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PARTIAL CHLORINATION

0F

SEWAGE

June, 1938

Dorian H. Diokman

INTRODUCTION

Under the direction of Dr. W. L. Mallmann of the
Michigan State College, Department of Bacteriology,
this work was carried out to determine the effectiveness
of partial chlorination upon the total bacteria count
and colon index of sewage. Dr. Rudolphs of New Jersey
and his associates conclude from laboratory experiments
that partial chlorination is practicable where adequate
distribution can be obtained and where E. coli reductions
or 90 to 95% are sufficient, providing the chlorinated
effluent can be discharged into bays or lakes where
dilution is automatic. A study of their work reveals
that their conclusions were based upon laboratory
determinations from a very limited number of samples.
Questions arise as to whether results from a great
number of samples taken frequently over a period of
several weeks or from actual partial chlorination in
plant operation would be as effective as their results
indicate. The work undertaken in this problem is an

attempt to answer these questions.

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The first part of the work deals with experiments
using East Lansing sewage. Special consideration was
given to the reductions in bacteria counts and colon
indices resulting from various chlorination periods
when the samples were partially chlorinated. The
second part deals with plant scale chlorination
experiments at Battle Creek, Michigan. In this work
consideration was given to the percent satisfaction
of the chlorine demand, the chlorination period, the
resultant reduction in bacteria count and the reduction

of the colon index.

EX PE RI LEN TAL

Chlorine Demand

Determination of the chlorine demand was made by
treating 100 ml. samples of sewage with 0.5 m1., 0.6 ml.,
0.7 m1. and like increments up to 1.5 ml. of chlorine
water containing 0.5 g. of chlorine per liter. One-tenth
instead of the customary five-tenth ml. increments were
used for more accurate determinations. The chlorine
water was prepared by diluting strong sodium hypochlorite
solution with distilled water and standardizing with a

standard solution of sodium thiosulphate. Due to the

fact that chlorine water loses its strength upon standing,

fresh solution was prepared every week and this solution

was checked several times with standard sodium thiosulphate.
After shaking the 53:31:; gently and allowing them

to stand for thirty minutes, a crystal of potassium iodide

and l ml.of starch indicator solution was added to each

bottle. The chlorine demand, in parts per million, was

calculated by multiplying the ml. of chlorine water in

the first sample to show a blue color by 5.

Chlorine Demand (1’. P. It): 14.1. in let bottle
showing blue X 5.

Chlorination of Samples

East Lansing Sewage: After determining the chlorine
demand of sewage from East Lansing, samples were treated
to give various demand satisfactions beginning at 100%
and decreasing atl6% intervals to as low as 40%.
Immediately after a thorough mixing with chlorine water,
a portion of the chlorinated sample was placed into a
glass-stoppered bottle containing steril sodium
thiosulphate and at five minute intervals thereafter,

portions of the chlorinated sample were similarly treated.

This procedure was used to halt the bacteriacidal
action of the chlorine at the end of 5, 10, 15, and 20
minute intervals. Thus it was possible to study the
effect of the chlorination period in conjunction with
the partial chlorination investigations conducted upon
East Lansing sewage.

Battle Creek Sewage: Chlorination of Battle Creek
sewage was conducted somewhat differently than at East
Lansing. This difference was due to the fact that this
experimental work was conducted on a plant scale in place
of the laboratory scale at East Lansing. In chlorinating
the Battle Creek sewage, an automatic wet feed chlorinator
(Wallace and Tiernon) was used to treat the effluent.

Since the outfall sewer is comparitively long and is
equipped at regular intervals with sampling stations, it
was ideally adapted to the study of the effect of the
chlorination period an plant scale.eh&errha$ions.

At the rate of flow during the experimental work,
it was determined that a detention period of 2.5 minutes
could be obtained. This was not considered long enough
for the purposes of our eXperiment so baffle boards
were placed at the end of the outfall. As a result, the
detention period was lengthened to 24 minutes. Then for

the 2.5 minute detention period, samples were taken at

approximately 20 second intervals and with the 24
minute period, samples were taken at 5 minute intervals.
This of course was made possible through the use of the
seven regularly Spaced sampling stations along the

outfall.

