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A considerable amount of research work and several special investigations were
undertaken during the year, some items being:—
The methane gas production of a temporary converted reservoir used for sludge
digestion at the Northern Outfall had fallen below the expected amount and radioactive
phosphorus (P.32) in the form of ammonium dihydrogen phosphate was
used to trace the flow of sludge through the plant. It was found that the capacity
of the plant had been reduced by spent sludge residues remaining on the floor of
the tank but no channelling was occurring. The sludge leaving the plant was found
to contain more sulphide than that entering the plant and examination of the dense
bottom layer showed a concentration of calcium sulphate and sulphides. It was
concluded that this sulphide production inhibited the growth of methane producing
organisms. The numbers of sulphate reducing organisms in various types of sludge
have been determined but the interpretation of the figures obtained has proved to
be very complex.
The incoming sewage was found to contain 8-10 parts per million of synthetic
detergent and the effluent from the activated sludge plant about 7 p.p.m. A few
tests made on the use of silicones to reduce foam formation in the effluent channel
indicated that their use would be uneconomic on any scale which would give
satisfactory results.
During the year, assistance has been given on questions relating to the use of the
sludge freezing process and to sewage treatment problems at the Atomic Energy
Research Establishment at Harwell and officers from Harwell have advised the Scientific
Branch on matters connected with tracer techniques.
An exhibition was held at County Hall to mark the centenary of London's main
drainage system and many aspects of scientific work relating to sewage treatment were
on view to the public. A working model of an activated sludge plant capable of purifying
120 gallons of domestic sewage a day was constructed and displayed by officers of the
Branch. Not only did this plant demonstrate the principles involved, but it has since
proved most valuable in the laboratory as a means of assessing the amount of treatment
required by certain gas liquors and trade wastes.
Trade waste discharges
This report covers the first full year's working under the provisions of the London
County Council (General Powers) Act, 1953. Industrial discharges have increased in
volume and complexity over the past few years in view of the many new processes
using a wider range of chemicals than formerly, and the new Act enables the Council
to exercise a close control over the discharge of trade wastes into the London sewerage
system.
The samples taken during the year, including those submitted for examination by
four Borough Councils, numbered 950 ; of these 193 were considered to contravene
the Act. Objectionable matter contained in quantity in various wastes included strong
acids and caustic alkalis ; petroleum spirit, oils, tar ; 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. Waste
heat contained in process and cooling waters was also a source of nuisance and possible
danger ; 40 cases of discharges above the temperature limit of 110°F. laid down in the
Act were investigated. It would indeed make for efficiency and economy if manufacturers
considered more carefully the means of recovering such waste heat.
The usual procedure, following the examination of samples which contravene the
Act, is for officers of the Scientific Branch and of the Chief Engineer's Department to
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 may have to be prescribed.
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