The Government is actively exploring sustainable and innovative approaches to expand the city’s land resources. One viable source of land supply is rock cavern development.

The relocation of suitable existing government facilities to caverns can release above-ground sites for housing and other beneficial uses. This would reduce the amount of land occupied by them, as well as relocate facilities which do not need to be above-ground and are incompatible with the surrounding environment and land uses nearby.

Mountain move

Sha Tin Sewage Treatment Works is one such facility. It will be relocated to caverns in Nui Po Shan of A Kung Kok to release the existing site of about 28 hectares for housing and other uses that will enhance Hong Kong’s living quality and bring extended benefits to the community and environment of Sha Tin.

Drainage Services Department Sewerage Projects Division Engineer Brian Chan said that moving the sewage treatment plant to caverns minimises any adverse impact on the environment and community.

“The whole sewage treatment works will be put inside the cavern and the cavern will serve as a natural barrier fully enclosing the sewage treatment works. With the implementation of an effective odour management system, the odour impact to the community will be minimised.”

Mr Chan added that moving the existing plant, which has been in operation for more than 35 years, provides an opportunity to formulate a long-term strategy for the ageing facility.

High-tech solutions

The relocated Sha Tin Sewage Treatment Works will consist of several caverns.

A successful local example of accommodating facilities in rock caverns is Stanley Sewage Treatment Works on which the layout for the Sha Tin treatment plant is based.

To reduce the required cavern space and shorten the construction period, advanced sewage and sludge treatment technologies will be used.

Water recycling is a multi-stage process in wastewater treatment plants.

Mr Chan explained that moving bed biofilm reactors will be used in the secondary treatment process at the relocated Sha Tin plant as they require less space than the traditional wastewater treatment.

“Compared to the conventional method, there will be some biofilm carriers inside the reactor and this biofilm carrier will enlarge the surface area for the biological treatment and therefore, the overall size will be reduced. In terms of the sewage treatment process, there will be about a 20% reduction in the areas.”

Sha Tin Sewage Treatment Works serves a population of about 630,000 in Sha Tin and Ma On Shan, which produce 250,000 cubic metres (m3) of sewage daily. After the relocation, the facility will be able to handle 340,000 m3 of sewage per day.

The first phase of works to relocate Sha Tin Sewage Treatment Works to caverns began in February. The Drainage Services Department hopes to start the second phase from the end of next year to early 2021 with the excavation of the caverns. The department plans to move the whole sewage plant in five stages. The project is expected to be completed by 2031.

Members of the public can visit the department's website for more details about the project and its latest developments.