Medical Officers of the Army of India.
whole operation as regards the working of the installation should only occupy three
or four hours daily, and as the result of experience the writer can testify that one or
two mehters can be relied on to perform their simple functions after due training.
With three large model installations going at the same time, no trouble whatever
was experienced in getting the necessary manipulation of discharging the filters
by mehters who had been carefully instructed at first, even when supervision was
at times withdrawn.
The filtering material of the first upward bed rests upon a false bottom in the form
of a grating (made of old railway rails) which is placed about a foot above the true bottom.
On this grating is first arranged a layer of old tins, bottles, and pots, of all shapes and sizes
and generally with their open mouths directed upwards; this layer should be 2 feet in
depth. Upon this is laid down a layer of coarse clinkers or burnt clay, which for half a
foot in depth should be fully the size of a closed fist, and for another half foot, of half this
size. Lastly, on top of this, a layer 1 foot deep of somewhat finer clinker, graduating
from1"—½"—1\3" from below upwards, and upon the whole, a layer 2" thick, of broken
limestone, to keep the fine clinker from floating.
For the downward filters, I recommend coarse burnt clay or clinker of such a size as to
p a s s a 1 ½ i n c h m e s h a n d t o b e r e j e c t e d b y a h a l f i n c h m e s h ; t h e w h o l e t o b e f u l l y t h r e e f e e t
deep and to have layers of broken limestone, 2 or 3 inches thick, at intervals of one foot
throughout.
One word on the practical point of the rate of admission of the sewage to the
apparatus; it would perhaps be well to have a valve on the inlet pipe to the first upward bed,
which could be only partially opened to diminish the rush and force of the in-going sewage,
as it is necessary that the flow should be gentle and equable. There would be some advantage
in providing a preliminary tank, antecedent to the first upward bed, and with its bottom at
a level of the water-seal in the latter, and this preliminary tank might well be of a capacity
equal to that of one of the downward filters. This tank would receive the sewage, and be con
- n e c t e d t o t h e i n l e t p i p e o f t h e f i r s t u p w a r d b e d , a v a l v e b e i n g i n t e r p o s e d ; b y s i m p l y o p e n i n g
this valve a definite quantity of sewage would be let into the fast upward bed and drive over
the same amount to fill one downward filter, and this could be repeated till both or all the
filter beds have been filled. This arrangement allows of equalization and control of flow
through the apparatus and requires the minimum of manipulation. Where a proper system
of removal by drains is not carried out, it is indispensable, as it then acts as a mixing-tank.
The second series of plans on Plate I represents the arrangement of the
apparatus when the natural gradients fail; the hydrolysing tank is sunk in an
excavation, and the effluent is raised by a Persian-wheel and is then passed on to
the filters. It is obvious that a hand or steam pump may more effectually
replace the Persian-wheel, which however is cheap and simple and requires only
one bullock to raise the effluent to a height of fifteen feet. But with a pump
greater advantages may be obtained, and thus with the addition of a compara
- t i v e l y t r i f l i n g p i e c e o f a p p a r a t u s , n o c a n t o n m e n t i n I n d i a n e e d b e d e p r i v e d o f t h e
immense advantages of automatic removal of its waste.
149
O O