An Agricultural Testament

by Sir Albert Howard

Chapter 8
Developments of the Indore Process

The Utilization of Town Wastes

THE human population, for the most part concentrated in towns and villages, is maintained almost exclusively by the land. Apart from the harvest of the sea, agriculture provides the food of the people and the requirements of vegetable and animal origin needed by the factories of the urban areas. It follows that a large portion of the waste products of farming must be found in the towns and away from the fields which produced them. One of the consequences, therefore, of the concentration of the human population in small areas has been to separate, often by considerable distances, an important portion of the wastes of agriculture from the land. These wastes fall into two distinct groups:

In practically all cases in this country both groups of waste materials are treated as something to be got rid of as quickly, as unostentatiously, and as cheaply as possible. In Great Britain most town wastes are either buried in a controlled tip or burnt in an incinerator. Practically none of our urban waste finds its way back to the land. The wastes of the population, in most Western countries, are first diluted with large volumes of water and then after varying amounts of purification, are discharged either into rivers or into the sea. Beyond a little of the resulting sewage sludge the residues of the population are entirely lost to agriculture.

From the point of view of farming the towns have become parasites. They will last under the present system only as long as the earth's fertility lasts. Then the whole fabric of our civilization must collapse.

In considering how this unsatisfactory state of affairs can be remedied and how the wastes of urban areas can be restored to the soil, the magnitude of the problem and the difficulties which have to be overcome must be realized from the outset. These difficulties are of two kinds: those which belong to the subject proper, and those inherent in ourselves. The present system of sewage disposal has been the growth of a hundred years; problem after problem has had to be solved as it arose from the sole point of view of what seemed best for the town at the moment; mother earth has had few or no representatives on municipal councils to plead her cause; the disposal of waste has always been looked upon as the sole business of the town rather than something which concerns the well-being of the nation as a whole. The fragmentation of the subject into its urban components -- medical, engineering, administrative, and financial -- has followed; direction has been lost. The piecemeal consideration of such a matter could only lead to failure.

Can anything be done at this late hour by way of reform? Can mother earth secure even a partial restitution of her manurial rights? If the easiest road is first taken a great deal can be accomplished in a few years. The problem of getting the town wastes back into the land is not difficult. The task of demonstrating a working alternative to water-borne sewage and getting it adopted in practice is, however, stupendous. At the moment it is altogether outside the bounds of practical politics. Some catastrophe, such as a universal shortage of food followed by famine, or the necessity of spreading the urban population about the country-side to safeguard it from direct and indirect damage by hostile aircraft, will have to be upon us before such a question can even be considered.

The effective disposal of town wastes is, however, far less difficult, as will be seen by what has already been accomplished in this country. Passing over the earlier experiments with town wastes, summed up in a recent publication of the Ministry of Agriculture (Manures and Manuring, Bulletin 36, Ministry of Agriculture and Fisheries, H.M. Stationery Office, 1937), in which the dustbin refuse was used without modification, the recent results obtained with pulverized wastes, prepared by passing the sorted material (to remove tin cans, bottles, and other refractory objects) through a hammer mill, point clearly to the true role of this material in agriculture. Its value lies, not in its chemical composition, which is almost negligible, but in the fact that it is a perfect diluent for the manure heap, the weakest link in agriculture in many countries. The ordinary manure heap on a farm is biologically unbalanced and chemically unstable. It is unbalanced because the micro-organisms which are trying to synthesize humus have far too much urine and dung and far too little cellulose and lignin and insufficient air to begin with. It is unstable because it cannot hold itself together; the valuable nitrogen is lost either as ammonia or as free nitrogen; the micro-organisms cannot use up the urine fast enough before it runs to waste; the proteins are used as a source of oxygen with the liberation of free nitrogen. The fungi and bacteria of the manure heap are working under impossible conditions. They live a life of constant frustration which can only be avoided by giving them a balanced ration. This can be achieved by diluting the existing manure heaps with three volumes of pulverized town wastes. The micro-organisms are then provided with all the cellulose and lignin they need. The dilution of the manure heap automatically improves the aeration. The volume of the resulting manure is multiplied by at least three; its efficiency is also increased.

