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ACTIVATED SLUDGE CONTROL
WITH A
SETTLOMETER AND CENTRIFUGE
By:
Owen K. Boe
U. S. Environmental Protection Agency
Region VIII .
-------
ACTIVATED SLUDGE CONTROL WITH A SETTLEOMETER AND CENTRIFUGE
There have been many articles written on the control of acti^ted
sludge plants. Nemke* recently published a good article summarizing many
of the key observation and theoretical control techniques that are used
for operating activated sludge plants. One area, however, that has not
received much attention in the literature is the use of the settl.ometer
and centrifuge. This! paper will attempt to lay out a systematic procedure
for utilizing some very simple tests to produce an operating control
plan. This procedure has been successfully used by EPA personnel in
Region VIII on many occasions to operate and control activated sludge
pi ants.
The system presented here is essentially derived from the concepts
presented by A1 West^. Bob Hegg^ also discussed the use of these control tests
and their relation to basic kinetics. The tests described in these articles
provide the basic information for establishing a material balance around
various components of the activated sludge system and for monitoring the
activated sludge quality. The material balance provides a systematic
procedure for the operator to monitor sources, location, and production
of solids. Control parameters such as sludge age are really just a
spin-off of one aspect of the material balance information.
Sludge quality is a much more difficult parameter to monitor but
is the real key to any successful activated sludge operation. A
series of graphs and trend charts will be developed which the operator
can use to visually observe and predict changes in sludge quality.
Experience has shown that changes in these trends are more sensitive
1
-------
to predicting changes in sludge quality than the use of a numerical
parameter such as sludge age.
2
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CONTROL TESTS
The process control procedures used at plants are designed to
provide sufficient information regarding the status of the plant process
in order to make appropriate operational changes, (i.e. adjustment of
return sludge flow rates, adjustment of quantity of activated sludge
to be wasted, adjustment of dissolved oxygen concentrations, etc.) These
tests are discussed in detail elsewhere so this paper will only briefly
summarize the tests.
The control tests initiated are dissolved oxygen determinations,
centrifuge tests, turbidity analyses, settleability tests and sludge
blanket depth determinations. Tests are usually conducted at least two
times per day, seven days per week or once per operating shift, and all
tests except sludge settleability are usually conducted five times per
day.
Dissolved oxygen (D.O.) tests are used to monitor the availability
of D.O. in the aeration basins.
Centrifuge tests are conducted on samples of mixed liquor, on samples
of return sludge, and on samples of waste sludge to determine average
concentrations throughout the day. The centrifuge test values are
expressed in percent solids by volume. Although it is not necessary
for control, a correlation between percent solids by volume and solids
by weight can be made.
Turbidity tests are performed on samples of settled effluent from
the final clarifier. Test results are used to monitor the ability of
the activated sludge to remove colloidal material from sewage. Although
3
-------
turbidity may not be directly related to BOD^, results provide a responsive
indicator for monitoring the quality of the activated sludge.
Settleability tests are conducted on samples of the mixed liquor
collected in the aeration basin near the point of discharge to the
secondary clarifier, and run in a standard Mallory Settlometer. Settleability
tests are used to evaluate sludge settling characteristics, floe formation,
and to provide information on return sludge rates.
Sludge blanket depth determinations are made on the final clarifier
with either an electronic device or a site glass, flashlight and an aluminum
pipe. Results are used to monitor changes in the depth of the blanket and
to determine the amount of sludge that is accumulating in the final clarifier.
Data obtained from the various control tests can be used to perform
calculations and develop various graphs. The results of the calculations
and the trends from the graphs are then used to interpret plant performance
and control plant operations.
4
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MATERIAL BALANCE
A material balance is a measurement of some specific material (i.e.
BOD & SS) in a manner which will account for all sources, removals,
storage, and generation of that material. Figure I shows a schematic
of an activated sludge plant and the minimum information that should be
collected for making a basic material balance around an activated sludge
plant.
