EPA-600/2-81- 155
August 1-981
PARALLEL EVALUATION OF AIR-AND
OXYGEN-ACTIVATED SLUDGE
by
Scott Austin
Fred Yunt
Donald Wuerdeman
Los Angeles County Sanitation Districts
Whittier, California 90607
Contract No. 14-12-150
Project Officer
Irwin J. Kugelman
Wastewater Research Division
Municipal Environmental Research Laboratory
Cincinnati, Ohio 45268
MUNICIPAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
-------
TECHNICAL REPORT DATA
(Please read Instntcnons on the reverie bef
1 RE>~O"HTNO".~~ "
EPA-6QQ/2-81- 155
ORP-Beport
4 TITLE AND SUBTITLE
PARALLEL EVALUATION OF AIR-AND OXYGEN-ACTIVATED SLUDGE
5>REPOHT DATE
August 1981
6 PERFORMING ORGANIZATION CODE
Scott Austin, Fred Yunt, Donald Uerdeman and Walter
E. .'Harrison
8 PERFORMING ORGANIZATION REPORT NO
9. PERFORMING ORGANIZATION NAME AND AD3RESS
County Sanitation Districts of Los Angeles County
1955 Workman nil] Road
Whi,ttier, California 90607
10 PROGRAM ELEMENT NO
AZB1B, D.U. B-113.Task D-1/3D
11 CONTRACT/GRANT NO.
Contract No. 14-12-150
12 SPONSORING AGFNCY NAME AND ADDRESS
riuniciparEnvironnental Research Laboratory - Cin., OH
Office of Research and Development
U.S. Environmental Protection Aaency
Cincinnati, Ohio 45268
13. TYPE OF REPORT AND PERIOD COVERED
Final, Feb. 1975 - Dec. 1976
14. SPONSORING AGENCY CODE
EPA/600/14
15 SUPPLEMENTARY NOTES
Pro.ject. Of f icer: Irwi n Kugelman (513) 684-7633
16 ABSTRACT
ABSTRACT
To
provide data on the relative merits of air and oxygen in the activated sludge pro-
cess, two 1900-m3/day (0.5-mgd) activated sludge pilot plants, one air and one oxygen
system, were operated side-by-side at the Joint Water Pollution Control Plant, Carson,
California. Both of the pilot plants met the applicable discharge limitations for
everything but three trace metals, but the oxygen system provided a more stable
operation.
Primary differences in performance concerned ammonia nitrogen removals and energy
consumption. Differences in sludge production were not significant.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b IDENTIFIERS/OPEN ENDED TERMS
*Air-activated sludge,
*0xygen-activated sludge,
Sludge production,
Sludge settleability,
Power consumption
c. COSATI Field/Group
* Sewage treatment,
* Activated sludge process,
Sludge,
Clarification,
Energy
13B
18 DISTRIBUTION STATEMENT
Release to Public
19 SECURITY CLASS (This Report)
Unclassified
21. NO OF PAGES
52
20. SECURITY CLASS (This page]
Unclassified
22 PRICE
EPA Form 2220-1 (Rev. 4-77)
-------
BEGIN
FIRST
LINE OF
TEXT
HERE dP
GUIDE SHEET
CENTER
OF PAGE
TOP OF
IMAGE
AREA
HEAJ,
DISCLAIMER
This report has been reviewed by the Municipal Environmental Research
Laboratory, U.S. Environmental Protection Agency, and approved for
publication. Approval does not signify that the contents necessarily reflect
the views and policies of the U.S. Environmental Protection Agency, nor does
mention of trade names or commercial products constitute endorsement or
recommendation for use.
BEGIN
LAST LINE
OF TEXT
9-1/8
I
3/8'
EPA-287 (Cm.
H-76)
PAGE NUMBER
BOTTOM OF
IMAGE AREA,
OUTSIDE
DIMENSION
FOR TABLES
AND ILLUS-
TRATIONS
-------
BEGIN
FIRST
LINE OF
TEXT
HERE li
r
DROPPED
HEAD,
BEGIN
SECTIONS L_
HERE L>
G GUJDE SHEET
CENTER
OF PAGE
TOP OF
,, IMAGE
.EQREWORD.
The U.S. Environmental Protection Agency was created because of Increasing
public and government concern about the dangers of pollution to the health
and welfare of the American people. Noxious air, foul water and spoiled
land are tragic(testimonies to the deterioration of our natural environment.
The complexity of that environment andjthe interplay of its components
require a concentrated and integrated attack on the problem.
Research and development is that necessary first step in problem solution;
it involves defining the problem, measuring its impact, and searching
|£|r_s_oJut_Lons.._|.The ^r)'|oip^ljnjncojnmentaj .Research. Labo,r.alory_de.velop.s new^
"~~^' improved technology and systems tojprevent, treat, and manage wastewatef
and
BEGIN
LAST LINE
and solid and hazardous waste pollutant discharges from municipal and com-
munity sources, |to preserve and treat public drinking water supplies, and to
minimize the adverse
pollution. Tbji-s/gpubl
provides a most
community.
vital
This report presents
and performance (data
economic, social,
i cat ion is one of
health, and aesthetic effects of
the products of that research and j
communications link between the researcher and the user
I
1
design details, operating experiences, and operating
for a parallel operation of an air-activated and an
oxygen-activated sludge pilot plant. Consideration of the operational re-
sults presented {herei
and potential mi
OF TEXT cf=»
n is recommended for design engineers, facility planners,
nicipal users of an oxj
1 3/8" i
i » »
Francis T.
Director
/gen-activated sludge system.
Mayo
Municipal Environmental Research
Laboratory
it
'
'&£?<'<
BOTTOM OF
IMAGE ARE;
OUTSIDE
niMCMcinM
^^" , s_* ( ITI ^1 \Ul V^l ^
1 FOR TARIFF
'$$*$ , TRATIONS
EPA-237 (Cin.)
K-76)
PAGE
JER
-------
BEGIN
FIRST
LINE OF
TEXT
HERE d-
TYPING
CENTER
OF PAGE
DROPPED
HEAD,
BEGIN
SECTIONS
HERE d:
A
TOP OF
IMAGE
AREA
-ABSIRACL
i
To provide data on the relative merits of air and oxygen in the activated
sludge process,(two 1900-m3/day (0.5-mgd) activated sludge pilot plants, one
air and one oxygen system, were operated side-by-side at the Joint Water
Pollution Control Plant, Carson, California. Both of the pilot plants met
the applicable discharge limitations fir everything but three trace metals,
but the oxygen system provided a more stable operation.
p I
Primary differences in performance concerned ammonia nitrogen removals
jlDjdjBnergy_ cc^n_sump_tion./2.,Di_fferences_ itn_sl_udge EIodu.ctjon_
cant. , "
This report was (submitted in fulfillment of Contract No. 14-12-150 by the_
3/8'
EPA-287 (Cira.l
H-7S)
PAGE NUMBER
BOTTOM OF
IMAGE ARE,
OUTSIDE
DiMENSION
FOR TABLES
'AND ILLUS-
TRATIONS
-------
BEGIN
FIRST
LINE OF
TEXT
HERE C|
DROPPED
HEAD,
BEGIN
SECTIONS
HERE
TVPOKG GUIDE SHEET
CENTER
OF PAGE
TOP OF
IMAGE
m
Foreword,
''Abstract ! . L. ........... iv
Figures... I ! vi
Tables.
v
Abbreviations and Symbols ....!... viii
-?. Ll _Jn^_rod_uC^ i 2H« -172 JLI-JL: -_u L. -_i-- -_^ -j_t j_^« J_L J^.*+A j_t -.u _! L
2. Conclusions. ! 2
Selection and Description of the Pilot Plants,
Ai r gsp^ajged turbine system. J ,
High purity oxygen system...!,.. ,,
Final clarifiers. i
Operation of the Pilot Plants.
'Startup J.
Pilot Iplant operational phases
Discussion of Results
Effluent quality...
Sludge production,
Sludge settleability,
Power
Depenc
consumption.
ability and maintenance
BEGIN
LAST LINE|____
OF TEXT
fe> 3/8"
V
EPA-287 (Cm.}
(4-7S)
PAGE NUMBER
BOTTOM OF
IMAGE ARE/!
OUTSIDE
DIMENSION
FOR TABLES
AND ILLUS-
TRATIONS
-------
BEGIN
FIRST
LINE OF
TEXT
HERE
CHOPPED
HEAD,
BEGIN
SECTIONS
HERE
WP1RJG G03DE SHEET
CENTER
OF PAGE
TOP OF
IMAGE
'AREA
FIGURES
Aeration basin and deep-tank submerged turbine aerator
Oxygen system reactor ( , ,
UNOX reactor with surface aerators ,
Soluble[COD versus aeration time
10
11
Page
4
6
11
23
Effluent soluble COD versus MCI^T 24
Nonfilterable COD and BOD5 ver|us VSS 27
Hexane extractables versus effluent suspended solids 29
SJudge growth ^petkj^._._.._._.._]_.._._. ^^.^_-±i.*±i.-^..±±-^_i 31_-
Analysis of net sludge production using MCRT
_as the independent variable...! 35
'Analysis of net sludge production using the food-to-
microorganism ratio as the independent variable 36
Initial-fettling rates.
38
BEGIN
LAST LINE
OF TEXT
b 3/8"
_ 1
EPA-287 (Gin.
H-76)
PAGE NUMBER
BOTTOM OF
IMAGE ARE.
OUTSIDE
DIMENSION
FOR TABLEE
'AND ILLUS-
TRATIONS
-------
BEGIN
FIRST
LINE OF
TEXT
HERE
DROPPED
HEAD,
BEGIN
SECTIONS
HERE £
WP1MG GU3DE SHEET
CENTER
OF PAGE
h
TOP OF
IMAGE
AREA
TABLES
Number
1
2
3
4
5
6
7
8
9
10
11
BEGIN
LAST LINE
OF TEXT C>
Design criteria for pilot plants
Summaryiof operational parameters--air-sparged turbine
system 1 ,
Summaryjof operational parametersoxygen system
Summary.of effluent qualityair system
Summary'of effluent qualityoxygen system
Effluent clarity >
Trace constituent removal by means of air-ac"t"iv,ated
s TTJdcje .77 . ^Y, ?. .77 77. 77". 77. 77", 77. 77. 77*. ."77.77 .77 ."77 ."
Trace constituent removal by means of
oxygen-activated sludge i.
Assumed oxygen transfer rates.!
8
13
16
21
22
26
32
40
Oxygen Astern operating characteristics 41
Power consumption
42
3/8"
EPA-287 (Gin.)
(4-76)
BOTTOM OF
IMAGE AREy:
OUTSIDE
DIMENSION
_ FOR TABLES
\?AND ILLUS-
. TRATIONS
PAGE NUMBER
-------
BEGIN
FIRST
LINE OF
TEXT
HERE
DROPPED
HEAD,
BEGIN
SECTIONS
HERE E
TTCPtNG GU8DE SHEET
CENTER
OF PAGE
TOP OF
IMAGE
EL
-AB8RE.V.I A J.I.ON SUND-SYMBOLS
ABBREVIATIONS
BOD
BODR
BOD5
COD
CODR
DO R
DTST
--tbiochemical oxygen demand
--ibiochemical oxygen demand removed
--.5-day biochemical oxygen demand
--(chemical oxygen demand!
(chemical oxygen demand;removed
--dissolved oxygen
--"deep tank submerged turbine
SR
JWPCP
MCRT
MLSS
MLVSS
NTP
RWQCB
SOTR
SVI
SWD
TPVSS
VSS
SYMBOLS
_
--.initial settling rate J
--'Joint Water Pollution Control Plant
--|mean cell residence time
--jmixed liquor suspended!sol ids
3-n/ni'xed liquor volatile suspended solids
--jnormal temperature andlpressure
--iRegional Water QualityfControl Board
--standard oxygen transfer rate
--jsludge volume index 1
--jside water depth J
--'total plant volatile suspended solids
--[volatile suspended sol'ds
a, B
C
c*
dC/dT
variables to correlate
clean water results
, to mixed liquor conditions
I system dissolved oxyge|i concentration
--(equilibrium dissolved oxygen concentration at
' zero uptake
--joxygen transfer rate
.mean cell residence time
--'microorganism decay coefficient
-- ivolumetric mass transfer coeficient
BEGIN
LAST LINE
V/Q --aeration period
Y --[growth yield coefficiei
.I. ,
OF TEXT C£>
!t
BOTTOM OF
[ IMAGE ARE/
^ OUTSIDE
DIMENSION
FOR TARl F?
M f [ ^x*
A ,_,. * J \>AMn 11! HQ
a 3/8 n . .-.-vi Ti'-x .:.'':: \ ANU ILLUS>-
JL_ V *££^&&£^ ! IKA
EPA-287 (Gin.)
PAGE NUMBER
-------
SECTION 1
INTRODUCTION
Since the introduction of high-purity, oxygen-activated sludge, a contro-
versy has existed concerning the relative merits of air and oxygen in the
activated sludge process, but very few data are available on side-by-side
operation of relatively large-scale systems with comparable engineering.
