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SEWERAGE
AND
SEWAGE
PURIFICATION
BY M. N. BAKER, PH. B., C. E.
ASSOCIATK EDITOM, *• ENGINEERING NEWS.'*
JOINT AUTHOK u SEWAGE DISPOSAL /.N THE UNITED STATES.'
AUTHOR "SF.WAGE PURIFICATION IN AMERICA,"
isH SEV/A<;E V.'ORKS."
Fifth Edition, Revised and Enlarged.
HBHT
UC-NRLF
157
• . ••
NEW YORK:
D, VA]Nr XOSTRAND COMPANY,
Park Place.
1913
THE
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No. 12. THEORY OF VOUSSOIR ARCHES. By
Prof. Wm. Cain. Third edition, revised and enlarged.
THE VAN NOSTRAND SCIENCE SERIES
No. 13. GASES MET WITH "IN COAL MINES.
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SEWAGE DISPOSAL
IN THE
UNITED STATES.
BY
GEO. W. RAFTER, M. Am. Soc. C. E.,
AND
M. N. BAKER, Ph.B.,
ASSOCIATE EDITOR "ENGINEERING NEWS."
Large Svo, 600 pages, 7 plates, 116 illustrations
in tJie text.
Part I. of this great work discusses the principles of
the subject in detail, citing foreign experience where
it will throw light upon the subject, but dealing chiefly
with American ideas and practice, and with the broad
principles of sewage purification, or other means of
disposal, which are more or less applicable every-
where. Each method of purification is discussed at
length, and many allied subjects never before treated
in a comprehensive manner are taken up.
Part II. is an exhaustive description of about forty
sewage purification plants as actually built in the
United States and Canada, with many details of cost,
methods of operation and the results obtained in actual
practice. Several appendices give English and Amer-
ican Statute Laws regarding stream pollution and its
prevention, and the duties and powers lodged in State
Boards of Health for the preservation of the purity of
inland waters, especially where used for public water
supplies.
SENT POSTPAID ON KKCEIPT OF $6.00 BY THE PUB-
LISHEBS,
D. VAN NOSTRAND CO.,
25 PARK PLACE, NEW YORK CITY.
SEWERAGE
AND
SEWAGE
PURIFICATION
BY M. N. BAKER, PH. B., C. E.
ASSOCIATE EDITOR, "ENGINEERING NEWS."
JOINT AUTHOR "SEWAGE DISPOSAL IN THE UNITED STATES.'*
AUTHOR "SEWAGE PURIFICATION IN AMERICA,"
"BRITISH SEWAGE WORKS."
Fifth Edition, Revised and Enlarged.
NEW YORK:
B, VAN NOSTRAND COMPANY,
. ?5 Park Place.
1913
COPTBIOHT, 1905,
BY D. VAN NOSTRAND COMPANY.
^IK Rights Reserved.
PREFACE.
One of the earliest volumes in this series
was " Sewerage and Sewage Utilization," by
Professor W. H. Corfield, of the Univer-
sity of London. Appearing in 1875, when
only a few score American cities had sew-
erage systems worthy the name, and when
sewage purification was nractically un-
known in this country, the little book was
and for many years continued to be of great
service this side the water.
When, after twenty years, the publishers
requested the author to revise the book, he
found revision, or even re-writirg, entirely
out of the question, so ill-suited were its
matter and method to modern American
conditions.
There being a strong demand for a brief
but comprehensive book on the subject, it
was decided that an entirely new one
should be written.
Professor Corfield entitled his discussion
365610
TV
" Sewerage and Sewage Utilization." The
present author prefers to use " Purifica-
tion," rather than " Utilization," in his
title. In making this change he does not
wish to detract from the importance or
possibilities of utilization, but simply to
put purification, or the sanitary problem,
first, and utilization, or the commercial
problem, second. In addition, utilization
is only one of several processes of purifi-
cation.
There are now in the United States some
fifty cities and villages, many institutions,
manufactories and houses, employing one
or another system of sewage purification.
The studies of the Massachusetts State
Board of Health have given an impetus to
intermittent filtration of late, but chemical
precipitation is practiced in many places
and broad irrigation is quite common, es-
pecially in the West, where " Water is
King," and the sewage is used for plant
drink rather than plant food.
It is hoped that this little book will be
of use to some engineers, especially those
whose practice has been in other lines of
V.
engineering, and to that vast and rapidly
growing body of sewer commissioners and
superintendents, boards of public works,
boards of health, mayors and city council-
men, and public spirited citizen in general,
all of whom are of late taking a growing
and most promising interest in sanitary
problems.
M. N. B.
104 Tribune Building,
New York, Dec. 31, 1895.
PREFACE TO THE SECOND
EDITION.
In the nearly ten years that have elapsed
since the appearance of the first edition of
this little book, the newer and so-called
bacterial processes of sewage treatment
have been announced, passed through an
experimental stage and come into extensive
use. Meanwhile the author has improved
many opportunities to visit American sew-
VI.
age purification works, old and new, and
during 1904 spent several months abroad,
chiefly in Great Britain, visiting sewage
works and meeting a number of the men
prominently connected with British pro-
gress in this field. As a consequence of
the events named above, the section of this
book which deals with the purification of
sewage has been largely rewritten and
somewhat extended. Few changes in the
other section, on sewerage systems as con-
trasted with disposal works, have been
deemed necessary.
M. N. B.
220 Broadway,
New York, May 5, 1905.
CONTENTS.
Page.
Why a Sewerage System is Needed 5
The Value of a Sewerage System 12
Good Engineering Advice Essential. 14
Preliminary Reports and Plans 15
Separate or Combined System 21
Subsoil Drainage 25
Final Disposal of Sewage 28
Population, Water Consumption, Volume of
Sewage, Rainfall 34
Method of Meeting the Cost 46
Design and Construction of the Conduit
System 58
Manholes 63
Sewer Grades 64
Flushing Devices 64
Y-Branches for House Connections 66
Ventilation of Sewers 68
Misapprehensions Regarding So-called Sewer
Gas 72
Dr. Billings' Opinion on Sewer Air and Ven-
tilation 74
Features Peculiar to the Combined System.. 77
Oatch Basins or Rainwater Inlets 80
Storm Overflows 81
vm.
Page.
Pumping Stations, Keceiving Reservoirs and
Force Mains 82
Tidal Chambers 84
Final Plans and Specifications . 8i
Securing Bids and Awarding Contracts 86
The Proper Lxecution of the Contract 90
Operating the System 92
Sewarge Commission, Board of Public Works
or City Council 93
Sewage Purification in its General Aspects.... 95
Sedimentation 104
Mechanical Straining 106
Chemical Precipitation 108
The Septic Tank 116
Artificial Aeration. — " Electrical" Processes. 121
Broad Irrigation or Sewage Farming 125
Sub-Surface Irrigation 131
Intermittent Filtration 131
Contact Beds 142
Percolating Filters 147
Sewage Purification Plants not Nuisances 140
The Present Status of Sewage Purification.... 150
SEWERAGE AND SEWAGE PURI-
FICATION.
WHY A SEWERAGE SYSTEM is NEEDED.
An abundant supply of pure water is
one of the greatest advantages which any
community can possess. This is so gener-
ally recognized that every American town
with a population reaching into the thous-
ands has, or is planning to obtain, a public
water supply. Such a supply having been
secured, distributed through the streets
and houses, used and enjoyed, what dispo-
sition shall be made of it ? Obviously its
removal may be the very reverse of its in-
troduction. As it was'distributed through
a network of conduits diminishing in size
with their ramifications, so it may be col-
lected again by similar conduits, increas-
ing in size, as one after another they unite
in a common outlet. But the outgoing
volume is far different from the incoming.
The influent was pure and limpid ; the
effluent has been fouled in performing the
services demanded of it, and should it ac-
cumulate and remain at any point it
would decompose and give rise to offensive
odors. Moreover, in its various fields of
usefulness, the once pure water may have
taken up germs of disease which formerly
habited the human body, causing sickness
and perhaps death, and which might give
rise to like dire results should they again
secure access to man. What, then, shall
be done with the fouled water that has
been collected ? In general, there are but
two answers : Either it must (1) be turned
into a body of water so large as to'dilute
it beyond all possibility of offence, and
where it cannot endanger human life by
polluting a public water supply, or (2) it
must in some manner be purified.
This fouled water is called sewage; the
conduits which collect it constitute the
sewerage system ; and the means adopted
to get rid of the collected matter is termed
sewage disposal. The terms sewerage and
sewage, it may be noted here, are often
confounded, even among engineers. The
use of sewerage to indicate the matter car-
ried by a sewer, is obsolete, so that one
might about as properly write or speak of
purifying water- works as of purifying
sewerage.
To go a little further with definitions,
it may be stated that conduits which cany
water collected from street surfaces, dur-
ing and after rains, or ground water col-
lected from beneath the surface, or both,
are called drains. Where one set of con-
duits removes sewage and another carries
surface and ground water, it is said that
the separate system of sewerage is in use,
a term which may be applied where the
drainage system has not yet been con-
structed, but only sanitary sewers, as they
are often called, have been provided.
Where one set of conduits conveys both
sewage and drainage water, it is called the
combined system of sewerage. Obviously,
various modifications of those two systems
are possible, both for whole cities and for
limited areas within one municipality.
To make the distinction between sewers
and drains more complete, it may be said
s
that sewers carry water fouled with or-
ganic wastes from the human system, from
various cleansing processes common to
all households, and also manufacturing
wastes; while drains convey rain or ground
water only. The drainage, however, may
contain much organic matter gathered by
the rain in passing over roofs, yards and
streets, or by the ground water as it per-
colates through polluted soil; but this
matter, in most cases, is far less likely to
give offense or menace health than that
contained in sewage.
Before entering into a discussion of
sewerage systems it will be well to con-
sider briefly why they are needed, for the
engineer and the sanitarian must for many
years to come meet the objections to this
class of improvements put forth by men
either ignorant of the principles involved
or, worse yet> of those whose first impulse
is to strenuously resist any new demand
upon the public treasury, without regard
to its character.
Public water supplies and sewerage
systems naturally go hand in hand. Where
neither exists water is generally drawn
from wells, often in close proximity to
privies and sink drains, and subject to
gross pollution from them. Should there
be a case of typhoid fever in a given house
typhoid germs, which always exist in great
numbers in the dejecta of the patient,
might readily find their way into the
well, and thus into the digestive system of
other members of the family, of visitors,
or of neighbors using the well. Thus the
disease is spread from one member of a
family to another and from family to
family. Besides this danger, there is
always the more remote one from the
dreaded cholera, should it visit the country,
and the ever present one of poor health
and consequent greater susceptibility to
all forms of disease.
A sanitary sewerage system cannot be
installed until a public water supply has
been provided. It is needed as soon as
that is accomplished, for while the wells
can then be abandoned the volume of
waste water is greatly augmented by the
water-works system. Its foulness is also
10
greatly increased through the introduc-
tion of water closets. Without sewers and
with a public water supply cesspools must
be employed. With cesspools begins a
continuous and far-reaching pollution of
the soil, much more serious than that
which commonly results from privies
and the surface disposal of slops. The
pores of the ground become clogged
with organic waste; nature's beneficent
process of oxidation is arrested ; putrefac-
tion sets in ; and poisonous gases are gene-
rated. These gases may find their way
through foundations into houses and also
directly into the outer air, especially dur-
ing sudden rises in the ground watrr level.
The cellars of houses on small lots may
be made damp by leaching cesspools.
Such wells as still remain in use are also
liable to pollution from cesspools on neigh-
boring premises. Water tight cesspools,
while possible in theory and often de-
manded by health ordinances, are a luxury
that only a few can afford, owing to the
cost of frequent emptyings. Even in per-
meable 'soils the emptying of leaching
11
cesspools as often as health and decency
demand will generally cost more than the
increase in taxes due to the construction
and maintenance of a sewerage system.
A village or town without water-works
and sewers is at great disadvantage as
compared with communities having these
conveniences and safeguards. Industries
and population are not so quickly attracted
to it; the health of the municipality is
almost sure to be poorer and its death rate
higher. These statements hold, only in
lesser degree, where a public water sup-
ply but no sewerage system has been pro-
vided. The full benefits of water-works
cannot be enjoyed until sewers are put in,
because many people will make the ab-
sence of sewers an excuse for the non-use
or limited use of the water supply.
Who can describe the trials and tribula-
tions which beset health authorities in
their efforts to secure the proper disposal
of privy and cesspool matter ? If there is
little but privy matter to be removed the
difficulties are not so great, because in this
country such a condition seldom exists,
12
except in small communities, where the
houses are set in ample lots, with gardens,
and with an abundance of farm land near
by, so that the vault matter is in demand
for fertilizing purposes. With denser
populations and larger areas, the emptying
of vaults is a more serious matter, requir-
ing the greatest care to prevent nuisances,
and often, if not generally, entailing ex-
pense upon the householder. Cesspools
are unmitigated nuisances, and however
well built or frequently emptied, the satis-
factory disposal of their contents is practi-
cally impossible. The matter has com-
paratively little value as a fertilizer and
dumping upon unoccupied land is met with
increasing protests, even if the land is
located in remote and sparsely settled
towns.
THE VALUE OF A SEWERAGE SYSTEM.
To express the value of a good sewerage
system in lives or dollars saved is simply
impossible. Other sanitary improvements
precede, accompany and follow this, each
13
adding to the healthfullness of the com-
munity. The decrease in the death rate
for a term of years can be given, but no
man can express in percentages the part
played by each factor. We know that
pure air, pure water, and a pure soil are
essential to good health and long life.
Among the greatest polluters of air and
soil, and by all odds the greatest enemy to
pure water, is the contaminating matter
from privies, cesspools and improper sys-
tems of sewerage and sewage disposal.
These are such truisms that to expand
upon them in these days of progress seems
almost absurd.
Only one illustration will be attempted.
More than 35,000 deaths a year are caused
by typhoid fever in the United States.
Keep from the lips of our people all water
containing germs from the excreta of ty-
phoid patients, and milk diluted with
such water, or contaminated with it
through washing milk cans and bottles
in it, and the disease would soon be prac-
tically wiped out. This can be effected
only by providing every one with a pure
14
water supply, which, with other much de-
sired ends, would be greatly advanced by
the provision of properly designed sewer-
age and sewage disposal systems for both
town and country.*
GOOD ENGINEERING ADVICE ESSENTIAL.
Simple and convincing as the arguments
for efficient sewerage systems seem, years
of agitation are often necessary to awaken
sufficient interest in the subject to secure
their introduction. One cause of this is
the failure to present to the people a well-
considered scheme, capable of beingunder-
stood in its broad outlines by the average
citizen and in all but its most technical
details by any live business or professional
man. How rarely this is done until years
have been spent in well nigh useless effort,
money as well as time often being wasted
* For the salutary effect upon the general health of
individuals, and especially of women, conferred by the
abolition of outside privies, more or less exposed to the
public view, cold in winter, insufferably hot and odorous
in summtr, impossible of access without getting wet dur-
ing rains or snows, see Waring's " How to Drain a
House," Second Edition. This book discusses other bene-
fits to health and otherwise, conferred by a proper system
of disposal for household wastes of the kind under discussion
here.
15
in this way. Good engineering advice is
needed from the very start in this or any
similar enterprise. Otherwise a chaotic
mass of opinions as to what should be
done speedily develops, factions spring up
and even political parties take sides on the
questions involved.
PRELIMINARY REPORTS AND PLANS.
Such preliminary studies as are required
need not be very expensive, but they are
essential to a proper understanding of the
subject. Among the data which should be
determined as early as possible are: (1)
The area to be served, with its topography
and the general character of the soil. (2)
Whether the separate or combined system
of sewerage, or a compromise between
these two, is to be adopted. (3) Whether
subsoil drainage shall be attempted. (4)
The best of the available means of final
disposal of the sewage, often the most
difficult of the problems involved where
purification is necessary. (5) Population,
water consumption and volume of sewage
for which provision must be made, together
16
with rainfall data, if surface drainage is to
be installed. (6) Extent and cost of the
proposed system. (7) Method of meeting
the cost of the sewerage system. (8) The
needs for sewerage peculiar to the locality,
with a study of the health and mortality
of the town.
These are the main points involved in
sewering and draining a town. It may
serve either as a mere outline, or the de-
tails suggested by the various heads may
be so worked out as to form a complete
design for the system.
There is nothing like public confidence,
and the quickest way to unsettle a com-
munity and to delay the introduction of
public improvements, is to lay before the
people a number of conflicting plans. A
well-considered preliminary study is likely
to at once commend itself to citizens and
taxpayers, and if months or even years go
by without further action it continues to
be a rock upon which to build in the future.
Succeeding engineers can but commend
what has been so well put in the past, if
they be possessed of sense and ability, and
17
the popular conception of what should be
done is strengthened with each endorse-
ment of previous recommendations.
