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APPENDIX B.
2
Sewage Disposal for the Island.
Time does not permit of the full investigation and study of a scheme for the disposal of the sewage from the urban population of Victoria. The tentative cost worked out for the Kowloon Peninsula must be modified owing to the difference in natural slopes, and the fact that the Island urban district is sharply divided into two distinct parts by the Naval Dockyard area. The figure for Kowloon was assumed as HK $23 per capita, capital cost of new installations. Since a large part of the existing sewers on the Island could probably be used for a new scheme, I suggest that it would be reasonable to assume that a cost for this area of H.K. $20 per capita can be taken for preliminary discussion. The cheapest routing for sewers is obviously with the prevailing gradient, and in order to avoid any unnecessary pumping, it is suggested that the treatment works should be at as low a level as possible. A natural site would be at the Western extremity of the urban area, at Kennedy Town. This could take the sewage from the area West of the Naval Dockyard. For the Eastern area, a site should be selected from the following :- the Wong Nei Chong, or Tai Hang valleys, or Sai Wan Bay. Provided the treatment works were suitably designed, there should not be any fly or smell nuisance from the plant. An alternative site would be the valley East of Aberdeen, but this would imply either pumping over the hills, or the construction of a sewer tunnel about two miles long, (the Beacon Hill Railway Tunnel is 13 miles long.). Which of these alternatives to select is merely a matter of relative cost the advantage of sites to the North of the Island would be the lower cost of transporting the sludge fertilizer to the New Territories from that side.
The chief concern of these notes is to emphasise that some form of treatment works is essential, and that with proper design and study, a complete scheme of disposal is feasible which will, by sale of the bye-products, by potential recovery of a large proportion of the water, and by protection from water-borne infections, make the cost of the installations low enough to merit in conjunction with the benefits to the community, very serious consideration.
General Notes on Sewage Disposal for Hong Kong.
The chemical and biological treatment of sewage is a specialised study on which I am not expert and the following notes are therefore submitted with reserve, since they have been taken from various technical articles, largely from American journals.
Reclaiming Water from Sewage.
Owing to the shortage of water in Hong Kong, an article in "Civil Engineering" for November 1946, (Vol. 16, No.11), on a proposal to reclaim sewage to replace ground water in the Los Angelos area is of special interest. Briefly, the plan proposes to treat the raw sewage by the activated sludge process and to force the effluent, after treatment and sterilisation, underground through wells, so that it would feed wells used by the population for domestic consumption. By separating the feeder wells from the suction wells by at least 1,000 ft., the water, even without
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