Deep sewerage tunnel to extend to west of Singapore

Work on underground 18km 'super highway', costing $3b, to start in 2016
Tan Dawn Wei Straits Times 14 Mar 13;

THE new extension of an underground "super highway" that carries Singapore's used water will cover the western part of the island, including the downtown city area and major upcoming developments such as Tengah New Town.

Construction on the new tunnel, which will be 18km long and cost about $3 billion, will start in 2016 and take about six years.

When it is ready, the new tunnel will carry waste water from these areas to a new water reclamation plant in Tuas.

There, the water will be treated before being either pumped out to sea or reclaimed as Newater, purified water mostly used by industries.

The new extension is part of the award-winning Deep Tunnel Sewerage System (DTSS), which runs about 20 storeys underground.

Minister for the Environment and Water Resources Vivian Balakrishnan announced this in Parliament on Tuesday but gave few details.

In response to queries, Singapore's national water agency PUB disclosed the specifications of the new tunnel extension yesterday.

But it added that it is still in the early stages of planning and will launch tenders for it later this year.

Phase 1 of the system - a 48km-long tunnel running from Kranji to Changi - was completed in 2008 at a cost of $3.65 billion. Phase 2 will be comparable in cost and scale. Running at depths of between 20m and 50m, the tunnel, about 6m in diameter, goes even deeper than MRT tunnels.

Currently, used water in western Singapore is collected through an existing network of underground sewers and intermediate pumping stations, and sent to water reclamation plants in Ulu Pandan and Jurong.

Together with plants in Kranji and Changi, Singapore treats about 216,800 Olympic-size swimming pools of used water a year.

Once the new extended tunnel is ready, the Ulu Pandan and Jurong plants and intermediate pumping stations will be progressively phased out and the land freed up for development.

By then, Singapore will have the capacity to treat more than 600,000 Olympic-size swimming pools of used water a year. It will be enough to meet the country's growing population, said PUB.

With the DTSS, water is carried largely by gravity to the plants as the tunnel is sloped, which saves energy needed for pumping stations to do the job.

At the recycling plants, the water goes through a series of screens to remove debris, then a bioreactor where micro-organisms break down impurities and organic waste. It also goes through two sedimentation tanks where particles are allowed to settle.

What comes out will either be pumped 5km out into the deep sea, or be further purified to produce Newater.

The sludge collected during the treatment is blended and thickened to reduce its volume, before being decomposed by micro-organisms. It eventually gets sent to incineration plants to be burned and used as landfill.

Hailed as a radical move to solve Singapore's long-term used water needs, the DTSS was named Water Project of the Year in 2009 at the annual Global Water Awards, which honour top achievers in the areas of water management and treatment.

Associate Professor Ng How Yong of the National University of Singapore's department of civil and environmental engineering said having a single large tunnel criss-crossing the island that consolidates smaller sewerage pipes makes for better management and control.

PUB said it will work to minimise surface road disruptions during construction.

"As with all major projects, we will coordinate closely with agencies on their service infrastructure including the Land Transport Authority for the MRT lines," said a spokesman.

It added that it will also incorporate new technologies into the new Tuas plant to save on manpower and improve its energy efficiency.

Prof Ng does not think competing tunnelling works for upcoming underground rail lines are a cause for worry.

"Planners would have planned where all your tunnels and MRT lines will be," he said.