Drainage Services Department

Ngong Ping Sewage Treatment Works

Ngong Ping Sewage Treatment Works (NPSTW) was commissioned in 2006 to cope with the sewage collection, treatment and discharge needs in Ngong Ping and its surrounding area arising from the increased number of tourists after the commissioning of the Ngong Ping Cable Car and associated tourism developments. NPSTW was the first tertiary sewage treatment plant with reclaimed water facilities in Hong Kong.

Located within the Shek Pik Reservoir catchment area and surrounded by country parks, Ngong Ping is an environmentally vulnerable area. NPSTW employs tertiary sewage treatment technology to protect the water quality of the water gathering ground and nearby receiving water bodies. The design treatment capacity of NPSTW is 1,100 cubic metres per day which can serve a population of 40,000 including residents of Ngong Ping and tourists. The plant is now treating about 450 cubic metres per day of sewage.

Ngong Ping Sewage Treatment Works (360° View)

Ngong Ping Sewage Treatment Works (360° View)

Ngong Ping Sewage Treatment Works

Ngong Ping Sewage Treatment Works

Ngong Ping Sewage Treatment Works

Ngong Ping Sewage Treatment Works

Ngong Ping Sewage Treatment Works Information Centre

To promote public awareness of tertiary treatment, the total water management in Hong Kong and the use of reclaimed water, an information centre was built in Ngong Ping Sewage Treatment Works for the visitors including students from school and universities, professionals from local and overseas institutions and the general public.

Ngong Ping Sewage Treatment Works Information Centre (360° View)

Ngong Ping Sewage Treatment Works Information Centre

Ngong Ping Sewage Treatment Works Information Centre

Coarse Screens

Fine screens and vortex grit traps are used to remove large objects and grit in the sewage to protect the downstream treatment facilities. Since the majority of the sewage collected is generated from the restaurants in Ngong Ping Market, grease separators are used in Ngong Ping Sewage Treatment Works to remove grease in the sewage.

Coarse Screens

Fine Screens

Grease Separators

Grease Separators

Inlet Works

Inlet Works (360° View)

Inlet Works (360° View)

Inlet Works (360° View)

Sequencing Batch Reactor

Secondary treatment is primarily used to remove organic matters and part of the nutrients which are degraded by micro-organisms. Ngong Ping Sewage Treatment Works (NPSTW) adopts Sequencing Batch Reactor (SBR) technology. The SBR is a fill-and-draw activated sludge treatment system. The operation of the SBR consists of four distinct periods: fill, aeration/mixing, settling and decanting, each tank in the SBR system is filled during a discrete period of time. During aeration/mixing period, mixing and aeration are carried out in the tank to maintain a certain level of dissolved oxygen for the growth of micro-organisms. Following the aeration/mixing period, the sewage together with the micro-organisms are allowed to be separated by sedimentation. The treated effluent is subsequently drawn from the reactor by decanting.

Sequencing Batch Reactor

Sequencing Batch Reactor

Sequencing Batch Reactor

Dual Media Filter

After secondary treatment, most of the nutrients in sewage have been removed, the sewage will then undergo tertiary treatment. Tertiary treatment mainly adopts the dual media filter comprising an upper layer of carbon grinds (anthracites) and a lower layer of silicon sands to filter the very fine suspended solids in the sewage. Thus the effluent will be further polished.

Dual Media Filter (360° View)

Dual Media Filter

Dual Media Filter Comprising an Upper Layer of Carbon Grinds (anthracites) and a Lower Layer of Silicon Sands

Dual Media Filter

Ultraviolet Disinfection System

After tertiary treatment, the effluent is disinfected by ultraviolet light before being discharged into Tung Wan of South Lantau Island via effluent export pipeline.

Ultraviolet Disinfection System

Ultraviolet Disinfection System

Ngong Ping Sewage Treatment Works Water Reclamation Facilities

To be in line with the Government's initiative of using reclaimed water under the Total Water Management Strategy, Drainage Services Department has introduced a pilot scheme of reclaimed water usage in the Ngong Ping Sewage Treatment Works (NPSTW).

NPSTW adopts a sequencing batch reactor, dual media filter and disinfection process to reduce organic pollutants, suspended solids, nutrients and pathogenic organisms in the sewage to a very low level.

The UV disinfected tertiary-treated effluent in Ngong Ping STW receives further chlorination to provide a safe supply of reclaimed water which is currently used for toilet flushing in nearby public toilets and the Ngong Ping Cable Car Terminal, and also for rearing aquarium fishes and controlled irrigation within the sewage treatment works. The current consumption of reclaimed water is about 150 cubic metres per day.

Ngong Ping Sewage Treatment Works Water Reclamation Facilities

Ngong Ping Sewage Treatment Works Water Reclamation Facilities

Ngong Ping Sewage Treatment Works Fish Pond (360° View)

Ngong Ping Sewage Treatment Works Fish Pond

Ngong Ping Sewage Treatment Works Fish Pond

Ngong Ping Sewage Treatment Works Fish Pond

Reclaimed Water is Used for Drip Irrigation at Ngong Ping Sewage Treatment Works

Reclaimed Water is Used for Toilet Flushing in nearby Public Toilets