New or Improved Method in Sewage Precipitation.
Year: 1895

page_text: Date of Application, 29th Oct., 1895-Accepted, 30th Nov., 1895
COMPLETE SPECIFICATION.
New or Improved Method in Sewage Precipitation.
I, GEORGE CARRINGTON PURVIS of 3 Buccleuch Place, Edinburgh in the
County of Midlothian, N.B. Doctor of Medicine, 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 :-
The invention relates to a new or improved method in sewage precipitation.
The principle of the invention consists in adding carbon dioxide (Co₂) to the
sewage and then lime (preferably in the form of milk of lime) in slight excess to
the sewage. The slight excess of lime not only insures the complete removal of
the carbon dioxide but also allows of this excess combining with and precipitating
organic or other substances present in the sewage.
Sulphur dioxide (So,) may be employed in conjunction with carbon dioxide
when the sewage is in a foul state due to sulphuretted hydrogen or its compounds
occurring in the sewage, but the use of sulphur dioxide (ie., for ordinary fresh
sewage) should if possible be avoided, the lime added must be again slightly
more than sufficient to combine with the sulphur dioxide and carbon dioxide added
to the sewage.
The carbon dioxide and the sulphur dioxide should be as thoroughly as possible
incorporated with the sewage, which should if possible be screened, either (1) by
means of a tower loosely packed with cake, brick, or some suitable material down
which the sewage descends whilst the gas (Co₂) or gases (Co, & So,) ascend (2) by
passing the gas or gases into the sewage under slight pressure, or (3) by making a
strong aqueous solution of the gas or gases under pressure and adding such a
solution to the sewage; or by any other suitable means.
The following example will suffice to shew the quantities of carbonic acid gas and
lime required for a sewage whch is practically neutral to test papers.
Carbon dioxide from 6 to 12 grains per gallon of sewage.
Lime (CaO) from 8.5 to 16 grains per gallon of sewage.
In other words 6 grains of carbon dioxide corresponds to 85 grains of lime, and
12 grains of carbon dioxide to 16 grains of lime.
These quantities, are of course liable to variation depending on the particular
kind of sewage, but the rule is, that for sewage which is neutral or almost
neutral to test papers the "excess of lime" (i.e. lime which is over and above
that which has combined with the carbon dioxide or the carbon dioxide and
sulphur dioxide present in the sewage) ought not to exceed 0.5 to 1.5 grain per
gallon of sewage. It is obvious that lime could be added first and the carbon
dioxide afterwards, but quicker precipitation and more uniforin combination is
obtained by adding the gas (Co₂) first and the lime afterwards. Further any
cheap salt of alumina and iron (such as the sulphate of either metal) may be
combined with the lime as precipitating agents, the lime, however, should still
be in slight excess of what is necessary to produce hydrates, and to combine
with the gas or gases passed into the sewage, but this addition of salts of
alumina or iron or both is not a necessary or essential part of my process.
The carbon dioxide may be cheaply produced by burning coke or other
carbonaceous matter in suitable furnaces or by decomposing carbonate of lime
(i.e. limestone) by the aid of heat in the latter case the lime obtained may be
employed for precipitation of the sewage as described above.

page_text: Sulphur dioxide is cheaply prepared by burning iron pyrites, it can also be
obtained by burning sulphur, also as a bye product in several metallurgical
operations such as copper smelting.
.
' t
Having now particularly described and ascertained the nature of my inven-
tion, and in what manner the same is to be performed, 1 declare that what I
claim is :-
-
To add (1) carbon dioxide or carbon dioxide and sulphur dioxide to the sewage
and then (2) a slight excess of lime preferably in the form of milk of lime-to the
sewage the lime added being such as to completely remove the gas or gases
added to the sewage yet not such as to render the sewage more than faintly alkaline
to ordinary test papers, substantially as herein before described.
'ca Dated this 28th day of October 1895.
JOHNSONS,
115 St. Vincent Street, Glasgow, Applicant's Agents.