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31
Sewage reaches the farm in Summers Lane by either the
low or high level sewer. The sewage from the low level sewer
passes through a screen, and is then pumped to join the high
level sewage. The mixed sewage is screened, and, after the
addition of lime and sulphate of iron, passed into one of three
precipitation tanks (each having a capacity of 226,260 gallons).
The tank effluent is next treated in a double set of bacterial
contact beds, in each of which it remains standing about five
hours. The effluent is finally run over several acres of meadow
before entering the brook at the bottom of the valley.
The sludge is drawn off after a precipitation tank has
been in use a week, and is pumped on to the land at the
highest level of the farm. It is there left to drain and
evaporate, and is then ploughed in, the land being used for
crops of cabbages, etc.
The dry weather flow of sewage is estimated at about
700,000 gallons per diem. In wet weather a portion of the
sewage is treated in the ordinary way, and the remainder by
broad irrigation. The sub-soil of the farm is clay, and there
is only a shallow surface soil over most of the area, so that
considerably more land has to be utilised than would be required
with more suitable soil.
The total area of the farm comprises close upon 80 acres
belonging to the Council, and 33 acres rented from the Burial
Board.
The filter beds number 16, and cover a total area of about
27,000 square feet. Nine of these beds are in fairly satisfactory
working order; they are constructed of clinker and
burnt clay to a depth of 2½ to 3½ feet, and underdrained; but