Bacteriological Determinations
Dilution of Samples:

In carrying out the bacteriological determinations,
it was found necessary to make various dilutions using
chlorinated sewage samples and distilled water.
Erlenmeyer flaskSof 150 ml. capacity were filled with
enough distilled water so that upon sterilization and
cooling, they «intained 90 to 99 m1. depending upon
the dilution desired. Then by using steril 1 ml. and
10 ml. graduated pipettes, dilutions of 1:100, 1:1000,
1:10,000, 1:100,000 and 1:1000000 were made.

Total Count:

From the various dilutions prepared, nutrient agar
plates were prepared and incubated at 57° C for 24 hours.
One ml. of the highest dilution of a sample of sewage
was withdrawn by means of a steril pipette and placed

into a steril Petri dish. Then with the same pipette a

one m1. portion was withdrawn from the next lower‘
dilution of this same sample and placed into a second
steril Petri dish. After portions from all the
dilutions had been placed into Petri dishes in this
manner, melted nutrient agar was poured into them, this
was mixed with the ml. of diluted sewage, cooled and
placed in a 57° C constant temperature room to incubate
for 24 hours. Because of insufficient time none of the
plates were incubated at 20° C.

The agar culture medium was prepared from a tap
water, meat extract, agar, peptone and salt according
to the procedure outlined in the ”Laboratory Manual of
General hicrobiology" by Giltner. It was found conven-
ient to make up several liters of this agar at a time
and then melt small portions as needed. After the agar
was melted, it was kept in a 45° C. oven until all the
plates were poured. This eliminated the necessity of
having to melt agar so frequently.

After the plates had been incubated for 24 hours,
the colonies were counted using an electrically illuminated
counting devise equipped with a magnifying lens. Calcu-
lations were based on data obtained from plates showing
between 50 and 500 colonies because of the fact that

within these limits, greater accuracy can be obtained.

Colon Index:

In addition to the total count determinations on
the chlorinated samples, their colon index was also
determined. While the agar plates were being poured,

5 fermentation tubes of nutrient lactose broth were
innoculated with 1 ml. portions from the particular
dilution being used. Thus 5 fermentation tubes, con-
taining 10 ml. of nutrient lactose broth, were
innoculated for each dilution of the chlorinated sample.
The use of five tubes for each dilution was chosen in
order to employ the "Most Probable Number" method of
determining the colon index and at the same time obtain
highly accurate results. The most probable number may
be computed, but the mathematics involved are rather
complex, therefore it has been found more convenient to
use the table which has been included (page 9). This
table has been worked out and is designed to cover all
possibilities that can arise when five tubes of each
are incubated for gas production.

Since this production of gas from lactose is onLy
a presumptive test indicating the presence of the colon-
aerogenes group and not a definitely positive reaction,
it is necessary to confirm the presence of this group

of organisms. In the present work, brilliant green bile

ere

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broth was used as the confirmatory medium. It was made
up according to the method as outlined in "AnaLysis of
Water and Sewage" by Theroux, Eldridge and Mallmann

(pp. 209-10, 2nd Ed.). From each tube of lactose broth
showing gas, a loopful of material was transplanted to

a Durham fermentation tube containing brilliant green
bile broth. The latter tubes were then incubated at

37° C for 24 hours; at the end of which time, all tubes
showing gas production were considered positive evidence
of the presence of the colon-aerogenes group and as such

were used in computing the colon index.

5/

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Most Probable Number of Organisms

With live Samples of Bach Dilution.

Significant Probable Significant Probable Significant Probable
e u e . *um e e

4 O
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1.4 504

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Explanation on following page.

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The most probable number of organisms present in that
volume represented by the dilution which corresponds to
the first figure of the significant number is given in the
table. For example, for a series x cc., 0.1 1 cc.,

0.0001 1 cc., the results secured might be 22100. The
significant number is 210. Examination of the table mows
the probable number to be 0.7. This is the probable number
of bacteria in 0.1 1 cc. of original suspension of the
organism.

In these tables, numbers from 0 to 2.0 are correct to
the nearest tenth. from 2 to 20 correct to the nearest 0.5

and above 20 correct to the nearest 5.0.