The material balance can provide the operator with much useful
information of what is happening or not happening in his plant. He will
be able to determine the impact of sludge waste and sludge return flows,
the generation or growth of the activated sludge, and the quantitative
change of any BOD and SS through the plant.
Many process control parameters make use of only a part of total
material balance information. F/M ratio, for example, uses only BOD of
the influent and suspended solids of the aeration tank. Sludge age uses
only the suspended solids of the aeration tank and the quantity of sludge
wasted. At times of good operations and when the plant is running at
"steady state" conditions, one of these control parameters may be all
that is needed. However, the operator needs to know what is happening to
all areas of his plant so that when a problem does arise, he can tell
which segment of plant operations is out of line.
5
-------
Figure I
MATERIAL BALANCE INFORMATION
-------
THE SLUDGE UNIT SYSTEM
One means of making a material balance is the sludge unit system.
This is a method involving simple tests and measurements which can be
used for describing a material balance around an activated sludge system.
The only extra equipment needed is a centrifuge for measuring the
concentration of sludge. Volume and flow measurements are done by
typical metering and known dimensions. The centrifuge is used to measure
sludge concentration because it saves time over the regular suspended
solids test. When sludge separates in the centrifuge, the amount is
measured as percent of the total volume.
Some examples show how this system can be used. Take for instance
an aeration tank. We need to know how many microorganisms are in the
total tank. Since the microorganisms cannot be easily measured in the
tank, a representative sample is taken from the tank and placed into the
centrifuge. A 15 minute spin reveals that the level of separated
sludge is 1.0 percent of the volume in the centrifuge tube. However,
before the microorganisms measured can be compared to the microorganisms
in the aeration tank, we must have a system to calculate this quantity.
Looking at our aeration tank system we see that the centrifuge reads
1.0 percent and the tank volume is 1.0 MG (million gallons). Therefore,
this quantity of microorganisms is defined as 1.0 sludge unit, or as
shown in the formula:
1.0% x 1.0 MG = 1.0 Sludge Unit
To see how this system works, let's look at a couple more examples:
1. Suppose the same aeration tank had twice as many microorganisms
present. Now, when we run the sample on the centrifuge we
7
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find that the separated sludge reads 2.0%. Now, the sludge
units are calculated to be:
2.0% x 1 MG = 2 Sludge Units
which shows twice as many microorganisms as before.
2. Let's also consider vihat would happen if we had two aeration
tanks instead of one. If both aeration tanks had a reading
of 1 percent sludge, then the sludge units would calculate to:
1st tank - 1% x 1 MG = 1.0 Sludge Unit
2nd tank - 1% x 1 MG = 1.0 Sludge Unit
Total Sludge Units = 2.0
We now have a system which can be used to measure the quantity of
microorganisms in the plant which only involves two numbers. The first
number is the percent reading taken from the centrifuge and the second
number is the volume of the aeration tank (in million gallons). Since the
volume of the tank usually stays the same, all that is needed to determine
the quantity of microorganisms is a reading from the centrifuge, and this
reading only takes a few minutes to determine. The time saved using this
procedure can be used for doing other necessary work at the plant.
If we wanted to we could convert the Sludge Units to pounds of sludge.
All that is needed for this is to run a suspended solids (SS) test and
a spin test on the sample. For the previous example which had a spin of
1%, the SS were found to be 1000 mg/1. This gives a spin ratio of
1000 mg/1 / 1%. To calculate pounds use the following formula:
lbs = % spin x spin ratio x 8.34 x Vol (million gallons)
-------
So, as in the previous example where the tank volume was 1 MG and the
spin ratio was 1000 mg/1 / 1%, we have:
lbs = 1% x 1000 mq/1 x 8.34 lbs x 1 MG
1% gal
Therefore:
lbs = 8340 lbs
The sludge unit system may sound a little different at first and
may sound like more work, but it actually provides the plant operator with
a tool that can be used over and over and in many different ways with
relatively little time involved. Also, as will be shown later, the use
of these units and data obtained from the settlometer provides the operator
with very useful data for controlling return sludge rates.
