THE ENVIRONMENT
The first stage, which collects sewage from the urban areas of Kowloon, Tsuen Wan, Kwai Tsing, Tseung Kwan O and the north-eastern part of Hong Kong Island for treatment at a sewage treatment plant at Stonecutters Island on the west coast of the Kowloon Peninsula, was brought fully into operation at the end of 2001. In addition to the treatment plant, which some experts considered as one of the most efficient of its kind in the world, the first stage comprises a number of preliminary treatment works at collection nodes, 23.6 kilometres of transfer tunnels up to 150 metres deep, and a tunnelled outfall which disperses the treated effluent into the western anchorage area away from core Victoria Harbour.
Since commissioning, the system has performed very well. The Stonecutters Island Sewage Treatment Works, which employs a chemical treatment process, has been consistently removing about 70 per cent of the organic pollutants and 80 per cent of the solids from the sewage prior to discharge. Since the first stage actually treats about 70 per cent of the wastewater generated in the harbour catchment, it has thus reduced the total pollution load on the harbour waters by about 50 per cent. The sludge that once flowed into the harbour each day, amounting to about 600 tonnes, is now effectively being removed at the treatment works and sent to Hong Kong's modern landfills for disposal. This has brought about marked improvements in water quality in the harbour. At the eastern end of Victoria Harbour, the levels of sewage bacteria have declined by about 90 per cent, significantly reducing public health risks. Throughout the core harbour area dissolved oxygen has increased by 15 to 20 per cent and ammonia has declined by 30 to 50 per cent, helping to restore water quality to a more natural and ecologically healthier condition.
The original proposal for the subsequent stages of the scheme envisaged collection. of the remainder of the untreated sewage around the harbour (from northern and western parts of Hong Kong Island) using a similar system of deep tunnels, centralised treatment at the works at Stonecutters Island, and eventual discharge of the treated effluent, after disinfection, through a long tunnelled outfall into the deep, oceanic waters to the south of Hong Kong.
This concept was reviewed in 2000 by a panel of international experts. In their report to the Government, the experts confirmed the use of deep tunnels and centralised treatment as an acceptable and cost-effective way of dealing with sewage. However, in the light of recent developments in sewage treatment technology they recommended that rather than pursuing the long outfall, the Government should consider upgrading the treatment level to a very high standard, and discharging the treated effluent into the harbour on a long-term basis.
The proposal to adopt a different procedure for the treatment of sewage has raised a number of issues that require further study. The most important of these are whether compact sewage treatment technology developed and applied in temperate climates can treat wastewater effectively under Hong Kong conditions, and whether it is an environmentally sustainable proposition for the relatively congested Victoria Harbour to receive large volumes of effluent, although highly treated, on a long-term basis. At the end of 2001, the Government initiated a series of trials and studies to address these issues. The work is progressing well and the results will be reported around the end of 2003, at which time the community will have an opportunity to debate the findings and express views on the general preference for a way forward. More details are available at the Government's home page.
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