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44
construction of sixteen new sedimentation tanks with a total
capacity of 20 million gallons at the northern outfall began in
September, 1950. In addition to these schemes the programme
included diffused air activated sludge plants to treat 30 million
gallons of sedimented sewage a day at the northern outfall
and the same at the southern.
Because of the delay and of the continuing deterioration
in the condition of the river water, the Committee have, in
consultation with the Ministry of Health (now Ministry of
Local Government and Planning) reviewed the situation and
propose an expansion of the programme to increase the
capacity of the diffused air activated sludge plants at each
outfall to 60 million gallons a day instead of 30 million, and
in addition to provide for the construction of sludge digesting
plant to treat all the sludge produced at both outfalls.
The completion of these works would enable all the
sewage at both outfalls to receive efficient sedimentation and
two-thirds of the effluents to be further purified by the activated
sludge process. The new sedimentation tanks at the northern
outfall works are due for completion in 1953 and until they are
in operation no great improvement in the condition of the river
water can be expected. As an interim expedient we propose
to install chlorination plant at an estimated cost of £8,000.
The estimated cost of the capital works envisaged in the
revised programme is as follows:— £
(i) Diffused air plant to treat 60 million
gallons of sedimented sewage a day at
northern outfall works 3,250,000
(ii) Sludge digestion plant, to treat all
the sludge produced at northern outfall
works 2,225,000
(iii) Diffused air plant to treat 60 million
gallons of sedimented sewage a day at
southern outfall works 2,800,000
(iv) Sludge digestion plant to treat all
the sludge produced at southern outfall
works 1,515,000
These estimates amount to £9,790,000 for the constructional
work, including mechanical and electrical works, to
which must be added £70,000 for expenditure on designing
works (i) and (iii), including site investigations, making a
total of £9,860,000.
The incidence of the expenditure on these projects is
difficult to forecast but it is likely to be £100,000 in 1951-52,