The above being true, great care should
be taken on the part of local authorities to
select the right man for the preliminary
studies, and the fortunate engineer should
exercise even greater care in fulfilling the
trust confided in him. The same holds
good regarding final plans and actual
construction.
Generally speaking, the smaller the com-
munity or the amount of money available,
the greater the need for the best obtain-
able advice, although of course the less
intricate the problem the cheaper its solu-
tion, even by the most talented expert. It
is only a false economy that dispenses
with engineering services, or employs the
cheapest, because money is to be had only
in small quantities. Experience is an ex-
pensive teacher, and the community that
realizes this at the start will pay the engi-
neer and secure the benefit of his training
in the school of well-directed experience,
instead of taking a more expensive course
18
of its own in the school of headstrong,
blundering, haphazard experience, which
so many municipalities have entered.
Let us now suppose that a village, town,
or city has so far decided in favor of a
sewerage system as to be ready to have
preliminary studies made. We will also
suppose that it has decided to have these
studies of a comprehensive character. The
authorities hesitate somewhat between em-
ploying a local engineer of good general
standing in his profession, and with some
experience in sewerage construction, and
an engineer of national reputation in this
line of work. Wishing the best they
half decide to engage the latter, but in-
quiry develops the fact that his charges
are high, although none too high con-
sidering his experience and knowledge,
that he must be paid for time spent in
travelling, and that a comparatively large
amount of ordinary surveying and simple
compilation of facts and figures must be
made, requiring a number of days from a
principal arid assistants. Both the local
man and the expert are finally engaged,
19
the latter to act principally in an advisory
eapaeity throughout the study.
Referring to the above outline for the
preliminary study, it will be seen that the
local engineer will make the surveys, collect
the information regarding population,
water consumption and rainfall and other
merely local data upon which the design
for a sewerage system will depend. This
he will submit to the expert for use in
preparing the report of the latter. It is
not necessary to separate any further the
work of the two engineers. The evolution
of the report and recommendations may
therefore be considered as the work of one
engineer from start to finish. Indeed it is
likely to be so to a very large extent in prac-
tice, the division of labor generally being
carried far to one extreme or the other:
That is, either the expert is called in to
amend and approve the results of complete
studies by an engineer with less experience
than himself, or he employs his own as-
sistants, local engineers or otherwise, to
do the bulk of the routine work involved.
20
The various parts of the study in their
order may now be taken up, as follows:
(1) The area to be served, with its topog-
raphy and the general character of the soil.
A contour map of the whole municipality,
showing the location of the several streets,
streams, ponds, or lakes and contour lines
for say each 5 ft. of change in elevation
is essential to the best results and must be
provided sooner or later if a sewerage
system is to be carried out on intelligent
lines. Such a map will be of service for
other purposes and would be a good invest-
ment for any municipality.
The general character of the soil can
usually be ascertained without much diffi-
culty by more or less casual observation,
and by inquiring among residents, build-
ers and others who have dug wells and
cellars, or observed the same while being
dug. The kind of soil is important as
affecting the cost of trenching, and its
natural wetness or drynoss, together with
the ground water level, will be a further
indication of the difficulties likely to be
met in construction, and of the necessity
21
or desirability of providing underdrains
for removing ground water or lowering its
level, which is further considered below.
(2) Whether the separate or combined
system of sewerage, or a compromise be-
tween these two, is to be adopted.
Obviously, these points depend almost
wholly upon local conditions, including
financial as well as natural factors. The
size and cost of combined sewers is truly
enormous as compared with those on the
separate plan, since the surface drainage
in times of heavy rainfall is many times
as great as the flow of sanitary sewage.
In the older towns and cities it is some-
times the case that drains designed to re-
move only surface water were con-
structed long ago, before modern plumb-
ing methods were introduced. Such drains
were loosely built, may have been poor in
grade from the start and were never de-
signed to receive sewage. To-day, how-
ever, they are serving as sewers and giv-
ing much trouble and offense through
stoppages and stagnation. Besides this,
they are polluting the soil by means of
numerous leaks. In designing a compre-
hensive sewerage system for such a city, it
sometimes happens that these old drains
can be relegated to their original purposes
and sanitary sewers introduced to care for
house wastes alone.
Where a town or city is entirely or prac-
tically without either sewers or drains, it
often happens that it may consider itself
fortunate if it can put in sanitary sewers
on the strictly separate plan, leaving sur-
face drainage for future generations, it
may be. Here financial limitations govern,
and this has been the experience of many
American municipalities now possessed
of first-class sanitary sewers.
Many a town is so situated that street
gutters and natural water courses alone
make ample provision for surface drainage.
Again, the street gutters may be insuffi-
cient, through various causes, and storm
drains thus be necessary, but there may be
numerous natural outlets for these at fre-
quent intervals, thus requiring only short
lines and thus comparatively small storm
drains. At the same time the only suita-
23
ble outlet for sewage may be at a point
remote from the city, thus necessitating a
long, large and costly outlet sewer, if the
combined system were to be employed, as
against a comparatively small and inex-
pensive outlet for sewage alone.
But strongest of all is the case for the
separate system when the sewage must be
purified. It is simply out of the question
for any city to build works large enough
to treat the full flow of a combined system
at times of maximum rainfall. Some of
the sewage must pass away entirely un-
treated, or very inadequately purified.
Generally speaking, each added drop of
water is so much more burden, for while it
is true that the sewage is thereby diluted,
it is also true that the capacity of the works
is taxed so much the more.
If crops are being raised, or even simple
intermittent filtration is in vogue, periods
of heavy rainfall are just the times when
a smaller rather than a larger volume of
sewage ig desired, while at chemical precipi-
tation works heavy increases in the sewage
flow are always unwelcome. The volume
to be treated is one of the greatest factors
in sewage purification, and the original
size of .a plant, and largely its cost, vary
directly with the volume, while cost of
operation is far more largely dependent
upon volume than strength of sewage.
The essential point is, that the combined
system means great extremes and sudden
fluctuations of flow, and whatever the
character of the industry such conditions
are consistent neither with economy nor
the best results.
Sometimes more or less limited areas of
a town may require the combined system
through lack of facilities for near-by dis-
posal of surface water, and again roof
water alone may need to be taken into the
sewers. As stated above, local conditions
and relative costs are the governing fac-
tors in deciding between the separate and
combined systems.
An old fallacy concerning the combined
system may be mentioned, although it has
now well nigh disappeared: It is that the
storm water will flush the sewers. Regard-
ing this it must be remembered that the
25
sewage flow is continuous and likewise the
dangers of and from stoppages, while rain-
falls are uncertain in frequency and
amount. As a matter of fact special pains
are now taken by the best engineers to give
combined sewers such a section that the
dry weather flow will be in a small chan-
nel as much as possible like that which
might be employed for sanitary sewers.*
(3) Whether subsoil drainage shall be
attempted.
As for providing underdrains for remov-
ing ground water, this will also in most
cases depend upon local conditions. It is
always an advantage to lower the ground
water level in places where it is high enough
to render the ground wet at or near the sur-
face through a large part of the year. As
sewers are generally placed below the level
of cellar bottoms and underdrains are most
commonly put below or at least not higher
than the sewers, it follows that when of
ample size underdrains will lower the
loiv i-;
i-xtended discussions 01' the combined and separate
systems may be found in Waring s "Sewerage and L :nd
Dra.nage," Staley & Pierson's " Separate System of Sewer-
age," and the many reports of engineers on proposed sew-
erage systems.
ground water level to a considerable depth
below the surface and render house foun-
dations practically dry. It may be neces-
sary to supplement the street underdrains
by branches running to the houses, and
even extending through large lots.
The advantage of rendering dry the soil
beneath and around habitations need nut
be enlarged upon here, as it is so generally
well known. But it may not be known to
all that underdrains are often such great
aids to good sewer construction as to war-
rant their introduction for the benefits
caused during construction alone. This is
the case where the trenches are so wet as
to render the making and setting of cement
joints difficult. By putting in underdrains
iii advance of the sewer proper the trench
may be kept dry and the work greatly
facilitated, even where temporary pumps
must be provided to remove the water col-
lected.
Where it is desirable for any reason to
keep down the sewage flow to the lowest
possible point, underdraius are also of
value without regard to sanitary condi-
27
tions. This may be the case where the
sewage is to be purified, or simply to be
pumped, or where several municipalities
use a joint outlet sewer, each contributing
towards the maintenance of the outlet in
proportion to the amount of sewage from
its individual system. The latter condi-
tions are found in a joint outlet in New
Jersey, where Orange, Bloomfield and
Montclair use the same trunk sewer to
the Passaic River, and have as the only
basis of dividing the cost of maintenance
the amount of sewage contributed by each.
Of course the aim in good sewer work is
to reduce the infiltration of ground water
to a minimum, but all engineers and con-
tractors know that in very wet soils tight
joints can be made only with difficulty and
practically never with absolute certainty.
The volume of flow in the outlet of the
sanitary sewers at East Orange, N. J., was
at one time fully half ground water, ac-
cording to careful estimates, and that was
after the sewerage system was well estab-
lished.
It must be remembered that with the
28
2-ft. lengths of vitrified sewer pipe now
almost universally used, there are 2,640
joints to the mile. These joints are made
of cement, and are not for a moment com-
parable with the joints of molten lead, with
their subsequent heavy calking, used in
water main construction.
In view of the above it is evident that
underdrains should be used where they
may be expected to benefit the health of a
community by lowering the ground water
level; where they will be sufficient aids to
sewer construction to warrant their intro-
duction for this purpose, to which is also to
be added their permanent benefit; and
finally, where it is desirable to employ them
to prevent an increase through infiltration
of the volume carried by the sewage, in
which case the benefit to health will also
accrue.
(4) The best of the available means for
the final disposal of the sewage.
Until recently this part of the problem, at
least in America, meant only into which of
the near-by streams or lakes or at what
point in tide water could the crude sewage
be discharged at the least cost and with the
minimum of offence. Too often the matter
of offence was given only scant consider-
ation, and sometimes none at all. Un-
fortunately many cities are to-day facing
the problem in the same manner, but the
advance of modern sanitation is rendering
this more and more imposible.
The cardinal principle in the ultimate
disposal of sewage is that no public water
supply should be endangered thereby.
Strange to say, this must be interpreted as
meaning that no city should endanger the
water supply of either itself or its neighbors.
This is almost inconceivable, for while one
can imagine a city mean or ignorant enough
to endanger the lives of the citizens of an
adjoining community, it seems incredible
that any municipality should be sufficiently
reckless to poison its water supply with its
own excreta. But both conditions exist and
must be combated. This deplorable state
of affairs may be explained in part by the
general ignorance of sanitary matters
which has prevailed until of late, and in
fact is seen still to exist when one com-
pares what is with what should l»e. It
does seem, though, that common sense and
common decency combined ought to be
sufficient to prevent a city from drinking
its own sewage or forcing it down the
throats of others.
Coming back to the cardinal principle
expressed above3 it may be asked "what
constitutes the endangering of a public
water supply?" No very definite answer
can be given at present, owing to our lack
of knowledge regarding the exact length
of time which disease germs from the
human system will live in water. The
Massachusetts legislature some time ago
said that no excreta should be discharged
into a stream within 20 miles of any
point where it is used for a public water
supply, but in the matter of new water
and sewerage construction it has practi-
cally placed the subject in the hands of
its State Board of Health. There are no
data to-day which will warrant an engin-
eer in saying that disease germs may not
be conveyed more than 20 in;les by the
waters of a stream and afterwards cause
31
sickness and perhaps death. The engineer
and sanitarian will consider the distance
which must be traversed by the sewage
and the dilution which it would receive
before reaching a public water supply, to-
gether with the minimum length of time
which would elapse before a disease germ
could pass from one human system to
another, a most important point. Unless
distance, dilution, and time are great, sew-
age should be purified or carried elsewhere
for disposal.
Of course there may be cases where
sewage disposal seems to claim preference
to water supply, in the use of a stream.
Each of these must be adjusted on its own
merits. The willful pollution of public
water supplies, even, if it seems remote,
should no longer be tolerated, and where
new sewerage systems are being built, it
is unnecessary that it should be.
Given a body of Avater, not used, nor
likely to be employee! for a public water
supply, the case is far different. Knowing
the amount of water and the probable
quantity and character of the sewage, it is
generally ea»y to determine whether all
the crude sewage of the city can safely be
discharged into the water in question.
Averages are of no use here. The water
available during a hot dry summer, when
the stream, pond or lake is at its lowest,
and banks and beds are exposed to the
sun, is what must be considered.
Partial purification may be sufficient
through a few months or all of the year
for some cities, and works have been car-
ried out on that basis. But most plants
in this country have been built under con-
ditions that demand continuous operation
at their utmost efficiency.
Where sewage is discharged into large
bodies of water, either lakes or the ocean,
it is generally necessary to make a careful
study of the prevailing currents in order
to determine the most available point or
points of discharge in order to prevent the
sewage becoming stagnant in bays or the
washing ashore of its lighter portions.
Such studies are commonly made by floats,
as direction of current is generally the
factor of prime importance.
33
When it is decided that purification
must be employed, it becomes necessary
to select the method best suited to local
needs and conditions. This matter can
better be discussed after the subject of
purification has been taken up in detail,
further on, and so will be dropped for the
present.
In concluding this phase of the subject,
or postponing its further consideration, it
may be said that until new advances have
been made in the recovery of fertilizing
matter from sewage, no compunction need
be felt in discharging such into any body
of water which can receive it without
harm. Where such water is available it is
often a mere question of the relative cost
of an outfall to it and a shorter outfall
with purification works to a nearer point
of discharge where purification is neces-
sary. Of course treatment of the sewage
is sometimes the only course which has a
shadow of practicability. Again all con-
sideration of such a procedure is often
rendered unnecessary by an especially
available point for the discharge of un-
34
purified sewage. Where there is uncer-
tainty it is best to keep on the safe side and
provide purification at the start. Uncer-
tainty to-day in these matters means
certainty in favor of purification to-mor-
row, so fast are we advancing in sanitation
and so rapid is the increase of population
and also of the pollution of our streams.
(5) Population, water consumption, and
volume of sewage for which provision
should be made, together with rainfall
data if surface drainage is to be installed-
The basis for population studies will gen-
erally be the United States census for a
number of decades past, with figures for
as many intermediate years as possible
filled in from State and local numerations.
From these figures percentages of growth
for decades or shorter intervals may be
computed and population curves plotted,
and from one or both of these, coupled
with present local conditions and future
prospects, the population for the next
30 to 50 years may be forecast by decades
or half decades. In small and rapidly
35
growing communities it must be remem-
bered that the percentage of increase is
generally less as the population becomes
greater.
It is desirable to design a sewerage
system large enough to serve for a number
of years to come, say 30, though parts of
the work need not be made so large, as
pumping or purification works where either
or both of these are necessary.
It is rarely the case that the whole popu-
lation of smaller communities is connected
with the sewers until years have elapsed
after the construction of a system. This is
due to lack of sewers on some streets and
to that strange perversity of human nature
which leads many people to put off the
making of sewer connections as long as
possible, notwithstanding the fact that the
soil of their premises is daily becoming
more and more polluted with excrementi-
tious matter, and that the yearly expense
of properly cleaning privies and cesspools
is greater than the interest on the invest-
ment necessary for making sewer connec-
3G
tions. In some communities allowances
for these delays may be made in designing
pumping or purification works, but the
pipe system should be large enough at the
start to serve each street and district for
an indefinitely long period. The advan-
tages of the use of city sewers are so great
that all property is bound to be connected
with them sooner or later, leased property
without these conveniences soon dropping
in market value. In view of these facts
the population figures are sometimes based
on an estimatad number of people per acre,
or per lineal foot of sewer, more especially
where a separate system of sanitary sewers
is being constructed. Safe figures of the
latter class cannot be laid down for gen-
eral application, but must be decided on
after a careful study of the community in
question, the character of its residence
property and general population. Often it
is necessary to divide a city into districts
for its population and rate of flow studies.
Thus the residence sections occupied by the
wealthiest classes will be comprised of a
37
comparatively small population per acre,
duo to the large size of the lots. The
population will grow more dense in the
passage through the sections occupied by
the less wealthy, the well-to-do and finally
the tenement sections. The portions of a
city devoted to manufacturing will in some
cities contribute sewage and manufacturing
wastes in pretty close proportion to the
number of employers, while in others, or
in different lines of industry, the sewage
yield will vary more especially with the
character of the goods being produced.
The total water consumption is of course
mainly dependent upon the population,
and these two factors together enter large-
ly into the amount of sewage requiring re-
moval and disposal. No fixed rule can be
laid down for water consumption, except
that in general it is on the increase in all
American cities, and in many places has
reached immense and sometimes alarming
proportions. It may be kept down by prop-
er inspection and the use of meters for
the prevention of waste, as it is absolute
38
waste and not beneficial use which is re-
sponsible for high water consumption.
