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conditions. So far, the problem of treatment, of the effluent at present discharged
from the outfalls, with activated sludge has not been directly attacked, at any rate,
for a sufficiently long period to justify any conclusions. On general grounds, and
having regard to the experience of the Birmingham Sewage authorities, it would
appear that the treatment of effluent, rather than raw sewage, is a most promising
method. It would have the advantage that a great part of the impurities would
be removed, as at present, in the form of a relatively dry sludge, and would probably
enable sufficient treatment with activated sludge to be given in a relatively short
residence period in the treatment tanks or channels.
Experiments on the keeping properties or stability of the effluent obtained in
the " paddle " plant have shown conclusively that, although the full oxidation of
all the matters in the original sewage has not been made an aim of treatment, the
effluent is unlikely to make any appreciable demand on the self-purificatory powers
of the River Thames. This is an important fact, as showing that the prolonged
stay in treatment tanks required to produce complete nitrification would be
unecessarv.
River
Wandle.
The condition of the River Wandle, to which attention has been called in past
years, both in and before it reaches the County of London, has been the subject of
investigation and conference between the various bodies concerned. There appears
to be general agreement that, in addition to the extensive scheme of the Wandle
Valley Drainage Board for improving the character of their effluent, attention
should be given to the stream itself throuhout the whole of its course.
River
Thames.
The systematic examination of the River Thames was continued in 1923 at
points from Waterloo Bridge to the Edinburgh Lightship, which is in the vicinity
of the discharge area for sludge from the Council's outfalls, and for other waste
materials. In addition to examination of the water, the survey of the river bottom,
which has been in process for some time, was continued throughout the year. The
results obtained from the examination of both water and material from the bed
showed that, from the Chapman Light at the upper end of Sea Reach onwards to
the estuary, the evidence of pollution and deterioration of the river was small and
rapidly decreased seaward. In the neighbourhood of actual discharge, no evidence
of widespread pollution was at any time found.
The year was remarkable for the high temperature reached in June. Having
regard to the temperature of the water and the decreased flow of the river at this
time provision was made for additional treatment of sewage at the outfalls ; but a
general fall of temperature caused improvement in the river water and the treatment
was discontinued.