SEWAGE.

New Zealander, Volume XXII, Issue 2452, 10 June 1865, Page 3

SEWAGE.

[FROM THB “ AUSTRALASIAN.”] Althouor of less importance to the fanxisr hero then to those in the old country, the developments of the sewage question are not without special interest. And not only so with fegard to the sewage itself, but also <>n account of the many branches of inquiry involved therewith. The mere differences of opinion amongst the leading authorities on such'subjects— from that of him who says the saving of sewage matter is alone needed to render land more productive each year in proportion to the growing wants of the inhabitants, to that of the many who say the-e matters are not worth having if any-outlay is to be incurred in providing them —these very differences have been the means of bringing a vast amount of knowledge to bear on the question, to the great advantage of agriculture generally, if not to the solution of the question itself. The grand experiment about to be tried. of enriching a wide ex ent of the Maplln Sands with the London sewage and thns making these as productive of grass as the famous Craigentenny Meadows, near Kdinburgh, is announced by Baron Liebig as hopeless—as,' in fact, a delusion based on ignorance; and he gives his reasons in support of this view ; while the English agricultural engineers and chemists predict an undoubted success, and a return of some thirty or forty per cent, per annnm on the outlay. The discussion has also brought out such particulars of the famous Edinburgh meadows as will enable the public elsewhere to judge how far it may be posdble to rival these, and make land worth £4O a year for grass alone, even with unlimited sewage These are too commonly talked of as sands which were barren before being subjected to the present system' of irrigation with sewage water ; bnt such was not by any means the case, as only a small portion consists of sand, and this lies so low that the water flowing over the upper portions of loam and clay carries down with it earthy particles, without which the sewage could have no bem-ficial effect. These meadows are on all occasions held np as an example of what may be done with land otherwise worthless ; and as the fertilising matters of London are enormous in quantity, and have of late years become a great nuisance, there appears to the uninitiated to be no season why that city should not have her fertile meadows too. If there was any ehance of a sewage system for Melbourne being carried out within a moderate space of time, we might have something to say about luxuriant meadows, and unlimited grass for cows, in the very height of summer, from the 1 w and unsightly lands along the course of the lower larra ; but at present we have only to do with the general aspect of the question, in so far as this will aid in showing how a valuable nuisance is to be beneficially got rid of. It is beginning to be generally acknowledged now that for sanit iry reasons, if for no other, the sewage from large towns must be applied to the land around, and the experiments tried In England, as yet, have tended little to show how this is to be done with advantage. Vor is mnch to be learned from the one Scottish success, for, valuable as the Craigentenny Meadows have become from the application of the Edinburgh sewage, tbe civic authorities of Leith are expending a sum of £66,000 in providing for the conveyance of all noxions matters from their town into the sea, and the expense is greatly increased by the supposed necessity for snch an outlet. Now, if land was to be easily rendered worth £4O a year by the application of these matters, and this with a smaller ontlay, such a piece of needless extravagance and waste would never have been tolerated by the inhabitants of Leith, especially with such sn example close alongside ot them. No; but being able to see and judge for themselves of the circumstances under which land may be so improved, and aware probably that they have no land suitable for the purpose, either from its position or natural ch racter, the first ontlay. without any chance of a return, bnt with the certainty of a final settlement of the question, is deemed the best; - while people at a distance look only to the indisputable fact, that land formerly almost worthless has been made elsewhere so productive, and think that the same result is obtainable everywhere, if similar means be used. But a part of this fact, and a part which must not be lost sight of, is, that these Edinburgh meadows eon ist of clay and loam where the sewage-waters first ran over them, w>th a gentle incline towards the low ground, which is almost a pare sand, so that drainage is effectually provided for by nature, and tbe quantity of water passing over the upper gto ind is so great that the sand below is enpp icd with clay enough in very fine panicles to allow the grass growing on it to derive foil benefit from matters which would otherwise be poisonous, for, as Liebig asys, in showing why tbe same result cannot be expected from tne Maplin or any other pare sands, “all experiments on the property of soils to sbs rb manure coincide in this, that the power acting | in sand is quite different from that in plant-

