This is to certifg that the

thesis entitled

The Effectiveness of Renoval of Bacteria by
Various Joncentrations of Lime anu Alum bloc

presented b1]
David nahLer

has been accepted towards fulfillment

of the requirements for

-ms Lenidegree in $3.936 I‘JQQA-Ogy

 

M-795

,‘A , _.____— ~—

THE WVENESS OF REIDVAL OF BACTERIA B! VARIOUS
CONCENTRATIONS OF LIME AND ALUM F100

‘9!

DAVID um
’

A THESIS
Sublitted to the ‘Granduate School of Michigan
State College of Agriculture and Applied
Science in partial fulfilment of the
Requirements for the degree of

EASTER OF SCIENCE

Department of Bacteriology
1947

ATHESIS

ACKMWLW

The writer rich» to express his sincere apprecia-
tion for the guidance end assistance in conducting
this investigation to‘ Dr. I. L. Inllnann of the
Department of Bacteriology and Public Health, and
Mr. A. E. Johnson of the Permtit COW.

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TABLE OF CONTENTS

Introduction

Experimental
1. Studies with a settling sludge blanket
2. Studies with a cone precipitator
5. Pilot Plant Studies

Discussion

-Conclusion

Citation of the Literature

The modern development of water purification started in the seven-
teenth century with the application of steam power for water works. Al-
so about this time the English scientist, Cavendish (1) removed the cal-
careous substance from London well water by adding lime, thus precipita-
ting the calcium and magnesium as carbonates. Softening on a plant scale
was first proposed by Thomas Hardy (2) about 1800, but it was not until
1841 that softening on a large scale was tried by Thomas Clark (5) of
‘Aberdeen.8cotland. Forty-sevenyears later a municipal softening plant
was built in America in 1901 at linnepeg Canada, followed by a plant
which.attracted much attention at Oberlin, Ohio in 1905. In 1908 water
softening was attempted on a large scale at Colunbus Ohio.

By this time softening had obtained e. foothold although for new
years the advantages were offset by the disadvantages such as clogging
sand filters, excess causticity, and lag of chemical reactions in cold
dilute solutions. The latter disadvantage proved to be the greatest
problem until it became known that prolonged stirring shortened the re-
action tina. It has been a common practice for many years to use a feur
hour reaction period.

Bacterial purification of water has been effected primarily by sedi-
mentation, filtration, and chemical disinfection. ‘Ihere the softening
process is not a part of the purification system sedimentation is induced
by alum coagulation in settling chambers. Both alun.and line treatment
remove 90 percent or more of the bacteria in the water, the percentage
removal being dependent largely on the density of the bacterial popula-

tion and the dosage of reagents.

-2‘

Line treatment.not only removes the bacteria by sedimentation but
actual kill of the organisms may also occur. Hoover (4) working with se-
‘veral Ohio water softening plants found that one grain per gallon.(g'g)
excess lime killed 99.98 percent of the coliform organisms in the water.
When 20-25 p.p.l. causticity wasmaintained in the lime treatment at Iron.
ton, Ohio, Edwards (5) found a decided reduction of micro-organisms. Scott
and Icelure (6) studying the effect of hydrogen ion concentration of bac-
teria of the colon-typhoid group found in nunicipal supplies that there '
was an effective removal if pH values were kept above 9.5.

lattie and Chambers (7) carried out an extensive study on the bee-
tericidal efficiency of lime treatment at various pH values using several
pathogens as well as coliform.organisms. Their findings show that the
pathogen death rate is higher than the nonpathogen at similar pH values.
They found that at pH range 10.1-10.5 complete hill of organisms was not
obtained at the end of a four hour contact period, an exposure of eight
hours for pathogens and ten hours for nonpathogens being necessary. In
order to obtain 100 percent hill of these organisms within the feur hour
exposure period pH values of 10.5-41.0 for pathogens and 11.01-ll.5 for
nonpathogens had to be maintained. Temperature influenced the rate of
kill, neither pathogen nor nonpathogen being 100 percent killed at 00 C.
at pH l0.01-10.5 in.a ten hour test period.

Bayliss (8) stated in 1950 that an alum floc could be used for the
removal of turbidity, color and micro-organisms. so believed that the re-
moval of turbidity, color and micro-organisms was an adsorption action.
Calvert (9) using 10—50 p.p.m. alum as a coagulant obtained an 89 percent

-3-

removal of micro-organisms in 15 minutes. Streeter (10) demonstrated
that an increasing bacterial removal. was obtained by increasing rates of
application of alum. Flinn, Weston and Bogart (11) came to about the same
conclusions using water of a low turbidity and color. A study was made
‘by Gehm (12) to compare methods of bacterial removal in sewage. He found
that by using an excess of ferric chloride (60 p.p.m.) 97 percent of the
total bacteria and 70 percent of the Escherichia 9_o_;_i_ were removed.

Spaulding (15) developed a method of softening water by utilising
the accumulated sludge to speed the chemical reactions. This process uti-
lized a unit called the Precipitator designed as a combination mixing, co-
agulation and settling tank which brings the unstable lime treated water
into equilibrium quickly by retaining previously precipitated carbonates
and hydroxides in contact with the flowing water. The process is reported
to give complete treatment in one hour instead of four hours in the con-
ventional process.

The studies presented in this thesis were instituted to investigate
the effectiveness of the Spaulding Pracipitator in the removal of bacteria
in comparison to the conventional four hour treatment. The Precipitator
and the conventional type tank were tested on both lime treatment and in
water clarification using elm.

Inasmuch as there has been a very limited amount of work reported
on the removal of bacteria by flocs, it seemed advisable to make a labor-
atory survey to ascertain if aore extensive studies on a pilot plant scale
would be worthwhile. Furthermore glass cylinder tests were a more con-
venient means of evaluating the influence of various concentrations and
various types of sludge in bacterial removal. Under such laboratory con-

.4.

ditions all variables were controlled which is impossible in a pilot
plant installation. Sampling methods and plating techniques were
worked out so that discrepancies would be minimised. Finally, although
these studies were initiated primarily for the reason given above, cer-
tain dataon the comparative value of the two processes namely the Pre-
cipitator and the conventional settling tank were obtained.