As part of the research effort involved with Federally-mandated secondary
treatment at the Joint Water Pollution Control Plant (JWPCP) in Carson,
California, the County Sanitation Districts of Los Angeles County constructed
two 1900-m-Vday (0.5-mgd) activated sludge demonstration plants. One incor-
porated the UNOX high purity oxygen process, and one used an air-sparged
mechanical aerator. The primary purpose of the study was to obtain data
pertinent to the selection and design of an activated sludge system at the
JWPCP, but the nature of the research facilities allowed a direct comparison
of the two activated sludge processes. The pilot plants were operated on
identical feed. Equal engineering care was taken in the design of the
aeration systems, and identical clarifiers were used. Unfortunately, the
research motivations in establishing the operating parameters for the two
plants were different. The oxygen system was operated to refine specified
design parameters, while the air system was operated to determine its
capabilities and limitations.
The JWPCP is a 15-m-Vsec (350-mgd) primary treatment plant treating a mixture
of domestic and industrial wastes. These facilties allowed a good comparison
of the two activated sludge alternatives for treating relatively concentrated
municipal wastewater.
-------
SECTION 2
CONCLUSIONS
Both activated sludge systems are capable of producing effluents meeting the
JWPCP discharge limitations for everything but certain trace metals, which
will require source control. But the oxygen system is somewhat more stable
and flexible in its operation.
The two systems obtained good removals of soluble organics, and factors
affecting solids separation in the final clarifier are most significant in
terms of their effects on effluent quality. The most notable detrimental
factors encountered in the study were excessive aerator power inputs, which
sheared the floes in both systems, and nitrification-denitrification, which
caused the settled sludge from the air system to resuspend.
The major difference between the two systems in terms of pollutant removals
concerns ammonia nitrogen. The oxygen system did not nitrify. At the JWPCP,
where the ammonia discharge limitation is high enough to impose no con-
straint, this characteristic is an advantage in that it eliminates rising
sludge resulting from nitrification-denitrification.
Claims have been made that oxygen-activated sludge processes produce less
sludge than air-activated sludge processes. In this study, a comparison was
made based on total plant solids and the difference was found to be insigni-
ficant at the 90-percent confidence level. The trend, however, was for the
oxygen system to produce more sludge.
Because of modifications to the pilot plant's aeration equipment that were
made to prevent floe shear, an energy consumption comparison was considered
inappropriate. A paper study indicates that substantial energy savings may be
expected with the oxygen system.
-------
SECTION 3
SELECTION AND DESCRIPTION OF THE PILOT PLANTS
AIR-SPARGED TURBINE SYSTEM
The location of the Districts' JWPCP in an urban area placed a definite land
constraint on the proposed secondary treatment system for that plant. When
preliminary site layouts were made for a conventional activated sludge system
with the standard 4.6-m-deep (15-ft-deep) aeration tanks and an optimistic
6-hr aeration period, no excess land was available for waste activated
sludge processing. Because of this land constraint, the Sanitation Districts
proceeded to evaluate activated sludge systems that could reduce the land
area required for secondary treatment. One of those alternatives was the
deep tank submerged turbine (DTST) system. The DTST system was selected not
only because of the land savings from the deeper tank (7.6 m or 26 ft) but
also because the submerged turbine is a more efficient oxygen transfer device
than the conventional coarse bubble air diffusers. The land savings from the
deeper tank and the possibility of reducing the aeration period made the DTST
system a realistic candidate system for secondary treatment at the JWPCP.
The aeration basin for the DTST system (Figure 1) was designed for a 3.5-hr
detention time (V/Q) at a design flow of 1900 m^/day (0.5 mgd). The aeration
basin was 6.1 x 6.1 m (20 x 20- ft) with a 7.6-m (25-ft) side water depth
(SWD) and 1.5-m (5-ft) freeboard. To insure a complete mix system, 0.51-m
(1.7-ft) baffles were provided on each wall running the full tank depth.
The design of the submerged turbine aerator itself was based on an ability to
supply sufficient oxygen transfer capability to treat the JWPCP primary
effluent in a 2-hr aeration period (V/Q). The turbine aerator had a 45-kW
(60-hp) drive unit with a 7.6-m (25-ft) long, 0.25-m (10-in) diameter steel
shaft and a 1.5-m (5-ft) diameter impeller. The shaft was supplied in two
sections of 6.1 -m (20-ft) and 1.5 m (5 ft) to provide the flexibility
of evaluating both a 6.1-m (20-ft) and 7.6-m (25-ft) water depth.
Air was introduced into the aeration tank at the perimeter of the mixer/
impeller through a sparged ring apparatus. Two 0.28-m^/sec (10-cfs) air
compressors were provided, with one acting as a standby.
HIGH-PURITY OXYGEN SYSTEM
One of the major advantages offered by the pure oxygen biological treatment
process is the ability to reduce the period of time required for treatment
of a wastewater by increasing the rate at which oxygen can be dissolved into
-------
BEGIN
FIRST
CENTER
TOP OF
HERE
DROPPED
HtAD,
BEGIN
SECTIONS
HERE n
~
=3
AIR
SUPPLY
i
I
\
/ \
/
\ /
. A / _
L.
V
r
1
f
,
1
4
U
J i
J
*
NOTE
Figure 1. Aeration basin and
i 1 . 5 m-
.1
u
^
5 1 m ~ 3.28
deepltank
4
E
I
ft.
( '!
|
I
|
i
'
'
1
1 -]
I
=
oi
l
'
j
[
'
v !
submerged turbine aerator. j
// ,~
??A-23? (Cm,}
'.:'.' 4 v;1:
PAGE NUMBER
XS
-------
the mixed liquor within the biological reactor. The results of preliminary
studies using Union Carbide's 0.6-1/sec (10-gpm) mobile pilot plant verified
this claim, as acceptable effluent quality was achieved at aeration periods
as short as 1.5 hr (V/Q).
Based on this preliminary testing, the oxygen pilot plant was designed for an
aeration period of 2.5 hr (V/Q) at the design flow of 1900 m^/day (O.S^mgd).
The biological reactor is 7.3 x 7.3 m (24 x 24 ft) with a 3.7-m (12-ft) SWD.
The total height of the basin is 4.6"m (15-ft) (Figure 2). As is typical with
the sealed reactor type of pure oxygen system, the reactor was subdivided into
four equal-volume, completely mixed chambers with inside dimensions approxi-
mating a 3.7-m (12-ft) cube. To insure complete mixing in each of the four
reactor stages, there are four anti-swirl baffles per stage located along the
diagonals a distance of 1.2-m (4*ft) from the center of the section. These
baffles are 0.36-m (1.2-ft) wide and extend the entire depth of the tank. An
extension is provided along the bottom 1.8-m (6 ft) of each baffle, which
runs toward the tank section center for a total of 0.61-m (2 ft). This
modification was included to insure good baffling during operation using
surface aerators, if so desired.
As a result of competitive bidding, Union Carbide Corporation was awarded a
contract for the construction of the pure oxygen biological reactor, which
was to be built into the existing pilot plant influent pumping station and
final clarifier system. The reactor was designed to incorporate a submerged
turbine/gas recirculation compressor arrangement for oxygen dissolution in
each reactor stage. The mixers in stages 1 and 2 were driven by 3.7-kW
(5-hp) motors, while those in stages 3 and 4 were driven by 2.2-kW (3-hp)
motors (Figure 2).
Having been introduced into the gas space above the liquid level in stage 1
of the reactor, the oxygen was withdrawn from the gas space above the stage 1
mixed liquor level by a compressor and pumped through the center of the
0.15-m (6-in.) diameter turbine shaft. The gas exited the shaft through a
rotating sparger located approximately 0.3 m (1-ft) from the bottom of the
reactor at the base of the shaft. Four rectangular turbine blades were
located about 0.3 m (1-ft) above the rotating sparger, which, when operated
at their normal speeds (130 rpm in stages 1 and 2, 82 rpm in stages 3 and 4),
maintained a completely mixed regime while dissolving sufficient amounts of
oxygen to meet the biological demand. Oxygen which did not go into solution
and carbon dioxide coming out of solution as a by-product of the biological
reaction in the first stage passed through an opening in the gas space into
the second stage where it was introduced into the mixed liquor by the same
compressor/turbine arrangement as the first stage. In like manner, the gas
proceeds through the third and fourth stages of the reactor, with the unused
oxygen and other gases being ultimately passed through a vent in the fourth
stage to the atmosphere.
The dissolved oxygen concentration in each stage was controlled by varying
the recirculated gas flow from the compressor to the sparger at the base of
the turbine shaft. This was accomplished by means of a 50-mm (2-in.) bypass
valve located between the compressor discharge and a rotary joint gas inlet
-------
BEGIN
FIRST
LINE OF
TEXT
HERE
DROPPED
HEAD,
7VP1MG GUIDE SHEET
CENTER
OF PAGE
TOP OF
, IMAGE
'AREA
-RECIRCULATION-
COMPRESSORS
SECTIONS!
NOTE: I m = 3.28 ft.
Figure 2. Oxygen' system reactor.
at the top of the turbine. By opening this valve, a portion of the recircu-
lation gas can Be bypassed back into the gas space, thus reducing the volume
of gas which is introduced ;into the Liquid through the turbine for dissolu-
tion.
The oxygen supply system is controlled through a pressure transmitter-set
point controller] arrangement in which the flow of oxygen from the storage
facility to itsjpoint of introduction at the first stage is automatically
controlled in order to maintain a constant pressure in the gas space above
the first stage.' When the pressure controller indicates a pressure that is
below the pressure set point, an increased signal is sent to a control valve,
which increases Ithe pure oxygen gas flow into the reactor and, hence, the
pressure in the igas space over the first stage. Likewise, if the gas space
pressure exceeds the set point value, Ihe gas flow is reduced until the
pressure approaches the desired value."
BEGIN
LAST LINE
OF TEXT
The flow of gas 'through the reactor is
monitored at all times so that the
amount of oxygen utilized during the treatment process can be determined.
Since the reactor is sealed, the monitoring of oxygen utilization is accom-
'Hshed by simply measuring the mass flow rate of pure oxygen into the
i
3/8"
EPA-287 (Cm.)
(4-76J
PAGE NUMBER
BOTTOM OF
IMAGE ARE,
OUTSIDE
. DIMENSION
_! FOR TABLES
VAND ILLUS-
! TRATIOMS
-------
BEGIN
FIRST
LINE OF
TEXT
TWKG GUIDE
CENTER
OF PAGE
HERE ripe actor and sub~tfacfing fhe mass flow pte of oxygen exiting the reactor vi_a
' ~~
TOP OF
tJMAGE
AREA
DROPPED
HEAD,
BEGIN
SECTIONS
HERE S
\
th'e vent stack rn the fourth stage. In the latter case, it is necesary to
measure and record the oxygen composition of the vented gas continuously,
[since a significant portion is composed of gaseous byproducts of the chemical
and biological ireactions that take place while the wastewater is under
aeration.
b; I
ree final sedimentation tanks were designed for the project using the
jDistricts' basic criteria for rectangular final sedimentation tanks. Two of
the tanks were of the same size to allow evaluation of both the submerged
turbine system and the high purity oxygen system at the same overflow rate of
|28.5-m3/m2/day (i70r>gpd/ft2) at the design flow 1 900 ^m3/ day (0.5-mgd). The
third tank was designed for an overflovl rate of 18.3 m3/m2/day (450 gpd/ft2)
at the 1900-m^/d'ay (0.5-mgd) flow. It (was used to evaluate lower overflow
rates in either (system and to provide the flexibility required to evaluate
flower aeration times and, hence, flows
of greater than I900~m3day (0.5-mgd)
ijin either pilot'plant.
Uj. ^ _ 6-1/2" 1
The two final sedimentation tanks designed for 28.5-m3/mZ/day (700 gpd/ft?)
ijwere 3-m (10-ft)j deep, 3-m (10-ft) wide, and 22-m (72-ft) long. These tanks
have a 2-hr hydr.aulic detention time and a flowthrough velocity of 3.2 mm/sec
|(0.6 ft/min) at |the 1900-m3/day (0.5-mgd) flow and 30-percent recycle. The
jthird final s£dnme"ntation tank had the (same width and depth as the two 22-m j
!j(71-ft) tanks, b'ut it was 34-m (111-ft): long. The hydraulic detention at 1900-
im-Vday (0.5-mgd)j flow and 30-percent recycle was 3 hr, and because it had the*
Jsame cross sectional area as the shorter sedimentation tank, the flowthrough
('velocity was the same. The same weir length was provided on all three
jjsedimentation ta'nks, so that at the design flow, the weir loading was 62.1-
irn3/m/day (5000«g'pd/ft2).
The design criteria used for the biological reactors and the associated
final sedimentation tanks have been summarized in Table 1.
BEGIN
LAST LINEl
OF TEXT £>>
I
3/81
BOTTOM OF
IMAGE ARE^
OUTSIDE
DIMENSION
FOR TABLES
>AND SLLUS-
TRATSONS
EPA-2S7 (Cin.)
