-------
EFFECTIVENESS OF
WATER TREATMENT PROCESSES
As Measured by Coliform Reduction
Part I
Water Treatment Plant Data
Part II
Special Cooperative MF-MPN Study
Graham Walton
Engineering Section, Research Branch
Division of Water Supply and Pollution Control
U. S. DEPARTMENT OF HEALTH, EDUCATION,
AND WELFARE
Public Health Service
Robert A. Taft Sanitary Engineering Center
Cincinnati, Ohio
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Public Health Service Publication No. 898
1961
For sale by the Sup•rintendmt of Doaumenta, U. S. Government Printing Oflca
Washington 25, D. C.-Price SO cents
ii
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Contents
Page
PART I. WATER TREATMENT PLANT DATA
Current Status and Study Procedures 1
Previous Studies 1
Treatment Processes, 1930 vs. 1956 3
Plants Studied 4
Analysis of Bacteriological Data 5
Coliform Bacterial Objective for Water Plant Effluent .. 11
Simple Chlorination 12
Collection of Data 12
Plants Studied 12
Discussion 14
Conclusions 16
Conventional Rapid Sand Filtration and Disinfection 17
Plants Studied 17
Discussion 20
Conclusions 87
Predisinfection, Coagulation, and Sedimentation 37
Plants Studied 37
Discussion 38
Conclusion 40
Coagulation, Sedimentation, and Filtration 40
Presentation of Data 40
Discussion 45
Conclusions 47
Presedimentation ... 47
Presentation and Discussion of Data 48
Conclusions 51
Excess Lime or Lime-Soda Ash Softening,
Coagulation, and Sedimentation 51
Plants Studied 51
Discussion 52
Conclusions 53
Apparent Deficiencies in Facilities or Operations
at Water Treatment Plans 53
Simple Chlorination 54
Disinfection, Coagulation, and Sedimentation 54
Conventional Rapid Sand Filtration and Disinfection .... 54
Summary Discussion , 56
iii
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Page
PART II. SPECIAL COOPERATIVE MF-MPN STUDY
Supplementary Study 61
Presentation of Data 62
Discussion 66
Conclusions 66
Acknowledgments 67
References 68
iv
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Abstract
During 1954-56 the author personally visited more than 80
water treatment plants in the United States which had been re-
ported to have adequate coliform bacteriological data and to treat
raw waters with monthly average coliform bacterial densities in
excess of those recommended by the Public Health Service. Data
from nearly 60 of these plants have been analyzed to determine
the effectiveness of various water treatment processes as measured
by their reduction of coliform bacteria.
As one of the requirements of the Public Health Service Drink-
ing Water Standards is that samples for bacteriological examina-
tion must be taken from representative locations throughout the
distribution system, these standards are not applicable where
only plant effluent samples are examined. Thus it was necessary
to assume a bacterial quality objective for plant effluent data.
Analysis of the data presented in this report shows that well-oper-
ated plants of good design consistently produced plant effluent
samples having not more than 2 per cent of all 10-ml portions
examined during any one month postive for coliform bacteria.
This is the assumed bacterial quality objective for water plant
effluents that is used throughout this report.
The limited data available indicate that "clean" waters contain-
ing monthly average coliform densities somewhat in excess of
50 per 100 ml can be treated by simple chlorination to produce
water conforming to the assumed bacteriological objective for
plant effluent. The terra "clean" implies that the water must be
free from particulate matter in which coliform bacteria are so
imbedded as to survive disinfection.
Although disinfection, coagulation, and sedimentation as prac-
ticed at some plants did produce water conforming to the assumed
bacteriological objective for plant effluent, there is evidence that
coliform bacteria imbedded in particulate matter may survive
such treatment. Filtration or other means for removing particulate
matter should be provided at any plant treating water containing
appreciable coliform loading.
Coagulation, sedimentation, and filtration are inadequate treat-
ment for waters containing any appreciable coliform loadings.
Continuous and adequate chlorination must be provided.
Adequately designed and well-operated water treatment plants
can treat raw waters heavily laden with coliform bacteria to pro-
V
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duce plant effluents conforming to the assumed bacteriological
objective. More intensified chlorination has made this possible.
The effectiveness of water treatment processes, particularly
chlorination, in removing or inactivating coliform bacteria raises
the question of whether the coliform bacterial content by itself
is adequate criterion of the biological safety of a potable water.
Although laboratory studies indicate the residual chlorine levels
required to kill or inactivate certain viruses are higher than those
required to destroy coliform bacteria, there are no epidemiological
data indicating that viruses survive treatment provided by a
modern, well-operated water plant. Additional research is needed
before this apparent inconsistency can be reconciled.
While indiscriminate pollution of our water resources cannot
be tolerated, it should be recognized that, if necessary, water
plants can treat waters heavily laden with coliform bacteria. Im-
portant factors in securing effective continuous treatment of such
waters are the adequacy of the plant and the abilities of the
operating personnel.
vi
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I. Water Treatment Plant Data
CURRENT STATUS AND STUDY PROCEDURES
Numerous State and other agencies have established bacterial-
quality standards or objectives for waters used as sources for the
production of portable water. Many of these have been influenced
by the Public Health Service recommendations (1) which may be
summarized briefly as follows. For waters acceptable for treat-
ment by simple chlorination, the average coliform bacterial density
should not exceed 50 per 100 ml for any month. For waters ac-
ceptable for treatment by conventional rapid sand filtration with
continuous postchlorination, the monthly average coliform density
should not exceed 5,000 per 100 ml, and not more than 20 percent
of all samples examined during any month should exceed that
coliform density. The use of auxiliary treatment-prechlorination,
presedimentation, or equivalent-does not permit an increase in
the monthly average coliform density, but does permit more than
20 percent of those samples examined in any one month to exceed
5,000 per 100 ml, provided not more than 5 percent exceed 20,000
per 100 ml.
Previous Studies
These recommendations have been based mainly on the work
of Streeter and his associates (2) (3) (4) whose studies in-
volved the collection and analyses of data from 14 plants located
along the Ohio River (1923-1924), from 7 plants located in Ohio
and the Middle Atlantic States (1923-1924), from 13 plants treat-
ing waters from the Great Lakes (1926-1927), and from 5 years
operation of an experimental plant at Cincinnati, Ohio (1924-
1929).
All data, except those for the experimental plant, were for
plants disinfecting water by postchlorination only. The annual
average chlorine dosages applied did not exceed 0.8 mg/1 at 18
of the 28 plants. Information on the chlorine residuals in the
effluents at these plants is lacking.
The only data involving prechlorination were from 14 months
operation of the experimental plant. During the first 11 months
the prechlorine dosage was regulated to provide approximately
0.05 mg/1 total residual chlorine in the water applied to the filter.
1
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This low chlorine residual was maintained to prevent destruction
of the biota on the filter. The filter effluent was rechlorinated to
provide a total residual chlorine of 0.05 mg/1 in the finished
water. Higher chlorine concentrations were considered undesir-
able due to possible development of tastes and odors.
Greater prechlorination dosages were used throughout the last
3 months. Average monthly concentrations of 0.36, 0.76, and
0.33 mg/1 were recorded for the water applied to the filter. This
increase in chlorine content resulted in considerable destruction
and sloughing of the biota on the filter. During the second month
the chlorine residual in the water dropped from 0.76 to 0.01 mg/1
as it passed through the filter. Throughout this period postchlori-
nation was used to provide between 0.05 and 0.10 mg/1 total
chlorine residual in the finished water.
In general, the coliform densities of the raw waters at the
plants studied were obtained using single-tube plantings in deci-
mal dilutions, presumptive tests, and were expressed in terms of
the "Indicated Number" (Phelps's Index).
In 1950, Streeter (5) made a resurvey of the bacterial effici-
encies of water treatment plants for the Ohio River Valley Water
Sanitation Commission. Data from six plants were analyzed and
compared to similar information from these same plants for the
period 1923-24. Again raw water coliform densities were de-
termined using single-tube plantings in a decimal dilution series
and reported in terms of the "Indicated Number." In all cases,
the presumptive test only was used.
In summarizing these data, Streeter (5a) states:
From the standpoint of tolerance, a limiting average coliform density of
10,000 per 100 ml (I.N.) would be adequately safe, but would involve the
continued dependence on intensified chlorination as an integral part of every
water purification plant.
However, in consideration of the desire to provide a safe and
palatable drinking water, he recommended (5a):
an ultimate bacterial-quality objective such that the monthly arithmetical
average "Most Probably Number" of coliform bacteria in the river at all
water supply intakes will not exceed 5,000 per 100 ml in any month; nor will
exceed this figure in more than 20 percent of the samples of raw water
examined during any month; nor will exceed 20,000 per 100 ml in more than
5 percent of such samples.
In a panel discussion in 1950, Faber (6) presented data for
six plants, five of which had average annual coliform densities
in raw water ranging from 5,000 to 2,000,0001 "Most Probable
Number" per 100 ml. All plants used prechlorination. According
to the information presented, the coliform densities in the waters
applied to the filters at all three plants reporting such data were
1 2.8 tlmw an Indicated Number of 890,040.
2
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zero, and those for the finished water at all five plants reporting
data were zero. The sixth, a Canadian plant, reported the finished
water to be of "safe sanitary quality."
The Public Health Service recommendation regarding the per-
missible average coliform bacterial density in water acceptable
for treatment by simple chlorination has been based on data re-
sulting from postchlorination of filter effluent water. From their
studies, Streeter and his associates (4a) concluded that water
conforming with the "Treasury Department Bxoli standard" can
be produced by simple chlorination of Ohio River water provided
the limiting B. coli index (I.N.) does not exceed 80 per 100 ml,
and from Great Lakes water, provided this index does not exceed
50 per 100 ml.
Treatment Processes, 1930 vs. 1956
Since 1930, pollution has resulted in increased bacterial loadings
of raw waters. Many plants are now treating waters having coli-
form densities far in excess of the limiting values recommended
by the Public Health Service.
Plant design and operation have also changed. Prechlorination,
or at least chlorination prior to filtration, is the common practice.
Many plants carry substantial chlorine residuals—as high as 1
mg/1 free chlorine—in their finished water. Numerous filters
have been constructed or rebuilt using coarser sand, and filtration
rates of 3 or more gallons per square foot per minute are frequent
occurrences during summer periods of peak production at many
plants. The problems due to mud balls and caking of sand in filters
have been eliminated to a large extent by better backwashing.
Improvements in coagulation and sedimentation have reduced
turbidities to a point where those in the water applied to the
filter are usually less than 5 units, and at most plants the practice
of filtration to waste to establish a "schmutzdeck" has been dis-
continued.
Finally, better plant control has been secured through more
adequate laboratory equipment, better trained personnel, and im-
proved laboratory procedures. Probably the most important ad-
vancement in the water treatment field in recent years has been
the increased use of chlorine which has resulted from the better
understanding of the chemical reactions involved and the disin-
fecting properties of free and combined chlorine.
It is also to be noted that the current Standard Methods (7)
recognizes only the "Most Probable Number" for reporting the
density of coliform organisms, while Streeter used the "Indi-
cated Number (Phelps's Index.) This is significant when one
considers that for single-tube plantings in a series of decimal dilu-
S
-------
tions the ratio of the average monthly "Most Probable Number"
to that of the "Indicated Number" is approximately 2.3 to 1*
Plants Studied
Although recognizing the numerous problems involved, it was
decided to base this study on data available from operating plants.
Through the assistance of State departments of health, a tentative
list of plants to be considered was prepared. These were selected
on the basis of (a) frequent average monthly raw water coliform
bacterial densities in excess of current Public Health Service
recommendations, and (b) the adequacy of the bacteriological
data available.
Some 80 plants were visited. Monthly summary records show-
ing average daily data, general information on the design and
operation of the plant, and data on bacteriological procedures
have been obtained from approximately 60 conventional filtration
plants, three simple chlorination plants, and one plant treating
water by coagulation, sedimentation, and disinfection.
A list of plants, data from which have been used in this study,
is shown in table 1. Treatment facilities and average chemical
dosages for the period covered at each plant are given in table 2.
The data on chemical applications are approximate as they are
based on averages of monthly average data from plant records.
Also, the purity of the chemicals varied. Further, some chemicals
which were used occasionally may not have been included in
summary data records available for this study.
Considerable difficulty has been encountered in evaluating the
data obtained from different plants. Rather cursory examinations
of bacteriological laboratory equipment and procedures for coli-
form examination of waters at these plants indicate numerous
departures from the 1946 edition of Standard Methods (8) . Prob-
ably the most important of these were (a) media of insufficient
strength—somewhere between 10 percent and 20 percent of those
plants visited used single-strength medium for 10-ml plantings—
and (b) failure to transplant 24-hour presumptive positives
immediately for confirmation. Other frequently encountered
departures were (a) use of media other than lactose or lauryl
tryptose broth for initial raw water plantings, (b) prolonged ex-
posure of media to heat in autoclaving, (c) use of distilled water
for dilution water (also use of tap water containing chlorine),
and (d) unsatisfactory dilution techniques, such as making mul-
tiple 10-to-l dilutions or the use of cotton-stoppered dilution
bottles or tubes which make it impossible to agitate the contents
properly. Although these data are from a select group of plants
4
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Table l
WATER TREATMENT PLANTS STUDIED
Alton, 111. Laredo, Tex.
American Sugar Refinery Co. Lawrence, Kans.
New Orleans. La. Lawrence, Maas
Anheuser-Busch, St. Louis, Mo. Lorain, Ohio
Appleton, Wis. Louisville, Ky.
Ashland. Ky.
Minneapolis, (Fridley), Minn.
Batavia, N. Y. Moline, IU.
Beaver Falls (Eastvale) ¦ Pa.
Beaver Falls (New Brighton), Pa. Nashville, Tenn.
Bridgeport, Conn. New Albany, Ind.
New Castle, Pa.
Cedar Rapids, Iowa Nltro, W. Va.
Celanese Fibers Co., Rome, Ga.
Cincinnati, Ohio Omaha, Nebr.
Columbus, Ohio Ottumwa, Iowa
Dallas (Elm Fork), Tex. Passaic Valley Water Commission,
Danville, Va. Clifton, N. 3,
Port Huron, Mien.
East Liverpool, Ohio Portsmouth, Ohio
East St. Louis, 111. Powthkeensle, N. Y.
E, I. DuPont, Spruance Works, Va. Pueblo, Colo.
Fieldcrest Mills, Inc., Spray, N. C. Quincy, 111.
Flat Rock, Mich.
Flint. Mich. Rome, Ga.
Frankenmuth, Mich. . . _
Salisbury, N. C.
Granite City, 111. Salt Lake City, Utah
St. Louis (Chain of Rocks), Mo.
Hackensack Water Co., New Milford, N. J. St. Louis (Howard Bend), Mo.
Huntinfton, W. Va. St. Louts County, (Central Plant), Mo.
Streator, 111.
Indianapolis (Fall Creek), Ind. _
Indianapolis (White R.), Ind. Waukegon, 111.
Weirton, W. Va.
Kansas City, Kans. Wyandotte, Mich.
Kansas City, Mo.
with respect to laboratory control, in some cases they must be
considered of questionable value for use in research.
Except for residual chlorine concentrations, which were com-
monly determined by the orthotolidine procedure and usually re-
ported as total chlorine, plant records were generally adequate.
Analysis of Bacteriological Data
As previously stated there were many variables in the quality
and precision of the bacteriological data obtained from different
plants. In general, raw water data have been based on at least
five daily samples per week, with each sample tested by one or
more plantings in each of a series of decimal volumes. Most of
the plants examined raw water by the presumptive test, but
several used the confirmed test or made the initial planting direct-
ly into brilliant green lactose bile broth.
Where possible, MPN values have been taken from tables (9);
however, those for a few plants using other than the decimal dilu-
tion system were calculated by Thomas's (10) approximate
method. Indeterminate results having all portions positive have
been assumed to have an MPN equal to or greater than that which
would have occurred if the next decimal dilution had been planted
and all portions found to be negative. Thus, if all portions of
5
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Tabm 2.—Treatment plant facilities and average chemical dosages
p
PAH
PAH
P
P
P
P4H
P
PAH
P
P
PAH
PAH
P
PAH
P
P
P
P
PAH
P
P
P
P
P
P
P
PAH
P
P
P
P
PAH
P
P
PAH
P
Treatment facilities and ehetmicais
So Ng Do Cib Mtb So Frs Se
Ne Do CS1 (MtpeSv) Fr* De Sc
ClMb So Ci Dc (MtpsSr) Ke So BVa Se
NgDcCaTc Mp So Fra Dc Kg Se
Mb Sm Calt Mhp Sm Dc Mtp So Frt Se Ne De
So Ca] Te Mtp 8m De So Fra Sc De
Ne De Cat Te A« CI (MtpsSvJCs Te Mtp Se R Fre(a) No Dz Sc.
De Cal Mtp So Fra Kp Ab Sc Dc...
Ng Dc CalTe Mtp8mo R Fib De KcSc
Tc C» A« So De So Fra Kc Dx So
De Cu Mtp Sra Frs Dc Kp Se
Sm Ne Dc Caub Mbp TcCai Mp S R De Fra Se
De Sm Cata Dc M tp Sm R C* So R Frs (a) Sc Nc
De Ca Te Mb So Kb Fra Di Sc
So 80 Caih Mb Sm R Tc 8 R Fra Dc So Dd Fac Kp Ng Dc
De Ca Mlp Scm Dc Fra Nc So
Dc Ca Mtp. St 4
•16
•17
>28
•16
•20
•24
•29
•42
•13
•16
•18
•18
•16
•31
•28
•33
•37
•20
•12
•16
•60
•12
•39
Ferrous
mi fate,
nig A
Ferric
sulfate
mg/1
Acti-
vated
ulna.
mg/1
Sodium
atami.
lutte.
mn
Acti-
vated
earbon,
mg/1
line,
mg/1
Soda-
Sfh
Carbon
dioxide,
mg/1
•6
•31
•103
•150
•10
•10
•22
•118
•16
•140
•24
•0.5
•0.8
•2.8
•4.0
¦4.5
(X)
•5.4
•34.0
•24
"9
•12
'2.25
•1.2
•4.6
•166
•228
•9
•228
(X)
(X)
'5.0
»6.2
•80
•69
•(X)
>10
•4.4
V4
•3.1
113
>18
48
*.4
•2.0
•34
•5.5
•6.7
•8
•1.6
•4.1
•8
•9
•36
•8
-------
36
PAH
37
P
38
PAH
30
P
40
PAH
41a
PAH
41b
PAH
42
P
43
PAH
44
PAH
45
PAH
46
P
47
P
48
P
40
P
SO
PAH
51
P
62
P
S3
PAH
64
P
S-l
P
C-l
D
0-2
D
C-3
D
CI So Ne Do Ci Mip So C5 Mp So Ci Nc Dc Fi* 8e
Ne Dc Cat Mop So Ft* Kp Sc
Be Gat Mb So CI Mt tell W Ne De So Fa Be,..
Dc Cd Mtp So Fra KpSe.
De Cafl Te Mt So DeKe So Fra Di 8e
DtCStKcBfb&BEfloKiB Ai\ o* u. rw
DeCbMtOa&MihnKe ft»J HeaeDx.
