IMPROVEMENTS IN THE TREATMENT OF SEWAGE
Year: 1885

page_text: We JOHN MAY HERBERT MUNRO Doctor of Science of the Agricultural College
Downton in the County of Wilts SAMUEL HENRY JOHNSON and CHRISTOPHER
CLARKE HUTCHINSON Engineers both of the Engineering Works Stratford in the
County of Essex do hereby declare the nature of our invention for IMPROVEMENTS
IN THE TREATMENT OF SEWAGE to be as follows:-
•
We treat the substance produced in the Gilchrist Thomas or Basic Process of
steel making known as "Basic Cinder" with acid we employ sulphuric acid of specific
gravity 1.50, in quantity sufficient to combine with the bases present and to alter
the insoluble salts of phosphoric acid into soluble salts employing just sufficient of
the acid to prevent the clear aqueous solution of the product from depositing ferric
phosphate on standing Generally speaking the proportion of rather less than 2 parts
by weight of sulphuric acid specific gravity 1.50. may be added to 1 part by weight
of the cinder the latter being previously reduced to a fine state of division by
grinding or otherwise. The product at first liquid afterwards becomes more or less
solid according to the amount of moisture and acid present and the composition of
the cinder The proper proportion of acid to be used should be previously
determined for each batch of material by a preliminary experiment with a small
quantity of the cinder For the purpose of this Invention it is desirable that the
resulting mass after treatment with acid should not be too hard, because this would
interfere with its easy solubility. We thus produce a mixture containing the
combined phosphoric acid in a soluble form also calic ferrous ferric and magnesic
sulphates etc and the material so produced we call for convenience in this Specifi-
cation by the name of Soluble Cinder and we use it for the precipitation of town
sewage in the following manner
The sewage should first be mixed with milk of lime in excess that is to say there
should be a certain quantity of lime added to it beyond that which is necessary to
render it alkaline and this excess should be a little more than is necessary to
precipitate all the phosphoric acid from the mixture of the' sewage with a suitable
quantity of solution of the soluble cinder made as above described The quantity of
lime will consequently vary with the proportion of soluble cinder that it is intended
to add to the sewage and the quantity of the latter depends 1stly on the degree of
clarification we desire to attain in the effluent water of the precipitating tank and
2ndly on the proportion of precipitated phosphates we desire to secure in the
sludge when it is contemplated to utilize it as a fertilizer after having been pressed
and dried. We therefore do not specify any particular proportions to be used
having sufficiently indicated what those proportions should be to any one skilled in
operations of this character-The precipitate produced by this treatment not onlý.
contains the phosphoric acid of the basic cinder but also that which existed in the

page_text: sewage, and it exists in the precipitate in the form of tricalcic and other phosphates
in a state readily available for assimilation by plants. A large proportion of the
colloid albuminoid bodies present in solution and all the insoluble nitrogenous
matter contained in the sewage are also carried down in the precipitate which
increase its value as a fertilizer. In the resulting sludge as in that from other
processes of precipitating sewage difficulty is experienced in filter pressing in con-
sequence of the slimy glutinous nature of the precipitate. We find however that
by a further treatment of the sludge with soluble cinder or superphosphate of lime,
or better with either in conjunction with lime coagulation and granulation of the
sludge take place which greatly facilitate the operation of pressing and the sub-
sequent drying of the sludge We also find that the cake produced is more friable
and better adapted for mixing with the soil in its subsequent employment as a
fertilizer than when lime only is employed It should be particularly observed here
that when the soluble cinder is employed along with lime for these purposes the
treatment of lime should always precede that of the cinder and the quantity of
lime employed should be such as will prevent any soluble phosphates being lost in
the effluents either from the precipitating tank or the filter press.
By the process above described we effect a more perfect clarification of sewage
than by the use of lime alone and an equal degree of clarification can be effected
with a greatly reduced proportion of lime when the dissolved cinder is employed
along with it.
When lime and dissolved. cinder are employed for the purpose of coagulating
sewage sludge to make it pressable the result is better as regards the granular
character of the sludge than can be effected with lime alone and there is a further
important advantage over lime for the purposé namely that owing to the sludge
being in a nearly neutral condition instead of being strongly alkaline less ammonia
will be lost on drying the sludge and the product will be more valuable as a
manure. By this treatment all the manurial value of the phosphates in the soluble
cinder is recovered along with that recovered from the sewage in the sludge.
Deted this 25th don of 100%

