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17
The activated sludge is pumped to the diffused air re-aeration
tanks which are on a ridge and furrow principle. After a period of
24 hours re-aeration, the re-activated sludge is returned in controlled
volumes to the aeration plant for re-use in treatment. The excess
sludge in the tanks above that required to be re-aerated for subsequent
use is returned to the pump well and settled out as a
mixture with the raw sludge in the circular settling tank.
Trade Waste:
Most of the trade waste flow is from the Ford Works. For
the time being, this is being treated by sedimentation in Dorr
Clarifiers, allowing a period of settlement of 3 hours.
The effluent from these tanks flows to a pump well which also
receives the effluent from the settling tanks. Pumps eject the
nixed effluent against any state of the tide into the Thames, while
at low tides the effluent can gravitate to the creek.
The strength of the domestic sewage in terms of oxygen
absorbed in 4 hours averages 13 parts per 100,000. After sedimentation
this figure is reduced to 9, whilst after 4 hours aeration,
it is reduced to about 2.5 parts per 100,000.
Rivers and Streams.
See 1930 report.
Owing to the fouling of the Seven Kings Stream, colour tests
were carried out in the northern part of the district to determine
the sources of pollution, following which the owners of property
ui that area were requested to disconnect the overflows from their
cesspools. The trouble seems to arise from the fact that the
Council's cesspool emptier empties free of charge the cesspools
only once per month, though there are few cesspools having a
Month's capacity. For emptying at more frequent intervals a
charge of 15s. Od. per load is niade. The majority of the residents
in the area concerned, during the summer months, supply teas at
week-ends and holidays to the members of the public who spend
their time at Hainault. The use by these persons of the lavatory
accommodation of the premises results in the overloading of
cesspools. If a public lavatory were conveniently situated, this
nuisance would be very much less. A scheme has now been put
forward and is in hand for a small sewerage plant to be installed
in this area as suggested in the Annual Report for 1927.
Closet Accommodation.
See 1930 report.