Odour Management

Septic process of sewage will produce hydrogen sulphide which has a repulsive odour. To reduce the impact of DSD's facilities on nearby residents, we have undertaken the following three odour control measures:

Adding deodourising agents into sewage to suppress odour at its source;
Covering facilities and components which are likely to emit odour; and
Installing deodorising systems.

In addition, we regularly measure the levels of hydrogen sulphide in our plants to monitor the effectiveness of the odour control measures and to timely adjust the plant operations as necessary.

Odour Control Measures at Siu Ho Wan Sewage Treatment Works

Dosing ferric chloride as a replacement of alum in the sewage treatment process for suppressing unpleasant smell and increasing the efficiency of sludge sedimentation
Installation of chemical scrubbers and activated carbon filter system for more effective control of exhaust from the sludge treatment system
Covering channels of the UV disinfection system
Carrying out weekly odour patrols by in-house staff and regular odour surveys by an accredited laboratory under the Hong Kong Laboratory Accreditation Scheme
Installation of a weather station to collect 24-hour data of hydrogen sulphide levels and wind speed within the plants for monitoring the odour situation
Installation of airtight fibreglass reinforced plastic covers and biotrickling filters for primary sedimentation tanks

Fiberglass reinforced plastic covers for primary sedimentation tanks

Biotrickling filters

Odour Control Measures at Stonecutters Island Sewage Treatment Works (SCISTW) under Harbour Area Treatment Scheme (HATS) Stage 2A

Installation of fibreglass reinforced plastic covers with a gas-seal design on the existing sedimentation tanks, flow channels and chambers
Installation of an exhaust system to collect foul gas within the covered tanks, channels and chambers
Treatment of foul gas by biotrickling filter technology before discharge into open air. Biotrickling filter technology is a reliable and environmentally friendly odour removal technology with a low operation cost and minimum maintenance requirements which can remove 99% or more of hydrogen sulphide gas, the main source of odour in STW, for effective odour control
Use of chemical scrubbers as the prime deodourisation technology for the sludge dewatering facility, as they can handle foul air of varying odour strengths within a compact footprint