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182
The sludge vessels made 1,842 trips and travelled altogether 202,628 nautical
miles.
Sewage
treatment.
For some years past experiments have been undertaken in connection with
the biological treatment of sewage on the activated sludge basis. During the year
tanks have been used for agitating the sewage by two different processes, namely
(i.) the diffusion of air through the sewage by means of porous tiles fitted in the
bottom of the tank; and (ii.) the agitation of the sewage by paddle wheels which
constantly expose fresh layers of the sewage to the air. The experiments have established
the fact that London sewage responds to this treatment. Later experiments
have been directed towards the treatment of the effluent discharged into the river
from the settling or sedimentation channels and it has been found that effluent can
be more expeditiously dealt with than crude sewage. The tanks have been altered
from time to time and the quantities of liquid which can be dealt with have been
largely increased.
The restricted flow of fresh water from the upper reaches of the Thames during
the summer decreased the means of dilution of the effluent discharged at the outfalls,
and consequently it was considered advisable to treat the sewage with chemical
re-agents until the flow of the river became more normal. This treatment lasted
for a period of 4½, weeks and expenditure of £1,729 was incurred in this respect.
Deposit of
sludge at sea.
The solids, known as sludge, which are obtained from the sewage after sedimentation
at the outfalls are conveyed to, and deposited in, the Black Deep in the
Thames estuary. The Deep is also used by other authorities for the deposit of
waste materials, and during the year an enquiry was held by the Board of Trade
into allegations that deposits in the Deep tended to cause the shoaling of the Edinburgh
Channel, one of the principal means of access to the Port of London for large
ships, and into the suggestion that the position of the area for such deposits should
be altered. The Council was represented at the enquiry, and on its behalf it was
pointed out that the average cargo of the sludge vessels contained no less than
92 per cent. of water. The amount of inorganic material deposited by the Council
does not exceed 1,000 tons a week. Spread over so large an area as the Deep this
quantity of solid matter is negligible. Evidence was adduced by other depositors
and the Board, after considering the various factors, decided that there was not
sufficient evidence to prove that the silting up of the Edinburgh Channel was due
to the deposit of materials in the Black Deep and that it saw no valid reason for
discontinuing at present the use of the Deep for the purpose.
The cost of buoying the Black Deep deposit area is apportioned among the
various authorities using it for that purpose. The Council's proportion for the year
1925 amounted to £182 14s. 10d.
Sludge
vessels.
The policy of constructing new ships to take the place of the old fleet of sludge
vessels has been continued during the year. The s.s. G. W. Humphreys, constructed
by Vickers, Limited, of Barrow, was put into commission on 23rd January, 1925.
As in the case of the other new vessels, the G. W. Humphreys has a cargo capacity of
1,500 tons. The cost was approximately £46,000. The Council has decided to
obtain a further vessel of similar capacity, to be named John Perring. and has
accepted the tender amounting to £55,300 of William Beardmore and Company,
Limited, of Dalmuir, for the construction of the vessel. When the new vessel is
delivered the fleet will consist of the Bazalgette, commissioned in 1887 and
reconditioned in 1921, of 1,000 tons capacity, the Henry Ward (commissioned in
1923), the J. H. Hunter (commissioned in 1924), the G. W. Humphreys and the
John Perring, giving a total carrying capacity of 7.000 tons as compared with
6,000 tons of the six old vessels. The tender of Mr. T. C. Pas, of Scheveningen,
Holland, amounting to £8,010 (including provision money), for the purchase of the
three old vessels, the Barking, the Binnie, and the Burns, was accepted.
The overhaul and quadrennial survey of the s.s. Bazalgette was undertaken during