Seven liter Pyrex glass cylinders were used for testing. For stir-
ring purposes glass rods were bent at 90° angles in a sig-sag fashion,
these being attached to wooden pulleys by means of a chuck. Belts con-
nected each pulley, the entire assembly being driven by an electric
stirrer. In this manner all sludge concentrations were agitated at the
same velocity.

In this study various types of sludges have been tried, these being
alum, lime, lime-alum, and lime ferric hydroxide. However as the alum
and lime—alum flocs are used more extensively in practical operation than
the other two mentioned, more comprehensive investigations were made with
these floss. The heavy concentrations of alum sludge (over 500 p.p.m.)
were preformed, the floc being accumulated in the following manner.

After optimum chemical dosage and proper pH for maxim flocculation had
been determined, the chemical was added to six liters of distilled water.
The mixture was stirred while pH adjustment was made and then the stirrers
were removed. The floc was peraitted to settle for several days. After
this period, the filtrate was decanted and the settled sludge was added
to previously accumulated sludge.

‘ Escherichia _c_o_1;l_ was used as the test organism primarily because
this organism is the standard for measuring water purity. This organism

-5-

was also selected because its growth requirements as to temperature, pH,
and nutrients are wide and it adapted itself well to these studies.
Twenty-four hour broth cultures or saline washing from 24 hour agar slants
were used, the latter being used when heavier inoculations were desired
then could be obtained with broth.

Part I - Studies with Settling Sludge Blanket

For the test six liters of acctuulated sludge plus tap water were
used, the sludge concentrations varying from 17 to 5500 p.p.l. Larger
amounts of flee were not included due to the slow settling rate. PH ad-
justments where necessary, were made with ll/l sodium hydroxide and l/l
hydrochloric acid unless otherwise designated. Fpur to six glass cylin-
ders containing various amounts of sludge and a raw water control comprised
each run.

Sludge concentrations and pH adjustments were nde prior to each
trial to calmly with the desired testing conditions. The 5; 293:; cul-
ture was added while the stirrers were operating so that an inediate
mixing would occur. Iixing was continued for approximately one hour.
During this period samples were withdrawn from the top of the cylinders
to determine the initial inoculum of cells. After the termination of mix-
ing the agitators were removed to allow settling. Samples were taken at
intervals of 50 minutes, 1, 2, 5, and 4 hours.

The point of sampling at the various time intervals was questioned
on the basis that the bacteria in the supernatant might decrease at the
surface during the four hour settling period. Accordingly samples were
collected at three levels in the supernatant. Il‘he data are presented in
Table l. The results are comparable, being well within the experimental
errors inherent to plant counts.

Tatle l. The number of bacteria at various levels in the super-
natant liquid above the settlinz sludge blenket

Levels above the settling No. of bacteria
sludge in inches per ml.
2 21,000
6 ?3,000

later Curface ?l,OOO

~6-

Lt the coupletion of each run, the supernatant fluid was decanted
and fresh tap water added preparatory to the next trial. In this manner
the same sludge blanket could be used repeatedly. Five trials were node
for each set of experiments in order to minimise variances due to experi-
mental error in settling rates, sampling, and plating.

Several sampling techniques were investigated as early exploratory
tests demonstrated that 1 ll. samples were not always consistent and rep-
resentative of the nulber of bacteria present. It was felt that a larger
sample might give a more representative sample , as the mmber. of bacteria
adsorbed on the floc particles might vary considerably. Accordingly a
comparative sampling was made using 1, 10, and 100 :1. portions. The 10
and 100 m1. portions were shaken prior to plating in appropriate dilutions.
The 100 ml. portions gave the most‘ consistent results so that in later
tests these portions were collected.

The glass cylinder tests made it possible to obtain comparative fig-
ures on the effects of sludge concentrations on bacterial removal because
it is possible to run a series of varying concentrations with a constant
bacterial content simultaneously. This eliminates any variables Ihich
would affect the results if tests on the various concentration were run
at different times in a pilot plant. _1ccording1y four concentrations
were tested, namely $500, 2400, 1200, and 500 p.p.n. at pH values of 7.6
and 9.0 respectively. The data presented in Tables 2 and 5 demonstrated
that the heaviest floc concentrations gave the most effective removal.
Them see little difference in the removal of bacteria in the concentra-
tions of 1200, 2400, and 5500 p.p.n. although the 3500 p.p.m. gave the
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Because there was little difference in the heavy concentrations,
lighter concentrations were included in the next series. Sampling in
this series was made only at 50 minute and 4 hour settling intervals.
The 50 minute period was selected to determine if there were possible
variations in the early stages of settling with the various concentra-
tions of‘sludge. In.this series presented in Table 4, sludge concen-
trations of 17, 54, 600, 1200, 2400, and 5500 p.p.n. were used.

The data for the 50 minute settling period are extremely'interest-
ing. It can be seen that 50 minutes was not a sufficient settling period
for 5500 p.p.m. of floc. However, with the exception of trial 1, the
three other concentrations of heavy sludge removed organisms effectively'
in 50 minutes. The light concentrations of sludge (l7 and 54 p.p.m.)
even with a 4 hour settling period were from.50 to 50 percent less ef-
ficient than were the heavy 311mg» after 50 minutes settling.

