Following the signing of the Clean Air Charter by the Chief Executive of Hong Kong SAR Government in November 2006, DSD formed an Energy and Emission Management Team (EEMT) in early 2007. The team is headed by a Chief Engineer with members from each branch at the senior professional level to drive the initiatives on energy saving and emission reduction at all front of our operations. The team met three times in 2008 to promote and monitor effectiveness of measures on energy saving and reduction in gas emission.

Energy Saving

In 2008 DSD saved an extra 1.15 million kWh of energy in addition to the saving of 0.91 million kWh in 2007, and 2.5 million kWh in 2006. These savings were achieved by implementing a number of energy saving measures, such as the replacement of "fat tube" fluorescent lamp with T5 lamp, the use of variable speed drive and high efficient motor for pumping, the adjustment of lighting in plants, and the additional use of solar energy and biogas. There were five installations of grid-connected electricity generation using PV panels at sewage treatment facilities completed in 2008. The estimated annual output is 101,000kWh, which is equivalent to the reduction in the emission of 71 tonnes of carbon dioxide.

Click Here for Highlight of 2008 Energy Saving Measures

Gas Emission

Other measures for reducing gas emission include the use of biogas for recovery of heat and power, the use of hybrid or environmentally friendly vehicles, the use of ultra low sulphur diesel, and the turning off of idle engines. In 2008, 6.3 million cubic meters of biogas were converted to 12 million kWh of heat and 9.4 million kWh of electricity.

Odour Management

Odour is another emission from sewage collection and treatment that needs to be addressed. Sewage by its nature is offensive. However, there are several factors that amplify this odour problem in Hong Kong. First, new residential area is moving closer and closer to the sewage treatment facilities when the new town is growing in size to accommodate more people. Second, a larger town area means that sewage would stay longer in the collection system before it reaches the sewage treatment plant. The long detention time together with the high temperature in the summer months make it an ideal situation for anaerobic bacteria to grow and produce rotten smell in the sewage collection system and the sewage treatment works.

DSD tackled the odour problem by increasing the frequency of pumping, and addition of chemicals in pumping station to prevent the production of hydrogen sulphide by the anaerobic bacteria. In our sewage treatment works, we covered the surface from which odour was generated and purified the air by wet chemical scrubber, activated carbon or bio-trickling filter deodorization system. As a result of these measures, the number of complaints on odour from our facilities reduced by more than 50% in 2008.

Bio-trickling filter deodorization system