Such a reform of the manure heap is practicable. Two examples may be quoted. At the large hop garden at Bodiam in Sussex, the property of Messrs. Arthur Guinness, Son & Co., Ltd., over 30 tons of pulverized town wastes from Southwark are used daily throughout the year for humus manufacture. This material is railed in 6-ton truckloads to Bodiam, transferred to the hop gardens by lorry and then composted with all the wastes of the garden -- hop vine, hop string, hedge and roadside trimmings, old straw, all the farm-yard manure which is available -- and every other vegetable and animal waste that can be collected locally. The annual output of finished humus is over 10,000 tons, which is prepared at an all-in cost of 10s. a ton, including spreading on the land. The Manager of this garden, Mr. L. P. Haynes, has worked out comparative figures of cost between nitrogen, phosphorus, and potash applied in the form of humus or artificials. The cost of town wastes f.o.r. Bodiam is 4s. 6d. a ton; lorry transport from rail to garden 3s. a ton; assembling and turning the compost heaps and spreading on the land 2s. 6d. a ton. The analysis of this humus was: 0.96 per cent. nitrogen, 2.45 per cent. phosphate, and 0.62 per cent. potash. Sixteen tons of humus therefore contain 344 lb. of nitrogen, 769 lb. of P2O5, and 222 lb. of K2O. The cost of this at 10s. a ton including spreading comes to £8 an acre. The purchase, haulage, and sowing of these amounts of NPK in the form of sulphate of ammonia, basic slag, and muriate of potash comes to £9 12s. 7-1/2d. There is therefore a distinct saving when humus is used. This, however, is only a minor item on the credit side. The texture of the soil is rapidly improving, soil fertility is being built up, the need for chemical manures and poison sprays to control pests is becoming less.

The manurial policy adopted on this hop garden has been confirmed in rather an interesting fashion. Before a serious attempt was made to prepare humus on the present scale, a small amount of pulverized Southwark refuse had been in use. The bulk of the manure used, however, was artificials supplemented by the various organic manures and fertilizers on the market. The labourers employed at Bodiam were therefore conversant with practically every type of inorganic and organic manure. One of their privileges is a supply of manure for their gardens. They have always selected pulverized town wastes because they consider this grows the best vegetables.

A second large-scale demonstration of the benefits which follow the reform of the manure heap has been carried out at Marden Park in Surrey. Many thousands of tons of humus have been made by composting pulverized town wastes with ordinary dung. In a paper read to the Farmers' Club on January 30th, 1939, Sir Bernard Greenwell refers to these results as follows: 'I have only two years' experience of this myself, but from the results I have seen we can multiply our dung by four and get crops as good as if the land had been manured with pure dung.' In 1938 I saw some of this work. Many of the fields on the estate had been divided into half, one portion being manured with humus and the other with an equal number of cartloads of dung. I inspected a number of these fields just as the corn was coming into ear. In every case the crops grown with humus -- wheat, beans, oats, clover, and so forth -- were definitely better than those raised with farm-yard manure. These results showed that this land wants freshly prepared humus, not so many lb. to the acre of this and that. In manuring we are nourishing a complex biological system not ministering to the needs of a conveyor belt in a factory.

Once the correct use of Southwark wastes was demonstrated a demand for this material arose. The sales increased; the demand now exceeds the supply. The details are given in Table 7.

Table 7
Sales of crushed wastes at Southwark
Tons crushed*
Tons sold
Income from sales
12 cwt.
9 cwt.
1 cwt.
9 cwt.
14 cwt.
5 cwt.
13 cwt.
15 cwt.
15 cwt.
8 cwt.
3 cwt.
1 cwt.
* A certain amount of these wastes is required by the Depot itself for sealing one of its own tips; so it is not possible to sell all the waste crushed to farmers.

