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SCMP Reporter

Potential greenhouse pollutant helps power treatment plants
Up to HK$15 million would  be saved annually under a plan by the Drainage Services Department to use sewage-generated biogas for power generation, officials said yesterday.
Under the plan, about HK$30 million would be invested this year to install two new biogas power generators at the Tai Po and Shek Wu Hui sewage-treatment plants to generate their own power.
The generators would significantly boost the use of sewage-generated biogas and are capable of delivering about  6 million kilowatt-hours of power annually.
Currently, only the Sha Tin sewage-treatment  plant uses all the biogas it produces to generate electricity for its own use.
The Tai Po and Shek Wu Hui plants use just half of the gases they produce - for heating or production of compressed air.
Use of the gas has helped the three plants save up to 19.5 million kWh, which it otherwise would have bought from CLP Power, achieving a net saving of HK$11 million.
With the new generators, they are expected to increase savings to 26 million kWh per year by 2009 and save HK$15 million annually.
Biogas is a methane-laden gas produced from sewage sludge.
It is seen as a form of renewable energy similar to landfill-generated methane gas and if it is not used, it is either burned off or released back into the atmosphere.
But methane is a greenhouse gas  that is considered to have a much stronger negative impact on the atmosphere than carbon dioxide.
The three sewage-treatment works serve about 1.2 million New Territories residents and handle about 400,000 cubic metres of sewage a day. They yield a combined total of  8 million cubic metres of biogas a year, half of it generated by the Sha Tin plant alone.
About 70 to 80 per cent of gases produced at all three plants are now being converted into various forms of energy, with the rest  stored or burned off.  Use of biogas generated at the three plants would increase to more than 90 per cent by 2009.
'We will continue to boost the utilisation rate and volume of biogas as our sewage works expand,' said Drainage Services Department assistant director Tai Tak-him.
However, since the power savings  were small compared  with the more than HK$1 billion annual operating cost of all 270 Hong Kong sewage-treatment works, he said  they would have little effect on sewage fees.
Treatment costs
Hong Kong's sewage is reduced to sludge at 270 plants
The amount in HK dollars it costs to process the city's waste annually $1b



Biogas from sewage to save HK$15m a year