(0761
PAGE NUMBER
-------
TABLE 1. DESIGN CRITERIA FOR PILOT PLANTS
Item
_ r1
Biological Reactors:
Average flow, m3/day (mgd)
Length, m (ft)
Width, m (ft)
Average water depth, m (ft)
No. of stages
Detention time (V/Q), hr
Oxygen Storage Tank:
Number
Volume, m3 (ft3) NTP
Capacity, m3/hr (ft'/hr)
Final Clarifiers:
Number
Length, m (ft)
Width, m (ft)
Average water depth, m (ft)
Overflow rate, m3/m2/day (gpd/ft2)
Detention time
(Q + 1/3 return), hr
Weir loading rate, m3/m/day (gpd/ft)
Flowth rough velocity
(Q + 1/3 return), mm/sec (ft/min)
Air
System
1900 (0.5)
6.1 (20)
6.1 (20)
7.6 (25)
1
3.5
--
--
--
Standard
2
22 (72)
3.0(10)
3.0(10)
28.5(700)
2.0
62.1 (5000)
3.2 (0.6)
Oxygen
System
1900 (0.5)
7.3 (24)
7.3 (24)
3.7 (12)
4
2.5
1
9900
(350,000)
' 140
(4940)
Large
1
34 (111)
3.0 (10)
3.0 (10)
18.3 (450)
3.0
62.1 (5000)
3.2 (0.6)
].
3EGIN |
LAST L1NEJ'
0? TEXT ^
I
i
a
/> 3 1
>"4 T /fi ' * (*-* ' '' ' " ^
MO/O \j ..-..'
V \ >.: ,-. : ' j
BOTTOM OF
I IMAGE AREA
t OUTSIDE
1 DIMENSION
1 FOR TARi FS
, , , . \ ^ A M Pi 11 1 1 1 Q
> .-.- ; . .; ( IHATIUNb
£P>A-2S7 (Cire.)
K-76)
PAGE NUMBER
-------
SECTION 4
OPERATION OF THE PILOT PLANTS
STARTUP
Air Sparged Turbine Pilot Plant
Upon completion of the clear water testing of the DTST aerator in December
1974, the DTST system was started up in January 1975. The pilot plant was
seeded with waste activated sludge from the Pomona Water Reclamation Plant.
From the middle of January until mid-February, the flow to the unit was
gradually increased from 380-to llOQ-m^/day (0.1-to 0.3-mgd). However, during
this period, the effluent was characterized by cloudiness and the biology was
marked by an apparent dispersed floe. A meeting with the mixer manufac-
turer's representatives was called in mid-February. The discussions indicated
that the probable cause for high effluent turbidity and dispersed floe was
shearing of the floe. To alleviate this problem the manufacturer agreed to
decrease the energy input to the basin by reducing the aerator speed from 54
to 46-rpm. The mixer horsepower was thereby reduced 37-percent. Once the
mixer speed was reduced, the improvement in effluent quality was almost
immediate. Within a few days, the cloudiness in the effluent disappeared and
a good biological floe appeared.
UNQX Pilot Plant
The oxygen biological treatment pilot plant was started up on June 27, 1975,
by drawing air into the reactor through the recirculation gas compressors
with no seed being added. The system responded very quickly, and by July 15,
1975, what appeared to be a good, stable sludge had been achieved. A series
of mechanical difficulties was encountered at this time that hindered the
normal progression of operation toward a steady-state condition. However,
after almost 45 days of operation, during which the unit had been seeded, it
became apparent that continued poor effluent quality (high turbidity and
suspended solids) was the result of causes other than these mechanical
startup difficulties.
During this period, the system was operated over various hydraulic and
organic loading rates and investigations were made as to possible toxic
compounds in the primary effluent. However, toxicity was soon dismissed as a
possible cause of poor effluent quality, not only by an examination of
primary effluent trace constituent concentrations, but also by the fact that
the DTST system was being operated concurrently without showing any signs of
toxic effects.
-------
Through further investigation, other possible causes (such as low pH and floe
shear through excessive turbine blade tip speeds) were eliminated. The major
factor was finally traced to an energy intensity problem related to oversized
gas recirculation compressors and resulting floe shear due to the flooding of
the spargers by excessive pumping rates. An expedient solution was achieved
in early September 1975 by drastically reducing the flow of recirculated gas,
the result of which was significant improvement in effluent quality in
general and a decrease in turbidity in particular. The improvement was still
not to the level that had been achieved in 1973 during the operation of Union
Carbide's 0.6-1/sec (10-gpm) mobile pilot plant, but the effluent being
produced was within the State and Federal discharge requirements.
As outlined earlier, the pure oxygen pilot plant was originally designed
with provisions made for conversion from submerged turbines to surface
aerators at a later date, if so desired. However, with the accelerated State
construction grants program and the ensuing decision to design a full-scale
oxygen surface aeration system at the JWPCP, immediate steps were taken to
convert the pilot plant to a surface aeration system.
On September 25, 1975, the pilot pl-ant was taken out of service following a
short period of good operation under diurnal flow conditions. On October 3,
1975, the installation of the surface aeration equipment was completed and
the system was restarted. The influent flow was gradually increased to 1500-
tn^/day (0.4-mgd), and beginning on October 23, 1975, the first period of good
steady-state operation was obtained and was subsequently sustained for a
3-wk period. Following this period, it was intended that the influent
feed flow be changed to simulate the JWPCP diurnal flow pattern but diffi-
culties relating to the operation of the system using surface aerators
prevented this progression.
Soon after the system was restarted with the surface aerators installed, a
great deal of gas was observed escaping above the clarifier inlet diffusers.
In addition, the oxygen utilization data gathered during the surface aerator
operation was not at all in agreement with similar data gathered both during
the earlier operation using submerged turbines and during the 1973 operation
of the 0.6-1/sec (10-gpm) mobile pilot plant. It was assumed, therefore,
that gas from trte fourth stage of the reactor was somehow being trapped
within the mixed liquor and was subsequently being purged as the liquid
entered the final clarifier. It was theorized that the only way in which
such large volumes of gas could be conveyed out of the reactor and into the
mixed liquor piping would be the result of the aerator umbrella creating
excessive turbulence in the trough downstream of the overflow weir in the
fourth stage of the reactor as illustrated in Figure 3. With such unmeasured
quantities of gas escaping, it was impossible to accurately measure the
critical parameter of oxygen utilization.
In mid-December 1975, a baffle was installed in front of the overflow weir in
the fourth stage of the pilot reactor by representatives of Union Carbide.
The purpose of the baffle was to prevent the aerator umbrella from extending
into the trough downstream of the weir. This baffle, however, was not
sufficient as the gas leakage was reduced but not eliminated entirely. It
became clear that in order to completely correct the problem, the pilot plant
10.
-------
BEGIN
FIRST
LINE OF
TEXT
HERE d
DROPPED
HEAD,
BEGIN
SECTIONS
HERE d
WP1WG GUIDE S
t
1
E
ID
\
<* e
N
1
,,
f
c^=
HI
IF
:E
T
X
TT
II
*
dl
CENTER" "" " "
OF PAGE
±
-^~~}
v
^=^ \^-*~^-^~
'
-
-'
X
t=
»*
I
0i
=j
w~
TOP OF
/IMAGE
r . , , *<--« r->r-*
^ )
Jg^
T
!
i
MIXED ^ L
LIQUOR
NOTE: | m = 3.28 ft
Figure 3. UNOX reactor with surface aerators
would have to be taken out of service and a much larger baffle installed.
Since a short timetable was available for completion of the first phase of
the full-scale oxygen secondary treatment design, it was necessary that the
research studies of design criteria and the actual design of the secondary
system be conducted simultaneously. Because of this, it was decided that
operation of the pilot plant be continued despite the difficulty in assessing
oxygen utilization.
The next 2-mo were spent developing methods of improving sludge settleability
so that critical design parameters related to the secondary clarifiers could
be evaluated. By mid-March 1976, goodi steady operation had been established
and a 5-mo studj[ of clarifier performance was begun. By mid-April, however,
it became apparent that even though steady-state operation was being main-
tained, the effluent turbidity was stijjl not equal to that which has been
obtained earlier during the mobile pilot plant studies. Microscopic studies
of the secondary effluent led to the conclusion that the floe was being
sheared by the aerators to a certain extent, which was the cause of the
BEGIN cloudiness in trie effluent. On April 29, 1976, the mixer speed in the fourth
LAST LINE si-age of the reactor was reduced from 68 rpm to 45 rpm, which represents a _
OF TEXT wredyction in power of about 33 percent.!
_ j _ ,
^3/8" « &:=: &&:₯:.:#:
BOTTOM OF
IMAGE ARE/
OUTSIDE
DIMENSION
FOR TABLES
AND ILLUS-
TRATIONS
EPA-287 {Cm.)
PAGE NUMBER
-------
The effect of the power reduction in the fourth stage of the reactor was two-
fold. First, the effluent turbidity was improved as expected following the
change. Second, the gas leakage into the clarifier was further reduced but
not eliminated. Following the extended steady-state operating period and
clarifier evaluation, the pilot plant was taken out of service and a larger,
more permanent baffle was installed in place of the one installed earlier.
On September 13, 1976, the pilot plant was re-seeded and since that time the
system has performed very well. There is no longer any gas leakage into the
clarifiers, and useful oxygen utilization data have become available.
PILOT PLANT OPERATIONAL PHASES
Air Sparged Turbine Pilot Plant
As previously mentioned in the startup subsection, initial startup opera-
tional problems were encountered from the high energy input to the aeration
basin, which were manifested in shearing of the floe. After these startup
problems were resolved in mid-February through slowing down of the aerator's
speed, the pilot plant started its first steady-state phase in February 1975.
The time period of February 1975 through March 1976 has been divided into
nine steady-state operational phases. The basic criteria used in defining
steady-state operational phase were the mean cell residence time (MCRT or Oc)
and aeration period (V/Q). These two major operational parameters or in-
dependent variables were held constant for a given mode of operation. The
resulting operational data for the nine phases are summarized in Table 2.
The pilot plant operational phases can be further divided into two areas.
Phases I through VI were conducted to determine the operational limitations
of the DTST system and to verify the organic and trace constituent removals
that the diffused air activated sludge pilot plant achieved during a previous
study. Although Phases VII through IX do not show much variation between the
basic operational parameters of MCRT and aeration period, extensive testing
of the final clarifiers was conducted during these phases. During Phases VII
through IX, a secondary operational parameter, recycle rate, was varied to
determine its,effect on the solids inventory, clarifier hydraulics, and
loading rates. Also, the DTST operation for Phases VIII and IX was conducted
to provide parallel operation data for comparison with the oxygen pilot
plant. Although Phases VIII and IX do not correspond to a specific phase
of operation for the oxygen system, they do represent parallel operational
periods and, for the most part, all of the pilot plant data can be used to
compare the two types of systems based on similar operational conditions.
Phase I represents the first steady-state operational period of the DTST
pilot plant. During this phase, the pilot plant was operated at a 5.6-hr
aeration period and a 6.8-day MCRT was maintained. The 7-day MCRT was
maintained to keep a high level of solids within the system. These solids
were maintained to ease the transition to the shorter aeration periods and
higher loadings for which the system was designed. Under these operational
conditions, partial nitrification was achieved. The partial nitrification
and the long detention time in the final clarifier resulted in denitrification
and, hence, rising sludge in the final clarifier. To alleviate the rising
12
-------
f)
a
m
z.
c.
