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and sewage sludge is being investigated in a pilot plant of 50 gallon capacity and consideration
is being given to extending the scale of operation.
(c) Various means of treating digested sludge liquor have been examined which
include:
(i) Coagulation with surplus activated sludge.
(ii) By diffused air activated sludge treatment.
(iii) By treatment on a conditioned percolating filter.
Method (i) was most successful and the details were worked out.
(d) The rate of aeration of water was investigated using various spacings of 7-in.
dome diffusers to obtain the most economical use of the air at selected air flows. It was
found that there was a certain spacing below which the efficiency of air usage decreased
considerably.
(e) Miscellaneous problems examined included those connected with synthetic
detergents, automatic samplers, deposits of chalk from sludge liquor, etc.
A member of the scientific staff attended a month's course at the Isotope School,
Atomic Energy Research Establishment, Harwell, because it is. considered that by the
application of this new technique valuable information on plant performance and design
can be obtained. Indeed the first stage of this development has been mentioned briefly
in (a) above.
Trade waste discharges
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 London County Council (General Powers) Act, 1953 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 1,890; of these 279 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. Waste heat contained in process and cooling waters was also a
source of nuisance and possible danger; 61 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 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 by the branch for this service covers a wide field and is of considerable
economic importance. Thus, in the particular case of paint and surface coatings for
houses, flats, schools, bridges, etc., the annual expenditure of the Council on materials
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