In the tests cited, an alum sludge was used. In the next series,
the effectiveness of an alum-calcium hydroxide floc was tested in re-
moving bacteria. In these tests bacterial removal was checked in 50
minutes, 1, 2, 5, and 4 settling periods. In this series of tests an
attempt was made to reduce the hardness of the water to 85 p.p.m. and
maintain a pH of 10.. As the same sludge was used for all runs, it was
impossible to maintain a pH of 10 and a hardness of 85 p.p.m. in all runs
therefore two series of tests were made, one with a constant hardness of
85 p.p.n. with a varying pH and a second with a constant pH of 10 and a
varying hardness. is before 5 trials were made with each set of condi-
tions and an average bacterial removal expressed in percentage-reduction
which is reported in the accompanying tables. The concentrations of
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-8-

The results obtained with a constant pH of 10 and a varying hard-
ness of 50-110 p.p.m. are presented in Table 5. An examination of the
table reveals that the percentage-reduction of bacteria in 50 minutes
was the same as that obtained after 1, 2, 5, and 4 hours settling. The
greater the concentration of the sludge blanket up to 2500 p.p.m. the
greater the pemntage-mduction bacteria, although the difference was
onJy an increase of. 2 percent between 1200 and 2500 p.p.m.

With a constant hardness of 85 p.p.m. and a pl! varying from 8.5 to
10, the results were comparable to those obtained with a constant pH
and a varying hardness, except 5000 p.p.m. removed 99 percent of the
bacteria whereas 2400 p.p.m. removed 98 percent. rthe results are pro-

' sented in Table 6. In general the bacterial removal was not as great.
This my be due to the difficulty in adjusting the sludge concentration
which involved breaking up and reforming the floc several times in order
to obtain the desired hardness.

The data obtained in the cylinder tests indicate that there is a def-
inite relationship between sludge concentration and bacterial removal.
The results demonstrated that when the concentration of sludge is in ex-
cess of 1200 p.p.n. marked removal of bacteria occurred with a one hour
settling period. Increasing the concentration above 1200 p.p.m. gave in-
creasingly better results as long as the sludge would settle within the
allotted time. However, these percentage reductions were not marked in-
asmuch as lower concentrations removed approximately 97 percent of the
bacteria. The rate of removal of the heavy concentrations of sludge was
greater than the lighter concentrations, the former showing as much as
a 50 percent better result in 50 minutes settling time than the latter
after 4 hours settling. The data obtained in the cylinder tests where

 

 

 

 

 

 

 

 

 

 

  

 

 

 

 

 

 

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ALOI _ DISTILLED
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leg. 1

no disturbance occurs due to water flow, as would occur under practi-
cal conditions, definitely show the value of heavy sludge concentrations
in removal of bacteria. The data warranted further studies wherein a
continuous flow system.is used.

Part II - Studies with.cone Precipitatcr

The results obtained with the cylinders definitely show that sludge
concentrations, comparable to those used in practice with a Spaulding
Precipitatcr, remove bacteria from the treated water effectively. How-
ever as these results were obtained with an undisturbed settling sludge
and because in the Spaulding Precipiator the water passes up through the
sludge, the second phase of this study was undertaken using an inverted
cone such as Spaulding used in his early work. In such a cone, raw water
and chemicals enter at the bottom, ascend through the previously accumu-
lated sludge blanket and finished water is taken off at the top.

The cone experiments were instituted primarily to determine whether
the expense of a pilot plant would be Justified and also to obtain further
data using an apparatus in which various short experiments could be made.

The cone precipitator unit consisted of the following pieces of equip-
ment: The cone, constructed of sheet metal was 6 ft. high, the top have
ing a diameter of 10 in. which tapered to an apex at the bottom. A
drawing of the unit is present in Figure I. an angle iron standard
supported the cone 2 ft. from the floor in an upright position. Four
stopcocks were located at various levels for sampling with a valve at
the spent for draining. An intake pipe (5/8 in.) was soldered into the
cone on the outside at a tangent about 12 in. from the apex. IA vertical

pipe with a funnel attached to its top was connected at right angles to

-10-
the intake pipe. Raw water and chemicals were fed into this pipe. The
outlet pipe orifice was located in the center of the cone about one inch
from the t0p. The cone had a capacity of 33 liters.

Raw water flow was controlled by an orifice box which was located
above the water intake funnel. An alum solution was fed into the water
intake funnel from a constant head beaker, the amount being regulated by
a stopcock. The line hydrate was added in a susPended state from a 2
liter, 5 neck boiling flask which had a spout attached to its side. A
motor driven stirrer was used to mix the material and keep the lime in
suspension. Distilled water was added to the lime flask from a constant
head beaker to assure a steady flow of lime water into the water intake
funnel. A charge of dry hydrate lime was added to the flask every 50
ndnutes to maintain a constant concentration of lime.

In order to duplicate conditions of softening plant operation, raw
water from the Red Cedar River was used. This also supplied a varied
bacterial flora representative of a sewage polluted water. Previous tests
had showed the bacterial flora to be abundant in this water even at low
temperatures. Hardness of the water varied somehhat necessitating opera-
tional changes several times a day. The pH of the effluent was maintained
below 10.5 at all times as previous work had showed that higher values
were bactericidal. For this reason the treatment was not always as some
plate as might be desired.

The cone was used first for determining the effectiveness of the
Spaulding Precipitator with a water detention period of one hour and the
conventional type or softening without sludge blanket and a detention

period of four hours.

.11-

The bacteriological procedure followed in full the recommended pro-
cedures of "Standard methods for the Examination of water and Sewage"(l4).
Tests were made for both total counts and colon indices. Colon indices
‘were determined by planting the decimal dilutions in triplicate and re-
porting the colon indices by the most probable number. In order to elim-
inate discrepancies in variable plate counts each 100 ml. sample was
plated in 8 replicate. Pour platings were made by placing 1 ml. of the
sample in 4 sets of saline dilution blanks and making appropriate dilu-
tion plates from each and four platings were made in a similar manner
starting with 10 m1. of the sample in saline dilution blanks. By average
the counts of the eight separate platings, discrepancies due to the plat-
ing technic and sampling were largely eliminated. Plates and tubes were
incubated for 48 hours at 57° 0. Inasmuch as past experience had demon-
strated that gas production was always due to coliform organisms, the
presumptive test was considered positive if gas appeared in the fer-ante»
tion tubes within 48 hours. In practically all cases gas was evident at
the end of 24 hours incubation. Forty eight hour readings on the agar
plates were used because it was desired to obtain the maximum numbers of
bacteria present in the water.

