Public Utilities Board (PUB) is a statutory board under the Ministry of the Environment and Water Resources. PUB manages the complete water cycle in Singapore. It is the national water agency, managing Singapore’s water supply, water catchment and used water in an integrated way.

Director of PUB Water Reclamation Department Tan Thai Pin said Singapore faces challenges as more lucrative land use competes with the need for urban water catchments. The solution is three pronged:

• Membrane technology to filter sewer water
• Timely implementation
• Trenchless Technology for pipe laying and rehabilitation.

PUB plans to rehabilitate 1,000 km over the next five years using CIPP, spiral wound lining and fold and formed. They will also use pipe jacking and microtunnelling to extend the sewer network.

Chief Executive of PUB Khoo Teng Chye has said that Singapore has come a long way from the days when it was faced with problems such as flooding, pollution and water shortages. Since then, PUB has been recognised through many international awards. Mr Khoo attributes PUB’s achievement to investing in water restoration and development, technology and by adopting an integrated and holistic approach to water management.

“Today, we have in place a long-term water supply strategy known as the Four National Taps, comprising water from local catchments, imported water, reclaimed water (branded NEWater in Singapore) and desalinated water,” he said.

Mr Khoo said that NEWater and desalinated water are the result of PUB’s continuous investments in R&D and technology.

“By leveraging on advancements in technology and decreasing costs, PUB was able to successfully introduce these two alternatives as viable sources of water for Singapore.”

Mr Khoo has said that PUB has also worked towards a more people-oriented approach to delivering water, by adopting the tagline ‘Water for all: Conserve, Value, Enjoy.’

“Securing an adequate supply of water is only half of the equation – managing the water demand is just as important. To ensure sustainability of Singapore’s water resources, PUB calls on all Singaporeans to play their part to conserve water, keep the water catchments and waterways clean and build a closer relationship with water by enjoying this precious resource.”

Wastewater management

PUB is vested with the challenging task of maintaining the sewerage reticulation system which has its origin in colonial times. The Sewerage Department of PUB identifies older sewers, restores their condition and keeps the health of the system in the pink to serve the increasing development in Singapore.

Sewer rehabilitation originally involved a large amount of excavation work and sewers were repaired mainly by the open trench method. The operation, while necessary, was time-consuming and often caused inconvenience to customers.

Today, PUB uses a number of Trenchless Technologies such as pipe bursting and spiral wound lining in sewer rehabilitation work as they continue to maintain the 3,400 km of gravity sewers, 220 km of pumping mains and 130 pumping installations of the sewer reticulation system.

PUB has also used Trenchless Technology to reline some 600 km of public sewers and private drain lines under the third phase of the ongoing sewer rehabilitation program. The Trenchless Technology used includes cure-in-place piping, spiral wound lining and fold-and-form technology.

The ongoing sewer rehabilitation program, current phase 2009–2014, will see the refurbishment of more than 1,000 km of this network. Much of this work will be undertaken using microtunnelling.

When asked about the future use of Trenchless Technology in Singapore, Mr Khoo said that PUB will continue to adopt the use of Trenchless Technology for the laying of sewers and for Singapore’s ongoing sewer rehabilitation program.

“This is to ensure that Singapore’s sewer system is kept in tip-top condition and free of leakages that could contaminate our rainwater collection system.”

Deep Tunnel Sewerage System

The Deep Tunnel Sewerage System, (DTSS) conceptualised and managed by PUB, is Singapore’s superhighway to meet its used water needs for the next 100 years in a cost-effective and sustainable way. One of the world’s largest used water collection and treatment projects, the DTSS conveys used water from homes and industries through a 48 km long deep tunnel sewer that runs 20–55 m below ground to a centralised water reclamation plant for treatment.

The major tunnelling challenges of the DTSS project included the high groundwater table; mixed face and very abrasive ground conditions; highly variable rock quality in the granite and sedimentary formations; and the major expressways directly above the tunnels, making avoidance of settlement and/or face collapse critical.

The DTSS comprises a 48 km deep tunnel, a water reclamation plant, a deep sea outfall and some 60 km of linking sewers. Relying entirely on gravity, used water is channeled through the deep tunnel to the water reclamation plant where it is treated before being discharged to the sea.

Trenchless Technology is being used in the construction of these deep tunnels and link sewers. The construction of the 48 km tunnels with diameters ranging from 3.3 m to 6 m and depths of 18 m to 50 m below ground were completed using tunnel boring machines.

A total of eight tunnel boring machines were used for driving the 48 km of tunnels. The eastern two-thirds of the North Tunnel were constructed through the Old Alluvium layer, a generally competent tunnelling material. The tunnel however, was deep below the groundwater table, in some areas more than 45 m, requiring constant control of the tunnel face to prevent face instability. Earth-pressure balance shield machines were used to control face instability. The link sewers, with diameters up to 3 m and depths of up to 40 m are mainly being laid by pipe jacking.

The DTSS was the recipient of the Global Water Awards ‘Water Project of the Year', the water project with the most significant contribution to water technology and environmental protection.