DISPOSAL OF SEWAGE.

New Zealand Mail, Issue 913, 30 August 1889, Page 19

DISPOSAL OF SEWAGE.

In connection with the sanitary questions that have cropped up lately, the following article taken from The Field will be rood with interest as bearing directly on the subject : An interesting demonstration of the practicability of effecting the removal of the feculent matter from recent sewage was reeeutly given at Kingston. The clear effluent, perfectly inoffensive arid unobjectionable, was afterward run into the Thames without any opooeition on the part of the Conservators. The sewage of Kingston and Surbiton districts, numbering at present nearly 40,000 inhabitants, i», on flowing into t he works, passed through a coarse ura ting, with aview of intercepting any solid materials that might interfere with the action of the pumps. It is then immediately mixed with a certain proportion of levigated clay and charcoal in a state of fine division, the latter being obtained from the chemical work 3 in which prussiate of potash is made. The charcoal at once deodorises the sewage, which flowa out of the building in which the admixture is made in a black, muddy stream. As this flows toward the settling tanks, a number of small rills of a solution of alum are allowed to fall into it. The black sewage is now conducted into one end of a very large tank excavated in the grounds. Along the centre of this, but nut quite reaching the further end, is a brick wall, which practically divides it. into two. The stream of sewage has to flow to the further end of tho tank, and return on the other side of the partition, and as the quantity held by the tank ia very large and the current small, the rate at which the sewage flows through

the tank .is very slow, so that the clay,., charcoal, and precipitated alumina front* the alum have abundance of time to unite with the feculent matter of the sewage,, and settle at the bottom of the deep tank in the form of sludge. The effluent, which is allowed to flow out of the top of the second division of the tank, is very nearly colourless and. trans but still not sufficiently pure to be received into the silver Thames ; it ia consequently allowed to flow into a second taDk, identical in construction with the first. In its slow passage through this the whole of the solid matter is deposited, and the effluent escapes at, the furtkor end, bright, dear, transparent and eO inoffensive that a nobl& duko is said to have drunk off a glass to the success of the Native Gunno Comply- — an example wo confess we did not follow.

Hitherto considerable difflcnlty has attended the disposal of tb© sludge which remains at the bottom of the tanks when the supernatant fluid has run off’. At the Kingston works it ia pumped in its serh'i-'fluid condition into filters, through which l the liquid part is forced by atmetepherfe pressure amounting to lOffib on the square inch. The solid is them removed from the filter presses,, dried by a current of heated air whil&t kept in metiou, aud finally packed in bags of lewt for sale as native gunno. The company have fftrong testimonials of its value* as a manure, ai?d it meets with a ready sale at 703 per ton. The whole of the processes are conducted without any offensire odour. Evers the very sludge containing ibe whole of the feculent matter of the sewage is unobjectionable to' the sense of email, one of the taftks half filled with this unpleasant looking substance having beera left exposed to the air some days, so that it rfiight be seen at the worst by the visitors. The dry native guano is perfectly having the appearance of dry black peat dfevrcoal. The sewage questioH has long silica paesed the styge when the sewage wa© regarded as of immense manorial value* and has arrived at the point when the problem to be solved is how to get rid of v an offensive material at fcho least possible cosh It is now known that the value of the fertilising and chemical materials contained in a ton weight of sewage is only a very small fraction of a shilling, and that to separate this from, the 20cwfc. of water -with which it is United costs more than the material is worth. But our sewage must be got rid of sd -any cost, and cannot any longer bo allowed to flow into our rivers and engender disease. The cheaper thia can be done the better, and tlia Native Guano Company have made* highly satisfactory progress in demonstrating that they can, when aided bp a, subsidy from the rates, take the feculent, offensive cowage of a district and convert it into two substances, one being a saleable useful manure, the other a harmless, inoffensive effluent, which can be allowed to flow into our river.** without detriment to the health or convenience of the public.—The Field.