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The flow was consistently less than 500 million gallons per day from early May until
early September, and at the beginning of July it fell to 170 million gallons per day. From
a survey of the analytical results obtained during the year the present position appears
as follows:
(a) The length of the river which was devoid of dissolved oxygen in the summer
quarter was less than in the previous year.
(b) At high tide the length of the river which contained sulphide on any one occasion
decreased appreciably but at low tide there was little change.
(c) The number of occasions when some dissolved oxygen was found off the
northern outfall works showed an increase and the incidence of sulphide decreased. The
suspended solids of this outfall considered as an average from daily samples showed a
decrease in the summer quarter, which may well be attributed to the fact that the
combined effluent now discharged contains less suspended matter than previously found
in the river during periods of low fresh water flow.
(d) Some general slight improvement is reported and although the increased flow
during the last month of the worst period to some extent contributes to this, the
substantially decreased loading from the northern outfall works due to the first stage
of the work, must be having a beneficial effect. The new sedimentation plant with the
present method of works operation has decreased the load on the river by approximately
70 tons of oxygen demand (B.O.D.) and 70 tons of suspended matter per day.
(e) The urgent necessity for further substantial reduction of the load on the river is
apparent. As the loading is decreased the zone devoid of oxygen will gradually decrease
but considerable further decrease of loading is yet required before oxygen is likely to be
present at all times.
The Scientific Adviser continued to be a member of the Thames Survey Committee
of the Department of Scientific and Industrial Research, and also 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 water of the river and are to report
in due course their 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 and, as a result of the happy collaboration which
exists between their staffs, the scientific work is carried out in the closest co-operation
with the staff of the Chief Engineer. In addition to daily consultations on the works,
the analytical results and research progress are discussed at a weekly meeting at the
County Hall between the Divisional Engineer (Main Drainage) and the Scientific
Adviser to suggest policy of operation and to discuss methods of improving efficiency
or overcoming difficulties.
The analytical work includes examination of the following samples: incoming
sewages, effluents from different sections of the plant, sludges sent to sea, sludges entering
and leaving digestion tanks, activated sludges, waters from the steam raising plant and
effluent liquors from Beckton Gas Works (North Thames Gas Board). Routine
observations of atmospheric pollution are also made daily.
Considerable analytical work was done on the new sedimentation tanks and as a
result of the operation of this section of the new plant the suspended solids content of the
primary effluent was reduced by one half and the B.O.D. (5 days) by one-third.
The research work undertaken at the works included the following :
(a) Investigation of flow patterns using radioactive chromium as sodium chromate
and radioactive bromine as ammonium bromide. This work may have far reaching
effects on the design of sedimentation tanks when the causes of the flow characteristics
are ascertained.
(b) In collaboration with the Chemical Research Laboratory of the Department of
Industrial and Scientific Research, a process of producing sulphur from calcium sulphate
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