The emergence of construction innovations does not only enhances safety and productivity in construction, but also helps different projects overcome challenges and constraints, while introducing a new chapter for the industry. The Sha Tau Kok Sewage Treatment Plants, located next to the Hong Kong border, has been undergoing expansion works since late 2018 and is expected to be completed by 2025. The plant’s sewage treatment capacity will be increased by 3 times to 5,000 m³ per day, in order to cope with the expected population growth and development of Sha Tau Kok area in the future. Recently, Ir Thomas HO, Chairman of CIC and Ir Albert CHENG, Executive Director of CIC, and Ar Clarence Leung, Member of CIC visited the site of Sha Tau Kok Sewage Treatment Works, to know more about how the project team overcame the limitations of land use and successfully built a safe and effective sewage treatment plant with innovative ideas and technology including Building Information Modelling (BIM), Modular Integrated Construction method (MiC) and Design for Manufacture and Assembly (DfMA).
Achieving “Zero Accident” with Construction 2.0
As the industry is now migrating into the era of Construction 2.0, the Drainage Services Department took proactive steps by integrating the three key pillars of Construction 2.0 into the Sha Tau Kok Sewage Treatment Works project, which are Innovation, Professionalization and Revitalization. According to Ms. Alice Pang, Director of Drainage Services Department, priority has been put on the spirit of mutual trust and cooperation among teams under this project. Binnies Hong Kong Limited and Build King – Kum Shing Joint Venture has been exploring possibilities in adopting various innovative technologies including BIM, off-site construction methodology, DfMA and MiC in which many young engineers were also involved.
The capacity of Sha Tau Kok Sewage Treatment Plants was 1,660 m³/day before the expansion. Effluent was discharged to the sea via a shorter submarine outfall. Since the capacity is expected to be exhausted soon, there is a strong urge to upgrade the sewage treatment capacity and standard. Ms. Alice Pang pointed out that the limited land use and tight schedule have made the construction project extremely challenging. The construction team needed to find ways to build a temporary sewage treatment plant to maintain current sewage treatment services, and at the same time demolish the original facilities to make room for a new plant. In view of this, the team decided that 80% of the project, including the temporary sewage treatment plant and office, should adopt off-site construction methodology. Prefabricated steel components and independent prefabricated building components were assembled in the factories, and then transported to the site for installation. This does not only save construction procedures and manpower on site, but also reduces accidents. Compared to conventional construction methods, off-site construction can definitely improve productivity, safety level, quality and sustainability of the project.
Building a New Submarine Outfall
During this project, the sewage treatment capacity will be increased to 5,000 m³/day which is 3 times of the previous capacity. The project team therefore has constructed a larger and longer submarine outfall. Mr. Bryan Hung, Graduate Engineer from Build King – Kum Shing Joint Venture, explained that the team has adopted the land-sea two-way Horizontal Directional Drilling (HDD) method to construct a new submarine outfall with approximately 1.7 km long. Such innovation effectively saves the construction time and scope of work, facilitating in risk management and control in a safe and efficient manner. Construction of the submarine outfall has been successfully completed in the first quarter of 2022.
Safety Assured with a New Concept
In order not to intervene the operation of the original sewage treatment service, the team raced against time to get the entire temporary sewage treatment plant completed within 18 months where the 750 m2 construction area involved two major facilities - EQ Tank and Moving Bed Biofilm Reactor Tank (MBBR Tank). Since the equalizing cylinder is 14 meters high, there will be a certain degree of risk if conventional lifting and stacking method are adopted. Therefore, the team made use of DfMA approach to divide the whole tank into 150 pieces of steel panels which were fabricated by laser cutting. They are then connected by thousand sets of bolted joints on site. The team had made a bold move by installing the EQ Tank from top to bottom. Ir Ken Pang, Assistant Resident Engineer from Binnies Hong Kong Limited, explained the construction sequence. They first completed the base of EQ Tank, then the top shell ring section and lastly the top roof. Nine sets of screw jacks were temporarily erected at tank base for lifting the tank ring-sections one by one. It only took 5 minutes to lift one ring-section. No working at height or welding is involved to ensure site safety.
Constructing MiC Means Speed and Flexibility
The construction area of the temporary sewage treatment plant is only just as big as 1.5 standard basketball courts. To cope with the daily sewage treatment capacity of 2,500 cubic meters, the project team has adopted a new sewage treatment technology - Moving Bed Biofilm Reactor (MBBR), which can process a larger amount of sewage in a smaller space. The team has applied MiC technology to construct the main facilities of the temporary sewage treatment plant. The water tank is divided into upper, middle and lower rings. Each ring is composed of four sections, where it is surrounded by stainless steel plates looking like wafers. The prefabricated steel plates were delivered to site, and then connected with bolts and nuts. The actual establishment period for each MBBR tank was 10 day and the whole process did not involve welding, which greatly shortened the construction time and enhanced safety level.
CIC actively promotes the adoption of innovative technologies in the industry to improve site safety and productivity. Ir Thomas HO, Chairman of CIC, is greatly impressed by the application of different new technologies at the site of Sha Tau Kok Sewage Treatment Works, he appraised the synergy among project teams and the involvement of young engineers. With the concerted efforts, there has been zero accident on the construction site since the beginning of the project in 2018, setting an excellent example for the industry!
