IMPROVEMENTS IN THE TREATMENT OF SEWAGE WATER
Year: 1872

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 WATER."
Sealed the 22nd May 1872, and dated the 20th March 1872.
PROVISIONAL SPECIFICATION left by the said Henry Young Darracott
Scott at the Office of the Commissioners of Patents, with his
Petition, on the 20th March 1872.
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 WATER,"
to be as follows:-
The chief object of this Invention is the extraction from sewage water
of the ammonia (which it contains) in a form in which it can be made
readily available as a marketable article. The process has the collateral
advantages of obtaining phosphates of alkaline earths in a condition very
suitable for a manure, and of effecting a further and more complete

page_text: purification of sewage water than can be brought about by a single
precipitation process.
In carrying out my Invention I commence by removing from the
sewage the grosser foecal matters and impurities, and for this purpose I
prefer the method of precipitation by lime. I then agitate with the
effluent water from such precipitated matters hydrated phosphate of
magnesia, which when allowed to subside will carry down with it, in
chemical combination the ammonia contained in the sewage water,
and with which ammonia the phosphate comes into contact.
When excess of lime has been used in the preliminary precipitation of
the grosser foccal matters, phosphoric acid in some soluble combination,
such as in the form of a phosphate, may be employed to separate the
free lime from the liquid before the phosphate of magnesia is added, or
the other and soluble phosphate may be added simultaneously with the
introduction of the insoluble phosphate of magnesia.
When the insoluble compounds (formed by the action of their phos-
phates) have settled, the supernatant liquid is to be drawn off, and these
solid compounds are collected, dried, and exposed to heat in order to
expel the ammonia which has been absorbed, and which may after
expulsion be collected by well known chemical methods. Or the com-
pounds may be carefully dried and sent into the market as manure.
As hydrated phosphate of magnesia is not perfectly insoluble some of
this substance will be carried away in the effluent water and be lost,
unless the water be applied to irrigation purposes; I therefore some-
times add to it a sufficient quantity of milk of lime to precipitate the
phosphoric acid dissolved in the water.
When I can obtain the calcareous substances containing both carbonic
acid and phosphoric acid in considerable proportions I calcine such sub-
stances, and having dissolved out the lime, I employ the lime for the
preliminary precipitation of the grosser foecal matters of the sewage,
and I use the phosphate of lime (which remains undissolved in the
water) for the preparation of the phosphate of magnesia required for
the collection of the ammonia.

page_text: SPECIFICATION in pursuance of the conditions of the Letters atent,
filed by the said Henry Young Darracott Scott in the Great
Seal Patent Office on the 20th September 1872.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, HENRY
YOUNG DARRACOTT SCOTT, of Ealing, in the County of Middlesex,
Major-General, C.B., send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the Twentieth day of March, in the
year of our Lord One thousand eight hundred and seventy-two, in the
thirty-fifth year of Her reign, did, for Herself, Her heirs and successors
give and grant unto me, the said Henry Young Darracott Scott, Her
special licence that I, the said Henry Young Darracott Scott, my
executors, administrators, and assigns, or such others as I, the said Henry
Young Darracott Scott, my executors, administrators, and assigns,
should at any time agree with, and no others, from time to time and
at all times thereafter during the term therein expressed, should and
lawfully might make, use, exercise, and vend, within the United Kingdom
of Great Britain and Ireland, the Channel Islands, and Isle of Man,
an Invention for "IMPROVEMENTS IN THE TREATMENT OF SEWAGE Water," upon
the condition (amongst others) that I, the said Henry Young Darracott.
Scott, my executors or administrators, by an instrument in writing under
my, or their, or one of their hands and seals, should particularly describe
and ascertain the nature of the said Invention, and in what manner the
same was to be performed, and cause the same to be filed in the Great
Seal Patent Office within six calendar months next and immediately
after the date of the said Letters Patent.
NOW KNOW YE, that I, the said Henry Young Darracott Scott,
do hereby declare the nature of my said Invention, and in what manner
the same is to be performed, to be particularly described and ascertained
in and by the following statement (that is to say): -
The chief object of this Invention is the extraction of ammonia from
sewage, in which term I include all such waste and polluted waters of
towns and factories as require purification before being cast into rivers