C«1 Mt Do Mp So Dd Fis Kp So Do
DcC»Mt8oClaMp8niSoRfta8eDe
Te Cut Mb (MtpdBv) So Dc Fra So Dd
Dx Mi C*1 Mt CaTe Mp 8 R Fra Ke 8c De.
Ai Ca Te M De S Kp Fr* (MtpoSrFw) Do Se
DeCaTeMbp8oFtsDeS«.....
De So Cat TcMpb 8m E Fra Nc Dc Sc
De Ca So CK Te Mhp Sm Ft* Ng Do Kp Se.
De CSI To Mtp Sm ra Kp Se De
Ng Dc Ca Te Mp So Frm Kp Be De
De Ca) Mb 8 (MtpeBr) Italic De Mb Se
CaJa Mtb Sm R So Fia De60 So Ke
De Cal Te MtpSoCTe) FlciDe (Dd) Se
SoCaTeNcDeSoNe DeSo —
Dolfi
NgDe
DcKep.
Applied 6 percent at time.
ApptUd 6-15 percent of time.
Applied IMS percent «f time.
Applied 26-85 percent of time.
Applied 85-45 percent of time.
AppHert 46-65 percent at time.
AppBed 65-66 pereeat of tine.
731
730
m
730
730
730
730
731
730
638
730
730
730
730
683
730
730
730
731
730
730
1,039
97
41.0
6.5
4.1
3.4
.8
38.0
40.0
7.4
1.6
.1
12.0
6.6
71.0
86.0
42.0
51.0
30.4
51.0
7.4
10.0
10.4
17.0
8.4
•7
•120
•12
•175
•186
•17
•96
•106
•204
•16
•(X)
•17
to
•19
•18
•28
•15
•30
<18
40
•14
•20
•12
*11
•5
•24
•18
•30
•26
20
(T)
•1.7
•1
•14
•10
•11
•22
<4.6
•.2
•36
vu
"ii46'
•1
(X)
"w"
•24
- §3
S>&$- A oto
CO 00
*1.7
•28
•15
•96
•7
•6
•169
•4
00 90
(X)
•13
•13
•75
•(X)
•1.5
•1.2
•4
T Applied 65-75 percent of time.
* Applied 75-85 percent of time.
* Applied 86-06 percent of time.
* Applied $ 96 percent of time.
X Used at least part time.
1 Understood to be used, but data not available.
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Table 2.—Treatment plaint facilities and average chemical dosages—continued
Plant
Coda
lMtmlmr
'sr
plant
1
P
2
PAH
3
PAH
4
P
5
P
S
P
7
PAH
8
P
9
PAH
10
P
11
P
12
PAH
13
PAH
14
P
15
PAH
16
P
17
P
18a
P
1%
P
19
PAH
20
P
21
P
22
P
23
P
24
P
25
P
26
P
27
PAH
28
P
29
P
90
P
31
P
32
PAH
33a
P
33b
P
34
PAH
35
P
Treatment facilities and chemicals
So Ng De Cm Mtb So Fra Sc
Ng Dc CU (MtpsSv) Fra Dc So
(3 Mb Bo Ci De (MtpeSvlKe So Ra.Sc
Ng De Ca Te Mp So fra De Ep Se
Mb Sm CaltMbp Sm De Mfe> So ftg Sc Ne Dc
80 C&I Te Mtp Sm Dc So Fra Se Dc .
Nc Dc Cat Tc As CI (MtpsSv) Ca Te Mtp Sc R Fre(a) Ne Dx Sc
De Cal Mtp Se Kp A« Sc De
Kg Dc Oal Te Mtp Smo E Fre De Ee Se
To Ca As So Dc So Fre Ko Dx Sc
Dc Cu Mtp Sm Fre De Ep Se
Sm Ne DeCaib Mbp Tc Cai Mp 8 R Dc Frg Sc
De Sm Cab De Mtp Sm R Ca So R Frs(a) Se Ne ..
Dc Ca Te Mb So Kp Fre Dx Sc
Se So Cub Mb Sm R Tc S & Frs De So Dd Fac Ep Ng Dc
Dc Ca Mtp San Dc Fra Nc Sc.
De Ca Mtps Sv (MiSo) De fts (Fe) Sc
Dc Ca Mp Sm Fra De In.
Ne De Ca 80 Ne De So Fr De J
Cab Mb (MtpeSv) R Caa Nc Te Mb Dc So Frs Ng Dc Se......
Do Ca Mb Tc Sc Dx Fra Sc
Do Ca Tc Mb So Kp Fra Dx So
De Css Mip So Fra Ng De Sc.
A De CiUMtpaSv) Dx Fre Dx 8c
So Dc Cal Mb So Tc Mb Ca Mb So Dc Frg Dc So
So Cal Dc Mib So Fra Do Ep Sc
Cal M 80 Fra Ke Nc Dc(x) Se
Te Cat Mbp &n(^DeTcMto&nRI>cFraSc.
De Ca Mib So Fre As Fs Kp Sc Dc
Ne De Ca Te Mi So F"ra Kp Se Dx Sc
Dc Ca Te Mi A CI So MpSo Fra Sc Dx Sc
Ca Mp So Cal De Mtp Sm Fra Dx Se
So Call Mb Sm Nc Dc Ca Mb Sm Fre Nc De Sc
A Cafl Mtp to
So (3 Mt Cai Mb Sm Cai Mb Cai No De Sm Do FVs Se
So Cal M So Fra 8c N Dc« Sc
Days
of
record
730
361
730
730
731
"30
730
719
730
730
731
731
730
624
731
731
681
730
730
730
730
730
730
730
730
73!
730
730
730
730
729
731
730
731
731
Complex
Phos-
phate,
me/1
<=1.3
•2.9
•.2
>4.0
•.4
X
Chlorine
fte
me A
•2.0
(X)
•14 5
(X)
•4.0
•3.6
•3.0
•2.6
•2.3
•3.6
•3.2
(X)
•11.4
•2.2
•3.5
•3.2
•4 2
•6.0
•5.0
•3.0
•2.1
•2 6
(X)
•3.6
•7.1
•3.6
•5.6
>1.2
•1.6
'.8
•1.4
(X)
•1.4
lateral
mg/1
•(X)
•1.0
«.7
»4.2
(X)
'.6
•.4
(X)
Post
mg/1
(X)
(X)
•0 2
•7
•.7
•.2
•2,3
•.8
'.2
(X)
•2
*1.2
«,3
«.3
«.4
*2
•.3
•6
(X)
•1.2
«.l
•1.2
•.3
•.4
•1.2
(X)
•1.0
•1.2
Total
mg/1
•2.0
•2.6
•14.5
•.9
4.2
•4.3
•3.7
2.6
•4.6
•4.4
•3.4
•1.6
•11.4
•2.4
•4.3
•3.2
•5.2
•6.3
•5.9
•4.6
•3.2
•2.4
•3.2
•5 3
4 0
•7.1
•1.2
3.8
•5.7
•1.9
•1.9
•6
•2.6
•7.0
•2.4
•1.2
Ammonia
Anhy-
drous,
mg/I
>0.2
(«
• .2
•1.1
•1.7
•.1
•1
•.3
Other,
mg/1
"0.5
•2.3
•1.1
•1.3
¦2.7
!. 6
1.4
•3.4
'.6
•.4
•.4
•1.4
•.6
Sodium
chlorite,
mg/1
•0.2
•.3
•.1
•2
•.1
•3.6
•.5
'.1
•.3
•2
•.2
Other*
Dosage,
mg/1
Chttnictti
-------
36
PAH
37
P
38
PAH
30
P
40
PAH
41*
PAH
41b
PAH
42
P
43
PAH
44
PAH
46
PAH
46
P
47
P
48
P
49
P
60
PAH
51
P
S3
P
63
PAH
54
P
8-1
P
C-l
D
0-2
D
0-3
D
CI So No De Ci Mip So CI Up So Ci Ne De Fi» Se
Ne De Cat Mop So Fra KpBc
De Cat Mb 80 Ci Mt SmB Dd Ne Dc So ft* 8e
Do CU Mtp 80 Fn Kp 8e..
Do Cm Te M t So Del
De Cle Nb Ub Ebi & So Ks « w w
DcCfeMtCaBMSm Ke Fn/ Bc-NeL,I•-
Cal Mt DeMpSo Dd FtiKpSeDc
Da Ca Mt So Cbt Mp Sm 80 R Fra 8e De.....
Te Cail Mb (MtosSr) 8a De Fra 80 Dd.
Dx Mi Cal Mt GsTe Mp8 B Fi» Ke Sc De...
As Ca Te M De 8 Kp Fra (ll^Srih) De Se
DeO»TeMb|pSoraDeSe
Do 80 Cat Te Mpt> Cla Sm B Fra Ne Dc Be.
DeCaSoOiTeMknSmFwNg
De CH Te Mtp Sm Aa Kp 8s De.
Ng Dc Ca Te Mp So Fra Kp Se Do
De Cal Mb 8 (MtpeBr) FraNg De Mb 8e.
Cals Mtb 8m R So Fra Dc(x) §0 Ke
De Cal Te MtpSo (Te) Fra De (Dd) 8e....
9o O* Te Ne De So Nc De So
Do Mi
NfDe...
DiKep
* Applied 6 percent ai time.
1 Applied &-1S percent ot time.
1 Applied 15-26 percent at time.
•Applied 25-86 percent at time.
* Applied 65-45 percent at time.
* Applied 45-55 percent of time.
•Applied 56-65 percent at time.
O
731
730
629
730
730
730
730
731
730
639
730
730
730
730
730
730
730
731
730
730
039
97
1.0
•2.2
•2.9
•8.4
•2.2
•6.0
•6.6
•7.6
>0.3
•3
«X
•.8
•0.6
•.3
•.3
•.8
'1.9
•3.6
•1
•9.6
•,3
•.6
•4.9
•8.0
>2.3
•1.5
•.7
•1.7
•.3
•.4'
•.3
•1.5
• 2
•1.0
•.3
•.1
•0.6
•2.6
•4.0
•1.7
•1.5
•2.4
•1,8
•2.5
•2.9
•8.4
•2.2
•8.6
•6.4
•7.9
•1.1
•3.6
•9.6
•2.0
•.8
•S.3
•8.2
•3.1
•1.7
•1.7
•.3
•2.6
•4.0
•1.7
•1.6
•2.4
•9
».6
•2.5
•2.0
•.6
•.3
•1.4
•3.5
•2.0
'1.1
•.5
•.2
•_4
•.2
•.3
».3
'.1
»{X)
•2.8
•.1
N«£d«
SO.
SO.
SO.
T Applied 65-75 percent of time.
•Applied 76-86 percent of time.
•Applied 85-85 percent of time.
•AnAtd 5 K percent of time.
Z TJeed at least part time.
T Understood to be used, bat data not available.
-------
KEY FOR TREATMENT
FACILITIES AND CHEMICALS USED IN
Tables 2
Type of Plant
p—Purification
H—Softening
D—Disinfection
Treatment or Device
A—Aeration
Ab..spray aerator
C—Chemical dosage for coagulation or soft-
ening
Ca. .alum
Ci..iron salts
CI. .lime
Cs. .soda ash
Ct. .activated silica
D—Disinfection
Do..chlorine gas
Dd. .dechlorination
Dx. .chlorine dioxide
F—Filters
Fa. .anthrsfilt
Fc. .roughing or contact
Fr..gravity (rapid)
Fa. .sand
K—Chemical dosage for corrosion correction
or water stabilization
Kc. .phosphate compounds
Kp..alkali feed for pH adjustment
M—Mixing device or tank
Mb. .baffle mix
Mh. .hydraulic (standing wave flume)
Mi.. injection or pump suction
Mp..sIow mechanical mix
Ms. .patented sludge blanket
Mt..rapid mechanical mix
(MtpsSv) . ."Liquon Reactor"; "Acella-
tor": or "Precipitator"
N—Ammoniation
Nc. .ammonium compound
Ng. .ammonia gas
R—Recarbonatlon
S—Sedimentation
Sc..covered basins (other than housed)
Sm. .mechanical sludge removal
So. .open basin (may be In plant build-
Sv. .upflow cylindrical tanks
(MtpsSv) . ."Liquon Reactor": "Aceela-
tor"i or "Precipitator"
T—Chemical taste and odor control
Tc. .activated carbon
3.33 ml plantings [abbreviated form for writing three 1-ml, three
0.1-ml, and three 0.01-ml portions (11)] were positive, the MPN
has been assumed to equal or exceed that for 3.330 ml positives,
or =S24,000 per 100 ml. Likewise, if all portions of the 3.33 ml
plantings were negative, the MPN has been assumed to be ^23.
Average bacterial densities include such data. Where practical,
averages including indeterminates due to all portions being posi-
tive, or all portions being negative, have been prefixed by a
sign, 5 or Those containing both high and low indeterminates
have been prefixed by a ± sign.
The bacteriological data for filter effluent samples are confirmed
test data unless otherwise noted. Usually they are the results from
examining one or more portions in each of two or more decimal
volumes.
Samples of plant effluent, and sometimes of filter effluent, were
taken daily at most plants. Usually five 10-ml portions were
examined by either the confirmed or completed test. Several
plants also examined 100-ml and 1-ml portions. Sometimes two or
more samples were taken during the day. For example, one plant
examined one 100-ml portion of each of 12 samples daily. All
results on these individual samples are indeterminate, being
either 5 or 5=1 per 100 ml. In such cases an average MPN for
the day has been calculated by considering the results from the
individual samples as those from a single daily composite, or as
twelve 100-ml portions of a single sample and the MPN has been
computed by the formula:
MPN per 100 ml=-^-log,.
10
-------
where
N—volume of portion (ml)
K=total number of portions
q—total number of portions negative
For plants examining only 100-ml portions of plant effluent,
the percentage of 10-ml positive portions has been estimated by
using the above formula to solve for the number of positive 10-ml
portions giving the same MPN as that obtained for the 100-ml
portions. Also in a few cases an average MPN for a group of
samples has been estimated using the above formula. Such a
method has been combined with Thomas's (12) log-probability
procedure to approximate an average MPN for filter effluent at
each of two plants that examined 1-ml portions only.
For computing averages of MPN for filtered and finished water,
values <2.2 per 100 ml (no positives in five 10-ml plantings) have
been considered to be 0 per 100 ml; however, indeterminates such
as all positive portions in a 51.0 planting have been taken as =2:240
per. 100 ml.
COLIFORM BACTERIAL OBJECTIVE FOR
WATER TREATMENT PLANT EFFLUENT
The Public Health Service Drinking Water Standards are those
generally accepted for potable water in this country. These Stand-
ards specify that the bacterial quality of the water shall be based
on a variable number, determined by the population served,, of
samples collected from representative locations throughout the
distribution system. Compliances with the Public Health Service
Drinking Water Standards cannot be determined using bacterio-
logical data for plant effluent samples only.
On the other hand, plant performance cannot be based on the
bacterial quality of samples taken from various locations through-
out the community. Inclusion of such data would reflect a change
in bacterial quality that might occur in the distribution system
and not permit a true evaluation of the treatment processes.
The coliform bacterial objective for water plant effluent used
in this paper is that not more than 2 percent of all 10-ml portions
of plant effluent examined during any one month shall be positive
for coliform organisms. This objective has been selected after
analysis of the data presented. Not only is conformance to this
objective readily obtainable, but in the opinion of the author, all
plants failing to produce waters meeting this objective had de-
ficiencies in either facilities or operation.
11
-------
SIMPLE CHLORINATION
The Public Health Service has recommended (1) that the aver-
age coliform bacterial density during any month should not exceed
50 per 100 ml for a surface water to be acceptable for treatment
by simple chlorination. This recommendation has been adopted
by various state and other agencies. Most of the data (2) (3) (4)
upon which the recommendation was based was from marginal
postchlorination of pretreated (coagulated, settled, and filtered)
waters to provide total residual chlorine concentrations between
0.05 and 0.1 mg/1. The applicability of such data to either un-
filtered surface water or to water chlorinated to provide a sub-
stantial free chlorine residual may be questionable.
Collection of Data
Although a special effort was made to locate plants having ade-
quate data for study of the effectiveness in reduction of coliform
bacteria by chlorination of untreated surface waters, only 4 plants
were found where the monthly average coliform density in the
raw water exceeded 50 per 100 ml. Two or three years of data
from each of three plants using simple chlorination, and from
three filtration plants using only postchlorination have been
analyzed.
Plants Studied
Plant C-l treated an average of 10 mgd of Great Lakes water.
The turbidity usually did not exceed 10, but occasionally reached
100 units. Data for pH and temperature were not available.
Treatment consisted of chlorination. The amount applied ranged
from 1.1 to 2.9, and averaged 1.7 mg/1. Residual chlorine con-
centrations determined by the Laux flash test averaged 1.0 mg/1
on samples taken after a theoretical contact time estimated to
be 20 minutes. Minimum daily residuals of 0.7 and 0.2 mg/1 were
recorded during 1958 and 1954, respectively.
Raw and chlorinated water samples were examined by the
County-City Health Department 5 or 6 days per week. Coliform
bacterial examinations of raw water samples were made using
11.1 ml plantings, confirmed test; and for the chlorinated water
with Ave 10-ml portions, confirmed test. Except for use of single-
strength broth for 10-ml plantings, bacteriological laboratory pro-
cedures were satisfactory.
Plant C-2 used water from a mountain stream as one of its
sources of supply. When water from this source was used the
average amount treated was approximately 17 mgd. Normally,
the turbidity was less than 5 units. It exceeded 10 units during
12
-------
only 8 of 35 months. The maximum recorded turbidity was 38
units. The pH was consistently recorded as 8.0. The water temper-
atures varied with the seasons, ranging from 32° to 55° F.
Treatment consisted of adding ammonia and chlorine. Average
dosages were 1.5 mg/1 chlorine and 0.12 mg/1 ammonia. A con-
tinuous recorder was used to measure the total residual chlorine,
which averaged 0.7 mg/1 after approximately 20 minutes contact.
Minimum daily averages showed only 0.3 or 0.4 mg/1.
Raw and chlorinated water samples usually were examined 5
days each week by the City Health Department. Coliform bacterial
examinations of raw water were made using 55.5 ml plantings,
confirmed test; and for the chlorinated water by five 10-ml plant-
ings, completed test. Bacteriological laboratory procedures con-
formed with Standard Methods.
Plant C-3 treated 4 to 20 mgd of impounded water. Turbidity
ranged from 0 to 20 units, and did not exceed 5 for 94 percent of
the determinations. This was a soft water with a pH ranging from
6.3 to 6.9, and averaging 6.6. Temperature varied seasonally
from 34° to 71° F. Treatment consisted of chlorination, also the
addition of lime and calgon to prevent corrosion and deposition in
mains. Chlorine additions ranged from 1.2 to 4.0, and averaged
2.4 mg/1. The total chlorine residual after 10 minutes contact
time, as determined by a continuous recorder, averaged 1.3, with
a minimum of 0.9 mg/1. That determined from one of two other
locations, which provided an average contact time estimated to
be either 20 or 60 minutes, usually ranged from 0.1 to 0.3 mg/1.
