Energy Efficiency
DSD recognises that fossil fuels are finite resources and is therefore strongly committed to the conservation of energy in seeking to reduce Hong Kong's ecological footprint. We place considerable emphasis in energy efficiency in sewage pumping and treatment which constitute the bulk of the department's energy expenditure.

We continuously look for better ways and better equipments to operate our plants. Energy Audit is regularly carried out on a plant by plant basis to identify Energy Management Opportunities. Improvements involve introduction of energy saving equipment, implementation of efficient operations, and phasing out of obsolete and inefficient sewage pumping or treatment equipments.

The work is concentrated in 4 key areas :
Effluent Disinfection
Variable Speed Drive in effluent pumping
Energy Efficient Motors
Deodorization Systems

Adopting alternative UV Irradiation Technology for Effluent Disinfection
LPHI system has technical advantages over MPHI system.
Medium Pressure High Intensity system (MPHI) Low Pressure High Intensity system (LPHI)
  more efficient disinfection
lower power consumption
longer lamp life

DSD tested and evaluated life cycle cost of MPHI & LPHI systems for local operations.
implement LPHI at new works.
Successful case : Ma Wan Sewage Treatment Works achieved 60% lower power consumption


Variable Speed Drive (VSD) in Sewage Pumping and sludge dewatering
Using energy efficient VSD

Advantages :
Lower Kilovolt-Ampere (electrical power) demand due to soft start of the motor
Smooth control of pump set during operation.
Successful applications :
sludge dewatering centrifuge in Siu Ho Wan Sewage Treatment Works Upgrading
Sewage pumping, eight 11KV 2.5 MW induction motors in HATS Stage I
Estimated power saving : up to 17%



Energy Efficient Motors
Apply contract specification to motors :
Motors of rated output 1.1KW to 90KW to meet EU and European Committee of Manufacturers and Electrical Machines and Power Electronics EFF Band 1 energy efficiency requirements (efficiency values >83.8% to >95%)
Motors of rated output > 90KW motors to have minimum full load efficiency of 95%
Site implemented : Siu Ho Wan Sewage Treatment Works Upgrading.
Estimated saving over conventional motors : 6%

Deodorisation Systems
a) Deploying 2 speed fans
high speed V for odour-generating operation e.g. sludge unloading, maintenance of sludge treatment/ disposal equipment
low speed V for normal operation

b)Design for odour containment
limit the volume of odorous gases, hence reducing size of De-odorisation unit and power demand

c)Automatic control of Dehumidifiers
Saving energy by automation. Apply heating only for moist foul air.

As a result of the conservation drive, DSD accomplished a remarkable increase in energy efficiency in sewage treatment : 2.77% saving in KWh/m3 over the previous year.

DSD Electricity Consumption in sewage treatment and sewage pumping
2002
2003
Change
Sewage treated (m3)
911 million
943 million
+3.5%
Power consumed KWh
229,646,835
231,002,217
+0.6%
KWh/m3
0.252
0.245
-2.77%

Other Energy Efficiency Best Practices
Sewage pump start/stop levels in Stonecutters Island Main Pumping Station was reviewed and optimized to minimize running hours and the no. of units in operation
Sewage pump start/stop levels in Pillar Point Outfall Pumping Station was reviewed and optimized to minimize running hours and the no. of units in operation
Biogas generated in treatment process in Shek Wu Hui Sewage Treatment Works is utilised for water heating instead of relying on electric water heater.