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plant has been very satisfactory and has substantially reduced the load on the river by
reducing the amount of suspended matter leaving this section of the plant by one-half
and the oxygen demand by one-third.
The present plant for secondary treatment has a capacity of 40 million gallons daily.
The final effluent from this either reached or approached Royal Commission standard
for a considerable part of the time. New diffused air plant to extend the capacity for
secondary treatment was nearing completion at the end of the year.
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 Chemical Research Laboratory of the Department
of Scientific and Industrial Research in the experimental biological production of
sulphur continued. Work on radioactive tracers was extended and the investigation
of a method suggested for the removal of synthetic detergent was begun. Tests on
automatic samplers and efficiencies of aeration using different types of diffuser 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 which have
increased in volume and complexity over recent years.
Samples included 2,810 submitted for examination by eleven metropolitan boroughs,
of which 561 were considered to contravene the Act. Objectionable matter contained
in quantity in various wastes included strong acids and caustic alkalis ; petroleum
spirit, oils, tar ; cyanide from plating shops ; tannery wastes containing excessive
amounts of sulphide ; and solid matters such as fats, vegetable fibres and stone grindings.
In some cases the wastes rendered the atmosphere of the sewer unbreathable. 52 cases
of discharges of process and cooling waters above the temperature limit of 110°F. laid
down in the Act were investigated.
Following the examination of samples which contravene the Act, officers of the
Scientific Branch and of the Chief Engineer's Department usually visit the premises to
discuss with the occupiers the problems involved in treating the discharges. A similar
procedure is followed when consideration is given to applications for permission to
make new discharges where standards have to be prescribed.
Safety in sewers
Regular examination of inflammable gas detector lamps of the expanding metal spiral
type and those based on selective diffusion is made to ensure that all lamps are in good
order and advice is given as required on the use of self-contained oxygen respirators.
Experiments have continued on methods of improving sewer ventilation.
Housing
The work done for this service covers a wide field of considerable economic importance.
The annual expenditure of the Council on paint and surface coating for houses, flats,
schools, bridges etc. and the labour charge for their application amounts to approximately
£4 million. The savings effected by ensuring that materials of suitable quality
are used greatly exceeds the cost of the advisory service. An inter-departmental paint
committee representing all the departments concerned keeps the position under review.
Approved lists of manufacturers' brands of paint are maintained and during the
year 22 new brands were approved after test, while a further 38 were found not to be of
the quality required. Some of the more frequent causes of rejection were low opacity,
poor surface finish or hardness, low flexibility and presence in exterior paints of lithopone
or excessive amounts of chalk.
Demands for the examination of building materials are increasing. The range of
materials received for assessment of quality or investigation of possible faults included
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