However, 0.0 mg/1 residuals frequently occurred.
Bacteriological data for raw and chlorinated waters were based
on samples taken once each week. Raw water coliform densities
were determined by examining 51.1 ml plantings, confirmed test,
and those for the chlorinated water by five 10-ml plantings, com-
pleted test, using samples from either one or both of two locations.
Bacteriological laboratory procedures conformed to Standard
Methods,
Operational procedure used at three conventional rapid sand
filtration plants permitted study of the effect of chlorination on
clarified and filtered waters.
Plant 26 postchlorinated filter effluent with an average dosage
of 1.2 mg/1. The pH of the water ranged from 6.9 to 7,7, and
averaged 7.4. The temperature of the raw water varied from
33° to 87° F, according to the season. Total residual chlorine
level in the plant effluent ranged from 0.2 to 1.0, and averaged
0.4 mg/1. This was after a theoretical contact time varying
between 2.5 and 5 hours.
Samples of filter and plant effluents were taken daily. Coliform
18
-------
examinations of filter effluents were made using one 1-ml portion,
confirmed test and of plant effluent, using five 10-ml portions, con-
firmed test.
Plant 35 secured water from the same source as Plant 26. The
coagulated, settled, and filtered water was treated with an aver-
age of 1.2 mg/1 of chlorine. This water had a pH ranging from
6.9 to 8.0 and averaging 7.5. The raw water temperature varied
from 32° to 87° F. Daily total residual chlorine levels, after a
theoretical contact time between 0.9 and 1.7 hours, averaged 0.5
and ranged from 0.3 to 1.0 mg/1.
Samples of filter and plant effluents were examined daily. Pro-
cedures were identical to those reported for Plant 26 except that
the presumptive test only was used for examining the filter ef-
fluent.
At Plant 53 the effluent from the filter had been treated by
coagulation, sedimentation, and excess lime-soda softening fol-
lowed by secondary sedimentation and recarbonation. The soften-
ing process resulted in water of high pH. That for the plant
effluent ranged from 9.1 to 10.9 and averaged 10.3 for the 2-year
period. Raw water temperatures varied from 32° to 80° F.
Disinfection was by marginal postchlorination. Chlorine dos-
ages varied from 0.1 to 0.8 mg/1 for daily averages; from 0.2 to
0.6 for monthly averages, and averaged 0.3 for the 2-year period.
The total residual chlorine concentration as determined on samples
taken after a theoretical contact time ranging from 5 to 10 hours
varied from a trace (<0.05) to 0.3 mg/1. They equaled or ex-
ceeded 0.1 mg/1 60 percent of the time, but 0.2 mg/1 only 1.9
percent of the time.
Samples of filter and plant effluents were collected daily* These
were examined for coliform bacteria using 51.0-ml plantings,
confirmed test, for the filter effluent, and five 10-ml portions, con-
firmed or completed test, for the plant effluent.
Discussion
Data from 3 plants totaling 84 months and 1,304 days for which
both raw and chlorinated water bacteriological records were
available, and also that from three conventional rapid sand filtra-
tion plants adding chlorine to filter effluent only, have been
examined.
In table 3, the plant months for each of the three simple chlori-
nation plants are classified by monthly arithmetical average
raw water coliform density. Then the total months in each group
are compared to the number of months during which coliform
bacteria were detected in one or more of the chlorinated water
samples. The greatest monthly average densities in the raw water
14
-------
Tables 8.—Effectiveness of simple chlorination in the reduction of coliform
bacteria, monthly data,
a
AW WATER—Coliform density
CHLORINATED WATER—
Months during which
coliform-poeitlve samples
were deteoted*
Ranee,
monthly average
MPN per 100 ml
Frequency, months
Plant
C-l
Plant
C-2
Plant
0-3
AU
plants
Number
Percent
0— 24
14
6
4
7
10
15
3
1
13
1
6
3
0
1
34
17
25
6
1
1
4
2
2
0
0
0
12
12
8
0
0
0
35— 49
50— 09
100—240
250—490
5500
Total or avg.
24
36
24
84
S
10
• All coliform positive sample* occurred at Plant 0-1*
were i?98, 340, and 5;660 per 100 ml at Plants C-l, C-2, and
C-3, respectively. The monthly average coliform loadings for raw
water exceed 49 per 100 ml during 39.3 percent of the time, and
99 per 100 ml during 9.5 percent of the time.
Coliform bacteria were found in the chlorinated water in only
8 samples, all from Plant C-l. Each coliform positive sample
occurred in a different month. The detection of coliform bacteria
at Plant C-l only cannot be explained on either the basis of raw
water loading or the reported chlorine residuals. It may be sig-
nificant that both the facilities and technical supervision were
considered inferior at this plant. For example, chlorination facili-
ties consisted of two 200 lb/day chlorinators.2 Failure of one of
these units during a period of peak flow would result in less than
average chlorine application. It was also observed that a residual
chlorine recorder installed at this plant had not been maintained
and was inoperative. However, during 23 of the 24 months of
record less than 2.0 percent of all 10-ml portions of chlorinated
water examined were positive for coliform bacteria. For the
month of poorest plant effluent only 2.3 percent of the 10-ml por-
tions examined were coliform positive.
Table 4 groups the daily data according to the coliform bacteria
in the raw water and compares the frequencies with which coli-
form were detected in the chlorinated water for the various
groups. Although the coliform densities in the raw water varied
from ^2.3 to ^2400 per 100 ml at each plant, there were only 22^
days during which they exceeded 240 per 100 ml. There appear
to be no significant differences in the effectiveness of chlorination
for daily coliforms loadings ranging from 0 to 240 per 100 ml.
The filter effluents at Plants 26 and 35 contained coliform bac-
teria in 49 and 87 percent, respectively, of the 1-ml portions ex-
amined. If the results from each plant are considered as those
* Plant O-l hu alnoe corrected this situation by the installation of two chlorinators bavins
400 lb/day capacity.
16
-------
Table 4.—Effectiveness of simple chlorination in the reduction of coliform
bacteria, daily data
RAW WATER—Coliform density
CHLORINATED WATER-
Oays on which
Coliform-poeitive samples
wets detected*
Ranee,
daily
MPN per 100 ml
Frequency, days
Plant
C-l
Plant
0-2
Plant
C-3
All
plants
Number
Percent
0-24
601
322
172
69
91
17
1
2
61
21
0
16
0
0
1
884
193
69
149
17
1
4
4b
0
0
2«
0
0
0
0 5
.0
.0
1.4
.0
.0
.0
26-49
60- 99
100-240
40
260-490
600-990
giooo
1
Total or average
642
6A4
98
1,304
6
,S
1 At Plant C-li coliform b&cterl* (VPN at 2.8 per 100 ml) were detected In 2 sample* of
chlorinated water examined on days for which raw water data were not available.
¦ Coliform densities 8.2, 5.1, 2.2 and 2.2; avg. 4.6 per 100-ml.
* Coliform densities 2.2 and 2.2; avg, 2.2 per 100-ml.
from a single sample, the estimated 2-year average mast probable
numbers would be 67 and 205 per 100 ml, respectively. The aver-
age coliform density of the filter effluent at each of these two
plants has also been computed by assuming the bacteriological
results from each examination of 10 consecutive 1-ml portions as
representing the result from a single sample, and then applying
Thomas's log-probability procedure (12) to obtain an average
value. This procedure gives 2-year average most probable num-
bers of 77 and 249 per 100 ml for plants 26 and 35, respectively.
No coliform bacteria were detected at either plant on examination
of 731 samples of the chlorinated plant effluents by planting five
10-ml portions of each sample.
In analyzing the coliform bacteria data for Plant 53, shown in
table 5, it should be remembered that the final treatment consisted
of marginal chlorination, with the chlorine application averaging
only 0.3 mg/1, of a lime-soda softened water having a high pH.
In contrast to the data previously discussed, both the frequency
of detection and average density of coliform bacteria in the plant
effluent increase directly with the coliform loading in the filtered,
water. Insofar as it could be determined, the variations in daily
average residual chlorine concentration (trace to 0.29 mg/1) had
little effect on the coliform density in the plant effluent.
Conclusions
The available data are insufficient to draw general conclusions.
Two of the three simple chlorination plants treated surface waters
containing monthly average coliform loadings in excess of 60 per
100 ml to produce water meeting the assumed bacteriological ob-
jective for plant effluent. The limited data indicate that it is
possible to treat waters containing somewhat higher loadings.
16
-------
Table 5.—Effectiveness of marginal chlorination of filtered water, high in
pH, in the reduction of coliform bacteria, daily data, Plant No. SS
FILTER EFFLUENT—
Culiform-density*
PLANT EFFLUENT
Daily
MPN per
100 ml
Fre-
quency
Days
Total chlorine
residual
Number of days on which
coliform deneityb, MPN
per 100 till, was:
Coliform
density*,
Avg. MPN /
100 ml
Range in
concentration
lng/1
Fre-
quency)
days
<2.2
2 2
5.1
9 2
16
323
-------
teriological data for raw water; (d) unsatisfactory bacteriological
laboratory procedures; and (e) obvious errors in plant records.
The geographical distribution of the 54 plants is shown in
figure 1. All provided at least chemical coagulation, sedimentation,
filtration, and disinfection. Several provided additional treatment
such as multistage coagulation and sedimentation, excess lime or
lime-soda softening, taste and odor control, and corrosion control.
The sizes of these plants are indicated by table 6, which groups
them according to average daily water production for the 2-year
period. The smallest plant produced slightly less than 100,000
gpd; the largest more than 100 mgd.
In table 7 the plants are classified according to the annual
average total chlorine application and the location at which chlo-
rine (as chlorine, chloramine, or chlorine dioxide) was first ap-
plied. For the purpose of classification, prechlorination includes
any addition of chlorine providing substantial contact time prior
Table 6.—Sizes of the water filtration plants
Atoms water production, mgd
Number of plant*
0.1- 0.9
S
SO
13
8
B
8
1.0- 4.9
5.0- 9.9
10-24...,..,.
26-4fl
5«0
Total
54
18
-------
Table 7.—Chlorination practices at the water filtration plants
Total chlorine
application, mi A
Number of plant* at whioh chlorine
was first applied as:
Number of plants
applying indicated
onlorine dosage
Pre-
ohlorination
Intermediate
chlorination
Post-
chlorination
2
6
12
7
6
18
2
0
0
0
1
1
0
0
2
3
0
0
0
0
0
4
8
12
8
7
13
2
47
2
S
64
0.1-0.9
1.0-1.0
2.0-2,6
3.0-3.0
4.0-4.6
5.0-8.9
510
Total
to filtration; intermediate chlorination, the addition of chlorine
immediately prior to filtration; and postchlorination, any addition
of chlorine after filtration. At least 24 of these plants normally
applied chlorine at two or more locations.
The plants are grouped in tables 8 and 9 according to the aver-
age residual chlorine in their effluents. In most cases only total
residual chlorine was reported, but some plants reported free
Table 8.—Residual chlorine concentrations in effluents from St water
filtration plants using chlorine disinfection
Reiidual chlorine
concentration, mgfl
Number of plant* reporting*—
Free chlorine radda*!
Annual
average
Minimum
daily awns#
Total chlorine residual
Annual
average
Minimum
daily average
3 0.04....
0.1
0.2
o.w.a
0.6-0.0
1.0-1.0
5 8.0
Total*
0
t*
0
8
10
4
1
12
12
as
25
a Five plants reported both free and total residual chlorine concentration*. At three plants
chloramine disinfection was used during one of the two years Included la this study.
b Plants 44 and <8.
Table 9.—Residual chlorine concentrations in effluents from £5 water
filtration plants using chloramine disinfection
Number of plant* reporting"—
Residua! chlorine
concentration, mg/1
Free chlorine rwiduaJ
Total chlorine residual
Annual
average
Minimum
daily ararage
Annual
avenge
Minimum
daily average
^ 0.04
0
4
0
o
0.1-0.2
2
0
o
5
0.8-0.5
2
0
4
7
0.0-0.9
0
0
0
B
7
1.0-1,5
0
|
8
l.f-l.fl
o
0
4
o
j J.O.,
o
0
8
j
Totals.
4
4
28
35
* Toot plant* reported both free and total chlorine rwtdoala.
19
-------
chlorine and a few both free and total. It is significant to compare
the chlorine residuals maintained at these plants with the low
total chlorine residuals (apparently around 0.05 mg/I practiced
at the time of Streeter's studies for the Public Health Service.
Discussion
In table 10, data from 54 plants totaling 107 plant years are
grouped according to the annual arithmetical average density of
coliform bacteria in the raw water. These ranged from 1,100 to
1,700,000 per 100 ml. Each group is then subdivided according to
Table 10.—Effectiveness of conventional rapid sand filtration and disinfection
water plants in the reduction of coliform bacteria, annual data
HAW WATER—Coliform density
Annual Range, average
MPN per 100-ul
0- 4,900.,
6,000- 9,900.
10,000- 24.000.
26.000- 49,000.
fiO.OOO- 69.000.
100,000-490.000.
600,000-990,000.
$1,000,000.
Totals
Frequency
plant yean
_
17
32
28
11
1
2
2
107
PLANT EFFLUENT—Plant rem
during which the percentage of coli-
form-positive 10-ml portion* was*
0.00
26
19
7
1
.01-.09
0
0
1
18
0.1-0,9
fi
3
1
3
2
0
0
0
14
510
1
1
0
0
0
0
0
0
• For plants examining only 100-ml portions of plant effluent, the percentage of positive 10-ml
portions giving the same MPN has been used.
the percentage of treated water portions which were found posi-
tive for coliform organisms. Coliform bacteria were detected in
the plant effluent, during 50 percent of these plant years in which
raw water loadings were less than 10,000 per 100 ml; but in only
32 percent of all plant years in which the loadings were less than
100,000 per 100 ml. There are only two plant years during which
the number of 10-ml portions of finished water, which were posi-
tive for coliform bacteria, equaled or exceeded 1 percent of those
planted. Both occurred with raw water bacterial loadings less
than 10,000 per 100 ml.
Data for all plant years in which coliform organisms were de-
tected in 0.2 or more percent of all 10-ml portions of finished
water examined during the year are given in table 11. For coding
purposes the plants have been numbered in the order of decreasing
annual average density of coliform organisms in the raw water.
Four of the plants (Nos. 8, 24, 44, and 53), data from which ap-
pear in this table, will be discussed in some detail later.
Data for 1,281 plant months are grouped according to monthly
arithmetical average density of coliform bacteria in the raw
water in table 12. The maximum monthly density recorded was
20
-------
Table 11.—Coliform bacterial data for raw and finished waters at conven-
tional rapid sand filtration and disinfection water plants for all years during
which 0.2 or more percent of the 10-mX portions of plant effluent examined
were positive for coliform bacteria
Plant
code
number
Year
RAW WATER—
CaUform denaity,
annual average
MPN per 100 ml
PLANT EFFLUENT—
10-ml portion*
Number
examined
Percent
poaitive
8
1954
•*59,000
1,250
0.72
15
1964
•>*39,000
<>1,565
•,27
24
1954
•28,000
1.825
.88
44
1953
•6,800
918
.22
1954
•0,700
012
.98
53
1954
•*2,300
1,825
.83
1953
•*1,100
1,825
1.70
* MPN by Thomas's approximate method. (10)
b Direct planting Into BGD lactose broth,
* Confirmed test.
d 100-ml portions.
* Percentage of 10-ml portions giving same MPN per 100 ml as percentage of positives
resulting from 100-ml portions.
Table 12.—Effectiveness of conventional rapid sand filtration and disinfection
water plants in the reduction of coliform bacteria, monthly data
EAW WATER—Coliform density
PLANT EFFLUENT—Plant months
during which the percentage of eoli-
form-poeitive 10-ml portion* was*
Monthly Range, average
MPN per 100 ml
Frequency,
plant months
0.0
0.1-0.0
1.0-1.9
52.0
0- 4,900..
m
211
313
210
120
53
18
17
310
198
801
198
113
51
18
10
19
10
8
10
4
1
0
0
3
2
1
1
1
1
0
1
7
1
3
1
a
0
0
0
5,000- 9,900
10.000- 24.000
25 000- 49,000
SO 000- 99.000
100.000-490,000
600,000-980,000
51,000.000
Totals.,
U81
1,204
S3
10
15
* For plants examining only 100-ml portions of plant effluent, the percentage of positive
10-ml portions giving same MPN has oeen used.
6,400,000 per 100 ml. This occurred at plant 1. Monthly densities
in excess of 1,000,000 per 100 ml were also recorded at two other
plants. Each group is further subdivided according to the per-
centage of coliform positive portions found in the plant effluent
during the month. Coliform bacteria were found during 7.6 per-
cent of the months in which the raw water density was less than
10,000 per 100 ml; and during 6.2 percent of those in which the
density was less than 100,000 per 100 ml.
Data for all 15 plant months in which the positive 10-ml por-
tions equaled or exceeded 2 percent of those examined are given
in table 18. Plants 8, 24, 44, and 53 again appear in this table.
During October, 1954, the treated water produced at plant 44
showed 11.5 percent of all 10-ml portions examined to be positive
for coliform bacteria. During May, 1953, plant 58 showed 9.7
percent of the treated water portions positive for coliform bac-
21
-------
Table 13.—Coliform bacterial data for raw and finished waters at conven-
tional rapid sand filtration and disinfection water plants for all months during
which, 2.0 or more percent of the iO-ml portions of plant effluent examined
were positive for coliform bacteria
Plant
eode
number
Yew
Month
RAW WATER-Coliform
density, monthly average
MPN per 100 ml
PLANT EFFLUENT-
10-mI portions
Number
examined
Percent
podtiye
8
1954
June
•550,000
110
4.6
Not.
•589,000
100
3.0
24
1054
June
•57,000
150
3.3
Sept.
•33,000
150
2.7
Dec.
•18,000
155
3.2
44
1054
Feb.
•12,000
72
2.8
Oct.
<10,000
78
11.5
53
1053
Jan.
•g 3,300
156
2.6
Feb.
'* 430
140
2.1
Mar.
•d. 710
155
2.6
May
¦* 2,200
155
8.7
Aug.
670
155
2.6
1054
Apr.
1,500
150
3.3
June
•5 4,600
150
2.0
July
8,800
156
3.2
" MPN by Thomas's approximate method. (10)
* Confirmed teat.
teria. Both these plants carry low residual chlorine concentrations
in the plant effluent.
Ten plants examined one or more 100-ml portions of plant
effluent samples. The number and volumes of the portions ex-
amined, also the frequency with which samples were taken during
the day, varied. The lower limits of detection of coliform bacteria
ranged from 0.09 to 0.69 per 100 ml. As previously noted, when a
plant examined two or more samples of finished water during
the day, the results have been grouped and treated as a single
sample.
In table 14, the sampling days are grouped according to the
coliform bacterial density in the raw water. For each of these
groups the frequency with which coliform bacteria were detected
Table 14.—Effectiveness of conventional rapid sand filtration and disinfection
water plants in the reduction of coliform bacteria at ten plants examining one
or more 100-ML portions of plant effluent, daily data
RAW WATER—Colifora density
PLANT EFFLUENT-Days on which
Range, daily
MPN per 100 ml
0- 4,800
0,00ft- 6,800
10,000- 24,000.....