CO
m
33
o
m
-1
i
1/1
I
L
I tW
j> m
i-^ ^
;
m
r~ ~ ~~
i
i
TABLE 2. SUMMARY OF OPERATIONAL PARAMETERS -- AIR-SPARGED TURBINE SYSTEI^
PARAMETER
DATES
Start
End
Duration, days
Flow Pattern
REACTOR
Influent Flow, m3/day (mgd)
Recycle, %
Hydraulic Detention Time
V/Q, hr
V/(Q+R), hr
MLSS, mg/1
Volatility, %
Mean Cell Residence Time
Reactor Solids, days
Total System Solids, days
Organic Loading Rate
BODR/MLVSS, kg/kg/day
BODR/TPVSS, kg/kg/day
CODR/MLVSS, kg/kg/day
CODR/TPVSS, kg/kg/day
BODA, kg/rrvVday (Ib/ft3/day)
Sludge Production
VSS/BODR, kg/kg
VSS/CODR, kg/kg
CLARIFIER
Overflow Rate, m3/m2/day (gpd/ft2)
Detention Time
V/Q, hr
V/(Q+R), hr
Solids Loading Rate, kg/m3/day (lb/ftj/day)
Return Sludge Concentration, %
SVI, ml/g
m
m
TL
^
co oo 3; O
;H Q -0 m
O " m m
2 a «
rn
r
i
i
i
PHASE
I
2/9/75
3/1/75
21
Steady
1200
(0 32)
90
5 6
2 9
3100
72
5 1
6 8
0 34
0 26
0 80
0 60
0 75
(12 0)
0 51
0 22
18 3
(450)
4 0
2 1
107
(1714)
0 7
252
II
3/9/75
3/29/75
21
Steady
1700
(0 45)
65
4 0
2 4
3400
73
3 7
5 4
0 38
0 27
1 07
0 74
1 00
(16 0)
0 64
0 27
21 3
(523)
2 8
1.7
117
(1874)
0 9
183
III
4/6/75
5/3/75
29
Steady
1700
(0 45)
45
4 0
2 8
2600
74
2 2
3 3
0 49
0 33
1 30
0 87
1 03
(16 5)
0 79
0 34
16 9
(415)
4 3
3 0
63
(1009)
0 9
163
IV
5/11/75
6/21/75
42
Steady
1900
(0 50)
40
3 5
2.5
4000
73
3 7
5 5
0 30
0 23
0 90
0 60
1 15
(18 4)
0 73
0 30
18 3
(450)
4 1
2 9
103
(1650)
0 9
165
V
7/20/75
8/30/75
42
Steady
1700
(0 45)
44
4 0
2 8
2300
73
1 8
2 8
0 70
0 47
1 61
1 06
1 34
(21 5)
0 70
0 35
16 1
(395)
4 5
3 1
54
(865)
0 9
227
VI
9/28/75
10/25/75
28
Steady
1500
(0 40)
29
4 5
3 5
3300
70
3 0
4.3
0 49
0 33
1 16
0 82
1 24
(19 9)
0 56
0 26
14 7
(361)
5 0
3 9
63
(1009)
1 2
200
VII
10/26/75
11/20/75
26
Steady
1500
(0 40)
38
4 5
3 3
3300
71
3 2
4 3
0 44
0 30
1 00
0 75
1 12
(17 9)
0 63
0 31
14 7
(361)
5 0
3 6
68
(1089)
1 1
160
VIII
11/27/75
12/25/75
29
Steady
1500
(0
40)
50
4
3
5
0
3600
70
3
4
0
0
4
5
44
30
1.00
0
1
(19
0
0
14
75
20
2)
63
30
7
(361)
5
n
3 3
83
(1329)
1 1
173
y
IX
3/4/76
3/25/76
22
Steady
1300
(0 34)
47
5 3
3 6
2900
70
3 6
5 9
0 45
0 29
1 10
0 68
0 97
(15 5)
0 60
0 27
19 4
(476)
3 6
2 5
83
(1329)
0 9
146
i
=
Tl 00
33 S
C/5 n
m
to
m
m
3 > 3 D O ^
O
m
tr
-------
sludge problem, the sludge was removed as rapidly as possible from the final
clarifier as indicated by the 90-percent recycle rate.
As the system showed signs of stabilizing, the aeration time was decreased to
4.0-hr and the MCRT was reduced to 5.4 days. At these conditions, the DTST
system was able to maintain good organic removals and effluent clarity, but
rising sludge was still a problem, which again resulted in an inordinate
amount of solids being carried over the weir into the effluent.
During Phase III operation, the aeration period was maintained at 4.0 hr, but
the MCRT was lowered from 5.4 to 4.0 days. Under these conditions the or-
ganic removals remained good. The problem of solids carry over in the final
effluent was alleviated by switching to the longer final clarifier as indi-
cated by the lower over flow rate of 16.8- m3/m2/day (412 gpd/ft2)
The aeration period was lowered to 3.5- hr in Phase IV, and to maintain rea-
sonable loading rates on the system at this short aeration period, the plant
solids were increased by increasing the MCRT to 5.6 days. Good treatability
was observed under these operational conditions.
Phase V operation constituted the highest sustained loading period of the
study for the DTST pilot plant. Although the aeration time was increased
slightly to 4.0 hr, the MCRT was reduced to 2.8' days. Even though the DTST
was able to treat the wastewater under these conditions, the pilot plant was
extremely sensitive to operate. This was reflected by a 2-wk period within
this phase when the effluent suspended solids averaged 30 mg/1. The pilot
plant, however, soon reached an overloaded condition after this short period
of good operation, and the effluent quality started to decline.
The aeration period was increased to 4.5-hr, and the MCRT was increased to a
more manageable 4.3-days in Phase VI. The DTST system responded to these
operational changes, and stable operation of the pilot plant resumed.
Phases VII and VIII were a continuation of Phase VI with the aeration period
and MCRT remaining the same for all three phases. However, the 30-percent
recycle rate in Phase VI was increased to 40 percent in Phase VII and 50-
percent in Phase VIII. During these phases, the effect of the sedimentation
tank hydraulics, overflow rate, and solids loading rate on the thickening of
the return sludge was studied. Also, the effect of the recycle rate on the
mass flow back to the reactor was studied.
The aeration period was further increased to 5.3 hr in Phase IV while the
MCRT was increased to 5.9 days. This operational mode was run to see if the
DTST system could operate under conventional conditions and not have the
nitrification-denitrification problems that were associated with Phase I.
UNQX Pilot Plant
Simply stated, the major objectives of the high purity oxygen pilot plant
studies were twofold: first, to gather information that would be pertinent to
the full-scale treatment plant design effort that was being conducted con-
currently and, second, to develop operational techniques which could simplify
14
-------
the startup and operation of this full-scale system. The 0.6-1/sec (10-gpm)
mobile pilot plant had provided treatability information and data to allow
some equipment sizing, but certian key design questions were left unanswered
at the completion of the mobile pilot plant testing. First, the clarifier
used during the preliminary studies was an unconventional circular model that
provided low overflow rates and a great deal of sludge storage capacity.
Since the full-scale system would be operated using rectangular clarifiers
that were smaller in relation to the biological reactor than had been the
case during the preliminary studies, it was imperative that the performance
of rectangular clarifiers be evaluated. This evaluation is critical since
the operation of a high purity oxygen system is generally limited by the
ability of the secondary clarifier to store and convey sludge solids.
The second key question to be addressed by the 1900-m3/day (0.5-mgd) plant
operation concerned the system oxygen requirements, particularly the daily
fluctuation in oxygen demand, which is a result of the diurnal variation in
flow and organic loading at the JWPCP. Information in this regard would have
a direct bearing on the selection of equipment for the cryogenic oxygen
generating system that is being provided to supply oxygen to the biological
treatment system.
The priorities of the 1900-mVday (0.5-mgd) pilot project following the July
1975 startup were to stabilize the system at design conditions as quickly as
possible and to collect data relative to the required design information.
Beyond this, information regarding system limitations and overall operation
would be documented. This phase of operation would require the more rigorous
approach to pilot operation of biological treatment systems wherein the
system performance would be evaluated over an entire range of organic loading
rates and aeration periods.
As a result of the startup difficulties outlined earlier in this report,
acceptable operation of the pilot plant could not be achieved before late
September 1975. Only 4 days of good operation (Phase I) were recorded before
the pilot plant was taken out of service on September 25, 1975, for, the
installation of surface aerators. From this point until mid-October 1976,
the operation of the pilot plant has been divided into eight periods, which
are representative of good steady operating periods and/or periods during
which specific objectives were being met. Operational parameters are sum-
marized in Table 3.
Phase I, though it includes only 4 days of testing, is significant in that
it represents the first successful pilot operation in which the system was
operated under a simulated diurnal plant flow condition.
Phase II represents the first period of good operation following the instal-
lation of surface aerators in the biological reactor. During this period,
attempts were made to stabilize the operation at the 7-day design MCRT
in order to begin the evaluation of the rectangular clarifier as well as to
further establish the organic removal and oxygen demand relationships. It
was during this period, however, that the gas "boiling" problem outlined
earlier was first discovered. By late October 1975, the difficulty became
15
-------
O !T ro
-n > rn
I oi oo x °
m m m m 30
30 O CD >> O
r>
3
O
m
-2.
C.
m
CO
s
I I I n CD
CD CD 5 55 m
^ m <2 £
***. 1
1 :r
0 - m m -> rn
M S 20
n m n
| 4
~ , ~^~ ~ ^ -- - \
. ~ ' . 1
TABLE 3. SUMMARY OF OPERATIONAL PARAMETERS -- OXYGEN SYSTEM
-^ . , . 1
\
PARAMETER
DATES
Start
End
Duration, days
Flow Pattern
REACTOR
Influent Flow, m3/day (mgd)
Recycle, %
Hydraulic Detention Time
V/Q, hr
V/(Q+R), hr
MLSS, mg/1
Volatility, %
Mean Cell Residence Time
Reactor Solids, days
Total System Solids, days
Organic Loading Rate
BODR/MLVSS, kg/kg/day
BODR/TPVSS, kg/kg/day
CODR/MLVSS, kg/kg/day
CODR/TPVSS, kg/ kg/day
BODA, kg/mJ/day (Ib/ft3/day)
Oxygen Utilization
02/BODR, kg/kg
09/CODR, kg/kg
Sludge Production
VSS/BODR, kg/kg
VSS/CODB, kg/ kg
CLARIFIER
Overflow Rate, m3/m2/ day (gpd/ft2)
Detention Time
V/Q, hr
V/(Q+R), hr
Weir Loading Rate, m3/m/day
(ft3/ft/dav)
Solids Loading Rate, kq/m^/day
(Ib/ft3/day)
Return Sludge Concentration, %
SVI, ml/g
r
?i
'
PHASE
I
9/22/75
9/25/75
4
Diurnal
1900
(0 51)
40
2 5
1 8
3800
75
1 8
3 4
0 70
0 31
1 67
0 89
2 15
(34 4)
1 36
0 71
0 97
0 48
18 7
(159)
3 7
2 8
79 1
(852)
98
(1568)
1 05
78
II
10/27/75
11/10/75
15
Steady
1500
(0 40)
40
3 1
2 2
2800
73
2 5
5 9
0 74
0 31
1 52
0 64
1 73
(27 7)
0 60
0 29
23 2
(570)
3 0
2 2
62 6
(674)
90
(1440)
1 06
153
III
12/1/75
12/30/75
30
Steady
1400
(0 37)
44
3 4
2 3
4200
74
3 4
6 8
0 52
0 26
1 11
0 56
1 62
(25 9)
0 64
0 28
21 2
(521)
3 3
2 3
52 2
(562)
127
(2032)
1 40
99
IV
2/1/76
2/17/76
17
Steady
1700
(0 45)
41
2 8
1 9
4600
72
1 9
5 6
0 60
0 20
1 31
0 45
2 03
(32 5)
0 63
0 29
25 4
(625)
2 8
1 9
68 9
(741)
168
(2688)
1 54
65
V
2/18/76
2/29/76
12
Steady
1900
(0 51)
42
2 5
1 6
3300
75
1 7
3 4
0 83
0 42
1 61
0 81
2 05
(32 8)
--
0 78
0 40
28 4
(698)
2 4
1 7
77 0
(829)
134
(2114)
1 18
83
VI
3/31/76
5/20/76
51
Steady
1900
(0 51)
40
2 5
1 8
3900
74
1 9
4 4
0 69
0 29
1 54
0 64
2 00
(32 0)
--
0 80
0 36
27 9
(686)
2 5
1 8
101 2
(1089)
152
(2432)
1 36
77
VII
6/21/76
9/14/76
85
Steady
1800
(0 48)
38
2 6
1 9
4100
77
2 7
4 8
0 57
0 33
1 15
0 66
1 76
(28 2)
0 69
0 33
27 5
(676)
2 5
1 8
99 4
(1070)
141
(2256)
1 22
83
VIII
9/30/76
10/13/76
14
Steady
1900
(0 51)
40
2 5
1 8
4420
75
2 1
3 8
0 48
0 27
0 95
0 54
1 63
(26.1)
1 52
0 81
0 84
0 42
18 1
(445)
3 8
2 7
101 5
(1092)
113
(1808)
1 34
113
IX
10/28/76
11/7/76
11
Diurnal
1900
(0 51)
39
2 5
1 8
3700
70
2 0
4 2
0 67
0 32
1 46
0 69
1 94
(31 0)
1 24
0 69
0 98
0 38
28 4
(698)
2 5
1 8
102 3
(1101)
147
(2352)
0 88
124
X
11/9/75
11/24/76
16
Diurnal
1600
(0 43)
47
3 1
2 1
3990
70
3 0
6 6
0 55
0 24
1 07
0 47
1 54
(24 6)
1 48
0 71
0 74
0 38
23 3
(573)
2 9
2 0
84 2
(906)
141
(2256)
0 99
114
XI
12/10/76
12/23/76
14
Diurnal
1600
(0 43)
39
3.0
2 2
3840
77
2 8
5.4
0 51
0 27
1 05
0 55
1 44
(23 0)
1 49
0 70
0 66
0.37
23 2
(570)
2 9
2 1
85 8
(923)
126
(2016)
0 94
101
1 y
o
-n
O f
~n n
T3 ,£
ri n
Cj) -
K
m
c/>
3,
m
m
=1
3
0 O ^
-------
clearly defined and a decision was made to forego the oxygen utilization
investigations until a later date so that the evaluation of the final clari-
fier could proceed.
The turbulence created at the clarifier inlet by the escaping gas resulted in
an unusual amount of solids being lost through the clarifier skimming system.
Because of the difficulty in both measuring and controlling this solids loss,
the actual phase average cell MCRT was less than the desired 7-day level.
