An Improvement in Aerobic Bacterial Filters for the Purification of Sewage and other Foul Waters.
Year: 1899

page_text: Date of Application, 17th May, 1899
Complete Specification Left, 19th Feb., 1900--Accepted, 16th June, 1900
An Improvement in Aerobic Bacterial Filters for the Purification of
Sewage and other Foul Waters.
I, WALTER MARDON DUCAT, Colonel late Royal Engineers, of 18, Devonshire
Terrace, Hyde Park, London, W., do hereby declare the nature of this invention
to be as follows-
-
My invention relates to aerobic bacterial filters for purifying sewage,. etc.,
and has for its object to conserve the natural heat of the sewage and that given
off in the process of purification, so as to guard against the retardation or suspension
of bacterial action in consequence of such heat being radiated into the surrounding
atmosphere particularly in cold weather.
The invention consists in enclosing the filter at a distance by a roof and walls
specially constructed to prevent radiation of heat.
The preferred construction of the roof would be a double roof with intervening
stratum of stagnant air, the structure and covering of the roof being of materials
which are the worst possible conductors of heat available for the purpose. For
the internal covering of the roof some such material as roofing felt would be pre-
ferred, whilst for the external covering, ordinary roofing thatch lined or not
with a material such as roofing felt would be the most suitable, care
being taken
that the space between the inner and outer coverings of the
roof is closed as airtight as possible so as to keep the air stagnant therein.
The framing of the roof would be as light as possible and be supported on the
filter and enclosing walls, and the latter would be constructed preferably of double
or hollow walls of brickwork or concrete, with an intervening stagnant air space,
the surfaces being tarred or lined with felt or plaster to further impede radiation
of heat.
It is however to be observed that neither the roof nor the walls need be of
double construction provided that they are adequate to prevent the radiation of
internal heat.
1-11
1000
COMPLETE SPECIFICATION.
An Improvement in Aerobic Bacterial Filters for the Purification of
Sewage and other Foul Waters.
I, WALTER MARDON DUCAT, Colonel late Royal Engineers, of 13, Devonshire
Terrace, Hyde Park, London, W., do hereby declare the nature of this invention
Di Q71

page_text: and in what manner the same is to be performed to be particularly described
and ascertained in and by the following statement:-
-
.
My invention relates to aerobic bacterial filters for purifying sewage and other
foul waters, and has for its object to converse the natural heat of the sewage and
that given off in the process of purification, so as to guard against the retardation
or suspension of bacterial action in consequence of such heat being radiated into
the surrounding atmosphere particularly in cold weather.
As the amount of heat generated by the decomposition of the sewage considerably
exceeds that which could at any reasonable cost for fuel be supplied artificially
to the filter, it is obviously very important (especially in dealing with the sewage
from a town or other area of any magnitude) to provide means whereby the heat
thus given off by the sewage may be conserved and economically applied in the
manner best fitted to effect the end in view. Now I have found that the uninter-
rupted maintenance of a temperature of at least 40 degrees Fahrenheit is essential
to such continuous and efficient bacterial action as can alone prevent the blocking
of a filter in cold weather with sludge resulting from incomplete and imperfect
purification of the sewage; and further it has been proved to my satisfaction that
it is insufficient for this purpose to maintain heat merely within the interior of
the body of the filter bed. Experience has convinced me that it is equally
.essential to continuity of action that the surface of the filtering material be
maintained at a temperature capable of sustaining the life of those higher
organisms which, in the upper part of the filter, feed on and break down the
sewage before the latter reaches the interior of the filter bed.
Owing to these considerations I have found it necessary not only to surround
the filter bed with a wall so as to protect the sides of the filter from cold and
prevent lateral radiation of heat, but further to completely enclose the upper
surface of the filter bed (usually left exposed) with a roof which, whilst adapted to
ward off rain, snow, hail etc., shall also act as an efficient non-conductive covering
and so serve, under all atmospheric conditions, to prevent the temperature of the
top of the filter bed falling so low as to cause interference with the activity of
the organisms normally found at or near the upper surface. To this end my
invention consists in enclosing the entire filter at a distance by a roof and walls
specially arranged and constructed to ensure retention of the natural heat of the
filter bed.
The preferred construction comprises a double roof with an intervening stratum
of stagnant air, the structure and covering of the roof being of materials which
are the worst possible conductors of heat available for the purpose, care being
taken that the space between the outer covering of the roof and the inner covering
or ceiling is closed as air-tight as possible so as to keep the air therein stagnant.
The framing of the roof is preferably made as light as is consistent with strength
and is supported on the filter and the outer enclosing walls, the latter being
preferably made double or hollow with an intervening space for stagnant air,
and with double doors (with an air space between) to give access to the space
surrounding the filter, the walls and roof being placed at such a distance from
the sides and top of the filter bed respectively as to allow of ready access being
had to the filter at all points whilst completely enveloping the filter bed in a
body of warm air. Air inlets with regulating dampers or shutters are provided
for the admission of the fresh air required for the due oxidation of the filter, and
air outlet shafts, preferably with non-return valves to prevent back draughts,
are arranged to afford the necessary ventilation through the roof, whilst the..
effluent channels are so trapped where they pass through the enclosing walls as
to prevent access of draughts from the external atmosphere to the space within
the walls.
Such a construction is illustrated in the accompanying drawings forming part
of this specification, wherein Figure 1 is a sectional plan view of part of a filter,
the section being taken at more than one level. Figure 2 is a transverse section on
line 22. Figure 1.

