HONG KONG URBAN COUNCIL
7
Merits of Modern, High-tech Incinerators
It is true that the old-style incinerators burn at a lower temperature, i.e. 400°C and cause pollution to the environment. The latest development in incinerator technology has, however, completely overcome the pollution problem which had been the main reason for closing down the municipal incinerators in Hong Kong in 1989. Modern incinerators which burn at 850°C are environmentally friendly. At this temperature, complete combustion takes place and all organic wastes are decomposed without the production of poisonous gas. The toxic chemical and metal compound in the wastes are segregated during the incineration process. It is also interesting to note that the amount of carbon dioxide produced by burning wastes is less than that produced by burning conventional fuels. Hence, incineration will not cause any methane gas emission or leaching. The residue after incineration which we call 'Bottom Ash' is chemically inert. Furthermore, modern incinerators can handle medical wastes in addition to domestic wastes. Hence, instead of building the Central Incineration Facility in Tuen Mun to handle medical wastes, animal carcases and Government security papers, it is more cost-effective if the Government can build a full-sized conventional incinerator to take care of all domestic and related wastes, be they from households, hospitals, clinics or Government departments.
Apart from being environmentally friendly, modern hi-tech incinerators will also help reducing the volume of wastes and prolonging the life span of the scarcely available landfill spaces in Hong Kong. As an initial treatment of municipal wastes, incineration reduces the volume of wastes to only one-tenth of their original volume and 25 percent of the incinerated tonnage before ultimate landfill. This will not only ease the pressure on landfills but will also prolong their life span by 10 times for the purpose of intake of municipal wastes.
Demerits of Sanitary Landfill
After the publication of the Waste Disposal Plan in 1989, Hong Kong has relied predominantly on landfills for the disposal of municipal wastes. Apart from the difficulty of locating suitable landfill sites in Hong Kong, disposal of wastes by the landfill method also causes insurmountable environmental problems: landfilled wastes release carbon dioxide over a long period of time and a large amount of methane gas which is highly inflammable and dangerous. These greenhouse gases damage the zone layer in the atmosphere and contribute towards the global warming phenomenon. Another problem caused by landfills is leaching, which is the process of liquid perineating through the soil and the landfilled wastes resulting in toxic compounds being drained away to their surrounding environment. These compounds are harmful to human and animal lives.
To reduce the environmental risks of methane gas emission, a very expensive and elaborate tube collection system will have to be installed to trap the methane gas released. Equipment and methods to control leaching are equally complicated and costly. A layer of protective membrane has to be laid on the landfill sites prior to using them and this bottom lining has a limited life span of about 20 years. Once
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