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It will be seen that the increase in the amount of oxygen absorbe'd by the liquids after
incubation for seven days, as compared with the amount absorbed at the time of collection, was
100 per cent. greater in the case of the effluent from the chemically treated and sedimented
sewage than it was in the case of the coke-bed effluent. In addition to this comparison it will
be observed that out of 10 samples of the coke-bed effluent, 8 were not putrescible, and the
other 2, if putrescible, were so only to a very small extent, as the indications were of a very
indefinite nature; also the .10 samples were free from sulphuretted hydrogen, whereas, in
the case of the 15 samples of crude sewage, of settled sewage and of chemical effluent they
were all putrescible and black in appearance, and 14 of them contained sulphuretted hydrogen,
and the other sample was very foul.
From these observations it is evident that the coke-bed effluent, when compared with the
effluent from the chemically treated and sedimented sewage, is one that would abstract from
the river water a much smaller amount of its dissolved oxygen than that which is abstracted
by the effluent at present discharged into the river. It would also, if discharged into the river,
impart to the water no offensive colour or odour, either at first or at any later stage.
VIII.—4s to the Extent to which the Liquid Capacity of a Coke-bed is affected by the Size of the Coke
Fragments, by the Length of Time during which the Coke has been soaking, and by the Draining
Period of the Bed.
In the Third Report on the Bacterial Treatment of Crude Sewage the results were given of
tests as to the capacity of coke-beds composed of coke of different sizes. The results of the
tests tended to show that as the shape of the particles of the materials of which a coke-bed was
formed, departed from the spherical form the capacity of a coke-bed became more directly
proportional to the size of the fragments of the material of which it was composed.
Experiments were conducted during February and March, 1900, to ascertain the variations
in the capacity of a coke-bed arising from the length of time during which the
material composing the bed had been soaking and by the length of time during which it had
been draining.