DISPOSAL OF NIGHT-SOIL AND TRENCHING GROUNDS.
Night-soil is generally disposed of by being buried in trenches, but
these are frequently too deep: purification largely depends on the
action of the ærobic bacilli, that is, the group of microbes which live
close to the surface of the soil and require air for their existence;
these swarm in the top layers of the earth, but are not found at a
greater depth than 1 foot and diminish enormously in number as this is
approached. In order to obtain the best results, both from a
purificative as well as a manurial point of view, the burial should be
merely superficial and not exceeding in depth the limit of ordinary
cultivation, in order to ensure the ground being thoroughly aërated.
[Sidenote: Selection of Site.]
The sites for trenching grounds should be carefully selected; light
sandy soil unshaded by trees and well open to the south and west will
give the best results. They should be well above flood level, at least 5
feet above the highest known flood, situated on the down stream side of
the bazaar, connected by good _pucca_ roads with it to allow of quick
carriage, as time is the most important factor in the disposal of
night-soil, and should not be in the direction of the prevailing winds
with the town. A fringe or belt of bamboos between the town and
trenching grounds will be found of the greatest use in keeping off flies
which might be blown into inhabited neighbourhoods, and which are a most
dangerous factor in disseminating disease.
[Sidenote: Burdwan Trenching Ground.]
At Burdwan in Bengal there is a successful example of what can be done
with trenching grounds from a financial point of view. There the
night-soil of the Northern Section of the Municipality, where the
latrine system is in force, and which has a population of about 23,000,
is mainly disposed of in a permanent trenching ground of 18 bighas in
area. This is collected from private latrines in covered buckets and
deposited in the conservancy carts at the public latrines, whence it is
removed to the trenching grounds, where trenchers are told off for each
latrine group, who excavate the trenches and are in charge of them;
these trenches are 3 feet wide, 1½ feet wide, 12 to 15 feet in length
and 1 foot apart. The carts empty the night-soil in from one end until a
height of 9 inches of liquid is attained, the excavated earth being then
replaced. During the rainy season Indian corn is grown, and in the cold
weather cabbage, cauliflower, Bengal pumpkin, and other kitchen
vegetables, for which there is a ready sale in the local bazaar.
The trenching ground during the current year 1913–14 has been leased out
for Rs. 600.
[Sidenote: Cultivation of Jute.]
In the damp climate of Bengal jute has been found to grow very
luxuriantly on newly-trenched ground and yields an abundant crop; it
exhausts the soil so much that after the crop has been cut the field can
be re-trenched, an important point when the subsoil water is practically
12 or 18 inches from the surface while the jute is growing. Another
advantage in growing jute is that in certain localities there is a
difficulty in finding a market for vegetables grown on a trenching
ground.
[Sidenote: Muzaffarpur Jail.]
In Muzaffarpur Jail the trenches were made 1 foot deep, 1 foot wide, and
1 foot apart, and varying in length according to requirements; 3 inches
of night-soil are filled in and covered over with the excavated earth;
20 trenches are always kept ready, being excavated the day before. Corn
is found to grow luxuriantly after the trench has been filled in for a
month, and other kinds of vegetables, excepting potatoes, after two
months. Urine and sullage water are buried in different fields and at a
considerably greater depth.
[Sidenote: Allahabad.]
At the Government Farm at Allahabad (United Provinces) the system known
as the Allahabad Shallow Trench was in successful operation, and
provided for the whole of the cantonment and half the municipal
population; there is an unlimited area of land available, the soil being
of various kinds, black cotton, sandy loam and stiff clay. The only
crops grown are grass and sorghum, and it is found that the manurial
value of the night-soil is not exhausted for three or four years.
Trenching can, however, be done every third year on the same land
without making it “sewage sick;” land which was worth Rs. 2 will, after
trenching, fetch about Rs. 10 per bigha for seven or eight years.
At Meerut for the year 1911–12 the sale-proceeds of night-soil and city
sweepings amounted to Rs. 12,871, and at Furrakhabad _cum_ Fatehgarh to
Rs. 18,317.