When it is remembered that the annual dustbin refuse in Great Britain is in the neighbourhood of 13,000,000 tons and that about half of this material can be used for making the most of the urine and dung of our live stock, it will be evident what enormous possibilities exist for raising the fertility of the zones of land within, say, fifty miles of the large cities and towns. A perusal of the Public Cleansing Return for the year ending March 31st, 1938, published by the Ministry of Health, shows that a certain proportion of this dustbin refuse is still burnt in incinerators. Once, however, the agricultural value of this material is realized by farmers and market gardeners it will not be long before incineration is given up and the whole of the organic matter in our town wastes finds its way into the manure heap. When this time comes the utilization of the enormous dumps of similar wastes, which accumulated before controlled tipping was adopted, can be taken in hand. These contain many more millions of tons of material which can be dealt with on Southwark lines. In this way the manure heaps of a very large portion of rural England can be reformed and the fertility of a considerable area restored. A good beginning will then have been made in the restitution of the manurial rights owing to the country-side. The towns will have begun to repay their debt to the soil.

Besides the wastes of the dustbins and the dumps there is another and even more important source of unused humus in the neighbourhood of our cities and towns. This occurs in the controlled tips in which most of the dustbin refuse is now buried. In controlled tipping the town wastes are deposited in suitable areas near cities and sealed with a layer of clay, soil, or ashes so as to prevent nuisance generally and also the breeding of flies. The seal, however, permits sufficient aeration for the first stage in the conversion of most of the organic matter into humus. The result is that in a year or two the tip becomes a humus mine. The crude organic matter in these wastes is slowly transformed by means of fungi and bacteria into humus. All that is needed is to separate the finely divided humus from the refractory material and to apply it to the land.

A very valuable piece of research work on this matter has recently been undertaken at Manchester. The results are described by Messrs. Jones and Owen in Some Notes on the Scientific Aspects of Controlled Tipping, published by the City of Manchester. The main object of the work was to establish the facts underlying controlled tipping so that any discussion on the efficacy of this process, as compared with incineration, could be conducted on the basis of carefully ascertained knowledge. The investigation, however, is invaluable from the agricultural standpoint. The experiments were begun in August1932 at Wythenshawe in a controlled tip on a piece of low-lying marshy ground subject to periodic flooding from the adjacent river Mersey. One of the subsidiary objects of the tipping was to reclaim the land for recreational or other uses in the future. Six experimental plots were selected for the tests, each approximately 16 feet by 12 feet. The material contained in the tip was ordinary dustbin refuse tipped to a depth of 6 feet. The first object was to ascertain the consequences of bacterial action on the organic matter in the interior of the tip, such as the generation of temperature, the biological as well as the chemical changes, and any alteration in the gaseous atmosphere in the interior of the mass. Having disposed of these preliminary matters, it was proposed to attack the main problem and to answer the question: Is controlled tipping safe?

Careful attention was first given to the seal. The surface of the plots was covered with a layer of fine dust and ashes, of a minimum thickness of 6 inches, obtained by passing household refuse over a 3/8 inch mesh. Such a seal, which contained about 2.5 per cent. of organic matter, proved to be a suitable mechanical covering and also prevented the breeding of flies. The sides and ends of the experimental plots were covered with clay well tamped down. The plots therefore behaved as if they were large flowerpots in direct contact with the moist earth below but separated from the outer atmosphere by a permeable seal of screened dust and fine ashes.

The unsorted household refuse under experiment represented an average sample and contained about 42 per cent. of organic matter, the remaining 58 per cent. being composed of inorganic materials. After tipping and sealing, there was a rapid rise of temperature, irrespective of the season, to a maximum of 160° F. towards the end of the first week. This was caused by the activities of the thermogenic and thermophylic members of the aerobic group of bacteria which break down cellulose, liberate heat, and produce large volumes of carbon dioxide. At the same time these organisms rapidly multiply and in so doing synthesize large amounts of protein from the mixed wastes. This on the death of the organisms forms a valuable constituent of the humus left when the bacterial activities die down after about fifteen weeks, as is indicated by the return of the temperature of the tip to normal. The controlled tip therefore behaves very much like an Indore compost heap.

