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to the discharge of effluent extend far above the highest point at which examinations
are made. Information as to conditions in the upper tideway will be needed
in order to test the effect of the improved treatment which is to be commenced
in the near future, and this can most conveniently be obtained by the aid of a boat.
At the outfall laboratories, systematic daily examinations ot the sewage reaching
the outfalls and the resulting effluent and sludge, as well as of the water of the
River Thames at both high and low tides have been continued. The systematic
analysis of samples in connection with the working of the outfalls have also been
made at these laboratories in addition to the research work undertaken in connection
with activated sludge. Much attention has been given during the year to
boiler control at the outfall works and on the sludge vessels.
Outfalls.
Throughout the year research has been continued into the biological treatment1
of sewage and of sewage effluent by aeration in contact with free humus, " activated
sludge " as it is usually called. Concurrently with this research on treatment a
systematic examination of the River Thames has been made, and many points have
been investigated. The comprehensive scheme adopted has placed in the possession
of the Council readily available information of the condition of the River Thames
on which to base an opinion as to when and how to undertake any modification of
the present method of sewage treatment.
Treatment
sffluent.
In March, 1926, a full report on the position at that time both as regards the
condition of the Thames and the results of researches on biological treatment of
sewage was submitted to a special sub-committee of the Main Drainage Committee.
Coincidently a report on the engineering aspect of the question was submitted by
the Chief Engineer. After considering these reports the Committee consulted
Professor H. R. Kenwood and Professor W. E. Adeney, both recognised authorities
on such matters. In view of the unanimity of opinion of the Council's officers
and these authorities, the Committee advised the Council to sanction the construction
of a first large unit for further treatment of a portion of the effluent now discharged
from the Northern Outfall.
Detailed drawings for this large plant which is intended to treat from five tc
ten million gallons of sewage are now being made. The plant, which embodies new
and important features, is the outcome of the long researches conducted at the
Outfalls. These researches have been described in some detail in a paper on " Modern
Methods of Sewage Disposal," by Colonel Butler and Mr. Coste, read before the
London Section of the Society of Chemical Industry in January, 1927, and printed
in the Transactions of that Society (J.S.C.I. 1927. XLVI 49-59T).
During the past year various points arising in connection with the form which
a large-scale plant should assume have been investigated, but for some time work
on the new overhead sludge store at Crossness interfered with the working of the
small experimental installation which has been in use for many years.
Whilst the questionof improvement of effluent has been approaching a solution,
attention has been directed to the collateral question of improvement of the sludge
sent to sea. So far experiments conducted under the direction of the Medical
Officer (General Purposes) and the Chemist have only been of a tentative character
and on a laboratory scale, the objects sought being a reduction of the volume of
sludge and the possible utilization of the evolved gases.
Treatment of
sludge.
A statistical examination of the data available shows that in the dry year
1921 the percentage of sludge varied from 51 to 8.9 and in the wet year 1927
varied from 4.7 to 9.7. The figures are based on the weekly averages at the
southern outfall.
The percentage proportion of volatile (" organic ") matter (V) is given approximately
by the equations—
(1921) V = 0.41 x dry matter + 1.6 (greatest divergence 0.4 per cent.)
(1927) V = 0.35 x dry matter + 1.85 (greatest divergence 0.5 per cent.)
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