Detention Days Sewage Temperature °C
1 5
2 10
4 20

Vulnerable equipment such as pretreatment units, pumps, and flow mea-
surement devices should be located in a heated enclosure. Secondary
sedimentation basins also need to be enclosed but may not need heating.

Some protection against freezing should be provided for aeration equip-
ment with minimum heat enclosures for compressors and unheated housing
for oxidation ditch rotors. Exposed surface aerators require excessive
maintenance in cold climates and, therefore, should not be considered.
Warmer temperature criteria are adequate for sizing submerged aeration
equipment. Air piping should not pass through the exposed water surface
because it may freeze shut during a power failure.

Extensive icing on an aeration basin can be a problem in an extended aera-
tion process. Suspended solids entrainment in the ice may cause failure
of the process. However, solids captured in surface ice may prove to be
an excellent method for concentrating and removing solids from an ex-
posed aerobic digestion basin because sludge that has been frozen de-
waters vary easily. This technique needs to be demonstrated before its
economics in cold climate areas can be defined.

Air lifts for sludge return have been proven to be satisfactory in many
smaller extended aeration units.

ORGANIC LOADING

The process parameter most seriously affected by the low temperature
was organic loading. The normal warmer temperature design loading
range for extended aeration is 0.01 to 0.1 Kg BOD/Kg MLSS/Day. but in
actual practice some plants operate efficiently at loadings approaching
0.2 Kg BOD/Kg MLSS/Day. At low temperatures, the performance decreases
rapidly as organic loading is increased (see chart below).


SECTION II
SUMMARY AND CONCLUSIONS

Waste water treatment research and development activities in Alaska have
been primarily directed toward adapting the biological processes for

use in cold climates. The feasibility of the extended aeration process

as an economical and effective means of secondary waste treatment has

been demonstrated in the laboratory and in the field. However, the pro-
cess requires more consistent operation and maintenance than many lagoon
systems in an area where costs are high and skilled operators are extremely
scarce.

FACILITY DESIGN

Additional long-term experience should further demonstrate economical

and efficient operation of cold operating temperatures. Cold tempera-
ture process design criteria must be used if systems with mixed liquor
temperature less than 10°C are to reach optimum efficiency. An obvious
key to successful operation of an extended aeration system at any tem-
perature is the solids separation process. Additional study is needed
to determine optimum mixed liquor dissolved oxygen levels for the separa-
tion and thickening process.

The heat transfer characteristics of each component in the treatment
system from collection and transport through each unit process should
be carefully considered in any cold climate project. Present thermal
design is based largely on empirical methods which are not necessarily
economical.

Utilization of exposed aeration chambers for the extended aeration pro-
cess is practical. Earthen basins are feasible where economic and con-
struction conditions warrant, provided impervious liners are utilized.
Provision of a stable sidewall surface that can tolerate mixing velo-
cities, wave action, freeze-thaw cycles, extreme temperatures and ice
movement is very important. Otherwise vertical sidewall construction
should be utilized to promote better mixing. Reinforced concrete block
and/or concrete grout should be considered as economical liner materials
where the design permits.

When basins with low sloping sidewalls construction are utilized, the
aeration devices should be clustered in the center of the basin for

best mixing. For heat economy, consideration should be given to mounting
the clarifiers within the aeration basin. \hen utilizing exposed basins,
heat loss effects must be evaluated in conjunction with detention time


7 MLES: 5000 mg/1
0.75 + (0.3) & Overflow
3 Rate: 3.3 Liter (0.8 gpm/ft?)
_ min m
0.50 4 (0.2) Mixed Liquor
Temp: <1°C

Sludge Blanket Rise Rate (centimeters/min)

0.25 J
(inches)
20 30 40
0 + a t
0.5 0.75 1.0

Sludge Ht in Tubes (meters)

FIGURE 21. RATE OF SLUDGE RISE Iil TUBES VS. SLUOGE HEIGHT

52


PAGE NOT
AVAILABLE

DIGITALLY


EIELSON AFB EXTENDED AERATION-PHOSPHORUS DATA

TABLE 14

Concentrations mg/liter as P

Horizontal Upf low

Feed Effluent Effluent

Date T-P 0-P T-P 0-P T-P O-P
12/08/71 12 14 am 13 13 15
01/12/72 10 10 10 10 3 3
02/09/72 12 12 1 10 9 10
02/23/72 13 14 12 13 13 13
03/01/72 13 13 13 13 13 14
03/08/72 14 13 13 13 13 13
03/15/72 VW V1 10 10 10 8
03/22/72 13 13 13 12 13 13
04/05/72 12 13 13 12 12 13
04/12/72 14 14 1 15 15 14

04/19/72 10 10 8.7 9.1 8.9 9.1
Average Percent Removal 7 5 8 9

76



5 cm (2 in.) of urethane foam between two 1.2 x 2.4 m (4 x 8 ft) plywood
sheets.

Feed and effluent samples were 24-hour composites, composited on the basis
of time and flow. Mixed liquor suspended solids were always grab samples.
From start-up in September to early November 1971, the BOD and COD analyses
were run once per week and suspended solids run once or twice per week.
Starting in November 1971, COD and suspended solids analyses were run three
times per week. BOD's were always run once per week. In December 1971, the
mixed liquor suspended solids were run daily and effluent suspended solids
were also run daily shortly thereafter. Starting the week of January 10,
1972, feed and effluent COD's were taken daily and frozen on the site. BOD's
and volatile suspended solids were run only on Wednesdays. Effluent BOD's
and percent removals for all weekdays except Wednesdays were based upon
daily COD's and the COD/BOD ratio as calculated weekly from the Wednesday's
samples. The following parameters were measured daily: 2-liter settlo-
meter tests at 5, 15, 30 and 60 minutes; outside ambient temperatures;
airflow and pressure; and sludge wastage pump rates. Feed rates were
recorded and adjusted daily. Rhodamine (R-HB) dye was injected with the
feed to qualitatively define flow patterns.

BOD and solids analyses were begun within 4 hours of sample collection.

COD samples were usually frozen until enough samples were accumulated for
economical analysis. All analyses were performed in accordance with Standard
Methods (5) and/or FWPCA-Methods for Chemical Analysis of Water and Wastes
(ey). _

The analytical data for the EAFB pilot units are summarized in a computer
printout which may be obtained by contacting the author. This printout
contains listings, daily in some cases, from September 1971 to May 1972,

of process parameters and chemical analyses. The tabulated parameters are:
feed strength: total coliforms, BOD, and COD; organic loading and detention:
mass BOD/mass MLSS/day and days; mixed liquor; solids temperature, DO,
settling rate, age, and wastage; clarifier loadings, lit/sq m/min.; effluent
strength and removals: total coliform, BOD, COD, and solids. Weekly COD

to BOD ratios and major perturbations are also listed.

OXIDATION DITCHES

There is only one oxidation ditch in Alaska for which any performance data
are available. This ditch, owned and operated by College Utilities Corp.,
is 4 miles west of Fairbanks and serves the University of Alaska, an ele-
mentary school, and a residential area. This ditch is exposed to the
environment and has a volume of 1200 cu m (0.3 MG) at a depth of 1.3 m (4.3
ft). The clarifier is enclosed in an unheated building and has a sludge
return, but no wastage system. A housing has been provided over the two
rotors. A diagram of this oxidation ditch is shown in Figure 11.

Performance data for this ditch were extracted from the reports of Grube
and Murphy (9) and Murphy and Ranganathan (10). Their analytical methods

23


SECTION VI
MAJOR FACTORS AFFECTING PERFORMANCE

ORGANIC LOADING EFFECTS

Cold room bench scale data tends to shown that for low organic loads, 0.14
Kg BOD/Kg MLSS/Day or less, temperature has little effect as long as clari-
fier overflow rate is kept very low, less than 8 lit/sq m/min (0.2 gal./sq
ft/min. At loadings less than 0.1, there were no sludge bulking problems.
Low temperature performance of the larger field units was much more sensi-
tive to loading.

