IMPROVEMENTS IN THE TREATMENT OF SEWAGE AND NIGHT SOIL
Year: 1874

page_text: LETTERS PATENT to Henry Young Darracott Scott, of Ealing, in the
County of Middlesex, Major General, C.B., for the Invention of
"IMPROVEMENTS IN THE TREATMENT OF SEWAGE AND NIGHT SOIL."
Sealed the 23rd February 1875, and dated the 14th December 1874.
PROVISIONAL SPECIFICATION left by the said Henry Young Darracott
Scott at the Office of the Commissioners of Patents, with his Petition,
on the 14th December 1874.
I, HENRY YOUNG DARRACOTT SCOTT, of Ealing, in the County of
Middlesex, Major General, C.B., do hereby declare the nature of the
said Invention for "IMPROVEMENTS IN THE TREATMENT OF SEWAGE AND NIGHT
SOIL," to be as follows:-
The object of this Invention is the treatment of sewage in such a
manner as to deodorize its fertilizing constituents without degrading
their value. The process is applicable to town sewage as well as to
solid foeces.

page_text: .
In carrying out my Invention on town sewage it is of advantage to
remove as far as possible the sandy particles. by means of catch pits,
whilst the organic and fertilizing suspended matters are still left floating
in the liquid. I allow these suspended matters to subside in suitable
tanks (No. 1) of the ordinary kind, or I remove them from the liquid
by a rough process of filtration; or, again, I may combine these two.
methods of clarifying the water. The deposit thus obtained wo may
call (D).
To the effluent, now to a large extent deprived of its sedimentary
matters, I add milk of lime in tanks No. 2 which produce a precipitate
of carbonato of lime mixed with some phosphate of lime, and also
notable quantities of organic matter. By this mode of treatment my
carbonate of lime precipitate being unmixed with silicious and argil-
laceous particles can be re-burned and re-used for the precipitation of
fresh portions of sewage water, whereas by the ordinary method of
procedure the deposit (D) being mixed with the lime precipitate silicates
of lime, iron, and alumina are produced in the process of calcination,
and thus the compound is injured as a precipitant.
After the lime precipitate has been reburned and reused several times
it becomes too rich in phosphate of lime, or rather too poor in lime
to be advantageously used as a precipitant, and I then apply it as I
shall immediately describe. I will call the precipitate (L). It is to be
observed that as the sewage water contains much carbonate of lime in
solution which is precipitated by lime the precipitate largely increases
in quantity at each precipitation. To the effluent from tanks No. 2
I add in tanks No. 3 an acid solution of a phosphate of iron, of lime,
or of alumina, which unites with the lime left in solution in the last
operation, and thus there is produced a precipitate consisting of a
phosphate of one of the above-mentioned oxides, together with notable
quantities of organic matter. The effluent is left in a bright condition
by this process, and is then fit to be run into streams of magnitude as
compared with the volume of the sewage; or it can be readily and
completely cleansed by a process of intermittent downward filtration.
By following the above plan I obtain my precipitated phosphate of lime
in a very valuable condition.
In the phosphate processes as ordinarily employed the carbonate of
mainitated! is mizad
th th

page_text: phosphate precipitate and degrades its value, often constituting 50 per
cent. of the solid matters obtained. I may call this phosphate pre-
cipitate (P).
I will now return to the deposit (D). This compound, if an attempt
were made to deal with it without deodorization, would prove very
offensive. I therefore, either whilst still in the depositing tanks or
while it is being removed from them, add a sufficient quantity of milk
of lime (prepared from (L)), and of acid solution, of a phosphate of iron,
or of lime, or of alumina, tó deprive it of noxious smell, and I appertain
the deodorants so as to leave the mixture slightly acid. I then mix
the precipitate (P) with (D), and remove the excess of water in any
convenient manner. In this manner I obtain a saleable and valuable
manure.
If the effluent is to be used in irrigation I may omit the processes in
tanks (2) and (3), and then I use ordinary lime for the deodorization
of (D) in lieu of the phosphatic lime (L).
It is manifest that the three compounds I obtain may be sold
separately. The compound (D) for instance is very valuable as a
desiccator in the manufacture of high class superphosphates. The
compound (L) again is a very valuable phosphatic lime in cases in
which limeing the soil is resorted to, and the precipitate (P) is in itself
a valuable manure, and may, by the addition of acid, be converted into
a high class superphosphate.
In cases in which it is difficult to obtain a market for (D) where (D)
is alone produced, or when lime precipitation must be employed and
neither (D) nor (L) can be-dispensed of readily, I vary the mode of
procedure. I then use lime alone for the deodorization of (D), and I
may also use some milk of lime to produce more rapid deposition of the
suspended matters; but I keep this precipitant as low in quantity as
possible. My object now is to distil off the nitrogen as `ammonia, and
to use the residue as a precipitant for the effluent from (D). To enable
this to be done I add a considerable quantity of lime to (D), and the
ammonia distilled off, I pass into an acid solution in the ordinary
manner in order to fix it. The salt of ammonia thus obtained may be
used to fortify the precipitate (P), or in any other manner. The residue
after having been used in the precipitation of the effluent from (D)
may be converted into a cement by a well-known process, or it may be

