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MEDICAL OFFICER'S ANNUAL REPORT SHEET 11 OF DRAFT
air Compressors. The latter supply compressed air to a storage
reservoir, whence it is drawn as required to the ejectors used for
raising the sludge from the sludge wells into which the sludge
gravitates from the settling tanks. The old hydraulic pumps at
Ely Place have been replaced by modern sewage ejectors worked by
compressed air drawn from the reservoir at the sewage works through
a new air main that follows practically the course of the old
hydraulic main, and since this plant has been working no complaints
have been received respecting the brook pollution.
The method of treatment remains the same as when the works
were installed and produces a very satisfactory effluent.
The outfall chamber contains the outfalls from the district
proper and from the Asylum the latter is a strong domestic sewage
in a fresh condition and contains at times washings from slaughterhouse
and piggeries.
The mixed town and asylum sewage runs through the main building
of the works down a stepped incline (known as the salmon ladder)
and during its course receives a proper mixture of slaked Buxton
lime and aluminoferric, the latter being the trade name of a mixture
of sulphate of iron and alum. The dosed sewage is then received
into settling tanks and is retained for such time as to allow the
sludge to settle, this time depends upon the temperature to a great
extent and is regulated by the works manager.
After treatment in the tanks is completed, the sewage is drawn
off in a thin film over adcill about 2 feet wide and drops a few
inches into the channels which lead it to the contact beds.
The manner of drawing off the sewage from the tanks is important
inasmuch as at this stage it is possible and desirable to
thoroughly aerate the sewage.
The contact beds consist of an underdrainage of perforated
stoneware pipes covered with about three feet of graded burnt ballast,
from the size of a walnut to that of a pea, the top layer consists
of about 9" of loam soil, and it is in this layer that the principal
amount of purification takes place.
The sewage is held up in the contact beds for a definite period
and is then drawn off into the effluent chamber with a minimum disturbance
of the material constituting the bed.
The contact beds are worked intermittently the period of rest
being governed by their condition and the atmospheric conditions.
The top layer of the beds tends to consolidation and this
condition is detrimental, it is therefore necessary at intervals
to thoroughly rest the beds and dig them over, cleaning them and
remaking the surface to a fine tilth.
It is remarkable that the lower portions of the beds keep very
clean, and beyond careful working do not require further attention
for years at a stretch.
Closet Accommodation.
This district is entirely a W.C. district, with, the exception
of two cottages in the north ward all the houses are now connected
to the water carriage sewerage system, and every house having a
watercloset has a proper check cistern fitted to the W.C.
Scavenging.
Since the issue of my last Survey Report in 1920 the Council