The instances are rare where it is safe to
allow for less than 60 gallons per capita
per day as the average water consumption
of a town, if most of the people patronize
the public water supply. If a general rule
were to be laid down 100 gallons would be
a safer figure. Obviously not all the water
which passes through a water- works system
reaches the sewers. In summer much of it
is employed for lawn and street sprinkling
and similar purposes, very little of which
reaches the sewers even where the com-
bined system is in use, and practically
none where a separate system of sanitary
sewers is employed. But while all this
tends to diminish the sewage yield the in-
filtration of ground water, already dis-
cussed, increases it, and average daily fig-
ures have been discussed above, while
works must be built on the basis of maxi-
mum daily, or even hourly, yields. Alto-
gether, then, 100 gallons per capita will be
none too large except in particular cases or
possibly for the immediate present, where
39
a portion of the works can be built for
future enlargement.*
The total daily flow of sewage is not
distributed evenly through the 24 hours.
The actual percentages at different hours
of the day vary widely, according to the
nature and occupations of the contributory
populations. In most towns there should
be scarcely any sewage, if the sewers are
tight enough to prevent infiltration, be-
tween say 10 P. M. and 4 to 6 A. M., a
period of from six to eight hours. As a
matter of fact few sewerage systems exist
where the flow during these hours is not
considerable. From two-thirds to three-
fourths of the daily flow generally occurs
during from — say nine to twelve hours of
the day, the particular hours varying some-
what in different communities and having
little or no significance in designing the
smaller portions of most pipe systems, but
affecting the outlets and being of great
* For an extended study of vater consumption, with
figures for a large number of American municipalities
and with much other data on tlie relation of this sub-
ject and of population to amount of sewage, see Rafter
& Baker's "Sewage Disposal in the United States."
40
importance where the sewage must be
lifted or treated before its final discharge.
Moreover, there are generally from one to
three hours in the day when the flow is
considerably above the average for the
heaviest ten hours. The actual amount of
sewage for these hours must be taken into
consideration in the separate system and
the plant designed accordingly. For ordi-
nary laterals, these fluctuations need not
be taken into account, for in the best prac-
tice these are generally more than ample
for their duty. As the sewers increase in
size and territory served, and as disposal
works are reached, the flow during max-
imum hours becomes of more importance.
Roughly speaking, 10 per cent, of the
total daily flow in one hour may be con-
sidered a perfectly safe limit.*
When the sewers are being proportioned
for their respective streets and districts,
density of population must be considered.
It is generally necessary to arrive at this
* Staley & Pierson, in the " Separate System of Sew-
erage," givtt ihu maximum hourly flow as twice the
mean hotirly flow, which would be about 8 3 per cent,
of the total daily flow.
41
in an arbitrary way, as actual figures, ex-
cept for the whole town, are seldom avail-
able except in communities long since
sewered, or that may be considered as
having reached their full growth. The
proper figures must be reached for each
community separately, so no attempt will
be made to give them here.
Rainfall data are liable to be very scarce
in all but the larger cities and towns, and
at points where the national and state
weather bureaus have stations or ob-
servers. Such defects in the records as ex-
ist through lack of observations, simply,
cannot be remedied, but it sometimes hap-
pens that figures for near-by towns will do
very well. But even when records are
available they may not be sufficiently de-
tailed for the purposes under discussion.
Monthly or weekly totals are of scarcely
any use, and even daily records do not
completely meet the necessities of the
case. What is desired where storm sewers
are to be provided is the duration and rate
of precipitation of the heaviest rains. A
very heavy shower of 15 minutes may
42
cause more inconvenience and damage, if
the sewers are inadequate, than a steady
rain extending over a day or two. There
is, of course, a limit to the size of sewers*
imposed by financial, and in some cases by
physical conditions. Oftentimes, where
sharp, heavy rainfalls occur, their complete
speedy removal is impossible, and the sur-
face water simply must be allowed to
stand for awhile. Sewers may generally
be so designed that they will speedily re
move the total rainfall except at long in
tervals when an unusual precipitation oc^
curs.
After a careful study of all the rainfall
records available and a consideration of
the slope and character of tha drainage
area, especially whether closely built up,
with paved streets, many roofs, small areas
in forest and under cultivation, or the
contrary, the rate of rainfall per hour
which shall furnish the basis of calcula-
tions may readily be decided upon by any
competent engineer. A maximum rate of
1 in. per hour may be considered as a
liberal figure in some localities. The pro-
43
portion of this which will reach the sewers
during a given time will depend upon such
local factors as slope of land, whether
its surface is covered with houses and
paved streets, cultivated fields, or forests,
and the permeability of such soil as is
exposed.
(6) Extent and cost of the proposed
system.
This is a matter largely dependent
upon the local treasury, or the willing-
ness of the people to incur indebtedness,
levy general taxes, or pay special assess-
ments for benefits, as the case may be.
The ideal plan is to afford every build-
ing in the community an opportunity to
connect with the sewerage system. This
cannot often be done at the start, and in
most instances sparsely settled outlying
districts must wait long and weary years
before the sewers reach them, although
their taxpayers may be called upon year
after year to pay taxes to redeem i,he
bonds, meet interest, maintenance and re-
pairs. The oldest and most thickly settled
portions of the community naturally will
44
be sewered first, after which the system
should be carried as far out in various
Directions as the funds available will per-
mit. The exact course followed will de-
pend largely upon the legislative authority
conferred upon a given municipality to
raise money for sewerage construction.
Practice in the several States, and often in
the various cities and towns of one State,
varies widely in these particulars. Some-
times the city authorities have full power
to lay out as complete a system as they
deem best, either issuing bonds for its con-
struction or levying assessments for bene-
fits upon abutting property owners for a
part or the whole of the work. Again,
there is authority only for the construction
of trunk sewers and other works for final
disposal, the building of laterals depend-
ing entirely upon the initiative of property
owners. All the local conditions, legal
and otherwise, must be ascertained before
the extent of the system can be settled.
All work should be planned and carried
out with the future in view and should be
complete and adequate in itself and in re-
45
lation to other parts of the system, so that
reconstruction will not be necessary for
years to come, if ever.
It appears from the above, and from a
simple common-sense view of the subject
without regard to what has been written,
that the extent of the system will be
governed very largely by the local pocket-
book and existing statutes, and that it
should be made to suit the most pressing
needs of the community and be capable of
easy extension as soon as possible.
The cost of the system will be a matter
for estimate in each case. Most sewer work,
especially for sanitary sewers, is so simple,
and there is now so much of it being esti-
mated upon and carried out by engineers
and contractors, that it is comparatively
easy to figure up the approximate cost of
a sewerage system. Local prices of labor
and freight rates on sewer pipe, cement and
brick, where the latter is used, are the
main factors, and must be decided upon
by each engineer in making up his cost
estimates. The technical papers now pub-
lish exhaustive detailed lists of bids for
46
sewer work all over the country, and
the reports of city engineers, superintend-
ents of sewers, sewerage committees and
boards of public works often abound in
figures or quantities and cost of work
actually done.
(7) Method of meeting the cost of the
system.
As stated above, this is often laid
down by law, so that there is little
choice to be had, except in the details.
But ample latitude is sometimes left and
generally the details of carrying out even
fairly definite laws afford a chance for a
considerable amount of variation, together
with much study.
Broadly speaking there are two methods
of raising money to defray the cost of a
sewerage system : (1) By making the work
a charge upon the whole municipality,
raising the money by taxation or a bond
isssue; and (2) assessing the cost upon the
property specially benefited. A combina-
tion of these plans is very common. The
first one is sometimes put into effect and
the second with comparative infrequency,
47
except for single streets or drainage dis-
tricts of a city with independent outlets.
The trouble with the second plan is that it
is not easy to determine the proportionate
amount of benefit which each property
owner receives, unless it be in the most
simple cises.
The cost of constructing and operating
a water- works system is met by the yearly
rentals charged for water furnished the
users of the same, but the general aim in
the case of sewers is to make their use as
popular as possible. Therefore, the most
common practice in this country has been
to charge nothing for using the sewer. An
entrance fee, sometimes designed to repay
the city the cost of supervising the work,
and sometimes intended to help pay for or
maintain the system, is often charged for
connecting with the sewers and paid once
for all.
The actual cost of house connections is
always, so far as the writer knows, borne
by the house owner.
Where the general public and the prop-
erty especially benefited, that is, actually
48
or potentially served by the system as con-
structed, share the cost, it is divided in
various proportions, seemingly without
rhyme or reason, in many instances. It
may be the city or it may be the property
benefited that pays all the way from one
to three-fourths of the cost, or perhaps
through a wider range. With the separate
system of sanitary sewers a popular plan
and an apparently fair one, where the
cost is simply to be divided as stated
just above, is to assess upon abutting
property the cost of the smallest-sized
lateral sewer, or in other words of a
sewer just large enough to serve the
houses on one street of moderate length.
The further cost of the system or ex-
tensions, would then be raised in the
general tax levy or by a sale of bonds.
The assessments for benefits are levied
upon the frontage bordering on the streets
in which the sewers are laid, or upon the
area of th'e lots, or are divided between
these methods. The whole subject under
discussion is a complicated one and has
49
never received the consideration it deserves
from municipal officers.*
But to one such an official, great credit
should be given for having made a very
exhaustive investigation of the problem
and presented a solution which aims to be
fair, conducive to the rapid extension and
use of his particular sewerage system, and
in many points admirably adapted to other
localities. This study was made by Mr.
F. H. Snow, City Engineer of Brockton,
Mass., and the plan recommended was
adopted by that city. A summary of Mr.
Snow's report is given below, the import-
ance of the subject, the lack of both popu-
lar and technical information regarding it,
and the value of the report itself, seeming
to warrant the devotion of a few pages to
this purpose. f
The population of Brockton is about
30,000. The sewerage system includes a
* A monograph, entitled "Special Assessments," by
Victor Kosewater. (Columbia College Studies in History,
Economics and Public Law) will be of interest and value
to those who wish to pursue the general subject further.
t This summary is condensed from an editorial digest
and discussion by the writer which appeared in " Engin-
eering iVeutt" of Ju y 19, 1894.
50
receiving reservoir, pumping station, force
main and filter beds. The first cost of the
system, so far as constructed, was raised
by an issue of bonds. The summary is as
follows :
In arriving at the proper plan for Brockton, Mr.
Snow studied with great care the various methods
of assessments already in use, after first having
shown that the benefits of a sewerage system were
partly public and partly private, and should be
borne accordingly. Public benefits are, of course,
to be met by general taxation. The proportion to
be paid by the public has been fixed by the Massa-
chusetts legislature at not less than one-fourth nor
more than two-thirds of the total cost of the sewer-
age system. For private benefits a variety of
methods are permitted by the statutes, such as
frontage and area assessments, yearly rentals,
entrance fees, or a combination of these.
******
Either the frontage or the area plan alone is
shown by Mr. Snow to be inequitable, diagrams
being used to illustrate how by either plan differ-
ences in the shape of lots may allow several houses
on one lot and only one or two on another, each
lot having the same area or frontage, as the case
may be. The entrance fee is also shown to be
unjust, unless it is graded in accordance with bene-
fits received, while, • in addition, a large fee would
51
be required at the start, when there were but few
connections, or else reliance on the general tax
levy would be necessary .
The method finally recommended by Mr. Snow
is given in his report as follows :
It is recommended that one-fourth of the total
cost of the sewerage system be raised by first
assessment, one-half by rental, and the remainder
by general tax. It is also recommended that first
assessmant be based on area and frontage of land
adjacent to sewers — 0.6 on area within 125 ft. of
the street line and 0 4 on frontage ; that the first
assessment be collected in one payment and
credited to construction account ; that the unit of
rental be 1,000 gallons of water reaching the
sewer, this to be ascertained from meter gagings
of the water department, and to be corrected for
water finding another outlet than the sewer by a
system of discounts ; 70 per cent, to be deducted
from water supply of shops and 20 per cent, from
water supply of houses having sill-cocks.
And it is further recommended that abuttors be
not compelled to enter the sewer as soon as com-
pleted ; that no one be allowed to enter without a
permit ; that no rent be charged users before Jan-
uary 1, 189.5, rents starting from that date ; that
such rents be charged from the first of the month
following that in which the permit is dated ; and
that all deficiencies be made up in the early years
by general tax levy.
It is further recommended that the following
prices be assessed per unit : For first assessment,
0.3 cents per square foot, and 15 cents per front
foot; for rental, 28 cents per 1,000 gallons enter-
ing the sewer ; and that $8.40 be charged for un-
metered connections, subject to a discount of 20
per cent, for sill-cocks.
These first assessments represent the value of
the sewerage system to land, in enhancing its price
without regard to whether the sewers are used by
the owners of the land. The amount raised by
general taxation will likewise represent the benefit
to the community as a whole, without regard to
the locat'on of the sewers. Benefits from actual
use of the sewers are to be paid by rental, acsord-
ing to the amount of sewage contributed, and the
sums so raised will be applied to paying off the
bonds, meeting interest and to maintenance. The
rentals will pay two-thirds of the total yearly
charges, leaving the balance to be met by general
taxation.
It is eminently fitting that rental should be
based on the amount of sewage contributed, since
upon the latter depends the size of the sewers, and
notably the cost of constructing and operating the
pumping plant and filter beds. Fortunately at
Brockton G5 per cent, rf the water connections
are metered and the records of the water depart-
ment are well kept, so that the sewer rentals can
easily be based on the water consumption. Obvi-
ously on many premises some of the water used
does not find its way to the sewers, hence the pro-
posed deduction of 20 per cent, of the consump-
tion for houses having sill-cocks for hose and of
70 per cent for shops.
53
The unit of 28 cts. per 1,000 gallons of water
was arrived at by computing the probable yearly
expenses of the sewerage system until 1900 and the
probable water comsumption for the same period.
It should be stated that the water consumption in
Brockton is phenomenally low, only 25 gallons p( r
capita. The yearly rate of $8.40 for unmetered
houses was chosen because the minimum rates for
metered water are such as to make it an object to
water users to have a meter when the water con-
sumption goes above a point that would call for
such a rental.
Coming to the amount to be raised yearly in the
tax levy, the problem is simple, the amount being
the difference between the total amount to be
raised and that provided for as outlined above.
Although this system has been worked out to
meet the situation of Brockton, which is in a num-
ber of respects unique, the general principles
involved may be applicable in other places. The
special conditions at Brockton are as follows; (1)
No sewers are yet in use, although the city has a
population of about 30,000; this renders possible
the adoption of any desirable system without the
unfairness, real or fancied, which follows a change
in the case of old systems. (2) It is expected that
the whole city will be sewered in a comparatively
few years, so that the total cost of the system can
be readily estimated, which is essential to this
plan. (3) The large percentage of metered water
54
taps and the fact that the city owns the water-
works, so that water and sewer departments can
co-operate, while each desires to keep the water
consumption down, are favorable to a yearly
rental plan, based on water consumption. Modi-
fications of these conditions might make the
system difficult of application or might cause fric-
tion when applied. Nevertheless- the principles at
the bottom of it seem correct, and this general
distribution of the burden of a sewerage system,
whether in these or other proportions, seems fair
and likely to be popular. General public and
individual private benefit are each recognized and
the latter is divided into two classes, (1) potential
benefit through increased value of a certain piece
of property because the sewer passes by it and may
be used, and (2) the actual benefit through use.
Two dangers which beset the extremes of the
two methods most usually employed to raise
money for sewers seem likely to be counteracted
to a large extent by this plan: (l) When the
•whole cost is put in the general tax levy or is met by
bonds, the interest and principal of which must be
met by taxes, it is difficult to secure money for exten-
tensions, every taxpayer wishing to keep the rate
down, and those living on sewered streets having
no direct interest in extensions. In the Brockton
plan the t~x levy is increased by only one-fourth
the total cost of the sewers, the bulk of the ex-
penditure being put upon those whose land is
55
improved or those who, by use of the sewers, are
saved the expense of cleaning cesspools or privy
vaults. The taxpayer feels that the sewerage
system is, to large extent, self-sustaining, like a
municipal water-works plant. (2) The other
danger is that where property benefited bears the
whole expense of sewers it will, in case of assess-
ments for frontage or area, try to keep the sewer
out of the street. But in Brockton a given prop-
erty owner will be paying towards one-fourth the
cost of the system whether the sewers are in his
street or not, and once in his street he need pay
only an additional one-fourth for property benefit,
unless he wishes to connect with the sewer. The
sewer once in, however, he will already be paying
towards one-half of the total cost of the system and
the additional expense for the use of the sewer will
seem small. Moreover, by economy in the use of
water his rental may be kept low, and most
people do not consider themselves extravagant
water users.
(8) The needs of sewerage peculiar to
the locality^ with a study of the health and
mortality, of the town.
Little need be said on these phases of
the subject. The adoption of a scheme
and the raising of money for its realization
may be greatly aided by showing that
local conditions imperatively demand the
-56
improvement. A study of the health and
mortality of the town, and comparisons of
the results with like studies of communi-
ties enjoying good sewerage systems is
often helpful in enlisting popular enthu-
siasm for sanitary progress. But such
work must be done wisely and false state-
ments and impressions regarding the rela-
tion between unsanitary conditions and
disease avoided as one would shun poison.
