This section is from the book "The Principles And Practice Of Modern House-Construction", by G. Lister Sutcliffe. Also available from Amazon: How Your House Works: A Visual Guide to Understanding & Maintaining Your Home.
The disposal of sewage by Broad Irrigation, so called to distinguish it from Intermittent Filtration, finds considerable favour with a great number of sanitarians, on the reasonable grounds that what is taken off the land ought to be put back on it, and that nature demands such a " circle of events". There can be no doubt that, theoretically, it is quite right that there should be no waste, and consequently the cry of "our sewage to the land or there will some day be no bread or meat" has much to commend it. Unfortunately the tendency of all civilized nations to congregate together in large centres makes it difficult to carry this worthy object into effect, and the difficulty of securing suitable and sufficient land within a reasonable distance of any large town or city makes it in some cases almost impossible, except at prohibitive cost, to dispose of the sewage by broad irrigation. The enormous bulk of sewage which has to be treated, its low mannrial value owing to its dilation with water, its varying quantity with ehanges of the weather, and its unceasing flow day and night and at all seasons of the year, tend to complicate the problem of sewage-farming to such an extent as to make this method of dealing with sewage very unpopular except under exceptional circumstances. So far as experience can at present enlighten us, it is evident that commercially-successful sewage-farming is unknown, and that it is difficult enough, even under the most favourable circumstances, to deal with large quantities of sewage, especially during rain-storm-, upon sewage-farms in a satisfactory manner, so as to secure an effluent which will not pollute in some measure the stream or river into which it flows, Dr. Lissauer after many experiments says: "The effluent water of irrigation-works ought not to be compared with good drinking-water, since it must nearly always contain some ammonia, often nitrates and nitrites, and always a certain amount of chlorine, which is almost completely unabsorbed by the soil".1
No doubt there are many instances where there is sufficient land available to so manipulate the sewage that portion- of the land may be given intervals of rest, which revivifies them in such a manner that a very high standard of purity of effluent can be maintained, but these are fortunate circumstances not enjoyed by the majority of sewage-farms.
No hard-and-fast lines can be laid down as to the quantity of land necessary to ensure a successful sewage-farm. Much depends upon the character of the soil, whether light and loamy, or heavy and composed of clay. Much, too, depends upon the manner in which the farm is levelled, laid out, and drained. Much depends upon the climatic influences, and upon the quantity and quality of the sewage.
At Altrincham the sewage from a population of some 10,000 persons was dealt with on 10 acres of land for some months, and for many years the sewage of 11,000 persons was successfully dealt with upon only 47 acres of land. At Abingdon, 20 acres receive the sewage from 10,000 persons, and this form of sewage-treatment is still to the front. At the sewage-farm at Clichy, where the sewage of Paris is dealt with, about 9 million gallons of sewage per acre per annum are successfully dealt with, and in one case 35 million gallons were dealt with on one acre of land in two months.2
1 Vide Minutes of Proceedings of the Institution of Civil Engineers, vol lxvii p. 356
2 Ibid. vol xxxix. p. 380.
Tlie following table shows very approximately the amount of sewage which is dealt with upon various sewage-farms, hut these amounts are of course largely varied in timet of heavy rain.
Name of place.
Gallons of Sewage dealt with in 24 hours per acre.
Nature of Soil
Subsoil of sea- sand.
Stiff loam upon day subsoil.
Rich loam with gravelly subsoil.
Light loamy soil upon gravelly subsoil. Poor vegetable soil with stiff clay subsoil.
Light sandy soil.
Fine loam on gravelly subsoil.
Fine loamy soil with gravelly subsoil.
Gravelly soil upon clay subsoil. Stiff loam and light subsoil.
Tunbridge Wells, ..
Sharp gravel and sand.
Open soil upon gravelly subsoil.
Professor Robinson says1 that the average cost of treating sewage on land, at 26 sewage-farms examined by him, was one shilling and tenpence halfpenny per head of the population, or about £7, 14s. 2½d. per million gallons of sewage.
The important points to be considered in dealing with sewage upon the broad irrigation principle, are as follows: -
The position of the land with regard to the town, both as to locality and surroundings, and also its level, so as to avoid if possible lifting the sewage; the first cost of the land, and whether it is of suitable soil; the cost of the preparation of the land with regard to levelling, draining, and carrying the sewage to all parts of it - it is of the greatest importance that these should be carried out with great skill and perfection, as upon them. other considerations being equal, it depandl whether the sewage can be properly purified or not; the choice of suitable crops and their rotation, and also whether there is a convenient market for the disposal of the produce. If there are no means of diverting the storm-water from the Farm, very special means must be taken for dealing with it, as otherwise the land is overflooded at the very time when it is in a wet condition, and consequently in the worst position to receive so much liquid There should be sufficient land, so that the various plots can be rested, not only when the crops are in a certain condition of growth, hut also that the land may be revivified by the oxygen of the sir, which is so important in all forms of sewage-treatment
1 Vide Minutes of proccedings of the Institution of Civil Engineers, vol. xlix. p. 184.
The limits of this article prevent any discussion as to whether the produce grown on a sewage-farm, or the animals that feed on its produce, are injuriously affected by any pathological process. Suffice it to say that all attempts to prove any such injurious effects have hitherto failed, and that, with reasonable precautions and proper management, a sewage-farm can be kept as healthy as any other farm. Professor Forbes says: "There can be no question whatever but that, where the local circumstances of climate and soil are favourable to irrigation, and the conditions essential to its successful application properly observed, sewage irrigation is the most natural and effective system for the utilization of sewage, since it is only by this means that we can render available the whole of the ammoniacal salts, upon which so very much of the fertilizing value of the sewage depends".