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 in early 2007 to implement the commitments of the Charter.

Energy Saving

In 2007 DSD saved an extra 0.91 million kWh of energy in addition to the early saving of 2.5 million kWh in 2006, and 1.76 million kWh in 2005. 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 of sludge, the adjustment of lighting in plants, and the additional use of solar energy and biogas.

Click Here for Highlight of 2007 Energy Saving Measures

Furthermore, process modification plays an important role in energy saving. We investigated the operation mode of an inflatable dam in the Yuen Long Bypass Floodway to balance the energy demand for pumping, the level of flood control, pollution prevention, and downstream irrigation requirement. We came up with a "5-day economic" pumping mode of operation by the end of 2007, which would save 120,000 kWh of energy per year.

On gas emission side, we understand biogas generated from the anaerobic digestion of sewage sludge is an alternative source of energy. The utilization of one cubic metre of biogas to generate heat and power, on average, would save 3.3 kWh of energy and that is equivalent to reduce the emission of 2.3 kg CO2 from the power utilities. In 2007 we made use of six million cubic metres biogas for heat and power recovery, and this measure alone reduced the emission of 14,000 tonnes of CO2. Having the experience on a successful operation of the combined heat and power generator using the local biogas, we would install additional equipment in the next few years to maximize the use of such alternative energy from our sewage treatment works.

Odour Reduction

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 plant.

DSD tackles the odour problem by adding chemicals in pumping station to prevent the production of hydrogen sulfide by the anaerobic bacteria. In our sewage treatment works, we cover the surface from which odour is generated and purify the air by wet chemical scrubber, activated carbon or bio-trickling filter deodorization system. Unfortunately, these systems are energy demanding. There was about 1% increase in total electricity consumption in 2007, which reflected that additional energy was needed in meeting the escalating demand in drainage services, such as odour control in sewage treatment and pumping in flood control.

On emission from vehicles, we adopted the use of hybrid vehicles in our works contract and we also required all vehicles to turn off the idle engines in our plants and construction sites.

Energy Consumption (Data)