The Drainage Services Department has completed large-scale maintenance works and replacement of electrical and mechanical facilities at the Stonecutters Island Sewage Treatment Works.

Secretary for the Environment KS Wong said the maintenance works were very challenging and efforts were made to minimise the works' potential impact on the public.

The Stonecutters Island Sewage Treatment Works has been running 24 hours a day since it was put into service in 2001. Some of its major electrical and mechanical facilities were approaching the end of their service lives last year, and replacement works had to be carried out.

The Drainage Services Department originally planned that bypasses of part of the preliminarily treated sewage from the upstream preliminary treatment plant into Victoria Harbour would be carried out in five occasions from 2018 to 2020 to facilitate the replacement and maintenance works.

The first and second bypasses were completed last year while the third in March. As the progress of the maintenance and replacement works was beyond expectation during the third bypass, there was no need to conduct the fourth and fifth bypasses as planned.

During every bypass, the department implemented mitigation and contingency measures as well as comprehensive water quality monitoring. Relevant information was put online regularly.

The water quality monitoring results revealed that the works’ impact on the water quality of Victoria Harbour was slight and transient, and the bypasses did not have significant impact on beaches, fish culture zones or coral sites near Victoria Harbour.