page_text: The improved method whereby this is effected has the collateral
advantage of yielding phosphates of alkaline earths in a condition very
suitable for agricultural purposes. It also effects a further and more
complete purification of sewage than can be brought about by a single
precipitation.
In carrying out my Invention I commence by removing from the
liquid to be treated all the grosser foecal matters and suspended impuri-
ties, and for this purpose I prefer the method of precipitation by lime.
I also prefer to make use of dolomitic lime in lieu of pure or ordinary
lime. Out of the dolomitic lime I first dissolve the lime by means of
clarified sewage water, and I then mix the solution of lime so obtained
with the sewage to be precipitated. I employ the magnesia which
remains undissolved in the liquid for the preparation of the phosphate
of magnesia, which I subsequently use for the extraction of the ammonia
from the polluted or sewage waters.
I sometimes employ for the preliminary precipitation of sewage
calcined calcareous phosphatic minerals, out of which I dissolve the
lime in the same manner as I practice with the dolomitic lime for the
removal of its grosser focal matters, whilst the undissolved phosphates
are made available for the supply of the phosphoric acid in the pre-
paration of the said phosphate of magnesia.
With the view of facilitating the separation of the lime from the
phosphates of such minerals I sometimes intimately incorporate with
them (previous to their calcination) a sufficiency of lime to produce
slaking in the calcined compound.
In any case, whether ordinary lime be employed or whether mag-
nesian lime or phosphatic lime be used as the source of supply of the
lime with which the sewage is clarified, the precipitate so obtained is
allowed to deposit in a tank or tanks, which I will call No. 1. This
deposit may be calcined and converted into cement or agricultural lime
according to methods now in use, or it may be mixed with town ashes
and employed as manure, or it may be converted into charcoal and be
used for the filtration of the sewage or for other purposes. In cases in
which straining or subsidence are employed for the removal of the
grosser focal matters it is still advantageous to use some process of
precipitation before applying the phosphate of magnesia, with which I

page_text: extract the ammonia. With waste waters comparatively free from
suspended matter the process of removing the ammonia may be applied
at once.
The chief object of the precipitation, so far as my present object is
concerned, is to avoid burthening valuable products to be obtained
with the comparatively worthless substances which would otherwise be
thrown down with them.
The effluent from tank No. 1 will probably carry away with it in
solution notable quantities of lime or lime salts which it is very desirable
but not essential to remove in tank No. 2, by the addition to it of super-
phosphate of magnesia, superphosphate of lime, phosphate of soda, or
phospheric acid, which will precipitate it as insoluble phosphate. These
substances may be used singly or in conjunction, but I prefer to employ
superphosphate of magnesia. The deposit thus formed may be collected
and dried for manure, or it may be subject to distillation, and be con-
verted into charcoal which will be useful for many purposes. The carbon
is of course supplied by the organic matter which the precipitate carries
down with it in settling. Appreciable quantities of ammonia will also
be found in this deposit. The lime carried away in solution from tank
No. 1 may be partially removed also by filtration through charcoal,
burnt ballast, or other suitable substance.
The effluent from tank No. 2 thus freed from lime passes on to tank.
No. 3, where, and in tank No. 3ª, the operation for the extraction of the
ammonia is to be carried out by extracting it with phosphate of mag-
nesia, with which it enters into combination readily. This salt is well
known to be very insoluble in weak ammoniacal solutions, and the idea
of taking advantage of this property for the extraction of ammonia from
them is not new. Various attempts have been made to effect the object
by bringing together in the ammoniacal liquid to be treated phosphoric
acid and magnesia in the form of soluble salts of those substances, in the
hope that the ammoniacal phosphate of magnesia would be precipitated;
but all such attempts have proved failures for reasons well known to
chemists. When forming this salt for purposes of analysis, chemists
invariably allow the liquid to stand for several hours after concentrating
the solution operated upon by evaporation, as the salt, notwithstanding
its insolubility in weak ammoniacal solutions, has the peculiarity of
precipitating very slowly. The conditions of concentration and long
standing are of course impracticable with sewage and other polluted water.