35,000- 49,000
<0,000- 80,000
100,000-240,000
380,000-490,000
600,000-890,000
51,000,000
Tot*I or average
Frequency,
days
2708
840
1772
230
803
m
30
6
154
0348
Coliform bacteria
were detected*
Number
72
33
63
20
31
26
0
0
4
248
Percent
2 6
6.2
3.6
8.7
8.9
3.0
.0
.0
2.0
3.9
Coliform density was
>1.0 per 100 ml
Number
5
2
8
2
0
0
0
0
0
18
Percent
0 18
.31
.fit
.87
.00
.00
.00
.00
¦ 00
.28
• Lover limit* of coliform detection varied from 0.09 to 0.69 per 100 mL
22
-------
in the plant effluent, also the frequency with which the coliform
density equaled or exceeded 1.0 per 100 ml, are given.
The maximum raw water loadings ranged from 5:24,000 to
=^23,000,000 per 100 ml. They exceeded 100,000 per 100 ml at
9 of the 10 plants. Coliform bacteria were detected in the plant
effluent on 3.1 percent of the days during which the raw water
loading was less than 10,000 per 100 ml, and on 3.8 percent of the
days during which it was less than 100,000 per 100 ml. The maxi-
mum density of coliform bacteria detected in the finished water
at any plant was 2.4 per 100 ml. The coliform bacterial density
equaled or exceeded 1 per 100 ml in only 0.28 percent of the days
on which finished water samples were examined.
Additional information on the relation of raw water bacterial
loading to the occurrence and density of coliform bacteria in the
plant effluent is given for each of these 10 plants in tables 15 to 24.
Table 25 summarizes coliform data for raw and finished water
and residual chlorine concentration in finished water for each
plant year. Those for the month of poorest bacterial quality of
plant effluent are shown in table 26 and for the month of heaviest
raw water coliform loading, in table 27.
Table 16.—Relation of the occurrence and density of colif orm bacteria in the
plant effluent to the coliform density in the raw water, daily data, Plant No. 1
RAW WATER—Coliform density*
Daily
MPNpwlOOuI
524.,
M0.,
2400,
34000.,
940000..
3400000..
£33000000.
Total or mrnge
Frequen
dty»
enqy.
1
2
14
157
164
188
15
481
PLANT EFFLUENT*
Frequency of
ooliform*pc*itive
•ample*
Daye
0
0
0
a
a
8
1
8
Percent
0
0
1.8
1.2
2.2
«.7
l.«
ivorwe ooliform eternity,
per 100 ml, for:
Coliform-
poejtive
¦ample*
0
0
0
0.33
1.W
.40
.30
.n
All
¦ample*
0
0
0
0.00
.02
.01
.01
.01
¦ Baw wttwr maple* examined by planting rincfo portions fa decimal volume*, presumptive
* Plant effluent sample* examined oring 651.0-ml. planting*, confirmed tort.
28
-------
Table 16.—Relation of the occurrence and density of coliform bacteria in the
plant effluent to the coliform density in the raw water, daily data, Plant No. 5
RAW WATER
PLANT EFFLUENT*"
ColiEorm density*
Number of
samples
examined
Frequency of
ooliform-poeitive
sample*
Average coliform density
MPN per 100 ml, for:
Range, daily
MPN per 100 ml
Frequency
days
Coliform-
positive
samples
All
¦ample*
Number
Percent
0- 4,000...
6,000- 6,900...
10,000- 24,000...
25,000- 40,000...
60,000- 99,000...
100,000-240,000...
260,000-490,000...
5800,000
No data
14
86
150
82
141
67
15
6
221
42
10S
468
246
423
171
64
18
eo3
0
1
0
•2
1
1
0
0
3
0
0,9
0
0.8
0.2
0.8
0
0
0.6
0
0.68
0
1.1
1.1
.68
0
0
.81
0
0.006
0
.009
.003
.004
0
0
0.004
Total or
average...
731
2193
8
0.4
.89
0.003
* Raw water samples examined 5 days weekly by 0.442-ml plantings, confirmed teat.
b Plant effluent samples examined every 8 hours by lBl,0-ml plantings, completed teat,
• Coliform bacteria detected in 100-ml portions of both 2 AM and 10 AM samples, July 28,
TABLB 17.—Relation of the occurrence and density of coliform bacteria in the
plant effluent to the coliform density in the raw water, daily data, Plant No. 12
RAW WATER
PUNT EFFLUENT1"
Coliform density*
Frequency of
coliform-positive
samples
Average coliform density,
MPNper 100 mi, for;
Bangs, daily
MPN per 100 ml
frequency,
days
Coliform*
positive
samples
All
samples
Days
Percent
0- 4,900
6,000- 9,900
10,000- 24,000
26,000- 49,000
60.000- 99,000
100,000-240,000
240,000-490,000
Total or average
301
80
160
63
84
61
2
60
29
46
18
30
20
0
IS.6
36.2
29.2
34.0
36.8
39.3
0
0.26
.26
.20
.30
.14
.18
0
0.04
.09
.06
.10
.06
.07
0
731
102
26.3
0.22
0.06
* Raw water Baraplee examined daily by planting & portions each of three decimal volumes
directly into BGB lactose broth.
~Plant effluent sampled every 2 hours with 100-ml portion examined by confirmed test.
For purposes of calculation the daily samples are considered as a single sample with twelve
100-ml portions examined.
24
-------
Table 18.—Relation of the occurrence and density of coliform bacteria in the
plant effluent to the coliform density in the raw water, daily data, Plant No. IS
RAW WATER
PLANT EFFLUENT*
Coliform danaity*
Daily
MPN per 100 ml
Frequently of
aolifatm-pocitiTe
Freaueasy,
aay»
•ample*
Day«
Percent
Average ooliform density,
MPN per 100 ml, for;
Ooliform-
poeitive
lample*
?24
?240
B40.
2400
34000
534000
5840000
No data....,
Total or average
54
13
01
119
01
7
32
323
1
2
6
a
10
0
2
7
1.9
18.4
3.0
5.1
11.0
.0
6.2
3.1
0.22
.36
.33
.22
.70
.00
.36
.38
630
34
5.4
.47
* Raw water umplea examined by planting alngle portions of decimal vohunea directly Into
BOB Lactoee broth.
11 Plant effluent sample* examined using five 100-ml planting!, confirmed test.
Table 19.-—Relation of the occurrence and density of coliform bacteria in the
plant effluent to the coliform density in the raw water, daily data, Plant No. 17
RAW WATER
PLANT EFFLUENT"
Coliform density*
Fiwmenoy of eoliform-
positive sample#
Average eoliform
density, MPN
per lOO ml
Range, daily
MPN per 100 ml
PrMueaoy
day*
D»y»
Percent
0- 4,800
8,000- 9,900
10,000— 24,000
25,000- 46.000
50,000- 99,000
100,000-240,000
250,000-49(1000
500,000-990,000
Total or Ant
290
143
194
0
01
42
0
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
MPN of
daily plant effluent
•ample* all lees
than 0.32 par
100ml
731
0
0
• Haw water sample* examined dally by 2 planting* aneh of S doelmal volumes, preaumptlva
b Plant effluent aamplee examined dally utng ftvt 100-ml portion*, oonftrmed teat.
25
-------
Table: 20.—Relation of the occurrence and density of coliform bacteria in the
plant effluent to the coliform density in the raw water, daily data, Plant No. 19
RAW WATER
PLANT EFFLUENT*
Coliform density*
Frequency of
coliform-positivo
samples
Average ooliform denwty,
MPN per 100 ml, for:
Daily
MPN per 100 ml
Frequency,
dayB
Coliform*
positive
samples
All
samples
Days
Percent
5»23
2
8
313
369
48
730
0
0
2
2
1
0.00
.00
,64
,S6
2.10
0.00
.00
.22
.22
.22
0.00
.00
.001
.001
.004
230
2400
24000
5240000
Total or average
5
.68
.22
.001
« Raw water samples examined using 1,111-ml plantings, presumptive test.
b Plant effluent samples examined using: five 100-mI planting, completed test.
Table 21.—Relation of^ the occurrence and density of coliform bacteria in the
plant effluent to the coliform density in the raw water, daily data, Plant No. £6
RAW WATER
PLANT EFFLUENT*
Coliform density*
Frequency of
coliiorm-poeitive
samples
Average coliform density,
MPN per 100 ml, for:
Range, daily
MPN per 100 ml
Frequency,
days
Coliform-
positive
samples
All
samples
Days
Percent
O- 4.000
6,000- 0,900
10,000- 24,000
25,000- 40,000 ...
50,000- 99,000
100,000-240,000..
2C5
142
119
71
0
64
69
0
0
1
0
0
0
0
0
0
0.8
0
0
0
0
0
0
0.34
0
0
0
0
0
0
0,003
0
0
0
0
Total or average
730
1
.2
.34
.001
* Raw water samples examined 8 or 7 days per week by 0.383-ml plantings, confirmed test.
" Filter effluent samples: once consisting of five 10-ml and three consisting of 100-ml portions
each, examined daily. For mathematical averaging these four samples are treated u a single
sample.
26
-------
Table 22.—Relation of the occurrence and density of coliform. bacteria in the
plant effluent to the coliform density in the raw water, daily data, Plant No. SS
RAW WATER
PLANT EFFLUENT"
Coliform density*
Frequency of coliform-
poritire samples
Average coliform
density, MPN
per 100 ml
Daily
MPN per 100 ml
Frequency
days
Days
Percent
230
940
2300
8400
24000....
5240000,
Total or Avg
7
2
396
5
317
4
0
0
0
0
0
0
0
0
0
0
0
0
MFN of daily plant ef-
fluent samples ell
<0.22 per 100 ml.
731
0
0
* Raw water samples examined dally by 0.111-ml plantings, presumptive test.
b Plant effluent samples examined dally using five XOO-ml portions, confirmed test.
Table 23.—Relation of the occurrence and density of coliform bacteria in the
plant effluent to the coliform density in the rata water, daily data, Plant No. S8
RAW WATER
PLANT EFFLUENT*
Coliform density*
Frequency of
coliform-positive
samples
Average colifotin density,
MPN/per 100 ml, for:
Coliform-
positive
samples
Range daily
MPN per 100 ml
Fre
quertoy,
days
Days
Percent
AU
samples
O- 4,800
6,000- 0,000
10,000- 24,000
25,000- 48,000
SO,000- 98,000
100,000-240,000.
345
117
120
24
17
3
3
2
3
1
0
0
0.9
1.7
2.5
4.2
0
0
1,1
.9
1.1
1.1
0
0
0.01
.02
.01
.05
0
0
Total or average
626
9
1.4
1.1
.02
* Raw water samples examined 6 days per week by 5.55-or 0,556-ml planting*, presumptive
test.
b Plant effluent examined 6 days per week by 150-m) plantings, completed test.
Table 24.—Relation of the occurrence and density of coliform bacteria in the
plant effluent to the coliform density in the raw water, daily data, Plant No. 47
RAW WATER
PLANT EFFLUENT*
Coliform density*
Frequency of
coliform-poritlv*
samples
Average ooliform density,
Mra/lOOml, for:
111
PI
Bangs daily
MPN per 100 ml
Frequency,
days
Days
Percent
All
samples
0- 990
1,000- 4,900
5,000- 9,900
10,000- 34,000.
320
201
117
92
2
0
1
0
0.6
0
.9
0
0.16
0
.16
0
0.001
0
.001
0
Total or average
730
8
.4
.16
.001
* Raw water samples examined daily by 55.5-ml plantings, confirmed teat.
b Plant effluent data based on combined results of 8 samples—Plant No, 1, Plant No. 2, and
Combined Plant Effluents—dally consisting of examinations of one, one, and five 100-ml plant-
inn, completed teat. For mathematical purposes these have been treated as one sample with
seven 100-ml portions examined.
27
-------
Tabus 25.—Summary of coliform and residual chlorine data for conventional
rapid sand /Stratum and disinfection water plants, annual data
Flast
Tear
RAW WATER—
CdifsRD deost?,
MPN per 100 ml
PLANT EFFLUENT
Coliform data
100-ml portion*
Number
examined
toctok
poeitire
10-ml portions
Number
eatwuitted
Percent
positive
Beadtul eMorine concentration. mgfl
Free
Annual
average
Minimum
daily average
Total
Arninal
average
1863
1864
1966
1966
1864
1963
1964
1862
1863
1864
1865
1866
1864
1864
1863
1863
1864
1866
1864
1863
1864
1851-62
1952-53
1863
1863
1864
1863
1864
1853
1863
1863
1963
1963
1963
1963
1966
1964
1960
1949
p*
»g
•5
•de
»5
»ab
fed.
1,700,000
1,100.000
800,000
610,000
460,000
87,000
83,000
75.000
61,000
70,000
66,000
68,000
39,000
68,000
63,000
66,000
40,000
61,000
30,000
49,000
43,000
46.000
16,000
44,000
23,000
38,000
33,000
38,000
13,000
38,000
7,800
38,000
16.000
37,000
17,000
34,000
33,000
33,000
33,000
1,280
1,266
1.098
1,095
4,385
4,350
1,666
1.665
1,830
1,826
1,826
1,826
0.65
.80
.00
.27
5.54
.68
.96
.00
.00
.16
.11
1,290
1,266
1,285
1,715
1,660
1,092
1,092
5,485
5,485
1,825
1,825
1,820
1,825
1,260
1,260
1.365
1,360
1,490
1,480
1,820
1,660
6,465
6,465
1,565
1,280
3,650
3,650
7,300
7,260
7,290
7,276
1,825
1,825
0.00
.08
.00
.00
.00
.00
.00
.04
.06
.00
.00
.16
.11
.72
.00
.00
.00
.00
.00
.00
.00
.00
.00
.00
.08
.00
.00
.00
.00
.w
.00
.00
A
.1
.6
.8
.00
.0
"0.8
.6
.8
3.1
6.1
a,5
".5
"1.0
".8
¦2.0
"2.0
.7
.7
"2.2
°2.3
"1.4
¦1.6
.4
,4
D1.0
"1.0
"1.7
"1.7
.6
.6
".8
".8
n0.7
.7
1.3
1.3
".6
.7
"2.7
n2.6
-------
21.
22.
23.
24.
25.
20.
27.
28.
2».
SO.
31.
32.
33.
34.
as.
SB.
37.
38.
38.
40.
41.
42.
43.
44.
tf.
1954
32,000
1953
Ȥ
27,000
IBM
Pah
29,000
1953
Psh
1954
28,000
1953
*
18,000
1954
•
28,000
1953
•5
23,000
1953
»
28,000
1954
*
21,000
1953
28,000
1952
15,000
1953
•5
25,000
1954
•5
23,000
1963
»jE
23,000
1954
»g
10.000
1954
22,000
1953
p«5
21,000
1954
19,000
1955
H
15,000
1954
~5
19,000
1955
10,000
1951
P*:
17,000
1952
•
13,000
1955
1954
:i
17,000
13,000
1952
15,000
1953
»
13,000
1952
13,000
1953
12,000
1954
12,000
1953
9,000
1953
p*
12,000
1954
»ab
11,000
1951
11,000
1952
9,000
1953
Ȥ'
10,000
1954
8.000
1953
9,800
1954
4,200
1914
»
8,800
1953
p
0,900
1953
7,400
1954
kf
0,300
1952
7,000
1953
0.000
1953
•A
8.800
1954
Mb
0,700
1954
5,800
1953
19S5
%
5,000
5.100
1954
•?
3,900
1,095
1,095
.00
.09
1,830
1,825
0.00
.00
313
315
.0
1.9
.00
.00
.00
.00
.00
.00
.88
.05
.00
.00
.00
.00
.06
.00
.00
.00
.00
.00
.00
.00
.00
.00
.00
.00
.00
.00
.00
.00
03
03
.0
.0
00
OS
.0
.0
00
00
02
13
00
25
.2
1.0
.00
.00
.00
.11
.e
1.0
.8
.8
.3
.6
0.4
0.4
.5
.5
.0
.1
1.1
1.6
.1
.1
.2
.9
1.2
.2
.2
,0
.0
.&
.5
-------
Co
O
Table 25.—Summary of coliform and residual chlorine data for conventional
rapid sand filtration and disinfection water plants, annual data—continued
Phot
code
no.
47
48
49
60
51.
52.
53
54
RAW WATER—
Coliform denrty.
Year
animal average
MPN per 100 ml
1954
"¦g 5,000
1855
«>5 4,000
1953
•5 4,400
1954
«5 2,400
1954
4,100
1653
3,700
1955
•=t 3,600
1B54
2,900
1953
3,500
1954
t>± 2,400
1953
3,100
1954
*5: 3,000
1954
»»¦* 2,400
1953
»«* 1,100
1952
•± 1.900
1953
•* 1,300
PLANT EFFLUENT
Coliform data
100-ml portions
Number
examined
2,555
2,555
Percent
positive
0.0S
.04
lG-ml portions
Number
examined
1.825
1,825
1,815
1,820
1,495
1,670
7,280
7,300
1,825
1,825
1,825
1,825
1,825
1,815
Percent
positive
.06
.00
.17
.11
.00
.00
.11
.01
.00
.00
.93
1.75
.00
.00
Residual chlorine concentration, tog/1
Free
Annual
average
0.1
.1
Minimum
daily average
(T)
(T)
.4
.4
Total
Annual
average
.3
.3
».6
».6
"1.1
".8
"1.2
"1.3
.4
.3
".9
.1
.1
.8
.8
Minimum
daily average
.1
.1
n.3
n.3
n.3
".4
"1.0
¦1.1
.2
.2
n.6
".6
(T)
-------
Table 26.—Summary of coliform and residual chlorine data for months of poorest
effluents at the conventional rapid sand filtration and disinfection water plants
Plant
code
no.
Year
Month
RAW WATER—
ColifanB deraity.
monthly average
MPN per 100 ml
PLANT EFFLUENT
Coliform data
Residual chlorine concentration, mg/1
100-mI portions
10-ml portions
Free
Total
Number
examined
Percent
positive
Number
examined
Percent
positive
Monthly
average
Minimum
daily average
Monthly
average
Minimum
daily average
1
1953
1954
1955
1955
1954
1B53
1954
1952
1953
1954
1955
1955
1954
1954
1953
1953
1964
1955
1954
1953
1954
1951-52
1953-63
1952
1953
1954
1953
1954
1953
1952
1953
1952
1953
1952
1953
1955
1954
Aug.
Not.
2.300,000
» 1,100,000
105
105
4.8
0.0
105
165
0 0
1.0
=0.7
.9
"0.1
0.6
"0.7
n.6
"2.0
a2.0
0.2
"O.O
"1.0
2,7
n.7
».8
"0.5
.6
"2.2
-2.1
2
3
4
5
Mar.
July
¦ 52.000
• 75,000
92
93
1.1
2.2
460
465
.4
.2
0 2
.1
00
.9
"1.1
".8
6
7
July
Mar.
Jane
140,000
» 8.500
•5 59,000
155
155
110
1.9
1.3
4.5
n2.0
"2.0
.4
8
9........
10
11
1*
Jan.
