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The amount of the preparation added to the sewage was not ascertained, but it was stated to be certainly much less than the proportion indicated by previous experiments (1 ton of crude phosphate to 500,000 gallons of sewage).
The result of this addition was to deodorize the sewage to a very considerable extent indeed; and when some of it was placed in a precipitating glass, and allowed to stand, a speedy separation of the suspended matters took place.
The milk of lime is added to precipitate the excess of phosphate added, and just sufficient milk of lime is allowed to flow in to neutralize the sewage, the reaction of which to test-paper is observed from time to time after the addition of the milk of lime.
During the passage of the sewage thus treated through the large tank, the suspended matters were very completely deposited, and the supernatant water ran over the sloping edge of the tank at its extreme end bright and clear, and almost odourless.
Some of this water was collected, and was kept sealed up in a stono jar until July 24th, when it was analyzed by Dr. Russell, with the following result:Sample of Emuent Water taken from Tottenham Sewage, treated March
25th, 1871. Parts per 100,000.
It was found, after the lapse of four months, quite sweet and without smell. The suspended matter was in very small quantity, and consisted merely of a little whitish flocculent matter, doubtless lime due to the slight excess used on the day when the sample was collected. The water was quite clear, and only on looking through a considerable depth could a brownish tint be detected.
The analysis of it shows that it contains as much actual ammonia as ordinary dilute London sewage, and also a certain amount of albumenoid ammonia.
It contains the merest trace of phosphoric acid, as indicated by the molybdate-of-ammonia test, and no sulphuretted hydrogen, nor any nitrates or nitrites.
Some of the deposit had been taken out of the tank, and was drying in a shed, the water which separated from it forming little pools on the surface of the mass ; both this water and the precipitate itself were free from all offensive smell.
It appears, then, that the suspended matters are entirely removed by this process, but the actual ammonia and, to a certain extent, the soluble organic matters are neither removed from the sewage nor oxidized; but an odourless precipitate is produced, which contains all the phosphate added, and contains it doubtless in the form of flocculent phosphate of alumina, the value of which, as a manure, is somewhat doubtful, being certainly not so great as the value of corresponding quantities of flocculent phosphate of lime.
The valuable constituents of sewage, with the exception of the suspended matter and the phosphoric acid, are not precipitated by this process, and cannot be utilized unless the effluent water be afterwards used for irrigation,
in which case the milk of lime would not be added, and the clarified sewago would still contain a quantity of phosphoric acid.
The advantage of this use of it, if it were found to answer from an economical point of view, would be the deodorization of the deposit in the tanks and of the sewage itself, which is certainly at present a great desideratum, especially as regards the tanks.
SECTION V.-The Dry Earth System. The Committee did not consider that it was its duty to undertake the examination of every plan that might be proposed for the treatment or utilization of excretal matters, but only those which were already well before the public, and known, or supposed, to be affording something like satisfactory results. It had sent out forms of questions with a view of procuring information respecting the results obtained in the use of Moule’s earthclosets, and there was every desire on the part of the Committee not to neglect the examination of any system which promised results satisfactory to the community.
Of eight forms of questions sent out relating to Moule's system, only one had been filled up and returned, and that one was from Lancaster. It appeared that about 24 lbs. of soil were used per head per day. The manure obtained is afterwards mixed with other town refuse, and the mixture is sold at 58. a ton. The analysis of the manure published by the Rivers Pollution Commission showed, however, that it did not contain more nitrogen than good garden-mould. It was stated to have been applied at the rate of about 6 tons per acre to grass land; but the produce of hay was by no means large. It should be added, however, that even at Lancaster, the only place where an attempt has been made to carry out the system on a large scale, some of the conditions prescribed by Mr. Moule, and essential to its success as a means of avoiding nuisance and injury to health, are entirely neglected. Thus there is an average of twenty-four persons using each closet; and instead of any arrangement for the deposit of earth on the fæcal matters after every use of the closet, a quantity of soil is thrown once a day over the matters collected ; and the result is, that the product is removed in a very offensive condition.
On behalf of the Committee, Dr. Gilbert has himself made some trials with Moule's earth system: 14 cwt. of air-dried and sifted clayey soil were set apart for the experiment. From one third to one half of the whole was used before it was necessary to empty the pit. When removed the mass appeared uniformly moist throughout, and (excepting in the case of the most recent portions near the surface) neither fæcal matter nor paper was observable in it; nor was the process of emptying accompanied by any offensive smell. . After exposure and occasional turning over on the floor of a shed, the once-used soil was resifted, and again passed through the closet.
Below are given the percentages of moisture and of nitrogen in the soil under the various circumstances of the trial :
Calculated upon the air-dried condition, the increase in the percentage of
nitrogen was only about 0·15 cach time the soil was used; and, even after using twice, the soil was not richer than good garden-mould. It is obvious, therefore, that such a manure, even if disposed of free of charge, would bear carriage to a very short distance only. It may be added that the percentage of nitrogen in the soil after using once, as given above, agrees very closely with that recorded in the report of the Rivers Pollution Commissioners, as found by them in the manure obtained, under professedly the same system, at Lancaster.
In conclusion, when it is borne in mind how small is the proportion of the nitrogen voided in the 24 hours that is contained in the fæces, how small is the proportion of the total urine that is passed at the same time, and how great is the dilution of the manurial matters by the amount of soil required, it is by no means surprising that the manure produced is of such small value as the results would show. It is obvious, too, that our domestic habits and practices would have to be entirely revolutionized to secure the collection and absorption of the whole of the urine, which contains by far the larger proportion of the valuable manurial matters voided. Moreover, assuming 2 or 23 lbs. of soil to be required for each use of the closet, if the whole of the liquid, as well as the solid excretal matters, were to be absorbed, there would probably be required from 9 to 10 lbs. of soil per head per day, or about 11 ton per head per annum. This, for London, taking the population at three and a quarter millions, would represent a requirement of about five million tons of soil per annum, or nearly 14,000 tons per day; and the quantity to be removed would, of course, be considerably greater. This illustration is sufficient to show the impracticability of any such system for large populations. Nevertheless it may readily be admitted that it would be of great advantage, in a sanitary point of view, in the cases of sick rooms, detached houses, or even villages, and that it might be even economical where the earth for preparation and absorption, and the land for utilization, are in close proximity
By Dr. T. SPENCER COBBOLD, F.R.S.
kind. I attribute this marked negative result to the following circumstances : First, the animal did not graze on the farm, but was fed exclusively upon vegetable products cut and carried from the land. Secondly, the porous nature of the soil and subsoil alike would rapidly carry off the sewage, and thus ensure the passage of parasitic germs into the soil itself. Thirdly, I noticed on the irrigated portions of the farm a remarkable absence of those'molluscan and insect forms of life which frequently play the part of intermediary bearers. Fourthly, the only mollusks I detected were examples of Lymncus pereger ; these were obtained from a small pit of water to which the sewage had no access, and when examined after death were not found to contain any cercarian larvæ. Fifthly, the flaky vegetable tufts collected by me from the sides of the furrows occupied by sewage-currents consisted chiefly of Batrachospermum moniliforme, in the filaments of which were numerous active free nematodes, but no ora of any true entozoon. Sixthly, the sewage had a strong smell of beer, suggesting the presence of sufficient alcohol to
CARLI.... he land has
doubled in t of the occu
CHELT overl7 58., the
plying and attending to sewage.
CROYI oper £10