125 



SCIENTIFIC NEAVS. 



[Aug. 1st, 1 5 



DOMESTIC SANITATION. 



No. 4. — Sewage Treatment. 



IF the refuse fluids or semi-fluids, domestic or indus- 

 trial, of our towns are not to be run into the rivers, 

 how are they to be safely or, if possible, usefully disposed 

 of? Let us bear in mind that, contrary to a delusion which 

 was at one time fashionable, sewage, though containing such 

 a vast quantity of useful matter, is not a mine of wealth. 

 Municipalities connot expect to meet with a company or a 

 contractor who will not merely guarantee them against all 

 complaints or actions for nuisance, but will pay them a good 

 round sum for the privilege of so doing. The plant-food 

 contained in sewage is so largely diluted with water and so 

 much mixed up with worthless matter — such as road-silt — 

 that a great part of its commercial value is eaten up by 

 labour, carriage, and the general expenses of '' handling " a 

 vast bulk of matter. If to extract 20s. worth of ammonia 

 and phosphoric acid from the sewage, it costs us 19s. in 

 materials, plant, and labour, capital will naturally seek out 

 some better investment. But seeing that we are bound, for 

 the sake of public health, to purify the sewage, we may, 

 or rather we should extract from it as much valuable matter 

 as possible, so as to recoup ourselves, in part at least, for 

 the expense of purification. 



And here we must utter a reminder often overlooked ; 

 town councils and local boards and individual ratepayers 

 very naturally count the cost of sanitary reform. But do 

 they ever ask what it will cost not to do it, to let nuisances 

 continue and increase ? We are sometimes told that our 

 population is even at present redundant, and that sanitary 

 improvements will prove a poor investment if they increase 

 the number of persons vainly seeking employment. But 

 what sanitary reformers aim at is a more vigorous, not a 

 more numerous population. Diseased persons, especially 

 the consumptive and the scrofulous, have often more numer- 

 ous families than those in robust health. This, however, is 

 a subject upon which we cannot here enter. 



When it became evident that our rivers could no longer 

 be used as general sewers, either with any regard to health 

 or to the very existence of certain important manufactures, 

 a crowd of strange devices sprang up. More than one in- 

 ventor has proposed to pump the sewage into barges and 

 convey it away to the sea. Not a few specially contrived 

 vessels for this strange purpose have been duly patented. 

 We think that a very simple calculation will enable us to 

 sweep aside at once all these projects. The sewage, say of 

 Leeds, amounts in fair weather to about twelve million 

 gallons daily, although in heavy rain this amount may be 

 nearly doubled ; and as twelve million gallons of water 

 weigh no less than 53,570 tons, to convey this burden away 

 there would be required a fleet of 200 barges, each carrying 

 250 tons. If the first barge was not able to reach the sea 

 and unload by the time the last of the 200 was full, a 

 greater number would be required. What, then, would be 

 the expense of building, maintaining, and working such a 

 fleet — an expense incurred in pure loss, since there would 

 not be the slightest set-off"? 



We are not aware that this scheme has ever been tried in 

 practice. 



A much more plausible arrangement has been actually 

 carried out by the Metropolitan Board of Works, and even the 

 stern logic of facts can scarcely convince the official mind of its 

 failure. Two huge underground reservoirs were constructed, 

 one at Cross Ness and the other at Barking Creek. In these 

 the sewage of the south and north sides of the metropolis 

 respectively was to be let accumulate, while the flood tide 

 was running up and during slack water. As soon as the 

 ebb began the reservoirs were let flow out, the theory being 



that before the flood tide returned all the sewage with its 

 abominations would be carried down to sea ; or that at least 

 no sewage matter would ever be found above the outlets 

 from the two reservoirs. This theory did not, however, 

 hold good ; after a very prolonged trial it was found that the 

 sewage worked up far above the outlets, whilst the lower 

 reaches of the river had become very offensive to the 

 inhabitants of their banks, as well as to the crews of vessels. 

 That there was not the slightest return for the heavy outlay 

 incurred is a matter of course. Hence we can only enter- 

 tain the hope that no other community will allow itself to 

 be committed to the adoption of this or of any similar 

 scheme. 



The only satisfactory principle of sewage treatment rests 

 on a fact which has been observed ages ago. Arable soils, 

 clay, and most kinds of carbonaceous substances powerfully 

 absorb and retain offensive matter, whether presented to 

 them in a dry or in a liquid state, and convert it, with the 

 aid of air and water, into plant-food. We avail ourselves 

 of this fact when we bury animal oflal, blood, faecal matters, 

 etc., in the earth, or when we thrust into the soil the blades 

 of knives, etc., which have contracted the smell of onions or 

 of fish. In all these cases we find the smell quickly disappear. 

 Or if we fill a flower-pot with ordinary garden-soil, and pour 

 upon it a little soap-suds, urine, or blood, or a mixture of all 

 three, we find a liquid draining out below which is colourless, 

 inodorous, and which on chemical analysis is found freed 

 to a very great extent from animal matter. 



Upon this one principle — according to the different 

 manner in which it is applied — rest the two main systems 

 of sewage-treatment. These systems have been errone- 

 ously thought antagonistic, but in a work which we had the 

 advantage of perusing in manuscript, and which we learn is 

 about to be published, it is shown that they differ merely in 

 a point of detail. It is plain that if we have a polluted liquid 

 to purify, we may either distribute it over a sufficient extent 

 of soil or we may invert the process and diffuse a suitable 

 kind of earthy matter through the polluted liquid. If we 

 take the former method, the process is called irrigation, but 

 if we adopt the second it is known 2& precipitation because after 

 or along with the earth we add to the sewage certain sub- 

 stances which cause the particles of earth, thus saturated 

 with the excrementitious matter, to subside to the bottom. 

 In both these methods, if properly performed, the nuisance 

 and danger arising from sewage are got rid of, and in both a 

 great part at least of the manurial matter is turned to its 

 natural account in the growth of crops. Which of the two 

 methods should be actually adopted must depend on local 

 conditions, soils, season, climate, questions of level, etc. 

 Atleast we think that no manof sound judgment and sufficient 

 experience would at once recommend either method for 

 universal and unqualified adoption. 



It is self-evident that in such a season as the present, and 

 still more in countries where persistent drought is of frequent 

 occurrence, sewage irrigation would be a priceless boon to 

 numbers of farmers, as manuring and watering the land 

 simultaneously. It is equally evident that in wet, drizzly 

 seasons like 1879, where the difficulty is how to get rid of 

 the rain fast enough, sewage irrigation would only heighten 

 the mischief, and every agriculturalist would wish to add 

 manures in the dry state. 



It is generally admitted that it is possible, by means ot 

 irrigation, to purify sewage so that it shall be fit, not, in- 

 deed, for drinking, but at least for turning into rivers, for 

 sprinkling roads, and, where engineering difficulties do not 

 interfere, for flushing. It must also be conceded that 

 sewage irrigation may be of great benefit to the land. 

 But, as commonly managed, it is difficult to combine these 

 two objects. The sewage flows from the town summer 



