The Manufacture of Humus from the Wastes of the Town and the Village
by Sir Albert Howard, C.I.E., M.A.
Formerly Director of the Institute of Plant Industry, Indore, Central India, and Agricultural Adviser to States in Central India and Rajputana.
Reprinted from a paper read at the Health Congress at the Royal Sanitary Institute held at Portsmouth from July 11th to 16th, 1938.
THE forest suggests the basic principle underlying the correct disposal of town and village wastes in the tropics. The residues of the trees and of the animal life, met with in all woodlands, become mixed on the floor of the forest, and are converted into humus through the agency of fungi and bacteria. The process is sanitary throughout and there is no nuisance of any kind. Nature's method of dealing with forest wastes is to convert them into an essential manure for the trees by means of continuous oxidation. The manufacture of humus from agricultural and urban wastes by the Indore Process depends on the same principle -- an adequate supply of oxygen throughout the conversion.
The Indore Process
The Indore Process, originally devised for the manufacture of humus from the waste products of agriculture, has provided a simple solution for the sanitary disposal of night soil and town wastes. The method is a composting process. All interested in tropical hygiene will find a detailed account of the big-chemical principles underlying the Indore Process, and of the practical working of the method, in the five papers cited at the end of this note.
Humus Manufacture at Tollygunge, Calcutta
Perhaps the best way of introducing the application of the Indore Process to town wastes will be to give an account of the recent work done by Mr. E. F. Watson, O.B.E., at the Tollygunge Municipality trenching ground, near Calcutta.
The conversion of house refuse and night soil into humus is carried out in brick-lined pits, 2 feet deep, the edges of which are protected by a brick kerb. The guard rim is made of two bricks laid flat in cement mortar, two quarter-inch rods in the join serving as reinforcement. The upper brick should project 1 inch over the pit to form a lip for preventing the escape of fly larvae. Each compartment of the pit has a capacity of 500 cubic feet and channels for aeration and drainage are made in the floor. The aeration channels are covered with bricks laid open-jointed, and are carried up at the ends into chimneys open to the wind. By this means air permeates the fermenting mass from below. At one point these channels are continued as a drain to the nearest low-lying land. It is an advantage when bricking the pits to give a slight slope towards the aeration channels as this helps in keeping the pits dry in wet weather. The area round the pit is protected by brick soling. Working details of these composting pits are shown in Fig. I.
FIG. 8. Plan and working details of composting pits at Tollygunge, Calcutta.
The method of charging the pits is most important, as success depends on correct procedure at this point. To begin with, a cartload of unsorted refuse is tipped into the pit from the charging platform and spread by drag rakes (Fig. 9) to make a layer 3 or 4 inches thick. Another cartload of refuse is then tipped on this layer and raked into a slope reaching from the edge to the middle of the pit and occupying its whole width. The surface of this slope is slightly hollowed by raking a little refuse from the centre to the sides. A little refuse is also raked on to the sill at the road edge to receive any night soil spilt on it by tipping. Half a cartload of night soil is then tipped on the slope and with the moistened refuse below it is drawn by drag-rakes in small lots until the breadth of the pit is covered. This done, the remaining half-load of night soil is poured on the freshly exposed surface of the slope and distribution by raking repeated until the slope (and the refuse on the sill) is altogether removed and forms a layer over the whole of the pit being charged. Another cartload of refuse is then tipped, another slope made, the sill covered, night soil added and raked away. The whole group of operations is so repeated until the pit is charged. This takes 2 days. The top layer of the first day's charge must be covered with 2 inches of refuse and left unmixed with the layer below. This helps to keep uniform moisture and heat in the mixed charge and to prevent the access of flies. The last operation on the second day is to make a vacant space at the end of each pit for subsequent turning and also for assisting drainage after heavy rains. This is done by drawing up 2 feet of the contents at one end over the rest. The surface is then raked level and covered with a thin layer of dry house refuse.
There is no odour from a pit properly filled, because the copious aeration effectively suppresses all nuisance. Smell, therefore, can be made use of in the practical control of the work; if there is any nuisance the staff employed is not doing the charging properly. They are either leaving pockets of night soil or else definite layers of this material, both of which interfere with aeration and so produce smell.
First Turn. -- Five days from the start the contents of the pit must be turned. The object of this turn is to complete the mixing and to turn into the middle, and so destroy the fly larvae which have been forced to the cooler surfaces by the heat of the mass.
The original mixing of the heap, as well as the turning, are best done with long-handled manure drags by men standing on the division walls or on a rough plank spanning them.
Second Turn. After a further ten days the mass is turned a second time, by which time all trace of night soil will have disappeared.
Watering. In dry weather it may be necessary to sprinkle a little water on the refuse at each turn. The contents must be kept damp but not wet.
In very wet weather, when the surface of the pits is kept continually cool by rain, there is much development of fly larvae before the first turn, but since these cannot escape and are turned into the hot mass and destroyed before they can emerge as flies, no nuisance results. Flies, therefore, are most useful in providing another means of automatic control.
FIG. 9. Long-handled drag-rake and fork used in composting.
