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184
Annual Re-port of the London County Council, 1910.
Treatment
and disposal
of sewage.
The sewage collected by the local sewers, which are vested in the local authorities, and by main
and branch sewers under the control of the Council, is conveyed by means of large intercepting sewers
to the outfall works. These are situated at Barking on the north side of the Thames, and at Crossness
on the south, and are respectively 11 and 13 miles below London-bridge. The sewage on its arrival
at the outfalls is subjected to chemical treatment—i.e., about one grain of proto-sulphate of iron
and four grains of lime are added to every gallon of crude sewage. The sewage is then discharged into,
and allowed to pass slowly through, large reservoirs or precipitation channels, where the suspended
or solid matters subside and the liquid or effluent passes over a weir into channels leading into the river
Thames. The residue in the precipitation channels, which is called sludge, is cleared out and pumped
into other channels, where the solids are allowed to settle still further. The resultant sediment, which
contains about 92 per cent, of moisture, is pumped into the Council's sludge steamers and conveyed to
the Black Deep in the Thames Estuary.

From the above figures it will be seen that at the Barking outfall one ton of sludge was extracted
from an average of 33,620 gallons of sewage treated, as compared with 33,815 gallons in the preceding
year, while at the Crossness outfall the average quantity of sewage treated to produce one ton of sludge
was about 51,737 gallons, as compared with 48,967 gallons in the preceding year.
The total quantity of sewage treated at the outfalls was more, by 3,660,977,592 gallons, than
the flow in the previous year, while the quantity of sludge sent to sea was more by 37,000 tons, or about
712 tons a week on an average.
At the Barking outfall there is a one-acre coke bed which has been maintained in action for over
seventeen years for the bacterial treatment of the effluent produced after chemical precipitation, am
the purification continues to be satisfactory, although the filtering capacity of the bed has diminished
The refuse intercepted at the gratings of each outfall is taken away for agricultural purposes, with
the exception of a small quantity which is dug into the ground or used as manure on the garden plots
attached to the workmen's cottages. In addition to this refuse, large quantities of sand and fine grave
are brought down by the sewers, in times of rain, and deposited in the precipitation channels, from
which the deposits are removed from time to time.
The sludge is taken to sea by the Council's sludge vessels, which are six in number, viz., the
" Barking,'' " Barrow,'' " Bazalgette," " Belvedere,'' Binnie," and " Burns," and each is manned by
a staff of officers and crew numbering 24. Each vessel carries a load of about 1,000 tons. During
the year under review, the vessels made 2,673 trips to and from the deposit area in the Black Deep ;
the distance travelled being about 267,300 miles. The vessels are insured for £108,000.
Main drainage
extension
scheme.
On 5th December, 1899, the Council approved in principle a scheme of main drainage extension
works necessitated by the increasing strain imposed upon the existing system owing to the growth of
the population. This scheme, the estimated cost of which is roughly £3,772,550, comprises the undermentioned
works :—
North of the Thames.
Barking to Old Ford—Two new sewers (Northern outfall sewer enlargement) and extra
works at Barking.
New sewer between high-level and middle-level sewers (Middle-level sewer No. 2).
New sewer between middle-level and low-level sewers (Northern low-level sewer No. 2).
Extension of middle-level sewer No. 1 to Scrubs-lane.
Enlargement of the Abbey-mills Pumping Station.
South of the Thames
New sewer from Crossness to Deptford (Southern outfall sewer No. 2) and extra works at
both stations.
New sewer from Crossness to Catford (Southern high-level sewer No. 2).
New sewer from Deptford to Battersea (Southern low-level sewer No. 2).
Practically all these works are now completed with the exception of the enlargement of the
Abbey-mills pumping station and the construction of the southern low-level sewer No. 2, and sections
3, 4 and 5 of the northern low-level sewer No. 2, and these are in course of execution. During the year
the erection of a new engine house at Abbey-mills pumping station was entrusted to Perry and Company
(Bow), Ltd., the amount of their contract being £58,362 3s. 4d. The gas engines for this pumping
station are in course of construction by the Premier Gas Engine Company, Ltd., at the contract price of
£23,558 5s. The centrifugal and other pumps are being supplied by Mr. John Cochrane for £8,400 ; the
hydraulic penstocks and valves by Messrs. J. Blakeborough and Sons for £2,205 ; and the travelling crane
by Messrs. T. Smith and Sons, for £475.