Improvements in the Treatment of Sewage and in Apparatus therefor.
Year: 1895

page_text: COMPLETE SPECIFICATION.
Improvements in the Treatment of Sewage and in Apparatus
therefor.
I, SYDNEY PITT, of Sutton, in the County of Surrey, Gentleman, (a commu-
nication to me from abroad by The Drainage Construction Company, of Boston,
in the State of Massachusetts, United States of America,) do hereby declare the
nature of this invention and in what manner the same is to be performed to be
particularly described and ascertained in and by the following statement :-
This improvement relates to the preliminary cleansing of sewage, to means for
securing its proper aeration and distribution so that it may be filtered properly and
absorbed in irrigation or otherwise disposed of, and to the means of purifying the
filtering or straining apparatus, these parts forming, when used together as herein
described, a sewage disposal plant of great value.
The invention will be understood from the drawings in which
Fig. 1 is a longitudinal section showing an irrigation plant embodying my
invention in its most complete form;
Fig. 2 is another form of irrigation plant in which the filtering mechanism is
operated;
Fig. 3 a portion of the vertical section of a sewage tank and means for aerating
and discharging its contents;
Fig. 4 is a section of a barrier to be used in the irrigation area;
Fig. 5 is a cross section of an improved form of absorption drain;
Fig. 6 is a cross section of a pair of filter beds; Fig. 7 being a plan of a
portion of these beds and Fig. 8 a longitudinal section of a portion of one of
the beds;
Fig. 9 shows another form of filter.
The elements of this invention are constructed for the purpose of separating the
solids from the liquid and so oxydizing the mass that putrefaction will be prevented
and a substantially pure effluent will result. My invention also relates to a new
process of purification of the sewage and also to a process for cleansing the filter
when it has become foul with the accumulation of sewage, to give a clear effluent.
Unless the stream of sewage when it comes from the sewer, is full and constant,
it is generally best to collect it in a tank from which it may be discharged in a
body. Such a tank is shown at A and as this is a point where the sewage may be
given a preliminary aeration, I prefer to combine with this tank suitable apparatus
for this purpose, as for example, an air pump indicated at B. An air pipe C leads
from this pump directly into the lower part of the tank and it may be provided
with suitable branches so as to distribute the air well through the tank, the ends
being closed by perforated caps so as to discharge the air in the form of spray.
The same result may be accomplished by leading a branch D from the main so
that it will deliver sewage above the full line, preferably in a direction downward
and forward. The stream of sewage from this branch carries air with it into the
tank, producing an aerating effect and giving a thorough stirring up to its contents.
A valve F controls this branch.
Having been given its preliminary aeration in this tank, the sewage is discharged
by the pump G into a distributing well H. located near the highest point of the
irrigation field. In its passage it may be passed through a strainer and a filter.
The strainer is shown at J and cousists of a barrier of broken stone (road metal)
which will hold back the coarser matters contained in the sewage. It is desirable

page_text: to have a number of these strainers so that when one strainer or section has
accumulated its quota of coarse matters the flow may be transferred to a second
section &c. so as to give ample time for the decomposition of what has been
retained in the section thrown out of use, and from which the liquid has drained
out. The voids between the stones in such a strainer should be sufficiently large
to allow its thorough ventilation when not in use, so that the oxydation or
decomposition of the particles which are retained by it will be thorough. When it
has been dried it can be easily shovelled over and will free itself, being so freshened
that it can be used again shortly.
Ordinarily and preferably, the next step in the process is that of filtering. For
this purpose, I prefer a pair of filters such as are shown in Figs. 6, 7 and 8.
Each filter is constructed as follows:-An excavation is made say six feet deep
and ten feet wide and as long as seems desirable, in view of the quantity of sewage
to be filtered.
In the bottom of this excavation are longitudinal pipes K for draining, each pipe
being partly imbedded in the bottom of the trench, the joints between the sections
of the pipe being left open. These drains are for the purpose of securing the free
removal of the effluent."
The bottom may then be covered to a depth of 8" more or less, with broken
stone (road metal) indicated at L or otherwise provided with a chamber for
receiving the distributing compressed air during the process of filtering. This
layer of broken stone affords free drainage for the filter with sufficient voids for
the ready distribution of air to be introduced.
