Improved Process for Treating Sewage Sludge.
Year: 1896

page_text: Date of Application, 6th Nov., 1896
Complete Specification Loft Ath Ave 100'7 A
2002
Improved Process for Treating Sewage Sludge.
I, BENJAMIN WALKER Wool Merchant The Green's Hawes R.S.O., Yorkshire,
do hereby declare the nature of this invention to be as follows:-
A process of absorbing Sewage Siudge by peat, peat moss, peat moss litter, peat
broat or dust, and the like, and driving off the moisture by heat, pressure, and
evaporation, and leaving a pigment, fuel, and manure.
Dated this 5th day of November 1896.
BENJAMIN WALKER,
I, BENJAMIN WALKER of Hawes, R.S.O., in the County of York, Wool Merchant,
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 invention has for its object a process of treating sewage sludge whereby
its smell is to a large extent eradicated, the sludge made more pervious and capable
of being more easily separated from its moisture by pressure, and also whereby the
sludge shall be made more combustible and thus can be used for obtaining gas
and filtering 'material, whereby it can also be used for a manure, and whereby a
pigment can be extracted from it. It has long been known that peat has its
advantages for filtering water, it having a very considerable antiseptic and
mechanical filtering power, but there are so many difficulties in the way of using
peat that it is not employed practically in water-works.
Now I have found that by adding from 1% to 15% of loose peat to sewage
sludge or even foul water containing as little as 2% of sludge material, the whole
can be absorbed and made portable and if a portion be dried sufficient to start a
furnace and get it to a red or white heat or other fuel be used preliminarily for
obtaining this heat, then the whole can be calcined by careful feeding and strong
draught without further addition of fuel.
In carrying out my invention I regulate the amount of peat according to the
amount of moisture contained in the sewage sludge at the rate of 1 of dry peat.
to 7 of water. Where the sewage sludge contains a large amount of grease, oil or
soap, as in the case of wool suds, the calcination is assisted very materially.
I prefer however to extract as .much water as possible before ealcining and
therefore for this purpose submit the mixed peat and sludge to pressure in a

page_text: hydraulic or other press. I have found, when using pressure in this way, that
even % of peat mixed with the sludge has been a very great advantage in assisting
the water to escape from the press and in preventing the pores of the canvas
employed in the press from being clogged up. 1% however of the weight of the
sludge is the minimum I should think valuable for practical purposes, and with
this amount in my experimental practice I have found no difficulty in pressing
bulks of all sizes from 3 cwt. down to 10 lbs, leaving a firm portable cake that can
be calcined in almost any kind of furnace or even in the open air in heaps, provided
always that the fire is started first with dried sludge cake coke or peat. In order
to carry on the present process successfully with small quantities of peat, I find
the use of peat dust is preferable and this dust must be mixed with the sludge
in a mixing machine. In practice I use the ordinary lime mixer now in use in
sewage works. In this mixer the peat and the sludge are thoroughly worked
up together. A larger amount of peat is more effectual in making sludge porous
and allowing the water to escape quicker, and by disintegrating the cake again and
re-mixing with fresh sludge it can be used over again many times. Though
it would seem a round about process I have got the best results from it in
practice; it mixes and presses quicker leaving a firmer cake. My reason for this
is that the pressed cake contains a large percentage of the precipitant and in
conjunction with the peat frees the water from the solid matter more readily: In
tanks containing 7 tons I have been able to syphon off large quantities of clear
water after adding disintegrated pressed cakes, thus showing conclusively this to
be the fact.
In order to
As the water leaves the press peat is deposited on the canvas, thus preventing
the pores from becoming choked and the cake is made porous from the centre and
enriched by the addition of peat for all purposes herein named.
economise working I arrange the machinery so that the disintegrator feeds direct
into the mixer and the mixer feeds direct to the press. If the settling tanks are
self acting, the sludge can consequently. be dealt with as made, and space thereby
economised. A small percentage of lime or gypsum added in the mixer will make
the smoke less offensive in caleining, or make the cakes more valuable as manure.
Where small quantities of sludge are made, and it is not considered desirable..to
employ special plant for pressing, the sludge when well mixed with peat can be
put into ordinary canvas bags or wrappers and placed in piles. The water per-
colates through the pores of the canvas bags and runs off or evaporates so that
after a time a comparatively hard material is found in the bag. In my experi-
ments, when calcining sewage sludge precipitated by iron precipitants, the ash
contains nearly all the properties of magnetite, consisting very largely of magnetic
oxide of iron. The degree of hardness in this ash depends upon the amount of
heat used. Where a powerful draught and high heat is obtained the ash is very
hard and chemicals do not attack it readily. It is therefore an excellent filtering,
medium. Indeed in my experiments I have frequently reduced the sludge to the
consistency of butter by means of filtration through this magnetic oxide so that
it can be shovelled off the filter beds (after being mixed with a small percentage
of peat) and then pressed and calcined. The filtering medium is not lost by this
operation as it is regained in the calcination. In forming my filter beds I make
use of the clinker from the furnace grate. This I sift into eight different sizes.
The filter consists first of a false bottom. I then add a layer of the very coarsest
clinker, then successively finer layers and finish with a top layer of the calcined
sludge of a previous operation. In order to make these beds as effective as possible
I arrange a system of ventilation which is set forth in the accompanying drawings,
in which
Figure 1 is a sectional side elevation showing the various filtering beds and
ventilating pipes, and
Figure 2 a transverse, section of the wall between the two filters and the
contiguous parts.
In these, A is a perforated iron or other partition, B air space below C D E F G

