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30
provision had to be made for considerable flows of trade
waste from Messrs. Ford's and other factories.
About 1931, therefore, designs were prepared for
a new works to give a high degree of purification to a
minimum D.W.F. of 3 m.g.d. domestic sewage, by means
of sedimentation and activated sludge treatment; provision
also being made for partial treatment of a flow of
2 m.g.d. trade waste from the Ford factory. The
required standard of the Port of London Authority is
being met by the mixture of the highly purified domest ic
effluent with the partially purified trade waste—a system
which has proved quite satisfactory in operation.
A new pumping station was provided to deal with
the domestic sewage flow, whilst the old station was
converted to deal with the trade waste arriving from
Ford's by a separate sewer.
The original settling tanks have since been adapted
to work in parallel with the new sedimentation tank and
provide further settlement capacity in the domestic
section of the plant.
The present works thus consist of two pumping
stations, separately lifting domestic sewage and trade
waste, and for the treatment of the domestic sewage,
a radial flow mechanical sedimentation tank with six
plain rectangular sedimentation tanks in parallel for
balancing flows, followed by activated sludge treatment
with simplex aeration tanks and diffused air reaeration
tanks. For the treatment of trade waste, there are
two transverse flow mechanical sedimentation tanks.
An automatic effluent pumping station lifts mixed final
effluent to the river when tides are too high for gravity
flow. Raw domestic sludge and activated sludge are
treated in heated digestors before disposal on ploughed
land, whilst trade effluent sludge, being inoffensive, is
sent direct to the land.