Some of the ways we can use the sludge unit system are outlined
below. Refer to Appendix A for a summary of definitions.
1. Aeration Sludge Units - ASU
This is a measurement of the amount of sludge found in the aeration
tanks. ASU's are calculated by multiplying the aeration tank volume in
millions of gallons (AVG) by the daily average aeration tank concentration
(ATC). The formula used for this calculation is:
ASU = AVG x ATC
Example:
Vol = 1 MG
ATC = 3%
ASU = 1 MG x 3%
ASU = 3 units
9
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2. Clarifier Sludge Units - CSU
This is a measurement of the amount of sludge found in the clarifier.
CSU's are calculated by multiplying the volume of sludge in the clarifier
in millions of gallons (CVlj) by the average concentration of the sludge-
in the clarifier. The volume of sludge in the clarifier is found by
finding the fraction of the total clarifier volume that is filled with sludge.
The percent of sludge is determined by the following foirula and
defining CVG as volume of clarifier and DOB as the measured distance
from the water surface to the top of the sludge blanket.
Now:
Percent Sludge = Average depth of Clarifier - D0B~) cyg
Average depth of Clarifier J
The average sludge blanket concentration is found by assuming the
concentration at the top of the blanket is equal to ATC and the concen-
tration at the bottom of the blanket is equal to RSC. These assumptions
are made since we know the sludge is compacting at the bottom of the
clarifier, but we can't really measure the average concentration. The
average concentration is then assumed to be:
Average Sludge Concentration = ATC + RSC
2
Now in order to find the total clarifier sludge units, multiply the
percent sludge by the average sludge concentration. Clarifier sludge units p
is then determined by:
CSU = CVG
Average depth of the clarifier - DOB
Average depth of the clarifier
ij jllC + RScJ
10
-------
Example: CVG = 0.70 MG
ATC = 3%
RSC = 12%
DOB = 8 ft
Average clarifier depth (ACD) = 10 ft
CSU =
CVG IaCD-DOB
RSC+ATy
| ACD
2 1
[VIM
CSU = 1.05 units
3. Total Sludge Units - TSU
This is the measurement of the total amount activated_sludge in the ?
system. Other techniques developed in the literature have been presented
but they do not account for varying amounts of sludge in the clarifier.
Total sludge units are calculated by:
TSU = ASU + CSU
Example: TSU = 3.0 + 1.05
TSU = 4.05 units
4. Return Sludge Units - RSU
This is the measurement of the daily average of sludge returned
from the clarifier to the aeration tank. Return sludge units are
calculated by:
RSU = RSC x RSF
Where: RSC = average concentration of return sludge
RSF = average flow of return sludge in mgd
Example: RSF = 2 MGD
RSC = 12%
RSU = 2 MGD x 12%
RSU = 24 units/day
11
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5. Waste Sludge Units - WSU
This is the measurement of the total quantity of sludge wasted
from the system each day. Sludge wasting can occur intentionally by
pumping sludge to a digester or it can occur unintentionally by being
carried over the clarifier weirs. Usually the amount of sludge lost
over the clarifier weirs is small in comparison to that which is inten-
tionally wasted. However, to check this out or to measure the quantity
of the sludge unit system, we can make use of the spin ratio.