Above this is a layer of coarse gravel M of such size and arrangement as will
prevent the material of the filter from being washed into the spaces between the
broken stones below. The trenches are then filled with clean sand N or other
suitable filtering material. As the filter is intended to receive compressed air and
discharge it at its upper surface and yet allow the effluent to escape below, I prefer
to trap it in the following manner.
A dead water trench O is formed by an outfall dam P at the end of the filter,
and the terminating wall Q of the filter is constructed to dip into this dead water
sufficiently to form a gate or trap to retain the compressed air forced into the
chamber L and compel it to pass up through the voids in the filter, and at the same
time to allow the effluent to pass off. The drain pipes K deliver the effluent into
the trench O.
The filter beds are best constructed in pairs in parallel lines divided by an
embankment so that the flow may be easily diverted from one bed to the other,
and means for aeration during the filtering process are provided by pipes R which
convey air under pressure from a suitable compresser throughout the filter, and
I provide an air chamber L under the filter, for the distribution of the air through
the filtering medium. The air chamber, however, is not always necessary.
The sewage is delivered to these filter beds by means of a channel T on the bank
of the outer side of each of them with branches T₁ at short intervals to secure an
even distribution of the sewage over the whole length of the beds. The sewage is
delivered on top of the trench and the liquid trickles downward through the
filtering material. Air is forced into the filter during the filtering operation and
escapes up through the voids in the filtering material, thus giving an opportunity for
thorough oxydation of the sewage. The sewage should not be delivered too
rapidly for fear of clogging and the filter beds should be used alternately each bed
being used for example, a day or two at a time. This process of aeration, while
the sewage is moving slowly through a filter or other apparatus for breaking up
and retarding the sewage flow, is new and is a very important feature and may be
carried out with other apparatus than that described.
The filtering operation having. taken place, the sewage may be delivered into
suitable absorption drains or may be conveyed to the irrigation field.
A convenient form of absorption drain is shown in Fig. 5. A trench is dug,
preferably to the depth of a foot and to the width of somewhat more than a foot.

page_text: Its bottom is filled to a depth of about 2" with crushed stone or coarse gravel, or
other suitable material, and on this is placed a tile drain U preferably of the horse-
shoe pattern and say of about 4" opening. The trench is then filled to within a
few inches of the surface of the ground with crushed stone and the remainder filled
in with earth and covered with sod as desired. This is mainly useful where a small
amount of sewage is to be cared for.
As a rule it is desirable to use an irrigation field. Such a field should have, if
possible, considerable inclination and should be sufficiently wide to allow it to be
used in sections so that full opportunity for absorption should be given. It is
desirable always that the sewage should be first collected in the well H or other
distributing device near the highest level. Below that is best located a strainer J
which in this instance, if a filter has been used, serves to break up and distribute
the strong flow from the well H and cause the sewage to be uniformly led to the
ground below. Such a strainer so placed will sometimes serve all the purpose of
an aerating filter.
V
As shown in Fig. 2, the irrigation area is divided by raised embankments V,
into three substantially equal parts. The lines marked 25, 26, and 27 in this view
indicate contours or lines of equal elevation. The heavier horizontal lines marked w
are embankments to catch the sewage in its flow down the slope, so as to prevent
its gathering into channels, giving it a uniform flow over or through each
embankment as the same is reached.
I prefer to use embankments constructed as shown in Fig. 4. They are made of
crushed stone, gravel, coarse sand, railroad cinders or other porous material, which,
while offering sufficient resistance to the flow to accomplish the equalizing effect,
are sufficiently porous to allow the sewage ponded behind the embankment to leach
away after the main flow has ceased. If the material is light or unstable, it may
be held in place by a paving or backing of stones or other suitable material
adequate to withstand the flow of the irrigating stream passing over the bank.
The depression thus formed above the embankment serves the purpose of the
furrow sometimes used in sewage distribution.
The operation of the system, as more especially shown in Fig. 1, is as follows:-
Sewage as produced is discharged into the tank until the tank is nearly full. Air
is introduced into the sewer either by the air pump or by throwing a stream of
sewage from the branch D in the manner above described, this process of aeration
continuing for some time until a considerable movement of sewage has been caused
and the whole body has become thoroughly aerated and the gaseous products of
decomposition have, to a large extent, been driven out.
The sewage is then driven through a force main E to the strainer J where the
large materials are held back, after which it is distributed by means of the
carrier T and its branches T on the top of the filtering bed. The sewage will
diffuse itself through the filtering material, the gravel and the broken stone, the
effluent flowing into the trench O and out under the wall Q through the trap
formed by the dam P.