page_text: subjected to calcination to form a cement without further treatment
as a precipitant.
In applying my process to solid foeces or night soil I separate the
liquids as far as convenient and then add lime and an acid solution of a
phosphate of iron, lime, or alumina to produce deodorization, and I find |
that I can effect this when the lime is added in the proportion of about
of the weight of the wet night soil. I leave the compound very
slightly acid, and then remove the excess of water by spontaneous
evaporation, or by heat.
'
I may use charcoal in conjunction with the above deodorants either:
after the focal matters have been conveyed to the manure manufactory,
or in the habitations of the people; but as my object is to produce con-
centrated manures (for these alone command a market) I keep the
quantity of charcoal used as low as possible, unless it be of that kind
which is used by sugar refiners, and which has itself a high fertilizing I
value. The compound obtained by this process may manifestly be
subjected to distillation, and the char obtained be employed in the
deodorization of fresh quantities of focal matters.
For the more perfect recovery of the nitrogen I may employ excess of
lime, as in the case of the deposit (D).
Although it is desirable to add excess of lime to the deposit (D) when
the object is the recovery of the whole of the nitrogen as a salt of
ammonia, I sometimes find it advisable to neutralize the excess of lime
with phosphoric acid or soluble phosphate for the sake of preparing
from the deposit a substitute for animal charcoal; but under such
treatment the yield of ammonia is smaller. I may also produce a
substitute for animal charcoal by charing the precipitate (P).
SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said Henry Young Darracott Scott in the Great Seal
Patent Office on the 14th June 1875.

page_text: methods of clarifying the water. The deposit thus obtained we may
call (D), and the manipulations to which I subject it are best performed
when the solids are mixed with about ninety per cent. and upwards of
the liquid, that is to say, when the mixture is of the consistence of what
may be termed a thin slip.
To the effluent from tank (No. 1) now (to a large extent) deprived of
its sedimentary matters I add milk of lime in tanks (No. 2) which
produces a precipitate of carbonate of lime mixed with some silicate
and phosphate of lime, and also notable quantities of organic matter.
By this mode of treatment my carbonate of lime precipitate being 1
unmixed with suspended siliceous and argillaceous particles can be.
calcined and reused for the precipitation of fresh portions of sewago
water, whereas by the ordinary method of procedure, the deposit (D)
being mixed with the lime precipitate, large quantities of silicates of
lime, iron, and alumina are produced in the process of calcination, and 1
thus the compound is injured as a precipitant.
After the lime precipitate has been reburned and reused several times
it becomes too rich in silicate and phosphate of lime or rather too poor
in lime to be advantageously used as a precipitant, and I then apply it
as I shall immediately describe:-We will call the precipitate (L). It is
to be observed that as the sewage water contains much carbonate of limo
in solution, which can nearly all be precipitated by lime, the precipitate
can be increased in quantity at each precipitation. The employment of
the precipitate (L) for the manufacture of cement, as specified in my
Patent, dated Twenty-sixth August, One thousand eight hundred and 2
seventy-one, it is unnecessary to describe. Clay may be added with the
milk of lime as there stated in the proportion required to give the best
results in the production of cement. To the effluent from tanks (No. 2)
I add in tanks, No. 3, by preference an acid solution of a phosphate of
iron, of lime, or of alumina, which unites with the lime left in solution g
in the last operation, and thus there is produced a precipitate consisting
of a phosphate of one of the above-mentioned oxides, together with
notable quantities of organic matter. The effluent is left in a bright
condition by this process and is then fit to be run into streams of magni-.
tude as compared with .the volume of the sewage, or it can be readily a
and completely cleansed by a process of intermittent downward filtra-

