85
-4-
13. Pumping of nightsoil. in attempt was made at Castle Poak in
1947 to empty nightsoil barges with a 4" centrifugal pump (described as of sewage type) and deliver it through a long pipeline to the maturing tanks, but satisfactory operation could not be achieved, The suppliers of the equipment decided that the pump was unsuitable for the duty required and the installation was accordingly dismantled.
14. Composting work at Tsun Wan. Since December, 1949, composting
of refuse in batches of about 30 to 40 tons, with nightsoil, has been carried on at Tsun Wan reclamation site, where compartments 12 ft. wide by 30 ft. long by 4 ft. high and a tank for temporary storage of nightsoil have been constructed, The refuse is carried by coolies from a barge and rough sorting removes a proportion of the inorganic content of the refuse.
The compost is made with about 3 parts by weight of garbage to 1 part of nightsoil and a sprinkling of lime is given to each layer of compost. The compost is turned and transferred to a new heap after three weeks and again after another three weeks. Four weeks later, i.e. after a total of ten weeks, the compost is made available to farmers without charge. Watering of the heaps in the first two stages is necessary once or twice a day in dry weather, to maintain proper moisture in the compost. Drainage and aeration are facilitated by a base of strong wire mesh and bamboos over a concrete floor with channels; there are also air vents in the side walls. Temperatures during fermentation reach 160°F. Inoculation of new material with old compost has proved notably beneficial.
All operations are executed by manual labour and the cost of production is about $30 per ton. 2,000 tons of raw wastes prod- uced about 1,200 tons of compost.
The agricultural value of the compost is well appreciated by the farmera but obicntion is expressed against the war 950620 of the compost and the presence in it of broken glass and crockery.
15. Pre-War composting installation. A form of composting process
using a bacterial inoculant preparation and a special type of plant, known as the Earp-Thomas digester, was in operation as a commercial venture in Hong Kong before the war from 1936 until the Japanese invasion. Difficulties with ancillary plant, in particular with pulverisers, were experienced and prevented the installation from achieving continuous, full-capacity operation. It is recorded, however, on file S.D. 405/48, that the performance of the digester itself was satisfactory; a temperature of 170°F was reached in it; all fly larvac and eventually all pathogenic organisms were destroyed. The material leaving the digester is described as a dark brown moist material. This was dried, sifted and, after addition of some chemicals to make a balanced fertiliser, the prod- uct found favour with local European gardeners, although complaints were made about some of the material supplied.
Proposals made by Dr. Earp-Thomas, through Dr. Y. Lin, for a plant to treat 500 tons of garbage and 170 tons of night soil por day, are enclosed at 23 on file A.G. 7/6/49. It is stated that the installation would require five digester units @ US$35,000 each and three curing chambers @ US$10,000 each and that the cost of production of the compost fertiliser would be about US$1.15 per ton.
16. Sites for a new installation.
It is recorded on the files that
several possible sites for a composting installation, namely at:
Kun Tong.
Gin Drinker's Bay West
Tsing I Island
Tsun Wan A. P.C. Reclamation