During this period, while the sewage is passing through the filter, air is forced
into the air chamber L and is compelled to rise, being retained in the trench by
means of the trap formed by the wall Q. An oxydizing process will be set up as
the air comes in contact with the stream of sewage which has been well broken up
in the filter and the sewage will be purified, the degree of purification depending
upon the adequacy of the air to supply the oxygen needed for purification. If but
little sewage is applied, there may not be any necessity for forcing air into the
filter, as the air which the filter would naturally contain would be sufficient to take
care of the supply of sewage, but under ordinary conditions, the use of an air
compresser would be necessary.
From the filter the effluent, which by this time has become very thoroughly
purified, passes to the absorption drains, where it leaches away or it is conveyed to
the well H, from which it flows down the slope of the irrigation area, where its
How will be equalized and restrained by the porous embankments u, so as to be

page_text: distributed with desired uniformity over the surface. The accumulations of sewage
will overflow the embankments or will gradually leach away. The upper side of
the embankments may be raked over when necessary to clear them.
There is shown in Fig. 9 another form of filter which also may be used under
certain circumstances. It has a tight hottom W, above which is supported a
perforated false bottom w, which forms with the bottom W a chamber to assist in
the free distribution of air. On this false bottom is placed the layer M of coarse
material which interrupts the direct passage of air, causing it to be diffused more
or less through the filter. On this is a layer N of filtering material. The filter is
divided by a diaphragm Wi
W2 is an opening for use in draining the tank. It should be provided with
suitable means for closing it and be connected by suitable drain pipe with the
irrigation area. R is an air distributing pipe for connection with the air
compresser.
This tank is fed with sewage from above, as before. The opening W2 being
closed, the sewage flows down on one side of the diaphragm W' and up on the other
side, escaping through the spout Q', to the irrigation area or well.
Its passage
through the filter is very slow and its suspended matters will attach themselves to
the particles of the filtering medium, causing a certain amount of clarification of the
liquid, and purification will be aided as before by the introduction of compressed air
during the filtering process.
In time the voids of the filtering medium in any filter will become clogged by the
accumulated matter and the clarification of sewage will become insufficient. It
should then be thrown out of use and drained. The draining process will be slow
as the upper surface of the filtering medium will be more or less gummy and it will
take considerable time for the air to permeate the filtering medium sufficiently to
cause the entire displacement of the liquid. The solid accumulated particles
attached to the particles of the filter will retain a considerable portion of the liquid,
and although exposed to the air which has taken the place of the escaped liquid,
being moist, will not be readily acted upon by it. If the filter has a draining outlet,
it should now be closed.
Bacterial oxydation will be set up to a certain extent, but cannot be thorough as
the volume of contained air is insufficient to supply the requisite oxygen, nor is
there any circulation such as will cause the displacement of the exhausted air
with a fresh supply. In order to continue and to increase this oxydation, air from
the air compresser is now forced into the interior of the filter so that it will
circulate slowly through the filter and mix thoroughly with the accumulated solids
upon which it acts.
After the process of oxydation has gone on for a sufficient time, the air supply
being shut off, the filter may, if necessary, be washed out by passing clean water
through it, and it may be again put into use. This process of cleaning a filter by
enforced aeration, is also new and of great value and may be carried out in a
variety of ways, as will be readily understood.
I do not wish to confine myself to the precise means that I have described for
aerating the sewage in the tank. The same effect may be produced, though less
conveniently and completely, by a propeller wheel or other mechanical contrivance
for mixing air with the water. I claim broadly mechanical means for the forcible
aeration of sewage in a tank or reservoir, preparatory to its disposal by surface and
subsurface irrigation. Neither do I wish to confine myself to the aeration of
sewage to be disposed of only by irrigation. The tendency of aeration to postpone
the putrefaction of sewage indicates that such treatment would be a highly
advantageous one preparatory to the delivery of sewage into rivers or harbours.
Neither do I wish to confine myself to the arrangement of pipes shown for the
aeration of filtration beds. The same character or effect may be produced by
causing the pipes R, R to be discharged into the material of the filter, rather than
into the voids of coarse material underlying it; or the pipe R may be laid under,
or in, the filter, discharging its air through perforations.

