The Pamphlet Collection of Sir Robert Stout: Volume 12
Chapter VII. — Sewage
As stated in the last chapter, we are badly off for the disposal of our sewage. Some few closets empty themselves into Rattray Street sewer, some empty themselves into our streets, in many cases by means of private drains, at times assisted by flood waters; others are emptied at irregular intervals by nightmen, and the soil deposited at a depot in a paddock a little beyond the Gas Works.
I need not tell you that this is not at all a satisfactory state of things. Matters would not be so bad if, instead of this hap-hazard system, we had earth closets universally in use, and regularly emptied. This, in fact, is a method much in favour in some towns in England. It would, at all events, be better than our present method, and would prevent our Bay from becoming a source of danger from contamination.
To show you that the Harbour is not the proper place for the reception of sewage matters, allow me to quote what Dr. Macadam, Professor of Chemistry in Edinburgh, says regarding such matters:†
† Haskoll on Engineering.?
Dr. Letheby, Medical Officer of Health for the City of London, says, regarding the mud deposited in the Thames:—
"It is black and foetid, and in a state of active putrefactive decomposition. When examined with the microscope, it was found to consist of broken-up sewage matter, with the remains of myriads of animalcules . . . . It is evident from this, as well as from what I know of the usual composition of the warp or mud of rivers, that this is a very large proportion of organic matter, and that by undergoing putrefactive decomposition, the mud which is accumulating in such large quantities at the sewer outfalls may be a cause for serious alarm, especially as it there meets with sea water, the sulphates of which may, by their chemical decomposition by the putrefying mud, occasion the escape of much sulphuretted hydrogen, and set up that remarkably offensive change which is characteristic of the action of sewage upon sea water."
It is thus seen that some better plan is urgently called for. The question then conies to be-out of the many systems elsewhere adopted, which is the one most suited for Dunedin. After much deliberation I have come to the conclusion that what is termed the Separate or Irrigation system is the one that will yield the best results.
The scheme that has occurred to me is the following:—The sandhills at the Ocean Beach should be properly prepared and utilized as a filtering area. Only a very small portion of these sandhills would be required; for Merthyr Tydvil, a town numbering 50,000 inhabitants, has only twenty acres of prepared land for the same purpose; and, as we shall see presently, the whole scheme is a complete success.
Accompanying this report is a plan drawn by Mr. Burt, C.E., embodying my modification of his former one, by means of which the City could dispose of its sewage in the manner I advise.
In Merthyr Tydvil a system of filtration and irrigation had page 11 been earned out two years when Dr. Dyke, the Medical Health Officer for that town, wrote of it as follows:—
"The result of this plan of disposing of sewage by 'downward intermittent filtration' may be seen in this sample of effluent water, taken from the outlet of the main drain. You will observe that the water is bright, perfectly pellucid, free from smell, and only tastes of common salt. It may safely be drunk;-in fact, is used by the workmen employed on the farms. During the process of irrigation no nuisance is caused, for the soil quickly absorbs all the fluids passed into it; in fact, in two or three hours after the water has ceased to flow on the land, an observer would say that the ground had not been wetted for days. The workmen say that no unpleasant smell is noticed, nor has the health of the persons employed in any one instance been affected by any presumed poisonous exhalations. The only imperfection of the plan is that at the end of the furrows nearest the lowest corner of a plot a slight deposit of scum is found. This scum is formed by the fine insoluble precipitate caused mainly, I believe, by the addition of lime to the sewage stream.* On the ridges of this prepared soil, cabbages, brocoli, carrots, turnips, parsnips, beans, peas, lettuces, onions, &c., are grown.† . . . . By passing the sewage through simple and inexpensive strainers, it is delivered on the land in such a state that no nuisance or inconvenience results."
The plan and mode of irrigation, as adopted at Merthyr, is as follows:—
* He advises, consequently, that no lime should in future be used.
† The area of Merthyr Tydvil is 18,000 acres; 3,000 occupied by houses and gardens, having a population of 50,000, living in 10,000 different tenements.