All the Eielson Air Force Base 1971 and 1972 data, and the 1971 data for
the College oxidation ditch are summarized in Table 6--Subarctic Alaska
Extended Aeration Units. Of all the parameters affecting low temperature
performance, organic loading is the most significant.

For this paper, organic loading (food to mass ratio) is defined as mass of
BOD input per day divided by mass of MLSS. It can also be expressed as
Feed BOD (mg/1)/MLSS (mg/1)/detention (days). Because the EAFB units had
oversized clarifiers in comparison to most extended aeration units, part
of the MLSS in the clarifiers was included in the organic loading calcula-
tion. Suspended solids in the clarifier sludge blanket varied from 100 to

200 percent of the MLSS concentration; 125 percent was taken as the average
ratio.

The following formula was used to calculate the loading on a daily basis:

Organic Load = mg/1_ BOD input
MESSapt ~25MLSSqp 2.7-DS) V D.T.

2.7 Vapi

Where:
MLSS = Aeration basin MLSS, mg/1

DS = distance (meters), sludge blanket surface to water surface
in clarifier.

actual measurement in horizontal flow clarifier.

unmeasurable (under tubes) in upflow clarifier; there-
fore, assumed to be 2.1 m.

The clarifiers were effectively 2.7 m deep; therefore,

the fraction filled with sludge is (222s)
2-7

Ve = volume of clarifier, cubic meters.

40


Air to

Aerators
oy
and Air-
lift =. Effluent Collectiof
pumps =
” Return ——
ad
—-
COMPLETE MIX HORIZONTAL FLOW
AERATION CELL CLARIFIER

Sewage Air Lift Pumps
Feed Va /
Aerators ing Sludge Collection Effluent Line
Returnin
Sludge 3 ‘© 6 ee
AERATION CELL WITH HORIZONTAL FLOW CLARIFIER
PROCESS FLOW SECTION
Wastage
Clear Effluent
S AERATION Me HORIZONTAL
Feagse et CELL Complete Mix FLOW BASIN
(Clarifier)

Return Sludge

FLOW SCHEMATIC
HORIZONTAL FLOW EXTENDED AERATION PILOT UNIT

Figure 10

22


HORIZONTAL FLOW CLARIFIERS

COMPARISON OF UP SIDE WITH TUBE AND

MLSS HORIZONTAL FLOW UPSIDE
Settlometer Total Total
Temp. Rate Both Overflow EFF. SS EFF. SS Overflow
°C Sides cm/min liter/min m mg/1 mg/1 liter/min me
1/2 Day Detention
13 0.2 16 43 51 18
13 0.3 19 94 169 23
a 1.3 2i 18 40 22
3 0.2 8.5 282 WW 1
6&5 0.3 9.3 53 151 9.3
1 Day Detention
6&3 0.2 12 26 27 12
2&3 1.1 12 V7 33 12

59


NUMBER
1
2

10

VW

12
13
14
15

LIST OF TABLES

Data Summary 1.3°C Cone Reactor
Data Summary 6.5°C Cone Reactor

Summary of Results of 33.7-Liter Reactor and
47.1-Liter Reactor at 12 Hour Detention

Summary of Results of 33.7-Liter Reactor at
24-Hour Detention

Oxidation Ditch--College, Alaska, Average
Performance Data

Subarctic Alaska Extended Aeration Units--
Average Performance Data

33.7-Liter Reactor--Results of Operating with Varying
Effluent Overflow Rates on the Settling Tubes

47.1-Liter Reactor--Results of Operating with
Varying Effluent Overflow Rates on the Settling Tubes

47.1-Liter Reactor--Sludge Levels in Tubes at
Various Effluent Overflow Rates

Comparison of Up Side with Tube Horizontal Flow
and Clarifiers

EAFB Extended Aeration Basins--Horizontal Velocity
Components

Cone Reactors Results of Nutrient Analysis
EAFB Extended Aeration--Nitrogen Cycle
EAFB Extended Aeration--Phosphorus Data

EAFB Pilot Units Total Coliforms Remaining
Before Chlorination

vi

PAGE
27
28

30

31

38

4]

48

54

59

66
71
75
76

77


el

Refriger4
ation
Unit

Mixing
Pump

Air Supply

To Aeration Chamber

Effluent
Pump
(Holter)
a
Settling effluent
Tubes uen
ht Effluent | Overflow
Recycle Line Reactor
Pump Side View
—
Holter (Holter ) =
Perfusion
Roller
Feed Y
Effluent
Tanks

Moisture Reactor
Trap Plexiglas
FIGURE 4

33.7-LITER (8.9-GALLON) REACTOR
SCHEMATIC OF APPARATUS


TABLE 15

EAFB PILOT UNITS

TOTAL COLIFORMS REMAINING BEFORE CHLORINATION

Average %

Average Average Total
Mixed Liquor Average % Eff. SS Coliforms
Period Side Temp. °C BOD Removal mg/1 Remaining
I Horizontal 12 81 36 1.7
I Up 12 82 99 10
Il Horizontal 4 10 134 14
II Up 4 -30 122 26
Ill Horizontal 4 84 7 1.8
ant Up 4 76 50 2.6

77


Clear
Effluent

Particles
rising above
sludge blanket

Beginning
of clear effluent
and sludge

interface

Sludge circulation
pattern

FIGURE 19. SLUDGE ACTION I SETTLING TUBES

50


The EAFB nitrogen data is listed in Table 13. Nitrogen removal was accom-
plished only at mixed liquor temperatures of 8°C or above. Apparently.

at 8°C, the sludge age Mass of MLSS must be above 13 days for

(ass of SS Lost Per Day!

denitrification to occur. At temperatures of 5°C or below, there was no
significant nitrification even with sludge ages of 100+ days. It can be
surmised from the data on Table 13, that denitrification, i.e., nitrogen
gas formation, was not contributing to the bulking (SVI>100) conditions

in period Il.

The phosphorus data on Table 14 shows less than 10 percent removal which is
to be expected with the conventional extended aeration process. One would
not think that phosphorus removal would be affected by low temperatures.

TOTAL COLIFORMS

The percent total coliforms remaining before chlorination at the EAFB pilot
units is listed in Table 15. The highest effluent coliform levels are gen-
erally associated with the highest effluent suspended solid levels and lowest
percent BOD removal. These data indicate coliform removal is not directly
related to temperature but is dependent upon effluent solids levels. Percent
total coliforms remaining can be somewhat misleading Tos a04 98 percent total
coliform removal (2 percent remaining) may represent 10 or more total
coliform counts per 100 ml. The coliform removals experienced at the EAFB

pilot plant are similar to removals found in warmer temperature extended
aeration units.

No bacteriological data has been published for the College oxidation ditch.

74


26.

27.

28.

29.

30.

31.

32.

33.

34.

36.

Thomas, Harold Allen, Jr. “Report on Investigation of Sewage Treat-
ment in Low Temperature Areas." For: Subcommittee on Waste Disposal,
Committee on Sanitary Engineering, National Research Council. May
1950.

Anonymous. “Operating Manual for Small Extended Aeration, Activated
Sludge Treatment Plants." Alaska Department of Health and Welfare,
Division of Public Health. Juneau, Alaska. 1963.

Morris, Grover L., Lowel? Vandenberg, Gordon L. Culp, John R. Geckler,
and Ralph Porges. Extended Aeration Plants and Intermittent Water
Courses. Department of Health, Education and Welfare, Robert A. Taft
Sanitary Engineering Center, Technical Services Branch. Cincinnati.
duly 1963.