Samples were collected at two points, the raw water from the orifice
box at 5 and 4 hour intervals depending upon the rate of flow and the
finished water from the final effluent at hourly intervals. Lack of
change in the number of organisms in the raw water did not warrant samp-
ling every hour. Twenty samples were taken in most cases; each sample
was either set up for bacteriological test immediately or refrigerated

for not more than 8 hours.

-12-
Lime—Llum.§§pgriments

As previously stated in this thesis, the objective of the study was
a comparison of the Spaulding Precipitator using a sludge blanket and
the conventional settling tank without a sludge blanket, therefore the
cone was used in the first test as a.Precipitator unit and, in the second
test, as a conventional settling tank.

The detention period in the first series was one hour with a flow
rate of 8 gallons per hour. A.carbonate hydroxide sludge blanket was
built up in the cone to a level of 15 in. from the surface in conformity
to Precipitatb‘ operation. It took 5 days to accumulate sufficient
sludge. To maintain a constant sludge level of 15 in. sludge was drawn
off from the apex valve every hour during operation.

In the second series, when the cone was used as a conventional sett-
ling tank, a 4 hour detention period was used to conform.to practical
operation. With this detention period the flow rate was decreased to
2 gal. per hour with the chemical feeds adjusted proportionally. his no
sludge blanket is used in this type of softening, accumulated sludge was
drawn off at hourly intervals.

The operating data, when the cone was used as a Precipitator unit,
are presented in.Tab1e 7. These data show the degree of variation en-
countered in the operation of the unit. in examination of the table
shows that the alkalinity and pH were fairly constant. A turbidity of
5 to 8 was maintained except for a period of 4 hours when the turbidity
was nearly as high as the raw water. The sludge levels varied from 11

to 22 in. with.an average of 16 in.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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-15-

The operating data, when the cone was used as a conventional sett-
ling tank are presented in Table 8. The alkalinity and pH were fairly
constant and compared to that obtained with the Precipitator tests. 1'he
turbidity during the early part of the run was approximately 15 in the
final effluent and in the latter part of the run it was 10 during the
last 5 hours, 7 to 8. The raw water had a tm'bidity of 5 to 8. Thus in
this case the final effluent had a turbidity throughout the experiment
higher than the raw water. This was unavoidable because the cone did
not adapt itself satisfactorily as a conventional settling tank.

The bacteriological data for the two series of tests are presented
in Table 9. It will be observed that the hourly samples vary'both in
total count and colon indioes. This would be expected in individual
samples so that in evaluating the data, it is necessary to use averages
of repeated tests. The data show that with a sludge blanket and 1 hour
detention the colon index was reduced fron.1l,900 to 1194, a reduction
of 90 percent. In the case of the 4 hour detention period without a
sludge blanket the colon index fell from 4500 to 1253, a reduction of
75 percent.

The results attained in the reduction of total bacterial counts are
similar to those obtained for the colon indices. The reduction in total
count for the 1 hour detention period with a sludge blanket was 95 per-
cent whereas only a reduction of 59 percent was obtained with the 4 hour
detention period without the sludge blanket.

As previously stated the cone, when Operated with a 1 hour detention

period and a sludge blanket, gave a final effluent with c turbidity of

approximately 7 to s 113116 the cone operated as a conventional type

 

 

 

 

 

 

 

 

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-14-

.oftening unit-yielded an effluent with a turbidity of approximately
15, which was higher than the influent. The bacteriological results ob—
tained with the cone operated as a conventional type softening unit re-
flect the turbidity data in that marked variability was obtained both.in
total count and colon indices. This is shown in Table 10. These data
show that the cone operated with a flow rate of 2 gal. per hour cannot
be operated satisfactorily and that the cone is not designed to act as
conventional settling basin. The data, as a whole demonstrate that a
sludge blanket helps materially in the removal of bacteria, but do not
necessarily demonstrate the inefficiency of the conventional water sof;
toning process in the removal of bacteria. The data however, do show a
marked difference in bacterial removal which is so marked that the data
cannot be ignored. The results are similar to those obtained with the
cylinder tests which further confirm the data obtained in the cone
studies.
00 tion iment with-A um

For the coagulation test with alum, the cone was first used as a
Precipitator and second as a conventional tank without a sludge blanket.
The cone was changed slightly. 1 4 in. intake pipe replaced the 5/8 in.
pipe in order to have sufficient area for carbon dioxide, which collected
in the pipe, to escape. It was necessary to prevent the gas from enter-
ing the cone as it would carrylthe £100 to the top of the cone hindering
blanket fer-etion. Preliminary beaker tests had shown the optimmn.pfl
for coagulation.to be 6. To obtain the desired clarification it was nec-
essary to use 80 p.p.m. of alum. Sulphuric acid (N/l) was added fron.a

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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-15—

constant head beaker to adjust the pH of the water. To give the flue
weight, clay was fed from.a three neck boiling flask into the intake
funnel in the same manner that line had been.added in the preceding
softening experiments.

Again comparative tests with and without the sludge blanket were made.
Twenty samples of the treated effluent were taken in each series of axe
‘periments. Total bacterial counts and colon indices were made as before.

The operating data for the experiments on alum coagulation with a
sludge blanket and one hour detention period are presented in.Table 11.
During the period of sampling the turbidity averaged approximately 6
in the effluent and ranged from 14 to 50 in the raw water. The pH was
slightly under 6. The sludge level was approximately 17 inches from the
surface of the water.

The Operating data for the experiments with alum without a sludge
blanket and a four hour detention period are presented in Table 12.

The turbidity ranged from 5 to 4 in the effluent and from 10 to 14 in
the rau'water. It will be noted that the turbidity without a sludge
blanket was lower than that obtained with a sludge blanket. The pH was
approximately 6.2 which is, at least, 0.2 higher than that obtained in
the experiments with a sludge blanket. The pH was approximately 6.2
which is, at least, 0.2 higher than that obtained in the experiments with
a sludge blanket.

