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29
The following paragraphs give a general indication of the source of origin of these
samples and of the consultative and advisory duties carried out for the various services
and departments of the Council.
Rivers and
drainage
Throughout 1952 the whole of the sewage flow to the Northern Outfall Works was
treated by sedimentation and approximately one-quarter of it subsequently by the
activated sludge process. At the Southern Outfall Works the whole of the flow continued
to be treated by primary sedimentation only. Regular sampling and examination were
done to assess the results of the treatment. In the case of both outfall works, the plants
functioned satisfactorily throughout the year and achieved as large a saving of B.O.D.
(biochemical oxygen demand) load on the water of the River Thames as could be
expected.
The sludge digestion plant at the Northern Outfall Works was subject to analytical
control, the rate of charge being decided accordingly, and it worked satisfactorily, the
gas produced (containing about 70 per cent. methane) being used for power production
at the works.
The composting of sewage products (mainly screenings) with household refuse was
continued and a large amount of the finished product was available for transport to
farms, mostly those at hospitals.
As mentioned in a previous annual report, in an endeavour to improve the condition
of the water of the River Thames a programme of additions to the existing sewage
treatment works has been agreed by the Council. At the end of the year the completion
of the new detritus pits at the Northern Outfall Works was approaching as was also
that of the 'old reservoir' sludge digestion plant. Progress had been made there on the
construction of the new sedimentation tanks. The other works approved in principle
by the Council comprise additional 60 million gallons per day diffused air activated
sludge plants at both the Northern and the Southern Outfall Works and, also at both
works, sludge digestion plants to deal with the whole of the sludge produced. None of
these had been started at the end of the year owing to the fact that they had not been
licensed for the supply of materials by the Ministry of Housing and Local Government.
Towards the end of the year the Minister received a joint deputation from the Council
and the Port of London Authority which emphasised to him the necessity, in view of
the condition of the water of the River Thames, for proceeding at the earliest possible
date with the additional works for treating the sewage of London in order to lessen the
pollution load on the river.
In the report for 1951 it was mentioned that consideration had been given to any
temporary palliative measures which could be adopted to improve the condition of the
water of the river in the summer months and that chlorination of part of the effluent
from the Northern Outfall Works had been tried as the only possible practicable policy.
In 1952 chlorination of that part of the effluent from those works which was not
subsequently subjected to secondary treatment was again started in May and continued
until the end of August. The dosage adopted was one-third of the chlorine demand,
which was about 40 parts per million; i.e., the addition of 13 parts per million of
chlorine. This was achieved by dissolving it in final effluent from the activated sludge
plant in absorption towers and adding the relatively strong solution to the primary
effluent to be treated. In spite of this, as will be explained in more detail later, the
condition of the water of the river at the end of August was bad over a long stretch of
its course and it was decided to cease chlorination—which was a very expensive procedure
requiring about 50 tons of chlorine per week—and use September as a 'control' period.
Actually, the water of the river in that month did not become generally worse, although
it still remained bad. It was concluded that chlorination on the scale which its great cost
and quantity made feasible did not produce sufficiently beneficial results to justify its
future use and the procedure was therefore abandoned; also that the only way of
improving the condition of the water of the river was by lessening the pollution load
added to it, which could best be accomplished by proceeding, as soon as possible, with
the additional sewage treatment works.