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at Barking and Crossness cover about twenty acres, and when completed will, with all machinery and equipment, have cost not very far from a million sterling. The County Council inherited the commitments of the Metropolitan Board as to these works.
At one point the chemical treatment of the sewage has preceded the screening, which will soon in all cases be the first operation. For screening, the flow of sewage is obstructed by an iron cage in which a quantity of solid matter, including corks, offal of all kinds, dead vermin, with various contributions from all sorts of factories, is deposited, amounting, perhaps, to a hundred tons a week. In former times the whole of this solid filth passed into the river with serious damage to appearances than would be caused by twenty times the weight of more soluble filth. There is no ready sale for this matter. At Barking the Council have paid £600 a year for its removal: a destructor is being erected in which it will be burnt upon transfer from the adjoining filth-hoists. Experts have differed as to the sufficiency of the chemical treatment of the sewage, but never, I believe, as to the expediency of some such treatment. The Council have adhered to the system of precipitation adopted by the Metropolitan Board by means of nearly four grains of lime in solution and one grain of proto-sulphate of iron per gallon, being equivalent to about a quarter of a ton of lime per million gallons. At Barking there are thirteen channels for precipitation, each 30ft. wide, varying from 8.oft. to 1,210ft. in length, and holding together about 20,000,000 gallons. By a skilful rearrangement of these tanks the Council's engineers have so managed the current that the sludge is deposited near to the settling tanks, from which it is forced by pumps through tubes, laid upon a jetty into the sludge ships. It has not been found profitable to reduce the water in the sludge beyond 85 to 90 per cent. In the warm season, from May to October, a process of deodorising is carried on, at an average cost of about £30,000 a year, by adding to the effluent a solution of permanganate of soda with some admixture of sulphuric acid. This is done at the outfalls and at about twenty stations upon the Metropolitan main sewers. It will be some time yet before all these operations are in perfect working order at Barking and Crossness, but if we suppose that time to have arrived when the daily dry weather flow of 160,000,000 gallons of sewage is duly screened and chemically treated and precipitated, and the 3,000 tons more or less of sludge daily carried off to sea, the effluent being further treated with permanganate of soda, will the result, poured into the stream at these points, equal in daily volume to the water supply of London, be worthy of a model city? I cannot reply in the affirmative, having no opinion to offer against the weight of authority which asserts that when we have done all this the effluent contains seven-eighths of the noxious salts of sewage.
The system has many opponents, and none more formidable or well informed than Sir Robert Rawlinson and Sir Henry Roscoe. The former has advocated entire abandonment of the system and conveyance of the sewage through Essex to the sca; the latter presented to the Main Drainage Committee a pamphlet leading to these conclusions : that the proposal of the Metropolitan Board, which the Committee have followed, is based on false principlesfirst, as regards the addition of lime and 'iron in the proportions recommended ; second, as regards the addition of permanganate of soda to the effluent after precipitation in the quantities suggested ; third, as regards the formation of underground settling tanks at Barking and Crossness; fourth, as regards pumping the sludge into tank steamers and sending it out to sea. I do not contradict, I am not qualified to criticise, this weighty opinion upon any point, nor do I believe that as to basis of principle the system adopted is in any respect defensible. Those who hold by it can do so only, it seems to me, upon claims of expediency sustained by the absence of any suggested and well supported alternative.
There are those who contend that British fisheries have been rendered more valuable and remunerative by the practice of pouring sewage into the estuaries of rivers. But no one who has witnessed the discharge of the sewage sludge of London in the Barrow Deep has been found to give evidence that it causes public injury. The Trinity Board direct the sludge ships, each containing a thousand tons, to the solitary channel between two sands, the northern and southern highways for vessels passing to the right and left. No vessels, except those specially constructed for this work, have been found suitable. The discharging valves are much below the water line when the vessel is charged, but the surface of the sludge when the tanks are full is above the water line and forces the discharge, the vessel rising until the last of the sludge is forced out, when the valves have become visible. The ships run about a mile while discharging, leaving a dark trail of that length which soon disappears. A portion of the 10 or 15 per cent. of solid matter is discoloured sand, which in the discharge grinds with some injury through the bearings of the vessel's screw.
No one can be satisfied with this process who regards it with the ideas of perfection, or of the utmost economy or utility. But there it is, and those who are loudest in condemning it invariably adopt a modified tone of dissatisfaction after careful examination of the process, together with suggestions for some other method of disposal. Early in last year the Council, moved by the discontent of members with their inheritance of this sewage system and by the adverse comments of such notable experts as the distinguished engineer and chemist above referred to, instructed Sir Benjamin Baker and their chief engineer, Mr. A. R. Binnie, to examine and report upon the whole system, and their joint production, which was presented last month, conveys in complete accord the opinions of two eminent men, both new to the works and as completely competent and free from prejudice as men could be.
