Tunnelling works completed for Phase 2 of Singapore's sewage 'superhighway'

SINGAPORE: Tunnelling works for the second phase of Singapore's Deep Tunnel Sewerage System (DTSS) have been completed, PUB said on Monday (Aug 21).

Described as a "superhighway" for used water, the infrastructure project will boost water recycling and improve long-term water sustainability in Singapore, the national water agency said in a media release.

Phase 2 of the DTSS involves the construction of a 98km-long network of deep tunnels and link sewers, as well as the future Tuas Water Reclamation Plant.

"These new infrastructure components extend the DTSS network to serve the western half of Singapore, including the downtown area and upcoming developments such as Tengah Town and Jurong Lake District.

"Spanning multiple tunnelling and construction contracts, the DTSS Phase 2 project involved over 5,000 workers at the peak of its construction works."

The system was first conceived in the 1990s as a means to meet Singapore's needs for used water collection, treatment, reclamation and discharge.

"It holds the key to enable PUB to reclaim and recycle water in an endless cycle, thus boosting our capacity to produce NEWater, Singapore's third National Tap and a weather-resilient source of water," the agency said.

Construction of the first phase of the system, with tunnels spanning 48km through the eastern half of Singapore, was completed in 2008. Phase 2 began in 2014 and is slated for completion in 2026.

The total cost of the DTSS will be about S$10 billion (US$7.4 billion) and it was designed to last for about 100 years.

HOW WILL THE DTSS CHANGE USED WATER MANAGEMENT?

Before the introduction of the DTSS, Singapore was divided into six used water catchment zones which were each served by a water reclamation plant, PUB said.

More than 130 pumping stations across the country were needed to bring used water to these plants for treatment before the treated water was discharged to the sea.

The DTSS was designed as a more cost- and land-efficient solution for used water management.

Over two phases, the DTSS comprises a 206km-long network of deep tunnels and link sewers that will convey used water via gravity to three centralised water reclamation plants in Changi, Kranji and Tuas, PUB said.

"The conveyance of used water via gravity instead of energy-intensive pumping stations enhances the robustness and reliability of the used water collection system. This also eliminates the risk of pollution in our rainwater catchments," the water agency added.

"The implementation of the entire DTSS will allow PUB to reduce the overall land footprint of the used water system across Singapore by half, freeing up to 150 hectares of land – nearly twice the size of the sprawling Singapore Botanic Gardens – for higher-value land use."

CHALLENGING PROCESS

PUB said that tunnelling work for Phase 2 of the project "was a challenging process" through highly built-up areas. 

"The tunnelling works had to be carried out by five different contractors, using pioneering construction methods and smart technologies for safe and smooth operations," the agency said.

"This served to greatly reduce disruption to above-ground infrastructure and the public."

Construction of Phase 2 also saw the implementation of new features that will allow authorities to ensure the integrity of deep tunnels and maintain them more easily.

"These include the use of concrete resistant to microbiological-influenced corrosion, isolation gates to allow for flow diversion, fibre optic cables for remote monitoring of a tunnel’s structural integrity and the use of air jumpers to control air flow within the tunnels," PUB said.

The Tuas Water Reclamation Plant, a key component of Phase 2, is expected to be ready by 2026.

The plant will be located with the National Environment Agency's Integrated Waste Management Facility to form Tuas Nexus, Singapore's first integrated used water and solid waste treatment facility that will be fully energy self-sufficient, PUB said.

In a statement, PUB chief executive Goh Si Hou described the DTSS as a "game-changer" for "one of the most water-stressed countries in the world".

"The Deep Tunnel Sewerage System is not only an engineering feat, but a key pillar in strengthening Singapore's water resilience to meet the long-term challenges of climate change and growing water needs," he said.

"This has been made possible through the bold vision and innovation of our pioneers, and decades of meticulous planning and hard work by our planners, engineers and contractors.

"We look forward to the upcoming completion of our water reclamation and NEWater plants, which will realise the full potential of the DTSS in the years to come."