In 2007, we operated 69 sewage treatment works with different levels of treatment throughout Hong Kong (details are shown at our website, www.dsd.gov.hk). The treatment level depends primarily on where the effluent is discharged into, as different water bodies in Hong Kong have different waste assimilation capacities and beneficial uses. The major pollutants removed from the sewage in our sewage treatment works are organic materials, often measured as biochemical oxygen demand (BOD), and suspended solids (SS). In certain areas, nutrients such as nitrogen that promote the growth of aquatic plant are removed to prevent algal bloom. In 2007 we removed about 98,000 tonnes of BOD, 133,000 tonnes of suspended solids, and 4,700 tonnes of nitrogen.

The pollutants removed from sewage produced 814 tonnes of sludge per day, or about 300,000 tonnes for the whole year. The sludge was dewatered to reduce its volume before it was sent to landfills for disposal. This saves landfill space and helps extend the life-span of our landfills. Other than sludge, screenings and grit were also removed from sewage treatment. In 2007 we disposed of about 297,000 tonnes of dewatered sludge, 21,000 cubic meters of screenings, and 6,600 cubic meters of grits.

To further improve the water quality of the Victoria Harbour, DSD awarded a $68.3 M consultancy contract in August 2007 to carry out the investigation, design and construction stage services for construction of a 21-kilometer long sewage tunnel systems, upgrading of the Stonecutters Island Sewage Treatment Works (SCISTW) with disinfection facilities and eight preliminary treatment works under the Harbour Area Treatment Scheme (HATS) Stage 2A. It was planned to advance the construction of part of the disinfection facility at SCISTW for completion by the end of 2009 to facilitate the early re-opening of the beaches in the Tsuen Wan area. Currently, there are 35 sewage treatment plants with disinfection facilities treating 126,000 m3 of sewage per day. We added a large scale UV disinfection facility at Siu Ho Wan Sewage Treatment Works in 2007, and plans are in hand to install two UV systems at Ta Po and Shatin Sewage Treatment Works in the near future.