page_text: in consequence of the large volumes that will have to be dealt with, and
their unceasing flow in most cases from the sewers, and the processes
alluded to have not extracted a sufficient quantity of ammonia to justify
the expense of the treatment.
The mode of operation which I adopt is this :-I take phosphate of
magnesia in a fine state of division (by preference in the form of a paste
and prepared in any convenient manner) and agitate the ammoniacal
liquid to be treated with it in tank No. 3. The result is that the phos-
phate of magnesia removes from the liquid the ammonia with which it
is brought in contact.
The conditions necessary to ensure success are (first) that the phos-
phate of magnesia shall be in the hydrated and not the anhydrous
condition, as this salt, after ignition, shows so little tendency to unite
with the ammonia as to be practically inefficient; second, that the
phosphate of magnesia shall be present in sufficient quantity and in such
excess as to render the whole liquid treated what may be termed milky,
for if introduced in sufficient quantity only to combine chemically with
the ammonia present in the charge under treatment, the amount of
ammonia extracted will, with any feasible amount of stirring or oppor-
tunity for subsidence, be insufficient to repay the cost of the process.
This will be readily understood, for although substances capable of
forming new chemical compounds will at once unite when mixed together
in a state of solution in their proper combining proportions, this result
is hardly to be expected when one of the substances is in a solid form,
and in order to secure anything like an efficient removal of the ammonia
from its dilute solutions it is necessary that the liquid should be crowded
(so to speak) with active particles of the solid substance. Even when
such a superabundance of the phosphate salt is present the whole of the
ammonia will not be extracted in one, nor indeed will every trace of it
be removed by several operations similar to that above described, and
therefore where possible it is better to employ a second, or even a third
phosphate tank, which I may call No. 3" and 3b, wherein the effluent
from No. 3, after the solid particles of ammoniacal phosphate of magnesia
and the unused (if I may so express myself) phosphate of magnesia have
subsided, may be agitated with a fresh charge of the magnesian phos-
phate. After these tanks have been refilled and emptied several times,
the waste of the magnesian phosphate being made up by fresh additions
of that salt introduced from time to time, the deposit is to be collected,

page_text: and may then be used as a manure, either alone or mixed with the
deposit from the other tanks, or the ammonia may be distilled from it
and collected in the ordinary modes, and the anhydrous phosphate
remaining may be again converted into hydrate by well-known methods,
and used for extracting the ammonia from fresh charges of the
liquid.
The effluent from the phosphate of magnesia tanks should be subjected
to a further treatment, for were the process to stop here there would be
a certain waste of phosphate of magnesia with each charging of the
tanks, as this salt is sparingly soluble in water. To arrest such loss I
treat the effluent liquid from Nos. 3, or 3ª, 3b, with milk of lime in tank
No. 4. The lime may with advantage be prepared from dolomite, as the
precipitate of phosphate of lime will then be mixed with magnesia,
which will be useful for the preparation of the phosphates of magnesia
required in the foregoing processes. The lime used for this precipitation
may also be prepared from minerals containing carbonate of lime and
phosphates intermingled, or of such lime combined with dolomitic
lime as I am enabled by means of the deposit thus produced to
economize in the production of the phosphate of magnesia required for
the above processes. I may use also sulphates or chlorides of iron and
aluminium for the removal of the phosphoric acid from the liquid, both
of the bases of these salts forming insoluble substances with it. Other
salts might be similarly used, but no corresponding advantage for the
increased expense would be gained.
The effluent from tank No. 4 will, after these operations; be found to
be purified to a considerable extent, as a certain proportion of organic
matter will be carried down with each precipitation.
It may be now
filtered through charcoal prepared from the deposit obtained in tank No. 1
(which will be found to possess deodorizing and decolorizing properties
in a high degree) by a process of carbonization, the tarry matters and
ammonia distilled off being collected and utilized; or the effluent may
be filtered through gravel or soil, or employed in irrigation. For efficient
filtration purposes a much smaller mass of filtering matter will suffice
than before these precipitations.
Although I consider the above to be the best mode of proceedure I do
not confine myself to it, for I may produce similar results by filtering
the clarified sewage water through the crystallised phosphate of mag-

