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33
River Thames
The pollution load with which any river will deal without becoming itself in an
offensive condition is limited ; it is, therefore, the condition of the water of the river
which is the governing criterion as to the degree to which it is necessary to treat sewage
before the final effluent is discharged to the river. Natural oxidation by the dissolved
oxygen in the river water is the final process of purification. In this operation the
dissolved oxygen is used up and, if the river is not to become putrescent, the rate of
reabsorption of oxygen from the air by the water at the surface must be greater than the
rate at which it is used up by the organic matter in the bulk of the water ; so that there
is at all times some dissolved oxygen present.
The condition of the water of the River Thames is a matter of great importance to
the Council and a weekly examination of it is, therefore, made at 25 points between
Teddington Weir and the sludge dumping area in the estuary, a total distance of 86 miles.
In addition, the water off the two outfall works is sampled daily at both high and low
tide.
An important factor in determining the pollution load with which the water of a
river will deal satisfactorily is the fresh water flow; in the case of the River Thames,
this is the amount coming over Teddington Weir after the Metropolitan Water Board
has, above that point, abstracted the quantity required for water supply. By statute, no
abstraction is permitted which will have the effect of reducing the flow over the Weir
to below 170 million gallons per day although the appropriate Minister can, by Order,
permit the reduction of the flow to as low as 50 million gallons per day. The summer of
1953 was not abnormal in regard to rainfall and the freshwater flow was above the
statutory minimum, the average daily figure for July to September (inclusive) being
225 million gallons per day. Nevertheless, the condition of the water of the river became
extremely poor and was bad over a considerable stretch of its course for many weeks,
particularly between London Bridge and Gravesend. The additional treatment of the
sewage, which will be available on the completion of the Council's new works, will
reduce the pollution load on the river and should counteract the progressive deterioration
which has occurred in recent years.
The Chemist-in-Chief 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. It should be emphasised
in this connection that there are many other sources of pollution gaining access
to the river as well as the effluents from the Council's works ; for example, other sewage
effluents, trade waste discharges, water from impure tributaries and contamination from
the large shipping traffic.
Mention should be made of research work done at the Southern Outfall Works
laboratory on the determination of iron in the ferrous and ferric states. This balance is of
importance in relation to the conditions which govern the presence of sulphide.
Sewers
Trade
waste
discharges
Samples of trade discharges and of deposits in sewers were examined from the aspect of
the control powers included in the Public Health (London) Act, 1936, and on this basis
many were found to be objectionable. For example, discharges from a chemical works
to a local sewer were found to contain carbon tetrachloride and monochlorbenzene,
both of which give rise to toxic vapours. Entry to the sewer was thereby rendered
hazardous. In the course of the sampling an officer of the Chemical branch and a
sewer inspector were partially overcome by the fumes. The firm was prosecuted and a
conviction registered. Another case in which four sewermen were affected by hydrogen
sulphide was found to be due to the discharge of iron sulphide to the sewer from a
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