As would be expected from the heterogeneous nature and uneven distribution of the contents of the tip, considerable variations were shown in the maximum temperatures attained. During the period of fermentation the bacterial flora (at first aerobic) use and reduce the oxygen content of the tip, and so pave the way for the facultative anaerobic organisms which complete the conversion of the organic matter into humus.

A detailed examination of the gases produced in the tips showed that in addition to nitrogen, carbon dioxide, and oxygen, a considerable quantity of methane (16 per cent.) and smaller proportions of carbon monoxide (2.8 per cent.) and hydrogen (2.5 per cent.) occurred. Traces only of sulphuretted hydrogen were detected. The presence of carbon monoxide, methane, and hydrogen would naturally result from the anaerobic fermentation which establishes itself in the second stage of the production of humus after the free oxygen in the tip becomes exhausted. These gases are similar to those produced by the decay of organic matter in swamp rice cultivation in India, where the supply of oxygen is almost always in defect. The absence of anything beyond a trace of sulphuretted hydrogen is reassuring, as this proves that the intense reduction which precedes the formation of the salts of alkali soils does not occur in a controlled tip.

The manurial value of the humus in the tips was determined by analysis and valuation. The average content of nitrogen was 0.8 per cent., of phosphoric acid 0.5 per cent., of potash 0.3 per cent. The estimated value of the dry material per ton was 10s. This value, however, will have to be multiplied by a factor ranging from 2 to 2.5, because experience has shown that the market price of organic manures, based on supply and demand, is anything from two to two and a half times greater than that calculated from the chemical analysis. The unit system of valuation applies only to artificial manures like sulphate of ammonia made in factories; it does not hold in the case of natural manures like humus.

One of the last sections of the Report relates to the danger of infectious diseases as a possible consequence of controlled tipping. The authors conclude that 'danger arising from possible presence of pathogenic germs in a controlled tip may be dismissed as nonexistent'.

One of the plots, No. 1, not only developed a high temperature but showed a much more gradual fall than the other plots. This was apparently due to the higher content of organic matter combined with better aeration. The results of this plot suggest that more and better humus might be obtained in a controlled tip if the object of tipping were, as it should be, to secure the largest amount of humus of the best possible quality. It would not be a difficult matter to increase the oxygen intake at the beginning by allowing more and more air to diffuse in from the atmosphere. This could perhaps be done most easily and cheaply by reducing the thickness of the seal by about a third. If the seal were reduced in this way, ample air would find its way into the fermenting mass in the early stages; the humus would be improved; the covering material saved could be used for a new seal. The controlled tip would then become a very efficient humus factory.

In countries where there is no system of water-borne sewage there has been no difficulty in converting the wastes of the population into humus. The first trials of the Indore Process for this purpose were completed in Central India in 1933 by Messrs. Jackson and Wad at three centres near Indore -- the Indore Residency, Indore City, and the Malwa Bhil Corps. Their results were soon taken up by a number of the Central India and Rajputana States and by some of the municipalities in India. Subsequent developments of this work, including working drawings and figures of cost, were summed up in a paper read to the Health Congress of the Royal Sanitary Institute held at Portsmouth in 1938. This document has been reproduced as Appendix C. A perusal of this statement shows that human wastes are an even better activator than animal residues. All that is necessary is to provide for abundant aeration in the early stages and to see that the night soil is spread in a thin film over the town wastes and that no pockets or definite layers are left. Both of these interfere with aeration, produce smell, and attract flies. Smell and flies are therefore a very useful means of control. If the work is properly done there is no smell, and flies are not attracted because the intense oxidation processes involved in the early stages of the synthesis of humus are set in motion. It is only when the air supply is cut off at this stage that putrefactive changes occur which produce nuisance and encourage flies.