U.S. Environmental Protection Agency. "Evaluation of Conditioning
and Dewatering Sewage Sludge by Freezing." Office of Research and
Monitoring. Water Pollution Control Research Series 11010 EVE 01/71.
January 1971.

Goodman, B. L. Manual for Activated Sludge Sewage Treatment and
Design Handbook of Wastewater Systems. Westport, Connecticut,
Technomic Publishing Company. 1971.

McKinney, Ross E. and W. J. O'Brien. "Activated Sludge--Basic Design
Concepts." In: Journal of the Water Pollution Control Federation,
Vol. 40, No. 11, Part 1. November 1968.

Eckenfelder, Wesley. Jr. and D. J. O'Connor. Biological Waste Treat-
ment. Long Island, Pergamon Press. 1961.

Anonymous. “Effect of Water Temperature on Stream Regeneration." In:
Journal of the Sanitary Engineering Division, Proceedings of the Ameri-
can Society of Civil Engineers, 87, No. SA6, Thirty-first Progress
Report. Committee on Sanitary Engineering Research. November 1961.

Terashima, Shigeo, Keiichi Koyama, and Yasumoto Nagara. "Biological
Sewage Treatment in Cold Climate Areas." In: Proceedings of the
International Symposium on Water Pollution Control in Cold Climates.
College, Alaska, University of Alaska. July 1970.

Heukelekian, H. and E. Wiesburg. "Bound Water and Activated Sludge

Bulking." In: Sewage and Industrial Wastes, Vol. 28, 4:558. April
56.

Zanoni, A. E. "Secondary Effluent Deoxygenation at Different Tempera-
tures." In: Journal Water Pollution Control Federation, Vol. 41,
No. 4. April 1969.

80


The residence time in clarifiers is much greater than 5 minutes and the
clarifier geometry usually favors better solids separation. For normal
sludges, the 0 to 5 minute rate was the highest settling rate. The 0 to
5 minute rate was not always the highest settling rate for bulking sludges.

Downing (22) (Figure 23) shows that settleability is improved by longer
detention times (10 hours) and very short detention times (4 hours) when
operating an activated sludge plant at warm temperatures. The EAFB hori-
zontal side data shows somewhat better settleability than Downing indicated,
but his data may be based on much higher MLSS data. He did not specify
temperatures. The EAFB low temperature long detention data (period III)
brackets his general curve.

A solids flux analysis was not performed for the EAFB units because it was
felt that solids flux has little meaning when SVI's are above 100. The two
EAFB clarifiers were operated at similar total overflows for direct compari-
son. Table 10 is a listing of total overflow and effluent SS for the two
types of clarifiers operated at the same temperature and same sludge settling
(0 to 5 min) rate, cm/min. The table should be considered only as showing a
trend even though each value listed is an arithmetic average of from 2 to 9
daily points, For the 1/2-day detention periods, the upflow clarifier was
operating at an overflow rate 13 percent above the horizontal flow clarifier.
But the up side effluent averaged only 6 percent richer in suspended solids.
The horizontal clarifier performance appears superior, 28 percent less SS,
for the 1-day detention period when the mixed liquor temperatures were 6°
and 2°C, while the up side was at 3°C. The above data isn't consistent
enough to show any strong trend, but it could be interpreted to mean that
the up flow with tubes clarifier has no advantage over conventional clari-
fiers at low temperatures. To hold reasonable effluent SS levels using

the data presented in Figure 18 through 22 and Tables 6 through 10, it
appears that the maximum low temperature (<10°C) clarifier design overflow
rate should not be above 12 lit/sq m/min (0.3 gal./sq ft/min) based on
average flow. There was no diurnal flow fluctuation at the EAFB facility

or in the cold room reactors; therefore, a peak flow criteria was not de-
termined. But in acknowledging the solids hysteresis effect (solid flow
damping effect) of clarifiers one would probably be safe in allowing peak
overflow rates to reach 20 lit/sq m/min (0.5 gal./sq ft/min).

The U.S. Army Cold Regions Research and Engineering Laboratory (CRREL) has
also investigated the use of tube settlers in low temperature extended aera-
tion units (23, 24). They have found that home-made (5 cm diameter pipe)
tube settlers perform satisfactorily.

SOLIDS ACCUMULATION AND WASTAGE

Little information is available on solids accumulation for biological
treatment process design for temperatures less than 5°C. Ludzack (18)
and Hunter et. al. (25), have observed that excess MLSS accumulation in-
creases with decreasing temperature. Cell yield and auto-oxidation rate
are utilized in the growth kinetics equation as defined in Section III.

57


TABLE 3

SUMMARY OF RESULTS OF 33.7-LITER REACTOR AND
47.1-LITER REACTOR AT 12 HR DETENTION

Feed: Primary Plant Effluent

REACTOR TEMPERATURE (AVG°C)

0.6 2.9 3.8 8.0
Reactor MLSS (mg/1) 4160 4097 4076 3737
% VSS 80 80 81 80
BOD 2489 2503 1477 1299
coD 5648 5788 5260 4705
ang. Kg Infl. BOD
Loading: Kg MLVSS-Day 0.12 0.10 0.10 0.14
. mg MLSS
Sludge Wasted: mi BOD Removed 0.42 0.33 0.32 0.33
Unfiltered Effluent
Suspended Solids (mg/1) 18 3 12 5
BOD (mg/1) 21 13 V7 9
BOD Removal (%) 89 92 90 96
COD (mg/1) 78 46 67 96
COD Removal (%) 76 73 78 83
COD/BOD Ratio
Influent 1.7 1.7 1.8 1.5
Effluent 4.2 4.3 4.0 6.3
Reactor 2.3 2.3 3.6 3.6

30


SECTION VIII
OTHER PERFORMANCE CRITERIA

NUTRIENTS

Nutrient removal (N and P) is an important consideration in establishing
performance criteria. In 1968, Grube (9) reported limited nitrogen data
(four samples) for the College oxidation ditch. He said, "The test results
indicate that nitrification during periods of low temperature (<12°C), is
almost nonexistent." No phosphorus data has been published for the College
oxidation ditch.

Results of nutrient analysis for cold room Pope reactors are presented in
Table 12. As expected, there was not a great deal of activity at the lower
temperature. There was an insignificant change in nitrate and total nitro-
gen 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 than at 1.3°C.
Total nitrogen removals were much higher at 6.5°C than at 1.3°C with little
detention time effects.

Additional studies were undertaken at a later time using the 47.1-liter
reactor in an attempt to determine the effect of denitrification on bulking
conditions. Sampling points included influent, effluent, reactor mixed
liquor and stations along the settling tube as shown in Figure 25. Samples
were anlayzed for solids (TS, TVS, SS, VSS) and nitrogen (NH35 N05. NO35

Kjeldahl). Dissolved oxygen levels were determined at the points sampled
using a polarographic probe. Reactor temperature during these studies was
~11°C and detention time 12 hours.

Samples were taken on six different days with results for a typical day
presented in Figure 26. Sludge level in the tube was just above the

T-4 sample point during sampling for this day. Denitrification was ob-
viously taking place. Ammonia-nitrogen dropped from 21 mg/1 in the influent
to 2 mg/l in the reactor mixed liquor while the nitrate-nitrogen increased
to 15 mg/l. The DO level dropped from 6 mg/1 in the reactor to 1.5 mg/1

at the lower end of the tube which was enough to cause a decrease in the
nitrate-nitrogen level for denitrification to begin. The DO concentration
continued to drop slightly to the top of the sludge height in the tube.
Denitrification continued while the ammonia and nitrite levels remained

the same. The DO level increased again at the top of the tube and in the
effluent with reaeration due to the configuration of the reactor. As a
result, denitrification ceased and the ammonia and nitrite-nitrogen were
converted to a nitrate. There is little doubt that the low DO level in the
tubes and the resultant denitrification contributed to the deterioration of
sludge settling characteristics as the reactor temperature was raised from
4° to 8°C. This fact does not explain the initial bulking conditions,
though less severe, at temperatures below 8°C since nitrification should not
be expected to occur to any significant degree below 5°C (36).

