NATIONAL SANITATION FOUNDATION
PACKAGE SEWAGE TREATMENT PLANTS
CRITERIA DEVELOPMENT
PART II: CONTACT STABILIZATION

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PACKAGE SEWAGE TREATMENT PLANT CRITERIA DEVELOPMENT
PART II: CONTACT STABILIZATION
NATIONAL SANITATION FOUNDATION
ANN ARBOR, MICHIGAN
Robert M. Brown, President
Charles A. Farish, Executive Director
FEDERAL WATER POLLUTION CONTROL ADMINISTRATION
DEMONSTRATION GRANT PROIECT
WPD-74
ANDREW T. DEMPSTER, Project Director
June 1968

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TABLE OF CONTENTS
Page
Project History		3
Contact Stabilization Definition		3
Description of the Contact Stabilization
Process		5
Startup and Solids Accumulation		8
BOD Removal	10
Oxygen Requirements	10
Nitrification	10
Solids Separation	10
Skimming	11
Temperatures	11
Mixed Liquor and Stabilization
Compartment Solids	11
Solids Wasting	11
Check List for Routine Maintenance and
Operation of Contact Stabilization
Package Sewage Treatment Plants	13
Performance Criteria and the Standard
Performance Evaluation Method	14
Prequalification	14
Figures	Page
1	Contact Stabilization Process
Flow Diagram	 4
2	Flow Pattern	 5
3	Research Site and Staff Photographs. . 6
4	Four Contact Stabilization Sewage
Treatment Plant Photographs.... 7
5	Relationship Between Suspended
Solids in Contact and Stabili-
zation Compartments and
Return Sludge Rates	 9
Page
General Test Conditions and Reporting .... 14
Startup Performance Evaluation	16
Variable Flow Pattern Performance
Evaluation	17
Deviations From Standard Methods	17
Flow Patterns	18
Responsibilities	18
The Manufacturer-Supplier	18
The Buyer-Owner	19
The Consulting-Supervising Engineer	19
The Installer-Contractor	20
The Regulatory Agency-Official	20
The Plant Operator	20
The Performance Evaluation
Organization	20
Discussion	21
Acknowledgments	21
References	23
Tables	Page
I Performance of Contact
Stabilization Plants	12
n Steady State Data, Fall and
Winter Studies	24
in Steady State Data, Spring and
Summer Studies	25
IV Variable Flow Pattern, Winter
and Spring Studies	26
V Variable Flow Pattern, Spring
and Summer Studies	27
TABLES AND FIGURES

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PACKAGE PLANT CRITERIA DEVELOPMENT
PART II: CONTACT STABILIZATION
I. GENERAL
The need for some form of treatment and
disposal of wastes has been one of mankind's
pressing problems since early times. With the
amount of effort and thought which has been ap-
plied to this problem, it would seem that he
should be further along in finding its solution.
Unfortunately, however, increased population and
successive changes in the environment have added
to the variables, and the problem has become
more difficult to solve. In the beginning, waste
disposal methods were primarily accidental, and
treatment was limited to natural physical, chemi-
cal, and biochemical reactions. When wastes
were discharged to receiving streams, the prob-
lem was simply moved to other populated areas
downstream, creating a threat to water supplies.
As a result of efforts to remedy this new threat,
additional treatment methods, including gravity
separation, chemical coagulation, aerobic bio-
logical oxidation, and incineration, were devel-
oped. Alone, or in combination, these methods
are the basic ones being used today to remove
objectionable fractions from wastewater before
it is discharged to a nearby watercourse.
As stated in Part I of the National Sanitation
Foundation Report: "Package Sewage Plant Cri-
teria Development,"1 man's present state of
mobility has led to the development of suburbia.
In their early stages of existence, suburban
communities may not have access to the inner
city's system for collecting and treating wastes.
In addition, the septic tanks, cesspools, or privies
used in rural areas are not suitable for the
disposal of wastes in these more densely popu-
lated suburban developments. Package sewage
treatment plants, which offer a relatively high
level of treatment, have been designed to meet
the needs for waste treatment in these areas.
In 1947, an underloaded "package" activated
sludge plant at East Palestine, Ohio,2 was at-
tracting attention. All of the activated sludge
was being recirculated through the aeration tanks
from the final settling tanks, with no wasting of
excess sludge. An equipment company became
interested in this process modification and de-
veloped the extended aeration type package plant.
Almost simultaneously, Ullrich and Smith3 were
developing new operational procedures which
would permit a conventional activated sludge
plant in Austin, Texas, to treat larger flows and
greater loads. A 15-20 GPM pilot plant utiliz-
ing the "Biosorption Process" was constructed
in 1950. This was essentially the same process
which is now commonly referred to as "Contact
Stabilization."
Ullrich and Smith described their modifica-
tion of the conventional activated sludge process
in the following distinct treatment steps:
"1. Activated sludge is brought into
intimate contact with raw sewage. Brief
mixing of the two is accomplished either
mechanically or with air. The activated
sludge adsorbs and absorbs a very high per-
centage of both the suspended solids and
dissolved pollutional material.
2.	After the brief mixing, the mixed
liquor flows to a clarifier where it is settled.
The effluent is clear, low in BOD and low
in suspended solids. This is the plant ef-
fluent ready for final disposal.
3.	The sludge from the clarifier which
now contains the original activated sludge
plus the adsorbed and absorbed suspended
and dissolved pollutional matter from the
raw sewage is conducted to an aeration com-
partment, where it is aerobically digested
in preparation for recycling. In other words,
the sludge from the clarifier is reactivated
by means of aeration so it can again be used
in the mixing compartment for removing
polluting materials thus making the process
continuous."
The pilot plant studies demonstrated that the
"Biosorption" (contact stabilization) process was
practical. The Austin plant4 was expanded by
converting a primary clarifier to a final clari-
fier and by adding two more final clarifiers, two
additional blowers, a grit removal unit and bar
screen, and auxiliary pumping equipment. With-
out adding any new aeration tank capacity to the
original 6 MGD activated sludge plant, the ca-
pacity of this plant operating as a "Biosorption"
unit increased to a 16.0 MGD average flow. The
plant was reported to be "most satisfactory"
1

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2
after it had been converted to contact stabiliza-
tion.
In 1951, Eckenfelder5 conducted a pilot plant
study on the oxidation of cannery wastes by
applying what is now known as the contact sta-
bilization process, but was designated at that
time as "high rate biological sludge treatment."
This pilot study was conducted at the H. J. Heinz
plant in Chambersburg, Pennsylvania, on tomato
and apple processing wastes. Average BOD re-
ductions of 85 percent were reported for raw
wastes with average BODs of 1250 mg per liter
from apple processing, and 450 mg per liter
from tomato processing. The air requirements
were 2.5 cu.ft. per gallon for the apple wastes,
and 1 cu.ft. per gallon for the tomato wastes.
Low pH values were adjusted by adding caustic.
In 1952, Eckenfelder and Grich6 reported on the
construction of a full scale plant at the same
H. J. Heinz facility. This plant treated peach
as well as tomato and apple processing wastes.
BOD removal efficiencies of 80-90 percent were
obtained with wastes from various combinations
of these products.
It was logical for contact stabilization to be
adopted by manufacturers of package plants.
Some manufacturers designed plants which could
be operated either as extended aeration or con-
tact stabilization units, with the result that plants
of the latter type could provide almost double
the treatment capacity without increasing their
dimensions or volumes. For purposes of sim-
plicity, extended aeration plants may hereafter
be referred to as EA and contact stabilization
plants may be designated as CS.
This principle of expanding the capacities
of existing conventional activated sludge plants
has been utilized in other large municipal plants
in this country. In addition, many small mu-
nicipalities have installed new CS plants with
capacities between 100,000 and 1,000,000 gallons
per day. CS plants, while not always shipped
as completed units, can still be classified as
package plants. They are pre-engineered using
standardized aeration, pumping and sludge col-
lecting equipment, and are installed in plant
structures that are field erected from prefabri-
cated steel components, or constructed of rein-
forced concrete.
Relatively few references to contact stabili-
zation are contained in the literature. In 1959,
Zablatzsky, Cornish, and Adams7 studied various
process components in the laboratory. Relation-
ships between sludge production and BOD re-
moval, and aeration time and oxygen uptake were
determined. As a result of this investigation, a
portion of an existing activated sludge plant at
Little Ferry, New Jersey, was converted to con-
tact stabilization. Full scale plant operation at
14 MGD indicated that the existing aeration tanks
were capable of treating 56 MGD if the air supply
and the dispersion units were increased suffi-
ciently.
In Greensboro, North Carolina, textile mill
wastes were treated by the CS process in a
modified activated sludge plant in 1958. Jones,
Alspaugh, and Stokes8 found that this process,
when used to treat a waste composed of approxi-
mately 1/4 mill waste and 3/4 domestic sewage,
removed between 85 and 90 percent of the BOD
and between 80 and 85 percent of the suspended
solids. These removals compared favorably with
those of trickling filters and conventional acti-
vated sludge units which had previously been
used to treat the same waste.
Sawyer9 analyzed various activated sludge
modifications, including contact stabilization, step
aeration, the Kraus Process, a "completely mixed
system" and a high rate activated sludge process.
A comparison of these processes indicated that
contact stabilization had the highest BOD loading
potential (144 lbs. per day per 1000 cu.ft. of
aeration capacity). In conventional activated
sludge plants BOD loadings are kept below 35 lbs.
per day per 1000 cu.ft. of aeration capacity when
good design practices are observed.
An analysis by Hazeltine10 in 1955 compared
BOD loadings for a conventional activated sludge
plant with those for a separate sludge reaeration
or CS plant. Both plants were theoretically
loaded with 35 lbs. of BOD per day per 100 lbs,
of sludge solids. The sewage had a BOD of
200 mg per liter, and the flow for both plants
was 24 MGD. In the conventional activated sludge
plant, an aeration tank capacity of 10 MG was
required for a mixed liquor solids concentration
of 1370 mg per liter. The volumetric BOD load-
ing was 30 lbs. per day per 1000 cu.ft., which
is just under the limit cited by Sawyer.9 The
CS plant with the same ratio of BOD to solids
loading required two 2 MG tanks, one for re-
aeration solids and one for mixed liquor, and
the volumetric loading was 74.5 lbs. BOD per
day per 1000 cu.ft. (33.4 cu.ft. per day per lb.
of BOD). Hazeltine presented these examples
to illustrate the fallacy of setting up volumetric
BOD loading criteria for aeration tanks without
giving consideration to their solids content.