The bacteriological tests for these experiments are reported in
Table 13. With a sludge blanket the average percentage reduction of coli-
for-.organisms was 98.6 for the 5 successive days of the experiment. The

total average bacterial removal as represented by the percentage reduction

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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NOTES 0! TABLE 11.

After sludge stood overnight, it was agitated 15 minutes to break
up Imp. 0

Raw water color approx. 50-60 on 5/4.

Settling times in 20 min.
9:40 Lil. c.#2- 40% on -581
2:00 MI. C.#l -55; c#2 44%, (#5- 42%

Where effluent shows pH 5.9 - 6.0 actual coagulation took place
at pH 5.7-5.8. pH increased in passing outlet pipe due to
aeration.

Dosages - Alum 5-5% grs., clay 2-2% grs. Acid to ph.AdJustment.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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in total count was 92. Without a sludge blanket, the total average of
the percentage reduction of coliforn organisms was 97.4 for the 5 days
and percentage reduction in bacterial counts at 86;.

These data indicate that the average reduction of both colon indioes
and total count was only slightly higher for the sludge blanket tests us-
ing one hour detention period than that obtained without s sludge blane
ket and a detention of 4 hours.

In these experiments the cone worked fairly satisfactory as a con—
ventional settling basin with a detention period of 4 hours. It is
rather interesting to note that although the turbidity of the effluent
was greater in the experiments with a sludge blanket, still the bac-
terial reduction was slightly more effective.

Pilot Plant Studies

The results obtained with cylinder tests and the cone precipitator
appeared to warrant an installation of pilot plants of both the Spaulding
Precipitator and a conventional type installation so that they could be
Operated simultaneously. In this manner all variables such.as water temp
perature, hardness of the water and bacterial content could be eliminated
and the only'variable would be the differences in operation characteris-
tic of each installation. The plants could be made large enough so that
they would simulate actual plant operation.

For the past several years Precipitator design has been altered to
meet the needs of each job and to utilize existing equipment in the plants
until today there are four types_of units in use. The types are (1) round
Precipitator, (2) square Precipitator, (5) double deck Precipitator, and
(4) rectangular’Precipitator. With the round and rectangular softeners

.17-

raw water and chemicals enter the center of the unit near the top, pass
downward through the mixing zone until the port is reached and then as-
cend outside the mixer through the sludge blanket to the effluent dis-
charge. The double deck and the square Precipitators have raw water,
chemicals and sludge mixed in a section outside the inflow filter zone
with the results that the ascending treated water is inside the mixing
zone.

The unit used in these studies, although a round tank, utilized the
latter method of water passage thrmgh the Precipitstcr. It is shown in
Figure 5. The outside Jacket of the Pracipitator was 8 ft. in diameter
and 8 ft. in height. Inside of this tank a cone was hung about 12 in.
from the bottom of the tank. The mixing zone was in the section between
the cone and the Precipitator tank. The sludge concentrator, attached
to the, inside of the cone at the bottom, was extended upward about 2.5
ft. Stilling baffles were welded to the outside of the cone in the mix-
ing acne. Sslpling cocks, a blow—off, a blow-back, and a drain were lo-
cated at proper levels on the side of the tank. The incoming mixture of
raw water and chemicals entered the tank at the 5.25 ft. level and de-
scended through the mixing zone to the port. The finished effluent was
taken off the top by 5/16 in. orifices into a collection trough. Accu-
mulated sludge was kept suspended and also mixed with incoming water-chen-
ical mixture by agitator arns located in the lower mixing zone. Agitatu‘s
in both units were am» by a 1,: 3.1:. motor with a gear reducing the rota-
tion of the agitators to 16 113.1. for each unit. Automatic sltflge blow-

Fig. 2. Shows general plan of the pilot plant with
Precipitator, conventional settling tank,

chemical mixing tank and feed tanks.

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Pig. 5 - Detailed drawing of Spaulding Precipitator

10.
11.
12.
15.
14.
15.
16.
17.
18.
19.

Speed reducer attach to § E.P. motor
OVerflow pipe

Outlet

Orifices in collector ring

Shaft attached to agitators
Sampling cocks

Inlet pipe from mifing tank

Sludge concentration

Agitatcrs

Stilling baffles

Drain pipe

Agitator assembly

20 minute time clocks

Solenoid valves

Strainer

flashback supply line

Flushback diaphran valves
Concentrator blcwcff diaphran valve
Bleeder lines from diaphram valves

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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SPHULDING PRECIP; THIOR

__._ .. ._-_._. _ _. —.. ..

rig. b

.13..

offs and blow backs were controlled by 20 minute time clocks which re-
leased sclenoid valves which in turn opened diaphrag- valves intc the
Precipitatcr.

The conventional type settling tank was constructed of 18 gauge steel
with a diameter of 6 ft. and a height of 8 ft. The minor, which had a
diameter of 24 in. and a height of 6.75 ft. was set 12 in. off of the
bottom of the tank. Stators and agitators blades were attached to a
shaft in the mixer. The influent from the mixing tank antared the mixer
15 in. from the top and descended through the mixing zone. After mixing,
sludge was allowed to settle and the treated water ascended through the
settling area to the i. in. effluent orifices and to a collector ring at
the top of the tank. Accumulated sludge was drawn hourly from this unit
by a grid lying on the bottom of the tank which seemed an even pull of
sludge from the entire area during the blow-off. Draining was done by
a valve in the bottom of the tank.

The Precipitator and the conventional settling tank were placed next
to each other with a mixing tank (1 ft. diameter and 5.5 ft. high) located
between the units. Lead-in pipes 16 in. free the top of the mixer fed
each tank the line—alum water mixture. Chemicals were fed into the mm:-
from a steel line tank and a wooden alum tank by electrc-chemical feeders.
Charges were added periodically to these feed tanks. Raw river water was
also fed into the mixer, its rate being regulated by a float valve. Equal
rates through both units were regulated by control boxes on the side of
each tank. In these boxes a butterfly valve regulated a float held at
a constant head over the orifice. The arrangement if the tank is shown
in Pig- 2 and Photographs 1 and 2.

