BIOLOGICAL SYSTEM FOR THE DISPOSAL OF NIGHT-SOIL.
Since this chapter was written, some 12 years ago much research work has
been carried out in 1906. This was in India first systematised by Dr.
Fowler in his report on “Septic Tanks in Bengal” and has been carried on
by Major Clemesha, I.M.S., Sanitary Commissioner, Bengal, whose work on
“Sewage Disposal in the Tropics” published by Messrs. Thacker, Spink &
Co., Calcutta, is a most useful one and should be consulted by those
interested in the subject.
In the present state of knowledge of the science, it would be unsafe to
discharge the effluent into a water-supply of small volume used for
drinking purposes below the point of discharge, or in fact into any
water which may be a potential source of water-supply, unless it be
first sterilised. This can be easily and economically done with chloride
of lime.
In dealing with the resultant liquid of bacteriological treatment it is
safest to consider it as a possible source of danger, and to discharge
it either into the storm-water drains of a town, on land for irrigation
purposes, for which it is most valuable, or into a large volume of
running water, as circumstances admit of.
The great advantage of bacteriological treatment of night-soil, and one
which it is impossible to overestimate, is, that it enables the excreta
to be disposed of when fresh, eliminates the necessity of stale
night-soil being carted through crowded thoroughfares at a very low rate
of speed, and consequent danger of the food and water-supply of the
people being contaminated by the germs of disease conveyed by flies, or
blown on in the dust. Latrines can be constructed over septic tanks, the
home of the anærobic bacilli, where the excreta at once passes in, or
dumping septic tanks can be worked at the night-soil depôts, where the
stuff is at present collected, as at Darjeeling.
In Military Cantonments, where enteric is generally more or less
epidemic, it is most important that the night-soil be treated by
biological methods before it be applied to the soil, as installed at
most of the mills on the banks of the Hooghly, and at the East Indian
Railway Workshops at Jamalpore.
[Sidenote: Septic Tanks.]
Of the various methods of bacteriological disposal, the closed septic
tank is, for climatic reasons, the most generally suitable for India. In
this the anærobic bacilli are provided with a congenial working place in
the closed tank; and the ærobic ones are similarly provided for in the
filter beds; the open septic tank, however, gives equally good results,
as the scum, which rapidly forms on the surface, and which generally
attains a considerable thickness, enables anærobic conditions to obtain
in the tank itself, but care must be taken that this scum is not broken.
[Sidenote: Filter Beds.]
The ærobic Contact Bed filters are merely open tanks filled with coal,
coke, or large cinders, through which the liquid is allowed to percolate
at intervals. The bacilli live and flourish in these, and do their work
during the periods from 2 to 4 hours the tanks are charged.
The percolating continuous filters are those over which the effluent is
continuously sprinkled and through which the fluid slowly percolates.
Experiments have conclusively proved that good results can be obtained
from either when a suitable sewage is applied.