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3
PROJECT HISTORY
In 1957, at a meeting of public health sani-
tarians, sanitary engineers, manufacturers of
package sewage treatment plants and users of
these plants, it was suggested by the Sewerage
Committee of the Engineering Section of the
Michigan Public Health Association that methods
for evaluating the performance of package sewage
treatment plants should be established. It was
proposed that some independent agency such as
the National Sanitation Foundation undertake a
study of these plants. No means of financing
the study were found, however, so the project
did not go forward at that time.
In 1961, The Great Lakes Upper Mississippi
Board of State Sanitary Engineers requested its
Sewage Works Standards Committee to investi-
gate ways of developing performance evaluation
criteria for package treatment plants. In 1962,
the committee recommended to the Board that
the committee chairman be permitted to explore,
with the National Sanitation Foundation, the pos-
sibility of the Foundation's undertaking such a
study. A resolution adopted by the Board recom-
mending that the National Sanitation Foundation
consider taking such action was responsible for
the creation of a Joint Industry-Public Health
Committee, which developed: (1) a methodology
for the study, and (2) an application for a U.S.
Public Health Service Demonstration Project
Grant to provide the necessary financial support.
Other organizations, including the Conference of
State Sanitary Engineers and the Association of
State and Interstate Water Pollution Control Ad-
ministrators added their support. In 1964, the
project was approved by the Demonstration Grants
Committee of the U. S. Public Health Service
and designated as Demonstration Grant Project
WPD-74, with a starting date of January 1, 1965.
Sponsorship was transferred to the Federal Water
Pollution Control Administration in 1966. Four
contact stabilization plants were loaned to the
Foundation by their respective manufacturers for
use in this phase of the study.
The Joint Industry-Public Health Committee
held its final meeting on January 15, 1965. At
that meeting, the Package Sewage Treatment
Plant Criteria Development Project came into
existence as an official National Sanitation Foun-
dation study. An Executive Committee, a Policy
Committee, a Technical Committee and an In-
dustry Committee were appointed shortly there-
after. The original members of these committees
are listed in the previous report.1
The Technical Committee met in Ann Arbor
on March 11 and 12, 1965. Plans for the re-
search site facilities were presented by Mr.
George E. Hubbell, of the consulting engineering
firm of Hubbell, Roth and Clark, Bloomfield
Hills, Michigan. Project methodology was also
discussed. The committee agreed to limit the
first year of the study to extended aeration type
package plants, and to study other process modi-
fications such as CS at a later date. These
recommendations from the Technical Committee
were approved by the Policy Committee on
April 12, 1965. Bids were immediately sought,
and the low bidder, Midwest Mechanical Con-
tractors, Inc., started construction on April 28,
1965.
Details and plans for the research site fa-
cilities, located on two acres of land adjacent to
the Ann Arbor Wastewater Treatment Plant at
49 South Dixboro Road, Ann Arbor, Michigan, are
presented in the Extended Aeration Report.1
Results of the EA study were first reported at
the Water Pollution Control Federation Con-
ference at Kansas City, Missouri, in October
1966.	The first printing of the Extended Aeration
Report1 was released late in December of 1966.
The project staff, which the former Project
Director, Mr. Brian L. Goodman, assembled dur-
ing the time of construction of the research site
facilities, was composed of Mr. John G. Havens
(Research Site Manager), Mr. Robert S. Great-
house (Project Chemist), Mr. Wendell J. Birdsall
(Research Assistant), and Mrs. Adeline W. Carter
(Project Secretary). Mr. John P. Karr (Research
Assistant) joined the staff early in 1966. Mr.
Goodman resigned from the project in November
1966,	and Mr. Greathouse resigned in January
1968. Several students were employed as re-
search assistants during the summer and fall of
1967.	Miss Nina I. McClelland and Professor Jack
A. Borchardt of the University of Michigan have
served as consultants to the project. The National
Sanitation Foundation has indeed been fortunate
in having a research staff that has demonstrated
a great interest in its work and has assumed
responsibility whenever necessary.
CONTACT STABILIZATION DEFINITION
The Technical Committee, in a meeting at
Ann Arbor on March 21, 1968, approved the fol-
lowing definition of the Contact Stabilization
Process:

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4
"Contact Stabilization is a form of the
activated sludge process where aeration
is carried out in two phases in two
types of tank: the contact tank where
raw sewage solids are adsorbed and ab-
sorbed on the microbio masses; and the
'stabilization' tank where the solids,
which have been removed in a final
settling tank, are partially stabilized by
reaeration before being recombined with
the incoming raw sewage. An aerobic
digestion tank may be included as a
part of the process.
For the purpose of criteria development
and subsequent testing of package plant
units, the sludge components wasted from
the process, whether or not a fraction
thereof is returned to the process, will
be included in the studies."
II. STUDY AND FINDINGS
GENERAL
The purpose of this project was to establish
a method for evaluating the performance of
package sewage treatment plants. Extended
aeration package plants have been and are being
used to treat sewage from suburban shopping
centers, motels, schools, and other establish-
ments that do not have access to municipal
sewerage systems. Contact stabilization package
plants are used for larger establishments of the
types just mentioned and for small municipali-
ties. The recent interest of the Federal Govern-
ment in improving stream conditions has, no
doubt, created an increased demand for package
sewage plants. Regulatory agencies throughout
the country have had an interest in performance
evaluation of the contact stabilization process;
therefore, a criteria development project for
package sewage plants should include plants of
this type. A flow scheme for the contact stabili-
zation process is shown in Figure 1.
Only four plants were available for this
phase of the study. Because of their large ca-
pacities, there was an understandable reluctance
on the part of manufacturers to provide the
project with new CS plants. Field erection of
prefabricated components is more costly than
shipment of a fully assembled unit.
AIR
INFLUENT
EFFLUENT
CLARIFIER
STABILIZED
RETURN
SLUDGE
RETURN
SLUDGE
SUPERNATANT
RETURN
WASTE SLUDGE
. NOTE:
AEROBIC DIGESTER
CAN BE OMITTED
AIR
WASTE
SLUDGE
WASTE DIGESTER SLUDGE
TO DRYING BEDS OR FILTER
CONTACT
COMPARTMENT
AEROBIC
DIGESTER
STABILIZATION
COMPARTMENT
CONTACT STABILIZATION PROCESS FLOW DIAGRAM
Figure 1

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5
The first plant was placed in operation in
September 1966. This was a 16,000 GPD EA
plant which was converted to a 30,000 GPD CS
unit. The second plant, of 50,000 GPD capacity,
arrived at the research site in April of 1967.
This plant could also be converted to an EA
plant, a feature that is quite common with these
two process modifications. The last two plants
were converted to CS from EA plants already
located at the research site, and had capacities
of 10,000 GPD and 20,000 GPD respectively.
The first plant has been operated as a contact
stabilization unit for approximately 15 months.
The second plant was started in May 1967 and
has been operated for approximately 12 months.
The remaining two plants were put in service
in December 1967 and have been operated for
a six-month period. The three largest plants
were constructed of steel and installed on a con-
crete pad above grade, while the smallest plant
was prefabricated of concrete and installed so
that two-thirds of it was below grade. The re-
search site staff operated and maintained the
plants during this latter part of the study in
much the same manner as the extended aeration
plants were operated and maintained. The re-
search facilities were essentially unchanged.
Two plants were located on one side of the 140 ft.
long control shelter, while the other two were
located on the opposite side. The flow control
equipment developed for the extended aeration
plants1 was also utilized for this study. Sewage
used in the operation of the plants was obtained
from the 48 inch main connecting the City of
Ann Arbor's sewerage system to its treatment
plant, which is adjacent to the National Sanitation
Foundation's research site. Raw sewage flows
through a one-fourth inch slot comminutor lo-
cated near the control shelter, and is then pumped
through a common header to the flow control
units for each plant. The flow control units not
only measure the quantity of influent to each
plant, but also control the hourly variations that
would be expected for different patterns of flow.
Flow measuring recorders and totalizers on
each control unit served as a means for actuat-
ing the sampling pumps at set flow intervals for
collecting samples from the effluent connections
to each plant. Similar sampling equipment was
also installed on the main distribution line, and
the samples were composited in conformance
with the particular flow pattern being used to
supply the contact stabilization plants with raw
waste.
Two flow patterns were used in operating
the plants, steady state and the variable flow
pattern. The latter pattern is illustrated by
Figure 2 and is specifically defined under Sec-
% TOTAL DAILY VOLUME
7
6
S
4
3
2
O
1200'
Figure 2. Variable Flow Pattern
tion F, Performance Criteria. This pattern was
considered to represent the normal variations
in daily flow rates under a variety of circum-
stances. The steady state flow pattern would,
as the name implies, evenly distribute the daily
flow.
Samples collected by the composite samplers,
and those collected from specific locations or
portions of the process were analyzed in the
National Sanitation Foundation Laboratory facili-
ties. The methods prescribed in the 12th Edition
of Standard Methods,14 unless otherwise speci-
fied, were employed in all analytical work.
Until May 1967, the laboratory was located in
the control shelter. At that time, the Ann Arbor
Wastewater Treatment Plant Superintendent,
Mr. Richard Sayers, arranged for the Foundation
staff to share the laboratory facilities in the
Ann Arbor plant. The limited laboratory floor
space in the control shelter, as opposed to more
adequate laboratory and office space available in
the Ann Arbor facility, made this move most
advantageous to the operation of the project.
The control shelter facilities were still used
for making COD determinations, and all of the
flow control and sampling equipment for the
plants was maintained in the shelter. The roof
of the shelter building, by virtue of its location
between the two rows of package plants, pro-
vided access to the plants located above grade.
Bridges were installed between the roof walkway
and the top of each plant.
DESCRIPTION OF THE CONTACT STABILIZA-
TION PROCESS
The Technical Committee adopted a defini-
tion for the contact stabilization process which
appeared earlier in this report. The list of

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Oi
Two Views of the NSF Package Sewage Treatment Plant Research Site.
Figure 3
I R
PACKAGE SEWAGE TREATMENT PLANT
RESEARCH FACILITY WPD 74
i !u NATIONAL SANITATION FOUNDATION
. .j ~ 			 ...
V , , HOBHll KJTHf CURK
MIOWfST MECHANICAL COKTRACTORS MC
Research Site Staff.
Control Panel for Programming Flow and Sampling Composites.

