Application of compact sewage treatment technologies in Hong Kong

Abstract

With the outcry for compact sewage treatment technologies in recent years, the Drainage Services Department of the HKSAR Government set up a pilot compact sewage treatment plant comprising a mechanical filter mesh and membrane bioreactors (MBRs) at the Shatin Sewage Treatment Works (STSTW) from July 2014 to September 2015 to acquire a better understanding of their performances with respect to the treatment capacity, ease of operation as well as maintenance and effluent quality. With calculations based on these well-informed assumptions, the footprint required for a mechanical filter mesh is about 1/8th of that of a conventional primary sedimentation tank. The pilot trial showed that the total suspended solid removal of the mechanical filter mesh installed was comparable to that of a primary sedimentation tank, and it could handle the diurnal peak loads and shock loads of the STSTW. With a deodorisation unit in place, the impact of odour nuisance was eliminated. As the mechanical filter mesh could effectively filter out hair and fibres, it could protect the downstream MBRs from fouling as well. For the two piloting MBRs, the immersed MBR was less sensitive to the operating mixed liquor suspended solids and had less downtime than the sidestream MBR. Meanwhile, less E.coli was detected in the permeate from the immersed MBR.