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Major Stamners, in his article of Dibdin's slate beds at Devizes,
says the whole process from start to finish is aerobic, the anaerobic
treatment in septic tanks being entirely done away with, and adds,
as a result of his visit, that the installation has been in continuous
use for over three years; during that time it caused no trouble and
has worked efficiently. In installations, when septic tanks are
employed, you always get trouble and expense with sludge, and
not infrequently passing on to the filter and contact beds, causing
clogging and inefficient action. In the primary beds at Devizes,
after three years' use, there was only a deposit of an average of
two inches at the bottom of humus; this formed a few months
after commencing work, and has not increased. At Devizes it is
calculated that under this system the annual expenses have
decreased from £700 per annum (which was the cost of the
chemical and sludge pressing process) to £200 per annum, so
that any extra capital charge which may be necessary at its installation
will soon be met by saving on working expenses. Lieut.Col.
Firth, Professor of Hygiene in the Royal Army Medical
College in Notters Hygiene, 1908, at page 514, says: "Dibdin's
suggestion advocating the use of slate debris supported on suitable
slate blocks for furnishing a matrix, appears to offer a reasonable
hope of minimising the sludge problem "as the extra spaces available
doubles the working capacity of the bed," and at any time the
accumulation of silt may be flushed from the slates and the bed
restored to its original condition as new. A detritus washed off
the slate slabs is found to dry inoffensively when exposed to the
atmosphere and to assume a condition resembling ordinary mould.
An installation of this kind at Devizes has dealt with the whole of
the "unscreened and unsettled" sewage of that town satisfactorily,
and by continuing in one slate-filled tank, the double effect of the
earlier digestive tanks and contact beds, marks a distinct step
toward simplification." I hear on good authority that the War
Office have made a decided move in adopting the slate bed method
in two of their largest camps, a step which, I feel sure, will bring its
merits before all public bodies.
Since writing the above, I have had the opportunity of reading
further experiments by Mr. Dibdin, explaining that the action of
the "living earth" or deposit on the slates is not due to purely
physical and chemical causes, but is the result of digestion. He
also demonstrates the rate of destruction of the varied food stuffs
placed upon the deposit, as these experiments have been carried
out on "deposit" removed from slates at our own works, the
result is of special interest to this Council. I have, therefore, with
Mr. Dibdin's permission, attached a full report from the January
7th, 1909, issue of the Sanitary Record.