70


TABLE 4

SUMMARY OF RESULTS OF 33.7-LITER REACTOR
AT 24-HOUR DETENTION

REACTOR TEMPERATURE (AVG°C)

1.9 6.8 10.5
Reactor MLSS (mg/1) 2595 3872 3896
% VSS 83 83 82
BOD 1693 2105 1808
COD 3712 5019 5178
+. Kg Infl. BOD
Loading: @-MLVSS=Day 9.09 0.07 0.07
. mg MLSS
Sludge Wasted: ig BOD Removed 0.42 0.16 0.14
Unfiltered Effluent
Suspended Solids (mg/1) 3 4 6
BOD (mg/1) 14 10 10
BOD Removal (%) 93 95 95
COD (mg/1) 5] 53 69
COD Removal (%) 83 84 80
COD/BOD Ratio
Influent 1.5 1.5 1.6
Effluent 3.7 5.3 7.7
Reactor 2.2 2.4 2.9

31


investigation of 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 developed
an equation for zone settling based on experimental data. They also sug-
gested upflow sludge blanket clarifiers as having greater potential for

cold regions application. Benedict (16) suggested that effects of sludge
settleability on gross COD removai was magnified at low temperatures and

as loading rates were increased.

Solids separation is a function of both biological characteristics of the
sludge and physical parameters of the settling unit. Cold room experience
indicates that turbid effluent is not necessarily due to failure of the
sedimentation unit and may be eliminated by building up a well-acclimated
activated sludge population. This will require operation at a relatively
low biological loading rate in order to obtain the degree of organic sta-
bilization necessary for low turbidity (17). The cone reactor operating
at 1.3°C did produce a turbid effluent at loadings of around 0.2 Kg BOD/
Kg MLVSS/Day, but with a very low clarifier overflow rate (Table 1).

Indications are that sludge bulking may be a problem in the activated sludge
process at the cold operating temperatures. This problem was reported by
Ludzack (18). Bulking sludges have not been reported in cold temperature
oxidation ditch studies (1, 10, 11); however, these ditches were operated
at much longer detention times (1 to 2.3 days) which may be a factor. Al-
though bulking sludges have not been a problem with the College oxidation
ditch, floating solids have. Raganathan and Murphy (10) reported, "In

the late summer, the whole ditch became covered with a mat of floating
solids, which were thought to have originated from the anaerobic activity,
raising the sludge deposit from the bottom of the tank."

The circular upflow clarifier for this oxidation ditch was evaluated in
terms of solids flux; lbs dry solids in clarifier feed per day per sq ft
of clarifier separation area (10). Solids flux may be controlling in
clarifier design for high MLSS values and low SVI's. The oxidation ditch
MLSS usually had low SVI--less than 100 most of the time.

Hansen and Culp (19) reported on experiments with a method of solids separa-
tion which successfully employed shallow depth sedimentation theory. The
settling unit consisted of small diameter tubes (2.5 cm) inclined at 5° and
0.6-1.2 meters in length. Detention times were very low; however, back-
washing was necessary for removal of accumulated solids. Hansen, et al.
(20), also reported on the use of steeply inclined tubes (60°) which permit
solids depositing in the tubes to continuously slide down by gravity. Plant
scale applications of the steeply-inclined settling tube concept have been
reported by Conley and Slechta (4). They concluded that for primary clari-
fication, complete removal of settleable solids and 40-60 percent of sus-
pended solids can be achieved with 0.6-m (2-ft) long settling tubes 5 cm

(2 in.) in depth at an overflow rate of 122 lit/sq m/min (3 gal./sq ft/min).
They indicated that until methods are developed to continually control the
biological process, tube settlers in the activated sludge process should

be considered as a device for improving effluent quality during upsets in
the biological process or peak flows. Flow rates should not exceed 41
lit/sq m/min (1.0 gal./sq ft/min), which should provide effluent with 20-40

46


20 cm (8") Concrete Wall

wee Headers and Piping Floatable Collection Behind
10 cm (4") Air Lift (2) Plywood Sheets (2)
oy ’ ~
M.L/Xeed
a Arey on Hole Clarifier
a Feed Slot

om ro
"Shear Box" t _
Aerators wo Sludge Sludge
e Hopper opper
0
—=

1

0 cm (4") Sludge Return Lines
HORIZONTAL SIDE SECTION AA

Air 20 cm (8"), Concrete Wall
EE rate RSS TS ° Backwash (3) and Effluent

Lf Collector (3) Pipes
__Y MA Feed Trough -M.L. Down
4d Flow
8 Q Channel
aE on
= ubes Effluent
M — — Connections
"Mono Spager' Not Shown
ip Pi AERATION = B
Air Pipes BASIN S
herators! = Hopper
= ection ~-L
(4") |Air Lift (2) 4 ” HESS)
ao hho cm (4")
4 f= CEf fluent
uy? A ‘ with 2
10 cm (4") Sludge Return Lines (2) 15 cm (6") Auxilary Air Lift Heat Trace
(2) Lines

UP SIDE SECTION BB

FIGURE 8. ETELSOM AIR FORCE BASE EXTENDED AERATION PLANTS--SECTIONS

19


Effluent Suspended Solids (mg/1)

20 °
i
A
A Legend
® Continuous Flow
0 <1°C
10+ oA A v4°c
Intermittent Flow
fo} on 1/2 hr
off 1/2 hr
O 3°
Vv v4ec
57 Intermittent Flow
Vv on 2 hr
2 off 1 hr
(gpm/ft*) © v8°C
0.2 0.4 0.6 0.8] MLSS ~ 4000 mg/1
1 1 i !
0 T T T
10 20 30

Overflow Rates Liters/min me

FIGURE 18

33.7-LITER AND 47.1-LITER REACTORS
EFFLUENT SUSPENDED SOLIDS
VS.
OVERFLOW RATES AT VARIOUS TEMPERATURES

49


VOLUME PERCENT AT 1/2 HOUR

VOLUME PERCENT OF ACTIVATED SLUDGE VS. DETENTION TIME
EIELSON AIR FORCE BASE EXTENDED AERATION PLANT

HORIZONTAL FLOW SIDE - 2 LITER SETTLOMETER

LEGEND: TEMPERATURE °C DETENTION DAYS

© 7-17 0.6
O 2-9 0.5
Oo 1-8 1.0
DOUNING (22)
100
° BA
8;
0)
4 e 4
9
|
° 3 ° oN
50 > {o)) % 0)
° 0
cv) oO
0 Oo
25 + g 0 =)
9 ° o g 6
9 ° 0°
t + . +- .
0 10 20

DETENTION TIME HOURS
FIGURE 23

58


ABSTRACT

In an effort to develop design criteria for biological treatment of low
temperature domestic sewages, the Arctic Environmental Research Laboratory
has designed and operated two parallel low temperature extended aeration
units near Fairbanks, Alaska.

The two units had exposed aeration basins utilizing submerged aerators and
were differentiated by type of clarifier. One unit had a conventional
horizontal flow clarifier while the other had a modified upflow clarifier
with tube settlers. The liquid temperatures varied from O0°C to 19°C. In
addition, a 0.5 GD subarctic, oxidation ditch and low temperature bench
scale units were studied.

