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55
Provision was made for additional treatment of sewage at the outfalls, but it
was not found necessary to resort to such treatment.
At the outfall laboratories systematic daily examinations of 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, and other analyses in connection with the working
of the outfalls have been continued. Much attention has also been given to chemical
work relating to fuel economy and systematic examinations of fuel, feed-water, etc.,
are now made on lines similar to the work at Greenwich power station. In addition
much experimental work needed to throw light on matters connected with the
river, and Sewage treatment, has been undertaken at these laboratories.
Outfalls.
The frequent occurrence of supersaturation with dissolved nitrogen of water
in the River Thames and its estuary has been the occasion of some investigation in
the river itself as well as in the laboratory. The anomalies observed in the estuary
made it desirable that some information as to the proportion of nitrogen found in
solution in the open sea should be obtained. A consideration of results obtained
on the water of the North Atlantic by one of the oceanographic expeditions of the
nineteenth century had raised the expectation that the dissolved nitrogen in water
some distance from the coast would vary very little from saturation, and the occasion
of the delivery of the S.S. “ John Perring ” seemed to promise an opportunity for
elucidating the point. By the kindness of the builders of the “ John Perrin,” I
was enabled to detail one of the chemical assistants to make investigations on the
voyage of the ship from the Clyde to Erith, and, as a result of this opportunity, it was
ascertained that
(1) Supersaturation with dissolved nitrogen occurred at all points of
observation from the Clyde to the Thames. It was, however, present in lesser
degree than had been observed in the neighbourhood of the Black Deep.
(2) The explanation of this phenomenon cannot be the same as that to
which is to be ascribed its persistent recurrence in considerably higher degree
at places such as Erith. There can be little doubt having regard to the distribution,
amount and other facts elucidated as to the excess of free nitrogen in
river water in the neighbourhood of the outfalls that its origin is to be found
in the breakdown of nitrogenous organic matter discharged as sewage into
the river.
(3) It has not hitherto been generally recognised that the most valuable
constituent of sewage, the nitrogenous organic matter, when discharged as
at the Council's outfalls into estuarine waters, becomes largely resolved into
its elements. The world's stock of combined nitrogen by this process of dissolution
into free elemental nitrogen and simple compounds of other elements is
thereby depleted to the very serious extent which the vast quantities represented
involve.
(4) Nor can there be much doubt that similar processes are at work in
respect of the sludge discharged into the Sea at the Black Deep. But that the
excesses of nitrogen observed in the estuary are to be ascribed wholly to this
cause is disproved by the findings on the voyage from Greenock to London.
For this reason the observations are valuable.
A new and so far inexplicable phenomenon has to be recorded, while a tentative
view as to the part played in the final stages of sewage disintegration—the end
changes—in their effect upon the gaseous content of marine waters, has to remain
in suspense until further knowledge justifies a conclusion.
Gases
dissolved in
sea and
estuarine
waters.
During the year, various minor, but important, matters have been investigated,
such as the effect of adding activated sludge in successive increments to the liquid
to be treated ; the effect of variations in depth of tanks used for treatment and the
immediate results of mixing activated sludge with effluent from the sedimentation
channels. Incidentally it was found that no advantage was obtained in treatment by
Biological
treatment of
sewage.