Perplexing

New Zealand Mail, Issue 879, 4 January 1889, Page 27

Perplexing

So far as can be judged from such information as is at present available, the Shone “ pneumatic-ejector ” system, so warmly recommended by Mr Higginson, appears to be the only feasible plan by which the Wellington Bewage can be conveyed to the open sea with* out the conveyance involving very heavy expense. But, although the estimated cost of establishing and carrying out this system is only halt that of the late Mr Clark’s “ risingmain” scheme, itstil! amounts to a sum which, in the present state of our civic finances, appears somewhat formidable. Probably the lowest coet would be fully £70,000, and that would require at least £3OOO a year to be provided to pay interest alone, for which a special rate would need to be struck. Now the fact cannot be ignored that any additional rating would press very hardly upon the Wellington citizens just now, and this ought to be avoided if possible. At the same time the persistent defilement of opr harbour is a very serious matte? as affecting the public health* and the evil is an increasing one, because the foul matter precipitated from the sewage has a tendency to accumulate slowly but steadily in a fan-shaped bank around the outlet of every town That sooner or later a radical change must be made froiy. the present plan, and that the, sewage will have to be discharged direct into Cook Strait, we have no doubt at all. But in view of the immediate expense of so radical a, reforgj it is <quite justifiable, and in- | Jeed desirable, for the City Council to i give full and fair consideration to the question whether it might not be feasible to mitigate the present evil pending the time when the-, city can afford, financial stress, to “ reform it altogether.” Several plans are now in course of tribal at various English cities and i towns. It would be well to., obtain all available paiticulars about these .experiments. Eor instance, the little ■ Cornish ci,ty of Truro has, lately been | considering ho\y beat to solve the I difficult q ( uesti,on of the disposal of its sewage matter. A good work has been I effected by the substitution of pipe sewers for the old stone drains, and the last of the old and worse than useless drains will soon he a thing of the past. But this unfortunately does not settle the whole

matter in Truro’s case any more than ia that of Wellington. Though Truro will have good sewers, their contents will be poured into the river to pollute its water and constitute a standing nuisance. To remedy this the town surveyor has drawn a plan providing an intercepting sewer and storage tanka for that portion of the town lying to the west of the river, and is engaged upon a Bcheme for the other part of the town. The idea is to collect the sewage matter in settling tanks, where it will be precipitated bv chemical agency, and the liquid portion afterward allowed to drain off into the river. Precipitation, if effectually carried out, o f course deprives sewage of its injurious parts, and the water which runs away is virtually harmless, but the action of the chemicals renders the precipitated matter useless, or at any rate very nearly so, for manure, and there is, moreover, an inordinate amount of “ sludge.” The cost of the Bcheme will be about £IO,OOO, and the Council are about to consider, first, whether the system will work efficiently; and, secondly, whether it is the best one they can adopt. Another plan has, however, been suggested to them. A new method of dealing with sewage has just been brought before the public by Mr William Webster, F.C.S., son of the well-known contractor who has had so large a share in executing the drainage works of the Metropolis. Mr Webster proposes by means of electricity to bring all the solid matter to the surface, where it can be collected, and the water then allowed to run off. It iff claimed for this system that the matter is not so seriously deteriorated for manurial purposes as it is by chemical precipitation, and that, moreover, there is notthesameamountof“oludge”' to deal with. The expense is estimated at about the same in each system. A correspondent of the British Architect draws attention to yet another method of treating sewage. He says the process, which is a very simple one, is the discovery of a civil engineer, and the original intention was to apply it to sewage in bulk, and this has been done with the greatest possible success in several eases, notably at the barracks at Chichester. A recent development of the invention has made it apolicable to private or public buildings of any size, and has thereby brought it within the scope of feasibleness. The process consists simply in treating the sewage with a salt of iron, supplied regularly in a certain fixed proportion ; the effect is not merely to completely do away with all offensive odour, but to actually destroy all the noxious elements of the sewage, reducing it to a fine black ash, and producing a perfectly clear effluent. The iron is supplied by means of a ferrometer. This consists practically of a glass-receiver, holding 31b of the specially-prepared chemicals* enough to last a household of fifteen persons for a week. The lower end ot this receiver is perforated by a series of holes, and dips iDto an earthenware vessel, through which ruus a constant flow of water, which gradually dissolves the chemicals, after which it ist. allowed to pass into the* drainage system of the building. It ja estimated that this system can be carried out at an annual cost of lOd per head. These are only three out of a perfect host of schemes for wholly or partially purifying town sewage before it is allowed to be discharged into river or harbour waters. It is a moot point, among unbiassed drainage engineers whether any of these devices can really he pronounced successful in alt respects. Some stand, every test buft the economic one, but failure in that respect is, unhappily, enough iu itself to be the death of any scheme. Ifc seems to be genially recognised that only under exceptionally propitious conditipna has sewage-farming any oha.aee of succeeding. The drawback that the sewage is most copious in quantity and poorest in fertilising quality just at the season of the year when the ground can least bear to ba drenched with the highly-diluted liquid, ia very much against it. Possibly the* difficulty might be avoided or mitigated by au improved method of filtration or precipitation, but this has not yet been satisfactorily accomplished.. On the other hand the dry earth plan, has proved a great disappointment to* those who were sanguine that sj. valuable and marketable manure might thus be produced. Practical experience demonstrated that theearth after being used over and over again half a dozen times—not a very pleasant condition—-only became equal

to common garden mould and possessed hardly any fertilising power when applied as manure. In this sewage question we find theory and practice at issue. Theory points to the valuable fertilising elements contained in sewage, and declares it to be sinful waste to throw it into the sea. Practice discovers that sewage, when either diluted with water or absorbed by dry earth, becomes economically worthless save in cases so exceptional that they may be eliminated from the problem -as it presents , itself in ordinary circumstances. There is of course a possibility that the continuous discharge of sewage over the sand-dunes along Cook Strait (as proposed by Mr Clark) might ultimately be the means of reclaiming a limited area, and of converting it into cultivable soil, but this could not be safely calculated upon as any set-off against the outlay necessarily involved. There is also a possibility that by combining some system of filtration or precipitation with the use of the Destructor, the more substantial and deleterious constituents of the sewage might be got rid of, or even turned to practical account, leaving a comparatively innocuous fluid residuum that might be allowed to run into the bay until the city could afford to spend L 70,000 or LBO,OOO in the larger and more complete scheme. We desire it to be distinctly understood that we do not advocate anv half measures in dealing with this important sanitary question. We are warmly in favour of the adoption of the Shone system, or any other equally efficacious, if this can be managed without laying too heavy burdens upon the ratepayers shoulders. But if this cannot be, then we urge that at least the evil while it continues to exist should be mitigated so far as possible, and that every feasible method by which this may probably be accomplished should receive the early and careful consideration of the City Council.