Dee.
b 7,700
b5 4,800
370
372
20.0
16.4
465
460
.0
.0
"1.0
"1.0
a
14
Aug.
•5 31,000
120
.8
2.9
16
Oct.
Aug.
b? 90.000
b? 5,100
130
130
11.5
9.2
..
°.8
".8
1«
1 7
1 8
CM.
Apr.
Oct.
Feb.
» 21,000
» 5.400
48.000
Ȥ 19,000 1
au
0.2
0.2
.6
0.0
.5
"0.6
0.7
n3.8
"2.4
19
600 .2
155 1.9
140 1 .7
-------
Tabxa 26.—Summary of eoUform and residual chlorine data for months of poorest
effluents at the conventional rapid sand filtration and disinfection water plants—Continued
no.
Tew
Month
RAW WATER
monthly avenge
MPN pet 100 ml
PLANT EFFLUENT
Cofitem date
foodoal chlorine concentration, mg/1
100-ml portions
10-ml portions
Free
Total
Number
examined
Bfinent
poatioo
Number
examined
Percent
position
Monthly
avenge
Minimum
daily avenge
Monthly
avenge
Minwnitm
daily average
20
1H0
1949
19S4
1953
1954
1953
1964
1SU
1954
1953
1063
1954
1953
1952
1953
1954
1953
1954
1954
1953
1954
1955
1954
1955
1951
1952
1955
1954
1952
1953
1952
1953
1954
1953
1953
1954
1951
1952
.9
».4
*1.7
"1.4
¦1.1
¦1.1
21
23*
23
24
Mir.
• 57,000
• 15.000
ISO
155
3.3
.6
1.0
.7
.6
.5
25
20
June
» 11,(100
90
1.1
150
.0
1.1
27
Feb.
•g 37,000
135
.7
.0
.0
ft1.0
28
29
30
31
32
33
-
M
35
U
JnIf
Aug.
p 14,000
» 8,800
305
310
0.3
.3
"1.9
*1.7
37
38
Sept
Oct
" 14.200
~ 4,100
25
27
4.0
7.4
125
135
.0
.7
¦1.5
"2.1
-------
10.
40.
41.
42.
43.
44.
45.
46.
47.
48.
48.
50.
51.
43.
84.
1863
1964
1963
ISM
1954
1863
1953
ISM
1961
1963
1954
im
1953
1966
1964
1964
1964
1964
IMS
1964
1963
1964
gg
F*.
Jan.
Dee.
Jan.
Oct.
Dec.
Mw
J£
27,000
14,000
1,9
1M
lO.fl
2,100
9,600
«
•? M,(
4.«
is »'fM
1,600
»¦* l.too
••5 2.306
310
76
78
317
310
166
160
166
ISO
166
.02
.06
I.3
4.0
II.6
0.9
.5
.6
1.3
1.3
.6
.3
3.3
9.7
(T)
0.1
0.1
.1
(T)
-------
Co
*»•
Table 27.—Summary of coliform and residual chlorine data for months of
greatest bacterial loadings of raw waters at the conventional rapid sand
filtration and disinfection water plants
Plant
code
Tear
Month
no.
1
1953
Sept.
1954
Oct.
2
1955
Oct.
3
1955
Sept.
1954
May
t
1853
May
1954
Dee.
5
1952
Nov.
1953
Dec.
6
1954
Aug.
1955
Oct-
7
1955
Sept.
1954
Sept
8
1954
Aug.
1993
Nov.
9
1953
Oct-
1954
Aug-
10
1955
Sept
1954
Jan.
11
1953
June
1954
Oct
12
1951-52
Sept.
1952-53
Feb.
13
1952
Apr.
1953
July
14
1954
Feb.
1953
Mar.
15
1954
June
1953
June
16
1952
Aiut-
1953
Sept
17
1952
June
1953
July
18........
1952
Jul.
1953
Mar.
19..
1955
Aug.
1954
Sept
RAW WATER—
Coliform density,
monthly average
MPN per 100 ml
"58.400,000
>>§2.300.000
>52,400,000
Pg 1.100,000
~ 700,000
160,000
160.000
160.000
82.000
110,000
91,000
280.000
180.000
100.000
80.000
100.000
08.000
110.000
65.000
98.000
73,000
110,000
48.000
95.000
58.000
65.000
56.000
110,000
36 000
130.000
22.000
130.000
49.000
120.000
36.000
69.000
60,000
•5
p
pg
»?
PS:
»
pat
bg
bE
•5
•s
b5
b5
p
~5
p5
'?
p5
p
pg
»W
PLANT EFFLUENT
Coliform data
100-ml portions
Number
examined
105
105
Pereent
positive
1.0
.0
93
360
360
130
130
150
155
.8
4.4
3.8
.0
0.0
.0
10-ml portions
Number
examined
105
105
120
140
130
93
93
450
465
155
155
150
150
110
90
100
120
120
125
145
155
450
450
140
95
280
310
615
600
615
620
158
150
Percent
positive
0.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
0.0
.0
.0
.0
.0
.0
Residual chlorine concentration, mg/I
Free
Monthly
average
0.2
.0
.6
.5
0.4
.4
Minimum
daily avenge
0.0
.0
.4
.3
0.4
Total
Monthly
average
*0.7
.6
.8
3.3
6.5
".5
".3
",9
"1.0
"2.0
"2.0
.7
.7
"2.2
"2.4
1.5
1.6
.3
.4
"1.0
"1.0
"1,7
"3.0
.6
.5
B.9
».8
"0.8
.8
1.2
1.4
.6
.6
2.5
2.7
Minimum
daily average
"0.3
.3
.2
2.1
3.5
n-5
n.3
n.4
n.8
"2.0
"2.0
.5
.1
"2.2
n2.2
1.0
1.3
.2
.3
n.9
n.8
"1.0
"2.5
.5
.4
°.7
°.6
"0.7
0.7
1.0
1.3
0.5
.6
"2.2
"2.3
-------
oo
©i
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
36.,
37..
38..
39..
40..
41..
42..
43..
44..
45..
, 1950
July
58,000
1949
Aug.
59,000
1954
Dec.
49,000
1953
Mar.
60.000
1954
July-
86.000
1953
July
67.000
1954
Apr.
May
•
70.000
1953
«
36.000
1954
June
•
57,000
1953
June
•
43.000
1953
tin*.
P
95.000
1954
Sept
P
70.000
1953
Sft
56.000
1952
Psfc
42,000
1853
Jane
78,000
1954
Jane
79.000
. 1953
Dec.
51,000
1954
Oct.
30,000
1954
Jan.
40.000
1953
Jan.
34,000
1954
Oct.
46.000
1955
Jan.
24,000
. 1954
Aug.
28,000
1S55
Jane
PS
32,000
1851
Jane
p5>
38.000
1952
July
Aug.
31.000
1955
•5®
88,000
1954
May
48.000
1952
Nor.
32,000
1953
June
P
25.000
1952
June
28.000
1953
Sept.
>
18.000
1984
June
P
25,000
1953
June
20,000
1963
May
P*
32,000
1954
Dee.
48,000
1951
June
P
31.000
1952
Not.
P*±
21,000
1953
Jane
29,000
1954
July
P?
44.000
1953
June
p$
33,000
1954
June
~5
9,300
1954
Feb.
p
27.000
1953
Feb.
p
26.000
1953
*5
25.000
1954
Nov.
b
14.000
1952
Jane
14,000
1953
Aug.
12.000
1953
Dee.
14,000
1954
April
asb
10,000
1954
Dee.
:i
24.000
1963
Jan.
15,000
.0
.0
4.0
.0
155
.0
155
.0
285
.0
285
.0
110
.0
135
.0
150
.0
270
.0
150
3.3
150
.0
150
.0
150
.0
150
.0
155
.6
130
.0
130
.0
130
.0
130
.0
155
.0
155
.0
135
.0
125
.0
155
O.O
150
.0
130
.0
130
.0
300
.0
150
.0
195
.0
240
.0
290
.0
195
.0
27
.0
27
.0
125
.0
125
.0
81
.0
78
.0
ISO
.0
150
.0
420
.2
420
.2
465
.0
450
.0
300
.0
310
.0
78
.0
78
.0
155
.0
130
.0
.7
.6
.5
.6
10
1.0
10
.9
1.0
1.0
.6
.7
.1
.1
.4
.4
T
.0
.2
.3
.4
.5
0.0
.0
.3
.4
.1
.0
.9
1.3
(T)
.1
.7
.6
-------
CO
Tabus 27.—Summary of coUform and residual chlorine data for months of
greatest bacterial loadings of raw waters at the conventional rapid sand
filtration and disinfection water plants—Continued
Phat
Year
Month
RAW WATER—
Cotiform density,
monthly average
MPN per. 100 ad
PLANT EFFLDENT
Colifonn data
100-ml portiooa
Number
Percent
positive
19-ml portions
Number
Percent
examined
positive
155
.0
155
.0
217
.0
210
.0
150
.0
155
.0
150
1.3
155
.0
150
.0
155
.0
620
.0
600
.0
155
.0
155
.0
155
3.2
155
S.6
155
.0
155
.0
Rtwdnal cUorioe eoneentration, mg/1
Free
Monthly
average
Minimum
daily »'
Total
Monthly
Minimum
daily average
4 6
4 7
4 8
4 9
60.
51
£2
a
84
1855
1954
1954
1955
1963
1964
1954
1953
IMS
1954
1953
1964
1953
1954
1954
1953
1952
1953
Oct
Oct
Not.
June
May
Dec.
Mar.
July
Oet.
Jaa-
S
Oct
¦Inly
.2
.1
(T)
jiwiimptlm tat
proximate formula
iactnw broth
-------
Conclusions
Data from 54 plants treating waters with monthly average
coliform densities frequently in excess of 5,000 per 10 ml have
been analyzed. Conventional rapid sand filtration plants providing
continuous and adequate disinfection can treat waters heavily
laden with coliform bacteria to produce a plant effluent conforming
to the assumed bacteriological objective. Increased chlorine ap-
plications have made this possible.
The number of 10-ml portions of plant effluent which were found
positive for coliform bacteria equaled or exceeded 2 percent of
those planted during only 1.2 percent of 1,281 plant months of rec-
ord. All of these months occurred at four plants. Two of the plants
maintained total chlorine residuals in the finished water aver-
aging only 0.1 mg/1. At each of the other plants the pretreated
and filtered water was subject to air- and bird-borne contamina-
tion. Water treatment plants which have adequate and properly
operated facilities can and should produce an effluent which does
not have more than 2 percent of all 10-ml portions examined dur-
ing any one month positive for coliform bacteria. This is the
assumed bacteriological objective applicable only to plant effluent
samples. Evaluation of the bacterial quality of the water actually
furnished to the consumers should still be based on the Public
Health Service Drinking Water Standards.
PREDISINFECTION, COAGULATION, AND
SEDIMENTATION
Plants Studied
All data sufficient for study of the effectiveness of predisinfec-
tion, coagulation, and settling as measured by the removal of coli-
form bacteria have been examined. Data from 19 plants, including
plants 33a and 83b, which were operated in parallel, have been
summarized. Data for plant 18b, where prechlorination was fre-
quently inadequate to maintain a residual in the settled effluent,
ie discussed separately.
There are wide variations in the treatment provided at the
different plants, and in some cases considerable variation during
the two-year period at a given plant. Six of the 19 plants routinely
used chloramine for predisinfection; the others normally used
chlorine only. Average chlorine dosages ranged from 1.3 to 140
mg/1. Median values for plants using chlorine and chloramine
were 3.6 and 1.5 mg/1, respectively. Theoretical contact times
ranged from slightly less than 2 to more than 100 hours. The
median times for both chlorine and chloramine were 12 hours. The
87
-------
average total residual chlorine in the water applied to the filters
ranged from 0,2 to 5.9 mg/1 and the medians were 0.8 mg/1 for
both predisinfection processes. Several plants recorded total resi-
dual chlorine concentrations of 0.0 mg/1 in the influent to filter
for 1 or more months. It may also be significant that the median
pH at plants using chloramine was 9.2, while that for plants
using chlorine was 8.0.
Discussion
All available bacteriological data, except those for Plant 18b,
are summarized in table 28. Those for the predisinfected, coagu-
lated, and settled water samples have been classified according to
Table 28.—Effectiveness of predisinfection, coagulation and sedimentation in
the reduction of coliform bacteria, monthly data
RAW WATER—Coliform density
INFLUENT TO FILTER—Percentage of month* during
which the percentage of Coliform-positive 10-ml
portions was—
Range, monthly
average MPN
par 100 ml
Frequency,
months
0.0
0.1-1.9
2.0-9.9 j 510
Thirteen
Plant* Disinfeotins
by Prechlorination
0- 4800....
04
89.0
9.3
1.7
0.0
£000- 0900
36
94.4
6.6
0.0
.0
10000- 24000
62
84.6
9.6
6.8
.0
26000- 49000
48
86.4
12,6
2.1
.0
60000- 99000
36
77.2
8.6
14.2
.0
100000-240000
6
83.3
.0
16.7
.0
280000-400000
20
100.
.0
.0
.0
600000-990000
13
100.
.0
.0
.0
51000000
14
86.6
.0
7.2
7.2
Total or Average
288
87.8
7.6
4.2
.4
Six pla
ata using preohlors
mine disinfection
0- 4900
46
60.0
20.0
17.8
2.2
6000- 6900
31
80.7
12.9
6.4
.0
10000- 24000
43
66.2
11.6
20.9
2.3
2SOOO- 49000
IB
81.8
12.6
6.2
.0
60000- 99000
6
60.0
33.3
16.7
.0
100000-240000.........
2
100.0
0.0
0.0
.«
260000-490000
1
100.0
0.0
0.0
.0
Total or Average
144
68.8
16.2
14.0
1.4
the percentage of 10-ml portions testing positive for coliform
bacteria. For the 432 plant months examined, there were 36
months during which the percentage of coliform positive portions
exceeded 2 percent of all those examined, and 3 months during
which they exceeded 10 percent of those examined.
The comparison of the frequencies of the various percentages
of positive portions in the settled water samples disinfected with
chlorine and chloramine is interesting. Although this points to
the relative ineffectiveness of the disinfecting properties of chlora-
mine as compared to those of chlorine, other factors were involved.
It should be remembered that it was not the objective of those in
88
-------
charge of plant operation to provide a coliform-bacteria-free water
for application to the filter, and in many cases a substantial com-
bined chlorine residual was maintained throughout the settling
basins even though a relatively low level of chloramine had been
applied.
Data from Plant 18b gave non-typical results (table 29) due
Table 29.—Effect of increased residual chlorine concentration on the detection
of coliform bacteria in predisinfected, coagulated and settled water, monthly
data. Plant No. 18b
influent to filter
Year and
month
RAW WATER-
Coliform density
monthly average
MPN per 100 ml
10-ml portions examined
for coliform bacteria
Residual chlorine
concentration, mg/1
Number
Percent
positive
Monthly
average
Minimum
daily average
, im
Jan.
Feb.
Mar.
Apr.
May
June
July
Aug.
Sept.
Oct.
Nov.
Dec.
£110000
20000
47000
03000
13000
13000
£ 36000
28000
21000
8400
5 22000
40000
130
126
130
130
130
126
130
130
126
no
120
130
7
1
0
16
36
12
16
12
41
8B
63
12
0.00
.03
.02
.00
.13
.06
.01
.04
.01
.00
.06
.10
0.02
.01
.00
.00
.00*
.00*
.00*
.00»
.00»
.00
.00
.02
Total or
Average
37000
1616
23
.04
/
1953
Jan.
Feb.
Mu.
Apr.
May
June
July
Aug.
Sept.
Oct.
Nov.
Dee.
40000
23000
36000
5400
6600
11000
24000
5 32000
11000
6200
3400
6000
130
120
130
130
126
130
130
130
126
136
120
126
13
6
2
11
18
6
6
0
0
0
1
0
0.04
.01
.01
.01
.60
.71
.74
.76
.83
.72
.78
.86
0.00
.00
.00
.00
.00
.66
.64
.66
.6?
.62
.47
.13
Total or
Average
17000
1630
5
1 Prechloramlne disinfection used May 15 to September 8, 1962.
to depletion of the chlorine or chloramine in the large open earthen
settling tanks which provided theoretical detention times around
35 to 40 hours. Daily combined chlorine residuals were frequently
recorded as 0.00 and monthly averages ranged from 0.00 to 0.18
mg/1 throughout 1952, during which 23 percent of all 10-ml por-
tions, and 5.5 percent of all 1.0-ml portions of settled water ex-
amined were positive for coliform bacteria by confirmed test.
Better disinfection was secured during the last 6 months of 1953
when total residual chlorine concentrations in the settled water
were maintained between 0.1 and 1.3 mg/lf with monthly averages
around 0.8. During this period only 1.0 percent of the 10-ml por-
tions, and 0 percent of all 1-ml portions examined were found
89
-------
positive for coliform bacteria. Data from Plant 18a, which oper-
ates in parallel with 18b, but prechlorinated to provide a monthly
average residual of 0,6 to 0.7 mg/1 after 2 to 3 hours theoretical
detention, show less than 0.7 percent of all 10-ml portions of
settled water examined during a two-year period to be positive
for coliform bacteria.
Conclusion
Prechlorination, coagulation, and sedimentation are more ef-
fective than coagulation, sedimentation, and rapid sand filtration
in the reduction of coliform bacteria. Data from 19 plants indicate
that much of the time prechlorination, coagulation, and sedimenta-
tion can produce water conforming to the assumed bacteriological
objective. Effective bacterial reduction is largely dependent upon
the maintenance of substantial chlorine residuals throughout the
coagulation and sedimentation basins.
Coliform bacteria embedded in particulate matter may survive.
One plant operator reported that he consistently found coliform
bacteria in the scum at the outlet end of settling basins.
As practiced at the plants studied, predisinfection using chlora-
mine was less effective than at plants using chlorine only.
Predisinfection, coagulation, and sedimentation are commonly
used as pretreatment to filtration. They alone should not be con-
sidered adequate treatment for raw waters subject to any ap-
preciable contamination.
COAGULATION, SEDIMENTATION, AND FILTRATION
Data from only 6 of the 54 plants could be used to study the
efficiency of coagulation, sedimentation, and filtration as measured
by removal of coliform bacteria. Three plants (Nos, 26, 35, and
53) routinely used postdisinfection only. Eecords for 3 other
plants (Nos. 29, 43, and 48) permitted a study of the effect of dis-
continuance of prechlorination. All the remaining plants applied
chlorine, or chloramine, prior to filtration.
Presentation of Data
Plant 26 was constructed during 1950. Normal treatment con-
sisted of the addition of alum (31 mg/1)* and lime (11 mg/1),
followed by mixing and fiocculation accomplished by tangential-
inflow into a circular tank (1 hour), sedimentation (12 hours),
and filtration (2.0 gpm/sq. ft.). Postdisinfection completed the
treatment.
* Vain* given In parenthaais are averasw data (chemical donee, theoretical detention
time, or rat« of filtration) for th« two-year period.