There has been so much ranting of late re-
garding deadly disease germs lurking here,
there and everywhere that many persons
on reflecting that they and most of their
neighbors still live, grow suspicious and
feel inclined to discredit the germ theory
of disease and the advantage of cleanliness
in all the departments of life. It must be
remembered that just as there are thou-
sands of visible forms of plant life, of
which only a very small percentage are
poisonous, so among the many invisible
forms of plant life known as bacteria or
microbes there are only a few harmful
germs. These , few, it must be taught,
give rise to dire results when allowed
57
access to private water supplies, like house-
wells, through leaching privies and cess-
pools, or to public water supplies by dis-
charging crude sewage into streams or
lakes from which such supplies are drawn.
Furthermore, unsanitary conditions, while
not giving rise to certain forms of disease,
may render the human system unfit to ward
off attacks of the same. Facts like these,
reasonably presented, may sometimes do a
world of good in an engineer's report,
while the too common exaggerations would
disarm instead of assure the people.
ADOPTION OF THE ENGINEER'S REPORT.
The report of the engineer having been
completed and submitted to the proper
officials its adoption by them them may be
assumed. Sometimes the plan recom-
mended has to be submitted to a popular
vote, but more often where a vote is taken
it is only indirectly upon the specific plans
proposed, the real question being whether
bonds shall or shall not be issued for the
execution of the scheme. After the gene-
ral report is adopted the next step is to
58
select an engineer to prepare detailed
plans and specifications preparatory to
advertising for bids from contractors.
Frequently the engineer who made the
preliminary studies is engaged as design-
ing engineer and sometimes to supervise
construction as well. This course has
the advantage of continuing the services
of one more or less familiar with local
conditions, and with the plan for sewer-
ing the town already partially worked
out.
DESIGN AND CONSTRUCTION OF THE CON-
DUIT SYSTEM.
The first work of the engineer will be
to design his pipe or conduit system. For
this task the topographical map already
mentioned will be a help, but this should
be supplemented by a profiles of all the
streets in which sewers are to be laid, in
order that the proper grades may be deter-
mined and the accessories of the systems
designed.
Numerous diagrams and tables are avail-
able for use in designing conduit systems,
59
rendering separate computations with the
aid of complicated formulae altogether un-
necessary, unless the engineer wishes to
make his own figures.* In the separate sys-
tem it is generally best to use 8-in. pipe as
the minimum size, in order to lessen the
risk of stoppages, although 6 ins. is ample
for the volume of sanitary sewage from an
ordinary residence street of medium length.
Pipe sewers are generally made of vit-
rified clay, with a salt-glazed surface.
Cement pipe (cement and sand) is also
used 'in some cities. The size* of pipe
sewer was for many years limited to a
diameter of 24 ins. but some of the manu-
facturers now make pipe 36 ins. in diam-
eter for general use. The 24 in. limit was
in force because of the difficulty and ex-
pense of making the larger pipe and the
comparative ease of laying brick sewers of
any size from 24 ins. up. Monolithic sewers
* Mathematical dipcussions of sewer formulae are beyond
the bcope of this work. See Baumeister's "Cleaning and
Sewerage of Cities " for a brief but able presentation of the
subject, illustrated by diagrams, and Flynn's "Flow of
Water in Open Channels, Pipers Sewers, Conduits, etc.," for
tables. Staley & Piersou's ' ' Separate Systems of Sewerage "
may also be consulted. More recent books are " Ogden's
Sewer Design " and FolwelTs Sewerage."
60
have been used for a limited extent, the
conduits being built in place from cement
mortar.* In very wet ground cast iron
pipe with lead joints is used, either be-
cause it is specially desirable to prevent
infiltration or because of fear of damage
through settlements.
The pipe should be laid to grade with
great care, and a good alignment should
be secured. Holes should be dug for the
bells of the pipe so that each length of
the latter will have a solid bearing through-
out. When the material is such as to make
uncertain a solid support for the pipe, sand,
gravel, concrete, plank or piles should be
employed for the purpose. If rock is en-
countered in trenching, it will Le necessary
to provide a bed for the pipe which will
not be washed into fissures by the stream
of sub-soil water which is likely to follow
the eewer when the ground is saturated. At
Little Falls, N. Y., in the case of a vitri-
fied pipe line for a water supply conduit,
such a washing-out of material occurred,
* Concrete, both plain and reinlomd vith steel, has bt-en
coming into n*e since the lit »t ed.tion c f this book was \N rit-
uu (it>U5;, but u.ore puniculaily for large fcew<,is.
61
causing settlements and the pulling apart
of joints. The trench was opened through
the rock portion and the pipe embedded in
concrete.
SUBSOIL DRAINS, OR UNDERDRAINS.
Where sewers are in wet sand or gravel,
subsoil drains, or, as they are more usually
called, underdrains may be laid beneath or
alongside the sewer to advantage, as dis-
cussed above. These are generally simple
agricultural tiles from 3 ins. in diameter
upward. They have no joints, being
simply hollow cylinders, and are laid with
their ends a fraction of an inch apart,
wrapped with a cheap so-called muslin
cloth, or other suitable material to keep
out the dirt until the matter in the trench
becomes thoroughly packed about them.
These underdrains may almost always be
emptied into the nearest stream, provided
it is not used as a public water supply.
This qualification is on account of the fact
that the sewers may leak and sewage thus
flow directly into the underdrains. Such
danger may seem remote, but it was con-
62
sidered sufficient to cause the city of Bos-
ton to refuse to pay a promised sum toward
the cost of the" sewers of South Framing-
ham, Mass., so long as the sewer under-
drainge discharged into a stream tributary
to one of the sources of the Boston water
supply. Boston had agreed to make this
contribution in order to induce the town
of Framingham to remove -its sewage
from the Boston water works. This made
purification necessary, which in turn de-
manded that all the sewage should be
pumped to the- filter beds and irrigation
area. Naturally the town did not wish
to pump and purify the underdrainage, but
after some years of delay and an offer of
an additional sum from the city of Boston
the town constructed reservoirs and filter
beds for the purification of the underdrain-
age, all of which must be pumped a small
lift.
Perhaps one of the best examples of
subsoil drains beneath sanitary sewers, or
at least the best example which has been
described and illustrated in detail, is at
63
Newton, Mass., where drains were placed
below many miles of sewers.*
MANHOLES.
Manholes should be placed at all changes
of grade and at all junctions between two
or more street sewers. These are built of
brick and afford access to the sewer for
inspection. In addition they are some-
times used for flushing. They are pro-
vided with iron covers, the latter often
being pierced with holes to afford ventila-
tion to the sewers. When the covers are
so perforated pails are often suspended
beneath to catch the dirt from the street
surface, especially when the manholes are
in macadamized gravel or dirt streets.
On long stretches of straight sewers
lampholes are somtimes put in between
manholes, consisting generally of a vertical
piece of pipe extending from the sewer
nearly to the surface and provided with a
cover. These are valuable aids to in-
spection.
* See Engineering News, January 2, 1896, for illustrated
description of this system.
64
SEWER GRADES.
The grades of sewers should be sufficent,
where possible, to give them a self-cleans-
ing velocity, thus rendering stoppages from
ordinary suspended matters impossible.
Baumeister, in his " Cleaning and Sewer-
age of Cities," makes the following state-
ments on this subject:
Practical experiments show that sewers of the
usual sections will remain clean with the follow-
ing minimum grades: separate house connec-
tions, 2 per cent. ; extreme cases, 1 per cent.
Small street sewers, 1 per cent. ; extreme cases,
0.7 percent. Main sewers, 0.7 per cent. ; ex-
treme cases, 0.5 per cent. The extreme cases are
for sewers carrying only rain or quite pure water.
The following empirical formula will give the
minimum grade for a sewer of clear diameter
equal to d inches and either circular or oval in
section :
100
Minimum grade, in per cent ~r>_i_ro
FLUSHING DEVICES.
Where very low grades are unavoidable
and at the heads of branch sewers where
the volume of flow is small, flushing may
be used with advantage. In some cases a
65
copious supply of water is turned into the
sewer through a manhole from some
stream, pond or lake, or from the public
water works system. Generally, however,
the water introduced is allowed to accu-
mulate before discharge, being held back,
for instance, by plugging up the lower
side of a manhole until the water accumu-
lates in it, then suddenly withdrawing the
plug and releasing the water, upon which it
rushes down the sewer carrying before it
practically all obstructions, except in ex-
treme cases.
Instead of relying upon clear water, as
described above, it may l,e sufficient at
some points on the system to simply back
up the sewage by plugging the manhole
outlet, thus flushing the sewer with the
sewage itself.
The necessity of frequent and regular
flushing has given rise to automatic flush-
ing tanks. These generally make use of
the siphon for self-discharge, although
there is on the market a purely gravity
flush tank, which tips by its own weight
when full. Whatever the means of dis-
charge the feed to the tank is regulated by
a valve or cock on the supply pipe, so the
tank will fill and empty once in a given
number of hours.
Y-BKANCHES FOR HOUSE CONNECTIONS.
Provision for house connections should
be made when laying sewers, in order to
avoid as much as may be tearing up the
streets after the pipe system is in and the
breaking of holes into the sewer. It is a
wise plan to lay the house connections
from the street sewer to the curb, or even
across the sidewalk, while the street is dug
up. At the least Y-branches for house
connections should be put in at frequent
intervals, say from 25 ft. apart upwards,
according to the character of the street.
When the sewer is put down deep quarter
bends are sometimes provided and the
house connection pipe carried vertically
upwards until within a few feet of the sur-
face to avoid deep digging. However the
house connection may join the sewer, or
any two sewers join each other, the direc-
tion of flow in connection and street sewer
67
should be as nearly the same as possible,
and the entering sewer should be at a little
higher level than the sewer entered in
order to increase the velocity of the in-
fluent sewage and thus lessen the tendency
to retardation and stoppage which natu-
rally results where two confined streams
with matters in suspension unite.
DEPTH OF SEWERS BELOW SURFACE OF
GROUND.
No general rule can be laid down for the
depth of sewers further than that they
must be deep enough to :idmit of house
connections with a proper fall, and on the
other hand should be p.s near the surface
as possible to save the expense of deep
trenching. Of course they must be kept
below the point at which clanger from
freezing might arise, but the natural
depth is usually sufficient to make such a
consideration unnecessary, especially as the
temperature of sewage is generally a num-
ber of degrees above that of the atmos-
phere at the street surface.
68
VENTILATION OF SEWEKS.
The ventilation of sewers is a subject
still fraught with many fears and per-
plexities. In the early days of sewers the
conduits were faulty in the design of their
cross-sections, in their grades and in their
construction. Practically all of these con-
duits originally carried surface water, and
through infiltration large quantities of
ground water. Many of these conduits,
as stated at the beginning, were built to
carry storm water alone, in other words
were simply drains. With the advent of
ample public water supplies and modern
plumbing, which, with its many fixtures
providing hot and cold water at every
hand led to high water consumption,
houses were connected with the drains,
thus converting them into sewers. Still
later, the convenience of this practice being
recognized, conduits were designed and
built to carry both drainage and sewage,
but these sewers on what we now call the
combined system were little or no better
in design and construction than the old
69
surface drains. The consequence of all
this was that the uneven bottoms made
long stretches of sewer little or no better
than cesspools, and this cause, with poor
construction, gave rise to stoppages which
still further aggravated the stagnation.
Decomposition, without the presence of a
plentiful supply of oxygen, evolved offen-
sive gases, which sought the upper air
through all possible channels. Street in-
lets for surface water and manholes for
cleaning belched forth gases whose malo-
dorous presence was easily recognized. Too
often these odors were noticeable in houses.
To prevent such a state of affairs various
methods of sewer- ventilation were tried,
which it is unnecessary to describe here.
In modern work of good design sewers are
built with the intention of removing all
sewage immediately before offensive de-
composition has time to begin. The
grades are as nearly perfect as possible,
the interiors are reasonably smooth to
prevent adhesion of putrescible matter,
and the manholes have perforated covers
to aid in ventilation. In some cities ven-
70
tilating shafts are provided to supplement
the manholes, these sometimes being the
soil pipes of the houses, the main trap
being omitted for this purpose. The latter
practice is recommended by some of the
best engineers and sanitarians of the day,
the theory being that by such means well
constructed sewers are kept so filled with
fresh air, and so free from bad gases, that
no harm can arise if occasionally a trap to
some wash bowl or water closet fails and
the sewer air reaches a dwelling room.
But notwithstanding these opinions the
majority of sanitarians still object to ven-
tilating sewers through houses and insist
upon the main trap.
It seems obvious that in the separate
system of sewers, with its small laterals, a
4-in. ventilating pipe is not needed every
50 or 100 ft. on both sides of the street to
change the air in a 10, 8, or even, as is
sometimes the case, a G-in. street sewer.
The most common practice is to assess the
whole or a considerable portion of the
cost of; such small sewers upon abutting
property owners. Where this is done it
71
may be difficult to say to one man out of
perhaps five, "you must for the general
good omit the usual main trap from your
soil pipe in order that the street sewer
may be ventilated ; or if you object to
that you may run a separate ventilating
pipe from your house sewer at a point just
outside your main trap to the top of ,ypur
roof." Naturally, most men would object
to such an alternative, preferring not to
risk, as they might think, with ample
support from engineers and others sup-
posed to know, the lives of themselves
ana their families, nor to spend money to
avoid such a risk while four of their
neighbors were not called upon for either
risk or sacrifice. To be sure some means
might be devised to assess the cost of
these extra pipes upon the town at large,
where the people refused to allow the
ventilation through their soil pipes, but
this would give rise to some trouble, at
the best, so that the wisest course might
be to provide extra ventilation, if ex-
perience showed it necessary, entirely at
town expense, and independently «f dwell-
ings. The matter of ventilation is further
discussed at the end of the next section.
MISAPPREHENSIONS REGARDING SO-CALLED
SEWER GAS.
Before leaving this subject a few words
seem necessary regarding misapprehen-
sions on the question of so-called sewer gas
and the conveying of disease germs there-
by. And first, there is no specific and defin-
ite sewer gas for which a chemical formula
or combination of symbols can be laid
down. The air in sewers contains in greater
or less degree some of the gaseous products
of decomposition whenever chemical
changes are taking place in the organic
matter conveyed by or deposited in the
sewers. This air is harmful if breathed,
just the same as any other foul air, and to
no greater extent, except for the slight
possibility that it may contain harmful bac-
teria. The disease germs which may be
expected in sewage are essentially water-
borne instead of air-borne, and develop in
the human intestines rather than in the
73
throat, nose or lungs, and therefore gain
access to man chiefly tli rough food and
drink. The germs carried by so-called
sewer gas must obviously be air-borne and
from their origin are not likely to be found
in sewage, or if found they would be in
small quantities ; but while all this is true
it does not make sewer air any more de-
sirable for breathing. The evils to which
impure air give rise are invidious, attack-
ing the weak and undermining the phys-
ical system of both weak and strong, ren-
dering them more susceptible to various
forms of sickness, notably the zymotic or
filth diseases. Thus it is evident that no
matter how much the nature of the dan-
gers from this source may have been mis-
understood in the past they are sufficiently
grave to demand all reasonable efforts to
ward them off. The first aim should be to
prevent, as far as possible, the formation of
foul air within the sewers, and the second
to keep such air as may form away from
mankind. After good design and construc-
tion of the sewer conduits, as such, have
been secured ventilation should be called
74
upon for the introduction of a plentiful sup-
ply of fresh air and the removal of 'foul
air to points where it will be diffused
throughout the atmosphere without offense.
Stagnation of air within the sewers must
be avoided.
DR. BILLINGS' OPINIONS ON SEWER AIR
AND VENTILATION.
Before leaving this subject some quota-
tions may be introduced to advantage from
the exhaustive work entitled "Ventilation
and Heating," by. Dr. John S. Billings,
formerly Siirgeon^General U. S. A., and a
recognized sanitary authority. Among
other things Dr. Billing's says :
The air of an ordinary modern, fairly well con-
structed and ventilated sewer appears to differ
from the street air chiefly in having a higher pro-
portion of carbonic acid.
* * * 1C * *
Specific pathogenic micro-organisms have not
been found in the air of sewers * * * * As
regards house drains and soil pipes, the condition
cf the air in them depends greatly upon whether
they "are properly ventilated or not. So long as
75
the fixtures connected with them are in daily use
these pipes are lined with a moist slimy layer of
organic matter, in which bacteria of various kinds
grow in immense numbers. If the supply of air
is abundant, these bacteria are mostly aerobic and
the substances produced by their action are, as a
rule, odorless and are rapidly carried away, by the
next flush of liquid, if soluble.