Effluent sludge units (ESU) is calculated by measuring the
total suspended solids in the effluent, dividing by the spin ratio, and
multiplying by the plant daily average flow. The formula is given as:
ESU = (TSS) (Flow)
Spin Ratio
Example: TSS = 30 mg/1
Flow = 4 MGD
Spin Ratio = 1000 mg/1 / 1%
ESU = (30 mg/1) (4 MGD)
1000 mg/1 / 1%
ESU = .120 units
Intentional sludge wasting (XSU) is calculated by taking the daily
average concentration of sludge wasted (WSC) and multiplying the volume
(in millions of gallons) of sludge wasted (WSF). Intentional waste sludge
units are calculated by:
XSU = WSC x WSF
Example: WSC = 15%
WSF = 0.05 MG
XSU = 15% x 0.05 MG
XSU = .75 units
12
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Total sludge wasted (WSU) is now calculated by adding the effluent
sludge units to the intentional sludge units, or:
WSU = ESU + XSU
Example: ESU = .12
XSU = .75
WSU = .12 + .75
WSU = .87 units
(Note that ESU <( XSU)
6. Sludge Age - Age
Sludge Age or mean cell residence time has been used by many authors
as an operational tool. The purpose is to define an average time that
activated sludge stays in the plant. To find sludge age we need only
to devide the total sludge units by the total sludge wasted per day, or:
Age = TSU / WSU/day
Age = 4.05/.87
Age = 5.0 days
7. Sludge Detention Time in the Clarifier - SDTc
This is a measurement of the average time that the activated sludge
actually spends in the clarifier at any given time. SDTc is found by
dividing the clarifier sludge units by the average daily return sludge
units and multiplying by 24 hrs/day to obtain the time in hours, tr:
SDTc = CSU/RSU x 24 hrs/day
Example: CSU = 1.05
RSU = 24
SDTc = 1.05/24 x 24 hrs/day
SDTc = 1.05 hours
13
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8. Sludge Detention Time in the Aerator - SDTa
This is the measurement of the average time that the activated
sludge actually spends in the aerator. This measurement is different than
the theoretical hydraulic residence time or the mean sludge residence
time (sludge age) in a very important aspect. The hydraulic residence
time defines the average time the raw sewage spends in the aeration
tank during the day. The sludge age defines the average time the sludge
spends in the system. The sludge detention time (SDTa) defines the
average time that the microorganisms are in contact with the raw sewage
at any given time. The important point here is that the operator can
control or change his sludge detention times by changing return rates;
whereas, the hydraulic residence time is controlled by design and the sludge
age is controlled by wasting. The sludge detention time affects the
efficiency of the organisms to absorb and make use of the BOD by changing
the contact time with the BOD. A comparison of sludge detention times
in the aeration tank to the clarifier also provides important information
for controlling sludge quality. This will be discussed in more detail
later in this paper in the discussion on sludge quality.
SDTa is found by dividing the aeration sludge units by the sludge
units being sent to the clarifier per day, and multiplying by 24 hrs/day.
The sludge flow to the clarifier is found by adding the plant flow (Q)
to the return flow (RSF) and multiplying by the concentration (ATC).
Therefore, the formula used to calculate SDTa is:
SDTa = ASU x 24 hrs/day
(Q + RSF) ATC
14
-------
Example: ASU = 3.0
Q = 4 MGD
RSF = 2 MGD
ATC = 3%
SDTa = 3.0 x 24 hrs/day
(4+2) 3%
SDTa = 4 hrs
The eight cases just presented provide good examples of how a
material balance of the activated sludge can be used to provide useful
information for plant operations. These same principals can be used
by an operator to balance clarifier suction ports sludge streams in
and out of digester, and many other uses.
15
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SLUDGE QUALITY
Sludge quality is the real key to having an activated sludge
plant provide a high quality effluent. Parameters such as sludge
age, MLSS, food loading, and oxygen uptake all affect sludge quality;
yet they all require some indifinite measurement of the biological
solids in the system. The state of the art for measuring these
parameters is improving rapidly, but there still remains the problem
of measuring the "active biomass". Cven if the analytical procedures
could be improved, there is still a lag in the measurement of physical
parameters to the change in the biological system. For example, if an
operator was maintaining a sludge age of 5 days, but decided to increase
to 8 days, he would need to operate at the new level for at least
one sludge age (8 days) to physically change all the sludge to a
residence time of 8 days. This, however, does not guarantee that
the numerous biological populations have all adjusted equally to the
new equilibrium point.