Photograph 1. Pilot plant showing softening units and

feed tanks .

A nannmsonm

 

 

Photograph 2

Photogrpph 2 - Shows piping into and out of

central Mixing Tank.

Inlet pipe into conventional settling tank.
Pipe fro-.alun tank.

Raw water pipe line

Pipe from line tank

Inlet pipes into Precipitator

Float regulating raw water flow
lixing tank.

-l9—

Iith continuous operation, it was found satisfactory to charge the
feed tanks every 12 hours, using raw water as the suspending mdiua. The
electro—chemical feeders were set to deliver the proper dosage of chem-
icals. The flow-rate through each tank was 6.5 gal. per min. giving the
desired detention tine of one hour in the Precipitator and four hours
in the settling tank. Btu-ing bacteriological testing the following tests
were made hourly, pH, alkalinity, turbidities, and settling rates of
Precipitator sludge. Hardness was determined daily. About every 10 days
the settling tank was drained and flushed out to prevent a gradual accu;
nulation of sludge. In addition sludge samples were collected every 12
hours for bacteriological testing. Occasionally sludge samples were
taken. from the settling tank when sludge as drawn. A daily operation
sheet, typical of a run is presented in Table 14. Bacteriological test-
ing was done as previously described.

Red Cedar River water was selected for these tests as the bacterial
population is high during the smer months. The water is slightly sew-
age-polluted so the colon index is generally high. The bacterial count
usually runs between 25,000 and 50,000 during the sumar acnths but this
year lichigan had an exceptionally dry season and because there was little
or no rm—off‘ water the population was unusually low. One series of,
tests was madensing the low count river water and a second run no
nade wherein coliforn organisms were: fed into the water ' to produce a
high count water. For the latter series, oisgherichig _c_9__1.i_. was fed from
a tank with a small injector pap into the river water line about 200 ft.
ahead of the units. The organisms were grown in nutrient broth and were
addedtothefoedtanktwicedaily.

 

 

Table 14 « Opefitional data of a typical days.}run with a lime—alum treatment at pH 9.7~l0.0

      

        
  
       
  

  
   
      
  
  
  
 

    

Féed Data Preci ter CTST

   
 
 
 
 

Sec.
. Bast. Blow 810
15

ter VOl'e
PreciCTST

 

   

   
         
    
      

   
  
    
   

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Remarks
Chnges.Alum 5-3

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Date ___9/28/4'6* Total gals. 2.4 hrs. 18,720 15! lime/in 1.58 a? alum/in 0.54 #0133 inn...“ ppm acid; Precip. =, Precipitator
CTST= convent. type sett. tank
5:50 A.M. - 1.61 Data in sludge bOdY'#2 000k are percent
5;00.A.M. — 1.62 settling in 5 minutes.

Lime "" 250 popome

 

   

-20-
Lingllum Studies

In the first series of tests, line-alum water softening procedure
was used. With Red Cedar River water, complete treatment resulted at a
pH of 10.5 to 10.5. Because bactericidal action my result to some ex-
tent at pH values above 10, it was decided to make two runs, one at 10.5
and the other at 9.7 to 10 where bactericidal action would not occur.
Bacteriological tests were made on the river flora at pH 8.5, 10 and
10.25 at exposure periods of l and 4 hours to determine bactericidal ac—
tivity. Ho reduction occurred at pH of 8.5 and 10, but some reduction
occurred at 10.25. When the water was treated at 9.7 to 10, undertreat-
ment occurred. It was necessary to keep the pH above 9.7 in these tests
because the line-slum floc became very fine and light at this pH causing
a considerable carry-over of the sludge with the effluent. These latter
testing conditions showed the effect of organisms removal by sludge blan-
ket without the variable of bactericidal action due to alkalinity which
night occur in tests at a pH above 10.

The first series of tests were made at pH 10.5 with complete treat-
ment. The units were operated continuously for these studies for five
days. Usually samplings were made hourly each day over an eight hour
period. The raw water sample proceeded the Precipitator sample by 1 hour
and the settling tank by four hours. This was done so that the sampling
of influent and effluents represent the same water in all cases. This
procedure was done in all experiments in the pilot plant testing. Space
does not permit presentations of all tests. In all cases, the plants
were operated until daily sampling gave approximately the same bacterio-
logical pictures. In Table 15 is presented a typical daily run, showing

the bacterial reductions, expressed in total counts and colon indices for

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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an 8 hour period. In this series, the turbidities were maintained at a
level lower than the influent. It will be noted in this series that the
turbidities were higher in the settling tank than those obtained in'the
Precipitator. The raw water counts were fairly constant throughout the
run, averaging 1585 bacteria per ml. The colon indices varied consider—
ably; This variation was characteristic of all sampling of raw water
from the Red Cedar River through the entire study. The total count of
the Precipitator effluent averaged 18 bacteria per ml. and the colon
index of 57 with reductions of 95.5 and 97.0 percent respectively. These
data show a lower bacterial reduction for the Precipitator.

In all of the studies, the turbidity was always lower in the Precip-
itator than in the settling tank. It was impossible to maintain the sane
turbidities in both tanks because identical treatment of the water re-
Bulted in a lower turbidity in the Precipitator. Because the turbidity
was always higher in the settling tank it night follow that more bacteria
were being carried over in the effluent. It could be argued that the
differences in efficiencies in bacterial removal were due to this factor
and not due to the effectiveness of the sludge blanket. Accordingly, a
second series of tests was made whereifi the turbidities were raised and
comparable turbidities were obtained by disturbing the sludge blanket in
the Precipitator to obtain a greater carry-over of sludge;particles into
the effluent.’ Again daily runs were made and daily sampling followed.