40
-------
The bacteriological data for raw and filtered waters are shown
in tables 30 and 31. In table 30 these data are first grouped ac-
Table 80.—Effectiveness of coagulation, sedimentation and filtration in the
reduction of coliform bacteria, daily data, plant no. 26
RAW WATER—Coliform Detwily*
Daily,
MPN per 100 ml
Frequency,
day*
FILTER EFFLUENT''
Frequency with which
1-rnl portioni were
coliform-positive
Dayt
Percent
Conform
density,
average
MPN/100m!
EffectivneM
in redurtion
of coliform
bacteria, percent
3230....
2300
(210Q)d,..
9500
24000....
(22000) a.,
5240000.
a
388
2
177
40
46
I
307
1
161
30
IS
SO
•82
*61
<170
•5230
•76
m
•70
377.4
97.3
<<86,7
98.7
<¦99.6
599.9
Total or * 21.200
Average (7000)<*
731
366
40
5 «67
d77
399.7
198,9
* Raw water eamplea examined dolly by 0.111-ml plantings, presumptive test.
11 Filter effluent samples examined daily using one 1-ml. planting', confirmed test.
c Estimated MPN per 100 ml — 280 logio / Portiona planted \
V Portions negative /
4 Estimated MPN obtained by assuming the results from each 10 consecutive dally samples
for raw water loading under consideration to be those from a single sample and applying
Thomas's log-probability procedure.
cording to the daily raw water coliform bacterial density. Then
the frequencies with which 1-ml portions of filter effluent were
positive for coliform bacteria are given for each raw water load-
ing, The average MPN's per 100 ml for filter effluents have been
estimated (1) by assuming all data for each group to be the result
of a single sample, and (2) by Thomas's (12) log-probability
procedure. In applying Thomas's procedure the results from each
10 consecutive daily samples for the raw water loading under
consideration have been assumed to be those from a single sample.
Indicated efficiencies are given for the various raw water loadings.
Table 31 summarizes the average monthly data for the 2-year
period studied.
Plant 35 treated water from the same river intake and in es-
sentially the same manner as Plant 26, Average treatment was
as follows: Approximately two-thirds of the water was presettled
(6 hours), all of it was then treated with alum (39 mg/1) and
lime (14 mg/1), after which it was mixed (10 minutes) and
settled (10 hours) in plain basins. From these it flowed through
any 1 of 4 types of rapid sand Alters, ranging from converted pres-
sure filters to units of modern design. All filters discharged to a
common clear well. In flowing to a second clear well, the water was
disinfected with chlorine or chloramine.
Coliform bacterial data for raw and combined filter effluent
water samples are given in table 32. Although the filter effluent
41
-------
Table 31.—Effectiveness of coagulation, sedimentation and filtration in
the reduction of coliform bacteria, monthly data, plant no. £6
Year
and
month
RAW WATER-
Coliform density,*
monthly average
MPN per 100 ml
FILTER EFFLUENT*
Effectiveness
in reduetion
of coliform
bacteria, peroeat
1-ml portioi
for eolilorn
w examined
3 bacteria
Coliform
density, •
monthly
average
MPN/lOOmJ
Number
Per Cent
positive
1052
January
7BOO
31
20
104
08.7
February
3 6200
29
13
60
98.8
Maroh
3 4300
31
14
61
98.6
April —
8800
30
o
36
99.6
May
6300
31
26
183
98.0
Jane
£16600
30
13
61
96.7
July
*41700
31
18
87
99.8
August
10700
31
24
149
98.6
September
522500
30
21
120
69.5
Ootober
$20500
31
16
73
96.6
November
518900
30
12
61
66.7
December
10000
31
16
67
98.3
Year
* 14900
306
200
81
06.4
10fi3
January
12100
31
18
87
66.3
February
517800
28
31
13
63
69.6
Maroh
6600
7
26
69 7
April
518900
30
8
31
66.8
May
517700
31
6
22
69.9
June
£29700
30
14
63
99.2
July
£22000
31
8
30
99.9
August
534400
31
10
40
99.9
September.....
§65700
30
14
63
99.9
October
555300
31
23
136
99.8
November.
§33300
30
14
63
99.8
December
£23300
31
21
113
99.6
Year....
S27800
365
156
56
99.8
• Raw water samples examined daily using 0.111-ml plantings, presumptive test
£Uter effluent samples examined daily using one 1-ml planting, confirmed test
0 Estimated MPN per 100 ml — 880 logie / Portions planted \
\ Portions negative )
data are for presumptive test only, the comparison of presumptive
and confirmed test data for the filter effluent of Plant 26, which
treated the same raw water, indicates that approximately- 100
percent of all these presumptive positives would also show pres-
ence of coliform bacteria by the confirmed test.
Plant 53 is a purification and softening plant. It is in the
large plant classification. Average treatment consisted of the
addition of alum (30 mg/1), lime (169 mg/1), and soda-ash (75
mg/1), followed by rapid mixing, flocculation (50 minutes) and
settling (2 hours), recarbonation and resettling (6 hours), and
then filtration at rates ranging from 1.6 to 8.0 gpm/sq. ft. Disin-
fection was by marginal postchlorination (0,8 mg/1), which pro-
vided total chlorine residuals ranging from less than 0.05 to 0.3
mg/1 after 5 to 10 hours theoretical contact time. The pH of the
filtered water varied from 9.1 to 10.9 and averaged 10.3.
Table 83 summarizes the coliform bacterial data for raw and
filtered waters.
Plant 29 treated water with alum (37 mg/1), usually carbon
(1.6 mg/1), and part time predisinfection with chlorine (1.2
42
-------
Table 82.—Effectiveness of coagulation, sedimentation and filtration in
the reduction of conform bacteria, daily data, plant no. SB
RAW WATER—Coliform Density*
Daih
MPN per 10
I ml
Frequency
days
FILTER EFFLUENT1'
Frequency with which
1-ml portion# were
coliform-poaitive
Days
Percent
Coliform
density,
average
MPN/100ml
Effeotlvness
in redaction
of coliform
baoteria,
percent
230...
940...
2800...
(2100)*.
8400...
24000...
7
2
396
5
317
5240000.
Total or *13.000
Average (6000)1
731
4
1
340
57
80
6
2S3
100
89
100
•85
*70
•198
d256
•5240
•214
«230
•5240
837
87
•5205
<>249
583.0
02.fi
91.5
<187.8
97.4
99.1
•>99.0
*99.9
*98.4
«95.
* Raw water samples examined dally by 0.11-ml planting*, presumptive test.
b Filter effluent samples examined dally, using one 1-ml plan tins', presumptive (LTB) test.
s Estimated MPN per 100 ml — >80 logio . Portions planted \
V Portions negative/
d Estimated MPN obtained by assuming the results from each 10 consecutive daily samples
for raw water loading under consideration to be those from a single sample and applying
Thomas's (12) log-probability procedure.
mg/1), either with or without the addition of ammonia, followed
by pumping, coagulation, and sedimentation in a plain basin (7
hours), and filtration. Postchlorination and pH adjustment com-
pleted the treatment.
Table 34 summarizes the daily bacteriological data for periods
during which predisinfection was omitted with those during
which it was used.
Plant 43 normally treated water by the addition of alum (80
mg/1) and chlorine (0.3 mg/1), followed by quick mixing and
Tabus 88.—Effectiveness of lime-soda softening, coagulation, sedimentation,
and filtration in the reduction of coliform bacteria, daily data, plant no. 63
RAW WATER—Coliform density*
Dally
MPN per 100 ml
Frequency
tequen
days
FILTER EFFLUENT1"
Frequency of coliform-
positive samples
Days
Permit
Coliform
density,
average
MPN perlOO ml
Effectiveness
is reduotion
of ooliform
bacteria,
percent
S 28
870.
_ 1800.
5 1600.
M00....,
5 5500
86000
5 86000
5190000
Total or ave-
rage *1740
84
848
93
200
20
SO
2
6
1
8
44
28
88
5
6
2
2
1
14.7
13.6
24.7
16.0
25.0
80.0
100.0
88.8
100.0
2 5
2.1
4.0
2.2
14.4
4.7
22.0
19
£240.0
780
121
16.6
52,9
389.1
99.2
99.7
590.9
99.7
$99.9
99.9
599.9
*99.9
*99.8
* Raw water samples examined by single tube plantings of two or more dilutions of 1,0,
0.1^ Q.«, 0.01, and 0.001 ml, presumptive teat MPN calculated by Thomas's approximate
b Filter sffluent samples examined by 51.0-ml plantings, completed test
48
-------
Table 34.—Comparison of coliform densities in raw and filtered waters for
periods during which predisinfection was used and not used, daily data,
plant no. 29
RAW WATER—
Coliform density»,
daily MPN
per 100 ml
FILTER EFFLUENT—Preohlorine or prechloramine disinfection:
Used
N
at used
Frequency
days
Coliform density1",
average per 100 nil
Frequency
days
Coliform density1*,
average MPN
per 100 ml
230
2
0 0
0
1800
no
3.7
10
84.0
10000
les
2.5
40
91.0
22000
7
8.4
18
105 0
5 35000
84
0,7
54
128.0
S 78000
44
14.7
49
06.0
5240000.
6
0,0
12
02.0
1 Raw water samples examined using single plantings of 0.1, 0.01, and 0.004 and sometimes
0.002 and 0.001 ml, presumptive test. MFN's calculated using Thomas's approximate method.
b Filter effluent samples examined using one 10- and one 1-ml portions, confirmed test. For
Snrposes of averaging the MPN has been conslderd 0 if both portions were negative, and 240
! both portions vrere positive.
primary settling (4 hours). The water was then treated with lime
(97 mg/1) and sometimes soda-ash, followed by flocculation and
postchlorination.
Predisinfection was discontinued during November 28 through
December 1, 1953. Bacteriological data for this period are shown
in table 35. Coliform bacteria were detected in the filter effluent
during 5 consecutive days starting November 29.
Plant 48 normally treated water by prechlorination (4.9 mg/1),
presedimentation (34 hours), the addition of alum (12 mg/1) and
sodium aluminate (0 to 4 mg/1), followed by quick mixing, floc-
Table 35.—Effect of the discontinuance of prechlorination on the occurrence
of coliform bacteria in the filter effluent, daily data, Plant No. 43
Date
Preohlorine
application, tag A
Coliiom density, MPN per I0i> mi
Rsw Water'
Filter effluent*
1853
Not. 17
0 3
230
<3.2
18
.8
3400
5 1
19
.8
3400
<3 2
20
.3
230
<2 3
ai
.8
3400
<3 2
22
.3
3400
<3 3
33
.3
3400
<2 3
24
.3
3400
<2 3
25
.3
3400
<3 i
26
.3
330
<2 3
27
.3
3400
<3 3
38
.0
230
<2 t
29
.0
3400
5 i
SO
.0
3400
6 l
Deo. 1
.0
3400
9 3
2
.8
3400
16 0
a
.3
2400
2 3
4
.3
2400
<3 8
5
,3
3400
<2 3
6
.2
2400
<2 3
7
.3
3400
<2 2
8
.3
3400
<2 3
9
.2
2400
<3.3
10
.3
3400
<2 3
11
.3
3400
<2 3
* Haw water samples examined using 1.11-ml plantings, 24 hour presumptive test.
b Filtered water samples examined using five 10-ml portions, confirmed test.
44
-------
culation {}/% hour) and primary settling (21/2 hours). Lime (28
mg/1) and soda-ash (28 mg/1) were added and the water again
flocculated (V2 hour) and settled (2% hours). After recarbona-
tion it was filtered and postchlorinated (0.4 mg/1).
Table 36 shows the effect of discontinuing prechlorination. The
residual chlorine concentrations in both settled and filtered waters
Table 86.—Effect of discontinuance of prechlorination on the occurrence of
coliform bacteria in the filter effluent, daily datat Plant No. A8
Date
*
RAW WATER
Coliform
density*.
MPN/lOOmI
INFLUENT TO FILTER
FILTER EFFLUENT
Total
chlorine
residual, mg/1
Coliform
density >\
MPN/100 ml
Total
chiorina
residual mg/1
Coliform
density1",
MPN /100 ml
, 1963
Mwch
1
4300
0.2
< 2.2
0.2
<2.2
2
4300
.2
< 2.2
.1
<2.2
8
mo
.6
< 2.2
.4
<2.2
4
9300
.8
< 2.2
.0
<2.2
8
4300
.2
< 3.2
.2
<2 2
6
4300
.4
< 2.2
.4
<2,2
7
030
.4
< 2.2
.4
<2.2
8
930
,2
< 2.2
.2
<2.2
9
4300
.0
16.0
.0
<2.2
10
030
.0
524.0
.0
S.l
11
1600
,0
524 0
.0
5.1
13
230
.2
524.0
.1
6 1
14
4300
.2
< 2.2
.2
<2.2
14
080
.4
< 2.2
.2
<2 2
15
2400
.5
< 2.2
.3
<2.2
IS
34000
.4
< 2.2
.3
<2.2
17
4300
.1
< 2.2
TO
<2.2
18
0300
.1
< 2.3
.1
<2.2
IV
0300
.2
< 2.2
.1
<2.2
20
4300
.2
<22
.2
<2 2
4 Raw water samples examined by 8.888-ml plantings, confirmed teet,
"Settled and Altered water samples examined by plantings five 10-ml portions, confirmed
test.
were 0.0 mg/1 for 3 days starting March 9, 1953. Coliform bac-
teria were found in the filter influent on 4 consecutive days start-
ing March 9, and in the filter effluent on 8 consecutive days
starting March 10.
Discussion
The results of bacteriological examinations of raw and filtered,
but unchlorinated, water samples for a 2-year period at each of
three plants have been summarized. At one plant the daily data
for periods during which predisinfection was used are compared
with those during which no predisinfection was utilized. The
effect of discontinuing prechlorination for a few days is shown
for two plants.
The available data include numerous indeterminates. Thus its
analysis has required certain assumptions. The procedure used
has been noted so that the validity of such assumptions can be
evaluated by the reader.
45
-------
The average coliform bacterial reductions effected by the coagu-
lation, sedimentation, and filtration processes range from 98.43
to 99.8 percent for the 3 plants studied. The percentage coliform
removals obtained for the least loading was 5^77.4, 5|63.0f and
<89.1 for Plants 26, 35, and 53, respectively. That for maximum
coliform loadings equaled or exceeded 99.0 percent for each of
these three plants. The superior performance at Plant 53 under
the lower loading is attributed to the disinfecting property of the
lime-soda treatment used in softening the water.
The average coliform densities in the filtered, but unchlorinated
waters, ranged from ^2.9 to 200 per 100 ml. For all raw water
loadings at all three plants it exceeded the assumed bacteriological
objective for water plant effluent.
The limited data available from these three plants indicate
that the bacterial efficiency of the combined processes of coagula-
tion, sedimentation, and filtration varies from less than 80 per-
cent for low raw water bacterial loadings to more than 99 percent
under high loadings. This led to checking Streeter's studies (2)
(3) to determine whether they provided evidence of such variation
in bacterial efficiency. The results are shown in figure 2.
• Tha average efficiency on analysing the data for Plant 36 by Thomas's log-probability
procedure was 96.8 percent.
• • CtMflin MT», * IIMU HI# tfTTMM OHIO ltW» MJMITt (Kf. (, Mll.THU »l)
o accMiinEB MTi, « nun thujim hot u»t mtcm (nr. i, ».w, r»iu m)
«L0UI»mU, IV. (NT. 1. MM. UIU IK)
A A PM»T M (TMU »M ~
/v- 6 HMT n (Till* tl)
o ontnaiwuii)
¦ ' ' ..til 1 1 1 1,1 I nl 1 1 1, | || | I..I 1 ¦ "
10 I AO 1800 10,000 100,000
•iv hth coupon out itt - uni no ioo »i.
Figure 2. Effectiveness of Coagalatioil Sedimentation and Filtra-
tion in Removal of Coliform Bacteria
46
-------
It is noted that the data from Streeter's reports has been
plotted in terms of MPN. The transfer from the "Indicated Num-
ber" to MPN was made as follows. A curve showing the relation
of "Indicated Number" to MPN for the results from five 10-ml
portions was used for all coliform densities not exceeding 23 per
100 ml. For all other data, most of which were the result of
planting one portion each of three or more decimal volumes, the
MPN was assumed equal to 2.3 times the "Indicated Number."
Streeter's combined data for all 9 Ohio River Plants (2) and
those for six other plants (2) are not shown. The former follows
the curve for the four Ohio River Plants for the higher bacterial
loadings, but terminates at 92.2 percent removal when the bacterial
loading is 23 per 100 ml. The raw water bacterial loading for the
six other plants ranges from 540 per 100 ml upward, and these
data, if plotted, would form a curve practically coinciding with
that for plant 53 for loadings above 500 per 100 ml.
Thfr curves showing the percentage coliform bacterial reductions
for various raw water loadings at Plant 26,36, and 53 differ great-
ly. This is believed due to the differences in the plants and their op-
eration. The higher removal of coliform bacteria at Plant 53 is un-
doubtedly due to the bactericidal effect of the excess lime-soda
treatment provided. Although Plants 26 and 35 treated essentially
the same water, the average turbidities of the coagulated and set-
tld waters were 6.3 and 11.6, respectively. Moreover, Plant 26 has
all conventional rapid sand filters while those at Plant 35 represent
the historical development of rapid sand filtration. Finally, it is
noted that the coliform examination of filter effluent at Plant 35
was by presumptive test only, while those at Plants 26 and 53 were
by confirmed test.
Conclusions
The limited data available show that treatment by coagulation,
sedimentation, and rapid sand filtration is inadequate for the
production of water conforming to accepted bacteriological re-
quirements. The over-all effectiveness of these processes as meas-
ured by the removal of coliform bacteria varies with the bacterial
loading. It may range from less than 80 percent for low raw water
loadings to more than 99 percent under high loadings.
PRESEDIMENTATION
Although several of the plants pretreated water by plain sedi-
mentation, the data from only 3 plants (Nos. 6, 25, and 82) were
both adequate and satisfactory for study.
47
-------
Presentation and Discussion of Data
At Plant 6 river water was presettled in a 25-rng reservoir.
Using the volume of water treated, the average theoretical deten-
tion time was 7 days, and for the months of maximum and mini-
mum pumpages it averaged 5 and 8.3 days, respectively.
Except for a 28-day period during July and August, 1954, daily
samples were taken and examined for coliform bacteria. These
examinations consisted of the presumptive tests of single portions
in decimal series from 1 to 0.001 ml for raw water, and from 10 to
0.01 ml for settled water.
Various methods have been used to study the efficiency of pre-
settling in coliform removal. Table 37 shows the monthly, also
Table 37.—Effectiveness of presedimentation as determined by the reduction
in coliform bacteria, monthly data, Plant No. 6
Year and month
Coliform density, average MPN per 100 ml
Raw water
Settled water
EffeotiveneM in reduction of
coliform bacteria, percent
1964
January
February
Ma/oh
April
May
June
July
August
September
October
November
December
Average
1955
January
February
March
April
May
June
July
August
September
October
November
December
Averse*
5 49800
5 66600
5 34000
5 4(1200
5 61600
£103000
5 86000
5114000
5 83200
5100000
5 60000
5 46700
5 69(00
5 38400
5 72600
5 80300
S 63800
5 66000
g 60000
5 87700
g 88700
5 80100
5 01000
5 48600
5 69400
5 64800
fB900
6400
52500
53100
£1400
54300
52900
53300
800
£6600
52300
54600
53500
54100
56800
56000
52800
56300
53700
±*6.1
±96.0
±80.4
±93.7
±97,1
±96.3
±91.3
±03.5
±97.5
±93 8
±97.0
±93.8
±93.2
±96.6
±97.4
±91.3
±96 9
±92 5
±96.0
±96.3
±93.8
±93.4
±94.3
±89.6
±94.3
the yearly, efficiencies based on the average coliform densities for
tile period studied. Monthly efficiencies range from 80.4 to 97.5
percent. The annual averages are 93.8 and 94.3 percent.