A system has been developed to provide an operator with a more
timely indicator of the changing sludge quality. This system involves
sludge settling tests and the observation of trends of the various
process parameters developed earlier. This system utilizes the
following major elements:
1. Settlometer
The settlometer is the key indicator for observing sludge
quality. Diligent use of the settlometer can provide an experienced
operator with days advance warning of an impending disruption or change
in process control. This advance warning provides the operator with
16
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valuable time to make appropriate process changes. The settlometer
information can also be instrumental when recovering from an
unavoidable operational upset. In this case the advanced indicators
can guide the operator through a series of process adjustments
without wasting excess time waiting for results from process changes
or without trying to make a major adjustment in too short a time.
The first things an operator should look at when running the
settlometer test are the floe formation and the blanket formation.
Through experience, an operator will soon learn that within a few
minutes he can detect certain characteristics which will describe
the sludge quality. Is the floe granular, compact, fluffy or
feathery? Does the floe settle individually or does it first form a
blanket? Is the blanket ragged and lumpy, or uniform on the surface?
After the operator has looked at these characteristics he then
should observe settling rates and compaction characteristics. Is the
blanket settling uniformly, or are segments settling faster than
others? Is the blanket entrapping the majority of the material or
are straggler floe escaping? Is the sludge compacting and squeezing
out water, or is it maintaining a constant density throughout? By this
time the operator should also realize how important a large diameter
settlometer is in order to reduce the effects of a narrow cylinder. Many ofq
these observations would not be noticeable in a 1000 ml graduated cylinder.
Observations such as these are important to the operator. They
are not easily translated to numbers so he should make appropriate
notes on his data sheet for future reference. There are, however,
numerical observations which can be made. Appendix B shows a typical
data sheet which can be used to record appropriate sludge settling
17
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parameters. Observations and recordings are made every 5 minutes for
the first half hour, and then every 10 minutes for the second half
hour. More observations are made in the first half hour to ensure
that the operator is taking the time to observe the floe formation
and blanket characteristics.
If the operator also measures the concentration from the original
sample with the centrifuge (ATC) he can make some informative
calculations from the data.
The calculation of interest is the conversion of the sludge
settling volume (SSV) to sludge settling concentrations (SSC). This
is done by the following formula at any given time(t) of settling:
SSCm = ATC x 1000
SSV(t)
An example of a settling test and appropriate calculations is
shown in Appendix B. One calculation taken from the example is:
ATC = 3.4%
SSV30 = 680 (at 30 min.)
SSC30 = 3.4% x 1000
680
SSC30 = 5%
This means that after 30 minutes the sludge has settled to a
concentration of only 5%.
SSC1s can be calculated for various times and be plotted
corresponding to the time and day they were observed. When several
days of data have been plotted, a trend will have been developed
which graphically relates to the settling characteristics observed
in the settleometer. Usually it is found that the 5 minute, 30 minute,
and 60 minute SSC's adequately represent the settling characteristics.
18
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The 5 minute SSC is an indicator of the critical floe and blanket
formation stage. Here the operator's observations and notes are
very important for future reference.
The 30 minute SSC correlates to the settling test used in
the sludge volume index measurement. Also, the majority of the
settling occurs before the 30 minute reading, so that the distance
settled reflects the settling rate of the sludge. For example, a
SSV3Q of 200 would indicate a fast settling sludge. A SSV3Q of
only GOO would represent a very slow settling sludge.
The 60 minute SSC represents the level of compaction that can
be expected from the sludge. This concentration, therefore, relates to
the return sludge concentration that is actually observed in the
plant. These numbers will seldom be the same due to flow characteristics
and other physical differences found in the clarifiers. The important
criteria, however, is that the settleometer characteristics are
reproducible for similar sludge quality characteristics. This then
enables the operator to make some decisions on return sludge flows
from settlometer data.
Before any operational decisions can be made, it is useful to
make some assumptions about the settlometer and the clarifier. It
needs to be added, though, that these assumptions do not necessarily
have to be accurate because we are primarily interested in the trends
that develope from day to day. These assumptions are:
(1) The sludge settling concentrations found at any given time
relate to the return sludge concentration if the sludge had
stayed in the clarifier for the same time.