In Table 16, is presented a typical daily run. In this run, there was
an average reduction in total count of 94.7 percent, and in colon index
of 97.5 for the Precipitator and an average reduction in total count of
92.2 percent and in colon index of 95.2 percent for the settling tank.

 

 

 

 

    

 

 

 

 

 

 

 

 

 

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These data show that where the turbidites were maintained at the
same point, the reductions in total count and colon indices were still
lower in the Precipitator. These data thus indicate that the Precipi-
tator with a sludge blanket is more effective in removing bacteria and
that the higher turbidity obtained in most of the studies in the sett-
ling tank does not account for the higher bacterial populations in the
effluent.

The two series presented show the results obtained with lime-alu-
treatment of a water with moderate bacterial populations. To obtain fur-
ther data where unusually heavy bacterial populations were present,Ԥgghp
‘ggli;_was fed into the river water line in excessive doses. Considerable
difficulty was encountered in obtaining a constant seeding of the tanks,
however this difficulty was finally overcome. Several runs were dis-
carded because of the marked variability in the coliforn.organisn.content
of the raw water. Three comparable daily runs were obtained. One of
these is presented in Table 17. The average colon index of the raw water
was 959,400. The average colon index of the Precipitator effluent was
19,410 with.a percentage reduction of 97. In all runs the colon index
was slightly higher in the settling tank effluent.

These data show that in a water with exeessive colon indices, the Pre-
cipitator with a 1 hour detention period gave a slightly better reduction
in colon index than did the settling tank with a 4 hour detention period.

To eliminate the possibility of bactericidal activity of high pH in
,the reduction of the bacteria which might have played a part in the tests
presented, a series was made using pH 9.7-10 in the final effluent. A

typical run is presented in.Table 18. The Precipitator gave a reduction

Table 17 - A typical pilot plant run using line-alum at pH 10.5 with

river water seeded with Each. coli. showing comparative reduction in

colon indices in the Precipitator and the conventional type settling
tank.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1 Raw Water ggcipi§%tgz Eifln.
Hourly Colon - Colon Colon
Samples Index Turbidity Index Turbidity Index Turbidity
1 2,500,000 6 25,000 16 25,000 19
2 950,000 45,000 18 25,000 19
5 950,000 45,000 15 95,000 19
4 950,000 9,500 15 25,000 19
5 950,000 5 45,000 '17 9,500 19
5 950,000 25,000 17 45,000 . 19
7 ' 450,000 4,500 17 9,500 19
a 950,000 5- 25,000 ' 16 45,000 19
9 450,000 9,500 16 111,000 19
10 250,000 25,000 12 25,000 19
11 4,500,000 4,500 12 25,000 19
the /
A Averge 959 .400 19 410 __ 29 ,450 A
Percent '
eductionl # 98.0 97.0

 

 

 

 

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-25-

of 89 percent in total count and 94.2 percent in colon index and the
settling tank a reduction of 78.4 percent in total count and 84.5 pera
cent in colon index. These data present the same general picture as that
presented in the studies using higher pH values. The relative relation-
ships of the Precipitator and settling tank were the same as in previ-
ously cited experiments but the percentage-reduction was less. This
difference is likely due to bactericidal activity at the higher pH
values. It is also possible that the greater differences shown between
the two systems at pH 9.7 - 10 might be due to some bactericidal activity
in the settling tank due to the longer detention period. The fact that
the Precipitator still shows a greater percentage-reduction that) does
the settling tank could be attributed to the greater efficiency of the
sludge blanket in actual lechanical removal of the bacteria.
Coagulation ggpgrinents with Line

The results obtained with the cone used as a conventional coagulation
tank were not entirely satisfactory due to the fact that the cone was
designed to silulate the action of the Precipitator. The data, however,
showed that the Precipitator gave aibetter removal of bacteria but this
could have been due to the fact that the tests were not comparable. Be-
cause the Precipitator has been used as a coagulator for water treatment,
it seemed advisable to run tests with the pilot plants where design made
possible the testing with.one variable, namely'one hour detention without
sludge blanket in the conventional tank.

In the first series, raw Red Cedar River water was used so that bac-
terial tests could be made with the natural water flora. No pH adjust-

ments were necessary during these tests as a good coagulation was ob-

tained at the resulting pH 7.6. The alum dosage was 2% grains with clay

-24-
being added also at the rate of 2% grains to induce better settling.
Sampling and testing was done as in previous pilot plant operations.
The results of a typical days run are presented in Table 19. The raw
water count averaged 1675.for this run with an average colon index of 5945.
The Precipitator gave an average reduction of 65.8 percent with an aver—
age count of 572. The colon index was reduced to 794, an average percen-
tage reduction of 86.7. The conventional tank without sludge blanket
gave an average reduction of 60.7 percent with.an average count of 659.
The colon index was reduced to 1457, an average percentage reduction of
74.2. These data indicate that the Precipitator with a sludge blanket
in one hour detention gives a batter bacterial removal both in total
count and colon index than does the conventional type tank with a four
hour detention period.

In the second series, Esch. coli was added as in previous experiments
with.liIe-a1un,treatlent to give an exceedingly high colon index. This
was done to see if the sludge blanket could cope with heavy bacterial ppp-
ulations. These tests were run at pH 7.6 with the same dosages of alum
and clay. only colon indices were checked in this series of tests. In
Table 20 are presented a typical days run. ln-exanination of the table
reveals that the raw water had an average colon index of 2,500,000. The
Precipitator reduced the colon index to 585,000 which giwes a.percentage-
reduction of 84.8. The conventional tank gave a colon index of 467,000
a percentage reduction of 81.4. Here again, the Precipitator with a heavy
bacterial population gave ”swam reduction.

