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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 comparc 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.
The position during 1957 was as follows :
(a) The average daily flow of fresh water over Teddington Weir during the
summer quarter was 304 million gallons, appreciably less than the corresponding
quarter of 1956 (442 million gallons). The flow fell to 170 million gallons per day on
44 occasions.
(b) Despite a smaller average flow, the length of the river devoid of dissolved
oxygen in the summer quarter showed little change when compared with that of
the previous year.
(ic) The number of occasions when some dissolved oxygen was found present in
the river off the two outfall works showed an increase and the incidence of sulphide
decreased.
(d) Examination of the number of sulphate-reducing bacteria per unit weight of
mud from the river bottom indicated an appreciable reduction from Greenwich to
the northern outfall and a slight reduction to Greenhithe.
The progressive deterioration in the condition of the water in the lower and middle
river sections, observed over a period of years, appears at least to have been halted by
the improvements at the northern outfall works. The urgent necessity for a further
substantial reduction of the pollution load on the river is still apparent.
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 new primary sedimentation tanks at the northern outfall works were the subject
of continued experiment during the year and investigation was made of the performance
at constant flow, the effect of continuous and intermittent scraping, composition of
the sludge as removed and other aspects of the work. The performance of this new
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