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36
D (8) Street Trading
The established street trading which was so prevalent a
few years ago has now practically ceased to exist, and only
two stalls of the mobile type are sited in the shopping area.
No nuisances have been detected at this source.
D (9) River Thames—Effluvia
Effluvia from this source were not so discernible during
the summer months, probably due to the abnormal rainfall
and low atmospheric temperatures which prevailed.
In June it was announced that the London County Council
were to construct sewage treatment works as an extension
to the Southern Outfall at Crossness, Erith. The new project
is said to be capable of treating to an adequate standard, the
whole of the flow from that part of London County which
lies to the south of the River Thames, and has a population
of about 1,600,000. The existing tanks and some of the
more modern pumping plant will continue to deal with storm
water when the new works have been completed. Sewage is
now delivered to the outfall works by two low level sewers
and one high level sewer, each of 11 feet 6 inches diameter.
These are not sufficiently high for sewage to gravitate through
the treatment works to the Thames at all states of the tide,
and a new electric sewage pumping station will therefore be
installed. Before pumping, the whole of the flow arriving at
the works will be screened by six low level and four high
level mechanical screens. The detritus will be extracted by
dredger pump and used for reclamation of low lying marsh
land. The 16 primary sedimentation tanks, capable of treating
up to twice the average dry weather flow, will be of the
rectangular type, arranged for de-sludging by travelling
scraper, followed by surface aeration units incorporating the
latest modifications in machinery and fed so as to permit
stepped aeration and re-aeration of activated sludge. They
will discharge to 32 circular final sedimentation tanks of 113
feet diameter provided with sludging mechanisms.
The sedimentation and aeration units will be divided
into two groups of separate plants capable of individual
operation: between will be a general sludge pumping station
for dealing with raw and activated sludge, and incorporating
the main control room.
The 16,-80 feet diameter primary digestion tanks will
each have a floating gasholder roof and a heating and circulating
unit and there will be 8 circular secondary digestion
tanks of 120 feet diameter. The sludge will be cooled before
secondary digestion to save heat and facilitate de-watering,
and after digestion it will be gravitated to sludge ships for