Relocation of Sha Tin Sewage Treatment Works to caverns

There is a pressing need to optimise the supply of land for various uses by sustainable and innovative approaches to support social and economic development. It is the established policy of the Government to adopt a multi-pronged approach to expand land resources. One practicable approach is rock cavern development, which is a viable source of long-term land supply. Releasing about 28 hectares of land after relocating the existing Sha Tin Sewage Treatment Works (STSTW) to caverns brings multifold benefits to the community. On one hand, the environment of the existing STSTW site and its surroundings will be greatly improved. Compared to the existing open-plant arrangement, the odour management of the relocated STSTW in caverns, with caverns as natural barrier, can be more efficiently enhanced so as to minimise the odour impact on the surrounding communities. On the other hand, developing the vacated site for residential and other beneficial uses will benefit the community by meeting various public needs.

The Drainage Services Department (DSD) is implementing the relocation of STSTW to caverns in the following stages:

(i) site preparation and access tunnel construction (which was commenced in February 2019 and scheduled for completion in 2022 tentatively);

(ii) main caverns construction and upstream sewage works;

(iii) sewage treatment facilities installation; and

(iv) decommissioning and demolition of the existing STSTW.

The future cavern complex for the relocated STSTW will be the largest of its type ever built in Hong Kong. Unlike building a sewage treatment works in an open space, the underground caverns must first be created to accommodate sewage treatment facilities. The construction of underground caverns is complicated and usually takes more time to complete as compared with other conventional site formation works. In order to minimise the cavern sizes required, the DSD has gone through a comprehensive assessment on the selection and verification of the suitability of the proposed advanced sewage treatment technologies. For instance, “lamella settler” will be adopted for primary sedimentation, an inclined plate clarifier formed by a bundle of evenly spaced stainless steel plates which could enlarge the effective settling surfacing area with a small footprint. For secondary treatment process, moving bed biofilm reactor will be used for biofilm carriers that could enable a higher surface area for the biological process in nutrient removal while the required size of the bioreactor tanks could be reduced. By adopting these compact technologies, cavern space can be reduced by about 20% as compared with traditional technologies.

The article is contributed by the Drainage Services Department, the HKSAR Government

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