Ripening of the Compost. After a further two weeks the material is removed from the pits to the platform for ripening. The whole process, therefore, takes one month. The stacks of ripening compost should be 4 feet high, arranged clear of the loading platform on a stacking ground running between two lines of pits (Fig. 10). The stacking process permits of sorting. Any material not sufficiently broken down, such as sticks, leather, coco-nut husks, and tin cans are picked out and thrown into an adjacent pit for further treatment. Inert materials such as brickbats and potsherds are thrown on the roads for metalling. Hand-picking is easy at this stage, as the contents of the pit have been converted into a rough, inoffensive compost. The ripening process is completed in one month, when the humus can be used either for manuring vacant land or as a top dressing for growing crops.
FIG. 10. Plan of compost factory at Tollygunge, Calcutta, after one month's use.
Cost. The capital cost is very small. A population of 5,000 in India yields some 250 cubic feet of house refuse daily, enough to mix with all the night soil. This will require a compost factory of sixteen pits of 500 cubic feet each, one pit being filled in two days (Fig. 10). With roads, platforms, and tools this costs from Rs. 1,000 to Rs. 1,500. The daily output is 150 cubic feet of finished compost, which finds a ready sale at Rs. 5 to Rs. 7. At the lower figure the sale proceeds of the first year will be about Rs. 1,800. This more than covers the working expenses. A factory of this size will need a permanent staff of five men.
A Simple Installation for a Village
When a rural community is too poor to own conservancy carts or to construct brick-lined pits, composting can be carried out in an open trench on any high ground, without the use of partition walls.
FIG. 11. Plan of a simple composting trench for a village. First and second day's produce stacked and Section 2 ready for filling.
The difficulty with unlined pits is the escape of fly larvae which breed in the walls of the trench and in the stacks of ripening compost. This disadvantage can be overcome either by bricking the vertical walls or by keeping fowls, which thrive on the larvae.
Some Further Developments
The Use of Humus in Collecting Night Soil. There is one weak point in these two applications of the Indore Process to urban wastes. In both cases night soil is collected, transported, and composted in the crude state. This gives time for putrefaction to begin and for nuisance to develop. It can be prevented by the use of humus in the latrine pails, which ensures the oxidation of the night soil from the moment of deposition, and so prevents nuisance and the breeding of flies. The pails should contain at least 3 inches of dry humus when brought into use each day, and the droppings should be covered with a similar layer of humus when the pails are emptied into the conservancy carts. In this way putrefaction and smell will be avoided; the composting process will start in the pails themselves. The use of humus will augment the volume and weight of the night soil handled, but this increase in the work will be offset by the greater efficiency of composting, by the suppression of smell and flies, and by a considerable reduction in the loss of combined nitrogen.
Composting Night Soil and town Wastes in Small Pits. Night soil can be composted in small pits without the labour of turning. These pits can be of any convenient size, such as 2 feet by 12 feet and 9 inches deep, and can be dug in lines (separated by a foot of undisturbed soil) in any area devoted to vegetables or crops. Into the floor of the pits a fork is driven deeply and worked from side to side to aerate the subsoil and to provide for drainage after heavy rain. The pits are then one- third filled with town or vegetable waste, or a mixture of both, and then covered with a thin layer of night soil and compost from the latrine pails. The pit is then nearly filled with more waste, after which the pit is topped up with a 3-inch layer of loose soil. The pit now becomes a small composting chamber, in which the wastes and night soil are rapidly converted into humus without any more attention. After three or four months the pits will be full of finished compost and alive with earthworms. A mixed crop of maize and some pulse like the pigeon pea (Cajanus indicus) can then be sown on the rows of pits as the rainfall permits, and gradually earthed up with the surplus soil. The maize will ripen first, leaving the land in pigeon pea. The next year the pits can be repeated in the vacant spaces between the lines of pulse. In two seasons soil fit for vegetables can be prepared.
Howard, A., and Wad, Y. D. The Waste Products of Agriculture: Their Utilization as Humus. Oxford University Press, 193 I.
Jackson, F. K., and Wad, Y. D. 'The Sanitary Disposal and Agricultural Utilization of Habitation Wastes by the Indore Method', Indian Medical Gazette, lxix, February 1934.
Howard, A. 'The Manufacture of Humus by the Indore Method', Journal of the Royal Society of Arts, November 22nd, 1935, and December I8th, 1936. (These papers have been reprinted in pamphlet form and copies can be obtained from The Secretary, Royal Society of Arts, John Street, Adelphi, W.C. 2.)
Watson, E. F. 'A Boon to Smaller Municipalities: The Disposal of House Refuse and Night Soil by the Indore Method', The Commercial and Technical Journal, Calcutta, October 1936. (This paper is now out of print, but the substance has been incorporated in a lecture by Sir Albert Howard to the Ross Institute of Tropical Hygiene on June 17th, 1937. Copies can be obtained on application to the lecturer at 14 Liskeard Gardens, Blackheath, S.E. 3.)
Howard, A. 'Soil Fertility, Nutrition and Health', Chemistry and Industry, vol. lvi, no. 52, December 25th, 1937.
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