Attempts at controlling this solids loss to sustain good operation at the
desired MCRT ultimately resulted in the loss of steady-state conditions and
an end to this phase of the pilot operation.
Because of the construction at the JWPCP, it became necessary to relocate the
pump suction lines of the pilot plant influent pump station. As a result of
this change, it was not possible to operate the pilot plant at the design
flow rate (1900 m^/day or 0.5-mgd) during most of December 1975. Though,
by strict definition, a steady-state condition was never achieved during this
period, Phase III of the pilot plant study represents a period of good stable
operation under adverse conditions. During this period, attempts were made
to improve sludge settleability. Moreover, the first attempt was made toward
correcting the gas leaking problem outlined earlier through the addition of a
baffle by representatives of Union Carbide^
During January and the early part of February 1976, several attempts were
made to stabilize the operation at both the design flow (1900
-------
finally terminated on May 20, 1976, when repeated power outages, created by
construction at the JWPCP, resulted in a pilot plant upset.
Continuing construction interruptions prevented a rapid return to steady oper-
ation. However, by June 21, 1976, the pilot plant was once again at steady-
state conditions and a second sustained period of good operation (Phase VII)
under design loading and conditions was begun. During this phase of opera-
tion, additional data were compiled relating both to organic and hydraulic
parameters. Specifically, a series of radioactive tracer studies were begun
during Phase VII which were designed to determine the movement of sludge
solids through the final clarifier.
At the conclusion of the first series of clarifier tracer studies, the pilot
plant was taken out of service and corrections were made to the baffle in the
fourth stage of the reactor. This revision was outlined earlier in this re-
port. After completing the baffle, operation was resumed in the longer of
the two pilot clarifiers in order to accommodate further testing of sludge
solids movement by the radioactive tracer method. Phase VIII summarizes the
nearly 4 wk% of operation in the long pilot clarifier, which represents the
only change from operation during Phase VII.
Following the tracer studies, the flow was diverted back to the shorter
clarifier and the diurnal flow pattern was again instituted. Some difficul-
ties were encountered with the operation of the flow controller, but the
pilot plant was stabilized in "the diurnal flow pattern by October 28, 1976.
Phase IX extended from October 28 to November 7, 1976, and was characterized
by a 1900-m3/day (0.5-mgd) average diurnally varied feed rate and a constant
return sludge flow rate.
The clarifier operation during Phase IX was generally unsatisfactory. During
the peak flow periods, the sludge blanket would rise to within 0.6 m (2-ft) of
the surface, which resulted in an increase in effluent suspended solids. The
peak flow in the diurnal cycle resulted in a clarifier overflow rate in
excess of the design peak loading of 37-m3/ m2/day (900 gpd/ft2), so on
November 8, a 1900-m3/day (0.5-mgd) peak flow diurnal flow pattern was intro-
duced. Phase X extended from November 9 to November 24, 1976, and includes
the data from the reduced diurnal flow pattern. During this period, the
operation of the pilot plant improved, but the clarifier sludge blanket
remained high during peak flow and the effluent suspended solids remained
above the Federally-mandated 30 mg/1.
Further investigation indicated that the variation in the recycle ratio re-
sulting from the constant return sludge flow and the diurnal influent flow
was responsible for the poor clarifier performance. During low flow, the
return ratio was high and the mixed liquor became more concentrated. When
peak flow was reached, this concentrated mixed liquor was pushed into the
clarifier and the clarifier loading was extremely high. This high solids
loading was responsible for the high blanket and poor effluent.
To overcome this difficulty, it was necessary to operate the return sludge
in a diurnal flow pattern. During Phase XI, December 10 to December 23,
18
-------
1976, the same diurnal influent flow pattern employed in Phase X was used,
but the return sludge flow was varied to maintain a constant recycle ratio.
The return sludge had to be manually adjusted; therefore, because of manpower
limitations, the pilot plant was operated at a constant flow of 1500 m^/day
(0.4-mgd) during the weekends. The frequent changes in operation modes
caused minor upsets, but the pilot plant did produce satisfactory effluent
quality.
19
-------
SECTION 5
DISCUSSION OF RESULTS
EFFLUENT QUALITY
Activated sludge systems consist of two component unitsthe aerator/reactor
and the final clarifier. The quality of the final effluent is related to the
interaction of the component parts, and poor effluent may be caused by an
inadequacy of only one part. The effluent quality of the air and oxygen
systems is described in Tables 4 and 5.
Soluble COD and BOD
A primary indicator of the adequacy of the reactor in terms of oxygen trans-
fer and treating the wastewater is the removal of soluble organics. In all
phases, for both pilot plants, the soluble BODc removals equalled or exceeded
95 percent. Phase average effluent soluble BOD5 concentrations were 6 mg/1
or less. These BOD measurements are low enough that differences between the
two systems are not considered significant.
A small but definite difference between the systems is, however, apparent in
the soluble COD data. The oxygen system produced effluent with consistently
higher soluble COD. The data plotted in Figure 4 indicate that the principle
cause of this is the lower aeration time maintained in the oxygen reactor.
The oxygen data fit an eyed-in linear extrapolation to the air data reason-
ably well. The actual function should turn upward at the lower aeration
times, reaching the influent concentration of 250+ mg/1 at zero aeration
time. Such a curve might be drawn to represent a better fit to the data in
Figure 4.
When the soluble COD data are grouped according to aeration time and plotted
against MCRT (Figure 5), it is apparent that, except at low values of less
than 3days, the MCRT has very little effect on soluble COD removal.
Suspended Solids
Secondary effluent solids concentrations depend on the effectiveness of the
final clarifier. High effluent suspended solids, however, may be an indica-
tion of poor clarifier design, poor aerator design, or poor plant operation.
During startup, both 190Q-m3/day (0.5-mgd) pilots plant experienced periods
of high effluent suspended solids and turbidity, which were alleviated by
reducing the power input to the final stages of the reactors.
20
-------
in c/>
So
m I
CB
o
3
a
m
%
n m
rT
00
h3-
"r\3'^_
H-1.
"1 ft
1
1
TABLE 4. SUMMARY OF EFFLUENT QUALITY, AIR SYSTEM
-
,
PARAMETERS
Aeration Period (V/Q), hr
MCRT (Total System), days
Flow Pattern
Suspended Sol ids
Influent, mg/1
Effluent, mg/1
Removal , %
Total BOD
Influent, mg/1 0
Effluent, mg/1 0
Removal , %
Soluble BOD .
Influent, mg/1 0
Effluent, mg/1 0
Removal , %
Total COD:
Influent, mg/1 0
Effluent, mg/1 0
Removal , %
Soluble COD
Influent, mg/1 0
Effluent, mg/1 0
Removal , %
Grease (By Hexane Extraction)
Influent, mg/1
Effluent, mg/1
Removal , %
Ammonia
Influent, mg/1 N
Effluent, mg/1 N
Removal , %
n
in H
VI | v~
PHASE
I
5 6
6 8
Steady
167
89
46.7
178
15
91 6
118
2
98 3
458
118
74 2
262
49
81.3
51 2
8.2
84 0
35.1
14.2
59.5
II
4.0
5 4
Steady
179
80
55 3
167
17
89 8
102
3
97 1
447
152
66 0
247
56
77 3
40 6
6 1
85 0
32 4
20.3
37.3
III
4 0
3.3
Steady
167
67
59.9
172
15
91 3
98
3
96 9
453
130
71.3
234
59
74 8
36 5
4 8
86.8
34.7
27.8
19 9
IV
3 5
5.6
Steady
170
22
87 1
171
8
95 3
101
4
96 0
460
77
83.3
241
56
76 8
37 8
1.0
97.4
34 7
31 6
8.9
V
4 0
2.8
Steady
204
110
46 1
224
16
92 9
126
5
96 0
513
191
62 8
265
72
72 8
-
_
_
31 4
27.8
11.5
VI
4.5
4.3
Steady
204
36
82.4
234
12
94 9
132
4
97 0
556
91
83 6
257
57
77 8
-
-
_
36.3
32.1
11 6
VII
4 5
4.3
Steady
165
37
77.6
212
12
94 3
129
2
98.4
483
92
81 0
270
55
79.6
-
_
_
33.3
27 5
17 4
VIII
4
4
5
5
Steady
216
54
75
226
13
94
109
2
98.
515
111
78
256
48
81
_
_
_
34
32
6
I
0
2
2
4
3
1
1
1
IX
5 3
5 9
Steady
177
29
83 6
211
18
91 5
119
2
98 3
517
84
83 8
282
54
80 9
_
_
_
37 7
30.7
18 6
>
0
Tl
m
m
m
=3
> ^
-------
°£s
W "^ Z
a
m
2
C
03
m
PO
33
m
O
u m n <" w
^ 1 A v i v-
1 0 !
1
TABLE 5. SUMMARY OF..E^L-UENT; QUALITY | OXYGEN SYSTEM \
^ 1
3
PARAMETERS
Aeration Period (V/Q) , hr
MCRT (Total System) , days
Flow Pattern
Suspended Sol ids
Influent, mg/1
Effluent, mg/1
Removal , 7,
Total BOD,,
Influent, nig/1 0
Effluent, mg/1 0
Removal , 7
Soluble BODS
Influent, mg/1 0
Effluent, mg/1 0
Removal , %
Total COD
Influent, mg/1 0
Effluent, mg/1 0
Removal , %
Soluble COD
Influent, mg/1 0
Effluent, mg/1 0
Removal , %
Grease (By Hexane Extraction)
Influent, mg/1
Effluent, mg/1
Removal , 7,
Ammonia
Influent, mg/1 N
Effluent, mg/1 N
Removal , %
PHASE
I
2 5
3 4
Diurnal
189
17
91 0
219
11
95 0
131
4
96 9
467
81
82 7
249
62
75 1
42 6
1 0
97 7
31 8
26 3
17 3
11
3 1
5 9
Steady
165
18
89 1
221
7
96 8
132
3
97 7
523
87
83 4
213
68
68 1
38 4
0 9
97 7
34 2
31 4
8 2
111
3 4
6 8
Steady
242
28
88 4
231
12
94 8
105
3
97 1
554
94
83 0
258
58
77 5
47 1
3 0
93 6
33 2
30 5
8 1
IV
2 8
5 6
Steady
201
54
73 1
238
20
91 6
122
5
95 9
561
122
78 3
279
59
78 9
55 8
4 4
92 1
31 6
31 3
0 9
V
2 5
3 4
Steady
172
28
83 7
219
21
90 4
121
6
95 0
486
100
79 4
283
67
76 3
41 6
2 5
94 0
36 4
31 0
14 8
VI
2 5
4 4
Steady
202
21
89 6
212
12
94 3
115
3
97 4
536
88
83 6
279
66
76 3
62 4
1 7
97 3
36 9
31 5
14 6
VII
2 6
4 8
Steady
142
17
88 0
187
8
95 7
93
2
97 8
438
82
81 3
255
64
74 9
63 8
1 6
97 5
31 6
29 5
6 6
VIII
2 5
3 8
Steady
140
14
90 0
176
5
97 2
90
1
98 9
400
71
82 2
260
58
77 7
45 8
1 3
97 2
33 8
28 9
14 5
IX
2 5
4 2
Diurnal
150
48
68 0
204
13
93 6
134
1
99 3
415
116
72 0
272
64
76 5
46 0
6 2
86 5
27 8
28 0
-0 7
X
3 1
6 6
Diurnal
130
34
73 8
173
12
93 1
100
2
98 0
431
97
77 5
280
63
77 5
39 2
2 8
92 9
34 3
28 7
16 3
XI
3 0
5 4
Diurnal
120
20
83 3
185
6
96 8
124
2
98 4
446
83
81 4
305
65
78 7
40 6
2 3
94 3
37 2
33 8
9 1
1
I y I
20g§ *
s- <-: -B. y 3
es
m
m
m
=1
n
m
-p
>
O
m
m
>
-------
BEGIN
FIRST
LINE OF
TEXT
HERE D
DROPPED
HEAD,
BEGIN
SECTIONS
HERE C
.
,
\
E*
Q"
o
U
Ld
CD
ID
1
^J
O
CO
|
LJ
U_
U_
,.
(\fter
TfflKG GU5DE SHEET
- -* ^ --, CENTER ---_.' ^ TOPOF
<-'.:"',-.-- .OF PAGE -' " -*- ,-- <-\- -- - -_--.*-* __ -'- >= L. - ^ , ' 2^'vocA
100
80
0
40
20
Q
1 1 1 i 1
A^^^^^^-S*^. *
Ti w ^
& 0
-
LEGEND
A OXYGEN
AIR
* BASED ON V/Q
l i i i I
-
|
1
i
0 <, 1 2 3 4 5 6
' ' / AERATION TIME, hr*
i
Figure 4. Soluble COD versus aeration time.
startup, the oxygen system met the Federal discharge standard of not
more than 30 mg/jl for a 30-consecutive-day. average in all phases except IV
and IX
traced
solids
During
. In both of these cases, the high effluent suspended solids can be
to high clarifier solids loadingi. In Phase IV, the highest clarifier
loading of the study, 168 kg/m2/|day (34- lb/ft?7day) , was experienced.