The River Pollution Commissioners, according to Dr. Dyke, report as follows:—
"The experience of these filter beds at Merthyr Tydvil has made plain what the experiments in our laboratory had previously established. Towns can cleanse their sewage within a much smaller quantity of land than any experience hitherto had might lead them to expect. Sewage irrigation offers the great advantage of a remunerative return.* Intermittent filtration may also now be confidently accepted as a sufficient remedy for the sewage nuisance. These two methods are essentially one, wherever thorough drainage accompanies-as it always should-the extensive form of irrigation, and they are the only methods which are perfectly trustworthy for the abatement of this sewage nuisance."
Dr. Edward Franklin says:—"Of the effluent water from these filtering areas, the result is highly satisfactory. Indeed on the 10th June, 1871, the water entry, the Taff, from the Merthyr filter, was considerably purer than the Thames water which we are often compelled to drink in London.†
* Plots were sold from £17 15s. to £64 per acre.
† All this time Dr. Dyke says, the whole of the sewage streams, 800,000 gals, per day, was being passed through ten acres of prepared land.
A farm of 50 acres utilizes the sewage of 4500 people. They having as their maximum a water supply of 40 gallons per head. The farm is nearly two miles from the town, with which it is connected by means of cast iron pipes, nine inches in diameter. Two engines (acting on the centrifugal principle) of 8-horse power, pump 80,000 gallons within 8 hours. There is a double sewage filter tank at the pumping station for the removal of solid matter, and a reservoir capable of holding 20,000 gallons, which acts as an equalizing reservoir, so that the pump need not always be at work. To this filter tank the sewage of the town is conveyed by 18-inch pipes, having a fall of five feet in a mile. The old sewage pipes are used for storm water. There is an emergency safety-valve opening into the Thames. The solid matter is mixed with ashes, and the contents of dust bins, and carted directly to the farm. No deoderant is used. During the past five years, says the Report, the sale of the produce has cleared the cost of the superintendence and irrigation. The entire expenditure of these works, including the purchase of the farm, which is freehold, amounted to £20,000. The cost of drainage is covered by an eighteen-penny rate. It is said that no case of typhoid has occurred since these works were formed. I should have mentioned that ventilating pipes are placed at the highest parts of the drain, these pipes running higher than the tallest chimneys. There are also tanks capable of holding a thousand gallons of water, placed in communication with the drains for flushing purposes.
In an article in the "Engineer" dated October 16th, 1874, irrigation is said to be at the top of all systems for the disposal of sewage. It goes on to say that a Committee was appointed to inquire into the best means for the disposal of sewage, and that the Committee, after having examined various systems at various places, report that in no instance where irrigation was tried, did it give an unsatisfactory result. Thus at Leamington, a town having a resident population of 30,000, the sewage is pumped to a height of 32 feet, and delivered to a Home farm of Lord Warwick's, two and a half miles distant. The farm consists of 400 acres, 250 of which are irrigated. The crops are all that can be desired, and Lord Warwick pays £450 a year for the sewage. This last is efficiently disposed of and thoroughly purified, the effluent being bright, possessing nothing noxious, nor unpleasant to the taste. At Doncaster, the results of irrigation are yet more promising, the Corporation receiving £800 a year rent for a sewage farm, 2¼ miles distant, the sewage being pumped to a height of 52 feet.
The article concluded in these words:—"Thus then we have page 14 the verdict of a very painstaking Committee, with every possible facility afforded them, deciding that Irrigation is the only practical way of getting rid of sewage with good results."
In our case, I believe no pumping would be required, if Mr. Burt's plan were adopted; for the pressure of the Water of Leith running through his main sewer would probably be sufficient to propel the contents on to the sand-hills previously lowered and prepared, the effluent water finding its way through the sand into the ocean. It is probable that the Government would grant sufficient of the sand-hills to the Corporation for the carrying out of this scheme, and a letting of these would help materially to defray the primary and working expenses.
In concluding this chapter, I would suggest that the sewer pipes be so constructed, that no exhalations could find their way into our dwellings. In Glasgow, I believe the experiment of burning sewer gas as they would common gas has been tried with success; at all events, such a mode of removing the gas is possible, seeing that it possesses from 70 to 95 per cent, of combustible material, including light carburetted-hydrogen, hydrogen, and carbonic oxide. In a recent number of the "Lancet" it is mentioned that Dr. Aldridge, of Southampton has devised means by which a water-closet may be so constructed as to effectually prevent the escape of sewer gas into it.
Storm and sub-soil waters should not be allowed to enter the sewers, as they have a tendency to obstruct them by the metal which they convey.