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43
The following paragraphs relate these activities to the various responsibilities and
services of the Council.
River Thames
The condition of London's river is of special concern to the Council. In addition to
effluents from the Council's own sewage treatment plants, there are sources of pollution
from other sewage works, impure tributaries, trade discharges, and contamination
from shipping. To assess the condition of the water under varying conditions of fresh
water and tidal flow, and to compare the state between seasons of the year and over
periods of years, regular weekly examinations are made involving chemical analysis of
water taken from 26 points over a distance of 80 miles. The area examined extends
from the upper limit of the tidal reaches at Teddington to the sludge dumping area at
Black Deep in the outer estuary.
Dissolved oxygen is continuously being absorbed by oxidisable matter present in
the water and the rate of renewal of oxygen from the air depends on the temperature,
the wind, and other factors. If the process of absorption requires more oxygen than
can be replaced from the air, putrescent conditions arise in which sulphate-reducing
bacteria produce hydrogen sulphide from water-soluble sulphate. The summer quarter,
July to September, with its higher temperature and normally reduced rainfall is the
critical period.
In 1958 the flow of fresh water during the summer quarter was greater than in any
year since 1930, and in consequence there was a marked improvement. At no point
was the river completely devoid of dissolved oxygen at high tide during this period,
and at low tide only off the Southern Outfall Works was dissolved oxygen absent for
the whole quarter. Although much of this improvement may be attributed to the
increased fresh water flow, the new sedimentation plant at the Northern Outfall Works
played a significant part in reducing pollution.
The Scientific Adviser continued to be a member of the Thames Survey Committee
of the Department of Scientific and Industrial Research, and of the Heated and Other
Effluents Committee of the Ministry of Housing and Local Government. Both committees
deal with aspects of the condition of the river and are to make recommendations
for its improvement.
Sewage treatment
The treatment of sewage at both outfall works is the joint responsibility of the Chief
Engineer and the Medical Officer of Health. Close daily collaboration is maintained
between their staffs and weekly conferences are held between the Divisional Engineer
(Main Drainage) and the Scientific Adviser, together with their senior officers, to discuss
analytical results and operational practice.
The primary sedimentation tanks at the Northern Outfall Works, installed in 1955,
continued to reduce the amount of suspended matter leaving this section of the plant
by one-half and the oxygen demand by one-third.
The present secondary treatment plant treated up to about 40 million gallons daily.
The final effluent from this approached Royal Commission standard for a considerable
part of the time. New diffused air plant to extend the capacity for secondary treatment
will shortly come into use.
Sludge digestion provided gas at the rate of half a million cubic feet daily.
During the year a considerable programme of research and development work was
carried out. Collaboration with the National Chemical Laboratory of the Department
of Scientific and Industrial Research in the experimental biological production of
sulphur continued. Work on radioactive tracers was extended and problems relating to
foam from detergents were investigated. Tests on automatic samplers were continued.
Trade waste discharges
The Council exercises control under the London County Council (General Powers)
Act, 1953, over industrial discharges into the London sewerage system ; these have