[Sidenote: Allahabad Shallow Trench System.]
The area required for the contents of a 60–gallon conservancy cart is 80
sq. ft., the most suitable dimensions being 16 feet long by 5 feet wide;
3 inches of the top surface of this space is removed and placed on the
embankments of the plot near which the first line of trenches is dug;
the subsoil thus exposed is then well cultivated and pulverized to a
depth of 9 inches, when the contents of the cart are tipped into the
centre of the trench; the liquid matter rapidly sinking into the
loosened soil, while the solid excreta remains on the top in a layer
less than ⅛ inch in thickness; 3 inches of earth are then similarly
removed from the next trench which is parallel to the first, no
intervening space being left, and thrown over the night-soil in the
latter. The practical working is very simple, as all that has to be
done, is to see that a sufficient number of trenches for the daily
supply are dug the day before and the earth from them placed over the
filled ones. It has been found from experience that night-soil, thus
treated, decomposes in less than a week and, if dug then, no trace is
observable; the effluvium disappears after three days, and crops are
successfully grown immediately after trenching. The Shallow Trench
System is by far the most scientific one, but requires a large area of
land, working out to 545 sixty-gallon carts per acre. At Muzaffarpur
during 1912–13, part of the night-soil was sold for Rs. 1,200, and part
of it trenched in the municipal trenching ground, which was leased out
for Rs. 1,045. The practical objection to this system is the fly pest.
It is therefore only applicable where the trenching grounds are remote,
and to the leeward side of the town. Sprinkling chloride of lime or
quicklime on the top of the trenches prevents the breeding of flies. The
researches of Majors Firth and Horrocks, R.A.M.C., published in the
_British Medical Journal_, however, show that the enteric bacilli is
capable of surviving in soil for much longer periods than has been
believed possible. These can exist apparently in ordinary soil for 65
days, in sewage-polluted soil for at least 53 days, while in soil
sufficiently dry to be blown about in dust for 25 days, and for about a
similar period when exposed to a hot summer’s sun. The authors of this
note have also proved experimentally the translation of infective
material from sun-dried and dusty soil by means of wind, as also by
flies which have walked over or fed on polluted earth, indicating the
advisability of treating night-soil, especially from Military
Cantonments, in septic tanks and filter beds before applying it to
soil—_vide_ Chapter IX, page 50.
[Sidenote: Area of Trenching Ground.]
In order to arrive at the area necessary for a deep trenching ground for
a bazaar of 10,000 inhabitants, and assuming that not more than ⅛th of a
gallon of night-soil per head per diem is removed, provision will have
to be made for 1,250 gallons or, say, 200 cub. ft. If the trenches are
made 1 foot wide, 1 foot deep, and 1 foot apart, and are filled with 6
inches of night-soil, 400 cub. ft. will be required daily, or allowing
for roads and divisions between the plots, say 12 acres, for a year’s
work, or, in other words, the area required is, one acre for 833
persons. The trenches should be divided up into plots or sections for
each latrine circle, excavated, when weather permits, at least a week
before they are used so as to aërate the earth; the bottom of the trench
should also be dug up to a depth of 9 inches for the same reason.
The following extract describes somewhat forcibly what may, and
undoubtedly does frequently occur in many instances:—
“Trenching again is a success in dry soils, but a good deal of ground is
required, and sufficient trenching ground is not always available within
practically workable distances of the night-soil producing areas (public
and private latrines), and often enough, whereas it may be quite
successful in a given ground in the hot weather, it will, in the same
ground, however fresh, prove an absolute failure in the rains, when,
owing to the high water-level in the subsoil, everything trenched is
brought to the surface by the gases of putrefaction, and the entire area
trenched becomes a pestilential bog, crawling with maggots, bubbling
with the foulest odours and swarming with blue-bottle flies, whose chief
delight is to frequent the houses in the neighbourhood and infect both
food and drink.”