19
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(2) The clarifier does not have any unusual flow patterns,
short circuiting, coning from return intakes, or other
factors which would make the clarifier not operate as
expected.
(3) Sludge detention time in the clarifier should be greater than
30 minutes to provide time for compaction. Any time less than
30 minutes will usually require a high return rate which will reduce
the sludge detention time in the aerators. (See discussion of SDTa.)
(4) The sludge detention time in the clarifier should be
less than 60 minutes to preserve an "active biomass".
Assumption #1 has been found to be reasonably reliable and in
several instances where the data appeared to be out of line, a problem
with the clarifier as described in #2 was found to be the limiting
factor.
Now with these assumptions in mind, we can compare the measured
return sludge concentration to the 60 minute and the 30 minute SSC. A
rule of thumb is then evident which says,
If RSC is } SSCgQ, increase return sludge rates.
If RSC is ^ SSC30, decrease return sludge rates.
Like all rules of thumb, other plant conditions have to be
considered such as return rate flexibility, aeration detention time,
etc.
The information derived from the settling test can be summarized
in the graph shown in Figure II. This is a graph of several days
data which reflects improved floe and blanket formation and good
settling characteristics. The RSC and ATC values are also added to
20
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Figure II
SLUDGE SETTLING TREND
Time/days
-------
the graph to add a visual relationship of settling characteristics
to process numbers. Fluctuations in the graph also represent typical
variances in day to day data. Note on the graph that the sludge was
settling very rapidly during Phase I. Also during this phase the
return sludge concentrations were much less than the 30 minute
settling concentration (RSC
-------
calculations. Sludge age is included in the graph but the important
information in process control is to find what parameters are changing.
An example of such a graph is shown in Figure III.
Graphing the data also allows the operator to visualize the
effects of daily changes and gradual trends. Through this type of
understanding the operator will be in a better position to determine
the magnitude and type of process adjustments that may be needed.
As noted in Figure III, daily calculation of sludge age does
not always make sense. On days when no wasting occurs, the sludge
age approaches infinity. This response is shown by the broken lines.
This information, however, does provide the operator with a valuable
rule of thumb.
"It is better to waste a little every day than a lot at one time.'1
When the operator follows this rule, he will be able to provide
a much smoother graph; but more importantly, the control and operation
of his plant will likewise be much smoother. Note in Figure III the
response to the aeration sludge units. The amount of sludge under
aeration changed rapidly after the period of no wasting.
Another rule of thumb has been developed which relates the
sludge detention time in the aeration tank to the detention time in
the final clarifier:
SDTa/SDTc > 1
This rule of thumb is based on observations of sludge quality
in various plants where it has been noticed that as SDTa becomes
closer to SDTc,.. that sludge quality is much more difficult to control.
23
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Figure III SOLIDS BALANCE TRENDS
t \
16 h
14
K, 12
C7>
<
dJ
f 10
oo
1.21
1.01
.81
n .61
.2
0®* 6.0
5.0 "
4.0"
3.0-
GO
<
GO
o
^ Sludge Age
\
Waste Sludge Units
Aeration Sludge Units
Clarifier Sludge Units
i ' 1 I I H
Time/Days
24
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Tank geometry, especially in some complete mix plants, may limit
the ability of the operator to control this ratio above one, but
this still should be a goal of plant operations.
3. Other Process Variables
Other process variables can also be plotted in trend charts to
aid the operator in maintaining control of his facility. Some of
the more useful ones include turbidity, depth of sludge blanket,
and sludge settling rates. Plots of typical values are shown in
Figure IV.