page_text: tion. By following the above plan I obtain a precipitated phosphate of
lime in a very valuable condition.
In the phosphate processes, as ordinarily employed, the carbonate of
lime (which is here nearly all separately precipitated) is mixed up with
the phosphate precipitate, and degrades its value, often constituting
fifty per cent. of the solid matters obtained; I may call this phosphato
precipitate (P).
With the view of ridding the phosphate precipitate as far as possible.
of carbonic acid (which is still carried down with the phosphate as
carbonate of lime in small quantities, notwithstanding the previous
limeing process which retains some of it in solution) I make use of
magnesia, or a salt of magnesia, in conjunction with the acid phosphate,
and by this means the precipitate is almost entirely freed from the
presence of carbonates.
+
In lieu of employing a soluble phosphate for this last precipitation I
sometimes use a soluble salt of iron or alumina, but such precipitates
having no further manurial value than what is due to the nitrogenous
matters carried down with them I only employ them in cases in which
there is no sale for phosphate manures. The precipitate may however
be subjected to distillation so as to recover the nitrogen, and the mineral
matters may be redissolved in acid to be employed again, or the charred
compound may be used as a deodorizer or decolorizer.
:-
⚫ Let us now return to the deposit D. This compound if an attempt
were made to deal with it without deodorization would prove very
offensive. I therefore operate upon it in the following manner either
whilst it is in the depositing tanks or as it is being removed from
them In this state it still contains ninety-two parts by weight of
water to eight parts by weight of solid matter, though considerable
latitude can be taken as to the proportion of water, and the process
answers perfectly with sludge in the condition in which it is usually
pumped from depositing tanks. I therefore add a sufficient quantity of
milk of lime prepared from (L), and a sufficiency of acid solution (by.
preference of a phosphate) of iron or of lime, or of alumina, so as to
neutralize the lime, or nearly so. When the compound will part with
no more water by drainage more acid may be added so as to leave the
mixture slightly acid. It is not however essential that this point should

page_text: be attained, for I find in practice that the sludge may exhibit a con-
siderable degree of alkalinity without any notable loss of ammonia taking
place in drying. When dry it is reduced to a powder and is ready for use
as manure. By proceeding in this manner I attain several important
objects,―
siderable degree of alkalinity without any notable loss of ammonia taking
place in drying. When dry it is reduced to a powder and is ready for use
as manure. By proceeding in this manner I attain several important
objects,
Firstly. I obtain the sedimentary matters almost without admixture
with carbonate of lime.
Secondly. I render them inoffensive.
Thirdly. The means employed for rendering them inoffensive add to
their fertilizing value.
Fourthly. I so far change the physical texture of the sludge that a
remarkable facility in parting with the water it contains is substituted
for strong retentiveness of that element. The addition of lime alone is
not sufficient for this object. Alkalinity increases rather than diminishes
the retentive properties of the sludge for water; it is only on the
neutralization of the lime by an acid which will yield a mineral and
(probably) crystalline precipitate that the drainage becomes easy.
I find that I can obtain facility of drainage by using sulphuric acid in
lieu of a phosphate made soluble by sulphuric or hydrochloric acid, but
it will be evident that the sulphuric acid may be used to more advantage
when it is employed in bringing into solution phosphoric acid (whereby
the value of the latter is greatly increased). I then use this solution in
neutralizing the lime employed in deodorization.
It is generally advantageous for small works to make use of high class
soluble superphosphates in lieu of a solution for neutralizing the lime, as
this avoids the necessity of chemical manipulation on the spot. I mix
the superphosphates with water before adding it to the limed sludge.
If the sludge is to be dried by mechanical appliances this phosphate
precipitate for the reasons already given will be found to be of great
assistance, but if it be intended to dry the sludge by settlement and
spontaneous evaporation (combined or not with drainage) the time
which elapses is sufficiently long to allow a second decomposition to set
up unless a considerable amount of lime is used. In such cases I find
one bushel of lime and upwards for the sludge deposited in twenty-four

