A biological wastewater treatment system installed in Singapore's Kallang River-Bishan Park was waterproofed using Sikaplan® WT sheet membranes. Singapore is renowned for the cleanliness of its streets. Any pedestrians caught littering in public spaces are more than likely to receive draconian punishments. The city-state has made a tremendous effort in recent decades to clean up the urban landscape and keep it trash-free.

While other countries in the region persist in discharging sewage – mostly untreated – into the sea, the Singapore authorities have built a ring sewer around the city to collect all urban and industrial wastewater and carry it to one of the numerous treatment plants on the outskirts of the city.


The "Clean waters for all" development program launched by Singapore's Department of Public Works likewise provides for all surface waters and watercourses in the parks to be returned to and maintained in a clean condition (thereby remedying the sins of the past). This is to be achieved by sustainable and, as far as possible, "soft" remediation methods. Atelier Dreiseitl Asia Pte. Ltd. – a company with a long track record in the design and installation of biological wastewater treatment plants – and Singapore-based Jason Liong Architects were appointed as the project's lead designers.

Mechanical and biological cleaning techniques that use a biotope comprising sand filter and planted substrate layer to treat lightly contaminated wastewater from remote settlements have been employed in Europe for decades. The sewage arriving at the top end of the biotope flows through the sand filter and planted substrate layers. Then, at the bottom end, the filtered and biologically purified product discharges into an open body of water or watercourse.


To ensure the controlled flow of wastewater through the filter and substrate layers, and prevent any infiltration into the ground, the biotope needs to be enclosed by a waterproof barrier. This is normally achieved through the incorporation of a buried sheet membrane, which is loose laid in an excavated and leveled pit.

A watertight seal is provided at all junctions between the membrane and the inlet or outlet pipe penetrations. After welding of the laps between adjoining membrane sheets and performance of a leakage test, the membrane is covered over by the filter and substrate layers, which are then suitably planted for the purpose of biological wastewater purification.


To provide the necessary hydraulic gradient for the system to operate, the gently sloping terrain in Bishan Park was fashioned into a series of terraced basins (inspired by the rice terraces of Indonesia and the Philippines), which were then lined with sheeting.

The product presented to the customer by our colleagues at Sika Singapore was Sikaplan® WT 5200-12HE, a sheet waterproofing membrane based on polyolefin (a synthetic formulation made from polyethylene) and capable of resisting the relatively high water temperatures and microbe exposure.

After detailed examination of our bid and installation proposal, the project owners opted for our product. During the summer months of 2011, 6,400 square meters of Sikaplan® WT 5200-12HE was manufactured at the Sarnen plant in Switzerland and delivered for installation by a local applicator.

The wastewater treatment system was finally completed and put into service in the fall of 2011. Today, visitors to the park are hardly aware of the wastewater treatment system concealed beneath the landscaping. Needless to say, in this park, walking on the "green spaces" is strictly forbidden.

A new project with the same type of system is currently under design. We are naturally hoping to be on board again with our sheet membranes.

Author: Hans-Jörg Stich