25
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Figure IV PROCESS VARIABLE TRENDS
00
GO
10.0
9.0
8.0
7.0
6.0
5.0
4.0
3.0
2.0 |-
1.0
10.0
9.0
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
Turbidity
Depth of Sludge Blanket
Granular floe
No distinct blanket
Floe starting to
less granular
be
1800
-
1600
-
1400
¦*
1200
-
1000
800
D
600
m
400
200
'
Blanket formation
much more distinct
Sludge Settling Rate
Time/Days
26
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TURBIDITY
Turbidity is the operator's handle on the performance of his
activated sludge system. A well performing activated sludge plant
should be producing an effluent with a settled turbidity of less than 3
units and sometimes down to 1 unit. Turbidity measurements can also
be used to measure the degree of severity of pin floe or other solids
scouring problems. Short term variations due to these type problems
may be attributable to hydraulic problems in the clarifier rather
than actual sludge quality deterioration.
DEPTH OF BLANKET, DOB
Depth of blanket measurements are important for an operator
so he can have early warning to clarifier malfunctions and to
problems associated with long storage times in the clarifier. An
average value for each clarifier is usually sufficient for process
control, but measurements should be periodically made at various
locations in the clarifier to detect any localized problems. Coning
or plugging of suction ports can lead to areas in the clarifier where
the sludge blanket will build. Sludge blanket depths refer to the
distance between the water surface and the sludge surface in the
clarifier.
27
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SLUDGE SETTLING RATE, SSR
Sludge settling rates can be used by the operator to numerically
relate one set of sludge characteristics to another. These settling
rates can be used by the operator to describe a rate of settlinq for
which the plant provides a good quality effluent. Generally this rate
will fall between 400 and 1200. This corresponds to a 30 minute reading
on the settleometer of 400 to 800 milliliters. As mentioned before,
this information should always be accompanied by notes which relate to
the more important, but not quantitative, data of floe and blanket
formation.
Conclusion
The key to having an activated sludge plant put out an excellent
effluent day after day is to monitor and regulate the sludge quality.
Sludge quality cannot be defined by any one magic number, so the
operator must make use of all the information available to him.
Changes in sludge quality can be most readily indentified by observing
trends of various process parameters. The system presented here has
been utilized at many treatment plants successfully. The tests
required for this system are simple to perform, quick to run, and
responsive to changes in the system. If time and background is available,
this information can be converted to kinetic relationships. Also,
more sophisticated use of this information has been published which
provides the operator with additional process control information.
Most important, however, is that by looking at the settlometer, the
operator can visualize the sludge quality in his plant.
28
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Appendix A
Column
No.
1
2
3
7
8
10
11
12
Symbol
Day
Date
ATC
ASU
Symbol Meaning
Self Explanatory
Self Explanatory
Explanation
For convenience use 8:00 AM to 8:00 AM
Aeration Tank Con- =Average of values recorded during the day
centration
Aerator Sludge
Uni t
DOB Depth of Blanket
CSU Clarifier Sludge
Uni t
TSU Total Sludge Unit
RSC Return Sludge Con-
centration
Total Aeration Tank Volume in million gallons
(AVG) Times the ATC from Column 1
=(AVG) (ATC)
= ( MG) (ATC)
=Average of values recorded during the day of the
distance from the water surface to the sludge surface
=(Volume of the clarifier (CVG)X(Percentage
of the clarifier filled with siudge)X(Average
concentration of the sludge in the clarifier)
-(CVG)X(Average depth of the clarifier-DOB)
(Average depth of the clarifier) x
(ATC+RSC)
2
=( MG) ( ft- DOB) (ATC+RSC)
_ft 2
=(ASU + CSU)
=Average of values recorded during the day
RSF Return Sludge Flow =Average return sludge flow rate for that day
(Note: time period for determining this rate
should be the same as the time period used
for determining daily sewage flow rate, eg.
8:00 AM to 8:00 AM)
RSU Return Sludge Unit
TURB Turbidi ty
ESU Effluent Sludge
Uni t
=(RSF) (RSC)
=Average of values recorded during the day
=Quantity of sludge lost in effluent each day
=(Effluent Total Suspended Solids Concentration)
(Flow) 7 (Ratio of TSS Concentration to percent
,by volume)
29
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Symbol Symbol Meaning
ESU (cont.)
