Improvements in the Construction of Bacterial Tanks and Filters for the Purification of Sewage.
Year: 1898

page_text: Date of Application, 19th Oct., 1898-Accepted, 26th Nov., 1899
COMPLETE SPECIFICATION.
Improvements in the Construction of Bacterial Tanks and Filters for
the Purification of Sewage.
I, FRANCIS WEBB WENTWORTH-SHEILDS, of Brentwood Villa, Sholing, South-
ampton, Civil Engineer, Member of the Institution of Civil Engineers, do hereby
declare the nature of this invention and in what manner the same is to be per-
formed, to be particularly described and ascertained in and by the following
statement:
This invention has for its object the improved construction of tanks and filters
whether separately or in combination for the bacterial treatment and purification
of sewage. Both the tanks and filters are aerated throughout the entire process,
and are intended to promote the developement and increase of aerobic rather than
of anaerobic bacteria for the purpose of purification. Special contrivances are also
provided to ensure that the sewage in every stage of its treatment shall flow or
he passed in an uniform body throughout the tanks and filters, with the excep
tion as regards the tanks that the flow of sewage along the lower part of the tank
is arrested and rendered quiescent by the means described hereinafter, so as to
allow the solid deposit or sludge to settle down to the bottom of the tank and to
remain there undisturbed to be dissolved by bacterial action.
The object of these provisions for uniform flow is to avoid in the tanks the
currents in some places and comparatively still water in others which are caused
when the sewage is put into or taken out of a tank at a single or few points
instead of being uniformly delivered and discharged; and to avoid in the filters
the same effect as well as the unequal filtration which occurs unless the whole
body of fluid be made to travel uniformly through the whole length of the filter-
ing material; all which matters mar and deteriorate the process of purification.
In carrying out this invention, the sewage enters the tank at one end and is
discharged at the other in the following manner-
A channel called herein the tank entrance channel is constructed all along the
entrance end of the tank, into which channel the outfall sewer delivers its con-
tents. The edge of the tank entrance channel next to the tank is made in the
form of a weir, over the lip of which the sewage is delivered into the tank in a
thin sheet so as to cause an equalised delivery over the whole end of the tank
and at the same time to aerate the sewage-At the other end of the tank, a
second channel called herein the tank effluent channel is provided, corresponding
to the former one in position, construction, and level, and having a similar weir
but with the lip turned the opposite way so as to be again next the tank, over
which lip the effluent sewage flows into that channel. The tank effluent is thus
again delivered uniformly along the whole tank end in a thin sheet over a weir-
lip, and is thus again aerated.
The following arrangements for creating uniformity of flow at top and quies-
cence at bottom are also provided in the tanks.
A screen is placed at the discharge end all across the tank at about three feet
back from the weir lip of the tank effluent channel, the top-of the screen being