They report that "it will be hopeless, as it is happily unnecessary, to attempt to get a chemically pure river in the lower reaches.” The sludge, they say, is a black offensive fluid not injurious to the health of the men employed in its manipulation at the outfalls or on board the sludge vessels. There is, they find, a marked improvement in the cleanliness of the foreshore near the Barking outfall, which was formerly covered with black mud but which is now returning to its original state of a gravelly foreshore with green algæ of the usual type, characteristic of the foreshore of the Thames in its cleaner parts. They have seen sufficient of the benefits already derived from the incomplete works to enable them to advise the Council without hesitation “to continue the operations now being carried out, as a great improvement in the state of the river will assuredly result when the entire volume of the sewage flowing from both the north and south sides of the Thames is chemically treated and pre
cipitated at Barking and Crossness.” They think it possible, as chemical knowledge advances, that the effluent may be improved, and it is obvious that such improved treatment can' without difficulty be applied to the existing works. They regard as "singular” the allegation that the process adopted is barbarous, which they believe to be a process “based upon modern chemical research and involving the use of chemical appliances of a novel and ingenious type.” As to cost they have no doubt that it is the cheapest system.
The Metropolitan Board made some experiments and pressed the sludge into manurial cake. But they could not dispose even of a small quantity of that manufacture. For such pressing, the sewage must be prepared with a much larger quantity of lime. The lime and iron treatment now adopted costs for materials about £18,000 a year, and for every grain to the gallon of dry weather flow ten tons of lime would be needed. Some processes involve the use of from thirty to forty grains of lime per gallon. Roughly, it may be said that every grain of lime so added would produce an additional one hundred tons of sludge ; and, if the sludge were pressed into cake, we must be prepared to find a market for certainly not less than eight hundred tons of such cake per day. The Board of Works gave the pressed cake to any persons who would fetch it away, but even so there was no demand; a.d the cost of production, including the extra quantity of lime required, could hardly be less than 45. per ton. There is no doubt about the cost of the method now in practice. When the weirs have fallen in the precipitating tanks and the effluent has passed into the river or into storage until the ebb of tide, the floors are partially covered with sludge. From that stage, account has been taken of the cost of gathering the sludge into the smaller tanks from which it is forced into the ships, as well as of the expense of the vessels, their crews, and the voyages fifty miles from Barking to the discharge in Barrow Deep. The reporting engineers have also examined these charges and are of opinion that the cost is under gd. per ton. If that estimate errs at all, I think it is on the side of excess. As to the sea and river, every observant opinion agrees with theirs, “that no evil influence of the slightest degree can be detected, and from a sanitary point of view this part of the process is beyond question most effectual.” By way of further apology for the system, it may be added that the dredgings of the Clyde, consisting principally of Glasgow sewage sludge, and those of the Tyne, the Tees, the Forth, and other rivers, are carried many miles out to sea and there discharged in preference to depositing them on lands near the rivers.
The low lands on both sides of the Thames are saturated with water and appear to need drainage rather than irrigation. It would be possible by pumping to lift the sewage to any part of England, but there is no evidence to suggest that such method of disposal would be profitable or permitted. There were many who hoped that it would be found practicable to convey the sewage through Essex to a discharge upon the vast and increasing beds of sand towards the North Sea, believing that as the agricultural uses of sewage became better known and appreciated the stream might be tapped on its way to any extent. But the engineers' report is decisive, that this plan would result in a filthy coast and failure. Their arguments are convincing that “if it were considered imperative to discharge the Metropolitan sewage into the sea in its crude condition without any risk of injury to the estuaries of the Thames, the Blackwater, and the Crouch, then the project for an outfall sewer fifty-six miles in length from Crossness to the deep water off Dungeness Point would be found worthy of serious consideration, as the selected point of discharge is free from the physical disadvantages pertaining to the Maplin Sands site. It is necessary to remember, however, that in any case crude sewage would still be discharged into the Thames during storms."
These arguments are irrefutable, but, in view of a model city, who can be content with “ treatment” which results in our pouring into the Thames within the precincts of London a stream, cleared, indeed, of the most palpable refuse, but still divested, in the opinion of experts, of so very little of the noxious and putrescible qualities of sewage ? I am disposed to wish that these precipitation works had been placed farther down the Thames, at Shellhaven on the Essex side and at an equally suitable point on the Kentish bank. But the works are fully contracted for and will soon be complete, and it is clearly the duty of the Council to make the best possible use of them. Our present efforts should, I suggest, be directed to the