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Figure 4
Four Contact Stabilization Package Sewage Treatment Plants
Utilized in Developing Performance Criteria.
-j

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8
essential elements of the process as described
by Ullrich and Smith3 was also quoted. These
are basic descriptions of the process. Each of
the plants used in this study had three compart-
ments under aeration. Raw sewage flowed into
the contact aeration compartment and was mixed
at the entrance with reaerated or stabilized ac-
tivated sludge. The mixed liquor was kept under
aeration and remained in the contact aeration
compartment for one half to one and one half
hours, depending on the rate of flow of the in-
fluent to the plant, and the flow of stabilized
sludge into the compartment. The mixed liquor
then flowed into the clarifier, where most of
the organics, which were stabilized by micro-
organisms in the reaerated sludge and converted
into flocculent particles, settled or separated
readily. A relatively clear effluent of low organic
content flowed over the clarifier weir. Settled
sludge was collected from the bottom of the
clarifier and returned to the stabilization com-
partment by airlift pump. After four to six
hours of aeration, it was again mixed with raw
sewage flowing into the contact chamber. Not
all the sludge collected in the clarifier was re-
turned to the stabilization compartment. A por-
tion of it was diverted to the third aeration
compartment, an aerobic digester, where the
volume of sludge was reduced by autooxidation.
If facilities were provided for separating the
digested sludge from the supernatant, the latter
was returned to the stabilization compartment
to be combined with sludge returned from the
clarifier. Periodically some sludge had to be
wasted from the digester.
The liquid fraction of the inflowing sewage
was under treatment only for the time that it
took to flow through the contact compartment
and the clarifier. Obviously, because of the
shorter time that the total flow of sewage was
being aerated, the volumetric capacities of the
compartments used in this process were less
than those required in the conventional activated
sludge process or the extended aeration process.
In the contact stabilization process, BOD is
rapidly adsorbed and absorbed by the biomass
during the contact period. During the stabiliza-
tion period, "biosorbed" organic matter is oxi-
dized. The use of a longer contact period per-
mits some oxidation to occur at this point, re-
ducing the time required for oxidation in the
stabilization zone for equivalent treatment. In
order to increase the contact time, the return
sludge rate (usually stated as a percentage of
the raw sewage inflow) must be decreased, or
the raw sewage influent must be decreased, or
both must be decreased simultaneously. Since
the returned sludge rate controls the detention
time in the stabilization compartment, it follows
that this period will also be increased. The
time required in either aeration compartment is
also a function of the concentration of biomass
in that compartment.
STARTUP AND SOLIDS ACCUMULATION
For purposes of evaluating and testing a
contact stabilization package waste treatment
plant, the startup period is defined as the time
required after the plant has been placed in
service to reach a given level of solids under
aeration. It is recognized that these plants may
provide an effluent of acceptable quality before
this level of solids has been attained. The rate
of accumulation of active solids in the CS process
is a function of:
1.	The suspended solids and BOD in the in-
coming sewage.
2.	The rate at which solids are lost from
the system, a factor which is closely re-
lated to clarifier efficiency.
3.	The proportion of incoming inert solids
that remain in the plant.
4.	The rate of oxidation of solids in the
process.
The return sludge rate determines the rela-
tive distribution of solids between the stabiliza-
tion and the contact compartments. In the contact
stabilization process, the solids in both com-
partments should be totaled when determining
the rate of accumulation or other ratios in which
solids are involved. These can be approximated
if the return sludge rate and the solids content
of one of the compartments is known. The basic
mathematical relationship is:
MLSS (IFQ + RSQ) = SCSS (RSQ) + SS (IFQ) (1)
where:
MLSS = Mixed liquor suspended solids in
contact compartment, mg per liter
SCSS = Stabilization compartment suspended
solids, mg per liter
SS = Suspended solids in raw sewage
influent
IFQ = Influent flow rate, assumed to be
unity
RSQ = Return sludge, percent of IFQ
Example: If the return sludge rate is 100 per-
cent, IFQ = RSQ = 1. Then, assuming that the

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g
raw sewage suspended solids concentration is
200 mg per liter and the stabilization solids
concentration is 5000 mg per liter, and substi-
tuting in equation (1):
MLSS (1 + 1) = (1) 5000 + (1) 200 and
MLSS =	= 2600 mg per liter
For a 50 percent return rate RSQ = 0.50 and
IFQ = 1.0 and similar concentrations of solids:
MLSS (1 + 0.50) = SCSS (0.50) + SS (1)
MLSS = 5000 (—) + 200 (—U) = 1800 mg
per liter
By rearranging Equation (1), the return sludge
rate can be estimated if the solids content is
known in both compartments.
RSQ can be calculated as a percentage as
shown in the following expression:
RSQ =
MLSS - SS
SCSS - MLSS
(2)
Example: The return sludge rate is desired for
a CS plant in which the solids concentration in
the stabilization compartment is 10,000 mg per
liter and the solids concentration in the contact
compartment is 3000 mg per liter. The influent
is assumed to average 200 mg per liter sus-
pended solids. By substituting these values in
Equation (2) the return rate can be estimated as
a percentage of the rate of influent flow:
RSQ =
3000 - 200
10,000 - 3000
= 0.40 or 40 percent
Since solids concentrations are usually de-
termined from grab samples, this value of the
return rate should be treated only as an approxi-
mation. Solids levels in the two compartments
can be determined graphically, as shown in
Figure 3. CS package plants are not normally
equipped with devices for measuring flows, but
Relationship Between Suspended Solids in Contact and
Stabilization Compartments and Return Sludge Rates
0)
«
I
a
s
a
0)
0
u
a
&
1
$
&
CO
a
S
%
K
3000
Mixed Liquor Solids in Contact Compartment
Note: The Influent Suspended Solids Assumed to be 200 mg/liter
Figure 5

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10
suspended solids determinations are usually
made; therefore, this method of estimating re-
turn sludge rates may be helpful. For complete
accuracy, time of sampling and factors which
affect dilution, such as backflow, skimmer opera-
tion when skimmings are returned to an aerator,
and digester overflow must be considered.
BOD REMOVAL
Mean percent BOD reductions in the four
plants utilized for this phase of the study are
shown in Tables n through V. The reader of
this report should clearly appreciate that this
data includes analytical results which were ob-
tained in developing criteria for performance
evaluation. IT DOES NOT IN ANY WAY REPRE-
SENT STANDARDS OF PERFORMANCE TO BE
ATTAINED BY PLANTS UNDER TEST.
OXYGEN REQUIREMENTS
For the complete oxidation of any given
waste, the basic oxygen requirements are simi-
lar in any biooxidation process. In the first
report on the Extended Aeration Process1 a
waste with certain properties was found to re-
quire 1490 cu.ft. of air per pound of BOD. When
the biochemical reactions for synthesis, oxida-
tion and autooxidation are considered, the total
oxygen demand can be calculated. The Water
Pollution Control Federation's Manual of Practice
No. 6n gives a range of 300 to 1500 cu.ft. of
air per pound of BOD for domestic wastewater.
It would appear that a change in the "treat-
ability" characteristics of the raw waste oc-
curred sometime during the development of these
criteria. The rate of oxygen utilization de-
creased during this period. Although the causa-
tive agent(s) was not identified by any available
physical, chemical, or biochemical means, every
effort is being made to prevent its recurrence.
The plants included in this study were nor-
mally capable of maintaining a residual dissolved
oxygen concentration in their aeration compart-
ments of 1.0 mg per liter or better, except in
the area of raw waste introduction. The plants
all used diffused aeration. The most important
factors in any aeration system are mining and
oxygen transfer. Good mixing will prevent the
deposition of solids In the aeration compartments
and promote adequate oxygen transfer. Periodi-
cally, as part of plant maintenance procedures,
the bottom of each aeration compartment was
checked with the hopper scraper to determine if
deposition of sludge was taking place. The
presence of such deposits could be an indication
that one or more of the diffusers is not func-
tioning or is improperly located. Diffuser mal-
function may cause a reduction in dissolved
oxygen concentration in the aeration compart-
ment. A dissolved oxygen probe can also be
used to reveal diffuser problems or the lack of
sufficient air flow from the compressors. Both
methods were used during the study of CS plants.
NITRIFICATION
No significant reduction in nitrogen was ob-
served in this phase of the study. Conversion
of ammonia to nitrate occurred to some degree,
as shown in Tables II through V. The nitrifi-
cation-denitrification phenomenon1 was not a
problem in the CS units under the regime in
which they were operated.
SOLIDS SEPARATION
Separation of solids by gravitational settling
of suspended particles that are heavier than
water is one of the basic factors in the natural
purification of water courses and in water and
wastewater treatment processes. The gravita-
tional effect is defeated when the suspended
solids are lighter than water, or when the up-
ward velocity of flow in any area of the settling
basin exceeds the rate of settling.
In activated sludge treatment plants and
their modifications, such as extended aeration
or contact stabilization, the activated sludge
particles in the mixed liquor form floes that
aid in establishing a uniform rate of settling
near the surface of the clarifier. At the point
at which the particles decelerate to a lower
settling velocity, an almost discrete solids-liquid
interface forms. The zone below this interface
is called the hindered settling zone, and its height
above the bottom of the clarifier is affected by
the concentration of solids in the mixed liquor.
Below the hindered settling zone, the settling
rate decreases as a result of the increasing
density and viscosity of the suspension surround-
ing the floe, and the transition zone is formed.
At some critical concentration, the solids begin
to compact and the compression zone occurs.
Zone settling is represented as the initial
constant settling rate of the sludge-liquid inter-
face which occurs in a batch sedimentation test.
It is a function of the initial concentration of
solids and of the physical and chemical proper-
ties and flocculating characteristics of the bio-
mass. It can be determined in the laboratory
and used to calculate clarifier overflow rate
limitations. The overflow rate is usually reported