A second procedure, which was used by Streeter, groups all
data by days having a common coliform density in the raw water.
Each group is then subdivided according to the coliform density
in the settled water. Table 38 summarizes the results. The ef-
ficiency in removal varies with loading, being 98± percent with
high loading and negative with low loading. A deficiency in this
48
-------
Table 88.—Effectiveness of presedimentation tn the reduction of
coliform bacteria, daily data, Plant No. 6,1954
RAW WATER—Coliform density
SETTLED WATER-
Coliform density
Effectives ea
in reduction
of collfarm
bacteria, percent
Percentage
of
Daily
MPN per 100 ml
Frequency,
4,000
3,400
340
11
88
36
*00
$W
$tt
16,1
40.8
88.6
Avg. Or total
9 4,890
78
-P8
100.0
24,000
391
$24,000
3,400
240
38
1W
«
* 0
00
w
13.«
S.4
33.0
Avg. or total
$ 1,480
331
377
100.0
2,400
43
$34,000
3,400
240
3
38
17
neg.
0
80
7.0
88.8
S9.i
Avg. or total
5 8.060
«».
mg.
100,0
49
-------
Table 40 shows the average monthly coliform data and efficiency
of coliform removal. The annual percent removals were 90.5 and
90.4 percent. Average removal for 14 months during which copper
sulfate was not used was 74.5 percent while that for the 10 months
during which the algacide was used for at least part of the month
was 94.8 percent.
Table 40.—Effectiveness of presedimentation or presedimentation plus copper
sulfate treatment, in the reduction of coliform bacteria, monthly data,
Plant No. SB
Year and Month
Coliform density, average MPN pe rlOO ml
Raw water
Presetted water
EffectiveneM io reduction of
coliform bacteria, percent
1653
January
February
March
April
May
June
July
August
September
October
November
December
Average
1054
January
February
March
April
May
June
July
Auguit
September
October
November
December
Average
17700
9300
9800
4600
13000
9900
18300
33700
fiOOOO
71000
94900
14900
3270
2850
2280
1680
2620
9 1460
3 460
3 390
790
3 780
f 11200
4870
23100
*2680
12100
4800
9700
9200
10800
38400
24700
70400
40300
6600
8000
3 1620
1770
1770
2110
? 8000
1680
3 890
i 330
? 810
* 8600
5 2480
5 2830
21400
2060
± 90. 5
± 90.4
a Copper sulfate added, usually 6 to 7 mar/1 on alternative days from July 18-Nov, 11, 1958,
and from June 14-Oet. 11,1054.
At Plant 32 river water is presettled in a 21-mg tank. The theo-
retical detention time ranged from 3 to 7 hours, and averaged 4Vfc
hours.
Coliform examinations were made of raw and presettled water
5 to 6 days each week. Data from these examinations are given in
table 41. In each case these examinations consisted of five plant-
ings in each of two decimal volumes (0.1 and 0.01 or 0.01 and
0.001 ml), presumptive test.
Indicated coliform removals ranged from-7.8 to 48.2 percent.
The annual averages were 17.0 and 26.8 percent for 1951 and 1952.
50
-------
Table 41.—Effectiveness of presedimentation in the reduction of eoliform
bacteria, monthly data, Plant No. 32
Year and month
Coliform demity, average MPN per 100 ml
Raw water
PreMttled water
Effeetiveneaa in reduction of
eoliform bacteria, percent
1051
January
February
March
April
May
June
July
August
September
October
November
December
Average
1952
January
February
March
April
Majr
June
July
August
September
October
November
December
Average
5 0300
3800
7100
7200
311100
£37000
£16500
£20400
32700
£33100
f 17800
8800
£17100
6200
6000
£10000
£ 8600
511300
£16700
£31000
£11200
10400
£ 9800
£ 0200
£21800
£12700
6800
? 8600
£ 6100
6700
£38000
£10600
£27300
f 22800
24000
£14800
£ 7400
*14200
3800
6000
£0600
4700
£12000
£16600
£11000
10200
£ 0200
£ 8200
£11300
~£03OO
£37.6
£ 7.0
314-1
20.8
±33.3
— 0.3
±86,4
± 7.1
330.3
— 7.8
±16.0
±16.0
±17.0
26.0
13.0
t4.0
44.7
±28,1.
±46.6
— 6.2
1.0
± 6.1
±10.9
±48,2
±26.8
Conclusions
The efficiency of presedimentation varies with the raw water
eoliform density as well as the holding time. Coliform bacterial
removals of 80 percent or more are indicated for heavily loaded
water held for several days. However, during periods of low
bacterial loadings presedimentation may be ineffective in removing
coliform bacteria.
Short-time detention of a few hours cannot be justified on the
basis of removal of coliform bacteria. Indicated removals are
both low and erratic.
EXCESS LIME OR LIME-SODA ASH SOFTENING#
COAGULATION, AND SEDIMENTATION
Plants Studied
Data from 3 plants (Nos. 19, 32, and 36) were adequate for
study of the reduction in coliform bacteria resulting from excess
lime or lime-soda softening, coagulation, and sedimentation.
Plant 19 treated water by adding lime (116 mg/1), alum (12
mg/1), and occasionally soda ash (16 mg/1), followed by mixing
and settling in a sludge blanket type clarifier. The pH of the
51
-------
ciarifier effluent ranged from 8.7 to 11.4 and averaged 10.7. The
theoretical detention time averaged 3.3 hours and ranged from 1.6
to 6 hours. Raw water ciarifier effluent samples were examined
daily using 1.111-ml and 11.1-ml total plantings, respectively, by
the presumptive test.
Plant 32 used short-time presetting <4.7 hours), excess lime
(92 mg/I), and coagulation with alum (5.8 mg/1) and ferrous
sulfate (5.2 mg/1), followed by quick mixing, flocculation, and
settling for 30 to 45 hours theoretical detention time. The pH of
the water after further addition of alum, chlorine, and ammonia,
and secondary settling, ranged from 8.5 to 10.4 and averaged 9.6.
Plant 36 was a purification and softening plant treating an
average of 40 mg of river water daily. The initial treatment con-
sisted of the addition of lime and short-time sedimentation. Coli-
form bacterial examinations, presumptive test, were made of raw
and finished water samples 4 or 5 days per week.
For the 2-year period examined, the lime dosage ranged from
80 to 180, and averaged 121 mg/1. Theoretical detention time
varied from 1.2 to 3.8 hours. The average was about 2*/& hours.
The pH of the treated water ranged from 9.4 to 10.4 and the yearly
averages were 9.9 and 9.8.
Discussion
The bacteriological data for Plants 19 and 32 were analyzed
by plotting log-probability curves of the data on coliform examin-
ations of the raw and settled waters. The results are summarized
in table 42. At each plant the percentage reduction in coliform
bacteria decreased as the raw water coliform loading increased.
That Plant 32 shows the greater removal was probably due to the
longer retention period.
Table 43 summarizes the monthly data for Plant 86, The
monthly average removals of coliform bacteria varied from 56 to
90 percent.
Table 42.—Effectiveneaa of excess time softeningjsoaffulation and sedimenta-
tion in the reduction of eoliform bacteria, Plants Nos. 19 and St
Plant
oode
number
Sampling point
or
treatment
OoUfc
wmdeodttop
Indieafc
tr 100 ml whtc
sd percentage*
h were exceeded for
of time
76%
60%
10%
1%
10
33
(A) Raw Water
rBj BUnket
oSSerEffliwnt......
Reduetlra
(A) Saw Water
fey Primary Settling
Buio Effluent
Reduction (A-B)%
3000
180
8200
610
28000
3100
78000
6300
460000
40000
$4.0
6300
13
OS A
10000
ft!
ea.>
19000
soo
63.0
40000
080
01.7
80000
6700
09.8
99.6
08,8
08.8
00.4
52
-------
Table 43.—Effectiveness of excess lime treatment and sedimentation in
the reduction of coliform bacteria, monthly data, Plant No. 86
Year and month
Coliform density, average
MFN per 100 ml
Efficiency in
reduction of
coliform bacteria, percent
Lime applied,
avg.gr/gal
Raw water
Settled water
1958
January
3580
500
86.0
9.25
February
10000
2350
76.5
7.42
March
4140
1760
56.7
6.86
April
8400
2000
63.0
6.27
May
7180
1550
78.4
7.21
June
19600
3880
81.2
7.25
July
16900
1870
88. B
6.50
August
8770
1960
77.7
5.92
September
8430
3100
68.2
6.73
October
6100
1560
74.4
7.14
November
8650
2070
75.8
7.81
December
8910
2220
75.1
7.80
Average
8960
2050
74.7
7.10
1954
January
3920
675
76.9
10.51
February
8720
470
87.4
8.65
March
7770
970
87.5
8.11
April
6560
1320
76.3
7.81
May
10300
1770
82.8
6.89
June
24800
3070
87.6
6.86
July
14200
2600
81.7
6.86
Angtiat
28700
5240
77.0
5.45
September
21000
5780
72.5
4.91
October
24600
4870
80.2
4.81
November
6040
2170
64.0
6.28
Deoember
4720
1010
78.0
6.89
Avenge
12400
2500
79.4
6.86
Conclusions
Limited data indicate that lime or lime-soda softening process
providing high pH levels has limited disinfection value. Important
factors influencing the effectiveness of such treatment for destruc-
tion of coliform bacteria are the pH level and the holding time.
Lime-soda ash treatment as practiced is inadequate for disin-
fection. In all cases chlorination should be the final safeguard.
Effective removal or inactivation of coliform bacteria can be ob-
tained only through additional treatment by filtration and disin-
fection with due consideration for the contact time and residual
chlorine level required at the pH involved.
APPARENT DEFICIENCIES IN FACILITIES OR OPERATIONS
AT WATER TREATMENT PLANTS
At some plants the bacteriological quality of the finished water
was noticeably below average. In such cases the available informs
tion has been carefully studied in an attempt to determine the
causes. The analyses made herein are hypothetical; proof would
require additional study at the plant levels.
53
-------
Simple Chlorination
Coliform bacteria were reported in the finished water at only
one of the three plants treating water by simple chlorination. The
postive samples did not occur at times of the high turbidity of
the water. The recorded chlorine application and total residual
levels appear to have been adequate. However, this was the only
plant of this type not providing a continuous record of the residual
chlorine concentration. There was also evidence which indicated
a lack of close technical supervision of the treatment.
Disinfection/ Coagulation/ and Sedimentation
Plant S-l treated water by presetting (100 hours) followed
by the addition of alum (20 mg/1), carbon (1.2 mg/1), chlorine
(4.0 mg/1), and ammonia sulfate (2.8 mg/1), after which the
water was settled (35 hours) in large open reservoirs. On several
occasions both the presetting time and that for settling the
coagulated water were much shorter due to basins being removed
from service for cleaning purposes. The residual chlorine, in
the form of chloramine, averaged 1.8 mg/1, but values as low
as 0.6 and 0.8 were recorded for the plant effluent during 1954 and
1955, respectively.
The records on finished water samples show that during the
poorest month, 12.6 percent of all 10-ml portions examined were
positive for coliform bacteria; also that for 6 of the 24 months
more than 5 percent of all such portions were positive for coliform
bacteria. Moreover, the plant operator reported examination of
samples of scum from the outlet of the final settling tank routinely
showed presence of coliform bacteria.
Although the residual chloramine level may be somewhat below
a desirable average, it is believed the poor results at this plant
were due to lack of filtration. The presence of coliform bacteria
in the scum at the effluent end of the final settling tank indicates
that coliform bacteria survive the treatment process due to being
embedded in particulate matter through which chlorine may not
penetrate.
Conventional Rapid Sand Filtration and Disinfection
Reference to table 13 shows that there were only four of the
conventional rapid sand filtration and disinfection plants having
more than 2 percent of all 10-ml portions of finished water ex-
amined during any month positive for coliform bacteria. All four
of these plants are considered to have deficiencies in facilities or
operation.
Two of them, Nos. 44 and 53, are excess lime or lime-soda soft-
54
-------
ening plants providing marginal chlorination giving total chlorine
residuals averaging only 0.1 mg/1 in the finished water. Daily
residual chlorine levels less than 0.06 mg/1 were occasionally
recorded at each of these plants. The difficulty of maintaining
adequate residual chlorine when operating at a level providing
such a low residual, together with the high pH resulting from the
softening processes, appear to be the cause for the relatively poor
records of these two plants.
Plant 8 is a purification plant producing between 5 and 10 mgd.
Treatment consisted of prechlorination, coagulation with alum and
lime, settling, filtration, aeration in open spray aerators, and stor-
age followed by addition of chlorine to the suction line of the
high pressure pumps. The average total residual chlorine in the
treated water for the 2-year period was 0.7 mg/1.
The average annual coliform densities of the raw water ex-
ceeded 50,000 per 100 ml for each of the two years. Coliform
bacteria were detected in only 3 of 502 samples of the plant efflu-
ent.
The dates on which positive samples were taken were May 3,
June 1, and November 29, all during 1954. It is considered signifi-
cant that immediately preceding each of these days the plant had
been shut down for 24 hours or more. A possible explanation is
as follows: The chlorine applied as prechlorination became de-
pleted when the water was retained in the settling tanks an extra
24 hours and after filtration this water was exposed to air- or bird-
borne contaminants in the open aerator. Finally, the postchlorina-
tion practice was such that the elapsed time between applying
the chlorine and taking the sample was inadequate for disinfec-
tion.
Plant 24 is a large purification plant. Treatment normally con-
sisted of presedimentation, the addition of chlorine, lime, and
alum, followed by flocculation and settling. Additional alum was
added and the water again flocculated and settled. After rechlor-
ination the water was filtered and then flowed into an open storage
reservoir from which it was pumped to the distribution system.
The average annual coliform densities in the raw water were
23,000 and 28,000 per 100 ml for the years 1953 and 1954, respec-
tively. Coliform bacteria were detected in the finished water on 6
of 730 days.
Data for these days and those immediately preceding the days
on which coliform bacteria were found in the plant effluent are
shown in table 44. It is noted that 14 of the positive portions oc-
curred in three samples taken on a Saturday, Sunday, and Mon-
day. The infrequent occurrence, the fact that the contamination
was either gross or minor, and the days of the week on which the
55
-------
Tablb 44.—Coliform and chlorination data for days immediately preceding
and on which coliform bacteria were detected in plant effluent, Pla/nt No.
Date
week
RAW WATER
Coliform
density*,
MPN per 100 ml
PLANT EFFLUENT—
Number of 10 ml
portloM
Total
chlorine
application,
mg/I
Free chlo-
rine residual
inpUnt
effluent
mg/I
Examined
Positive*
1683
March 29
4300
5
0
30
9300
5
0
0.8
31
Tues.
21000
S
1
5.1
1064
Jan. 25
4600
5
0
1600
6
0
27
Wed.
4600
5
1
2.7
0.6
May 25
9200
ft
0
26
9300
5
0
0.7
27
Thur.
4300
5
1
6.7
June 24
93000
5
0
25
43000
5
0
1.2
26
Sat.
23000
6
5
7.9
Sept. 3
4800
5
0
4
4300
6
0
0.9
5
Sun.
4300
6
4
4.3
Dec. 4
24000
5
0
5
16000
5
0
6
Moil.
16000
5
8
2.4
0 4
• Confirmed tast.
gross contamination occurred, leads one to wonder if some of the
results were not due to accidental contamination in sampling or
in the laboratory. Of course, the storage of treated water in an
open reservoir also provided opportunity for chance contamina-
tion.
SUMMARY DISCUSSION
This study was made to re-examine the effectiveness of various
water treatment processes as measured by the reduction of coli-
form bacteria. It was undertaken with the knowledge that many
plants were treating raw waters containing bacterial densities in
excess of the recommended maximum permissible loadings estab-
lished as the result of studies made by Streeter during; the 1920's.
That the present findings differ from those of earlier studies is
due to the more intensified treatment, particularly chlorination,
and to more skillful plant operation. Data from the only plant
practicing marginal postchlorination, such as used by the plants
studied by Streeter, substantiate his conclusions.
The data analyzed in this study were obtained from existing
operating records of water plants. With one or two exceptions,
the author personally visited all water plants in the United States
known to have adequate data and raw water bacterial loadings
frequently in excess of the Public Health Service recommenda-
56
-------
tions. The data available at each of these plants were examined
and, if suitable, have been utilized, even though some of them did
not fully meet the standards desired. The decision to include as
much data as possible was made to prevent introducing additional
bias by using data from only the better operated plants of the
already selected group of plants having adequate bacteriological
data for survey purposes.
Throughout this study the coliform bacterial densities have been
used as the sole criterion for determining the effectiveness of the
treatment provided. The quality of the treated water has been
based entirely on results for plant effluent samples. Data for
samples collected throughout the distribution system were ex-
cluded because they would reflect contamination which occurred
in the distribution system. Thus, it appeared logical to set a more
stringent objective for bacterial quality of plant effluent than that
required by the Public Health Service Drinking Water Standards,
which applies to samples collected at representative locations
throughout the distribution system.
Analysis of the data for conventional rapid sand filtration and
disinfection plants indicates that it is practical to provide treat-
ment such that not more than 2 percent of all 10-ml portions of
plant effluent samples examined during any one month show pres-
ence of coliform bacteria. This percentage of positive portions was
equaled or exceeded during only 15 of 1,281, or 1.2 percent of all
plant months examined for rapid sand filtration plants. Moreover,
all plant months during which two or more percent of the 10-ml
portions were coliform positive occurred at only four plants and
each of these plants had, in the opinion of the author, a deficiency
either in facilities or operation. This analysis resulted in adopting
an assumed bacteriological objective for plant effluent, which per-
mits not more than 2 percent of all 10-ml portions of plant effluent
samples examined during any one month to be positive for coli-
form bacteria. Failure to conform to this objective does not imply
that the water delivered to the consumers is not potable. The
potability of water should be evaluated by the Public Health Serv-
ice Drinking Water Standards, which permit not more than 10
percent of the 10-ml portions from samples collected during any
one month from representative locations throughout the distri-
bution system to be positive for coliform bacteria.
Although a special effort was made to secure data from plants
treating surface waters by simple chlorination, the total consisted
of 84 plant months from only three plants. The average monthly
coliform density in the raw water equaled or exceeded 100 per
100 ml during 8 plant months, and 50 per 100 ml during 83 plant
months. Coliform bacteria were detected in more than 2 percent
57
-------
of the 10-ml portions examined during only 1 of the 84 plant
months, and the raw water coliform density for that 1 month was
only 27 per 100 ml. It is also noted that apparent deficiencies in
operation and facilities were observed at the only plant having
finished water samples showing presence of coliform bacteria.
