Sewage services offer unlikely energy source

Local | Michael Shum 14 Nov 2019

Wastewater discharged from our homes go through deep tunnels under the sea to reach the Drainage Services Department's sewage treatment facility in Stonecutters Island, one of the two water treatment works that process wastewater before it is discharged into the ocean. There, it undergoes chemical-enhanced sedimentation to settle flocs into sludge.

"The deep level tunnels were built as a part of the Harbour Area Treatment Scheme aimed to clean up the Victoria Harbour," said Albert Tse Yuet-kar, chief engineer of the sewage treatment plant.

Sludge sedimented from the sewage is then transported by two vessels to T-Park in Tuen Mun, a sludge treatment facility.

The two vessels, Clean Harbour 1 and 2, are the first two "electric-diesel" cargo vessels registered in Hong Kong, which cut emissions for a better environment.

At T-Park, the sludge is incinerated to generate electricity, while heat is also generated for a spa in the facility.

"The volume of the sludge is reduced by 90 percent after incineration, which can greatly cut down the burden at landfills," Tse said.

Speaking of environmental protection, Sussana Tsang Wai-wah, a senior engineer at the department, said, "Hongkongers have improved a lot."

"People's awareness toward environmental protection has gone up a notch as the number of suggestions and complaints has surged over the years," Tsang said.

"We have already identified the procedures that might emit smell and covered it up," Tse explained.

"We will usually tell district councilors beforehand if we have to open up those covered areas for maintenance. But for emergency repairs, we ask for tolerance and understanding from residents nearby."

The Stonecutters Island facility was relatively isolated when it was first built, but homes got closer and closer to the plant, Tse added.

For a visit to the Stonecutters Island treatment plant, citizens will have to wait as the open day that celebrates the department's 30th anniversary, which was originally scheduled for later this week, is postponed.

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