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Tabulated Data and Results

11

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TABLE I

East Lansing Samples
Total Count Data

12

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Series Demandgfidgzdne T fiél Co t

Number p.p.m. p.p.m. % Sat. Raw 5 Min. 10 Min. 15 Min. 20 Min.
1 3.3 3.3 100 91,000 70,000 27,000 8,000

2 3.3 3.3 100 5&55,000%_23,000 2,500 2,200 2,250

3 2.2 2.2 1 100 25,000 2,300 1,800 1,800 495

4 4.95 4.95 100 55,000 23,000 2,500 2,200 2,250

5 4.95 4.45 90 38,700 540 282 212 228

5 5.5 5.5 100 117,000 5,500 950 380 825

7 5.5 3.3 50 154,000 157,000 79,500 48,400 17,450

$_* 8 4.95 3.95 80 133,750 33,525 8,355 2,203 8,155
___ 9 4.95 3.45 70 133,750 130,000 24,300 14,755 5,900
h—‘io 5.5 3.45 70 154,000 98,250 43,400 32,380 10,280
11 5.5 3.3 50 49,400 42,200 45,700 10,700 24,200
__‘12 5.5 $.2175 50 49,400 47,300 82,500 57,800 77,000
_+13 '5.5 +m2.20— 40“ 49,400 215,400 590000 259,000 153,000

 

 

TABLE II

East Lansing Samples

Colon Index Data-

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Chlorine
Series Demand‘Added olon Index
Number p.p.m.!p.p.m. % Sat. Raw 5 Min. 10 Min. 15 min. 20 Min.
1 3.3 3.3 100 500 r 35 r 15 r
2 3.3 3.3 100 25 r 350 350 350 50
3 2.2 2.2 100 200 o 0 o 0
4 4.95 4.95 100 800 r 800—? ‘350*fl _—m350 o
5 4.95 '1195 2 9o 15"& "5‘rl— 450 it 200 20
5 5.5 5.5 100 800 r 50 r 350 o 50
7 5.5 3.3 _ 50 350 r 800 r 1.3 M 500 r 1.3 u
8 4.95 3.95 I »80 ‘I2T5mumt‘lj5—i' 80 r 30 r 5 c
_* 9 4.95 3.45 70 2.5 M 800 r
I_ 10 5.5 3.45 70 '350 r 1.1 hula—1.3 M 350 r 350 r
11 hw5.5 1% 3.3 “I 50 1.7 n. 300 r 170 r 170 c 350 r
_¥12 5.5 2.75 50 1.7 M 400 r 500 r 350 r 300 r
-~13 5.5 2.20 40 1.7 n 250 r 250 r 170 r 170 r

 

 

14

TABLE III

East Lansing Samples

Total Count and Colon Index Reductions

 

Percent Reductions

 

 

 

 

 

 

 

Series Total Count Colon Index
Amber 7% Sat. 5 Min. 10 Min._l§ gin. 20 Min. 5Min.10 Min. 15 Min. 20 gig!
1 100 23.0 70.0 . 91.0 93.0 96.8“
100 72.0 95.0 95.5 95.5 98.6 98.5 ’ 98.5 99.9

 

100 8.0 28.0 28.0 98.0 100 100 100 100

 

 

 

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TABLE IV

Battle Creek Samples

Total Count and Colon Index

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Series Chlorine Detent. Total Count E.4ooli
Number Stat1on,§5815u21_25r155 _§er 5.0. 2 Red. 1555 9 Red
14 East 0 1,055,800 3.5 m
West 0 533,400 3.5 n
1 20 Sec.‘- 8,475 99.8 7.0 1' 99.8
2 40 .. 525 99.99 2.5 T 99.99
3 50 .. 475 99.99 3.5 I 99.99
4 80 .. 440 99.99 1.3 m 99 99
5 100 .. 425 99.99 3.5 T 99.99
5 120 j. 230 99.99 2.5 I 99.99
7 140 ..1-__1_ 240 99.99 800 99.99
Outfall 1.0 150 .. 200 99.99 1.8 m 99.99
15 East 0 725,000 9.0 5
west 0 L 508,000 18.0 11
1 0.5 20 .._,__14’000 98.0 180 m 98.7
2 0.75 40 .. 15,200 98.0 150 m 98.8
3 1.0 50 .. 912 99.99 140 99.99
4 0.7 80 .. 1,870 99.99 3.5 m 99.99
5 1.0 100 .. 2,055 99.99 1.1 m 99.99
5 120 .. 458 99.99 1.7 m 99.99
7 140 .. 1,015 99.99 2.5 1 99.99
Outtall 0.75 150 .. 454 99.99 5.0 m 99.99

