In 2008, we operated 67 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 2008 our sewage treatment plants removed about 114,000 tonnes of BOD, 144,000 tonnes of suspended solids, and 4,900 tonnes of nitrogen.

The pollutants removed from sewage produced 810 tonnes of dewatered 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 the landfills. Other than sludge, screenings and grit were also removed from sewage treatment. In 2008 we disposed of about 16,000 cubic meters of screenings, and 6,800 cubic meters of grits.

To improve on the bacteriological water quality of the receiving water, especially the Victoria Harbour, DSD commenced the construction of a large disinfection facility for treating 1.7 M cubic meters per day of effluent at Stonecutters Island Sewage Treatment Works in April 2008. It is anticipated that the facility would be completed by the end of 2009 and contribute to the improvement of the water quality in the Tsuen Wan area.