'
Phase IX, the average solids loading was lower, but during the peak of
jthe diurnal flow pattern, the solids leading exceeded those in Phase IV. A
major cause of the periodic high loadinigs in Phase IX rested in the return
[sludge
operation'. During Phase IX, the feed flow was varied in a diurnal
Flow pattern, but the return sludge flow was held constant. During low flows,
the relatively high return sludge ratio] would result in a concentrated mixed
liquor
trated
in the reactor. When the influent flow was increased, the concen-
mixed liquor was forced into the clarifier at a hiqh flow rate and
;orresponding high solids loading rate. Two steps were taken to correct this
BEGIN condition. The return sludge flow was varied in proportion to the influent
LAST LINE £l2_w to mainta"in| a more nearly constanti mixed liquor concentration, and the
OF TEXT qp-
3
_i
BOTTOM OF
iMAic ARE;
OUTSIDE
DIMENSION
FOR TABLES
3/g" A : :-:.:-.. .-::-.:. v yAND ILLUS-
\l ..:.::.::: y-n *$: .:;.: :- , TRATSOWS
EPA-2S7 (Cm.)
(4-7S)
PAGE NUMBER
-------
BEGIN
FIRST
LINE OF
TEXT
HERE
DROPPED
HEAD,
BEGIN
SECTIONS
HERE
GUIDE SMEET
)F
1
i
>|
JC
X W
E"
Q"
0
o
LL)
m
^
o
c/)
^
LJ
LL.
LL.
UJ
]} u «J u d\J ^*ji '^ wr u twiw **u u I^UB u -r^"\n /"M~
OF PAGE XSIMAGE
100
90
80
70
60
50
40
30
20
!0
n
i i i ~l i i
-
_
N .
\ * * »
*" - A J.J.
*
A "
LEGEND
OXYGEN
2.5-3.lhr
" 3.4 hr
AIR
~ A 3,5-4 5 hr
53 -5.6 hr
_
* BASED ON TOTAL PLANT VOLATILE SUSPENDED SOLIDS (TPVSS)
J l 1 I I I
!
i
f
f
.
i
/-I
*
3 4
MCRT, days*
Figure 5. Effluent soluble COD versus MCRT.
I
i 1
low to the unit was decreased from a 1,900-m^/day (0.5-mgd) average flow to a
1900-m3/day (O.ff-mgd) peak flow. 1
The deep tank submerged turbine system [met the 30-mg/l effluent suspended
solids standard lonly in Phases IV and IX. Phases VI and VII were charac-
terized by generally low effluent suspended solids with a few unusually high
days. Without those days, the 30-mg/l [standard would have been met in those
phases as well, j The poorer performance of the air system is due in part to
characteristics ,of air activated sludge and in part to the way the system was
operated. j I
Three basic causes of high effluent suspended solids were observed during the
DTST study. Durjing startup and Phases {ill and V, the sludge did not floc-
culate and settle well. These conditions were attributed to excessive shear
in the reactor d'uring startup and the low MCRT's of 3.3 and 2.8-days main-
BEGIN
LAST LINE
OF TEXT r
i. a j lieu uui iny riia^co ill aim », p capci. i; I vc i jr . i
' 1 | BOTTOM Or
1 1 ( IMAGE AREX
Those low MCRT'sjwere used to control the nitrification-denitrif ication that | OUTS1DE
had occurred during Phases I and II. during the early part of the study, the 1 DIMENSION
D-TST plant was operated in a manner conducive to partial nitrification. WhenJ Ff)n TAH, FS
A ip i ]
'J V _ t^^Kiiii^^iica
^AND SLLUS-
J TRATIONS
EPA-287 (Gin.)
PAGE NUMBER
-------
the sludge was stored in the clarifier, nitrate and nitrite nitrogen were
reduced to nitrogen gas. Bubbles formed which attached to sludge particles
and resuspended them. Nitrifying bacteria grew more slowly than other
activated sludge organisms, and the nitrification-denitrification conditions
were eliminated by reducing the aeration time and/or the MCRT. In Phases III
and V, however, the rising sludge was replaced by bulking sludge, and no
improvement in effluent quality was achieved.
During Phases VI, VII, and VIII, the system was operated at the same aeration
time and MCRT, but the recycle rate was varied from 30-percent to 40 percent
and 50-percent. At the 30- and 40-percent recycle rates (Phases VI and VII,
respectively) the pilot plant produced a generally good effluent, but at the
50-percent recycle rate (Phase VII), the clarifier was overloaded and the
pilot plant produced poor effluent.
Although the oxygen pilot plant produced low suspended solids effluent more
frequently than the air system, it is unfair to conclude from that infor-
mation alone that oxygen activated sludge produces a lower suspended solids
effluent. The oxygen system in these studies was operated much more con-
servatively than the air system. The oxygen system was operated within the
known capability of such a system with an emphasis on refining certain design
parameters, but the air system was operated to define the limitations of the
deep tank turbine aeration system.
Both plants did demonstrate an ability to produce a good quality effluent.
The air system, however, did prove to be more sensitive to operate. The main
causes of this sensitivity is the tendency of the system to achieve partial
nitrification, which resulted in rising sludge, and the measures that were
necessary to control that condition.
Effluent Clarity
Clarity of an effluent is an aesthetic quality which is difficult to quantify.
Since suspended solids greatly affect this quality, only periods with compar-
able effluent suspended solids concentrations can be used for comparisons.
Those phases which averaged between 20 and 30 mg/1 suspended solids were
selected, and the data are presented in Table 6.
The turbidity in these effluent samples exhibited a correlation with sus-
pended solids for each system, but the air system had slightly lower turbidi-
ties for given suspended solids concentrations. However, the Secchi disc
transparencies, which were measured in the secondary clarifiers, indicate
that the air system should have produced a much clearer effluent. Visibility
in the final clarifiers was 20 to 40--percent greater in the air system. This
confirms a general observation that whenever both systems were operating
well, or rising sludge was present in the air system, the liquid fraction in
the clarifier was much clearer in the air system than in the oxygen system.
Similarly, the supernatant in the laboratory settling tests was visually much
clearer for the air system than the oxygen system. No explanation for this
is available at this time.
25
-------
BEGIN
FIRST
LINE OF
TEXT
HERE E
DROPPED
HEAD,
BEGIN
SECTIONS
HERE
WPQW6 GUIDE SHEET
CENTER
OF PAGE
TOP OF
I "
'1
TABLE 6. "EFFLUENT CLARITY
i , !
_.. _, 6-V2" -'-
SYSTEM '
Air
}
Oxygen
PHASE
IV
IX
III
V
VI
SUSPENDED
SOLIDS,
mg/1
22
29
28
28
21
TURBIDITY,
NTU
12
16
17
21
14
SECCHI DISC
TRANSPARENCY,
m (ft)
0.68 (2.2)
0.63 (2.1)
0.49 (1.6)
0.44 (1.4)
0.55 (1.8)
_-
I
t
1
Total COD and9B00;'
I
Since the secondary effluent suspended
solids are primarily escaped biologi-
cal floe, a direct correlation should exist between the effluent volatile
suspended solids (VSS) and the effluent BODs and COD. Cell material
(C5H7N02) requires 1.42 times its massjin oxygen for complete oxidation.1
If the effluent iVSS are considered to be cell material, the nonfiltrable
(soluble) COD and the nonfiltrable ultimate BOD will be 1.42 times the VSS.
Figure 6 compares the nonfiltrable
the effluent VSS concentrations.
COD
and ultimate BOD concentrations to
A least squares pinear regression analysis was conducted on the oxygen COD
data. The resulting line failed to pass through the origin, but the dis-
crepancy was not! statistically significant (40-percent confidence). The
slope of the regression line was, therefore, adjusted to pass through the
origin. A similar analysis was conducted on the air COD data, and the same
line was established. For both systems:
I
I Total COD - Soluble COD = 1.49 VSS
The COD to VSS riatio of 1.49 is
the theoretical |1.42 value.
a reasonable experimental approximation of
1. Metcalf & Eddy, Inc., Mastewater Eng ineering, McGraw-Hill Book Company,'
New York, New York, 1972, p. 490.
E7A-287 (Cin.)
(4-76)
PAGE NUMBER
TRAT10NS
-------
TCP 0?
DROPPED
HEAD,
BEGIN
SECTIONS, ,
HERE t> (
u
I
_1L.
BEGIN
LAST LINE
OF TEXT E>_
I
120
0
- 100
o»
E
UJ
Q
UJ
o
90
80
70
60
y 50
CD
a: 40
.j
fe 30
o
20
10
0
i i I
LEGEND
COD
A OXYGEN
AIR
BOD5 .
OXYGEN
AIR
0 10 20 30 40 50 60 70 80
VSS, mg/i
90
Figure 6. Nonfiltrable COD and BODs versus VSS.
3/8"
c=4
BOTTOM OF
IMAGE AREA,
OUTSIDE
DIMENSION
FOR TABLES
AND ILLUS-
TRATIONS
EPA-287 (Cm.)
(4-76)
PAGE NUMBER
-------
BEGIN
FIRST
LINE OF
TEXT
HERE
DROPPED
HEAD,
BEGIN
SECTIONS
HERE
TCP! RUG GUIDE SHEE"
CENTER
OF PAGE
TOP OF
>, IMAGE
BEGIN
LAST LINE
OF TEXT
*- v
>
JS
F
fj
$_yisual inspection of Figure 6 indica
Tlinear correlation with VSS. The hi
for either system was 21 mg/1.
Hexane Extractab'les (Grease)
;T.h~e phase-average effluent hexane extr
;mgd) pilot plants and the two smaller
effluent suspended solids in Figure 7.
two parameters is evidenced in Figure
0 and a slope of! 0.086 is the linear n
large-scale systems. A linear regress
yields a hexane 'extractable to suspend)
hexane extractable concentration backgi
1
While a theoretical relationship betwei
been established to substantiate the e.
final clarification for grease removal
the grease removal efficiencies of the
elfcept-the- var ratton6cVus'ed~b;y h rgh-ef 1
I
Ammonia-Nitrogen
$
Four oxidation s,ta,tes of nitrogen are
vated sludge system. Nitrogen in wast<
(-3). Reduced nitrogen is found free
acids. In the presence of dissolved o;
nitrogen may beioxidized to nitrite ni
gen (+5) through a process called nitr-
with the appropriate bacteria present,
elemental nitrogen (N? gas) by denitri
!
Ammonia nitrogen may be removed by niti
No indications of nitrificaton in the <
nitrate and nitrjite nitrogen were near
the associated solids handling study 11
moval was due to cell synthesis. 3
Low ammonia nitrogen removals are char<
systems since nitrification generally <
process. There iare usually two reason:
2. Stahl, J. F.;, Hayashi, S. T. Austii
Operation of Small Scale Activated
Water Pollution Control Plant, Los
Whittier, California, April 1974.
3. Austin, S. R., Memorandum - Reduce<
Secondary Treatment System, Los Am
Whittier, California, January 1978!
ies that the BODg data do not represent |
ghest-phase average total 8005 recorded
ictable data from both 1900-m3/day (OT?
scale-pilot plants'1 are plotted against
| A direct relationship between these
[. The line drawn with an intercept at
egression of the data from the two
ion of all data shown in Figure 7
id solids ratio of 0.067 and a soluble
ound level of 0.9-mg/l.
in grease and suspended solids has not
cperimental data, the importance of
has been emphasized. No difference in
air and oxygen systems was found
"luent suspen"ded~so"Vi'ds. *>
'mportant in the operation of an acti-
>water is normally in the reduced state
is ammonia or as a component of ami no [
cygen and specific bacteria, ammonia
:rogen (+3) and then to nitrate nitro- '
fication. In a reducing environment,
these oxidized forms may be reduced to
:i cat ion.
ification or by conversion to cells.
»xygen system were observed. Effluent
zero, and a mass balance performed for
idicated that all reduced nitrogen re-
icteristic of most high purity oxygen
Joes not occur during the reaction
, given for this phenomenon: first,
i, S. R., Shamat, N., Summary Report -
Sludge Pilot Plants at the Joint
Angeles County Sanitation Districts,
i Nitrogen Mass Transfer in the JWPCP
jeles County Sanitation Districts,
I
AREA
BOTTOM OF
IMAGE ARE;
OUTSIDE
DiWiENSION
FOR TABLES
ILLUS-
TRATIONS
EPA-287 ICin.l
PAGE NUMBER
-------
FIRS"
LiME OF
*-vy
^ r*
HERE r-~
: SHEE
CENTER
OF PAGE
TOP OF
xSiMAGE
=1 AREA
10
o> 8
E
UJ 7
CO '
<
LU
o:
2 6
UJ
DO 5
4
UJ
1 2
UJ
II 1111
LEGEND
A LARGE SCALE OXYGEN SYSTEM
SMALL SCALE OXYGEN SYSTEM
LARGE SCALE AIR SYSTEM
* SMALL SCALE AIR SYSTEM
JL
I
I T
*
J_
I
20 30 40 50 60 70 80
EFFLUENT SUSPENDED SOLIDS, mg/i
90 100
Figure 7>. Hexane extractables iyersus effluent suspended solids.
r-
LAST LINE'
OF TEXT d;
3/8
EPA-287 (Cin.f
(4-7G)
PAGE NUMBER
1 OUTSIDE
-* DIMENSION
J FOR TABLES
VAND ILLUS-
, TRATSONS
-------
BEGIN
FIRST
LINE OF
TEXT
WP1KG GUIDE SHEET
CENTER
OF PAGE
HERE c^juj-e oxygen systems are high-rate systems, which usually means that the
[process is operated at a low MCRT, thus reducing the possibility that
DROPPED nitHfying organisms will establish themselves within the biomass; second,
HEAD post pure oxygen systems are sealed reactors to maximize oxygen utilization.