page_text: The body A of the filter bed may be constructed as described in the Specification
of my previous Letters Patent No. 654 of 1897 in which the filtering material
forms a nidus for the organisms upon whose vitality and activity the efficient action
of the filter depends, and is enclosed within perforated walls a and rests upon an
impervious foundation or floor B. According to my present invention, the filter
bed is surrounded at a distance of (say) three feet from its perforated walls
by double or hollow walls C of brickwork, concrete, rubble, or other such suitable
non-conductive material as may be best available, the space between the inner
and outer thicknesses c¹² of the walls being closed at top and rendered air-tight
by the surface of the walls being tarred, plastered, covered with felt or otherwise
suitably treated. Access is afforded to the space 1 between the enclosing walls C
and the perforated walls a of the filter by means of double doors E having an air
space e between them, these doors being placed preferably at the corners of the
end walls as shewn.
The roof consists of trusses F resting upon the walls a and C and serving to
support an outer covering G of ordinary roofing thatch or other available weather-
proof non-conducting material, the latter being if desired lined with roofing felt,
and also (if the outer covering be of thatch) with wire netting or other material
impervious to rats and similar vermin. The inner covering H of the roof may
consist of a boarded ceiling as shewn, attached to the underside of the rafters &c.,
and lined with roofing felt or other non-conducting material, a secure closure being
made between the outer covering G and inner covering H of the roof throughout
the whole extent of the eaves and elsewhere where necessary, so as to ensure the
maintenance of a stratum of stagnant air between the two coverings.
The crude sewage is distributed over the upper surface of the filter bed by means
of a series of tipping trouglis I which extend transversely of the filter and are
supplied at both ends from channels i. The effluent drains into a series of cul-
verts J built on the floor B and extending from side to side of the filter bed so
as to open through the perforated walls a, the walls of these culverts being con-
structed of perforated bricks or other foraminous material with drainage
apertures in the bottom course, whilst the bottom of each culvert constitutes a
channel sloping longitudinally from the centre towards each end. Each channel b
is continued at both ends across the space D, and discharges the effluent beyond the
outer enclosing walls C through a syphon or trap b' whereby cold draughts from
the external atmosphere are prevented from gaining access to the space within the
walls C.
During cold weather, when the doors E are kept closed, air is admitted to the
filter by means of pipes K whereof one passes through the double walls C opposite
the mouth of each culvert J, the pipe K in each case terminating within the mouth
of the corresponding culvert J. A "hit and miss" damper k or other convenient
form of regulating valve is provided in each pipe K for the purpose of controlling
the supply of air, which is delivered from the inner end of the pipe within the
culvert and after passing over the surface of the film of warm effluent flowing
in the channel b and so becoming heated, passes into the body of the filter bed
through the apertures in the walls j of the culvert.
In warm weather the air, besides gaining entrance to the filter by way of the
pipes K, is admitted directly to the space D by way of the doors E and passes
into the body of the filter bed through the perforated walls a and lines of aerating
pipes a laid horizontally in the body of the filtering material as described in
the Specification of my previous Letters Patent above referred to.
Air outlet shafts L of any suitable construction are arranged to pass through the
ceiling H and outer covering G of the roof and terminate in cowls 7, each air
outlet shaft being provided preferably with a non-return valve to prevent back
draughts.
It is to be observed that, although the construction above described is generally
to be preferred, neither the roof nor the walls need be double, provided they are

page_text: adequate to prevent the radiation of heat from within the space which they
enclose.
In conclusion I desire to lay stress on the vital necessity of maintaining, under
all atmospheric conditions, the upper surface of the filter bed at a temperature
sufficient to ensure continuance of the action of those higher organisms whose
presence and activity in that part of the filter are absolutely essential to the break-
ing down of the crude sewage before it passes to the body of the filtering medium.
Failing such maintenance of the temperature at and near the surface, suspended
matter passes into and through the mass of the filter until finally the whole bed
becomes clogged with a deposit which is incapable of being further acted on by the
organisms even when the temperature essential to their maintenance in activity
is restored. Thus it will be seen that unless the measures which I find necessary
are adopted, truly continuous filtration under varying atmospheric conditions is
unattainable, and the necessity of removing, thoroughly washing, and replacing
the clogged filtering material, or replacing the same by fresh material (which con-
stitutes a considerable item of expense) must be resorted to after, practically, every
occurrence of a fall in the temperature of the external atmosphere below that
point at which the life and activity of the organisms which work in the upper part
of the filter bed can be maintained.
Having now particularly described and ascertained the nature of the said
invention and in what manner the same is to be performed, I declare that what
I claim is:-
1. An aerobic bacterial filter for purifying sewage and other foul waters in
which the filter bed is enclosed within a protective covering comprising walls
and a roof both placed at a distance from the filter bed and of such materials and
construction as will prevent loss of heat from within the enclosed space and the
consequent lowering of the temperature of the filter bed to that point at which
the vitality of the organisms, upon whose activity the continuous efficiency of the
filter depends, becomes suspended.
2. An aerobic bacterial filter constructed substantially as described and provided
with double enclosing walls and a double roof having an air outlet or outlets as
specified.
.
A. M. & WM. CLARK,
Chartered Patent Agents, 53, Chancery Lane, London.