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21
Many otherwise experienced authorities on sewage disposal
have expressed a difficulty in grasping the principle of the action
which takes place on "Plate Beds," commonly known as slate
beds, in consequence of that material forming the most convenient
and economical form of plate. It is, therefore, with a view to
making the process clear to those who have not followed biology
in relation to the life processes at work in river water, tidal mudbanks,
&c., that the following detailed account of some experiments
which I have made is set out as clearly and succinctly as possible:—
The idea which some apparently have that the destruction of
waste organic matters must be due to purely direct physical and
chemical causes seems to be the main stumbling block. As a
matter of fact the work accomplished is purely the result of
digestion. On looking at a mass of the deposit on a slate which
has been employed for some time in a bed, the casual observer
would notice nothing but a collection of debris, which is forthwith
dubbed "sludge" and, offhand, relegated to that category, therebydenoting
the foul accumulation of matters obtained in a sedimentation
tank of the ordinary pattern. On smelling the mass, however,
it is at once realised that it differs from ordinary sludge in that it
is inoffensive. On allowing a portion to dry, it does so rapidly
and without the production of offensive emanations given off by
"sludge."
These two facts point to a difference, and invite closer
examination. This may be conveniently made as follows:—
Place a portion of the deposit on a small piece of slate about
3 in. or 4 in. square for convenience, or other suitable support, and
warm it very gently by applying heat to the under surface. A
considerable movement will soon be seen to take place on the
immediate surface, and gradually a heaving mass of minute worms
will struggle to escape from the heated underlayer. These are
clearly arobic organisms whose power of digestion is considerable,
and it is to a great extent their casts which form the inoffensive
humus which escapes from the slate layers with the effluent, thereby
preventing the accumulation which is the cause of the choking of
the old coarse contact beds.
Next, take a fragment from the surface of the deposit by
touching it with the point of a wire and place it on a microscope
glass slide with a droplet of water, covering the whole with a thin
glass cover in the usual manner. Now examine this with a ¼in. or
higher power. It will be at once seen to be largely made up of
innumerable living organisms of great complexity and variety,
other than the worms.
From these simple examinations it will be evident that instead
of an inert mass of matter we have a hive of active and voracious
living organisms, from the lowest type of bacteria up to the highly