******
In hospitals, before the introduction of antisep-
tic methods of treatment of wounds, the pyogenic
organisms were of course very numerous in the
hospital drains, and there are several cases in
which localized outbreaks of erysipelas and un-
healthy wound action appeared to be connected
with the passage of the house drain air into the
ward.
******
Distinguished English sanitarians believe that
typhoid fever has been spread through the gases
coming from foul sewers, but I know of no satis-
factory evidence of such an occurrence. Diph-
theria and typhoid fever are diseases which pre-
vail more extensively where there are no sewers
than in the sewered part of the cities, even where
the sewers are badly constructed.
While I do not attach much importance to sewer
air as a means of transmission of specific disease,
I believe that its continuous inhalation is dangerous,
owing to the large amount of volatile organic mat-
76
ter which it contains, and for that reason, as well
as to prevent the formation of explosive mixtures
and of unpleasant odors, continuous ventilation
should be provided for all sewers, house drains
and cesspools.
In well constructed sewers Dr. Billings
considers ventilation an easy matter, which
can generally be effected by frequent open-
ings to the outer air, and always at each
dead end of a sewer. Special tall ventilat-
ing shafts, or ventilation through factory
furnaces or chimneys he considers as of lit-
tle value, stating that the influence of such
shafts or chimneys extends only to the
nearest air inlet.
Ventilation through house soil pipes is
approved where the sewers and house con-
nections are properly designed, constructed
and operated, and all are under the con-
trol of the municipal engineer, provided
also the houses on a given street are nearly
uniform in height. Where opposite condi-
tions prevail, so that the air in the sewers
is bad, and the tops of the soil pipes of one
house would end under the windows of
another, the Doctor thinks that main traps
77
should be placed on all soil pipes and air
inlets and outlets be placed on the sewers
at intervals of 300 to 400 ft.
FEATURES PECULIAR TO THE COMBINED
SYSTEM.
Coming now to sewers of the combined
system their most notable differences
from separate sanitary sewers are their
greater size and the use of catch basins or
inlets for the admission of surface water.
They are generally of brick, stone, or con-
crete, or a combination of two or more of
these, instead of being chiefly of vitrified
pipe. Still another distinctive feature is
the provision of storm overflows, by means
of which the main sewers, when over-
charged at times of heavy rainfall, may
empty a part of their contents through a
short conduit into some water course. At
such times the sewage is diluted by the
rain-water, while the stream which re-
ceives the overflow is also of an unusually
large vplume. The relief thus afforded ren-
ders possible smaller conduits than could
78
otherwise be used without backing up sew-
age into houses or flooding streets and
cellars on the lower levels of the city.
SIZE, SHAPE AND MATERIAL OF COMBINED
SEWERS.
The actual size of the sewer of course
depends upon local conditions, as to a large
extent does its shape and material. Where
the depth of flow varies greatly it is de-
sirable to give the sewer a cross-section de-
signed to suit all flows as fully as possible.
Experience has shown this to be an approx-
imation to the cross-section of an egg plac-
ed upright on its smaller end. With this
section a maximum depth and velocity of
sewage is secured for a minimum flow,
rendering deposits and stoppages far less
liable. With sewers having a flow more
nearly constant and equal to their full cap-
acity the form may be modified to that of
an ellipse, a horse shoe with an arc of a
circle for an invert, or bottom, a circle,
or some modification or combina-
tion of these, according to circumstances.
For the larger sewers brick is by far the
most common material, both because of
its cheapness and of its adaptability to any
shape. Stone inverts are sometimes em-
ployed on heavy grades, notably where
much sand is carried in suspension, in or-
der to present a more lasting surface to the
scouring and wearing effect of gritty ma-
terial. Concrete is sometimes used for in-
verts, where leakage may be expected, or
in material liable to movement, but more
commonly it affords a foundation for the
brickwork. The concrete is also sometimes
extended up the sides of the sewer, and
sometimes completely around it.* If the
material is liable to much settlement, as in
marshes and bogs, the sewer may be con-
structed on a timber platform, the latter
sometimes being supported by piles, gener-
ally having at least a thin layer of concrete
between it and the invert.
It not infrequently occurs that sewers
must be constructed through rock. In com-
paratively rare cases this is sufficiently solid
to warrant the use of an unlined tunnel,
where grades are sufficient to permit a
* See foot note, i>age CO.
80
rough surface. But generally stones and
uneven walls left after blasting make lin-
ing necessary, which is commonly com-
posed of brick, with any spaces behind the
ring or rings filled with brick or stone
masonry, or concrete.
CATCH BASINS OB RAINWATER INLETS.
A catch basin is generally placed at each
street corner, with a grated opening, or
otherwise, giving the surface water access
to a chamber or basin beneath the sidewalk,
from which a pipe or other conduit leads to
the sewer. Catch basins may be provided
with water traps to prevent the sewer air
from reaching the street, but these traps
are liable to lose their seal through evapo-
ration in dry weather, unless they are re-
newed by manual labor from the public
water supply system. To prevent the
carrying of street washings into the sewers
catch basins should be provided with silt
chambers of considerable depth with over-
flow pipes leading to the sewers, and thus
lessen the bulk of the heavy suspended
matters in the silt chamber to be removed
81 "
by buckets and carted away at proper in-
tervals. In the case of long street blocks
catcli basins may be placed in the centers
of the blocks, as well as at street corners.
STOEM OVERFLOWS.
Storm overflows are simple in theory,
and often so in construction, the main
point being to ensure an overflow into
another conduit when the flow reaches a
certain elevation in the sewer. Where
main and intercepting sewers are at right
angles to each other the connection is
sometimes so made that the dry weather
flow drops into the intercepting sewer, but
the flood flow, with its greater volume and
velocity, shoots over the interceptor, in
part, and into and through the overflow
sewers. The lower portions of main sewers
formerly discharging at many points into
a stream or lake are sometimes utilized in
this manner when intercepting sewers are
added.
The junction of large sewers, and other
complications in combined sewerage sys-
tems, sometimes afford ample opportunity
82
for the engineer and contractor in design-
ing and building masonry suitable for such
places.
Sewers designed to remove surface drain^
age alone are practically the same as com-
bined sewers, without house connections,
and need no discussion here.
PUMPING STATIONS, RECEIVING RESER-
VOIRS AND FORCE MAINS.
A large percentage of the sewerage sys-
tems of the United States and Canada
operate wholly by gravity, but it is some-
times necessary to pump a part or all of
the sewage of a city. The lifts involved
are usually quite low, so that high-priced
pumping machinery is not required. It
may be necessary to thoroughly screen the
sewage before it passes to the pumps, or to
provide these with valves not likely to be
injured by the miscellaneous bulky sub-
stances in the sewage.
The Shone hydro-pneumatic system, used
successfully at the World's Columbian
Exposition and elsewhere in this country
and abroad, may sometimes be used to lift
83
sewage to higher levels. In this system
compressed air from a central station is
automatically discharged into a receiving
chamber with which the sewers are con-
nected, whenever the chamber fills to a
certain point. The air under pressure
forces the sewage through the outlet pipe.
Where pumping is necessary receiving
reservoirs with more or less storage cap-
acity may sometimes be provided with
advantage, to equalize the work demanded
of the pumps and perhaps to permit shut-
ting down the pumping plant at night.
Such reservoirs are generally covered,
unless in very isolated localties, and may
be ventilated by connecting with the
smokestack, or the gases from the venti-
lator may be conveyed to the furnace fire.
Force mains are generally required in
connection with pumping plants, but some-
times the latter are so near the point of
outlet, serving as mere vertical lifts, that
the discharge pipes from the pumps cut no
figure. When employed the force main
will naturally be of cast iron, similar to
that for a water supply system.
84
TIDAL CHAMBERS.
Besides receiving and storage reservoirs
at pumping stations these may be required
where the disposal of sewage is into tide
water under such conditions that it is
necessary to discharge it on ebb tides.
The main distinguishing features of such
reservoirs, as compared with these des-
cribed above, is an arrangement of gates
which will permit of emptying the reser-
voir in a brief period. These gates should
be easily handled in order to reduce the
cost of attendance. This may sometimes
be effected by mechanical power provided
by the outflowing sewage.
FINAL PLANS AND SPECIFICATIONS.
Before bids for construction are invited
full plans and specifications should be pre-
pared by the engineer. The plans should
be in sufficient detail to make the general
design and all the accessories of the sys^
tern perfectly plain to bidders, and the
specifications should be explicit upon every
85
point which comes within their scope.
Blue prints of the plans and printed copies
of the specifications should be ready for
all inquiring bidders in advance of the
date fixed for opening bids. The specifi-
cations are usually accompanied with the
form of contract to be executed between
the city and the successful bidder. In the
matter of specifications and forms of con-
tract the engineer should generally work
in conjunction with an able lawyer, the
city's permanent legal representative, or
otherwise, according to circumstances.
Years of experience on sewer work in a
particular city may fit an engineer to cope
single-handed with all the legal questions
involved, but in the long run co-operation
with members of the legal profession will
prove advantageous. When difficulties
with contractors arise the city's legal ad-
viser is pretty sure to be called in, so it
is well that he should be consulted at the
start. Outside of his own particular city
the engineer may be practically helpless
in legal matters, owing to the wide di-
vergence of laws relating to public im-
86
provements in cities of the same and
of different states.*
SECURING BIDS AND AWARDING CONTRACTS.
In no department of the engineer's work
can more money be saved his employers
than in the securing of numerous truly
competitive bids from able contractors and
in deciding to whom the contract should
be awarded. On the proper performance
of these duties depends not only the
first cost of the improvements, but the
interest and maintenance account and to
a large extent the successful operation of
the undertaking. It is more essential to
secure an able and honest contractor than
a low bid; more important that the work
be done well than that it be done cheaply.
The number and character of the bidders
on a given job will depend upon the im-
portance of the work, the publicity given
to the proposed letting and the character
* A form of specification and contract is given in Staley &
Pierson's ''Sepatate System of Sewerage" Prof. J. B.
Johnson's " Engineering Contracts ai d Specifications " is a
valuable book devoted exclusively to the subjects named in
its title.
8?
of the plans, specifications and foi-ms of
contract. In these days of numerous con-
tractors eager for work at a fair price it is
only necessary to present a clear idea of
the work to be done and just conditions
for its execution to secure an abundance of
proposals on almost any job, provided
only the opportunity to bid be brought
to the attention of the possible bidders.
Most cities and towns are obliged by law
to advertise all contract lettings where
more than a small cost is involved. It is
generally required that the advertisements
shall appear in one or more local news-
papers and permissible that it be inserted
in others. The local newspapers, even in
the large cities, reach only a small pro-
portion of possible bidders, almost ex-
clusively those of the city in which the
papers are published. For this reason,
and because of the better results which ex-
perience teaches are to be secured thereby,
thv3 practice of advertising engineering con-
tracts in engineering journals is rapidly
growing in favor of late. When such a
course is pursued the work in hand is
brought to the attention of the contractors
of a great section of the country, or of the
whole country, if of sufficient importance,
instead of to those of one city, and the
number of bids received is in like propor-
tion. But this is not the only advantage.
The wider competition renders far more
difficult, yes, practically impossible, ex-
cept under the most corrupt city govern-
ments, the growth of a ring of local con-
tractors who through combinations, per-
sonal favoritisms and even worse, maintain
prices at a high point, at the same time
generally doing poor work.
The. bids having been received, they
should be referred to the engineer for tab-
ulation and recommendation. From his
estimates of quantities he can determine the
relative aggregate prices of the several
bidders, and from his knowledge, through
acquaintance and inquiry, of the bidders,
and of the probable cost of the work in
question, he can decide upon and report the
most favorable bid. As stated above this
is by no means always the lowest bidder,
and it should net be obligatory upon the
89
city to award the contract to the parties
who offer to do the work for the least
money. Unfortunately the experience of
many cities in having their officials award
contracts to favored bidders has led to leg-
islative enactments affecting some local-
ities which make it imperative that con-
tracts shall be given to the lowest bidder,
although often the privilege of rejecting
all bids and readvertising is given. This
is a long step in advance, but where the
officials can be trusted time and expense
can be saved both city and contractor by
allowing an award to other than the lowest
bidder, if demanded by the best interests
of the city, based on past records of con-
tractors and the danger of poor work at ex-
cessively low prices. Such a course, aside
from obliging a city to accept an undesir-
able bid, discourages designing contract-
ors and those who, in their eagerness for
work, figure too low, and does not call
upon responsible men, of good judgment,
to be to the trouble and expense of put-
ting in bids the second time.
90
THE PROPER EXECUTION OF THE CON-
TRACT.
The contract having been awarded and
construction started, it devolves upon the
engineer to give the contractor all neces-
sary lines and grades, and any information
needed and not provided in the plans and
specifications. It is also his duty, both per-
sonally and through his inspectors, to see
that the work is done according to the
plans and specifications. This requires the
most careful and conscientious attention on
the part of able men. Every detail of con-
struction must be watched with an eagle
eye and no work not subject to complete
examination after it has been executed
should be allowed to proceed in the ab-
sence of the inspectors. On pipe work or
conduit construction, especially, one in-
spector should never be called upon to look
after work in more than one street at the
same time. Pipe and brick must be ex-
amined with the greatest care, the former
piece by piece. Cement should be sub-
jected to proper test to show its fitness for
01
the use to which it is to bo put. This re-
quires at least a simple testing laboratory,
and the provision of a fully-equipped one
is money well spent where naich work is to
be done. After the sewers are completed
they should be tested for obstructions, the
small sewers by passing a ball through, or
otherwise, and large ones by having a man
go through them.
REGULATIONS FOK THE USE OF SEWERS.
These include all necessary precautions
for the prevention of obstructions, chief of
which, perhaps, is the proper laying and
joining to the street sewer of house con-
nections. This work is often, if not gen-
erally, done by plumbers, but all such
should work under a license, revokable for
non-compliance with city and town ordin-
ances, and should be under the supervision
of the engineering, sewer or health de-
partment. The size, grade and material of
house connections should be specified in the
above regulations, and in order that pros-
ecutions and punishments may be possible
for offenses against these and other rules
92
it is necessary to have an ordinance or or.
dinances passed, embodying all the neces-
sary rules and regulations and providing
penalties-.*
OPERATING THE SYSTEM.
The sewers completed their operation is
nearly always very simple, especially where
pumping or purification is not necessary.
A superintendent of sewers, in fact if not
in name, is generally employed to have
general charge of the sewerage system.
This official often oversees house connec-
tions and frequently has charge of minor,
and sometimes of important extensions of
the system. He removes stoppages and
looks after flush tanks and other devices
for keeping the sewers clean. If pumps
are used these are likely to be in sole
charge of the pumping engineer> although
he may be under the superintendent.
Where purification is employed a man in-
dependent of the superintendent may or
may not have charge. All purification
* A model ordinance will be found in the ' ' Separate Sys-
tem of Sewerage. "
93
plants should be under the immediate di-
rection of the most competent men attain-
able, within reasonable limits, as intelli-
gence and knowledge are absolutely essen-
tial to their continued, and often to their
temporary success. Politics and political
berths should be kept clear of this depart-
ment of the sewerage system, if from no
other — it should be from all parts.
SEWERAGE COMMITTEE, BOARD OF PUBLIC
WORKS OR CITY COUNCIL.
The above considerations suggest the
question, should the construction and oper-
ation of a sewerage system be entrusted to
a sewerage committee entirely independent
of other departments of city government, to
a board of public works charged with other
municipal improvements of an engineering
character, or to the city council ? The
answer to this, like that to so many otln-r
questions already raised in this volume, is
that local conditions often determine what
is best.
It is interesting to note that English
cities and towns, as ck-arly shown in Dr.
Albert Shaw's " Municipal Government in
Great Britain," manage in an admirable
manner practically all their public works
through their city councils and committees
of the same, always relying, however,
upon able and experienced engineers and
others for technical advice and the details
of operation. In this country the mistrust
of city councils has been, and largely is
PO great that the first thought of tax-pay-
ers on undertaking the installation or ex-
tension of some important public work is
to entrust it to a special and independent
body of men.
*- The English system has the advantage
that all public improvements are thereby
carried out with due consideration to their
relation to reSeh other and to the finances
of the^ity as a whole. A board of public
works entrusted with streets, sewers, water
. and lighting plants, if the two latter be
operated by the city, would be a close ap-
proach to the English plan, and would in
many instances have its advantages over
that plan under American conditions.
Generally speaking independent sewer
95
commissions, if only composed of the
right men — and it is this which counts
more than any system — have built and are
managing sewerage systems with good re-
sults in this country. But from the nature
of the case they cannot always so plan
their work, for instance, as to interfere as
little as possible with good street pave-
ments, because they have no control over
the time and place of laying such. What-
ever the system, an able city engineer, or
engineer of the sewer department, should
be given the practical settlement of all en-
gineering questions.
SEWAGE PURIFICATION IN ITS GENERAL
ASPECTS.
Having treated the other phases of the
subject as fully as the space available will
permit, there remains for consideration the
important matter of sewage purification.
This has been reserved to the last, except
for the incidental references to it already
made, because it is quite complete in itself
and demands independent handling. The
main principles of sewerage construction,
96
aside from disposal works, have been es-
tablished for many years, but the best
means of rendering sewage fit to discharge
into water courses or other bodies of water
not suitable for the reception of crude sew-
age are problems of yesterday, to-day and
even of the future. Enough has been
settled, however, to render no longer valid
the plea that sewage purification is as yet
in too experimental a stage to forbid efforts
in that direction. We know to a certainty
how sewage may be rendered harmless.
Further knowledge will probably be in the
line of making present processes do more
work without additional cost. The facts
are, that the two older systems of sewage
purification now in use, land treatment
and chemical precipitation, were practised
for many years in a blind rule o'thumb
way, and often with good results, before
their fundamental principles were dis-
covered. Since the discovery of these
principles, or natural laws, we can do
nearly always what formerly was done only
occasionally.
Blood pulsed through man's veins for
97
countless centuries before Harvey dis-
covered the law of circulation, and many
maladies incident to blood and circulation
were helped or healed in utter ignorance
of the law, but since and by means of the
discovery what a revolution there has been
in medicine and hygiene ! We look for-
ward to more progress in these particulars,
but we do not for this reason hesitate to
avail ourselves of all that has been accom-
plished. But this is exactly what some
people would do in the matter of sewage
purification, or at least they offer as an
excuse that the science is in too tentative a
stage to warrant the adoption of any plan
as yet, their real motive too often being
a desire to keep the municipal purse strings
pulled tight.
What is most needed now is not new
processes, but the careful carrying out of
well-known methods, with observations on
the results obtained under all the varying
circumstances which naturally arise in
different localities and under varying con-
ditions at the same works. We have a
host of suggestive and many conclusive
deductions drawn from careful and long-
continued experiments, both at home and
abroad, but we need, particularly in Amer-
ica, to have more of the scientific spirit
and method which have made the labora-
tory work so successful applied to the
daily operation and study of actual sew-
age works. Instead of caviling at the
uncertainties of sewage purification those
who raise questions might better take their
turn at efforts to perfect, simplify and
cheapen the already admirable processes
now available. They may rest assured
that the worst yet attained by intelligent
effort along the new lines of work is
infinitely better than the shameful prostitu-
tion of streams and lakes now going on
throughout this broad land, a marring of
the beautiful face of nature, rendering
limpid waters black and repugnant, chang-
ing their refreshing breezes to sickening
odors, while life-giving water is made a
death-dealing poison, and all through
sewage pollution.
Before taking up sewage purification in
detail it will be well to consider what sew-
age is, from the standpoint of the chemist
and bacteriologist, and what should be
expected or desired in the way of its
purification. Sewage, when fresh, and as
it appears at the mouth of an outlet sewer,
is generally a cloudy, opaque grey
liquid, with some large particles of sus-
pended matter not easily broken up in
transit, as orange peels, rags, paper and
various nondescript articles too numerous
to mention. It very often has a faint,
musty odor, and in both looks and .smell
is sometimes quite comparable with the
suds-water of family laundry work.
Nearly all of the sewage is simply water,
the total solids in supsension averaging
perhaps 2 per 1,000, of which a half
may be organic matter. It is this 1 part
in 1,000 which is to be removed or so
changed in character as ttfW 'rendered
harmless.
These facts regarding the composition
of sewage are far different from the
popular conception, which pictures a vile
mass, indescribable in appearance and odor.
Such ideas are gained in part from the
100
known contents of cesspools and from im-
properly constructed and neglected sewers,
but they arise largely in vivid imagina-
tions. They would be applicable in many
respects to sewage allowed to stagnate and
take on putrescible decomposition, as hap-
pens in cesspools and obstructed sewers, or
where the sewage stands on the surface of
poorly graded land disposal areas, or
accumulates in any similar manner before
being purified.
The greatest danger from sewage is in
the harmful bacteria which it conveys,
but even these are not to be feared if kept
out of the human system, to which they
rarely gain access except through water
used for domestic purposes or in connection
with milk supplies.
Generally speaking, sewage swarms with
bacteria, engaged, when sufficient oxygen
is present, in the laudible occupation of
converting unstable organic matter which
might become offensive into fixed mineral
compounds of a wholly unobjectionable
character. These plants may number
millions to the teaspoonful, and yet be
101
wholly invisible, so minute are the organ-
isms and so hidden is the mighty work in
which they are engaged. To isolate the
harmful from the harmless with certainty,
if at all, is an achievment for some future
Pasteur.
The organic matter and the bacteria al-
ways accompany each other. If all the
bacteria should be removed or killed, but
some of the organic matter remain, an-
other crop of microbes would develop as
if by magic as soon as seed was sown, al-
though the renewal of disease germs in
their orginal quantities would rarely, if
ever, occur except from a source the same
as or similar to the original. But, remove
all the organic matter and all the bacteria
food is gone— and without food death
comes swiftly, even though the bacteria
be legions.
From the above it may be inferred that
all sewage purification processes are valu-
able in so far as they remove or change
the composition of organic matter. Mechan-
ical straining, sedimentation and chemical
precipitation are largely removal processes,
102
while septic tanks, broad irrigation, inter-
mittcnt filtration, contact beds and perco-
lating filters change the putrescible organ-
ic matter into stable compounds.
Either form of land treatment may be
employed where practically complete puri-
fication is desired. Straining or sedimen-
tation will remove only a small portion of
the organic matter. Chemical precipita-
tion and the use of septic tanks will do
more, but must be supplemented by irri-
gation or intermittent filtration where a
high degree of purity is required. Con-
tact beds and percolating filters, generally
preceded by septic tanks, but sometimes
by sedimentation or chemical precipita-
tion instead, may be relied upon to pro-
duce a non -putrescible effluent relatively
free from suspended matter, but generally
high in bacteria. Aeration may also be
be called in to supplement other processes,
but the part which it can perform is far
more limited than is supposed by many.
The object of sewage purification, then,
being the removal of organic matter, and
certain modes being available for the
103
partial or complete accomplishment of
this end, the question is, which is the most
desirable ? Like nearly all the other ques-
tions which have arisen in the course of
this book, and like most other questions in
engineering, other sciences or the arts,
there is no one answer. The degree of
purification required and the local condi-
tions which make one system cheaper than
another in construction and operation all
have their weight in selecting a system of
disposal.
It sometimes happens that a partial re-
moval of the organic matter contained in
sewage is ample, in which case the 20 to
30 per cent., more or less, that can be
accomplished by either sedimentation or
straining will be sufficient. If better re-
sults are wanted and some 50 per cent., or
slightly more, of purification is needed,
the sedimentation may be accelerated by
the use of certain chemicals, which con-
stitutes chemical precipitation, or the sep-
tic tank may be employed. If neither of
these will suffice, the effluent from either
process, or in fact from sedimentation or
104
straining, may be applied to a sewage farm,
intermittent filters, contact beds or perco-
lating filters ; or where plenty of hii'd is
available, all previous treatment may be
dispensed with and intermittent filtration
or irrigation, commonly known as sewage
farming, or a combination of these two
land processes, may be brought into requi-
sition to do all the work. Obviously where
only partial purification is required there
may be a wide range of choice between
the methods named.*
Although the object of sewage treatment
may sometimes be the removal of bacteria,
the chief aspect of most of the sewage
works now in operation is to prevent nuis-
ances in the nature of foul sights or odors.
Where public water supplies are involved
the aim is to keep the sewage out, or to
purify the water, or both.
SEDIMENTATION.
This is effected by allowing the sus-
* See " The Partial Purification cf Sev age," by C< 1. Geo.
E Waring, Jr., Ewjin- ering Aevsof Jau. 4. 1894, for an ei-
t<-ndt d d.scussion of the subject named in the title just
quoted.
105
pended matters to settle in tanks. The
partially clarified liquid is drawn off, leav-
ing the solid matter, called sludge, at the
bottom for subsequent disposal. This pro-
cess, as has been intimated, is akin to
chemical precipitation, so the shape of the
tanks, the relative merits of continuous
and intermittent settlement and the treat-
ment of the sludge will be taken up later
on.
Experiments with sedimentation at Law-
rence, Mass., during the last three months
of 1893, indicated a subsidence of 18.2 per
cent, of the albuminoid ammonia and 12 per
cent, of the bacteria in the crude sewage
during a period of four hours. The same
experiments in 1894 showed a much better
average for organic matter, as measured
by the albuminoid ammonia, but about the
same results for bacteria, the respective fig-
ures being 30 and 14.6 per cent. In 1895,
there were removed 48 percent, of the total
albuminoid ammonia, and 31 percent, bac-
teria; in 1897, about 35 per cent, of each.*
* Reports of the Massachusetts State Board of Health,
1893, p. 41,6, f^r 1894, p. 454, 1805, p. 451, and 1897, p. 416.
106
These experiments were discontinued early
tinned early in 1898.
It is hard to imagine conditions in actual
practice which would warrant the con-
struction of tanks of sufficient capacity to
admit of four hours settlement where only
a 30 to 40 per cent, removal of the organic
matter could be expected. With smaller
tanks the work done would of course be
less, so sedimentation is not likely to be
employed except where a small amount of
purification at a slight expense is all that
is needed.
MECHANICAL STRAINING.
This admits of a great variety of prac-
tice, ranging from attempts to remove
rags, paper and other large substances to
an approximation to intermittent filtration.
Wire screens or filters of various materials
may be employed. Generally little is ac-
complished, but in well-constructed and
operated plants screening or straining may
be an important factor in the purification
effected. As a preliminary to intermittent
filtration, coke strainers, or thin filter
107
were used at Lawrence during the last
seven months of 1894, removing 52.4 per
cent, of the albuminoid ammonia in the
original sewage.* These beds ranged from
IK to 8 ins. in thickness during the experi-
ments, and the sewage passed them at an
average rate of about 345,000 gallons a
day for six days in the week. A depth of
6 ins. of coke is given as desirable and it
is estimated that when straining ordinary
sewage from 5 to 8 cu. yds. of coke would
have to be removed per 1,000,000 gallons
filtered.
Mechanical straining through coke or
sand at the rates named might perhaps
more properly be termed continuous rapid
filtration. Some of the better of the re-
sults given are about the same as those
secured in the same experiments by means
of chemical precipitation, using 1,000 Ibs.
of sulphate of alumina per 1 ,000,000 gal-
* Keport of the Massachusetts State Board of Health for
1894, p. 455. The rep rts of the Massachusetts State Board
of Health from 189t to 19u2, inclusive, contain accounts of
various further experiments with coke, anthracite and
bituminous coal as screens. From 3 to 15 ins. of these ma-
terials, working at rates of 1,000,000 gallons a day and up-
vards, r< moved from 32 to 62 per cent, of the total album-
incid aii iiionia.
108
Ions of sewage, or 7 grains per gallon, and
allowing four hours for precipitation. The
mechanical straining usually employed is
insignificant in results compared with the
above. The same may said of sedimen-
tation. Both processes in these experi-
ments, as well as the chemical tests carried
on simultaneously, were intended to facili-
tate and relieve the work of filter beds.
CHEMICAL PRECIPITATION.
Sedimentation alone removes only such
suspended matter as will sink by its own
weight during the comparatively brief
time which can be allowed for the purpose.
Some of the lighter matters may of course
be carried down by the heavier particles,but
the total results are comparatively small.
If the process could be continued long
enough, practically all matters in suspension
might be removed, but those in solution
would remain and putrefaction might be-
gin in the sludge, if not in the sewage
undergoing clarification. By adding cer-
tain substances chemical action sets in and
precipitation occurs. Some of the organic
109
substances are brought together by the
formation of new compounds, and as they
fall in flaky masses they carry with them
other suspended matter. As in sedimen-
tation or straining, a part of the bacteria
are removed by mere entanglement, while
every grain of organic matter removed
decreases by so much the bacterial food
supplies, and thus the potential number of
bacteria,
A great number and variety of chem-
icals have been employed as precipitants,
but years of experience have resulted in
the general adoption of lime, sulphate of
alumina and some of the salts of iron,
more especially ferrous sulphate or cop-
peras, or a combination of two of these, as
best suited for the chemical precipitation
of sewage. The character of the sewage
and the relative cost of the several chemi-
cals in a given locality should be deter-
mining factors. Lime is cheap almost
everywhere, but the comparatively large
quantities required increase greatly the
amount of sludge. Sulphate of alumina
is not so readily obtained, and often must
110
be transported such a distance as to make
freight rates quite a factor in its cost. It
is often used in conjunction with lime,
producing a less amount of sludge than
lime alone and in some cases doing more
effective work. Where either an acid
sewage or one containing iron salts is to
be treated, lime may be used without the
sulphate of alumina and a considerable
saving effected. If the acid or iron salts are
discharged at intervals the sewage must be
tested from time to time to determine
when to modify the amount of chemicals
artificially applied. A very interesting
example of this sort is found at Worcester,
Mass., where large quantities of acid and
iron are discharged into the city sewers
from manufacturing establishments.*
In buying chemicals of any kind great
care should be exercised in determining the
available amount of the active agent, as
the amount of calcium oxide in lime, or of
alumina in sulphate of alumina, different
products varying greatly in this respect,
» See Engineering Xeu-ss, No. 15. 1F90, and July 28, 1892 ;
also Rafter and Baker's " Sewage Disposal in the United
States."
Ill
notably the lime from different quarries
and kilns.*
The chemicals should be added to and
thoroughly mixed with the sewage before
the latter reaches the settling tank. The
mixing may be effected in nearly all cases
by projections into the channel leading to
the tank, called baffle plates.
Experience has demonstrated that the
tanks should be long and narrow j and that
they should be operated on the continuous
rather than the intermittent plan. The
width of the tank may be, say one-fourth
its length. In the continnous plan the
sewage is constantly flowing into one part
of the tank and discharging from another
in a more or less clarified state. In the
intermittent system a tank is filled and
then the flow turned elsewhere, allowing
the sewage in the first tank to come to
rest. Where the continuous plan is used
'the sewage generally flows through a set
* For tl e theory of the actions of the various re-agents,
the qiiHulities employed and their costs, both in experimen-
tal and practical work, see Rafter and Baker's "Sewage Dis-
posal i:i the United States." Tl>e brief limits rf tl.i-»v lume
render! i possible much more than a discuhsion of g. neral
principles; detailed ninires, UDHCCOII pam d by ihn data
upon \Nhieh they are based, am apt to be misleading.
112
of tanks without change of gates or other
interruption until one compartment needs
cleaning. This compartment being cut out
and left to itself for a while, the clarified
sewage is then drawn off gradually from
the top through a hinged pipe, the upper
and open end of which takes sewage from
the surface on opening a valve in the hor-
izontal portion of the drain pipe beyond
the hinged joint. When the effluent is
decanted to the top of the deposited sludge
the valve just mentioned is closed and
another one, in the sludge pipe, opened,
allowing the sludge to flow out, or to be
pumped out for final disposition. The
tank should then be thoroughly cleaned,
after which it may be treated with disin-
fectants or deodorants, if desired, before
being again put in use.
The disposition of sludge is one of the
most vexed problems connected with sew-
age disposal. It is a pasty, semi-liquid
mass, ordinarily containing from 90 to 95
per cent, of water and 10 to 5 per cent, of
solid matter. The most common method
of disposal, and perhaps the one most gen-
113
erally available and satisfactory, is to
squeeze as much water as is possible out
of the sludge by means of presses designed
for the work. This greatly reduces the
bulk of the material. The liquid from the
press goes back to the tank for further
treatment. The sludge cake, as it is called,
may be handled easily. It is sometimes
burned and sometimes hauled away by
farmers for use as a fertilizer. There have
been great expectations on the part of pro-
jectors of chemical precipitation works
that the farmers would vie with each other
in securing the sludge, and even pay good
money for it. The general experience,
both in this country and abroad, has been
that a city is lucky if it is able to induce
anyone to haul the sludge away for it.
In some cases peat or some other absor-
bent is mixed with the sludge to render it
more easily handled and removed in, bulk.
Again, it is run out on the surface of coarse
sand and gravel beds and its liquid parts
reduced by draining and drying. Some of
the difficulties connected with this last
method are :
114
(1) In wet weather little drying takes
place, and during the colder mouths the
sludge accumulates in considerable quan-
tities. (2) Manual labor must be em-
ployed to remove the sludge from the
draining and drying beds. (3) Where
chemical precipitation is employed suitable
land, in character and extent, is often not
to be had.
At Birmingham, England, large volumes
of sludge are pumped through force mains
distributed through portable pipes to
and covered with earth.
There remains another method available
for some seaside cities, and that is dump-
ing in the ocean by means of large steam
sludge ships. Thousands upon thousands
of tons are so disposed of from the sewage
works of London and Manchester, Eng-
land, and Glasgow, Scotland.
The capacity of the settling tanks is
often the chief factor in determining the
cost of installing precipitation works. As-
suming that the sewage should be one hour
in passage through the tanks, and that the
maximum flow is twice the average, pro-
115
vision must be made for one-twelfth the to-
tal daily flow, where house sewage only is
treated. This makes no allowance for throw-
ing out a portion of the tanks for cleaning
or repairs. It would certainly be erring
on the safe side, if at all, to provide a tank
capacity equal to one-eighth the total max-
imum daily flow. Where sewage from a
combined system is treated, it is of course
practically impossible to provide a tank
capacity sufficiently large to treat all the
sewage. Either the excess of storm water
must be discharged into natural water
courses along the lines of the sewers or
pass by the works without treatment. If
ample tank capacity is available it may be
possible to treat all the sewage during the
first part of a moderate rain. This would
mean the purification of the foulest portion
of street and other washings, after which
in many localities it might be admissible
to forego all attempts at purifying the
sewage, as the results which could be ob-
tained would be comparatively insignifi-
cant. During such a heavy rainfall the
sewage of a combined system would be
116
many times diluted, and where the effluent
from the works discharges into a stream
the latter is also greatly increased in vol-
ume. It is evident that where purification
is proposed in connection with a new sew-
erage system the separate plan will prac-
tically always be adopted. Most purifica-
tion plants in this country have been built
at the same time as the collecting system,
and in such cases the separate plan has
been used. Worcester, Mass., was forced
to adopt purification after many miles of
combined sewers had been built, and after
it had converted a brook with a consider-
able drainage area into an outlet sewer.
Its later sewers have been built for house
wastes only, and hundreds of thousands of
dollars have been spent since the sewage
works were built in excluding surface
water from the sewers.
THE SEPTIC TANK.
The septic tank, as we now know it, has
been developed since 1894. In effect, it is
a sedimentation basin, so designed and
operated as to lessen the sludge deposit by
II1
dissolving a portion of it and by reducing
another portion to gaseous form. This re-
duction or hydrolysis of the sludge is
brought about by anaerobic bacteria, which
work in the absence of air, and are thus
directly opposed in character to the aero-
bic bacteria or nitrifying organism of sew-
age farms, intermittent filters, contact beds
and percolating filters. Since inorganic
matter is not acted upon by the bacteria,
its exclusion from the septic tank is desir-
able. To this end, small grit chambers are
provided, through which the sewage passes
on its way to the septic tank. The high
specific gravity of the sand and other min-
eral matter in the sewage causes much of
it to sink in a brief period of time, while
the remainder of the suspended matter, in-
cluding the lighter organic sludge, passes
into the septic tank. Since the admission
of air to the septic tank would tend to dis-
place the anaerobic bacteria by aerobic,
the tank inlets and outlets are generally
submerged a foot or so beneath the normal
sewage level. The tanks are made long
and narrow, thus affording time for sedi-
118
mentation, and have a sewage depth of 6
to 9 feet. For convenience in removing
sludge, their bottoms slope to one or more
sumps or gates.
Whether or not septic tanks should be
covered has not been universally agreed.
It is held by some that a roof, excluding
light and air, is a great help, if not a ne-
cessity, to the highest efficiency; while
others argue that roofing is unnecessary
to full bacterial action, except in very cold
climates, and that a roof need be provided,
if at all, only for such tanks as are near
dwellings or much-traveled highways, and
which on that account might give offense
to residents or passers by.
Any fairly water-tight material may be
used in constructing septic tanks ; probably
concrete, either plain or reinforced, is now
used more commonly than any other ma-
terial. The roof, as well as the walls and
bottom, may be of concrete, or where low
first cost is an object, wood may be used
for roofing.
Since the action of the septic tank is due
tc anaerobic bacteria, while further purifi-
119
cation is effected by aerobic germs, and
since the septic effluent is not only high in
anaerobic germ contents, and nearly if not
quite without available oxygen, the septic
effluent is sometimes aerated before being
passed to filter beds. Weirs over which
the effluent flows in a very shallow stream
or a series of overflow steps are used for
purposes of aeration.
The amount of sludge removed by septic
tanks cannot yet be safely predicted for a
given sewage works until actual tests have
been made. Such figures as are available
show wide variations at different localities.
No one should be deluded by observations
of the amount of sludge remaining in a
septic tank, since large volumes of sludge
in a finely divided state may pass off in
the effluent. Volume for volume, however,
this finely divided suspended matter will
make far less trouble than the sludge from
ordinary settling tanks or from chemical
precipitation works. Some of it is already
a mineral ash, subject to no further organic
change, and the balance is partly reduced
120
to mineral matter and also to food for the
low forms of organic life.
Such sludge as remains in septic tanks
may be disposed of by the means already
described.
In some cases, probably due to the char-
acter of the sewage or to improper opera-
tion, sludge from septic tanks is offensive
when first exposed to the air. Under such
a condition the sludge disposal should be
carried on at a remote point, or the sludge
should • be buried quickly a few inches
beneath the earth. Investigations should
also be made to determine whether the
odors cannot be prevented by a change in
the design or operation of the tank.
Were it within the scope of this book,
and less free from conflicting claims, it
would be interesting to attempt to trace
the history of the septic tank. The sub-
ject involves claimants in Great Britain,
the United States, Germany and France;
and also many early tanks installed and
used with success, though with little or no
understanding of the principles involved,
long before the name septic tank came into
121
use. It is now generally recognized that
the man who gave the septic tank its name
and brought it into scientific prominence
was Donald Cameron, of Exeter, England,
but up to early in the year 1905 it was not
generally conceded that Cameron's work
entitled him to patent control of the septic
tank process. The question was then in
the courts of the United States for trial,
but had never been legally raised in Great
Britain, so far as the author of this book
could learn.
ARTIFICIAL AERATION. — " ELECTRICAL "
PROCESSES.
While the oxygen of the atmosphere
may be made one of the greatest agents in
purifying sewage, some writers and others
have laid too much stress upon the value
of artificial aeration. Mountain streams,
which tumble over rocky beds, are noted
for their purity, and this has been attributed
largely to the aeration which the water
receives. It should be remembered that
122
the waters of such streams are generally of
a high degree of purity to start with, often
being little different from rainwater just
from the clouds, and that the aerating
process is quite commonly a long one. It
has been further observed that even badly
polluted streams show greatly improved
chemical analyses at points a number of
miles below the source of contamination.
But here, sedimentation, and the action of
both animal and vegetable life in their
more minute forms, play a notable part in
the purification process, and the time-
element is also important.
It has been well established by the
Massachusetts State Board of Health in
its Lawrence work that the two essentials
for the removal or transformation of the
organic matter in sewage are oxygen and
time, where dependence is placed on a
nitrifying or oxidizing process. The time-'
element has been largely ignored by some
theorists, a few of whom have put their
theories into practice. Purification plants
have been built, and more have been projec-
ted, in which the great reliance has been put
123
upon artificial aeration, either by forcing
air into the sewage or by causing the
latter to fall through the air in drops or
streamlets. This has been accompanied
by rapid filtration, generally through
sand. Now aeration of the sewage, or of
the filtering material, may be employed as
an aid to sewage purification, but like all
things else it has its limits. It can main-
tain a supply of oxygen which is of use up
to a certain point and this will be of value.
All in excess of this amount is of no
value, and even this is not of use
unless time is given for the action of the
oxygen and of the nitrifying organism.
The latter develops rapidly in the presence
of oxygen and organic matter, transform-
ing the latter into mineral compounds.
These facts are overlooked by some of the
promoters o.f aerating processes,the assump-
tion seeming to be that given a plenty of
air the desired work will be accomplished
.almost instantly. The facts are that sew-
age soon loses all the available oxygen
taken up by it during aeration and needs
to be aerated again and again until all
124
the organic matter is transformed. The
time-element can best be secured, almost
invariably in some form of filter bed.
Perhaps there is an even greater
misunderstanding regarding so-called
electrical methods of sewage purifi-
cation. These processes, which have
met with but little favor, simply pre-
pare by electrical means some chemical
agent which performs all the work accom-
plished and might be obtained in some
other manner, although possibly at greater
expense. In the Woolf and Hermite pro-
cesses either sea water or a solution of
common salt, according to the readiness of
obtaining one or the other, is partially de-
composed by an electric current, and sodium
hypochlorite is formed. The solution is
mixed with the sewage and acts as a deo-
dorizer and germicide, its efficiency de-
pending on its strength. The organic
matter remains in the sewage and is sub-
ject to secondary decomposition later on.
The product obtained by this process
might be of value under certain conditions,
125
the same as other good disinfectants are,
but there seems to be no reliable inform-
ation to show that anything further
can be expected of it.
The direct treatment of sewage by elec-
tricity has been talked of for some time
but it still remains a dream.
BROAD IRRIGATION OR SEWAGE FARMING.
Where sewage is applied to the surface
of the ground upon which crops are raised
the process is called broad irrigation, or
sewage farming. The practice is in most
respects similar to the ordinary irrigation
of crops with clean water, the sewage be-
ing applied by a variety of methods, ac-
cording to topographical and other natural
conditions and the kind of crops under
cultivation.
The land employed for this method of
purification should preferably be composed
of a fairly light, porous soil. The crops
should be such as require, or at least
develop best under a large amount of
126
moisture. Where the soil is heavy and
wc-t, and the crops cannot stand much
water, the sewage must be applied spar-
ingly, and so a large amount of land
and much labor must be provided. As
broad irrigation areas may be prepared at
comparatively small expense it is some-
times feasible to make use of land not so
well suited to the purpose as might be
desired, provided it can be obtained
cheaply enough and too much stress is
not laid upon the raising of crops. The
less the attention paid to cropping, gene-
rally speaking, the greater the amount of
sewage which can be put on a given area
of land. Wet, clayey soils can take but
little sewage under any circumstances,
but sometimes improve with cultivation
and the application of sewage.
The application of an average of from
5,000 to 10,000 gallons of sewage per day
to one acre of land is considered by many
as a liberal allowance. On the basis
of 100 gallons of sewage per head of
population this means that one acre of
127
land is, sufficient for a population of from
50 to 100 persons. More could be purified
if the crops would stand it, but for each
kind there is a limit which if passed
means the destruction of the crop.
Allowing even 10,000 gallons of sewage,
or 100 persons, to an acre in a city of 20,000
inhabitants would require 200 acres. To
find suitable land at a low price near
cities is not always easy. The larger the
city the greater the difficulty. Labor, too,
is a big item in sewage farming on this
side the Atlantic, especially near cities.
As a partial offset to this, great cities
afford excellent and never-failing markets.
Another great obstacle to adequate finan-
cial returns from sewage farming in
America is the deplorable fact that
political ends and not business principles
govern in large numbers of our cities,
though there is good reason to predict
a great change in this respect ere
long. Where such conditions do prevail,
however, the positions of both superin-
tendents and laborers on sewage farms are
ulinost sure to be considered rewards for
128
and encouragements to party service, with
results most unfavorable to the enterprise
in hand. Sewage farming means the sell-
ing as well as the raising of crops, and
perhaps of live stock, and so requires
business ability and agricultural skill.
The latter must be accompanied with the
faculty of handling considerable bodies of
men.
These apparently discouraging state-
ments are meant rather as warnings. They
are necessary because of the glowing repre-
sentations which have been made regard-
ing the profits of sewage farming by those
who have not looked at all sides of the
question. I am not unmindful of the re-
sults of sewage farming abroad, but Euro-
pean conditions are far different from ours.
Many of the European farms are most ad-
miral ly managed, both from an agricul-
tural and business standpoint, and not a
few of them have to contend with soil
far less favorable than could be found
in many sections of the United States.
I do not say that an American city could
not conduct so great an enterprise in a
129
creditable manner, for we have many
well-conceived and well-operated munici-
pal works of great magnitude. I do say
that high prices for land near large cities,
costly labor, a constant warfare against
corruption with too frequent surrenders,
and our sudden and complete changes in
government all make sewage farming more
difficult here than abroad.
For the present, sewage disposal cannot
be accomplished in this country at a profit.
It is sometimes possible to regain through
the raising of crops a part of the expense
entailed in removing and purifying sewage,
and this is the only method by which any
considerable portion of the expense has yet
been recovered here or elsewhere. We
should be thankful for the day of small
things, and wherever a revenue can be ob-
tained from irrigation area or filtration
beds our efforts should be to secure it. But
the logic of figures will often show that
some method of disposal that carries with
it no financial returns is the cheapest, in
which case instead of crying over spilt and
wasted sewage, we may laugh over a sav-
130
ing in capital, interest and maintenance.
Wherever irrigation, pure and simple,
that is the application of water to crops
for the sake of moisture, can be practiced
to advantage, sewage farming should re-
ceive serious consideration, for in such
localities every drop of water is valua-
ble. As ordinary irrigation may yet be
used in the East as well as in the West,
(it is already practiced to some extent in
the South) the use of sewage for mere
watering as well as fertilizing may some
day be seen -here and there throughout the
length and breadth of the land. This is a
subject which demands careful investiga-
tion and perhaps might be taken up with
advantage by some of our agricultural ex-
periment stations and by any live official
in a position to do so.*
* For an article on "The Use of Sewage for' Iriigation in
the \\ est " ste Angineei ing iYe«w for .Nov. 3, Ife9j ; the sub-
stance of the article is a.so given in Kafter and Baker's
" Sewage Disposal in the United States.1' A later treatment
of the subject may be found in "Sewage Irrigation," Nos.
3 and 22 of Water Supply und Irrigation Papers of the U. fc.
Geological Survey, by Gto W. Rafter, M. Am. Soc. C. E.
In March, 1905, the author cf this book visited the sewage
farm of Pasadena, Cal., and also land to which some of the
sewage of Los Angeles is applied. As a result, he is more
than even convinced of the wisdom of using sewage for ir-
rigation wherever water is scarce.
131
SUB-SURFACE IRRIGATION.
Before passing on to intermittent fil-
tration a word should be said regarding
sub-surface irrigation. The system is cap-
able of use on a small scale, chiefly for
private dwellings, various public institu-
tions and small communities where for any
reason surface disposal would be objection-
able. Tiie sewage is distributed through
agricultural drain tiles, laid with open
joints, and placed only a few inches below
the surface. Provision should be made
for changing the disposal area as often as
the soil may require by turning the sewage
into sub-divisions of the distributing pipes.
The sewage is generally discharged auto-
matically at intervals on the filling of a
tank to a certain height. Where surface
application can be practiced it would gen-
erally, if not always, be preferable to this
system.
INTERMITTENT FILTRATION.
This method of sewage purification is
capable of producing the highest results
132
under favorable conditions, and those con-
ditions prevail perhaps more widely in this
country than like ones for any other sys-
tem.
The process is a most simple one.
With a competent man in charge large
areas of beds can be operated with cheap
labor. The construction of the beds is
nearly as simple as their operation, only
common labor being required, except for
putting down pipe and accessories.
The essential features of filter beds are
some 4 to 5 feet of medium-sized sand,
located above the natural ground water
level; a pipe system for distributing the
sewage to one or more points on each bed,
and another beneath the bed, for collecting
the purified liquid. In operation, the sew-
age is turned on to one bed for a given
length of time, and then to another, in
order to give the first a rest, or literally a
breathing spell. When the beds become
clogged with the matter retained on their
surface and in their uppermost part, they
may be raked over, or the sludge, and with
it a thin layer of sand, may be scraped off.
133
If the beds are scraped, it will eventually
be necessary to make good the sand re-
moved, although this will not be required
until perhaps a foot has been taken off,
which should not result for a long time.
Intermittent filtration is a nitrifying
process effected through the agency of ox-
ygen and bacteria, and requiring time for
these two factors to act. A more complete
definition is perhaps that given in the
Report of the Massachusetts State Board
of Health for 1893, as follows:
The process * * * consists of intermingling
the sewage in the pores of the filtering material,
with sufficient air for a sufficient time, in the pres-
ence of micro-organisms which quickly establish
themselves there.
Experience has taught that a good filter-
ing material is one composed of clean,
sharp sand with grains of uniform size,
and having interstices forming about one-
third the total volume. The interstices
serve as air spaces. When the sewage is
admitted to the sand not all the air is
driven out, and hence thtre is a store of
oxygen to be drawn upon by the bacteria*
134
As more and more sewage is added the
oxygen is exhausted, the nitrifying bac-
teria diminish in numbers, as they cannot
live without air, and the efficiency of the
purification process diminishes. If the ap-
plication of sewage ceases, the beds grad-
ually become drained as the sewage goes
down, air is drawn into the pores of the
bed, until finally a new supply is secured
and the operation can be repeated. The
sewage in filter beds spreads itself in thin
films over the sand grains, thus giving
bacteria an opportunity to develop, feed
upon the organic matter, and so break it
up as to cause the formation of new com-
pounds, until the organic matter is trans-
formed into inorganic.
If intermittent filtration were a mere
straining process, then the finer the sand
used the higher the degree of purification.
As already pointed out, it is a nitrifying
rather than a straining process, so the aim
must be to select a material of the size best
suited to that end, and which will at the
same time give the highest rate of filtra-
tion with the least expenditure of labor.
135
The finer materials give a luw rate of fil-
tration and a high degree of purity. The
sewage not only enters the sand slowly,
but a long time is required to drain it out
and renew the air. If crowded, poor re-
sults and ultimate clogging follow. With
coarse material the sewage passes through
too rapidly for nitrification to take place.
The drainage and air renewal can therefore
be effected quickly. It is thus evident that
with very fine material the sewage must
be applied slowly, with long intervals of
rest, while with very coarse material the
rate of application must be yet slower and
the rests far more frequent, though short.
As compared with material of a medium
size, the fine does not give sufficiently bet-
ter results, in actual practice, to warrant
its adoption, nor does the higher rate pos-
sible with the coarse material. The slow
rate of filtration and the tendency to clog,
on the one hand, and the very frequent
manipulation of gates to throw the beds
into and out of use, on the other, are
against the extremes. Moreover, the very
coarse materials are not so certain in their
136
removal of bacteria as fine ones. Here, as
elsewhere, a happy mean is to be sought.
R( jecting the extremes, the Massachusetts
State Board of Health, in its report for
1891, gives as the range of available ma-
terial sand having 10 percent, of its weight
composed of grains finer than 0.03 to 0.98
millinuUTS (0.0012 to 0.0392 ins.).
All material in filter sands finer than
O.C1 mm. (O.C004 ins.) is classed as organic
matter. The maximum size of the coarser
materials included in the above range was
about 0.5 in. in diameter, and the mini-
mum size of the finest material was 0.01 in.
in diameter.
As the work done by a filter is largely
determined by smalltr particles of sand,
and as a sand of uniform size is desired, the
Massachusetts State Board of Health has
adopted two standards for comparing dif-
ferent materials. The sand is subjected to
mechanical analysis to determine the per-
centages, by weight, of the total which
have grains below a certain diameter. The
diameter at the 10 per cent, point is taken
as the effective size, and the uniformity
137
coefficient is the ratio between the diameter
of the grains at the 60 and 10 per cent,
points.
Although a range in the size of the sand
grains may be allowed, the coarse and
finer particles should be fairly well inter-
mingled. Or, in other words, there should
not be strata of fine and coarse material in
a filter bed. The effect of stratification is
well expressed in the report of the Maspa-
Qhusetts State Board of Health for 1892,
as follows:
We have thus found that with a coarse material
above a fine one in the same filter thsre is a chance
of trouble from a clogging of tlio fine material be-
low the coarse ; and this is far wo.se than surface
clogging, for the latter can be completely remedied
by disturbing the surface or by scraping. We have
also found that a fine sand supported by a coarse
sand will keep its lower layer saturated and act as a
water seal, allowing the passage of water, but not
of air, and may in this way prevent tha necessary
circulation of air, and reduce the action of the filter
to mere straining.
******* *
The above examples are perhaps extreme cases.
With less marked differences in sand sizes, or with
gradual instead of abrupt transitions from ccarse
138
to fine, the causes of failure might be reduced, or
even in some cases entirely eliminated. In the
many cases where the fields available for sewage
filtration contain layers of various materials, the
different sands must be separately studied, in order
to detormine the probabla action of existing com-
binations; and in case the natural conditiors are
unfavorable, changes may be made which will im-
prove the action of the filter.
Not all communities are so fortunate as
to have ideal filtering material conven-
iently located for sand filter beds. If net,
then the choice may be between extending
the outfall sewer to a distance, with or
without pumping, and the adoption of a
site giving poor material and thus requir-
ing a larger area, or an inferior sand may
be the only kind available far or near.
The Lawrence experiments, to which ref-
erence has freely been made, have now
been carried on for about seventeen years,
and the results of fifteen years' studies of
a great variety of material under widely
different conditions are on record in the
published reports of the Massachusetts
State Board of Health. Actual results ob-
tained at city filter beds are also available,
139
so that with expert advice any community
may ascertain the approximate possibilities
of such materials as are at hand. While
a wide range of sands and gravels may be
counted on for giving good results, under
proper conditions, it is necessary to deter-
mine those conditions in order to know
what area of beds to provide, and how to
apply the sewage after the disposal grounds
are ready. The area and volume of sand
or gravel required for the intermittent
filtration of sewage are so large that the
transportation of material any great dis-
tance is out of the question. Generally
speaking, the beds are constructed in ma-
terial as naturally deposited, top soil and
loam of course being removed, together
with any pockets of other unsuitable ma-
terial.
The sewage is carried to the several beds
through open or closed channels built in
the embankments, with distributing cham-
bers where two or more beds join together.
Ordinary sewer pipe, half pipe, brick, con-
crete or even wood conduits may be used.
The distributing chambers may be of any
140
of the above materials, excepting sewer
pipe, but are generally of masonry. Wood
carriers or accessories are to be avoided, if
possible, on account of becoming sewage-
soaked, and thus liable to give off bad
odors.
The sewage should be brought onto the
beds so as to disturb their surface as little
as possible, and great pains should be taken
to distribute it evenly over the whole bed.
The underdrains should rarely, if ever,
be placed more than 50 feet apart, and
should be provided with manholes, or
inspection chambers at all intersections.
Underdrains are sometimes put much
nearer together than this. Their size and
depth will be governed by the amount of
effluent they are expected to remove, the
ground water level and possibly other local
conditions.
Before admitting sewage to the beds it
is generally advisable to screen it, at least
sufficiently to take out paper, rags and
large floating matter. The screening cham-
bers often serve to some extent as settling
tanks, but must be of pretty large size to
141
remove any considerable proportion of the
total matters in suspension.
Crops are sometimes raised on filter
beds, which is equivalent to practicing
broad irrigation in summer and filtration
the remainder of the year. The beds gen-
erally being thoroughly underdrained, and
the soil often more permeable than that of
a broad irrigation area, larger doses of
sewage may probably be applied to crops
on filter beds than those growing on ordi-
nary sewage farms.
The size of each bed should be such as
to permit an easy and equable distribution
of sewage over it. Where the total filtra-
tion area is small it must be divided so as
to permit of intermittent operation; that
is, if a bed is to be in use and at rest for
equal periods, then at least two beds would
be necessary, and so on according to the
relative periods of use and rest. Some
additional area should also be provided
for use while beds are being scraped or in
case of an emergency. If a large area is
laid out so that the size of the beds is lim-
142
ited only by convenience in use, then an
acre may be a very acceptable size.
As to degree of purification which may
be expected, and the rate of filtration, it
may be said, without going into details,
that practically all of the organic matter
may be removed from sewage by inter-
mittent filtration at rates approximating
100,000 gallons per acre per day, with the
best material and all conditions favorable.
With unfavorable conditions the rate may
be as low as 30,000 gallons per acre per
day or even less.
CONTACT BEDS.
To make possible an increase in the low
rates feasible with intermittent filtration
under even the best conditions, and also to
lessen the clogging of such beds (the two
efforts being largely identical), the Massa-
chusetts State Board of Health early began
to experiment with various preliminary
processes of sewage treatment, including
rapid filtration of various sorts and sedi-
mentation. A little later than these exper-
143
iments, and in some instances coincident
with them, a number of men began exper-
iments on their own account. These in-
cluded the late Colonel George E. Waring
in America, and Scott-Moncrieff, Dibdin
and others in Great Britain. In the latter
country intermittent filtration has almost
always been supplemental to broad irriga-
tion or sewage farming. The clayey na-
ture of most of the available land and the
density of population, made imperative
some change in sewage treatment in Great
Britain, and from about 1892 on gave rise
to a multiplicity of new schemes. Except
for details these schemes may be narrowed
down to contact beds and percolating fil-
ters, with the septic tank, which has been
described already, available as preliminary
to either of these, and also to broad irriga-
tion and sewage farming. Although, as a
rule, it is dangerous to credit these newer
processes to a single man, the contact bed
may be ascribed to W. J. Dibdin, for some
years Chemist to the London County Coun-
cil. The percolating filter, as described in
subsequent pages, cannot be so readily
144
credited to a single individual, since the
Massachusetts State Board of Health, Col-
onel Waring, Scott Honor i off and several
others had a hand in its development.
Both the contact bed and the percolating
filter, in their working form and the extent
of their use, are essentially British. It
may also be stated here that the septic
tank was combined with contact beds al-
most if not quite from the beginning of
the development of the former by Donald
Cameron.
The contact bed differs from the Ameri-
can type of intermittent filter in being
composed of much coarser material, gen-
erally enclosed by water-tight walls and
floor, the basin thus formed being pro-
vided with inlet and outlet gates. It also
differs from the intermittent filter in that
when in use the outlet gates are closed,
the bed filled quickly and held full for two
hours or so, then emptied quickly and kept
empty for two to four or five hours. The
series of operations is called a cycle, and
there are from two to four cycles in each
24.hours. The filling and emptying gates
145
are frequently worked automatically by
means of specially designed apparatus.
Contact beds are built -for operation
singly, in pairs and in groups of three;
the sewage in the last two cases passing
through two or three beds in succession.
When built in pairs a coarse and a fine
bed are provided. The coarse material is
approximately from 3-4 to 2 ins. in great-
est diameter, and the fine material from
1-4 to 1 in. The material now most com-
monly used in contact beds abroad is hard
clinker from soft coal or from refuse de-
structors, but coke, broken stonea gravel
and other substances may be employed.
Care should be taken to select a material
which does not readily disintegrate. The
coarse beds are sometimes called primary,
and the fine ones secondary, and sometimes
the terms single and double contact beds
are used.
The relatively large size of the material
composing these beds, and of the intersti-
tial spaces, permits quick filling and emp-
tying, and facilitates also a rapid renewal
of the air supply in the free spaces or pores
146
of the bed. The latter, in turn, favors an
enormous bacterial development and a cor-
lespondingly speedy breaking down and
transformation of the organic matter of
the sewage. As can be understood, hold-
ing the sewage in the bed in contact with
the bacterial agents gives the beds their
name.
Some form of preliminary treatment,
most commonly septic or sedimentation
tanks, has been found advisable before
applying sewage to contact beds, particu-
larly where only a single contact is pro-
vided. A high degree of bacterial removal
is not commonly effected by contact beds,
unless very fine material is employed, but
the organic matter in the sewage may nev-
ertheless be so transformed as to prevent
nuisance from subsequent putrefaction,
which is usually the main object of sewage
treatment. With such an object it is re-
ported that satisfactory results have been
obtained when passing settled or septic
sewage through double contact beds at
rates of from 500,000 to ], 000,000 gallons
an acre of total surface area.
147
PERCOLATING FILTERS.
Trickling, streaming and intermittent
continuous filters are some of the names
that have been applied to the last class of
filters awaiting consideration, but both
reason and usage are on the side of the
term percolating filters.
The essential features of percolating
filters are the use of large-sized material,
with the freest possible aeration and drain-
age, and a uniform distribution of the
sewage over the filter in drops, small
streams or spray. The sewage has an un-
interrupted passage through the drainage
system of percolating filters, just as through
intermittent filters, but tLe sewage is ap-
plied continuously, or with numerous brief
interruptions that break the continuity but
a little, in the case of percolating filters,
and the distribution is so even and rapid,
and the pores of the filters are so large,
that no sewage stands oa the percolating
filters, whereas the surface of intermittent
filters is often flooded hours at a time.
Percolating filters are generally built on
148
a solid floor of concrete or other water-
tight material, and enclosed by open-
jointed walls, the latter consisting of large
fragments of the medium, laid up with
open joints, or regular sized moulded or
cut pieces, laid pigeon-hole fashion. Tne
body of percolating filters is composed of
clinker, stone or other fairly cohesive ma-
terial, in particles from the size of a hen's
egg or a man's fist up to that of a man's
head, the larger pieces being placed at the
bottom.
Distributors for percolating filters may
be revolving radial arms of wrought-iron
pipe, perforated, or revolving radial weirs,
or fixed pipes provided with mere perfora-
tions or with spray nozzles. Drains, formed
in the concrete or other solid floor, or con-
sisting of specially moulded tiles, are used
to ensure thorough drainage.
The effluent from percolating filters,
even when the original sewage is given a
preliminary treatment, is usually high in
finely divided suspended matter, and also
in bacteria, but, as a rule, the effluent is
non-putrefactive and, being largely min-
149
eral matter, is easily removed or reduced
in quantity by a brief period of sedimen-
tation. The rates claimed for percolating
filters, dosed with septic sewage, range
from 1,000,000 to 10,000,000 gallons an
acre, but in the present state of the art
2,000,000 to 3,000,000 gallons seems high.
SEWAGE PURIFICATION PLANTS NOT
NUISANCES.
There is often much opposition to sew-
age purification plants by those living or
owning property near by on the ground
that such works must of necessity be a
nuisance. From experience gained by
visiting many such plants, both in this
country and abroad, and from studying
the subject in other ways for years, I know
that well conducted plants are entirely in-
offensive, either within or without their
enclosures. The employees about such
works are as healthy as similar classes
of men in other occupations, and
the same holds true of the families of these
men living on the European sewage farms.
150
The crops raised on sewage farms are as
safe eating as those of the same kind rais-
ed elsewhere. There are objections, how-
ever, to applying sewage to crops for hu-
man consumption which are to be eaten
without being cooked, but meat and milk
from sewage farms is usually as good as
when produced under other conditions.
Good design and construction, followed
by proper methods of operation, are all
that are needed to make sewage purifica-
tion a success, when once the right system
has been adopted and put into use. No
one system can be said to be the best for
all localities. The special problems of
each community must be met and solved
case by case and out of several systems
and combinations of systems the best for
the conditions at hand must be chosen.
THE PRESENT STATUS or SEWAGE
PURIFICATION.
In the United States, chemical precipita-
tion is no longer being adopted for new
plants. The septic tank has come more
rapidly into favor than contact beds or
151
percolating filters, but some men of prac-
tical experience seem strongly inclined to
plain sedimentation rather than the septic
tank. Comparatively few percolating fil-
Uis have been built, but small contact
beds are in use in a number of cases. In-
termittent filtration has for years been the
system most in use in America, and seems
likely to continue to lead where sandy land
for filter beds is available at a reasonable
price. In our Far West, sewage irrigation
is frequently practiced, but as a rule the
sewage is merely a substitute for water in
sections where irrigation is a necessity.
What appears to be the most successful
sewage farm in the United States treats
the sewage of Pasadena, Cal. Large and
paying crops of walnuts are raised each
year. On a visit to the Pasadena sewage
farm in March, 1905, the author was told
that a large number of orange trees would
be set out soon, and that sewage would be
put on these in the summer and on the
walnut trees in the winter.
Early in 1904 the author visited twenty-
four sewage works in Great Britain and
152
three on the continent of Europe. lie
found numerous chemical precipitation
plants and sewage farms still in use, at
the works visited and elsewhere, but many
of these were being converted to, or sup-
plemented by, the newer processes. The
septic tank was widely used. Contact beds
were numerous and percolating filters were
fast becoming so.
In America the septic tank, contact beds
and percolating filters are far less often
used, compared with other processes, than
in Great Britain. Local conditions abroad,
it should be remembered, are widely dif-
ferent from local conditions here. The
streams of Great Britain are small and the
population dense, requiring more sewage
works than are yet felt to be necessary in
the United States, and the clayey soil and
absence of good natural filtering ma-
terial in England and Scotland compels
the adoption of clinker, coke and other
substitutes. All these things should be
remembered in selecting a mode of treat-
ment and filter bed material for American
sewage works.
153
If it seem to any that the newer pro-
cesses of sewage treatment have been but
briefly discussed, the author would point
out the fact that in 1904 there was pub-
lished a whole volume in this series, enti-
tled, " The Treatment of Septic Sewage,"
by George W. Rafter, M. Am. Soc. C. E.
Later in 1904, the author of the book now
being brought to a close, embodied his re-
cent observations in Great Britain and at
Paris, Frankfort and Wiesbaden, in " Brit-
ish Sewage Works." Present day sewage
treatment, from the viewpoint of British
authorities, is set forth in Barwise's " The
Purification of Sewage," Rideal's " Sewage
and the Bacterial Purification of Sewage,"
and Dibdin's "The Purification of Sewage
and Water." The first American book on
sewage was Rafter and Baker's " Sewage
Disposal in the United States," a large
treatise on the subject published early in
1894, before the septic tank, contact beds
and percolating filters had come into pub-
lic view. A revision of this treatise is
under consideration.
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No. 47. LINKAGES: THE DIFFERENT FORMS
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No. 48. THEORY OF SOLID AND BRACED
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No. 49. MOTION OF A SOLID IN A FLUID. By
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No. 90. ROTARY MOTION AS APPLD3D TO
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No. 93. RECENT PRACTICE IN THE SANI-
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Dr. C. Meymott Tidy.
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