page_text: and to alter the insoluble salts of phosphoric acid into soluble salts employing by
preference just sufficient of the acid to prevent the clear aqueous solution of the
product from depositing ferric phosphate on standing. 'Generally speaking the
proportion of rather less than two parts by weight of sulphuric acid specific.
gravity 150 may be added to 1 part by weight of the cinder, the latter being
previously reduced to a fine state of division by grinding or otherwise. The
product at first liquid afterwards becomes moro or less solid according to the
amount of moisture and acid present and the composition of the cinder. The
proper proportion of acid to be used should be previously determined for each
batch of material by a preliminary experiment with a small quantity of the cinder.
For the purpose of this invention it is desirable that the resulting mass after
treatment with acid should not be too hard because this would interfere with its
easy solubility. We thus produce a mixture containing the combined phosphoric
acid in a soluble form, calcic ferrous, ferric and magnesic sulphates etc and the
material so produced which is similar to a product of a former Patent granted to
Dr Munro No 7740 in the year 1885 we call for convenience in this Specification
by the name of soluble cinder, and we use it for the precipitation of town sewage
in the following manner.
The sewage should first be mixed with milk of lime in excess, that is to say,
there should be a certain quantity of lime added to it beyond that which is
necessary to render it alkaline, and this excess should be a little more than is
necessary to precipitate all the phosphoric acid from the mixture of the sewage
with a suitable quantity of solution of the soluble cinder made as above described.
The quantity of lime will consequently vary with the proportion of soluble cinder
that it is intended to add to the sewage and the quantity of the latter depends,
1stly on the degree of clarification we desire to attain in the effluent water of the
precipitating tank, and 2ndly on the proportion of precipitated phosphates we desire
to secure in the sludge, when it is contemplated to utilize it as a fertilizer after
having been pressed and dried We therefore do not specify any particular pro-
portions to be used having sufficiently indicated what those proportions should be
to any one skilled in operations of this character. The precipitate produced by
this treatment not only contains the phosphoric acid of the basic cinder but also
that which existed in the sewage, and it exists in the precipitate in the form of
tricalcic and other phosphates in a state readily available for assimilation by plants.
A large proportion of the colloid albuminoid bodies present in solution and all the
insoluble nitrogenous matter contained in the sewage are also carried down in the
precipitate, which increase its value as a fertilizer. With the resulting sludge as
with that from other processes of precipitating sewage difficulty is experienced in
filter pressing in consequence of the slimy glutinous nature of the precipitate. We
find, however, that by a further treatment of the sludge with soluble cinder or
superphosphate of lime, or better with either in conjunction with lime, coagulation
and granulation of the sludge take take place which greatly facilitate the operation
of pressing and the subsequent drying of the sludge. We also find that the cake
produced is more friable and better adapted for mixing with the soil in its
subsequent employment as a fertiliser than when lime only is employed.
It should be particularly observed here that when the soluble cinder is employed
along with lime for these purposes the treatment of lime should always precede that
of the cinder, and the quantity of lime employed should be such as will prevent
any soluble phosphates being lost in the effluents either from the precipitating tank
or the filter press.
The following method of treating the sludge is suitable, but the quantities may
be varied, without departing from the principle of the invention.
Take three fourths of cwt of quicklime for every five tons of the wet precipitated
sludge before pressing, slake, and by the addition of water and stirring form it into
a concentrated milk of lime, add this to the sludge and thoroughly agitate, then
add soluble cinder or superphosphate of lime in proportion to render the mixture
only faintly alkaline.

page_text: This treatment causes the solid materials of the sludge to part more freely from
the liquid in the pressing operation.
In the place of soluble cinder we may substitute superphosphate of lime in
proportion sufficient to neutralize the limed sludge.
We sometimes (and especially should the sludge have been left faintly acid by
the preceding operations) add raw basic cinder in the form of powder to the sludge
before pressing it renders the pressing operation more easy and the pressed sludge
more valuable as a manure. Sometimes we add raw basic cinder to the sludge after
pressing.
By the process above described we effect a more perfect clarification of sewage
than by the use of lime alone, and an equal degree of clarification can be effected
with a greatly reduced proportion of lime when the dissolved cinder is employed
along with it.
When lime and dissolved cinder are employed for the purpose of coagulating
sewage sludge to make it pressable the result is better as regards the granular
character of the sludge than can be effected with lime alone, and there is a further
important advantage over lime for the purpose, namely, that owing to the sludge
being in a nearly neutral condition instead of being strongly alkaline, less ammonia
will be lost on drying the sludge and the product will be more valuable as a
manure. By this treatment all the manurial value of the phosphates in the soluble
cinder is recovered along with that recovered from the sewage in the sludge; and
the sludge contains a proportion of sulphate of lime in place of carbonate of lime,
also enhancing its manurial value.
Having now particularly described and ascertained the nature of our said
invention and in what manner the same is to be performed we declare that what
we claim is :-
(1.) The treatment of sewage with basic cinder rendered soluble by acid in such
manner as to obtain therefrom a precipitate and a comparatively pure effluent
water substantially as described.
"
(2.) The treatment of sewage sludge with basic cinder rendered soluble by acid
or with superphosphate of lime and then pressing the same in a filter press; thereby
effecting more efficiently than heretofore a separation of the solid from the liquid
parts substantially as described.
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