Siu Ho Wan Sewage Treatment Works (STW) is being designed to provide Chemically Enhanced Primary Treatment (CEPT) to the wastewater mainly generated from the Tung Chung/Tai Ho New Town and surrounding areas in the Lantau Island. The design capacity of the STW is 180,000m3/day. An effluent disinfection system is constructed at Siu Ho Wan to control the potential discharge of pathogens to the North West waters and to minimize the possible adverse impact onto the marine environment including the Chinese White Dolphins.

AECOM conducted a desktop review in May 1999 to assess the feasibility of using UV radiation and ozone to disinfect the CEPT effluent from Siu Ho Wan. This was followed by a disinfection pilot test program at Stonecutters Island to collect more site-specific basis for option comparison. The UV disinfection pilot test took place in September 1999 and consisted of (1) dose response tests, (2) fouling tests, (3) headloss analysis, (4) disinfection by-products and (5) photo-reactivation tests. A pilot test unit using medium pressure, high intensity lamps with similar reactor configurations as proposed for the full-scale facility at Siu Ho Wan was used. In the initial stage of the detailed design, AECOM had conducted further pilot study using high intensity UV disinfection systems.

The intensive testing program helps to determine the optimum UV doses in achieving the necessary effluent quality criteria. AECOM analyses the pilot test data and develops relevant design parameters for the full-scale facility. We also address various design constraints and operation issues such as plant hydraulics, effluent pumping, choice of chemical coagulants, disposal of mercury UV lamps, power supply etc. The scope of the project also includes all other associated civil, geotechnical, electrical, instrumental ion, mechanical, structural works necessary for the completion of the works elements.