Organic loading was the parameter most seriously affected by the low tempera
tures. It was found that BOD removals above 80 percent at liquid tempera-
tures below 7°C could generally be maintained at loadings of 0.08 Kg BOD/Kg
MLSS/Day or less.

As in warmer climates, intentional sludge wastage was found to be required.
Low temperature solids accumulation rates indicated that the standard was-
tage criteria of 0.5 Kg SS/Kg BOD is usually adequate.

Other parameters investigated and reported were:

1. aeration for oxygen transfer and mixing.

2. comparative clarifier performance.

3. nutrient and total coliform removals.

This report was submitted in fulfillment of Project Number 16100, by the
Arctic Environmental Research Laboratory. Work was completed December 1973.

ii


TABLE 5

OXIDATION DITCH--COLLEGE, ALASKA

AVERAGE PERFORMANCE DATA

Ditch Liquid Overflow

itcl iqui * 2s

Detn. Temp. %BOD MLSS Percent Liter/m, min Effluent
Date: Mo/Yr Days °C Removal mg/1 Volatile (gal/ft“/day) SS mg/1
) oy67-3/68 2.04 10-11 92 1700 -- 6.8 (240) 21

(2) 4 769-12/69 Stated 11-20 ot 5) 2800 -- 18
Sines 1.04 8-14 52(45) 1600 71 13 (470) 222(4)
Dein 1.84 16-20 g(4-5) 45008) 50 7.3 (260) 5984)
Mereay7 0.9+ 14-19 g2(5) 4260 -- 15+ (530+) 35

(1)

Grube, G. A. (1)
(2)

Unpublished Data, compliments of Institute of Water Resources, University of Alaska

(3)
(4)
(5)

Data included when activated sludge was passing into effluent

Ranganathan, D. R., and Murphy, R. S. (10)

Septic tank sludge not included in influent BOD

(6)
(7)

Data compliments of College Utilities Corporation

38

Solids in quiescent sections of ditch have exceeded 20,000 mg/1


PAGE NOT

AVAILABLE

DIGITALLY


ACCUMULATION (Kg SS/Kg BOD)

0.8

0.6

0.4

0.2

0.0

SOLIDS ACCUMULATION
EIELSON AIR FORCE BASE EXTENDED AERATION UNITS
Kg MLSS/Kg BOD APPLIED

TEMP. DETENTION

(PERIOD) °C DAYS
( I 7-17 0.6
QM Horizontal (Il 2-9 0.5
( Ill 1-8 1.0
we ee ee eee eee eee nee eee eens
( I 7-19 0.6
Oup ( I 2-7 0.4
( III 1-8 1.0
iL Q (11)
Oo (1)
I
om oti)
QM (Ill)
4 (1)
NSF Package Plant Data (13)
Mature MLSS
AT kg_$S
4 Kg BOD
t f
0 1000 2000 3000 4000

MLSS x DETENTION (mg/1+days)

FIGURE 24

61


SECTION III
INTRODUCTION

GENERAL

Alaska is the largest of the 50 United States. It has varied climate in-
cluding arctic and subarctic zones where temperatures less*than -45°C (-50°F)
are common in winter. The population is small and widespread with 302,000
people (based on the 1970 census) inhabiting 586,000 square miles of land
area. Settled areas requiring domestic sewage treatment include large muni-
cipalities, 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 and excessively so in
remote areas. Skilled personnel for operation and treatment plants are
scarce or nonexistent. Costs of shipping to Alaska are also very high and
increase with the degree of remoteness.

With increased development, population growth, and a greater awareness of
environmental considerations, the problem of. waste disposal in Alaska is
assuming larger and larger proportions. The effect of man's waste on the
arctic and subarctic ecosystems has received little attention in the past
and is not well understood. Because of recent increased interest in these
areas, some information is now becoming available on man's possible impact.
For example, in the winter, dissolved oxygen (DO) of ice-covered Alaskan
rivers may reach extremely low levels of 3 mg/l or less under natural condi-
tions. Because of the retarded ability of Alaskan streams to replenish
dissolved oxygen during the long winter period, it becomes essential that
the natural balance is not upset by man. Under these conditions, the

best available waste treatment must be provided.

In discussing biological waste treatment processes, Alter (2) states,

"In. view of present technology, aerobic processes appear to offer the
greatest promise for cold region sewage treatment." The anaerobic process
is severely retarded at colder operating temperatures. One of the major
advantages of biological processes is that the greatest portion of the
energy required for treatment is supplied by the biological system itself,
thereby reducing shipping costs, etc., associated with materials required
for chemical treatment. Aerated lagoons have proven suitable for facilities
where minimum attention is a requirement and sufficient and suitable land
area is available. Extended aeration may be used where greater sophistica-
tion can be tolerated, suitable land area is not available, or greater
process control is required and appears to have great potential for reliable
and economical secondary treatment in Alaska.

SCOPE AND PURPOSE

This report describes investigations conducted on bench scale units at the
Arctic Environmental Research Laboratory; at a pilot plant located 22 miles


8b

TABLE 7

33.7-LITER (8.9-Gallon) REACTOR
RESULTS OF OPERATION WITH VARYING EFFLUENT

OVERFLOW RATES ON THE SETTLING TUBES

INFLUENT REACTOR EFFLUENT
Overflow
Susp. Susp. Rate

Reactor! Solids BOD cop Solids liter/min-m' Solids BOD % BOD coD % COD
Temp. °C (mg/1)  (mg/1) — (mg/1) | (mg/1) SVE (gpm/ft2 ) (mg/1)  (mg/1) Removal (mg/1) Removal
0.35 95 244 292 3973 238 16 (.4) 10 12 95 69 76
(.3-.5)
0.7 112 253 370 4237 238 12 (.3) 8 22 91 7) 79
(.4-.9)

24 (.6) 20 29 89 87 77
4.2 94 193 229 4147 --- 12 (.3) 10 7 91 60 74
(2.8-6.4)

24 (.6) 14 20 90 70 69
3.8 77 142 283 4067 229 20 (.5) 10 14 90 62 78
(3.5-4.1)

33 (.8) 13 20 86 69 76
(1) Values in parenthesés are minimum and maximum for that period.


$$

TABLE 8

47.1-LITER (12.5-GALLON) REACTOR
RESULTS OF OPERATION WITH VARYING EFFLUENT OVERFLOW
RATES ON THE SETTLING TUBES

INFLUENT REACTOR EFFLUENT
overflow?)
(1) Rate
Reactor Solids BOD coD Susp. (gpm/ft2) Tube Solids BOD % BOD coD % COD

Temp. °C (mg/1) (mg/1) (mg/1) Solids SVI 1iter/m@min Size (mg/1) (mg/1) Removed (mg/1) Removed

2.4 77 177 303 3957 --- = 8 (0.2) 2x 3.5 2 19 89 35 88
(1.4-3.5 (continuous )
4x 3.5 2 19 89 39 87
2.9 86 185 275 4157. 214 12 (0.3) 2x 3.5 4 12 94 50 82
(on 1/2 hr-
off 1/2 hr) 4x 3.5 3 10 95 52 81
4.4 93 223 32) 4095 235 20 (0.5) 2x 3.5 4 12 95 55 83
(on 1/2 hr-
off 1/2 hr) 4x 3.5 5 12 95 69 79
7.8 87 194 313 4504 209 20 (0.5) 2x 3.5 12 20 90 69 78
(on 2 hr-
off 1 hr) 4x 3.5 14 23 88 64 80

(1) Values in parentheses are minimum and maximum for that period.
(2) Notes in parentheses indicate the time cycle of effluent flow through the tubes.