Whether or not it will always be necessary to erect permanent installations for converting night soil and town refuse into humus, experience only can decide. In a number of cases it may be easier to do the composting daily in suitable pits or trenches on the lines described in Appendix C. In this way the pits or trenches themselves become temporary composting chambers; no turning is required; the line of pits or trenches can soon be used for agricultural purposes -- for growing all kinds of fodder, cereal, and vegetable crops. At the same time the land is left in a high state of fertility.

A number of medical officers all over the world are trying out the composting of night soil on the lines suggested. In a few years a great deal of experience will be available, on which the projects of the future can be based.

As far as countries like Great Britain are concerned, the only openings for the composting of night soil occur in the countryside and in the outer urban zones where the houses are provided with kitchen gardens. In such areas the vast quantities of humus in the controlled tips can be used in earth-closets and the mixed night soil and humus can be lightly buried in the gardens on the lines so successfully carried out by the late Dr. Poore and described in his Rural Hygiene, the second edition of which was published in 1894.

Since Dr. Poore's work appeared a new development in housing has taken place in the garden cities and in colonies like those started by the Land Settlement Association. Here, although there is ample land for converting every possible waste into humus, the water-borne method of sewage disposal and the dust-carts of the crowded town have been slavishly copied. In an interesting paper published in the British Medical Journal of February 9th, 1924, Dr. L. J. Picton, then Medical Officer of Health of the Winsford Urban District, Cheshire, pointed out how easy it would be to apply Dr. Poore's principles to a garden city.

FIG. 1. A model layout for 20 cottages.

What is needed are a few working examples of such a housing scheme and a published account of the results. These, if successful, would at once influence all future building schemes in country districts and would point the way to a considerable reduction in rents and rates. The garden-city and water-borne sewage are a contradiction in terms. Water-borne sewage has developed because of overcrowding and the absence of cultivated land. Remove overcrowding and the case for this wasteful system disappears. In the garden city there is no need to get rid of wastes by the expensive methods of the town. The soil will do it far more efficiently and at far less cost. At the same time the fertility of the garden city areas will be raised and large crops of fresh vegetables and fruit -- one of the factors underlying health -- will be automatically provided.

Such a reform in housing schemes will not stop at the outer fringes of our towns and cities. It will be certain to spread to the villages and to the country-side, where a few examples of cottage gardens, rendered fertile by the wastes of the inhabitants, are still to be found here and there. More are needed. More will arise the moment it is realized that the proper utilization of the wastes of the population depends on composting processes and the correct use of humus. All the trouble, all the expense, and all the difficulties in dealing with human wastes arise from following the wrong principle -- water -- and setting in motion a vast train of putrefactive processes. The principle that must be followed is abundant aeration at the beginning: the conversion of wastes into humus by the processes Nature employs in every wood and every forest.


Greenwell, Sir Bernard. 'Soil Fertility: the Farm's Capital', Journal of the Farmers' Club, 1939, p. 1.

Howard, Sir Albert. 'Preservation of Domestic Wastes for Use on the Land', Journal of the Institution of Sanitary Engineers, xliii, 1939, p. 173.

-- 'Experiments with Pulverized Refuse as a Humus-Forming Agent', Journal of the Institute of Public Cleansing, xxix, 1939, p. 504.

Jones, B. B., and Owen, F. Some Notes on the Scientific Aspects of Controlled Tipping, City of Manchester, 1934.

Picton, L. J. 'The Economic Disposal of Excreta: Garden Sanitation', British Medical Journal, February 9th, 1924.

Poore, G. V. Essays on Rural Hygiene, London, 1894.

Public Cleansing Costing Returns for the year ended March 31st, 1938, H. M. Stationery Office, 1939.

Next: 9. Soil Aeration

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