 

 

 

 

TABLE Iv (comm'n)

Battle Creek Samples

Total Count and Colon Index

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Series Chlorine Detent. Totel_Count E. coli

Number Station Residual_Period_rferlslc.l2% Bed.l Index
15 East 0 502,400 800 1
E55;_m_w_m_0 9H“*_ ‘9‘” 880,000 250 m

1 1.5 20 Sam 274,000 50.4 25 T 95.2

2 1.0 40 ..4 110,000 84.0 350 0 33.3

3 1.0—_ -503 .. 9 23,000 95.7 8 m 98.5

4 __0.5 80“ .. 350,000 49.4 35 1 93.3

Y 5 0.5 100 .. 19,000 97.3 9 1 98.3

5 0.5 120 .. __ 500 99.9

7 0.4 140 .. 11,900 98.4 17 1 95.8

Outfall 0.4 150 .. 59 99.99 50 T 88.5

 

 

 

 

 

 

 

 

 

 

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Battle Creek Samples

Additional Data

 

 

 

 

 

 

 

 

 

 

 

 

Series Total Suspended Oxygen
Number Station Solids Solids 8.0.D. pH Consumed
14 East 78 153
West 67 153
Outfall 77 119
15 East 862 56 164 6.60
West 898 61 170 6.62
Outtallmwm—879“ 72 147 6.16
16 East 942 87 190 6.75 20.6
West 891 81 194 6.72 20.0
Outfall 913 68 127 6.17 22.3

 

 

 

 

 

 

 

 

 

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67

CONCLUSIONS
Reduction of Total Bacteria: East Lansing Sewage.

From the work on East Lansing sewage it is evident
that partial chlorination in amounts as low as 70% of
the chlorine demand will effectively reduce the total
bacteria. In fact the data in this work indicates that
chlorination amounting to 70% of the chlorine demand
will reduce the total bacteria count by more than 90%-
However, these reductions from 70% of the chlorine
demand were only obtained when a chlorination period
of twenty minutes was used.

Amounts of chlorine of less than 70% of the
chlorine demand did not reduce the total count, but in
some cases actually increased it.(Table I - Series 12,15).
From the curves it may be seen that the higher demand
satisfactions gave more rapid reductions than did the

lower satisfactions (Curves from Table III).

Reduction of Colon Index: East Lansing Sewage.

As might be expected, partial chlorination is much
more effective in reducing the number of E. 0011 than in
reducing total count. This is probably due to the fact that
in the total count tsere are inculded a great number of
Spore formers. Since these organisms are not readily

removed by chlorination, the effectiveness of this agent

68

in reduction of total count is less than in reduction
of E. coli. Chlorination in amounts as low as 40% of
the chlorine demand gave marked reductions, although
from the rather incomplete data in this respect it is
apparent that at least 705 of the chlorine demand is

necessary to consistently give reductions in the colon

index of over 90%.

Reductions of Total Count and Colon Index: Battle
Creek Sewage.

It was 1 possible to carry out more than
preliminary experiments on a plant scale at Battle
Creek, but from the data obtained it is evident that
very complete reductions in both total count and
colon index were obtained. When chlorinating with such
amounts as to produce a residual of 1.0 p.p.m. at end
of the outfall, practically complete reductions in both
total count and colon index were obtained within 20
seconds after chlorination (Table IV - Series 14).

Even Upon reducing the chlorine so as to leave only
0.4 p.p.m. residual at the outfall, practically complete

reductions were obtained within 160 seconds.

69

SUfiMAHY

I Partial chlorination of 70% of chlorine demand
gives reduction of more than 90% of total bacteria count.
II Partial chlorination as low as 40% of chlorine

demand effectively reduces the colon index.

III Partial chlorination of 70% of chlorine demand
consistently gives reductions of more than 90% of
colon index.

IV A chlorine residual as low as 0.4 p.p.m. in
plant scale operation gives practically complete
reductions in total count and colon index in less

than 160 seconds.

 

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