Influent Aeration . . Effluent
Sedimentation
~ Chamber Basin -}———»»
Air

Sludge Recycle

a

a Sludge
a Waste

FIGURE 1

BASIC ACTIVATED SLUDGE TREATMENT PROCESS


EPA-660/2-74-070
December 1974

EXTENDED AERATION SEWAGE TREATMENT
Ii COLD CLIMATES

by

H. J. Coutts
C. D. Christianson
Arctic Environmental Research Laboratory
ational Environmental Research Center
College, Alaska

Program Element 1BB044
ROAP 21ASG, Task 01

NATIONAL ENVIRONMENTAL RESEARCH CENTER
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CORVALLIS, OREGON


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 mg/1 as opposed to 3000 mg/l for the 1.3°C reactor.

Overall results of operation of the 33.7-liter and the 47.1-liter tube set-
tler reactors are presented in Tables 3 and 4. These reactors were operated
at 12 and 24 hour hydraulic detention times with daily sludge wasting to
maintain the MLSS at 4000 mg/1. Sludge wasting was accomplished by drawing
off the required amount of mixed liquor, a portion of which was used for a
solids analysis to determine the exact amount of solids removed. Loading
and wastage values are approximate since they do not reflect the variable
quantity of solids in the clarifier. Clarifier overflow rates were varied
from 4 to 35 lit/sq m/min (0.1 to 9.8 gal./sq ft/min) by pumping some of

the effluent back into the mixed liquor.

Effluent BOD and COD values of 9 to 21 mg/1 and 46 to 96 mg/1, respectively,
indicate that a considerable amount of biological activity takes place at
low operating temperatures. Effluent organics were well stabilized as indi-
cated by the high COD/BOD ratios which varied from 7.7 to 3.7. These com-
pared with influent COD/B0D ratios of 1.8 to 1.5. Amounts of sludge wasted
varied from 0.42 mg suspended solids/mg BOD removed at the low temperatures
to 0.14 at 10.5°C amd 24-hour detention time. The pH of both reactors ranged
from 7.2 to 7.6 during the sample periods reported.

EIELSON AIR FORCE BASE UNITS

Organic removal performance of the EAFB extended aeration units is sum-
marized in Figure 12 for the horizontal flow clarifier, and Figure 13

for the upflow clarifier side. These graphs, percent BOD removal, and
temperature vs. date, include a running account of the operational pertur-
bations to which the systems were subjected. The data are broken down into
three periods: a high and low temperature range at a high organic loading,
and a low temperature range at a low organic loading.

These data periods were selected to arbitrarily exclude unsteady state con-
ditions due to startup, and the changing of major operational parameters
such as detention time and temperature. Rhodamine-B dye, which was in-
jected to define flow patterns, tended to upset the system. Most of the
dye poison data, when effluent BOD was greater than feed BOD, was excluded
jin the period III summary for the up side.

The dates of the time periods for steady state analyses are:

Period/temperature/loading Horizontal side Up side
1/7-19°C/High 10-25-71 to 12-21-71 10-25-71 to 12-21-71
I1/2-9°C/High 1-20-72 to 2-26-72 2-1-72 to 2-26-72
III/1-8°C/Low 3-23-72 to 5-1-72 3-20-72 to 4-20-72

29


ilHg-N (Ammonia)

NOg-Nl (Nitrite)

NO3-1 (Nitrate)

Kjeldahl-N (Nitrogen)

Total Nitrogen

Total Nitrogen
Removals (%)

9-P04
(Ortho-Phospnate)

RESULTS OF NUTRIENT ANALYSIS

TABLE 12

CONE REACTORS

13 Hour Detention Time

1.3° REACTOR

6.5°C REACTOR

Filtered | Unfiltered Filtered | Unfiltered
Influent} Effluent | Effluent | Influent] Effluent | Effluent
22 19 18 19 1 1
213 09 -05 VW 13 215
13 2.13 2.02 21 9.17 12.13
4] 28 29 37 3 3
4] 30 31 37 12 15
----- 27 24 on 67 59
20 18 18 19 18 18

Hour Detention Time

1.3°C REACTOR

6.5°C REACTOR

Filtered | Unfiltered Filtered | Unfiltered
Influent] Effluent | Effluent | Influent| Effluent | Effluent
NKg-" (Ammonia) 21 19 19 21 ] ]
NO9-N (ilitrite) -06 03 03 06 14 +12
NO3-N (Witrate) fan -68 254 07 8.03 14.45
Kjeldahl-N (itrogen) | 36 26 27 35 3 3
Total Nitrogen 36 27 28 35 im 18
Total Nitrogen
Removals (4) J wwe 26 24000 | wee 68 50
0-P04
(Ortho-Phos phate) 7 14 15 19 18 16
(1) Total nitrogen results reported are the sum of the nitrite, nitrate

and Kjeldahl nitrogen analysis.

71


EIELSON AIR FORCE BASE PILOT PLANTS

In cooperation with the Alaskan Air Command, the Arctic Environmental Re-
search 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 this facility was to in-
crease the knowledge of biological waste treatment at cold temperatures and
to develop design criteria.

EAFB is located 35 Km (22 miles) southeast of Fairbanks and has a similar
subarctic climate. The mean annual temperature at Fairbanks is approximately
4°C (25°F) with a minimum and maximum recorded temperatures of 55°C (66°F)
and 38°C (+99°F), respectively (7). The area has approximately 200 days

per year with temperatures below freezing (0°C).

The initial extended aeration pilot plant studies conducted at EAFB were
performed in a 570-cu m (»150,000-gal.), inverted, truncated

pyramidal basin with low sloping sidewalls. The side slope ratio was 1:2
(8). Two submerged tube settler modules, 1.2 x 1.5 m (4 x 5 ft) surface
area, were used as the sludge separation and return devices. Because of
extreme subarctic winter conditions, tube settler modules were much under-
sized in comparison to the aeration basin. Operating these settler modules
at an overflow rate of 20 lit/sq m/min (0.5 gal/sq ft/min) limited the
hydraulic detention to a minimum of approximately 5 days, causing excessive
icing problems in a basin with such a large exposed surface-to-volume ratio.
Because of the many operational problems associated with this system, it was
decided to use a more conventional configuration for pilot extended aeration
units,

A large, concrete, vertical wall tank, 9 x 9 x 4.6 m (30 x 30 x 15 ft) deep
nominal dimensions, was divided into two equal-size pilot extended aeration
treatment units (Figure 7). The units were sized to operate any nominal
detention from 1/4 to 4 days, and were differentiated by the clarifier
design. The south unit had a conventional horizontal flow type clarifier.
The north unit, hereafter called the up side, had a rectangular upflow type
clarifier with tubes. Aeration in the up side was provided by 27 Walker
process (W.P.) “monospargers." The monospargers were set up in such a way
(Figure 7) that either 1/3, 2/3 or all could be operated at any one time.
Sludge return was accomplished by means of 10-cm (4-in.) and 15-cm (6-in.)
air lifts. Suction for the 10-cm air lift was taken from the bottom of the
hoppers in the clarifier, one hopper per each airlift. The 15-cm auxilary
airlifts which did not have suction manifolds were provided to remove any
heavy sludge concentrations below the tubes. The flow pattern in the up
side (Figures 7, 8 and 9) was such that the mixed liquor flows over the
surface of the clarifier in three horizontal troughs, down behind the tube
section in a downflow channel, exiting just below the tubes but above the
hoppers. Heavy suspendeds immediately fall into the hoppers and effluent
flows up through the tubes. Sludge that falls into the hoppers is collected
by the airlifts and returned to the aeration basin. Above the tubes, ef-
fluent is collected in a submerged manifold. The section above the tubes
was divided into three parts for the purpose of backwashing the tubes, 1/3
at a time. During a backwash cycle, approximately 1 hour per day. effluent
is drawn through 2/3 of the tubes to backwash the other 1/3.