Inasmuch as the sludge blanket represents, in part, sludge whichihas
been adsorbing bacteria from the water for some time, a check of the iludge

 

 

 

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Table 20 - A.typical pilot plant run using alum-clay at pH 7.6
with river water seeded with E. coli showing coaparative reduc-
tion in colon indices in the Precipitator and the conventional

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

settling tank.
Raw River _P‘fcc1plt.tor Setting—Fa?
Hourly 4 later Egglgggt _;§If1uent
. 8559100 Colon Index;__ Colon Index Colon Index
1 25,500,000 500,000 . 950,000
2 " 250,000? 95,000 150,000 .
5 fit 4,500,000 450,000 1 250,000 f
4 '7" 2,500,000 950,000 950,000
5 2,500,005 _ 950,000 #450,000
0 2,500,000 450,000 750,000—T
7 2,500,000 200,000 450,000
3 2,500,000 450,000 250,000 }
3 2,153,000 505,000 467,000 *1
34.0 51.4

 

 

 

.-

~25—

was node to determine the bacteria content. In these tests, sludge samples
were collected over a period of: days of operation to detenine whether an
increase of bacteria occurred particularly'when a water with.a heavy bac-
terial population was used. Both.liIe-alun and alum-clay sludges were
tested both.with light and heavy bacterial populations. In.Table 21 are
presented data using a line-alum sludge blanket. lith both heavy and light
bacterial populations, no increase in population of the sludge occurred in
8 days of operation. In Table 22, are presented the data using an.a1ump
clay sludge blanket. Here again there was no change in bacterial popula-
tion over 9 days operation.

It is apparent from these data that the draw'off of sludge to retain
a constant level carries off sufficient used sludge so that the bacterial
population remains constant.

Discussion

The results presented in this comparative study of the two types of
water softening are extremely interesting in that they show the possibility
of bacterial renoval in pilot plants. Inasluch as both plants were operb
ated simultaneously with the sane water and identical chemical treatment,
the results are definitely comparable. It would be expected that bacteria
would'be feloved but the data show definitely that a sludge blanket removes
lore bacteria than a settling procedure. It is also interesting to note
that a sludge blanket removes more bacteria in an hour detention period
than that obtained in a four hour detention period in the absence of a
sludge blanket.

In the softening of a sewage polluted water supply, any process that
will remove more bacteria, although the softening process is not necessar-
ily a bacterial removal procedure, is significant from a public health

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standpoint. The greater the removal of bacteria in each step of the puri-
fication process, prior to post-chlorination the less repponsibility is
placed on the post chlorination to assure a water free of health hazard.

If it is possible to obtain lore couplets water softening in a sludge
blanket Precipitator in one hour detention period than that obtained in a
four hour detention conventional “tar softener and at the seas time
greater bacterial removal is also obtained than the process has a marked
advantage.

The studies on the clarification of water by alum treat-ant also gave
similar results in bacterial removal. This is particularly significant be-
cause in these studies, bactericidal action of high alkalinity'was not en-
countered. The sludge blanket treatment for clarification has been used
in smll installation in bottling plants but the data presented in these
pilot plant studies would indicate a useful application in municipal water
supplies where polluted water is used.

It is particularly interesting to note that in the three methods of
testing, nsnely cylinder tests, and laboratory cone Hecipitator and pilot
plant operations, the sludge blanket treatment gave the best results. It
is apparent that in passing the water through a blanket of sludge flee the
bacteria are in closer contact to the floc and hence bacteria are removed
more rapidly and more effectively.

it the start ofthe studies, it was thought that the holding of used
sludge in the tank might serve to recontaminate the water because the sludge
could conceivably be heavily laden with bacteria. However in the studies
it was found that the bacterial population of the sludge blanket rapidly

-27-
reaches a constant in keeping with population of the effluent. In earlier
laboratory tests, sludges with populations as high as 11,000,000 still ef-
fectively removed bacteria introduced by the effluent.

Conclusion

 

(1) In the lime—alum treatment for softening water, the sludge blanket
treatment for one hour removed more bacteria than that obtained with the
conventional treatment without sludge blanket for four hours.

(2) Experiments finds in cylinders in laboratory experiments, and in
pilot plant operations with.a small experimental cone Preoipitator and
practical pilot plants were in agreement in results attained.

(5) In the aluuhclay'treatment for clarification of water, the sludge
blanket treatment for one hour removed more bacteria than that obtained

with the conventional treatment without sludge blanket for one hour.

-23-

BIBLIOGRAPHY

(1-5) Hoover, C. P., later softening. I. W. and Sam, 90: 144-147

(4)
(5)

(6)

(7)
(8)
(9)
(10)
(11)
(12)
(15)

(14)

(1945)

Hoover, C. P., Water softening as an adjunct to water pm‘ifica-
tion. Jour. of A. W. W. Le, 17: 751-759 (1927)

Edwards, E. '1‘. , Use of line as a water purification agent at
Ironton Ohio. Conf. Water Purif. 10th Ann. Report (1950)

Scott, R. 5., and G. I. McClure. The hydrogen-ion concentration
of lime treated water and its effects on bacteria of the
colon-typhoid group. Jour. of A. W. W. 1., 11: 598-604,
(1924).

Hattie, Elsie, and C. I. Chambers. Relative resistance of coli-
forn organisms and certain enteric pathogens to excess
lime treatment. Jour. of A. W. W. 1., 55: 709-720 (1945)

Bayliss, J. R., Coagulation. W. W. and Sew., 77: 147-150 (1950)

Calvert, C. K., Raw water preparation for filtration. I. W. and
Sew. , 86: 205-205 (1959)

Streeter, H. 17., Line method in water purification. Public Wks.,
64: 17 (1955)

Flinn, A. D. , R. S. Weston and C. L. Bogart. Waterworks Handbook,
5rd. Edi., 650-660. mate‘s-Hill Boo/f Company Inc.

Gehm, H. I. , Bacterial reduction by chemical treatment. Sewage
Works Eng., 15: 558-540 (1944)

Spaulding, C. H., Some new practices in water softening. W. I.
and Sew., 85: 155-157 (1958)

Standard Methods for the Examination of Water and Sewage, 8th
Edi. (1958) Pmcmcen PubLlc ”calf/2 Hssocrgfm/y

ROOM USE UnLY

 

 

 

 

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