bearing soils. Sand absorbs, liks othsr poroas substances, certain sails from solutions, but ia an infinitely smaller proportion then earth, and, what is the most important, it does not decompose them. The plant bearing earth acts not only by accumulating and concentrating the nutritive elements of plants, but it rende s them also fit fur assimilation ; and, like a sanitary police, preserves the health of the plant by removing everything detrimental u its life. Free ammonia, acting like a joison in the process of germination, is, when in contact with the soil, immediately neutralised. Sulphide of potash and chloride c potassium are decompose •, and while the acids of these salts are drained away by the rain, the potash is retained in toe most proper state tor absorption by the roots.” Thus -ewage matter is of itself actually poisonous to growing plants until the active rincipiea in it have been modifitd lor their use by contact with clay j and their application to a pure sand will render this even more barren than it was before. But day separates and absorbs for future use everything that is valuable, and in all attempt- to utilise sewage this must uot.be forgotten—especially here.

Another advantage the Edinburgh meadows have is, that the contenta of the sewers can ho conveyed to them without any other expense than that consequent on the needful attendance to open drains, and in very few instances indeed has any outlay on machinery tor this purpose been made to pay. Recent discussions, before the Society of >ns and elsewhere, as to the best mode of disjtosing o’ tho London sewage, have made this difficulty especially apparent owing to the vast quantity to be got rid of. This is estimated to amount to somewhere about thirty thousand millions of gallons in the year j and the cost of aising this to a sufficient height, without allowing anything for after distirbuuon, would be about five hundred pounds a day. Even such an expenditure would be profitable if the supposed value in comparison with guano and other artificial manures about a million a year, could be afterwards realised, but it cannot, and principally because of the puantity pf water allowed to flow through the sewers being so enormous. Occupiers of land to which it could be led would gladly pay a moderate price for it in summer, when the water is at least in proportion to the manure, but in winter, when the quantity of water is so vastly increased by tK« rams, and the manure so highly diluted, they would not have it on their land at any price, la fact, this vast quantity f water would quits d stroy any land not thoroughly drained, and would do more harm than good to land that was, wishing out of it in its passage through quite as much of the fertilising ingredients as it would leave behind, when the sewage matters are so highly diluted It is the knowledge of this difficulty of application, that iuducea many to support the Maplin Sanaa scheme rrho do at all believe in the productive capabilities of these. Any attempt to dispose of the sewage by turning this on to cultivated land-, and *bna deriving a revenue from it, must end In disappointment, and a great additional outlry in getting rid of what cannot by any possibility be allowed to accumulate ; but if the outflow be on such a wide extent of sands, these will absorb the whole of it without any further trouble, even if they are not fertilised thereby. Even the discussion at the Society of Arts, in which many of the men with most experience of the different plans tried in B gland took part—even this discussion did no more than lead to a hope that a thorough and constant ventilation of the subject would, in time, show how the fertilising matters now the cause of so much trouble, could be rendered economically available in an agricultural point of view ; bat as yet nothing more thua negatives have been proved. If the vast, quantity of water not flowing througn most of the large towns of England did not mix wi>h the sewage matter this would be more managable, and might be deodorised with profit. Such is allowed to be the ease, and this is in fact the only view of the subject of immediate or practical interest to ns, as we have neither the sewers nor the water to flush them with. Various and desultory experiments ia thig direction have been tried here, but not, w 0 Believe, except on a very small scale, with clay, which, as Liebig points out, is the natural deodoriser of excrementitiohs matter, » n d the one substance which is needed to make this a safe and at the same time inodorous manure. Form r failures are easily to be accounted fir, but we helieve enough has been learned from these to almost insure success in a further trial, if we will biit take advantage of the full amount of knowledga now available to ns.