W7


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:

Environmental Health Effects Research
Environmental Protection Technology
Ecological Research

Environmental Monitoring
Socioeconomic Environmental Studies

aFwons

This report has been assigned to the ENVIRONMENTAL PROTECTION
TECHNOLOGY STUDIES 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 environmental quality standards.

EPA REVIEW NOTICE

This report has been reviewed by the National Environmental

Research Center--Corvallis, and approved for publication. Mention
of trade names or commercial products does not constitute endorsement
or recommendation for use.


lp

TABLE 6

SUBARCTIC ALASKA EXTENDED AERATION UNITS
AVERAGE PERFORMANCE DATA

, Major Overflow
Clarifier Liquid Loading Lit 2
Flow Temp. % BOD —_BOD/ MLSS Percent 1 ering mn Effluent
Period Location Pattern Range °C Removal MLSS Day mg/1 Volatile (gal/ft“ day) SS_mg/1
I EAFB Rect. Hz (1) 7-17 81 0.10 2330 82 20 = (710) 36
II EAFB Rect. Hz (2) 2-9 10 0.14 1710 84 9.3 (330) 134
III EAFB Rect. Hz (3) 1-8 84 0.03 3360 78 12 (420) V7
I EAFB Rect. Up (1) 7-19 82 0.12 2370 80 20 (710) 99
II EAFB Rect. Up (2) 2-7 -30 0.11 2750 83 10 (370) 122
III EAFB Rect. Up (3,6) 1-8 76 0.04 2740 79 12 (420) 50
1971 College
Oxidation Circular Up
Ditch (4,5) 8-20 84 0.05 3000 60 8.7 (310) 28

(1) From October through December 1971, period I average feed BOD = 173 mg/1.

(2) For February 1972, average period II feed BOD = 143 mg/1.

(3) For March to May 1972, average period III feed BOD = 128 mg/1.

(4) Ranganathan, K. R., Murphy, R.S., (10) Institute of Water Resources, University of Alaska, Report #IWR-27,
May 1972. Septic tank sludge not included in influent BOD. Solids in quiescent sections of ditch have
exceeded 20,000 mg/1.

(5) Not including data when solids were being wasted into effluent; i.e., effluent BOD >influent BOD.

(6) Rhodamine-B Dye poisoning data excluded.


were performed in accordance with Standard Methods procedures (5), and
with the use of an electronic DO instrument.

The Minnesota Department of Health has reported on an oxidation ditch under
cold temperature conditions. This ditch serves the city of Glenwood which
is located about 120 miles northwest of Minneapolis. The ditch loop was
build in a horseshoe shape; total loop length was about 386 m (1265 ft).
The ditch was 3.8 m (12.5 ft) wide at the bottom and 5.6 m (18.5 ft) wide

at the surface at the nominal 0.9 m (3 ft) operating depth. Total capacity
at operating depth was 1700 cu m (0.44 MG).

Performance data for this ditch were extracted from the Department of Health
report (11).

25


The high loading rate was achieved by use of a 1/2-day hydraulic detention.
Operating temperatures fluctuated from about 18°C to 7°C from October 4,
1971, to January 3, 1972, depending upon ambient temperature and cooling
pond efficiency. After converting to a spray-type cooling pond, the aera-
tion basin temperatures ran from 2-9°C at the higher loading, period II,
and from 1-8°C at the lower loading, period III.

For period I (Figures 12 and 13) performance of both units is about com-
parable and averages above 80 percent BOD removal. Intentional wastage
of mixed liquor suspended solids (MLSS) in early November seems to have
improved performance. Starvation (lack of feed) and lower mixed liquor
temperatures in late December appeared to reduce performance on both sides.

For period II, data from January 1 to about January 23, 1972, are considered
to be transitional (unsteady state). The up side 15 cm air lifts were not
working during the transition period. For the rest of period II, the up
side performance is very poor as compared to the horizontal side; in fact,
the up side effluent BOD was usually larger than the influent; i.e., losing
activated sludge.

The feed rate was reduced by approximately 1/2 on February 26, 1972, but not
until March 20, did the performance for both sides improve. From then on,
the performance ranged from 75 to 96 percent BOD removal except for dye
poisoning. The horizontal side performed slightly better, probably due

to the ability of its clarifier to retain a higher MLSS.

Figures 14 and 15 are chronological plots of mixed liquor and effluent sus-
pended solids. Intentional wastage of MLSS is indicated on these graphs.

The mixed liquor suspended solids fluctuated more widely than did the BOD
removal. The drops in biomass population (MLSS) were due to the intentional
wastage of the mixed liquor or to autoinduced wastage out of the clarifier.
The bacterial population seems to follow the conventional sigmoidal eco-
logical cycle, where the population (activated sludge biomass) increases
until some force triggers its decline. Starvation may also alter biomass
settleability.

After intentional wastage of mixed liquor (November 1-5), the biomass usual-
ly recovered quickly. as can be seen in Figure 14. The up side MLSS did not
appear to recover as well as shown in Figure 15. After the December wastage,
the MLSS for the horizontal side did not recover for the rest of period II.
Autoinduced wastage kept the MLSS <3,000 mg/1.

The effect of the auxillary 15-cm airlift is shown in the data for the up
side on Figure 15. The airlift was off (air line frozen) from about
January 1 to January 23, 1972, and the aeration basin mixed liquor suspen-
ded solids during that time dropped to less than 300 mg/l. Essentially, all
the MLSS was stored beneath the tubes. The airlift problem was the reason
period II data analysis for the up side did not start until February 1.

After switching to the 1-day detention (period III) on February 25, 1972, it
took approximately 3-4 weeks for the horizontal side mixed liquor suspended

34


Air to
Aerators

and Air-
lift
Pumps

Sewage Feed

Complete Mix (CM)
—<_ Effluent to
“ "> Tube
( Complete Settlers

/ Mix (CM)

AERATION CELL

Sludge

La

Air Lift Pumps
WW serators TM

Retyrning |

\

{ e

t \ cM
Aux. “
Air-
lift

[ sro

udge hse.

Down Flow
Channel

{Effluent Line

>_~

AERATION CELL WITH TUBE SETTLER CLARIFIER

PROCESS FLOW SECTION

Was tage

Sewage
Feed

AERATION
CELL

Complete
Mix

Return Sludge

Clear Effluent
re

Upside
Clarifier

FLOW SCHEMATIC

FIGURE 9

UPSIDE EXTENDED AERATION PILOT UNIT

20


TEMPERATURE EFFECTS OF

LOADING ON PERFORMANCE

1007-
|
|
|
got en ne ~~ ARM TEMPERATURE TREND
—_ 1 ~s
~ ~ 1 -~.
~
~
l ~s <% n
80 7- I .“p
N hg
a NAVY
= | N ve y
z | V2oyp
# LOW \
2 _. | TEMPERATURE | AVOID FOR N
3B 70 DESIGN LOW TEMPERATURE \
= RANGE I DESIGN ‘.
rs) l N
ra |
2
60 + J
|
|
50 +
1
|
40 } + t t
0 0.04 0.08 0.12 0.16 0.20

ORGANIC LOAD Kg BOD

Kg MLSS DAY

For sewage temperatures of 7°C or less, no extended aeration plant should
be designed to operate at an organic loading above 0.08 Kg BOD/Kg MLSS/Day

Pilot extended aeration units treating domestic sewage at less than 8°C

operated satisfactorily at a MLSS concentration up to 4000 mng/1.
above this value have been reported by other investigators.

