By treating ever-more wastewater rather than discharging it into its harbor, Hong Kong has been creating a growing mountain of sludge, which is set to overwhelm available disposal sites. With more sewage treatment capacity now under development, the Chinese Special Administrative Region is investing in one of the world’s largest fluidised-bed sludge incinerators.
By drying the sludge and burning 90% of the remaining solids, the plant at Tuen Mun, on the west side of the New Territories, will greatly reduce Hong Kong’s reliance on landfills. And because of its isolated coastal location, overlooking Deep Bay, the project includes a 600-cu-meter-per-day seawater desalination plant that will provide water for the site. Additionally, the plant will include incinerator boiler furnaces that produce steam to drive electricity-generating turbines, making it more than self-sufficient in terms of energy use.
The plant’s capacity will well exceed expected sludge production in 2014, when the next phase of Hong Kong’s ambitious Harbour Area Treatment Scheme (HATS) is scheduled to end. To put that in perspective, the plant’s 2,000-tonne-per-day capacity will be roughly twice that of the U.K. incinerators serving London, explains Fergal Whyte, head of East Asia energy, resource and industry at London-based Arup Group Ltd. With the site levelled, piling for the 350-m by 60-m plant is now moving forward, he adds.
Arup is lead designer on the plant's roughly $700-million, 37-month turnkey construction contract, which started onsite last December. Last October, Hong Kong’s Environmental Protection Dept. awarded the contract to a consortium led by Paris-based Veolia Environnment S.A. The agreement also includes the plant’s operation for 15 years. The design-build element is being handled by Veolia Water SCL and locally based Leighton Asia and its affiliate, John Holland Pty., of Melbourne, Australia.
The Tuen Mun plant is a key element in HATS, which started construction 16 years ago. Its initial phase included the chemically enhanced primary sewage treatment plant at Stonecutters Island. Completed in 1997, the plant, which handles 1.7 million cu m a day, has facilitated “remarkable water-quality improvements” in parts of the harbor relieved of raw sewage discharges, according to a government report. But, given that it treats 75% of the harbor area’s wastewater, the Stonecutter's plant is the primary source of some 800 tonnes of sludge a day going to landfill.
In addition to the Tuen Mun plant, the next stage of HATS includes more than 20 kilometers of deep rock tunnels, measuring 0.9 to 3.0 m in diameter, that will collect wastewater from preliminary treatment facilities and transfer it to the Stonecutters plant, which is being enlarged. The project, now under construction, will deal with the remaining 25% of the harbor area’s wastewater, from northern and southwest Hong Kong Island, and will raise daily sludge output to 1,500 tonnes.