page_text: and H layers which can be of any desirable number of clinker or gravel, each in
succession from the bottom to the top being successively finer than the last, the
top layer or layers being composed of the powdered calcined sludge. If there are
two layers of this sludge the finer powder is placed on the top. L' L L L
etcetera are a series of stone-ware pipes extending from the top of each layer to
the longitudinal flue M. This flue M is supplied with a damper N at the end and
is carried off to a chimney. 00 are the mixer walls of the filter bed. R effluent
having stop cock Q. R R are air pipes extending from the air space below,
preferably at each corner of the filter bed and open to the atmosphere at the top.
Any other means of introducing air freely to the said air space can be used, the
object being a thorough aeration and consequent oxidation of the water and its
impurities in the beds of the filter. In Figure 2 the dotted lines S S show a
variation in which the pipes L L L L etcetera could be brought through the
brick-work instead of being placed outside as shown in full lines. Of course
where the lines are arranged as in the dots the pipes L1 L2 L3 L etcetera at the
outside are dispensed with. When the dried sludge contains about 25% of grease
as is the case of sludge consisting largely of wool suds I have obtained, by
destructive distillation in gas retorts, from 18% of its weight illuminating gas,
25% tar oil and ammonia water, and 56% of charcoal or ash containing a large
percentage of magnetic oxide of iron. This charcoal I use again for heating the
retorts and for filtration as already described. Where these ashes are very rich
in iron they can be ground up as a brown paint and where the cake is very rich
in ammonia it can be allowed to ferment in heaps after the manner of a stable
manure and then forms a valuable manure.
Having now particularly described and ascertained the nature of my said
invention, I wish it to be understood that I am well aware that it has even been
proposed to mix peat and even peat charcoal with the material in filter beds, also
that peat has been proposed to be used to be placed in sewage tanks in order
to lessen the effluvium therefrom, and I make no claim for any of these, but that
what I claim as my invention is:—
1. The intimate mixture of peat with sewage sludge before pressing or calcining,
whereby the sewage sludge is made more porous and more combustible.
2. The construction of a filter bed formed largely of clinker and calcined sewage
sludge substantially as and for the purposes described.
3. An arrangement of filter bed consisting of numerous layers, each layer being
separately connected to the open air or to a chimney or other source of draught
by means of stand-pipes substantially as described.
4. The system of utilising sewage sludge taken as an entire process substantially
as herein described whether used finally as a manure, as a further filtering material,
or as a pigment, substantially as herein described.
Dated this 3rd day of August 1897
WM. P. THOMPSON & Co.,
Of Liverpool, Manchester, Birmingham and London, Patent Agents.