View report page

3
DIVISION I—GENERAL.
BY
PROFESSOR FRANK CLOWES, D.Sc. (Lond.), F.I.C.
(iChief Chemist to the Council).
1.—Aeration of Coke-beds.
2.—Microscopical Examination of the Deposit on the Coke.
1.—Aeration of COKE-BEDS.
The preliminary experiments which indicated that the aeration of the coke-beds was satisfactory
(Second Report, page 9) have been repeated, and the new results fully corroborate those
which were quoted in the second report.
2.—Deposit on the coke.
It was stated in the Second Report [page 6 (d)] that "the surface of each piece of coke had
in course of time become covered with soft matter": and it was ascertained that this matter contained
some fine coke particles and sand grains, cotton and woollen fibres and diatoms, but consisted
largely of chaff, straw, and woody fibre.
As this deposit upon the coke increased, the sewage capacity of the coke-bed decreased.
A series of gaugmgs of capacity of the thirteen-foot coke-bed showed that the decrease of capacity
was proceeding at the rate of one per cent. of the original capacity per week. As this threatened
a short life to each coke-bed when it was dealing with raw sewage, experiments have been undertaken
with the view of preventing, or at any rate considerably retarding, the choking of the cokebed.
As has been already stated, the matter which was deposited upon the coke consisted largely
of cellulose (chaff, straw, and woody fibre). Cellulose is known to be only very slowly acted upon
by bacteria. It seemed advisable, therefore, to attempt the separation of these cellulose matters
from the raw sewage before it was introduced into the coke-beds.
A few rough preliminary experiments were made in order to ascertain whether this matter
could be separated by sedimentation without separating the putrescible matters of the sewage.
In the first experiment the raw sewage was allowed to flow, on its way to the coke-bed,
through a wooden trough which had several cross divisions reaching half-way from the bottom to
the top. In this trough the matter which separated by sedimentation consisted almost wholly of
particles of chaff, straw, and woody fibre. This sediment remained perfectly inoffensive when kept
in the moist or in the dry condition. The dry matter burned readily when it was kindled. The
portion deposited at the entrance to the trough contained about 52 per cent. of combustible matter,
whilst that deposited near the end of the trough contained about 70 per cent. This result appears
to indicate that the waterlogged cellulose matters may be separated by sedimentation, and may
subsequently be dealt with in a furnace or destructor.
In order to ascertain how far this process of rapid sedimentation prevented the choking of
the coke-bed, another preliminary experiment was made by feeding the raw sewage into the cokebed
through a tank. The sediment thus obtained was not foul. The rate of choking of the cokebed
was reduced from about 1 per cent. per week of its original capacity to 0.64 per cent.
A further trial is now being made by filling the coke-bed through a settling trough; and
in this trough the rate of flow of the sewage will be varied, with the view of ascertaining the rate
which is most suitable for depositing grit and cellulose without allowing deposition of fæecal
putrescible matters.
Note.—In the Second Report on the Bacterial Treatment of Crude Sewage, p. 8, line 6, it will be understood
that the statement "the volume ot the coke amounts to 960 cubic feet," includes the air spaces of the coke,
and that these volumes are together equal to 960 cubic feet.