page_text: I claim broadly the forcing of air under pressure under or into the filtering
material of the filter bed or area while the filtering process is going on, for the
purpose of oxydizing the sewage, and also after the filter has been drained for
the purpose of purifying the filter and rendering it available again for filtering
purposes.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, 1 declare that what I
claim is:
1. A plant for purification and disposal of sewage consisting of a tank provided
with means for aerating its contents, a strainer, a filter bed also provided with
means for aerating its contents during the filtering operation, and an irrigation area
arranged together in the manner described whereby oxydation of the sewage is
first accomplished and it is then distributed as and for the purposes set forth.
2. In a sewage disposal plant, an aerating tank adapted to collect sewage and
provided with means for discharging it therefrom, in combination with mechanism
substantially as described independent of said tank whereby the contents of said
tank may be aerated while contained therein, as and for the purposes set forth.
3. In a sewage disposal plant, the filter above described, having an air chamber,
a layer of filtering material above this and an air retaining outlet located below
the filtering medium and adapted to compel the air to pass off through the filter
while allowing the free discharge of the effluent, all as and for the purposes set
forth.
.
4. In a sewage disposal plant, the filter above described, in combination with
means substantially as described whereby air under pressure may be fed to said
filter, said filter having an air chamber above which suitably supported a layer
of sand or other filtering material and provided with the outlet trapped to prevent
the escape of air therefrom and cause said air to escape through the filtering
material and at the same time allow the escape of the effluent, all as set forth.
5. In a sewage disposal plant a filter having a bottom of broken stone or the
like covered with suitable filtering material and provided with an outlet at or
below the level of the broken stone layer, trapped to prevent the escape of air, the
whole arranged to allow the air to pass off through the filtering material, in
combination with air pipes communicating with the voids in said filter and suitable
means for supplying the air under pressure thereto, all as and for the purposes set
forth.
6. In a sewage disposal plant the filter above described having an air chamber
provided with an outlet trapped to prevent the escape of air, above which is
supported a layer of filtering material free for the escape of air, in combination
with one or more series of draining pipes located in said filter in the manner
described whereby circulation of air may be maintained therein, irrespective of
said drain pipes, as set forth.
7. That process of purifying sewage which consists in diffusing it over a confined
mass of small stone or the like, containing air spaces, whereby the solid particles
shall be held back and caught and the effluent allowed to escape, and during the
said process of diffusion, subjecting the sewage to a process of oxydation by the
constant circulation of air or the like throughout the said confined bed under a
pressure greater than the atmosphere, all as set forth.
8. That method of treating sewage which consists in discharging it upon a
sloping area provided at intervals with equalizing barriers, having open voids
which allow portions of it to pass through, retaining other portions therein, thus
retarding the mass sufficiently in its course to cause its equal spreading and yet
allowing the ultimate escape of the liquid portions all as set forth.
9. That method of treating a sewage flow which consists in passing it through
one of a series of barriers of broken stone or the like whereby the coarser portions
of the sewage will be held back, and allowing the liquid to drain off, and when
said barrier has become more or less choked with solid matters, turning said flow

page_text: to another barrier and allowing said first barrier to clear and purify itself by
contact with the atmosphere, as set forth.
10. That improvement in the art of sewage disposal which consists in subjecting
confined pieces of broken stone or the like, which form a filtering or straining
medium, and are more or less coated with solid matter to the action of a current
of air or the like forced into and caused to be circulated through said medium
continuously under pressure after the filtering process has ceased and the filter has
been drained, whereby the organic matter accumulated therein is brought into
contact with a continuous supply of oxygen so that it will become oxydized, as set
forth.
11. That improvement in the art of sewage disposal which consists in draining
the filter which has become foul with solid particles, and then subjecting the
particles of broken stone or the like which form the filtering or straining medium
while drained to the oxydizing influence of a constantly changing supply of air or
like gas, which is caused to permeate and circulate through its voids under pressure
sufficient to cause intimate contact between the air and its foul particles, as set
forth.
12. That improvement in the art of sewage disposal which consists in passing the
sewage through a depositing chamber wherein matters in suspension will be
deposited on the surfaces of the gravel or other suitable material with which it is
supplied, and the subsequent draining of the chamber and the continued forcing
into it of air or the like when it has been drained, whereby the organic matter
accumulated therein will come in contact with a constantly replenished supply of
fresh oxygen and will become thoroughly oxydized, in the manner described.
Dated this 7th day of March 1895.
SYDNEY PITT.