The Shatin Sewage Treatment Works Stage III Extension comprised the rehabilitation and extension of the existing treatment plant and is now providing a high quality effluent discharge in Victoria Bay in accordance with the strict effluent standards set by the Hong Kong Government. The works include design, supply, delivery, installation, testing and commissioning of the M & E installations in various sections of the Works, involving; grit removal system, chemical dosing system, sludge collection and removal system for the primary and final sedimentation tanks, air diffuser aeration system, surplus activated sludge thickening system, anaerobic sludge digestion system and sludge dewatering system. Biogas generated from the anaerobic sludge digestion is used to provide hot water for the existing anaerobic sludge digestion tanks that in turn generate electricity to power the plant. The works include:

• Design;
• Supply;
• Delivery;
• Installation;
• Testing; and
• Commissioning of the mechanical and
• electrical installations in various sections of the Works.

Installation includes:

• A grit removal system;
• A chemical dosing system;
• Sludge collection and removal system for the primary and final sedimentation tanks;
• An air diffuser aeration system;
• A surplus activated sludge thickening system;
• An anaerobic sludge digestion system; and
• A sludge dewatering system.

Other works include:

• Electrical switchboards;
• A process monitoring system; and
• A SCADA/PLC control system.

Process;

• Dry weather flow (summer 2004) 250 Mld/day
• Dry weather flow (winter 2004) 230 Mld/day
• Dry weather flow (summer 2011) 340 Mld/day
• Dry weather flow (winter 2011) 308 Mld/day
• Peak flow 1020 Mld/day (three x dry weather flow/summer 2011)
• BOD5 = 57,000 kg/day
• Population Equivalent (0.06kg/day) = 950,000
• Characteristics of Crude Sewage
• The average characteristics of the crude sewage (Year 2011)
• discharged into Shatin sewage treatment works will be as follows:-
• Pollution loadings :-
• BOD5 [Year 2011]: 57,000 kg/day
• TSS [Year 2011]: 67,000 kg/day
• TKN [Year 2011]: 15,700 kg/day
• Range of chloride contents in crude sewage/pretreated wastewater
• chloride ions : 2000 to 7,000mg/L
• Range of crude sewage
• Wastewater temperature : 15 to 32ºC
• Design Removal Goals
• SS (% of removal) after primary sedimentation process : 50%
• BOD5 (% of removal) after primary sedimentation process : 40%

Final Effluent Standard;

• Parameters: Effluent Standards
• BOD5: 20 mg/L (at 95 percentile)
• 40 mg/L (maximum)
• TSS: 30 mg/L (at 95 percentile)
• 60 mg/L (maximum)
• Total Nitrogen: 20 mg/L (annual average)
• 35 mg/L (maximum)
• NH3-N: 5 mg/L (annual average)
• 10 mg/L (maximum)