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11
in terms of gallons per sq.ft. of clarifier sur-
face area per day. For settling to occur, the
overflow rate must be less than the measured
rate of zone settling.
One of the parameters which is useful in
management of the treatment process is the
sludge volume index (SVI). It is defined as the
volume in milliliters which is occupied by one
gram of mixed liquor solids after a fixed settling
period, and is calculated from the following ex-
pression:
svi = Sett;„So1- x 1000
SS
(3)
where:
Sett. Sol.
SS
Volume occupied by 1 liter of
mixed liquor solids after 30 min.
settling time, ml
Suspended solids in mixed liquor,
mg per liter
Sludge density index (SDI) is the reciprocal of
the SVI, times 100.
SKIMMING
The four- CS plants used in this study had
various forms of skimming devices for remov-
ing floatable solids. One of the plants had a
mechanical skimming paddle that skimmed the
floatables on the surface of a rectangular clari-
fier from one end to the other, where a com-
bination skimmer and air lift transferred them
to the returif sludge channel. They then were
mixed with the return sludge and conveyed back
to the stabilization compartment, or to the aero-
bic digester.
Skimmers can increase the surface overflow
rates beyond safe limits during peak flows, and
therefore should not be operated during these
periods. This means that controls should be
available on the skimming devices so that the
rate of skimming can be adjusted or entirely
shut off.
TEMPERATURES
All of the CS plants were operated under
both summer and winter temperature conditions.
There was no significant drop in BOD removals
during the coldest periods. One clarifier which
was installed above grade had ice forming in
the bottom during the early subfreezing periods.
Placing straw around the bottom half of the
clarifier ended this problem for the remainder
of the winter months. The other above grade
plants were also protected in this manner.
MIXED LIQUOR AND STABILIZATION COM-
PARTMENT SOLIDS
Various levels of solids have been utilized
in the contact and stabilization compartments of
CS plants. During this study, one plant was
operated at a comparatively low solids level in
order to maintain a sludge age of three days or
a BOD loading of 0.3 lbs. per lb. of aerating
solids. The mixed liquor concentration at this
loading was approximately 1000 mg per liter.
The plant operated satisfactorily in terms of
solids removals, but BOD removals were below
the solids removals. This would be expected
when short contact times or low solids levels
prevail.
At the other extreme, a 400,000 GPD CS
plant located in Penetanguishene, Ontario,!1 is
routinely operated with a mixed liquor concen-
tration of 4000 to 7000 mg per liter and a 100
percent return sludge rate. The organic loading
on this plant is low with a BOD5 averaging about
100 mg per liter. BOD removal is approxi-
mately 84 percent. Reported performances of
other plants in various locations are shown in
Table I.
The strength and characteristics of the raw
waste, tank capacities, and return sludge rates
all affect the solids levels in a contact stabili-
zation plant.
SOLIDS WASTING
Contact stabilization plants require periodic
solids wasting. Solids are synthesized at a
relatively rapid rate and will accumulate in the
system unless a portion of the return sludge is
directly wasted from the process, or diverted to
an aerobic digester. Long residence periods in
the digester will reduce the solids content of the
sludge by oxidation and endogenous respiration.
This process, however, is slow, and, as a result,
some wasting of solids to a drying bed, a hold-
ing tank or a tank truck should be anticipated.
Solids in the digester can be concentrated by
decant thickening, with the supernatant liquor
being returned to the stabilization compartment.
The thickened sludge can also be discharged
from the digester at this time. Continuous re-
turn of the supernatant can be achieved by a
separator in the digester which provides for
overflow of the supernatant back into the stabili-
zation compartment. The digesting sludge which

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TABLE I
PERFORMANCE OF CONTACT STABILIZATION PLANTS
BOD5
mg/Iiter
Detention Time,
Hours
Suspended Solids,
mg/Iiter
Return
Sludge
BOD 5
Reduction
Type of Waste and Location Code
Influent
Contact
Stabilization
Contact
Stabilization
Percent
Percent
Municipal Sewages-
97
1.5
4.0
7050*
13,000**
100
84.0*
Municipal Sewage2
358
0.52
5.2
2540
6900**
56
94.1
Municipal Sewage3
108
1.30
4.25
2239
8629
44
88.0
Municipal Sewage3
210
0.18
1.00
2500
4500
100
90.0
Sewage and Textile Waste4
225
0.60
5.50
2950
6950
67
77.0
Sewage and Textile Waste4
320
1.10
3.10
3326
7650
68
88.0
Tomato Cannery Waste5
412
0.80
1.60
2250
3600
100
85.0
Tomato and Apple Waste5
492
1.00
2.00
2500
4400
100
89.7
Tomato and Peach Waste5
740
0.65
1.30
3600
5900
100
58.0
~Average Value
~~Suspended Solids Estimated from Return Sludge Rate
Location Code:
Source of Data:
1.	Penatanguishene, Ont.
2.	Austin, Texas
3.	Little Ferry, N.J.
4.	Cone Mills, Greensboro, N.C.
5.	Chambersburg, Pa.
1.	Jones, Dr. P. H., "Water and Pollution Control" (Canadian), Feb., 1968, Page 31.
2.	Ullrich, A. H. and Smith, Mansel W., "Sewage and Industrial Wastes," Vol. 29, No. 4, (April,
1957), Page 411.	*3, 4, and 5 are from
^3. Zablatsky, H. R., Cornish, M. D. and Adams, J. K. ( "Biological Waste Treatment"
t4. Jones, F. L.; Alspaun, T. A.; and
^5. Eckenfelder, W. W., Jr. and Grich,
id Adams, J. K. I "Biological Wasl
Stokes, H. B. \ Eckenfelder, W.
, E. R.	' D. J., Pergamon
W., Jr. and O'Connor,
Press, 1961, Page 213.

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13
settles in the separator can then flow by gravity
or be pumped back into the digester,13
Two of the contact stabilization plants studied
had separators installed in the digesters, but
separation of the solids into clear supernatant
and digested sludge did not always occur. This
resulted in some accumulation of solids in the
stabilization compartment, since the return sludge
which was discharged into the digester would
flow back into this compartment. In addition,
the separators did not always prevent floatable
solids from returning with the supernatant.
Manual decanting of supernatant is one method
for preventing any solids except those in the
supernatant from flowing back. This is accom-
plished by shutting off the air for approximately
two hours, in order to allow the digester liquor
to separate into digesting sludge and relatively
clear supernatant, which is then decanted.
Records kept on the wasting of sludge from
the aerobic digesters indicate that more sludge
is produced and not completely oxidized when
the solids concentration in the aeration com-
partments is low. This is due to the fact that
the food to microorganism ratio is greater when
the active sludge mass or solids concentration
is lower, and the net sludge accumulation in-
creases as a result.
CHECK LIST FOR ROUTINE MAINTENANCE
AND OPERATION OF CONTACT STABILIZA-
TION PACKAGE SEWAGE TREATMENT PLANTS
1.	Determine that power is being supplied to
the unit and that all pumps and motors are
operating or operational as required.
2.	Grease and oil equipment, clean air filters,
check pressure relief valves, and perform
related work as recommended by the manu-
facturer.
3.	Hose down walkways, sideboards, and splash-
spray zones as needed.
4.	Check air lifts and return lines for clogging.
5.	Operate skimming device(s) as needed.
6.	Perform recommended simple laboratory
analytical procedures and adjust operating
variables as indicated. The recommended
or required analytical procedures for a given
plant may include, but are not necessarily
limited to, any or all of the following de-
pending on the requirements of the particu-
lar regulatory agency having jurisdiction
and the needs of the installation:
a.	Influent, effluent, mixed liquor, stabiliza-
tion compartment, return sludge, and di-
gester suspended and volatile suspended
solids. (Rapid photometric methods for
the determination of suspended solids
have been found to be reliable.)
b.	Influent and effluent five day biochemical
oxygen demand.
c.	Mixed liquor, stabilization compartment,
digester, and effluent dissolved oxygen
concentration.
d.	Influent, mixed liquor, stabilization com-
partment, digester, and effluent pH and
temperature values.
e.	Mixed liquor, stabilization compartment,
and digester thirty minute settled volume
determinations (SV30).
7.	If effluent disinfection is required, insure
that an adequate supply of disinfectant is
available and that the feed device is operat-
ing properly.
8.	Scrape down the insides of clarifier hopper
at least daily.
9.	Remove litter from the plant area and per-
form grounds keeping operations as required.
10.	Repaint exposed painted surfaces as needed.
11.	Inspect aeration equipment thoroughly in-
cluding diffusers, impellers, and the like
which may be submerged. While this may
not need to be done as frequently as some
other items of maintenance, it should not be
overlooked and the manufacturer's recom-
mendations should be carefully followed.
12.	Remove and dispose of, in a sanitary manner,
any material that may accumulate on inlet
bar screens and the like. Check and clean
the comminutor if one is a part of the plant.
13.	Check, clean, and maintain any such plant
support units such as a sand bed, sludge
holding tank, trash trap, and the like.
14.	Replace worn parts or equipment as needed.
Pay particular attention to pulley belts and
the like which may require relatively fre-
quent replacement. Maintain a small stock
of such items including belts, fuses, heaters,
and similar items which are essential to
plant operation.
15.	Maintain recommended solids level in stabili-
zation compartment for any given return
sludge rate by wasting a portion of return
sludge to digester.