The coliform bacteria removal effected by coagulation, sedimen-
tation, and filtration was studied when plant data were suitable.
The average removal was approximately 98 percent, which is that
reported by Streeter. It should be noted, however, that the per-
centage removal varies greatly with the coliform density in the
raw water, ranging from less than 80 percent for low loadings to
more than 99 percent for high loadings. Obviously chlorination
or some other form of disinfection is essential if the water pro-
duced is to meet either the assumed bacteriological objectives or
the bacteriological requirements of the Public Health Service
Drinking Water Standards.
Predisinfection, coagulation, and sedimentation provided more
effective bacterial removal than the conventional rapid sand filtra-
tion process without disinfection. Results, however, are somewhat
erratic. There is limited evidence indicating that bacteria em-
bedded in particulate matter may survive chlorination.
Many water treatment plants using conventional rapid sand
filtration and disinfection processes are treating raw waters
heavily laden with coliform bacteria. That they can treat such
waters to produce potable water conforming to the assumed bac-
terial-quality objection is a tribute to those individuals responsible
for their design and operation.
Of the four filtration plants whose effluents exceeded 2 percent
coliform positive portions in any month, two were softening plants
using marginal chlorination to provide a total chlorine residual
in the finished water averaging only 0.1 mg/1. Daily average
residual chlorine concentrations of less than 0.05 mg/1 were re-
corded on several occasions at each plant. The facilities at the
remaining two plants provided opportunity for air- or bird-borne
contamination of the filtered water.
The coliform removal resulting from presedimentation, also
from excess lime or lime-soda softening has been studied where
the data were available and reasonably adequate. In view of the
relative small number of plants involved, the indicated removals
should not be considered conclusive.
There has been considerable progress in the science and in the
practice of water treatment since the period of Streeter's studies.
Chlorination, together with improvements in other processes, has
made it possible to treat raw waters containing coliform loadings
far in excess of the permissible loadings recommended as the re-
58
-------
suit of the 1920 studies. This apparent ease with which bacteria
are removed or inactivated makes it essential that careful consider-
ation be given to the use of the coliform bacterial examination as
the sole criterion of biological safety of water.
Practical application of the bacteriological standard stated in
Public Health Service Drinking Water Standards, 19U6, requires
that the water delivered to the consumer shall not have a colifonh
density in excess of 1 per 100 ml. The relation of coliform bacteria
to pathogenic biological organisms has been assumed to be such
that water containing that density of coliform bacteria shall be
free from infectious levels of biological organisms. This raises the
question whether treatment processes are equally effective in re-
moving or inactivating other biological pathogens.
In general, epidemiological evidence supports the adequacy of
the coliform bacterial examination for determination of biological
safety of water produced by well-operated conventional rapid sand
filtration, and disinfection plants. Although there are numerous
reports of water-borne outbreaks in the literature, the writer
knows of only three incidents in the United States in which water
apparently conforming with accepted bacteriological standards has
been incriminated as the agent of transmission. These are the
series of gastroenteritis outbreaks in 1930-31 which occurred in
6 cities securing water from the Kanawha and Ohio Rivers (14),
the 1986 outbreak of gastroenteritis and typhoid fever in Min-
neapolis (15), and an outbreak of gastroenteritis in Milwaukee
during 1938 (16). In two of these incidents, although the water
conformed to the bacteriological requirements of accepted stand-
ards, coliform bacteria were detected in some of the potable water
samples, and in the remaining case it was not determined
whether the causitive agent was chemical or biological.
A review of the available information indicates that enteric
viruses, such as polio, Coxsackie, ECHO, and infectious hepatitis,
Rtight be transmitted through water to produce disease in suscep-
tible individuals. The presence of polio, Coxsackie, and ECHO
viruses in sewage has been demonstrated (17) (18) and there is
epidemiological evidence that virus causing infectious hepatitis
survived water treatment processes (19).
If it is assumed that the removal of such viruses by coagulation,
sedimentation, and filtration is of the same general magnitude
as that for coliform bacteria, the effectiveness of chlorine disin-
fection becomes of vital importance. Laboratory investigations
(20), (21), (22), have demonstrated that certain enteric viruses
are more resistant to chlorine disinfection than coliform bacteria*
It is also noted that Endamoeba histolytica survive chlorine dis-
infection levels which provide a complete kill or inaetivation of
coliform bacteria (28).
69
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Chlorination, together with improvements in other processes,
has made it possible to treat raw waters containing coliform bac-
terial loadings far in excess of the permissible loading recom-
mended by the Public Health Service. The capacity of improved
water treatment processes to remove bacteria suggests that waters
containing coliform bacterial densities considerably in excess of
present recommended loadings are acceptable for treatment. The
utilization, however, of raw waters heavily contaminated with
sewage may create other problems.
Although bacteria are readily removed or inactivated by water
treatment processes, our knowledge of the fate of viruses and
other pathogenic organisms is very limited. The problems of
taste and odor, which are of major concern to water plant opera-
tors, should also be considered. Last, but not least, the psychologi-
cal reaction of the public against obtaining their drinking water
from "dirty water" are involved. Thus, it should be recognized
that the production of a safe and desirable drinking water is most
easily and economically accomplished when the plant processes a
good grade raw material.
Some factors to be considered in evaluating a plant's capacity to
treat water containing high densities of coliform organisms are
the qualifications of the operators, the availability of adequate
chlorinators, the locations at which chlorine is applied, the resi-
dual chlorine levels maintained, and the frequency of their deter-
mination. Special precautions, such as a residual chlorine recorder
with alarm system, are desirable when treatment consists of
simple chlorination, or where the chlorine demand of the water
varies greatly over short intervals of time.
60
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II. Special Cooperative MF-MPN Study
SUPPLEMENTARY STUDY
During 1956-57, fourteen water treatment plants throughout
the United States participated with the Robert A. Taft Sanitary
Engineer Center in a special study, one objective of which was to
secure additional data of uniform and outstanding quality for
evaluating the efficiency of water treatment plants in removal
or inactivation of coliform bacteria. Ten of those water plants,
data from which have been used in this paper are:
Atlanta, Ga. Dallas, Tex.
Hackensack Water Co. Kaiser Aluminum & Chemical
New Milford, N. J. Corp.4 Chalmette, La.
Quincy, 111.
Data from the other 4 plants have not been included, as they
either covered only a limited period of operation, or the plant
sampling location had been selected to secure water having positive
but low level coliform density.
Particular efforts were made to secure bacteriological data of
outstanding quality. Consideration was given to the quality of
the laboratory work in the plant selection, and all participating
plants agreed to follow general procedures as outlined by the
Sanitary Engineering Center. Morover, a bacteriologist from the
Center spent 2 to 4 days at each plant to assist laboratory person-
nel in standardizing the MF procedures, and made a return visit
to the plant if difficulties were encountered. EHC powder indicator
for all MF examinations was supplied by the Center. Finally, only
the last 12 of the 18 months of data from each plant have been
utilized.
In general, raw water and plant effluent samples were examined
5 days each week, except during the last 2 weeks of December,
when collection of data was omitted due to anticipated delay
in receipt of the delayed MF samples mailed to the Center,
* Bacteriological examination of water aamplM from Kaiser Corp. Water Plant were mad*
by Division of Laboratories, Louisiana State Department of Health.
Kansas City, Kans.
Fridiey Plant,
Minneapolis, Minn.
Laredo, Tex.
Omaha, Nebr.
Wyandotte, Mich.
61
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Portions of raw and finished water samples were examined by
each, of three procedures-MPN dilution, immediate MF, and de-
layed MF. All laboratory work, except that involved in the com-
pletion of the delayed MF procedure, was performed at the water
plants.
Although portions of each raw water sample were examined by
each of the procedures, only the results of the MPN dilutibn, con-
firmed test, are used in this report. For plant effluent, data for all
three procedures are included. In these tests, the lower limits at
which coliform bacteria were detectable by the MPN dilution pro-
cedure were 2.2,1.0, and 0.69 per 100 ml at 6,1, and 3 plants; by
immediate MF procedure, 0.5, 0.25, and 0.14 per 100 ml at 6, 3,
and 1 plants; and by delayed MF procedure, 0.5, 0.25, and 0.14 per
100 ml at 2, 7, and 1 plants, respectively.
Presentation of Data
Only data for those days on which results by all three bacterio-
logical procedures were available have been used. In table 45
the data for all plants are first grouped according to raw water
bacteriological density, then by the percentages of days in each
group on which coliform were detected in the plant effluent by any
and each procedure, and days on which one or more of the three
procedures indicated that coliform densities in the treated water
were equal to or greater than 1 per 100 ml.
The fact that coliform bacteria were detected in plant effluent
samples on days during which raw water loadings were in excess
of 50,000 per 100 ml at only 1 plant, led to further analysis. Table
46 compares the coliform data from this plant (lx) with those
from Plant 5, the only other plant treating raw waters having
a similar range in coliform density. In table 47 plant (lx) data
for the first 6 months of the study are compared with those ob-
tained during the last 6 months.
The coliform data for all days on which coliform bacteria were
detected in plant effluent samples are given in table 48. On 54
days coliform bacteria were detected by only 1 of the 3 procedures
used in examining each sample. Such detection occurred nine
times by MPN dilution, 13 times by immediate MF, and 32 times
by delayed MF procedure. Portions of seven samples were positive
for coliform bacteria by two procedures, once by MPN dilution
and immediate MF, twice by MPN dilution and delayed MF, and
four times by both MF procedures. All three procedures detected
coliform bacteria in only four samples.
Altogether, coliform bacteria were detected in one or more
portions of 65 plant effluent samples. Positive results were ob-
tained 16 times by the MPN dilution procedure, 22 times by the
62
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Table 46.—Effectiveness of conventional rapid sand filtration and disinfection
water treatment plants in the reduction of coliform bacteria, daily data,
special MF-MPN study
RAW WATER—
Coliform d entity,
PLANT EFFLUENT—Percentage of days on which—
Coliform bacteria were detected by—
Coliform Density 51 per 100 ml
MPN/l&ml
Frequen-
cy, days
Any
prooeas
MPN
Dil.
Proc».
Immed.
MF
Pioob.
Delayed
MF
Pro«t.
Any
Ptm.
MPN
DiL
Proo*.
Immed.
MF
Proeb.
Delayed
MF
Proc*.
0- 8400
2500- 4000
5000- 0900
10000- 24000
25000- 46000
U000- 99000
100000-340000
250000-400000
5JOO0O-99O0OO
51,000,000
1058
m
109
318
199
85
77
14
12
4
2.6
1.9
2.5
8.8
2.5
<14.7
<19.1
.0
.0
.0
0.4
1.2
1.0
1.3
.5
.0
*1,8
.0
.0
.0
1.0
.0
.5
.6
1.0
*2.4
*5.2
.0
.0
.0
1.2
.5
2.0
3.1
2.5
*3.5
*6.5
.0
.0
.0
1.0
1.2
1.0
1.8
1.0
.0
*5.2
.0
.0
.0
0.4
1.2
1.0
.3
.5
.0
*1.3
.0
.0
0
0.3
.0
.5
.3
1.0
.0
*3.9
.0
.0
.0
0.4
.0
.5
.6
1.0
,0
*3.9
.0
.0
.0
_ * Limit* of detection! 2.2/100 ml for 8 plant*; 1/100 ml for 1 plant and 0,68/100 ml for
s Slants.
» Limits of detection: 0.5/100 ml for 6 plants; 0.26/100 ml for 8 plants and 0.14/100 ml
for l plant
. * Limits of detections 0.5/100 ml for 2 plants; 0.25/100 ml for 7 plants and 0.14/100 ml for
1 Slant.
4 An positive data from plant Ix
Table 46.—Comparison of coliform data for raw and finished waters for
periods of special MF-MPN study at Plants, lit and 5, daily data
Raw water
coliform density.
MPN pet 100 ni
PLANT NO. li
PUNT NO.#
Frequency of
raw water
eoliform
density,
dayi
Percentage
which oolifoi
were detect
effluei
of dayi on
rm bacteria
Ml to plant
it at—-
Frequency of
raw water
odiform
denaity,
dan
Percentage of days on
which ootuora bacteria
were detected in piant
effluent at—
Any level
51/100 ml
Any level
51/100 ml
0- 2400,,.,
2500- 4000....
.MOO- 9800....
10000- 34000....
25000- 40000....
50000- 09000.,
IMOOft-MOWO....
2MO0O-49O00O....
«00000-*90000....
Sl.OOOtOOO
Total or
Average..
1
3
0
51
67
28
40
13
11
1
0.
0.
0.
0.
3.0
14.3
15.0
0.
0.
0.
0.
0.
0.
0.
8.0
0.
10.0
0.
0.
0.
1
10
14
09
78
21
28
1
1
3
0
0
7.2
1,4
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
324
5.4
2.7
220
0.9
0.0
68
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Table 47.—Comparison of eoliform data for raw and finished waters for first
ana second six-month peno1/100 ml. At or above this density the frequencies of
detection were 13, 10, and 12 by MPN dilution, immediate MF,
and delayed MF procedures, respectively.
64
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Table 48.—Comparison of Coliform densities of raw and finished waters for
all plant days on which coliform, bacteria were detected in plant effluents,
special MF-MPN study
Plant
code
number
61,
38.
BO.
61.
33.
60.
60.
61.
38.
£0.
61.
60.
60.
60.
34.
60.
33.
60.
19.
34.
34.
31.
34.
38.
60.
19.
38,
19.
19.
<0.
34.
30.
34.
6.
34.
34.
38.
38,
34.
3x
34.
38.
38.
38.
38.
6.
38.
34.
38.
38.
19.
Is
1*
60.
38.
U
1*
U
l*
It
1*
I*
U
1*
1*
RAW WATER—
Coliform deneity,
MPN par 100 ml
PLANT EFFLUENT—Coliform deniity per
100 ml aa determined by—
MPN
dilution
procedure
u
2.1
< 0 .25
80
< .69
.8
110
< 2.2
< .6
130
< 2.1
.26
170
< 2.2
< .6
330
< 2.2
< .6
330
< 2.2
< .6
230
< 2.1
< .26
230
< .69
.6
830
< 2.2
< .6
490
< 2.1
.26
690
< 2.2
< .6
700
< 2.2
< .6
790
< 2.2
< .6
790
2.2
< .6
1300
< 2.2
.8
1300
< 2.2
1.0
1700
< 2.2
< .6
1700
< 1.0
1.2
1700
2.2
.8
1700
2.2
< .6
3200
< 2.2
< .5
3300
< 2.2
2.0
2300
< .69
< .33
3400
< 2.2
< .«
2400
< 10
.25
3400
< .69
.33
2600
5 1.8
< .6
3300
< 1.0
< .26
3600
8.1
< .6
8600
2.2
< 0.6
4600
< 2.2
< .36
4900
$23.0
< .6
0800
< .68
< .14
7900
< 2.2
< .#
7900
< 2.2
< .6
7900
1.1
< .33
7900
1.1
1.0
13000
< 2.3
< .6
18000
< .66
< .6
13000
< .22
8.0
13000
< .69
< ,33
18000
< .69
< .83
13000
< .69
< ,33
13000
< .69
< .38
nooo
.88
.28
22000
< .69
.33
34000
2.2
< .8
34000
.88
< .33
24000
.88
< .33
38000
< 1.0
< .26
33000
< 3.3
11.0
33000
18.0
8.8
86000
< 3.3
< .5
86000
< .69
< .88
79000
< 3.2
.8
79000
< 3.2
.8
79000
< 2.2
< .6
79000
< 3.3
< .8
130000
< 3.3
4.8
180000
< 3.3
< .8
170000
< 3.3
.6
840000
< 3.3
1.8
340000
3.3
8.0
840000
< 3.3
< .6
MF
immediate
prooedure
MF
delayed
procedure
<0.26
< .5
.26
< ,26
.23
1.0
11.8
.25
< .6
.6
< .26
12.8
.26
2.28
<
.26
<
.26
<
.26
.28
<
.28
<
.26
<
.26
.28
<
.26
.88
.6
<
.26
<
.33
<
.6
.28
<
.26
<0.29
.28
< .36
.14
.28
.26
< .33
8.3
.26
< .26
.87
1,87
.88
.88
.28
1.87
< .36
.88
.88
.28
7.0
8.0
.28
.33
.8
< .6
.8
.8
1.5
.8
1.8
< .8
8.8
.8
65
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Discussion
The maximum daily coliform densities in the raw waters ex-
ceeded 50,000 per 100 ml at 9 plants, 100,000 per 100 ml at five
plants, and 250,000 per 100 ml at two plants. In spite of such
heavy loadings coliform bacteria were detected in only 2.8 percent
of all plant effluent samples, and at a level 1 per 100 ml in only
1.2 percent of these samples. Excluding the data from Plant (lx)
only 0.73 percent of all plant effluent samples were determined
by any one of three procedures to contain one or more coliform
bacteria per 100 ml.
Examination of the MPN dilution coliform data for Plant lx
effluent samples shows that the efficiency of this plant in remov-
ing or inactivating coliform bacteria was poor compared with
that of other plants. A comparison of data from this plant with
those from Plant 5, the only other plant treating raw water
having a similar range in coliform density, indicates either the
facilities or operation of Plant (lx) were responsible for its rela-
tively poor efficiency. The marked improvement in the bacterial
quality of the water produced by Plant (lx) throughout the final 6
months period indicates that the plant facilities were adequate.
This improved treatment is believed due to increased chlorina-
tion. During the first 6 months the total residual chlorine in 7
of 17 samples collected from one or more locations in a relatively
restricted distribution system did not exceed 0.10 mg/1 while
the minimum residual chlorine in all 20 such samples collected
during the second 6 months period was 0.20 mg/1.
The comparison of the results of examination of plant effluent
samples by three different procedures is interesting. First, it
should be remembered that all three procedures were consistent
in that they gave negative results for 2,217 or 97.1 percent of all
samples. Such consistency does not exist for those samples in
which coliform were detected. For 19, or 29 percent of coliform-
positive samples, 1 of the 3 procedures gave coliform densities 4
or more times that density at which these bacteria should have
been detected but were not by at least one of the other procedures.
Some of these discrepancies may have occurred through errors in
technique, others by chance.
Conclusions
The special MF-MPN study provided coliform data of superior
quality and procedures capable of detecting bacteria at low densi-
ties.
Nine of the 10 participating plants produced water conforming
to the assumed coliform bacterial objective for plant effluent.
66
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The records for the only plant which produced water of ques-
tionable quality during the early part of the study, but water of
excellent bacterial quality throughout the last 6 months, demon-
strate the importance of adequate chlorination.
ACKNOWLEDGMENTS
This paper has been possible only because of the excellent
cooperation given by many individuals. The State Departments of
Health and the Regional Public Health Offices assisted in the
selection of the water plants. Those water plants listed elsewhere
in this report, as well as many others, data from which have not
been used, provided records and other information.
Many valuable suggestions have been made by Dr. Richard L.
Woodward, Chief of Engineering, Water Supply and Water Pol-
lution Research Branch.
67
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68
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