BEGIN rs a result, there is a reduction in tlie pH of the mixed liquor through the
SECTIONS '[dissolution of carbon dioxide which further inhibits the growth of nitrifying
HERE cjpcteria. | |
Ammonia nitrogen removals up to 60 percent were observed in the air system.
In fact, controlling nitrification was
of the air pilo^ plant. Nitrification
rising sludge and high effluent suspended solids.
In order to control nitrification, the
a major consideration in the operation
followed by denitrification caused
aeration time and MCRT were reduced.
The ammonia nitrogen removals after Phase II may be attributed to cell
synthesis.
Trace Metals, Cyanide, and Phenols
TOP OF
MAGE
AREA
ert-ai-n-trace consti Wt'eh'ts-were-morritored- during the-act-rvated-s-Tudtje
studies at the JWPCP. The data from the 1900-m3/day (0.5-mgd) pilot plants
confirmed the data from the small-scale systems, so a reduced sampling
schedule was employed on the larger systems. The data from all four systems
are presentedqln/flT.ables 7 and 8. The Discharge limitations imposed by the
California Regional Water Quality Control Board (RWQCB) on the JWPCP are also
included. !
Chromium, nickel, and zinc are the three trace constituents that are in vio-
lation of the RI^QCB standards and will {require source control in the Joint
Outfall System. SRemovals of these metajjs were similar in the four activated
sludge systems with 67 to 74-percent of the chromium, 23 to 50-percent of the
nickel, and 55 to 68 percent of the zinc being removed.
i i
The influent arsenic concentrations were near the detection limit, so the re-
moval data are of minimal value. Removals of the other metals ranged from
|l40 to 83 percent, with neither the air nor the oxygen systems having a clear
advantage. '
Cyanide and phenols are organic complexes that are subject to oxidation.
Cyanide removals ranged from 64 to 86 percent with the oxygen system obtain-
jling the higher Removals. Removal of phenols was 98 percent or higher, with
the air system producing effluents at or below the detection limit.
BEGIN
LAST LINE
OF TEXT
(SLUDGE PRODUCTION
One of the most(important claims made on behalf of pure oxygen is that the
net growth of solids in these systems will be less than a similar air system
when operated all the same MCRT. Since!a large portion of the cost of waste-
water treatment iis usually associated with solids processing and sludge
handling, this claim would represent ajsignificant savings in both capital
and operating costs. The claim is based on a comparison between the two
$ 3/8" M
/ I
EPA-287 (Cm.)
(4-76)
iiiill
PAGE NUMBER
BOTTOM OF
IMAGE ARE/
OUTSIDE
DIMENSION
FOR TABLES
\>AND ILLUS-
, TRATIONS
-------
ffl
1 "8
I 5>
O
3
ca
m
tr>
rn in iii
33 O (,)
: o
- x u ro
"- - m
U
- I r TI to
> .
a ;
|L-^
ir1'
- f . - , -
^ J_
TABLE 7. TRACE CONSTITUENT REMOVAL cBY MEANS OF AIR-ACTIVATED SLUDGE
" ^ ^ _~\
**
Constituent
Arsenic
Cadmium
Total Chromium
Copper
Lead
Mercury
Nickel
Si Iver
Zinc
Cyanide
Phenol s
RWQCB Standard
Average,
mg/1
01
02
005
20
10
001
10
02
.30
10
50
10% of
Time,
mg/1
02
03
--
30
20
002
.20
.04
50
.20
1.00
1900-m3/day (0 5-mgd) Pilot Plant
Influent,
mg/1
01
017
28
22
15
--
.26
010
1.36
0.14
2 88
Effluent,
mg/1
01
008
08
06
06
--
18
006
0 58
0 05
0 01
Removal ,
%
0
53
71
73
60
__
31
40
57
64
99+
1 6-1/sec (25-gpm) Pilot Plant
Influent,
mg/1
02
020
47
33
15
0007
30
012
1 43
38
1 41
Effluent,
mg/1
01
008
14
11
06
0003
23
005
46
08
01
Removal ,
%
50
60
70
67
60
57
23
58
68
79
99+
% Samples
Over
W% Standard
0
0
100
2
0
0
63
0
35
3
0
\
\
-
G)
O
m
m
m
=1
2
^ r j U § | S
o r T' fi! o ^ I
& r r; d m % 0
m >
> CD
-------
03
m
) S»
fc
CO
-c ft
SSK
m --:
a
1
2 P
U
o T -H c D w
o H x 2 2° P-)
hi m T "' 5
o o
I'
C
IT.
C
a,
GO
i
. ^ __ - - _ . ._ , ^. ^ ^ . _, . . _ . -j . . . , , _,
&>
i
TABLE 8. TRACE CONSTITUENT REMOVAL BY MEANS 0^ OXYGEN-ACTIVATED SLUDGE
Constituent
Arsenic
Cadmium
Total Chromium
Copper
Lead
Mercury
Nickel
Silver
Zinc
Cyanide
Phenols
RWQCB Standard
Average,
mg/1
01
02
005
20
10
001
.10
02
30
.10
50
10% of
Time,
mg/1
02
03
30
20
002
20
04
50
20
1 00
1900-m3/day (0 5-mgd) Pilot Plant
Influent,
mg/1
..
* 024
27
22
* 14
--
23
* 015
1 01
--
--
Effluent,
mg/1
* 007
07
06
* 03
--
15
* 004
40
--
--
Removal ,
%
*71
74
73
*79
--
35
*73
60
--
--
0 6-1/sec (10-gpm) UNOX Mobile Pilot Plant
Influent,
mg/1
02
024
46
35
15
0007
.30
.013
1 27
35
1 62
Effluent,
mg/1
01
004
.15
06
08
0002
23
.003
57
.05
03
Removal ,
%
50
83
67
83
47
72
23
77
55
86
98
% Sampl es
Over
10% Standard
0
0
100
0
0
0
80
0
55
0
0
*Results of only one analysis
&
m
S
m
m
" m
> -H
CD m
m
i > .' U O =; »
7''j^^5>°
i u , rg $ Q -!
L
3D £ O
m > -o
-------
BEGIN
FIRST
LINE OF
TEXT
GUIDE SHEET
CENTER
OF PAGE
HERE E^fsyjtems that shows the net sludge production (VSS produced/CODo) of air |
systems to be greater for any given organic loading rate (CODR/MLVSS) than a
TOP OF
IMAGE
'AREA
DROPPED
HEAD,
BEGIN
SECTIONS
similarly operated oxygen system.
From an analysis of the data collected
both from the small- and large-scale
units the Districts have concluded there is little difference between the
HERE
^"1"*"
oxygen systems in terms of sludge production. When an analysis of
iTTfll^TraTetrw^
biological reactor (which is the method used by proponents of pure oxygen),
the data does indeed indicate that theloxygen system produces less sludge.
It is the belief of the authors, however, that the mass of solids within the
entire biological system must be considered in order to obtain a true indica-
tion of the level of sludge production! This means that the solids that are
present in the final clarifiers must be included when the total system solids
are calculated.] When the data is re-eyamined in this way, the oxygen system
will no longer demonstrate an advantage over air systems in terms of sludge
production. This reversal is due to the fact that a greater portion of the
total system solids will be contained within the clarifiers of an oxygen
system than is typically encountered iri air-activated sludge systems. As was
o'StTrned -e-ar-l-ieF,HmprVve'd--shjdge- sett-Ting- and -oxygentransfercap"ab~rl ity E^
allows the oxygen system to be operated as a high-rate system. As a result,
as much as 50 percent of the total system solids will be carried in the final
clarifiers. If'the air and oxygen systems are compared based on reactor
solids only, then4ia significant portio^i of the oxygen solids will be elimin-
ated form the9a1nahysis, thus falsely indicating a higher organic loading rate'
than that imposed on the air system.
'
A sludge growth [kinetics analysis based on total system solids is presented
in Figure 8. Linear regression lines (developed by treating the MCRT as the
independent variable) are shown for the air and oxygen data along with the 90-
percent confidence limits for the location of the oxygen line. It is not
possible to reject, with 90-percent confidence, any line falling within
these limits asithe true line from whi£h the oxygen data were generated.
Since the air system regression line falls within these confidence limits,
the oxygen growth kinetics are not distinct from the air kinetics at the 90-
percent confidence level. I
I I
The observed net! sludge production data (which includes the VSS in the waste
sludge plus the'effluent) are plotted as points in Figures 9 and 10. Iden-
tical data are presented in both figures. The graphic display of the data
points shows that it is difficult to determine which system has a higher net
sludge production.
BEGIN
LAST LINE
OF TEXT J
The curves superimposed on the data in
the growth kinetics shown on Figure 8.
Figures 9 and 10 were developed from
The two linear regression lines for
the air and oxygen system shown on Figure 8 (developed using the MCRT as the
independent variable) are: I
1/8C = 0.58 (F/M) - 0.21
1/9C = 0.81 (F/M) - 0.32
Air System
Oxygen System
i
3/8'
EPA-287 (Csn.
14-76)
PAGE NUMBER
BOTTOM OF
IMAGE ARE>
[ OUTSIDE
I DIMENSION
FOR TABLES
fAND ILLUS-
TRATIONS
-------
BEGIN
FIRST
LINE OF
TEXT
HERE
TWWG GUCDE SHEET
CENTER
OF PAGE
DROPPEC
HEAD,
BEGIN
SECTI
HERE
0,4
0.3
o
T3
o
CD
LJ
O
UJ
C3
Q
ID
_l
CO
3
O
o:
o_
0.2
UJ
£E
-0.
-0.2
I T I 1 I
LEGEND
A LARGE SCALE OXYGEN SYSTEM
SMALL SCALE OXYGEN SYSTEM
LARGE SCALE AIR SYSTEM
' SMALL SCALE AIR SYSTEM
OXYGEN SYSTEM DATA
AIR SYSTEM DATA
90% CONFIDENCE LIMITS
OF OXYGEN DATA.
0 O.I 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 I.I
FOOD-TO-MICROORGANISM RATIO (CODR/VSS), kg/day/kg
BEGIN
LAST LINE
OF TEXT
Figure 8. Sludge growth kinetics
3/8
EPA-287 (Cm.)
(<9-7S)
PAGE NUMBER
TOP OF
IMAGE
AREA
BOTTOM OF
IMAGE ARE/!
OUTSIDE
DIMENSION
FOR TABLES
ILLUS-
TRATIONS
-------
BEGIN
FIRST
TVPDHG GUIDE SHEET
CENTER
TOP OF
TEXT
HERE D
DROPPED
HEAD,
BEGIN
SECTIONS
HERE £
BEGIN
LAST LINE
OF TEXT C
I
£
!
£
0.5
o>
"^ 0.4
"cc
Q
O
O
co 0.3
CO
o
;
SLUDGE PRODUCl
9 9
o KJ
/ \ -
i i i i
\x
i-Cx
^^
mm ^H
LEGEND
1 I 1 1 1
*<
7^^.
^
A LARGE SCALE OXYGEN SYSTEM
SMALL SCALE OXYGEN SYSTEM
" LARGE SCALE AIR SYSTEM
SMALL SCALE AIR SYSTEM
I i i i
) ! 2 3 4
1 1 1 1 1
5 6 7 8 9 10
^
MCRT (TPVSS), days
i !
Figure 9. Analysis of net sludge production using MCRT as the independent
variable. j
These equations are in the form of
i
1/9C = Y (F/M)-kd
where : '
1
ec = MCRT
, -r
F/M = food-to-microorganism ratio
Y = growth yield coefficient
^IMAGE
.AREA
BOTTOM OF
IMAGE ARE/
OUTSIDE
DIMENSION
FOR TABLES
3/8"
y
? [Cin.>
PAGE NUMBER
YAND ILLUS-
, TRATtONS
(0-76)
-------
BEGIN
FIRST
LINE OF
TtfPIMG GUIDE SHEET
CENTER
HERE
DROPPED ;
HEAD,
BEGIN j ^
SECTIONSlL -* 0 4
HERE ' ' ^
cr
o
O
o
CO
0.2
BEGIN
LAST LINE
O
O
CC
Q_
UJ
0.
0
LEGEND
A LARGE SCALE OXYGEN SYSTEM
SMALL SCALE OXYGEN SYSTEM
LARGE SCALE AIR SYSTEM
SMALL SCALE AIR SYSTEM
OXYGEN
'AIR
TOP OF
IMAGE
'AREA
0
34567
MCRT (TPVSS), days
8
10
Figure 10.