page_text: above top water level. The screen goes down through the sewage to within about
two feet of the bottom of the tank, and rests on a solid wall which closes in that
bottom space and retains in the lower part of the tank the deposit or sludge as
before mentioned-Finally, a dip plate is placed across the tank in the centre of
that three feet space-The upper part of the dip plate is solid from above top
water level to within about a foot and a half above the tank bottom, and that
bottom space is either mainly or wholly left open-The solid part of the dip plate
is thus lower at its bottom edge than the solid part of the screen at its top edge
-The sewage therefore passes through the upper part of the screen and the lower
part of the dip plate, being thereby drawn uniformly through the openings in
the screen throughout their entire width and depth; and consequently in corre-
sponding uniformity through the_tank.
The action of the tank proceeds continuously throughout the year, the solid
sewage matters being dissolved by bacterial action alone-A pipe should be laid
however to empty the tank if required, or to run off any accumulation of insoluble
matters which may collect in it, but this will only be wanted at very distant
intervals.
The filters are constructed as follows. A channel termed herein the filter
channel carrying on or conveying the tank effluent or other liquid to be filtered, is
constructed to run without interruption past the entrance end of every filter. A
secondary channel also runs alongside the first and along the same filter end, and
is open to each filter, but closed or stopped opposite each side wall thereof so as
not to communicate with any other filter-The channels run side by side and are
separated by a single partition in which a penstock or valve for each filter is
placed; whereby the fluid to the filter can be admitted to or shut off from at will;
any secondary channel and its filter.
As above stated, each secondary channel communicates directly with its own
filter It is formed in the same manner as the tank effluent channel and with a
similar weir lip next the filter, so that the fluid admitted to the channel is
delivered uniformly over the weir lip in a thin sheet into the filter-In the case
of tanks and filters in combination, it is thus aerated for the third time-Then
about a foot clear from the weir lip, a screen as before described is placed all
across the filter, but with openings from top to bottom throughout; and a similar
screen is also placed in like manner about a foot from the discharge end of the
filter. The two foot spaces are left open to be filled with fluid only and the coke
breeze or other filtering material is filled in throughout the length and width of
the filter between the screens. The filter is then filled with the fluid to be purified,
and allowed to stand full for. a time if so desired. The effluent is thus drawn
uniformly through the filtering material from one screen to the other, and is then
discharged by a drain leading out of the foot space at the discharge end of the
filter.
By these arrangements the fluid to be purified is aerated on entering and by
means of the clear spaces for fluid at either end it is drawn uniformly through the
whole width depth and length of the filtering material which further aerates it.
Thus partial or unequal purification is obviated.
The dimensions given above are approximate only and may be varied according
to circumstances.
The screens may be made with iron rods or wire as commonly used in screening
sewage, or with thin brick walls having narrow spaces left between the bricks, or
in any other way suitable.
The dip plates may be made with thin brick walls solid above and open below
and carried on piers and arches or on iron girders; or with boards on edge close
above and open below; or in any other way suitable.
All the openings in the screens both in tanks and filters are carried above top
water level so as to offer no impediment to the surface water passing through
them.
As the depths and cubic contents of all tanks and filters should for effectiveness

page_text: be in certain proportions to the amount and condition of liquid to be purified,
and as the bacterial filters which purify by absorbing air and aerating the fluid
passing through them should be provided with suitable filtering material and
should have alternate periods of work and rest, all which proportions and condi-
tions are already well ascertained and known, it is assumed that these particulars
will be duly provided for.
Where there are dwellings adjacent, the tanks are recommended to be enclosed
or covered in such a manner as to exclude bright sunlight but admit air; but this
is not essential to purification.
as above described.
Figure 1 is a plan of one tank and two filters in combination, but the internal
arrangements of each are the same when they are used separately-Figure 2 is a
Figure 3 is a longitudinal
longitudinal section along the centre of the tank.
section along the centre of either filter. Figure 4 is a transverse section midway
on the tank and filters--a is the outfall sewer-b is the tank entrance channel--
is the tank is the tank screen standing on a low wall which retains the
bottom deposit in the tank-e is the space between the tank screen and the dip-
plate is the dip-plate-g is the space between dip-plate and lip of weir of
tank effluent channel. h is the tank effluent channel is the filter channel.
is the penstock-k is the secondary filter channel is the space between the
filter-screens mm, which space is filled with coke breeze or other filtering material
as shewn in Figures 3 and 4. nn are the open spaces for fluid at either end of the
filter. o is the purified effluent discharge pipe which should be provided with a
valve or stop cock to open or close at will. p is a pipe, to be alike provided with
a valve or stopcock, to run off the deposit in the tank when required. q (dotted
line) is top water level. The arrows shew the course or travel of the fluid to be
purified, which enters the tank at a as crude sewage and is discharged from the
filter at as purified effluent.
The accompanying drawing shews the construction
Having now particularly described and ascertained the nature of my said
invention, and in what manner the same is to be performed, I declare that what
I claim is:
1. A tank for the bacteriological treatment of sewage whether raw or partially
purified, wherein the sewage shall be delivered uniformly and aerated at each end,
in combination with the provision of a screen and dip-plate at the discharge end,
all as hereinbefore generally described and shewn in the accompanying drawings.
2. A filter for the bacteriological treatment of raw or partially purified sewage
or of sewage tank effluent, wherein the fluid shall be delivered uniformly and
acrated on entering, in combination with the provision at each end of the filter of
a screen and a clear space for the fluid, all as herein before generally described
and shewn in the accompanying drawings.
1000