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14
16. Waste solids from the system as required to
maintain the solids within the desired range.
It should be emphasized that daily and con-
scientious maintenance and operational attention
is required in order to achieve the certified
level of performance.
Most of the routine chemical and physical
determinations in this study were carried out
in accordance with the provisions of the 12th
Edition of Standard Methods for the Examination
of Waste and Wastewater.14
III. PERFORMANCE CRITERIA
AND
THE STANDARD PERFORMANCE EVALUATION METHOD
The findings detailed in Section II have been
translated into performance evaluation criteria
for contact stabilization package sewage treat-
ment plants. These criteria are as follows:
1.	The plant shall display a sustained contact
and stabilization suspended solids buildup
during the startup period.
2.	The plant, when its design loading is not
exceeded, shall achieve a sustained design
BOD5 removal after the process reaches
maturity.
3.	The aeration system shall be capable of
transferring sufficient oxygen to meet peak
design loads in addition to any other de-
mands made on the system such as main-
taining the contents of all aeration compart-
ments completely in suspension, the opera-
tion of the air lifts, and the like.
4.	The aeration system, when operating at the
midpoint of its rated capacity, shall have
such flexibility or admit of such adjustment
as not to affect adversely the process effi-
ciency.
5.	The solids separation system shall be capa-
ble of separating and retaining within the
plant sufficient solids so as not to affect
adversely the over-all process efficiency.
6.	The floatable solids retention and skimming
system of the solids separation compartment
shall be capable of retaining and returning
to the aeration compartments sufficient
floatables in such a way as not to affect
adversely the over-all process efficiency.
7.	When subjected to cold weather operating
conditions after reaching process maturity,
the plant shall achieve essentially the same
degree of process efficiency as at other
times of the year providing that it and its
process support equipment are protected
from freezing.
8. The plant shall have such flexibility as to
permit ready maintenance of the desired
range of suspended solids under aeration.
Based on the fundamentals of the processes
involved, the findings of these studies, the in-
vestigations of others as cited, and the per-
formance criteria developed, the following method
for the evaluation of the performance of contact
stabilization package sewage treatment plants has
been devised:
A.	PREQUALIFICATION
1.	Prior to the performance evaluation of
any contact stabilization package sewage
treatment plant, the manufacturer of such
plant shall supply to the testing agency,
group, or organization sufficient evidence
to establish to the satisfaction of such
agency, group, or organization the basic
feasibility of the plant with respect to its
intended service.
2.	As a part of his application for perform-
ance evaluation of a particular plant model
or model series, the manufacturer shall
set forth the basic description of the plant
and design data including complete draw-
ings and specifications for the plant and
all of its equipment and appurtenances.
The application shall be accompanied by a
complete installation, operation, and main-
tenance manual which includes a thorough
discussion of the process fundamentals
involved.
B.	GENERAL TEST CONDITIONS AND
REPORTING
1. The waste utilized as feed for the unit
during these evaluations shall be a com-
minuted domestic waste free of any

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15
industrial waste which in any way might
affect the performance of the plant being
tested. Stale or septic sewages shall not
be utilized. The sewage utilized as feed
for the plant shall be sampled *daily dur-
ing the test period. The samples shall
be twenty-four hour samples composited
strictly according to the plant influent flow
pattern in use at the time of sampling.
Analysis of these samples must establish
that the characteristics of the waste uti-
lized as feed during the test conformed
to the following:
a.	Five day biochemical oxygen demand
(BOD5) - a mean concentration based on
all data of 200 mg per liter plus or
minus 30 percent, provided further that
none of the samples yield a BOD5 value
of less than 50 mg per liter or more
than 400 mg per liter.
b.	Suspended solids (SS) - a mean concen-
tration based on all data of 220 mg per
liter plus or minus 30 percent, provided
further that none of the samples yield
an SS value of less than 55 mg per
liter or more than 440 mg per liter.
c.	Percent volatile suspended solids - no
values less than 65 or more than 85
percent.
d.	Temperature - no values less than 10
degrees or more than twenty-five de-
grees Centigrade.
e.	pH - no values less than pH 6.0 or
greater than pH 8.0.
2.	All samples shall be strictly taken and
preserved as provided in the latest edition
of Standard Methods for the Examination
of Water and Wastewater14 except as may
be otherwise provided herein.
3.	All analytical methods employed shall	be
those set forth in the latest edition	of
Standard Methods14 except as may	be
otherwise provided herein.
4.	During the test period the plant shall be
operated and maintained according to the
manufacturer's instructions except as these
may in any way be in conflict with the
provisions of the Standard Performance
Evaluation Method in which case the pro-
visions of the Method shall be complied
with.
5.	The Standard Evaluation Method can be
carried out at any time of the year pro-
vided that:
a.	The plant being tested has reached
process maturity as defined in 7a. be-
fore the solids under aeration fall to
8.0° C.
b.	During the test period the temperature
at no time falls below 5.0° C.
c.	The plant and its equipment is pro-
tected from freezing, if the test is
conducted during cold weather.
d.	The temperature of the aerator con-
tents at no time exceeds 30.0° C, if the
test is conducted during warm weather.
6.	The performance evaluation of a plant
shall be independent of its design and
construction except that structural weak-
ness or defects and failures of its process
support equipment noted during the test
shall be reported as a part of the test
results.
7.	The Standard Performance Evaluation
Method shall consist of two main parts:
a.	Startup Performance Evaluation: the
period between actual startup of the
plant and its achievement of a MLSS
concentration value designated by the
manufacturer. The stabilization com-
partment suspended solids concentration
and the return sludge SS concentration
must be adequate to sustain the MLSS
minimum under the variable flow pattern
as defined in this report.
b.	Variable Flow Pattern Performance
Evaluation: a period of 18 consecutive
weeks on a 5 day per week basis be-
ginning with the plant's achievement of
the MLSS levels as defined in 7a., plus
any other conditions set forth in Para-
graph 7.
c.	During the variable flow period, the
MLSS concentration will be adjusted to
the range recommended by the manu-
facturer, plus or minus 20 percent. The
plant will be hydraulically loaded at its
rated dally capacity and in accordance
~The term daily shall refer to Sunday through Thursday. During the performance evaluation of
each plant, additional composite samples of the influent and effluent shall be taken on Friday and
Saturday, but analyzed only for BODg and suspended solids.

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with an increased or decreased hourly
flow rate as outlined in Section F.
The rate of return sludge from the
settling compartment to the stabiliza-
tion compartment shall be in accord-
ance with the manufacturer's recom-
mended rates, plus or minus 10 per-
cent. The wasting of return sludge to
the digester and the digested sludge
from the digester shall be carried out
at a rate that will maintain the range
of solids required in the contact and
stabilization tanks.
8.	The information and data developed during
each phase will be reported and sum-
marized separately in the certified per-
formance evaluation report.
9.	The certified performance evaluation re-
port shall be signed by the chief corporate
officer of the testing organization and by
the official of the organization in respon-
sible charge of the evaluation. The re-
port shall contain but not necessarily be
strictly limited to the following:
a.	All data and information developed in
detail during the evaluation. This in-
formation and data shall be grouped
according to the two main parts of the
evaluation and used only in the calcula-
tion of the results of section to which
the data pertains. Probability plots for
SS, BOD5, and COD shall be included.
b.	A certification statement signed by the
testing organization officers specified
above which states that the Standard
Performance Evaluation Method was
used in the testing of the plant, that
no deviations from this method were
made during the test, and that the re-
sults reported are true to the best of
his information and belief.
STARTUP PERFORMANCE EVALUATION
1.	The plant shall be completely assembled
according to the manufacturer's directions
and all of its equipment checked to deter-
mine that it is free of mechanical defects
and operable. The plant shall be examined
to determine that it is structurally sound.
All defects noted shall be reported. If
no defects are detected this fact shall be
reported.
2.	If no defects are detected and the plant
is judged to be structurally sound, it shall
be filled with domestic waste (previously
defined under B-l) as rapidly as possible
and immediately placed into full operation.
Sampling and testing shall begin as soon
as the plant is filled and placed into opera-
tion and shall continue until the end of
the two parts of the Standard Performance
Evaluation Method.
3.	Aerator contents residual dissolved oxygen
levels shall be maintained between 1.0 and
3.0 mg per liter as nearly as possible.
In no case shall the residual dissolved
oxygen level be permitted to fall below
0.5 mg per liter except in the immediate
vicinity of raw waste introduction. In the
event these minimum dissolved oxygen
levels cannot be maintained, the test shall
be suspended until corrective measures
are taken.
4.	The raw domestic waste utilized as feed
for the unit shall have been passed through
a 1/4 inch slot comminutor prior to enter-
ing the unit. During this phase of the test
it shall be applied in a variable flow pat-
tern as defined elsewhere in this method.
5.	Daily twenty-four hour influent and effluent
samples composited strictly according to
the influent flow pattern shall be collected.
The frequency of sampling to make up the
required composites shall be at least once
hourly.
6.	The rate of flow applied to the unit under
test shall be measured and recorded con-
tinuously and the volume of waste applied
daily shall be totalized and reported. The
total volume of waste applied to the unit
daily shall be the rated capacity of the
unit, plus or minus five percent.
7.	The daily influent and effluent composites
shall be subjected to laboratory analysis
(except as noted in Section B-l) to deter-
mine the following:
a.	Five day biochemical oxygen demand
(mg/1).
b.	Suspended and volatile suspended solids
(mg/1).
c.	pH,
The temperature of the influent and efflu-
ent shall be determined at maximum flow
period and at 8:00 a.m.
8.	At the midpoint of the maximum flow
period a grab sample of the mixed liquor,
digester and stabilization compartment
contents shall be taken as near the center
of each aeration compartment as possible.