Analysis of net sludge production using the food-to-microorganism
ratio as the independent variable.
k(j = microorganism decay coefficient
The net sludge production (VSS/CODp in kg/kg) is defined as follows:
iNet sludge Production = Y/(l + kd6c)
1 i
The air and oxygen curves shown in Figure 9 were derived using the above I
formula for netisludge production withjY and kj being supplied from the
linear regression analysis in Figure 81 Though the linear regression lines ijj8011
Figure 8 were sh|own to be statistically insignificant at the 90-percent
confidence limits, it is interesting to note that the curves in Figure 9
OF TEXT cfindicate that the oxygen system has a higher net sludge production
EPA-287 (Cfn.)
PAGE NUMBER
DIMENSION
FOR TABLES
ILLUS-
TRATIONS
in^TiiC I \Jl \
YAND
-------
BEGIN
FIRST
LINE OF
TEXT
HERE n
DROPPED
HEAD,
BEGIN
SECTIONS
HERE £
TWWG GUIDE SHEET
CENTER
OF PAGE
TOP OF
;A__linear regression analysis was also conducted on the data in Figure 8 usijigj
F/M as the independent variable, rather than the MCRT. The linear regression*
analysis assumes that the independent variable is exact and adjusts the line
to best fit theidata. Therefore, using F/M as the independent variable
rather than thejMCRT produces siightlyjdifferent lines than those shown on
AREA
BEGIN
c
OF TEXT
Figure 8. The linear regression lines
variable are: !
produced using F/M as the independent
1/9C = 0.50 (F/M) - 0.15
1/9C = 0.32 (F/M) - 0.02
The air and oxygen curves presented in
viously given formula for net sludge pi
from the linear Degression lines given
Air System
Oxygen system
Figure 10 were derived using the pre-
oduction with Y and kj being supplied
above. This analysis shows that at
MCRT's of above i5 days, the oxygen system again has a higher net sludge pro-
duction than the air system.
Be£ause_qf_ __
pitas es of the oxygensystem operation
data_form_the_ l_a_st_fouc,
..,-,-.. _., _r_. ...... ,,ave not been used. On both Figures 9"
and 10, those data would have tended to move the oxygen system sludge pro-
duction curve upward at the lower MCRT s.
SLUDGE SETTLEABjLlpITY
^ ~ I / \j
Two parameters are commonly used to indicate sludge settleability. The
sludge volume index (SVI) is the inverse of the settled sludge concentration
expressed in ml/(g, and the initial settling rate (ISR) is the maximum rate at
which the sludge interface drops during the test.
I U
The 30-min SVI data were presented previously in Tables 2 and 3. The
phase-average oxygen system SVI varied[from 65 to 153 ml/g, with an average
of 99 ml/g, and Ithe air system produced SVI's of 146 to 252 ml/g, with an
average of 167 ml/g. I
The ISR data resulted from one series of tests which was conducted during a
period when the !performance of both pilot plants was charcterized as "good."
In this series of tests, the oxygen sliidge settled about three times as fast
as the air sludge (Figure 11). These are the results of only one test, but
they are in qualitative agreement withIthe general experience at the JWPCP.
The oxygen sludge definitely settles better and gravity thickens better than
the air sludge. I However, it is not possible at this time to determine the
extent to which |this is an innate property of oxygen-activated sludge or a
function of the reactor design. 1
I I
One factor which affected the sludge settleability in both of these systems
was the power input. During the starttip of each pilot plant it was necessary
to reduce the mijxer power in order to pVoduce an acceptable effluent. Ex-
cessive power input shears the floe, wJjich can cause poor settleability of
sludge and a1 turbid effluent.
3/8"
EPA-28? (Cin.)
(4-7S)
PAGE NUMBER
BOTTOM OF
IMAGE ARE/
OUTSIDE
DIMENSION
FOR TABLES
ILLUS-
TRATIONS
-------
BEGIN
FIRST
LINE OF
TEXT :
HERE C
DROPPED
HEAD,
BEGIN
SECTIONS
HERE
TTVPiWG GU'JBE SHEET
CENTER
TOP OF
1, IMAGE
20
10
5
E
UJ
UJ
en
<
h-
0.5
0,2
O.I
0.05
I T r i i 1 I i
NOTE: Im/hr = 3.28 ft./hr.
OXYGEN
AIR
1,000
2,000 5,000 10,000
SUSPENDED SOLIDS, mg/I
20,000
| 'Figure 11. Initial; settling rates.
POWER CONSUMPTION
In the present economic climate, one of the most important factors involved
in the comparison of air- and oxygen-activated sludge processes concerns
energy consumption. Since power intensity problems in both pilot plants
required the aeration equipment to be operated at speeds lower than design, a
comparison based on the pilot plant data is inappropriate. Additionally, the
effects of scale would be difficult to
aerator efficiencies will produce more
predict, so estimates based on typical
applicable results.
The standard oxygen transfer rates (SOTR's) presented in Table 9 are represen j (MAGE
tative of present mechanical aeration technology, although specific equipment OUTSIDE
may differ fromjthose values. In the ease of the submerged turbine, a 50:5D_J DIMENSION
BEGIN
LAST LINE
OF TEXT empower split between the mixer and compressor was assumed. As indicated in
BOTTOM OF
() 3/8"
EPA-287 (Cm.)
(4-73)
PAGE NUMBER
_J FOR TABLES
\>AND ILLUS-
TRATIONS
-------
BEGIN
FIRST
LINE OF
TEXT
HERE DJFfable
DROPPED
BEGIN
WONG GUIDE SHEET
CENTER
OF PAGE ^
9, different mechanical
efficiencies were assigned to the mixer and __
^compressor to obtain wire power consumf
The oxygen trans
SECTIONS *
HERE dt»
fer equation
dC = ct K a
^^^r i
dT L
is:
t *! i i i
* '
itions .
(1)
TOP OF
AREA
where:
kd-
J.
jj£ = oxygen transfer rate, mg/l/hr
dt
KI a = volumetric mass transfer coefficient, hr"1
L ]
C* = equilibrium dissolved oxygen concentration
at zero uptake, mg/1
C = system dissolved oxygen concentration, mg/1
fa, 3 = variables to correlate clean water results
, to mixed liquor conditions.
By adding a power intensity term (V/P)J it is possible to obtain an equation
in which the IteW'side has the same units as the SOTR.
SOTR -!£(») .
V
(8C*-C)
where:
V = tank volume (]03-m3)
P = power (kW)
It is now possible to apply the standard
constant K|_aV/P land then determine the
dition. '
conditions in Table 9 to obtain the
oxygen transfer rate under field con-
The air system was a completely mixed ifeactor with dissolved oxygen (DO)
maintained at Kmg/1. Using an equivalent depth (the depth associated with
a saturation DO jof C*) at 0.4 of the air introduction depth, and the con-
ditions listed i,n Table 9, the calculations are straightforward.
Since the oxygen system is muilti-staged, the model is slightly more -com- I
plicated. Based on the conditions observed in pilot studies (DO, gas purity, i
and oxygen uptak'e rate, see Table 10) and communications with manufacturers, a
model was developed which allowed the calculation of required K|_a's in each I
stage. Since KLa is proportional to power, the data allow the power fraction!
BEGIN ln eac'1 sta9e to! be calculated. The transfer efficiency at field conditions !
LAST LINEi[Ln__each stage was calculated, and an average based on the power distribution §
OF TEXT jJfJFmndes the ove'rall efficiency. The power required to extract the pure I
3/8"
EPA-287 (Cin.)
(4-7B)
BOTTOM OF
IMAGE ARE/
OUTSIDE
DIMENSION
FOR TABLES
AND ILLUS-
TRATIONS
PAGE NUMBER
-------
CO DO ^ O
~n co
ji_nL
I
-4
T
CO
TABLE 9. ASSUMED OXY'GEN TRANSFER RATES
a Standard Conditions Gas Purity = 21% 02, Water Temperature = 20°C, Dissolved Oxygen = 0 mg/1.
a = 1 00, B = 1 00
Efficiencies Gear Box = 0 96, Coupling = 0 95, Motor = 0 92
c Efficiencies Blower = Q 70, Coupling = 0 95, Motor = 0 92
n co
V
> Tl O O ^ C"3
z o ^ c 5 o
pj 30 S q > -I
^
System
Surface Aerator
Submerged Turbine
Total System
Mixer
Compressor
Standard Oxygen
Transfer Rate3
(Delivered Power)
kg/kWh (Ib/hp-hr)
2 13 (3 50)
1 70 (2 80)
Power
Consumption
(Delivered)
kWh/kg
(hp-hr/lb)
0 469
(0 285)
0 588
(0 348)
0 294
(0 179)
0 294
(0 179)
Power
Transfer
Efficiency
0 839b
0 839b
0 612C
Power
Consumption
(Wire)
kWh/kg
(hp-hr/lb)
0 559
(0 340)
0 830
(0 505)
0 350
(0 213)
0 480
(0 292)
Oxygen
Transfer
Rate3
(Wire Power)
kg/kWh
(Ib/hp-hr)
1 79
(2 94)
1 20
(1 98)
m
(ft
m
m
=1
-o Z
> -H
£1°
m > TJ
> O 0
m y
w C
-------
TABLE 10. OXYGEN SYSTEM OPERATING CHARACTERISTICS
Stage
1
2
3
4
Gas
Purity
% 02
80
70
65
50
Dissolved
Oxygen,
mg/1
9 1/3
7
5
2
Power
Fraction
0.46
0.27
0.15
0.12
oxygen from the atmosphere must be added to the aerator power in order to
provide a fair comparison.
The results of these calculations are presented in Table 11. The oxygen
systems use substantially less energy in this analysis. The surface
aerator oxygen system, in fact, is estimated to require only 52-percent of
the energy used by the air system, and the submerged turbine oxygen system
is projected to need 62-percent of the energy used by the air system. Be-
cause of land constraints at the JWPCP, depths greater than 5-m (15-ft)
were required for the air system, so surface aeration was not evaluated
for the air system
DEPENDABILITY AND MAINTENANCE
In the JWPCP studies, the oxygen-activated sludge process has proven to be
very stable and has generally recovered from upsets very quickly. The major
operational problems have been associated with the appurtenant equipment,
which is much more complex than is encountered in most air systems. Because
of the potential for explosions in the enriched atmosphere, oxygen-activated
sludge systems must be equipped with an explosive vapor detector. This
equipment has proven subject to frequent failures, which have automatically
shut down the total aeration system.
One maintenance item that has not been quantified, and had not been expected,
concerns life of the clarifier flight chains. The oxygen effluent has proven
to be much more aggressive to the cast links than the air effluent. This is
probably a result of the higher dissolved oxygen content and the lower pH of
the oxygen effluent.
t 3/8"
EPA-237 (C,n.)
(4-76)
ILLUS-
TR AT IONS
PAGE NUMBER
-------
( -, - CO
> m
, o CD
j en w
m rn m
La O CD
m -i =-
jc U
17; sj
5> O
-
O
n
f- ^ ~G
m
O
O
TABLE 11.' POWER CONSUMPTION
CD "
m
Z. i -&':
C rv>
£ ' " -.
ffi I'----
33 [,.
System
Air
Oxygen
Oxygen
Aerator
'Type
Submerged
Submerged
Surface
Water
Depth',
m (ft)
7.6 (25)
4.6 (15)
4.6 (15)
Power Consumption (Wire Power),
kWh/kg 02 transferred, (hp-hr/lb 02 transferred)
Aeration
Equipment3
1.28 (0.78)
0.44 (0.27)
0.31 (0.19)
Oxygen
Generation"
0.35 (0.21)
0.35 (0.21)
Total
1.28 (0.78)
0.79 (0.48)
0.66 (0.40)
Turbine plus compressor: Water Temperature = 23 C, a = 0.80, 3 = 0.95,
b Based on JWPCP design, 90% oxygen utilization.
fJ^O^gf S
ph'j^i^i
l-,i. i,|fjm|o
i C/) >s ~^
_JJ.
CD
-------
BEGIN
FIRST
LINE OF
TEXT
GUIDE SWEET
CENTER
OF PAGE
DROPPED
HEAD,
BEGIN
SECTIONS,
HERE
gjrAs_ a biological/process, the air system seemed to be more sensitive than the
oxygen system. Due to the air system's!tendency to nitrify and the associated
rising sludge, it was necessary to operate the air system at low aeration
times and low MGRT's. Operating in this marginal region has contributed to
the sensitivitylof the air system.
i I _J
^Mechanically, the air system was much simpler and less subject to malfunctions
:'h-arr-t h e~oxyg e rrfsy s t em": 1
TOP OF
* I MAGE
'AREA
-4
9-1/8"
6-1/2"
BEGIN
LAST LINE
OF TEXT
EPA-287 (On.)
(4-7B)
PAGE NUMBER
BOTTOM OF
IMAGE ARE^
OUTSIDE
DIMENSION
J FOR TABLES
VAND ILLUS-
TRATIONS
------- |