page_text: nesia, or through a mixture of this salt and animal or other charcoal, or
I may use a filter of animal or other heavy charcoal, as the bottoms of
tanks No. 3, 3, 3b, and by keeping the phosphate of magnesia in sus-
pension in the liquid above allow the liquid to filter through the bottom
instead of being drawn off at the top.
Again, in lieu of stirring the phosphate of magnesia in with the liquid,
I may keep it in a state of suspension in the liquid, by pumping air into
the tanks, and I may also keep it in suspension by allowing the clarified
liquid to rise from the bottom upwards and flow over the top. By
properly regulating the depth of the tanks, the flow of liquid, and the
amount of phosphate of magnesia, I may even render the process con-
tinuous; but I have found this and the other processes above mentioned
less easy to carry out than the first described process where ordinary
subsidence is employed for the separation of the liquid from the deposits
obtained.
In
cases in which there is difficulty in arranging for so great a number
of tanks I may combine the first and second precipitations by adding,
first, the lime to the sewage as it flows through the sewer, and then,
when this has had time to act, by adding also in the trough which
conveys the sewage to the first settling tank the phosphoric acid or
soluable phosphate to precipitate the lime still remaining in solution, or I
may introduce the soluble phosphate into the conduit which leads to the
phosphate of magnesia tank, and allow the phosphate of lime to settle
in it with the magnesian salts; or again, I may dispense altogether with
the operations to be performed in No. 4, but at the cost of losing some
of the phosphate of magnesia.
Again, in lieu of introducing into tanks 3, 3ª, &c., phosphate of mag-
nesia as such, I may make use in the tanks themselves of substances
which will by combination form this salt; for instance, I may from time
to time put into tank No. 2, or into the channel that leads to it, an
excess of superphosphate, such as superphosphate of magnesia, and
allow the liquid so charged to pass into tank 3, 3, &c., to be there
agitated with a large quantity of magnesia to be used by preference in the
hydrated state. The result of this treatment will be the production of
phosphate of magnesia in a condition to combine with the ammonia of
the liquid, either when the phosphate is in process of formation, or sub-
sequently to its formation, on coming into contact with it.

page_text: There are other means also by which the special object here in view
may be accomplished, such object being the procuring that the
ammoniacal liquid to be dealt with shall for reasons already given be
treated with a very large proportion of phosphate of magnesia as com-
pared with the amount of ammonia in the volume of liquid under
operation at any one time. Such other means however of introducing
the phosphate magnesia do not yield as satisfactory results as the direct
introduction of this salt, as above described.
Having now described my Invention of improvements in the treatment
of sewage water, and having explained the means whereby I carry the
same into effect, I wish it to be understood that I claim as the Invention
secured to me by Letters Patent, as aforesaid, treating sewage from
towns and manufacturing processes with hydrated phosphate of magnesia
in the manner or manners herein set forth, for the purposes of purifying
such waste liquid and obtaining the ammonia contained therein.
In witness whereof, I, the said Henry Young Darracott Scott,
have hereunto set my hand and seal, the Nineteenth day of
September, in the year of our Lord One thousand eight hundred
and seventy-two.