Explanation
=(TSS) (Flow)
Ratio of TSS to %
=(TSS) (Flow)
mg/1%
XSU/ Intentional Waste
day Sludge Unit
WSU/ Total Waste Sludge
day Unit
AGE Sludge Age (# of
Days)
SDTc Sludge Detention
Time in the
Clarifier(s)
SDTa Sludge Detention
Time in the
Aerator
Q Average Daily
Sewage Flow
SSVm Sludge Settling
Volume
SSC(t) Sludge Settling
Concentration
=Quantity of sludge intentionally wasted from
the system each day
=Total for the day (Note: time period for deter-
mining this quantity should be the same as the
time period used for determing daily sewage flow
rate, eg. 8:00 AM to 8:00 AM)
=WSC X WSF
=ESU + XSU
=Average length of time a given quantity of
sludge remains in the system
=TSU/WSU/Day
=Average length of time a given quantity of
sludge remains in the clarifier
=(CSU) (24 hr/day) /RSU
=Average length of time a given quantity of
sludge remains in the aerator
=Volume Aer. Tank X ATC X 24 hr/day
(Q + RSF)ATC
= ASU (24)
(Q + RSF) ATC
=Sewage flow for a given time period eg. 8:00 AM
to 8:00 AM
=The volume of settled sludge as determined from
the settleometer at any time (t).
=The concentration of settled sludge at any
time (t).
=ATC X 1000
SSV(t)
30
-------
Column
No. Symbol Symbol Meaning Explanation
21 SSR Sludge Settling =The increase in sludge concentration per hour
Rate
=1000 - SSV30
hr
31
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Appendix B
facility
Clear Creek
Saturday
HCTIVATED SLUDGE PLANT
DAILY DATA SHEET
0a{, 6/12/73
SETTLEOMETER TEST INFORMATION
ATC RSC DOB TURB & FLO INFORMATION
Timt of
test 1 1
TIME
>T» 0/
ftfA 0/
nno r»
Turb—ITU
I
INF
FLO
T'me
SSV JSC*
CC/I %
rs
ssv ssc*
ec/l %
im
ffl
*
SSV ssc •
ec/l %
HIV"
— iO
/o
0
1000
3.4
0
1000 1 2.8
0
1000
900a
3.4
8.6
6.C
3.2
1.5
S
950
3.58
s
910
3.08
S
lOOp
2.8
9.0
3. C
3.7
10
890
3 .82
10
820
3.42
10
5QQp
3.0
9.1
3.5
3.5
IS
830
4.10
IS
740
3.79
15
lOOOi
>3. if Iq.n
4,!
3.0
20
770
4.42
20
670
4.18
20
2S
720
4.73
23
620
4.52
25
:
*
30
680
5.00
30
570
4.92
30
40
620
5.48
40
490
5.72
40
Sub-Tot
50
r 70
5.97
SO
430
6.52
50
Total
60
520 1
6.54
60
380
7.38
60
i
Aver.
3.1
8.9
4.2
3.3 "
r.5
WASTING INFORMATION
RSF INFORMATION
lime
Wasting
Began
Time
Wasting'
Ended
Total
. Time
Wasted
(mini
flow '
Rate
(CPM)
Callotfs
V.'asted
(GAL)
WSC
Began
<%>
WSC
'Ended
(°/q)
Averse-
WSC _
(%>
Sludge
Units
Wasted
(CAU
-------
References
1. Jim Nemke, "Visual Observations Can Be Process Control
Aids," Deeds & Data, WPCF, September 1975.
2. A1 West, "Operational Control Procedures for the Activated
Sludge Process," Part I, II, III-A, III-B, Return Sludge
Control and Appendix, National Field Investigations Center,
U.S.EPA, Cincinnati, Ohio.
3. Bob A. Hegg and John R. Burgeson, "Activated Sludge Operations -
Integrating Control Testing and Basic Kinetics," Deeds &
Data, WPCF, August 1975.
4. "Procedures Used in Conducting Selected Activated Sludge Control
Tests," U.S.EPA, Region VIII, Denver, Colorado.
33
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