4

Levels


SETTLING RATE--CENTIMETER/MINUTE

2.0

0.0

2-LITER SETTLOMETER TEST, 0-5 MINUTE RATE
EIELSON AIR FORCE BASE PILOT EXTENDED AERATION PLANT

Horizontal Side

LEGEND:
TEMP. °C DETENTION DAYS
0 7-17 0.6
2-9 0.5
4 9 #9 Gis 1.0
%
% 094
0.4
A)
>
rs 0 oo
=
iS a ° O
0 Oo
f 0.2
oO
> 4
%
re) [oKe) oo ¢ °°
exe) oo foxe) o o D?¢o
o—e——_9—, $ By -e55-—-
1000 2000 3000 4000

MIXED LIQUOR SUSPENDED SOLIDS (mg/1)
FIGURE 22

56


Reactor
Mixed Liquor,”

DENITRIFICATION STUDY SAMPLE STATIONS

FIGURE 25

72


Vag = volume of aeration basin, cubic meters.

D.T.

detention time, days.

For each period, the loading could be converted to a volatile mass basis
by dividing the loading by the average volatile fraction of the MLSS; i.e.,
MLVSS/MLSS.

Organic loading is usually reported in terms of mixed liquor volatile sus-
pended solids, MLVSS. This was not done with the EAFB data since it was
desired to compare loadings from other reports (12)(13) in which volatile
fractions were not always reported.

In period I for both sides, the BOD removal averaged 81 to 82 percent. For
period II at the same feed rate, the performance dropped to less than 20
percent removal. Aeration basin temperature was the only operational vari-
able that could effect the drastic reduction in performance. Temperatures
averaged 12°C for period I and 4°C for period II. Decreasing the average
clarifier overflow from 20 to about 9.9 +0.6 lit/sq m/min (0.49 to 0.24
+0.01 gal./sq ft/min) did little to compensate for the temperature effects.
It was felt that the systems for period II had not yet reached equilibrium
but would continue to lose efficiency. In period II solids passing through
the clarifier reduced the MLSS which increased the organic loading, thereby
forcing the process to self-destruction.

Period III data further illustrates that loading is the main temperature
sensitive variable. During this period, performance recovery was excellent
even though it took 3 to 4 weeks to attain steady state. The 3 to 5 week
equilibrium state is not enough time to make accurate predictions of long-
term performance. The removal for the horizontal flow side averaged 84
percent at an average loading rate of 0.03, even though the total overflow
was increased from period 11 to 12 lit/sq m/min (0.3 gal./sq ft/min). The
up side did not perform as well at the same temperatures and overflow rate
even though performance data were excluded when there were indications
that Rhodamine-B dye injections were poisoning the system.

It should be noted that the EAFB system was operated using primary effluent
as feed. If raw sewage was used as feed, it is estimated that the percent
BOD removal would be up to 5 percent higher assuming the detention time
would be increased to keep the loading down.

For the EAFB units, the volatile fraction of the MLSS decreased, as expected,
with increased detention time. The College oxidation ditch, due to its low
bottom velocity, tends to accumulate partically digested activated sludge

as indicated by the low volatile fraction. Information presented for

ditch removals exclude data when solids were being discharged into the
effluent.

Overall temperature effects of loading on performance for many other ex-
tended aeration units is shown in Figure 16. Most of the warm 12-25°C
temperature data were extracted from the 1960 U.S.P.H.S. survey of several
extended aeration plants (12). Some of the plotted data represents more
than five performance analyses and some represent only one or two. The

42


7-12°C data are from the College oxidation ditch (10), AERL cold room reac-
tors, and the EAFB units. The 1-7°C data were obtained from the cold room
reactors and the EAFB units. Weekly average data from EAFB were plotted
for period III. For this graph, all data with effluent suspended solids
greater than 100 mg/1 were excluded since it is felt that proper intentional
wastage of excess activated sludge would limit effluent suspended solids to
less than 100 mg/1. This graph is then based only on expected performance
when intentional wastage separate from effluent is practiced.

Notice in Figure 16, as loading increases, BOD removal drops off quite
rapidly at low temperatures (below 5 to 8°C). For warmer temperatures
(above 12°C), loss of performance with load is moderate.

Wuhrman (14) also presented data which show that, as loading increases,
performance decreases; more so at temperatures less than 11°C than for
temperatures greater than 13°C. His data are more in the activated sludge
range; i.e., loadings greater than 0.2.

SOLIDS LEVELS AND SEPARATION

In startup of an extended aeration plant, performance is usually low until
enough biomass (MLSS) has been built up for adequate bioadsorption. Gen-
erally speaking, a low MLSS concentration also represents a high organic
loading which might tend to force the process to self-destruction were it
not for the clarifiers which, at startup, are underloaded in terms of
solids handling. A typical curve of performance vs. the product of MLSS
and detention is shown in Figure 17. The upper curve is from the National
Sanitation Foundation observation of 10 package extended aeration units (13)
Summarized EAFB data is plotted on this graph. The EAFB period I data would
not have appeared better than the NSF package plant data if the abscissa was
in units of MLSS only. The NSF data is for temperatures greater than 11°C.
The comparative poor performance of period III data is attributed to the low
temperature and the fact that the feed was primary effluent.

Extensive surface icing on an aeration basin should be avoided because it
may rob the basin of its MLSS. In discussing 1970 EAFB experience (Clark,
et al. (8) stated that the sludge accumulated in the growing ice, reducing

the suspended solids level in the pond from approximately 2,500 mg/1 to
less than 200 mg/1.

Solids removal plays a very important part in the efficiency of the acti-
vated sludge treatment process. The degree of sludge separation directly
influences the quality of effluent from wastewater treatment plants with

bigher concentrations of effluent solids contributing to higher effluent

In activated sludge operation, solids separation is the most important
physical process contributing to overall process performance. Clarifier
performance can usually be met by design, whereas, performance of bio-
chemical-adsorption usually cannot. Reed and Murphy (15) conducted an

44


S.E. of Fairbanks, at Eielson AFB and; at the College oxidation ditch. The
research was concerned primarily with adapting methods develoned in the
contiguous United States to the extreme climates found in Alaska, and
included investigations in the following areas

1. low temperature process performance

2. low temperature solids separation

3. degree of environmental protection required for equipment and processes
4. aeration chamber mixing

5. waste sludge production

The purpose of these research efforts was to develop adequate waste treat-
ment methods and design criteria for use under the extreme climatic condi-
tions found in the subarctic. These methods would hopefully provide the
basis for facilities that were economical to construct, simple to operate,
and require as little maintenance as possible, while providing the desired
degree of treatment.

BASIC PROCESS DESCRIPTION

Stewart (3) defines activated sludge wastewater treatment as involving
"physical and biological processes in a system having special configuration
and operation such that the wastewater is substantially purified and ren-
dered less reactive." The basic activated sludge system includes an aeration
tank and settling tank, as shown in Figure 1. Untreated wastewater enters
the aeration tank where biologically degradable materials are stabilized by
microorganisms (activated sludge). The aeration tank mixture (mixed liquor)
is displaced to the settling tank where the activated sludge settles to the
bottom and is returned to the aeration tank. The treated wastewater leaves
the process as overflow from the settling tank. Excess cell material pro-
duced is removed from the system either by deliberate wasting of sludge

or unintentional wasting of suspended solids in the settling tank overflow.

Many variations in the activated sludge process are possible and most of these
are described by Stewart (3). Discussion here will be limited to the ex-
tended aeration process which is a long detention form of the activated

sludge process. In extended aeration the aeration tank detention may vary
from 1/2 to 3 days but is usually 1 day.

The design of activated sludge waste treatment processes basically requires
knowledge of three factors: organism growth rate or process reaction time;
cell yield or excess sludge production; and endogenous respiration or auto-
oxidation rate. Organism growth rate generally does not enter into design
considerations for the conventional or extended aeration activated sludge
treatment at normal temperatures because it is not a limiting factor in the
process. Cell yield and auto-oxidation rate are utilized in the growth
kinetics equation as follows: