[Illustration:
A SUB-SURFACE IRRIGATION SEWAGE-DISPOSAL PLANT.
_Sewage._ _Frontispiece._
]
Practical Methods of Sewage Disposal
FOR RESIDENCES, HOTELS AND INSTITUTIONS
BY
HENRY N. OGDEN
M. AM. SOC. C.E.
_Professor of Sanitary Engineering, Cornell University_
AND
H. BURDETT CLEVELAND
ASSOC. M. AM. SOC. C.E.
_Principal Assistant Engineer, New York State Department of Health_
_FIRST EDITION_
_FIRST THOUSAND_
NEW YORK
JOHN WILEY & SONS
LONDON: CHAPMAN & HALL, LIMITED
1912
Copyright, 1912, by
HENRY N. OGDEN
and
H. BURDETT CLEVELAND
PUBLISHERS PRINTING CO., 419–421 LAFAYETTE ST, NEW YORK
------------------------------------------------------------------------
CONTENTS
CHAPTER I. INTRODUCTORY
PAGES
The problem of sewage disposal. Composition and character of 1–13
sewage. Action of bacteria. Soils and their value for sewage
treatment. Three essential conditions for effective sewage
purification. Rates of operation. Preliminary and final
treatment.
CHAPTER II. THE SETTLING TANK
Function and capacity of settling tanks. Their construction. 14–36
Siphon chambers. Use of concrete. Pipe connections. Roof.
Baffle boards. Imhoff or Emscher tanks.
CHAPTER III. VALVES, SIPHONS, AND SIPHON CHAMBERS
Hand valves. Gate valves. Flap valves. Various types of 37–54
siphons. Alternating and plural siphons. Air-lock siphons.
Dosing apparatus.
CHAPTER IV. SUB-SURFACE IRRIGATION
Advantages of sub-surface irrigation for sewage disposal. 55–72
Details of system. Tables for use in constructing. Siphon
chambers. Sub-surface tile. Alternate use of separate
portions of area. Underdrainage.
CHAPTER V. SEWAGE FILTERS
Relative efficiency of various types. Sand Filters. Tables for 73–97
use in constructing siphons. Dosing and distribution methods.
Maintenance. Contact Beds. Methods of construction. Alternate
and timed siphons for filling and discharging. Table for use
in constructing. Sprinkling Filters. Their construction and
operation. Complicated and undesirable for small
installation.
CHAPTER VI. BROAD IRRIGATION
Fertilizing elements in sewage. Value of sewage for irrigation. 98–111
Area required for sewage irrigation. Methods of applying the
sewage. Maintenance of irrigated areas.
CHAPTER VII. ESTIMATES OF COST
Cost of material: of laying sewers and drains; of sand; of 112–128
excavating and refilling; of rock excavation; of concrete
work; of valves; of dosing devices; of filling material for
beds; of finishing and cleaning up. Table to show items to be
considered in estimate of cost.
LIST OF FIGURES
A sub-surface irrigation sewage-disposal plant _Frontispiece_
FIGURE PAGE
1. Plan of settling tank 15
2. Longitudinal section of settling tank 17
3. Sketch of settling tank with longitudinal 19
partition wall
4. Forms used for building side walls for concrete 23
tank
5. View of settling tank, showing baffles, sludge 26
pipe, drain pipe, and inlet and outlet pipes
6. Section showing tank with concrete roof and form 28
for constructing roof
7. Form for manhole opening 30
8. Plan and longitudinal section of modified Imhoff 33
tank
9. Vertical cross-section of modified Imhoff tank 34
10. Sludge valve for floor of tank 38
11. Sludge valve for side wall of tank 39
12. Sluice gate valve made by Coffin Valve Co 40
13. Ordinary gate valve 40
14. English slide valve with wedge-lock handle 41
15. Flap valve attached to length of sewer pipe 42
16. Flap valve with metallic seat attached 43
17. Flap valve with loose-link hinges 44
18. Intermittent dosing apparatus made by Ansonia 45
Manufacturing Co.
19. Simplest form of automatic siphon 46
20. Van Vranken automatic siphon 47
21. Miller automatic siphon 48
22. Double alternating siphons of the “Merritt” type 49
23. Triple alternating siphons of the Miller type 50
24. Single “Merritt” automatic siphon 51
25. Air-lock siphon for admitting and releasing 52
sewage from each one of four beds in regular
order
26. Plan and section of sub-surface irrigation system 61
27. Plan and section of a portion of a sub-surface 62
irrigation system
28. Y-branch of vitrified tile pipe 64
29. Eighth bend of vitrified tile pipe 64
30. Sub-surface tiling 65
31. Photograph of tile laid as if for sewage disposal 66
32. Sub-surface tiling with broken stone or gravel 67
surrounding pipe
33. Sub-surface systems on irregular ground 68
34. Special casting of double Y-branch with swinging 69
gate
35. Double Y-branch with valves on branches of main 70
carrier
36. Sub-surface tiling system with underdrains 71
37. View of sand-filter beds for village in 75
Massachusetts
38. Layout for intermittent sand filtration 78
39. Intermittent sand-filtration beds 79
40. Portion of distributing troughs for sand filters 80
41. General view of disposal plant at Bedford 81
Reformatory
42. View of sand filter with distribution trough. 82
Settling tank is at the end of the bed
43. View of diverting manhole 83
44. Plan of diverting manhole 84
45. Five-way diverting manhole 85
46. General plans of contact-bed system near Albany, 89
N. Y., opposite page
47. View of sprinkling filter at Dansville, Pa., in 95
winter
48. Distribution of sewage and arrangement of check 106
levees on a hillside
49. Distribution of sewage on a hillside of moderate 107
slope
50. Square beds for orchards according to some 108
Western practice
51. Grain-field in spring in process of irrigation 109
PRACTICAL METHODS OF
SEWAGE DISPOSAL
FOR
RESIDENCES, HOTELS AND INSTITUTIONS
CHAPTER I
INTRODUCTORY
The problem of sewage disposal for a single house differs from the
corresponding problem for a city chiefly in two ways: first, because in
the city it is becoming, if it has not, indeed, already become, a
necessity, and city authorities, though somewhat reluctantly, are
willing to grant the necessary appropriation to secure engineering
advice which will solve the problem in a scientific as well as economic
fashion. In the case of a single house, whether a farm-house or a villa,
the necessity of employing competent engineering advice has not been
generally recognized, and no attempt has been made to solve the problem
of sewage disposal in a scientific manner.
Cesspools have been considered the only way of caring for sewage in
places where a running stream was not available, or where attempts were
made to protect such a stream from pollution, and while, in these last
few years, crude attempts have been made to utilize the so-called septic
tank, such attempts have generally been so unintelligent that the
results have been anything but satisfactory. Since it has been
understood that insects, such as flies and mosquitoes, play an important
part in the transmission of disease, the danger of overflowing cesspools
and of open ditches in which stagnant sewage is present, has been
appreciated; also the higher standards of living which have made
themselves felt throughout the rural community have demanded in
farm-houses and country homes sanitary conveniences which have hitherto
been wanting.
Gradually every house is using more and more water for various purposes,
and living conditions, which in the past tolerated a scanty supply drawn
from a pump, are no longer endured. The increased water supply and the
demands of extended plumbing mean a greater amount of sewage—so great an
amount that, in many cases, soils which could receive and digest the
waste waters from houses supplied by wells are clogged and made
impervious by this greater amount.
Further, the danger to wells from the infiltration of cesspools is more
feared, and it is understood as never before that in order to maintain
the highest degree of health in a family the drinking-water used must be
above suspicion and not subject to contaminating influences in the
vicinity.
Again, communities are being aroused to the intrinsic value of
maintaining streams in a pure condition—partly because of the value of
fish and ice coming from the streams themselves, and partly on the broad
ground that watercourses belong to the country as a whole, and must be
kept pure for the sake of succeeding generations, not spoiled for them
on account of the selfishness of a few at the present time.
Thus it is that to-day the problem of sewage disposal, while arousing
general interest, is recognized as one which requires more than the
common sense of an average person, that the force and principles
involved are understood to be not those in common use, and that, for
successful disposal of sewage, special knowledge and judgment are
required.
Whatever the character of the sewage and whatever the kind of soil
available for treatment, the method of dealing with sewage most obvious
to most people has been to discharge the sewage directly into the
nearest watercourse. This has been the practice of cities as well as of
individual houses in the past, and the practice is very difficult to
check because of the economy of this method of disposal. In many cases
there is no objection to this method, and where a large stream is
available, where no use is made further downstream of the waters for
drinking purposes, and where the volume of water in the stream is
sufficient to dilute the sewage to a point where no odors or
objectionable appearances result, it would seem most uneconomical to
adopt any more complicated method of disposal than by simply carrying
the outfall pipe into the main bed of the stream.
In New York State, and in a number of other States, the number of which
is continually increasing, such direct discharge, however, is not
permitted by law except under certain conditions. In New York State it
is required that any house, butter or cheese factory, manufacturing
establishment, or village shall obtain the permission of the State
Commissioner of Health before such a method of discharge be adopted, and
in order to obtain this permission it must be definitely shown that the
conditions of the stream are such that no reasonable objection to this
method could be urged. The policy of the various Departments of Health
in the United States is gradually becoming more and more rigorous in the
matter of prohibiting the discharge of crude sewage into watercourses,
and it is wise to make very sure that the discharge of sewage into
streams is above the suspicion of a nuisance before adopting this as a
suitable method. Rather would it seem better to provide for some method
of treatment and allow only purified sewage to go into the stream than
to run the risk of being forced in a few years to reconstruct the entire
line of outfall pipe, with perhaps an entire reconstruction of the
plumbing within the house.
The problem of treatment is the question of so modifying the character
of a large volume of dirty water that it shall neither injure the
quality of any drinking-water into which it may be discharged, nor cause
objectionable odors, nor present disagreeable appearances in any body of
water into which it may be emptied.
In order to properly understand a reasonable method of treatment some
consideration must be given to the composition of sewage. This is
chiefly water with which is mixed a small amount of animal, vegetable,
and mineral matter. Roughly speaking, the amount of mineral dirt is
about one tablespoonful to a barrelful of water, and the combined amount
of animal and vegetable matter amounts to another tablespoonful. It
seems almost impossible that so small a quantity of organic matter as
one tablespoonful in a barrel of water could cause offense in any way,
and yet engineers, city officials, and householders know by bitter
experience that, when spread out on the surface of the ground or when
allowed to stand in pools, water so polluted will undergo putrefaction
resulting in most disagreeable odors and in complete stagnation. The
problem of sewage treatment, then, consists in removing from the
barrelful of water, the tablespoonful of organic dirt, whether animal or
vegetable, in such a way that no odors shall be occasioned by the
process and at the same time so that the cost of the process may be a
reasonable one.
Unfortunately, the greater part of this organic matter is in solution,
dissolved, like salt in water, so that, though undeniably present, it
must be removed by some process more complicated and less obvious than
that of simple straining. It would be comparatively simple if the
polluting substances remained floating or suspended in the water. Then
they could be strained out through a fine sieve or settled out in a
tank, either with or without the aid of chemicals. But for particles in
solution, straining, by itself, is useless and, while in large plants
frequent use is made of sieves as a complement to the main process of
purification, in small plants it is of so little value as hardly to
deserve consideration.
Another factor enters to lessen the value of the use of screens or
sieves in an installation for a single house. A great deal of the
organic matter found in sewers requires both agitation and time for its
subdivision into particles small enough to be acted upon in any process
of purification adopted. If a screen is used, large particles of
putrescible matter are held on the screen since not enough time has
existed to break down their mass, and thus the screen itself becomes a
most emphatic disturbance and a most objectionable feature of the
purification plant.
For efficient purification, therefore, some method of reducing and
modifying the character of organic solids, particularly those in
solution, must be selected. In seeking a method by which this may be
accomplished, scientific men found years ago that this very process was
being carried on continually by natural forces, although at a very slow
rate of purification. All organic matter, however formed and wherever
present, is subject to the natural forces of decay. Fruits, vegetables,
and meats of all kinds, exposed to the air, rapidly lose their original
character and form and in the course of time disappear entirely. Except
for this provision of nature, the accumulation of organic wastes since
the beginning of the earth’s occupation by human beings would be so
great that the earth would be uninhabitable on account of the deposits
of waste matter which would have formed by this time. Nature, then,
recognizes the need of disposing of organic wastes, and her method is
the one which apparently must be followed by human beings if successful
treatment is to be secured.
Only a few decades ago, it was found that this process of decay was due
to the activity of very small organisms known as bacteria, and their
agency was proved by experiments which showed that if vegetables or meat
were kept free from bacteria, no decay, fermentation, or putrefaction
took place. It was proved that the air itself was not responsible
because in certain experiments air was allowed to enter through a
filtering medium fine enough to strain out the bacteria and no decay
took place, although oxygen and air were both freely admitted. It is
well understood by the housewife that fruits can be kept indefinitely if
they are cooked sufficiently to kill any bacteria present and then
sealed in bacteria-free, air-tight jars. When such preserves spoil, it
is because some bacteria were left in the jar or have since been
admitted through an imperfect top. When decay is allowed to proceed, the
obvious result is, first of all, a softening of the material, as in the
case of a rotten apple, a liquefaction, as it is more technically known.
Following that part of the process is a gradual breaking down of the
material, the residue being of an earthy character which is assimilated
by the soil into which it falls.
The bacteria required for the putrefaction of organic matter are among
the most widely distributed of all the micro-organisms. They are always
found in the air, except on mountain tops, in deserts, and over the
ocean. They are very numerous in surface waters, such as streams and
ponds, and their relative number everywhere increases as the amount of
organic matter increases, so that the greater the need for them the
greater is their number. It has been found that the great majority of
these bacteria require air for their energetic development, and this
fact is most important when it comes to the practical construction of a
piece of apparatus for making use of these bacteria. It has also been
found that, for several reasons, these bacteria work most effectively in
the soil and can take care of a larger quantity of organic matter there
than elsewhere. This is partly because in the surface layers of the
soil, particularly where that soil has been cultivated, a great number
of the particular bacteria involved in decay are always to be found.
Pure, clean sand from the desert contains almost none of these
beneficent bacteria. Rich garden soil is fairly teeming with them, so
that, curiously, the more organic matter and the more bacteria present
in any soil, the more active that soil will be in taking care of other
organic matter.
Then, again, the soil particles, particularly in sandy soil, are so
separated as to allow between them a certain and appreciable amount of
air, and by means of this air the activity of the bacteria is made
continuous and the products of their activity utilized. Without such an
admission of air, the bacteria are choked and diminish rapidly in
numbers. There is, however, a definite degree of purification and a
certain quantity of organic matter which can be taken care of by the
bacteria incident to any particular soil. Up to that quantity
purification proceeds more or less satisfactorily according to the
intelligence shown in feeding the bacteria in such a way as suits their
convenience. If, however, that quantity be exceeded, all purification
stops, the bacteria are apparently discouraged, and no further
improvements can be expected. A fine-grained soil will not be so useful
as a coarse-grained soil because the former does not allow sufficient
air in the interstices of its soil particles. Another practical reason
for not making use of soils of fine grains is that such soils can absorb
only a small amount of liquid because of the mechanical construction of
the material. On the other hand, soils whose grains are too coarse are
undesirable because their mechanical construction is such that the
liquids containing organic matter in solution pass through so rapidly
that time enough is not given for bacterial action.
As a result of the principles just enumerated, it may be said that there
are three distinct and essential conditions for the successful disposal
of sewage through the soil. These three conditions are, first, a rate of
application suitable to the soil which it is proposed to use; second, an
interrupted or intermittent delivery of the sewage so that the bacteria
can obtain, between consecutive doses of sewage, the necessary amount of
oxygen for their own preservation and well-being; and, third, a resting
period in which is carried forward that intimate association between the
partly decomposed organic matter and the oxygen or air present in the
pores of the soil by which the final oxidation is obtained.
The rate of application varies, as already indicated, with the size of
particles found in the soil, and it should also vary with the
purification desired. The larger the particles, the higher may be the
rate of application, but less efficient will be the process. With grains
of sand as fine as 1/200 of an inch, and with a rate of application not
greater than five gallons per square yard of surface per day, filtration
through such an area has been proved to be capable of removing from the
foulest sewage all the objectionable material and converting the liquid
into what is an equivalent of the purest spring water. If the rate
appropriate to this particular soil is exceeded, the efficiency
decreases, and the unmistakable and inevitable result is to stop all
purification and convert the filter into a stagnant cesspool. If, to
take the other extreme, the soil particles are increased until they are
as large as hen’s eggs, then, if the rate of application is not greater
than 200 gallons per square yard of surface per day, and if the method
and rate of application are suitable to this large amount, the resulting
effluent is sufficiently freed from its objectionable matter so that the
liquid can be turned into any body of water without danger of odors or
other nuisance. If this rate is exceeded, or if the method of
application is not carefully considered, the resulting effluent is foul
in the extreme and the process itself becomes a nuisance.
It can be seen by this brief explanation that it is not possible to
assign any particular rate of application to any particular kind of
treatment, since in all the methods of purification which have been
worked out considerable variation in the details of that particular
method have been practised. It will be possible, therefore, in
succeeding chapters to indicate by the size of filters recommended only
limiting or average values for rates of purification, since those rates
are always dependent upon other factors than the particular method being
discussed. It must also be remembered that soils may exist which have no
porosity whatever, and through which it is impossible for sewage to make
its way. Such soils are not available for sewage purification, and, no
matter how small the rate or how careful the method of application, such
areas will fail to produce any practical purification. Soils like clay,
peat, and fine water-deposited silt are of this sort. Clay soils may
sometimes become pulverized by cultivation so that they will ultimately
be able to take care of a moderate amount of sewage. In such a case it
is possible to dispose of sewage successfully in the top six inches of
soil which, by continual cultivation, has been made out of the stiff
clay. In such cases, the difficulty is not that of oxidizing the sewage,
but that of taking care of the effluent, which must be held between the
cultivated soil and the raw clay underneath.
The second requirement mentioned is secured by discharging the sewage
onto the soil area at intervals, the number of doses per day depending
upon the size of particles in the bed. There has been a general
principle established that the size of these doses ought to be smaller
as the size of the particles increases, so that, whereas in the case of
sand beds the total daily dose is usually divided into from one to three
parts and each part delivered onto the bed with an appropriate interval,
in the case of coarser materials used for sprinkling filters, the time
interval between doses is much reduced and in some installations
recently constructed in England that interval has been measured in
seconds. The variations in the rate of flow of sewage onto any filter,
however, are so great that any such requirement as designing discharging
apparatus to work at intervals of a few seconds is useless, and if as
small an interval as one minute is provided for the coarsest material
for the maximum rate of flow at any time of the day, the installation
will probably be successful for the lesser rates occurring at other
times of the day. As an indication of the way in which this modification
is made, it is customary, when the size of soil particles is that of
peas, to make the interval between successive discharges about one hour,
so that the dose applied at any one time would be equal to 1/24 of the
daily volume. With gravel filling, the particles being the size of
English walnuts, the interval between doses is shortened to five
minutes, and the amount of any one dose is thus made 1 about 1/280 of
the total daily volume. With the coarser filling, as when a size as
large as hen’s eggs is used, the interval would be cut down to about one
minute. It should be added that the intervals last mentioned are
characteristic only of some devices used for dosing sprinkling filters
and that there is a wide divergence of practice among engineers when
dealing with any particular size of sand or stone particles in all kinds
of filter beds.
The third requirement, namely, the occasional resting of the bed, is met
by providing some additional area over that theoretically required, so
that the flow may be diverted from part to part of the total area (which
is usually divided into beds for this purpose), and in this way each
part is allowed, in turn, a period for resting. For example, if the
required area be divided into two beds and a third bed added equal in
area to one of the two and a regular rotation of dosing be practised,
each bed would rest not only the time between the regular twelve-hour
period dosing, but might also be given a complete rest, occasionally,
for an extended period. This third requirement is probably less
imperative with the coarser particles and there are many examples of
coarse-grained beds which have been continuously operated for a period
of years. It is found, however, that with such treatment clogging is
inevitable, and that such clogging is partially relieved by a period of
rest somewhat proportional to the length of time the beds have been
operated. It is, then, only shortsighted policy to economize at the
beginning and attempt to save money by not building an additional area,
since the clogging of the whole plant is bound to occur in the course of
time, and then another plant must be built or the material forming the
bed taken out, washed, and replaced. Otherwise the sewage must go
unpurified to the outfall while the bed is recovering from the long
period of overwork.
It is convenient to divide sewage purification into two processes, the
preliminary process and the final, or finishing process, and, while the
preliminary process, in itself, never accomplishes purification, yet it
is of considerable value in facilitating and increasing the rate and
efficiency of that purification. The most common preliminary treatment
is sedimentation, by which the larger solids in suspension are allowed
to settle in a tank or tanks so that the filter beds later used are
relieved from the accumulation of those deposits. Under the name of
septic tank such a receptacle for suspended solids has been exploited as
a complete method of purification, and many underground tanks have been
constructed in various parts of the country which have, at the time of
their installation, been considered competent to furnish all the
necessary purification. When it is remembered that less than one-half of
the organic matter in sewage is in suspension and that the best results
in any sort of a tank succeed in depositing only one-half of those
suspended solids, it can readily be seen that a tank, whether called
septic or settling, cannot be a complete method of treatment. In
reality, such a tank does little more than take out from the sewage the
greasy material and a certain proportion of the suspended matter.
Whatever part of this is organic matter may, by a particular arrangement
of the tank, be considerably reduced in quantity, so that the intervals
of cleaning can be extended, but in every tank the removal of the
deposits is necessary, and subsequent treatment is required if adequate
purification is accomplished.
The final, or finishing, process may be carried out according to any one
of several methods. It may be done by discharging the tank effluent into
a system of agricultural drains laid just below the surface of the
ground, called sub-surface irrigation. It may be done by removing the
top soil from a bed of sand placed by nature, and needing little except
suitable surface distribution to insure the most efficient purification.
For a small plant, instead of a sand filter, for which the sand is found
naturally in a suitable location, an artificial filter may be built by
preparing an enclosure and carting in sand for filling.
Where no sand is available, or where its use would be uneconomical,
broken stone may be used to ensure final treatment. With stone, on
account of its large voids, the enclosure must either be water-tight,
and the outlet pipe must be provided with a valve or other device so
that the sewage under treatment may be held in the enclosure or tank
long enough to deposit the solids in suspension and to be acted on by
the bacteria concerned. This method is known as the contact bed
treatment. Or, finally, the desired results may be obtained by spraying
the sewage onto a deep layer of broken stone, the method being called
the sprinkling filter treatment.
The choice of the final treatment, in any particular case, depends on
the character and slope of the ground, on the availability and cost of
sand or of broken stone, and on the amount of sewage to be treated. It
is hoped that the following pages will give to the reader both an
intelligent appreciation of the advantages and disadvantages of each of
the several methods of sewage purification discussed, and also
sufficient insight into the necessary details of construction so that
the method chosen can be put into successful operation.