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A return sludge grab sample shall be
taken at the same time, if possible. Also,
at the same time, the dissolved oxygen
content and temperature of the contact
aeration compartment contents in the im-
mediate vicinity of the raw waste intro-
duction point, and the immediate vicinity
of the compartment exit, shall be deter-
mined. Also, a dissolved oxygen content
and temperature shall be taken at the
center of the stabilization compartment
and digester. The mixed liquor, stabili-
zation compartment, digester, and return
sludge samples shall be subjected to labo-
ratory analysis to determine the following:
a.	Suspended and volatile suspended solids
(mg/1)
b.	pH.
c.	Thirty minute settled volume (SV30,
ml.). (Sludge volume index computed
for mixed liquor samples only.)
9. As soon as the mixed liquor suspended
solids concentration reaches the level
recommended by the manufacturer, plus
or minus 20 percent, the startup evalua-
tion shall be terminated and the variable
flow pattern evaluation shall start at once
without any interruption of feed to the
unit or lapse of time.
D. VARIABLE FLOW PATTERN PERFORMANCE
EVALUATION
1.	The provisions of Section C, subsections
3, 4, 5, 6, and 8 shall be complied with
during this phase of the evaluation.
2.	The period of variable flow pattern per-
formance evaluation shall be the next
consecutive 18 - 5 day weeks following the
startup performance evaluation period.
3.	The daily influent and effluent composite
samples (see B-l and C-5) shall be sub-
jected to laboratory analysis to determine
the following:
a.	Five day biochemical oxygen demand
(mg/1, BOD 5).
b.	Suspended and volatile suspended solids
(mg/1).
c.	pH.
d.	Methyl orange alkalinity (mg/1).
e.	Ammonia-nitrogen (mg/1, NH3-N).
f.	Total phosphate (mg/l-P),
g.	Chemical oxygen demand (mg/1, COD).
17
In addition to the above, the daily effluent
composite shall also be subjected to the
following analyses:
h.	Nitrate-nitrogen (mg/1, NO3-N).
i.	Nitrite-nitrogen (mg/1, NO2-N).
j. Dissolved oxygen (mg/1).
The following analyses shall be made on the
influent composite two times per week:
k. Nitrate-nitrogen (mg/1, NO3-N).
1. Nitrate-nitrogen (mg/1, NO2-N).
4.	The temperature of the plant influent and
the effluent shall be determined during
both the maximum flow period and at
8:00 a.m.
5.	The digester shall be sampled in accord-
ance with Section C-8 and the following
determinations or analyses made:
a.	Return sludge wasted to digester (gals.).
b.	Digested sludge wasted from the di-
gester (gals.).
c.	Supernatant when wasted from the sys-
tem (gals.).
d.	BOD 5 (mg/1) of supernatant when wasted
from the system.
e.	Suspended solids and volatile suspended
solids (mg/1) in:
1.	Return sludge
2.	Wasted digester sludge
3.	Supernatant from digester when
wasted from system
f.	SV30 of digesting sludge (two times per
week)
g.	Total phosphates (mg/l-P) in wasted
digester sludge or in supernatant wasted
from system.
h.	Dissolved oxygen (mg/1) and tempera-
ture (°C) in digester as specified in
Section C-8.
E. DEVIATIONS FROM STANDARD METHODS
The following deviations from the procedures
described in Standard Methods for the Examina-
tion of Water and Wastewater14 may be used for
suspended solids determinations:
1.	Glass fiber filter mats may be used in
place of asbestos in a Gooch crucible.
2.	Spectrophotometric measurements may be
used.

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18
F. FLOW PATTERNS	Hour	Variable Flow Pattern
When
the variable flow pattern
is in effect,
9:00AM
-
10:00AM
4.5
the percentage of the
total daily
flow
applied
10:00AM
-
11:00AM
6.5
during each hour of the day shall be as
follows:
11:00AM
-
12:00N
6.5





12:00N
-
1:00PM
6.5
Hour
Variable
Flow
Pattern
1:00PM
-
2:00PM
6.5





2:00PM
-
3:00PM
4.5
12;00M -
1:00AM

1.5

3:00PM
-
4:00PM
4.5
1:00AM -
2:00AM

1.5

4:00PM
-
5:00PM
4.5
2:00AM -
3:00AM

1.5

5:00PM
-
6:00PM
4.5
3:00AM -
4:00AM

1.5

6:00PM
-
7:00PM
5.0
4:00AM -
5:00AM

2.5

7:00PM
-
8:00PM
5.0
5:00AM -
6:00AM

2.5

8:00PM
-
9:00PM
5.0
6:00AM -
7:00AM

3.0

9:00PM
-
10:00PM
5.5
7:00AM -
8:00AM

3.0

10:00PM
-
11:00PM
5.0
8:00AM -
9:00AM

4.0

11:00PM
-
12:00M
5.0
IV. RESPONSIBILITIES
The proper use and performance of a pack-
age sewage treatment plant is dependent on the
many parties that are to be involved in its de-
sign, manufacture, application, operation, and
supervision. The responsibilities of each per-
son, agency, or organization were outlined in the
National Sanitation Foundation report on Extended
Aeration Sewage Treatment Plants1 and are re-
peated in this report with the modifications
necessary for the contact stabilization process.
A. THE MANUFACTURER-SUPPLIER
1.	It is the responsibility of those who manu-
facture and supply package sewage treat-
ment plants to insure the durability and
workability of the plant's structure and
process support equipment. It is further
their responsibility to guarantee such
durability and workability to the buyer-
owner.
2.	It is the responsibility of the manufacturer-
supplier to define and warrant the over-
all process efficiency to be expected in
connection with the treatment of a stated
waste having specified characteristics,
excepting that such warranty is valid only
so long as the responsibilities of the other
parties are met by them.
3.	The manufacturer-supplier should provide
the services of a qualified technician who
is thoroughly knowledgeable concerning
the equipment and processes involved to
check the installation of the plant, super-
vise the startup of the plant, and in-
struct the buyer-owner's operator in the
proper operation and maintenance of the
plant. Such a qualified individual should
also be supplied for a recheck of the plant
after the mixed liquor suspended solids
concentration recommended by the manu-
facturer has been achieved to insure that
the plant is operating properly, and to
further instruct the buyer-owner's opera-
tor. Technical service in addition to the
above should also be provided at the
owner's request and at his expense, ex-
cept as any guarantee or warranty be-
tween the parties may apply.
4.	If the plant is installed by the manu-
facturer-supplier he should guarantee such
installation. If the plant is installed by
other than the manufacturer-supplier he
should supply the installer with adequate
installation instructions.
5.	The manufacturer-supplier should pro-
vide the buyer-owner at the time of plant
startup with a complete manual outlining
the proper operation and maintenance
procedures including adequate drawings
and descriptive literature so as to render
these matters understandable to a quali-
fied operator of such plants. This manual
should also include a complete but readily
understood discussion of the principles
involved in the processes employed by the
plant, as well as a thorough description
and discussion of the test methods re-
quired for the intelligent operation of such
processes.
6.	Also at the time of startup of the plant,
the manufacturer should supply the owner

-------
19
with a complete replacement parts list
for the plant and all of its equipment in-
cluding up-to-date information on the
availability of replacement parts, parts
suppliers, and any known applicable sub-
stitute parts. Further, such parts list
should contain a recommendation concern-
ing the types and quantities of spare parts
which the buyer-owner should maintain on
hand to facilitate emergency repairs. Any
unusual tools that might be required for
the proper repair or maintenance of the
plant and its equipment should also be
brought to the owner's attention by suita-
ble mention in the parts list or mainte-
nance manual. The availability of re-
placement parts for a specified period of
time should be a part of the manufacturer -
supplier's warranty to the buyer-owner.
7. It should be the responsibility of the
manufacturer-supplier to furnish certified
copies of the Standard Performance Evalu-
ation Method results available pertaining
to the particular plant model series in-
volved as a part of any submission of
plans and specifications to a reviewing
regulatory agency or official that may be
required by law or regulation. It should
be his further responsibility to provide
the same information to the buyer-owner
and his engineering consultant.
B. THE BUYER-OWNER
1.	It is the responsibility of those who buy,
own, and operate package sewage treat-
ment plants to secure or provide the
services of a competent engineer to set
up specified critical flow ranges and load-
ings for sizing the plant within the general
or specific requirements of the regulatory
agencies or officials having jurisdiction,
to determine plant location, and to per-
form related engineering services as out-
lined herein.
2.	The owner of a package sewage treatment
plant has the responsibility of providing
as the plant operator a person who is
conscientious, of adequate intelligence,
and in good physical condition and who,
therefore, is capable of learning to oper-
ate and maintain the plant within a rea-
sonably short period of time, given ade-
quate instruction.
3.	In the event the original plant operator
leaves the employ of the owner it is the
owner's responsibility to secure immedi-
ately a replacement who has the same
attributes as those set forth for the origi-
nal operator and to provide the new op-
erator with suitable training for the job.
4.	It is the responsibility of the buyer-owner,
through his engineering consultant, to se-
cure from the agencies or officials having
jurisdiction the approvals, permits, or
licenses required by law or regulation for
the construction and operation of the plant
unless this is specifically delegated by
contract to another of the parties.
5.	It is also the responsibility of the owner
to give general supervision to his opera-
tor and to provide the operator with all
necessary tools, materials, parts, and the
like required for the proper operation and
maintenance of the plant. It should be
noted in this connection that the owner
himself is ultimately responsible for the
performance of the plant.
6.	The owner of a package sewage treatment
plant is responsible for any failure of
the plant to perform as set forth in the
manufacturer-supplier's warranty or as
required by law or regulation when such
failure is the result of organic or hy-
draulic loadings or waste characteristics
which differ from those in the warranty.
It should be further noted that the owner
is, in most jurisdictions, solely responsi-
ble for any failure of the plant to per-
form as required by law or regulation
regardless of cause.
C. THE CONSULTING-SUPERVISING ENGINEER
1.	The owner's engineer is responsible for
the setting of organic and hydraulic load
levels to be applied to the plant, and for
selecting the plant(s) which in his best
judgment are capable of reliably treating
the waste at these loadings in such a
manner as to conform with all applicable
laws and regulations.
2.	Not only is the engineer responsible for
defining the load levels to be treated, but
he is further responsible for defining both
the organic and hydraulic pattern of load-
ing and the specific characteristics of the
waste to be treated. It is the additional
responsibility of the engineer to disclose
fully all of these characteristics, load-
ings, and conditions to the manufacturer -
supplier and the buyer-owner as well as
the regulatory agencies and officials hav-
ing jurisdiction.

