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division i—chemical and general.
I.—INTRODUCTORY SUMMARY.
Early in 1898 a First Report was printed by the Council on the bacteriological
examination, by Dr. Houston, of London crude sewage as it arrived at the Outfalls at
Barking and Crossness. This was followed by a Second Report, giving the results
obtained by the chemical and bacteriological examination of the crude sewage and of
the effluent from the coke-beds at Crossness. A Supplementary Report on the deposit
found upon the coke of the coke-beds was issued in October, 1899.
The present Report gives a similar statement of the results obtained in the
experimental bacterial treatment which has been carried out at the Northern Outfall
(Barking) and of the experimental treatment carried out at the Southern Outfall
(Crossness) since the issue of the last Report.
, The superintendence of the chemical work has rested in the hands of Mr. E. Brooke
Pike, the chemist at the Northern Outfall, and of Mr. J. W. H. Biggs, the chemist at the
Southern Outfall, and the successful carrying out of the processes has been due to the
careful work of these gentlemen and to the co-operation of Messrs. H. Stokoe and E. J.
Beal, superintendents at the Outfalls.
The bacteriological work has been in the hands of Dr. Houston, who makes a
separate statement of his results in Division II. of this Report.
The process employed at both Outfalls has been that of "intermittent contact"
with frequent aeration of the coke surfaces.
The acre coke-bed at the Northern Outfall has received an effluent resulting
from sewage which has been mixed with solutions of lime and iron sulphate and has
then been subjected to sedimentation. The smaller coke-beds have received sewage
which has not been mixed with chemicals, and which has, as a rule, not been freed from
its suspended solid matter by sedimentation.
Since the cellulose substances in the suspended solid matter of the sewage are
only dealt with slowly by the bacteria in the coke-bed, they tend to accumulate on the
coke and to diminish the sewage capacity of the bed; they also tend to diminish the
extent of purification from the dissolved organic matters of the sewage. Hence the
acre bed, which receives the effluent from chemically treated and sedimented sewage,
has yielded better results than the smaller experimental beds.
A very rough process of sedimentation of the sewage, without the use of
chemicals, was effected at the Southern Outfall by allowing the crude sewage to flow
through a large tank on its way to the coke-bed. This sedimentation considerably
retarded the choking of the coke-beds.
Last Christmas an experiment was made (see page 15) on the whole of the South
London sewage by allowing it to flow at a comparatively rapid pace through one of the
large settling channels at the Outfall Works. In this way the larger portion of the solid
suspended matter of the sewage was deposited; a portion of the effluent from this
sedimentation process was treated in a small bacterial coke-tank and was found to
undergo the usual amount of purification, and to furnish an almost clear and entirely
inoffensivp and nonputrescible effluent. No reduction in the capacity of the coke-bed
occurred during the period of experiment.
From this experiment it may be inferred that simple rapid sedimentation of the
crude sewage on the large scale, followed by intermittent bacterial coke treatment will
furnish an effluent suitable for the lower river, together with a sludge deposit which
could be dealt with in the usual way.
It seems reasonable that the experimental treatment of the sewage by rough
screening, followed by rapid sedimentation without the previous introduction of
chemicals, might now be attempted on a larger scale, and that by this means an effluent
of much greater purity than that at present discharged might be sent into the river.