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178
CHAPTER XXXVI.
Powers and
duties of the
Council.
Met opolitan
main
drainage
area.
Main Drainage.
The Council is charged by statute with the responsibility for the provision and maintenance of
an efficient main drainage system for the Administrative County of London. Its powers and duties
in this respect are derived mainly from the Metropolis Management Acts, 1855, 1858 and 1862, and
under these Acts the Council is specifically required to provide and maintain the necessary sewers and
works for preventing, as far as may be practicable, the sewage of London, collected by the local sewers,
from passing into the river Thames within the County. The treatment and disposal of the crude
sewage also forms an important part of the Council's work.

Treatment
and disposal
of sewage.
The whole of the sewage of the County of London is dealt with by the Council, but power is
reserved to the Council in the West Kent Main Sewerage Act, 1875, to connect any of its sewers
with the West Kent sewer, which passes through the southern portion of the metropolitan boroughs
of Lewisham and Woolwich. This power has not been exercised.
The sewage collected by the local sewers, which are vested in the metropolitan borough
councils, 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 Londonbridge.
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 solid matters in suspension 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 37,601 gallons of sewage treated, as compared with 33,620 gallons in the preceding
year; while at the Crossness outfall the average quantity of sewage treated to produce one ton
of sludge was about 57,124 gallons, as compared with 51,737 gallons in the preceding year.
The total quantity of sewage treated at the outfalls was more, by 7,284,605,707 gallons, than
the flow in the previous year, while the quantity of sludge sent to sea was less by 93,000 tons, or about
1,790 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 eighteen years for the bacterial treatment of the effluent produced after chemical precipitation,
and 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 gravel 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.