-------
20
3.	The engineer is responsible for determin-
ing the location of the plant, the design
of adequate inlet and outlet sewers, the
design of required auxiliary structures
and appurtenances as required, as well
as necessary power lines and the like.
4.	It is ordinarily the responsibility of the
engineer to represent the buyer-owner in
securing the required permits and licenses
or to delegate this by contract or agree-
ment to another of the parties.
5.	It is the responsibility of the engineer to
oversee generally and to inspect the in-
stallation and construction of the plant and
its appurtenances specified in the contract
drawings, and to require such corrections
to be made by the manufacturer-supplier/
installer as may be necessary in order
to conform to the approved drawings and
specifications.
D.	THE INSTALLER-CONTRACTOR
1.	In the event that an installer-contractor
rather than the manufacturer-supplier in-
stalls the package sewage treatment plant,
it is the responsibility of such installer-
contractor to make the installation in ac-
cordance with the manufacturer-supplier's
instructions.
2.	It is the further responsibility of the
installer-contractor to insure that good
workmanship standards are maintained
and that the over-all process efficiency is
not limited by any defect in installation,
E.	THE REGULATORY AGENCY-OFFICIAL
1.	In the course of the normal discharge of
their duties, regulatory agencies and offi-
cials having jurisdiction should carefully
review all of the available information
concerning the package sewage treatment
plant proposed for use in each particular
case. This review should include the
Standard Performance Evaluation Method
results which pertain to the particular
plant model or model series which is
being proposed. After such review it
should finally be the responsibility of the
agency-official to make a value judgment
as to the capability of the proposed plant
to treat the specific waste, in view of the
loadings and loading pattern, to the degree
required in each case.
2.	Following the installation of the plant, the
regulatory agency-official should normally
make an inspection of the plant. The
agency-official should require the owner
to submit for review certain test results
and operating reports and should conduct
such tests and inspections as required to
insure that the performance of the plant
meets the waste treatment requirements
in each case.
3. In the event that the agency-official deter-
mined that the plant was not meeting the
waste treatment requirements, the owner
should be required to take the necessary
steps to insure the required level of
treatment.
F.	THE PLANT OPERATOR
1.	The plant operator is responsible for the
conscientious and proper operation and
maintenance of the plant under the over-
all responsibility of the owner.
2.	It is also the responsibility of the operator
to make such observations and to conduct
such tests as may be required for the
proper operation of the processes involved
in the plant, to record the results of such
observations and tests, and to make these
results known to the owner who, further,
may be required to make them known to
the regulatory agency-official.
3.	The operator has the responsibility of ad-
vising the owner as to the tools, supplies,
and parts which may be required from
time to time for the proper operation and
maintenance of the plant and to do so in
sufficient time to insure that such items
are available when needed.
4.	It is a prime responsibility of the opera-
tor to become fully acquainted with the
plant and all of its appurtenances, espe-
cially including the processes involved in
the treatment system, and to take full
advantage of all training offered by the
manufacturer-supplier, owner, and regu-
latory agency-official.
5.	The operator is responsible for informing
the owner at once of any process inter-
ruptions or observed losses of efficiency
of such a nature or extent as to render
the waste treatment level less than that
required by law or regulation.
G.	THE PERFORMANCE EVALUATION ORGANI-
ZATION
1. It is the responsibility of the agency,
group, or organization which conducts

-------
21
plant performance evaluations to do so
strictly in accordance with the Standard
Performance Evaluation Method and to
certify the results of such testing to the
manufacturer of the plant. In addition to
the detailed test results a data summation
shall be supplied.
2. Standard Performance Evaluation Method
data should be used by a recognized test-
ing organization in a certification pro-
gram. Such a program would make
standard performance information readily
available for use by those concerned in
making judgment decisions regarding pack-
age sewage treatment plants.
From the foregoing seven sections on the
responsibilities of the various parties concerned
in the design, manufacture, testing, use, and
supervision of package sewage treatment plants,
it is clear that each of these parties influences
and contributes to the final over-all plant per-
formance actually observed in the field. In the
final analysis, no one of these factors can be
said to be truly more important than any other
for it requires the best efforts of all concerned
to achieve the desired result.
V. DISCUSSION
This report entitled, "Package Sewage Treat-
ment Plants Criteria Development, Part II: Con-
tact Stabilization" completes the three year
study conducted by the National Sanitation Foun-
dation on package plants. The first report on
Extended Aeration Package Plants1 was released
in September 1966 and contains, in addition to
information on the development of criteria for
the performance evaluation of extended aeration
plants, many details on the test equipment, re-
search site layout, and laboratory procedures.
Much of the latter material has been omitted
from this report.
Sometime during the contact stabilization
phase of this study, the "treatability" character-
istics of the raw waste changed. Symptoms of
the problem included: (1) production of a layer
of tenacious "frothy solids" on the top of aera-
tion chambers; (2) development of sludge parti-
cles which settled quite slowly; (3) production
of rising sludge in the settling compartment;
(4) discharge of a turbid effluent which contained
as suspended matter some of the very fine and
light unsettled solids or rising sludge. Meticu-
lous operational management of package plants
could not prevent these manifestations. During
this same period, the new and efficiently oper-
ated activated sludge plant serving the City of
Ann Arbor was similarly affected, and its process
efficiency dropped below the anticipated levels.
The factor(s) causing the upset were not identi-
fied, but every effort is being made to prevent
its recurrence. During this period the treat-
ment efficiencies of all four contact stabilization
plants in the study were comparable with that
of the Ann Arbor plant. In 1966 and 1967, the
Ann Arbor plant recorded mean reductions in
BOD and suspended solids of 88 to 90 percent.
The purpose of this phase of the study was
to develop performance criteria for contact sta-
bilization type package sewage treatment plants.
It should be emphasized that the data which ap-
pears in this report was collected during the
period of criteria development and not under
necessarily normal operating conditions. In
order to establish acceptable minimum and
maximum levels of performance, operating
parameters were varied somewhat from those
described in Section m of this report. No data
selection was practiced in preparing Tables II
through V. All results are reported.
Operation of these plants indicated that this
process can satisfactorily remove the major
portion of both suspended solids and the bio-
chemical oxygen demand in domestic wastewater
without the creation of an odor or noise nuisance
in the surrounding area. The data which was
collected did not disclose any variation of per-
formance capability attributable to plant capacity.
VI. ACKNOWLEDGMENTS
This project was made possible by Demon-
stration Grant WPD-74 from the Federal Water
Pollution Control Administration's Research and
Training Grant Program. The research site
for the studies was also made possible by the
Federal Water Pollution Control Administration's
granting permission for the use of a portion of
their projected Midwest Regional Laboratory
property.

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22
The manufacturers listed below supported
the contact stabilization plant criteria develop-
ment project by providing package treatment
plants of this type for the study:
Chicago Pump Co., Hydrodynamics Division
FMC Corporation
Chicago, Illinois
Davco Manufacturing Company
Thomasville, Georgia
Defiance, Incorporated
Tallevast, Florida
Water Pollution Control Corporation
Milwaukee, Wisconsin
The National Sanitation Foundation greatly appre-
ciates the aid that these companies generously
gave to the project.
The Foundation acknowledges the cooperation
and support of the City of Ann Arbor through
its Superintendent of the Ann Arbor Wastewater
Treatment Plant, Mr. Richard Sayers. The city
provided laboratory and office space for the
National Sanitation Foundation's project staff.
The untimely death of Mr. C. Preston Witcher,
the former Superintendent of the Ann Arbor plant
and an advisor to the Technical Committee, oc-
curred in April 1968. The aid that Mr. Witcher
gave in the initial stages of the project is deeply
appreciated.
The direction that the Technical Committee
has given to the contact stabilization plant cri-
teria development project is gratefully acknowl-
edged. The committee's members from industry
were chosen from the organizations that provided
plants for the study. The committee's member-
ship is listed below:
Mr. Donald M. Pierce, Chairman
Chief, Wastewater Section
Division of Engineering
Michigan Department of Public Health
Lansing, Michigan 48914
Mr. George H. Eagle, Vice Chairman
Chief Engineer
Division of Engineering
Ohio Department of Health
Columbus, Ohio 43216
Mr. Eagle was represented by
Mr. L. T. Hagerty at two meetings of the
committee
Mr. Sidney A. Berkowitz
Director
Bureau of Sanitary Engineering
Florida State Board of Health
Jacksonville, Florida 32201
Mr. Richard S. Nelle
Division of Sanitary Engineering
Illinois Department of Health
Springfield, Illinois 62704
Mr. Ralph Porges
Head, Water Quality Branch
Delaware River Basin Commission
Trenton, New Jersey 08603
Mr. R. J. Schliekelman
Director, Water Pollution Division
Iowa State Department of Health
Des Moines, Iowa 50319
Mr. Tom H. Forrest
Director of Technical Sales
Chicago Pump, Hydrodynamics Division
FMC Corporation
Chicago, Illinois 60614
Mr. Forrest was represented by
Mr. Edward Matras at one meeting of the
committee
Mr. James B. Hostetler
Engineer
Davco Manufacturing Company
Thomasville, Georgia 31792
Mr. Paul M. Thayer
Vice President - Engineering
Water Pollution Control Corporation
Milwaukee, Wisconsin 53201
Mr. Thayer was represented by
Mr. Frank Schmit at two meetings of the
committee
The Executive Committee, the Policy Com-
mittee, and the Industry Committee are listed in
the first report.1 Their membership is essen-
tially unchanged. Acknowledgment of their con-
tinuing guidance to this portion of the study
is also made.
The National Sanitation Foundation's project
staff should be cited for their extreme devotion
and efforts in making the project function suc-
cessfully.