page_text: hours from the sewage of five thousand gives satisfactory results when
conditions are favorable for drying. Where gas lime can be obtained
this also may be used as the deodorant, but it should be used in larger
quantity. It is best to grind it to a slip, but it can also be used as
supplied.
If the sludge is to be dried quickly by machinery, such as wringers or
presses, a very small proportion of lime and acid is necessary for deo-
dorization, but the facility of expressing the water increases rapidly with
the amount of precipitated phosphate produced amongst the fibres of the
sludge. Excellent results are obtained when the dry compound contains
from eight to ten per cent. of tribasic phosphate of lime. It is best to
add the lime before the phosphate solution. I mix the precipitate (P)
with (D) before drying, and then remove the excess of water in any
convenient manner. In this manner I obtain from sludge a saleable and
3 valuable manure.
I am well aware that both lime and phosphate of lime, magnesia,
alumina, and iron have been used for the deodorization and precipitation
of town sewage. The novelty of this part of my process therefore consists
not in the use of these materials, but in their application to the muddy
slip or sludge which remains after the greater part of the liquid has been
removed. Ordinary town sewage contains in dry weather from five to
fifty grains of suspended matters per gallon, or from one thousand four
hundred to fourteen thousand parts of liquid for each part of solid. In
my process the liquid is reduced before the application of chemicals to
ten or twenty parts of liquid to one part of solid, and by this means the
deposition of carbonate of lime, which adultorates the fertilizing value
of the suspended matters, is reduced to a minimum. Other deodorants
may be used in conjunction with the above, such as charcoal, or carbolic
acid or soot.
If the effluent is to be used for irrigation I may omit the processes in
tanks (2) and (3), and then I use ordinary lime for the deodorization
of (D) in lieu of the phosphatic lime (L). I may also employ the
processes in tanks (1) and (2), and omit that in tank (3).
It is manifest that the whole of the three compounds obtained may be
dealt with separately in the market. The compound (D) (for instance)
is very valuable as a desiccator in the mannfacture of high class super-
phosphates. The compound (L) is again a valuable phosphatic limo in

page_text: cases in which limeing the soil is resorted to, and the precipitate (P)
is in itself a valuable manure, and may, by the addition of acid, be con-
verted into a high class superphosphate.
In cases in which it is difficult to obtain a market for (D) when (D)
is alone produced, or when lime precipitation must be employed, and
neither (D) nor (L) can be disposed of readily, I vary the mode of pro-
cedure. I then use lime alone for the deodorization of (D). My object
now is to distil off the nitrogen as ammonia, and to use the residue as a
precipitant for the effluent from (D). To enable this to be done I add a
considerable quantity of lime to (D), and the ammonia distilled off I
pass into an acid solution in the ordinary manner in order to fix it. The
salt of ammonia thus obtained may be used to fortify the precipitate (P).
or in any other manner. The carbonaceous residue after having been
used in the precipitation of the effluent from (D) may be converted into
a cement by a well known process, or it may be subjected to calcination ]
to form a cement without further treatment as a precipitant, or again it
may be employed as a deodorizer of fecal matters. I may also prepare a
valuable substitute for animal. charcoal by treating the dried deposit as
bones are treated in the preparation of that material.
Having now described my Invention of improvements in the treatment a
of sewage and night soil, and having explained the manner of carrying
the same into effect, I claim as the Invention secured to me by Letters
Patent as aforesaid,―
First. The separation from raw town sewage of the greater portion of
the liquid matters, and the subsequent treatment (as herein set forth) of 1
the solid matters that are deposited therefrom, so that such solid matters
may be more conveniently converted into fertilizing substances, as herein
set forth.
Second. The removal by precipitation of the carbonic acid from the
untreated effluent or liquid resulting from the above process, and
reusing the precipitate so obtained, as and for the purpose herein set
forth.
Third. Treating the effluent (after the precipitation therefrom of the
carbonates, as herein set forth) by a second precipitation process in
order that a precipitate may be obtained free from the grosser matters
and the carbonic acid contained in the sewage.

page_text: Fourth. Subjecting the precipitate obtained by this second precipi-
tation to a process of distillation for the purpose of obtaining therefrom
valuable products, such as charcoal and ammonia, as herein set forth.
i
In witness whereof, I, the said Henry Young Darracott Scott, have
hereunto set my hand and seal, the Twelfth day of June, in the
year of our Lord One thousand eight hundred and seventy-
five.
HENRY Y. D. SCOTT. (L.s.)