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BACTERIAL TREATMENT OF CRUDE SEWAGE.
I.—BRIEF SUMMARY OF THE ORIGIN, METHOD AND RESULTS OF THE
EXPERIMENTAL BACTERIAL TREATMENT, WITH A STATEMENT OF
CONCLUSIONS AND RECOMMENDATIONS.
Introductory.
The period of experimental treatment by bacterial agency at the Council's
Outfalls has for the present been concluded, and. the time appears opportune therefore
for briefly stating why the experiments were undertaken, the nature of the experiments,
the results which have been arrived at, and the recommendations which
they suggest.
Origin of the Experimental Bacterial Treatment.
The whole of the raw, unsettled sewage of the Metropolis was formerly
allowed to flow without any previous treatment into the Thames. The result was
that the stream, more especially in summer time, became insupportably foul. The
foulness arose partly from sewage mud or sludge deposited on the foreshores, partly
from black sewage scum floating on the surface of the river, but also from putrid
changes occurring in the sewage substances dissolved in the water itself.
It was decided to remove the main source of this nuisance by subjecting the
sewage to straining or screening, and then to settling or subsidence, and to pass
the more or less clear effluent from this settling process into the Thames many miles
below London. Under this scheme the coarse screenings are now disposed of on
farm land and the foul settled matter, or sludge, is carried out and discharged
on a falling tide in the estuary. The sedimentation of the sewage has in recent
years been much facilitated by the addition in moderate proportion of chemical
solutions.
The above treatment, which is still in operation at the Outfalls, has prevented
entirely the fouling of the foreshores and of the river surface with sewage sludge.
Those who proposed the above remedial measures, however, stated that the
sewage effluent would still carry into the river a large amount of putrescible matter
in solution, and recommended that, as opportunity occurred, the effluent should be
further purified by land treatment or by other means, before it entered the river.
This further treatment has never yet been attempted on the large scale.
No suitable land for land treatment existed at the Sewage Outfalls, and no other
method of treating the effluent was known at the time.
The Massachusetts experiments on the treatment of sewage effluent in cokebeds,
which enabled the bacteria present in the sewage to effect the necessary
additional purification, were subsequently published. They appeared suitable to the
purpose in view, and the Main Drainage Committee of this Council accordingly
authorised my predecessor to start an experimental trial of the process at the Council's
Outfalls.
At the time of my appointment as Chemical Adviser to the Council, the
results arrived at by my predecessor were so promising that I strongly recommended
their continuance on an extended scale; and for four years, with the assistance of
the Chemical staff and with the co-operation of the Superintendents at the Outfalls,
I have conducted this experimental purification of the sewage effluent, and have
arrived now at results and conclusions which I am convinced are of the greatest
importance, and are worthy of the most serious consideration of the Committee
and of the Council.
Description of the Bacterial Experiments.
When I recommended the Committee to continue the experimental treatment,
there was a large bacterial coke-bed, one acre in area, at the Northern Outfall which