-------
REFERENCES
1.	Goodman, Brian L., "Package Sewage Treatment
Plant Criteria Development, Part I: Extended
Aeration," National Sanitation Foundation Report
of FWPCA Demonstration Grant Project, WPD-74,
September 1966.
2.	Ohio Department of Health, "A Study of Aerobic
Digestion Sewage Treatment Plants in Ohio -
1959-60."
3.	Ullrich, A. H., and Smith, Mansel W., "The Bio-
sorption Process of Sewage Waste Treatment,"
Sewage and Industrial Wastes, Vol. 23, No. 10,
Page 1248 (October 1951).
4.	Ullrich, A. H., and Smith, Mansel W., "Operation
Experience with Activated Sludge - Biosorption at
Austin, Texas," Sewage and Industrial Wastes,
Vol. 29, No. 4, Page 400 (April 1957).
5.	Eckenfelder, W. Wesley, Jr., "Pilot Plant Investi-
gations of Biological Sludge Treatment of Cannery
and Related Wastes," Proceedings of the Seventh
Industrial Waste Conference, Purdue University,
Page 181 (1952).
6.	Eckenfelder, W. Wesley, Jr. and Grich, Edward K.,
"Plant Scale Studies on the Biological Oxidation
of Cannery Wastes," Proceedings of the Tenth
Industrial Waste Conference, Purdue University,
Page 549 (1955).
7.	Zablatzky, H. R„ Cornish, M. R., and Adams, J. K.,
"An Application of the Principles of Biological
Engineering to Activated Sludge Treatment," Sew-
age and Industrial Wastes, Vol. 31, No. 11, Page
1281 (November 1959).
8.	Jones, E. L., Alspaugh, T. A., and Stokes, H. B.,
"Aerobic Treatment of Textile Mill Waste," Jour-
nal of Water Pollution Control Federation, Vol. 34,
No. 5, Page 495 (May 1962).
9.	Sawyer, C. N., "Activated Sludge Modifications,"
Journal of Water Pollution Control Federation,
Vol. 32, No. 3, Page 232 (March 1960, Part 1).
10.	Hazeltine, T. R., "A Rational Approach to the
Design of Activated Sludge Plants," Biological
Treatment of Sewage and Industrial Wastes, Vol. 1,
Page 257, Reinhold Publishing Corporation, New
York (1956).
11.	"Units of Expression for Waste Treatment,"
Water Pollution Control Federation Manual of
Practice No. 6, Page 4 (1967).
12.	Jones, Dr. P. H., "Waste Water Treatment by
Contact Stabilization at Penetanguishene, Ontario,"
Water and Pollution Control (Canada), Page 31,
February 1968.
13.	Walker, J. D., and Drier, D. E., "Aerobic Diges-
tion of Sewage Solids," Paper presented at 35th
Annual Session of Georgia Water and Pollution
Control Association, September 7, 8, and 9, 1966.
14.	Standard Methods for the Examination of Water
and Wastewater, 12th Edition, American Public
Health Association (1965).
15.	Eckenfelder, W. W., Jr., and O'Connor, D. J.,
Biological Waste Treatment, Permagon Press,
Oxford, Pp. 209-213, 1961.
23

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24
TABLE II *
FALL AND WINTER STUDIES
CONTACT STABILIZATION PACKAGE SEWAGE TREATMENT PLANTS
FULL DESIGN LOADING - STEADY STATE FLOW PATTERN
INFLUENT	EFFLUENT
Item
No. of
Samples
Min.
Max.
Mean
No. of
Samples
Min.
Max.
Mean
Percent
Removal
BODg (mg/1)
415
64
344
167
408
1.0
320
33
80.2
SS (mg/1)
425
94
534
192
426
2.0
304
47
75.5
VSS (mg/1)
425
80
504
158
425
1.0
300
30
81.0
MBAS (mg/1)
312
2.0
9.8
5.2
312
0.3
5.3
1.4
73.1
COD (mg/1)
387
59
490
286
387
5.0
320
74
74.1
NH3 - N (mg/1)
388
4.0
40
12.8
388
0.0
23
6.2

N03 - N (mg/1)
394


***
394
0.1
27.8
8.7

P04 - P (mg/1)
382
8.8
105
55.2
382
8.0
55.6
22.9
58.5
MIXED LIQUOR AND STABILIZATION COMPARTMENT SOLIDS
Item
Samples

Min.
Max.
Mean
Percent
Volatile



MLSS (mg/1)
MLVSS (mg/1)
428
417

80
60
6170
5350
2685
1942
72.3



SV30 (ml)
410

10
990
572




SVI
410

17
738
213




SCSS (mg/1)
SCVSS (mg/1)
210
209

21
17
9870
7830
3551
2827
79.6



RSSS (mg/1)
RSVSS (mg/1)
422
216

40
30
10,400
7880
4694
3534
77.0**



~These data were collected during the period of criteria development and are not the result of
testing under the conditions established for certification testing.
~~Calculated from paired samples only.
***The mean NO3 - N in the influent for this series of data was 0.5 mg/1.

-------
25
TABLE m *
SPRING AND SUMMER STUDIES
CONTACT STABILIZATION PACKAGE SEWAGE TREATMENT PLANTS
FULL DESIGN LOADING - STEADY STATE FLOW PATTERN
INFLUENT	EFFLUENT
Item
No. of
Samples
Min.
Max.
Mean
No. of
Samples
Min.
Max.
Mean
Percent
Removal
BODg (mg/l)
53
75
320
156
53
4.0
58
23
85.3
SS (mg/l)
53
110
416
179
53
7.0
118
28
84.4
VSS (mg/l)
53
72
346
142
53
5.0
80
19
86.6
MBAS (mg/l)
53
1.5
6.8
4.7
53
0.0
2.8
1.1
76.6
COD (mg/l)
53
60
558
288
53
11
162
61
78.8
NH3 - N (mg/l)
40
6.2
18.2
11.1
40
0.8
10.5
4.9

NO3 - N (mg/l)
53


***
53
0.8
21.8
8.9

PO4 - P (mg/l)
40
10
64
27.3
40
9.2
42.0
20.2
26.0
MIXED LIQUOR AND STABILIZATION COMPARTMENT SOLIDS
Item
No. of
Samples
Min.
Max.
Mean
Percent
Volatile


MLSS (mg/l)
MLVSS (mg/l)
52
52

268
128
4170
2690
1498
1009
67.4


SV30 (ml)
50

10
210
108




SVI
50

24
225
72




SCSS (mg/l)









SCVSS (mg/l)









RSSS (mg/l)
RSVSS (mg/l)
51
31

440
730
7930
5080
3143
2415
68.2^


~These data were collected during the period of criteria development and are not the result of
testing under the conditions established for certification testing.
~~Calculated from paired samples only.
~~~The mean NO3 - N in the influent for this series of data was 0.6 mg/l.

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26
TABLE IV *
WINTER AND SPRING STUDIES
CONTACT STABILIZATION PACKAGE SEWAGE TREATMENT PLANTS
FULL DESIGN LOADING - VARIABLE FLOW PATTERN
INFLUENT	EFFLUENT
Item
No. 'of
Samples
Min.
Max.
Mean
No. of
Samples
Min.
Max.
Mean
Percent
Removal
BOD5 (mg/1)
248
112
305
184
236
6.0
236
46
75.0
SS (mg/1)
252
98
282
171
251
0.0
238
24
86.0
VSS (mg/1)
248
88
234
145
248
0.0
198
19
86.9
COD (mg/1)
244
164
652
369
241
20
272
74
79.9
NH3 - N (mg/1)
124
10.0
25.0
18.5
124
1.0
20
10.6

NH3-N (mg/1)
128


*#*
128
0.2
20.2
4.5

P04 - P (mg/1)
120
22.0
72.0
37.2
120
12
40.8
26.5
28.8
MIXED LIQUOR AND STABILIZATION COMPARTMENT SOLIDS
Item
No. of
Samples
Min.
Max.
Mean
Percent
Volatile
MLSS (mg/1)
252
660
5260
1942






79.9
MLVSS (mg/1)
249
420
4530
1552

a.
0
CO
>
CO
248
50
850
343

SVI
248
41
495
177

SCSS (mg/1)
246
600
8010
2924






80.4 ~~
SCVSS (mg/1)
125
850
6640
2492

RSSS (mg/1)
540
1000
8400
3485






81.6**
RSVSS (mg/1)
43
1170
6400
3332

~These data were collected during the period of criteria development and are not the result of
testing under the conditions established for certification testing.
~~Calculated from paired samples only.
~~~The mean NO3 - N in the influent for this series of data was 0.2 mg/1.

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27
TABLE V *
SPRING AND SUMMER STUDIES
CONTACT STABILIZATION PACKAGE SEWAGE TREATMENT PLANTS
FULL DESIGN LOADING - VARIABLE FLOW PATTERN
INFLUENT	EFFLUENT
Item
No. of
Samples Min.
Max.
Mean
No. of
Samples
Min. Max.
Mean
Percent
Removal
BOD 5 (mg/1)
87 100
297
167
86
1.0 220
37
77.8
SS (mg/1)
88 126
344
184
88
3.0 318
45
75.5
VSS (mg/1)
88 70
278
149
88
0.0 218
35
76.5
MBAS (mg/1)
83 1.9
10
5.6
83
0.0 2.4
0.6
89.3
COD (mg/1)
88 140
676
368
88
16 392
89
75.8
NH3 - N (mg/1)
88 6.0
22.1
17.1
88
3.3 22.1
10.7

NO3 - N (mg/1)
88

**
88
0.3 16.0
3.5

P04 - P (mg/1)
87 21
80
52.9
87
23.2 53.6
36.3
31.4
MIXED LIQUOR AND STABILIZATION COMPARTMENT SOLIDS
Item
No. of
Samples
Min.
Max.
Mean
Percent
Volatile


MLSS (mg/1)
ML VSS (mg/1)
91
91
1300
970
6650
4550
3406
2561
75.2


sv30 (ml)
91
90
950
531



SVI
91
39
486
156



SCSS (mg/1)
SCVSS (mg/1)
68
68
2970
2270
8460
6840
5572
4264
76.5


RSSS (mg/1)
RSVSS (mg/1)
91
91
1110
740
11,580
8830
6935
5062
73.0


~These data were collected during the period of criteria development and are no the result of
testing under the conditions established for certification testing.
**The mean N03 - N in the influent for this series of data was 0.4 mg/1.

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