Deep Tunnel Sewerage System

by LCNA:Centre for Liveable Cities, Singapore

The Deep Tunnel Sewerage System (DTSS) was conceptualised in the 1990s as a sustainable, cost-effective solution to meet Singapore’s used water collection, treatment, reclamation and disposal needs in the long run. Spanning two phases over more than 20 years, Phase 1 was completed in 2008 while Phase 2 is due to be completed by 2025.

Background
In the late 1960s, the Public Works Department drew up the Sewerage Master Plan to guide the development of a comprehensive sewerage system to cope with rapid population growth and industrialisation in post-independence Singapore, as well as to improve the quality of life. The master plan divided Singapore into six sewage catchment zones, each served by a sewage treatment works (later renamed water reclamation plants). Pumping stations channelled sewage to these plants, where it was treated to international standards before being discharged into the sea. The implementation of the master plan meant that all of Singapore was served by a modern sanitation system by 1997.1

However, Singapore’s water supply faced an increased risk of contamination due to pipe damage owing to infrastructure degradation over time. Another issue with the existing system was the large land area occupied by treatment plants and pumping stations. To address these problems, the government sought a sustainable long-term alternative that would allow Singapore to meet its growing needs without a need for continual expansion and upgrading. This led to the conception of the Deep Tunnel Sewerage System (DTSS) in 1995.2

Description
In March 1997, then Minister for the Environment Yeo Cheow Tong revealed that the government had commissioned a feasibility study for DTSS.3 Then Prime Minister Goh Chok Tong confirmed the following year that the project would be implemented.4

The DTSS project comprises four components: two deep tunnel sewers; two water reclamation plants (WRPs); a network of link sewers; and deep-sea outfall pipes. Both deep tunnels have diameters of up to 6 m and stretch across Singapore at depths of up to 55 m underground. They are connected to the existing sewerage system by the smaller link sewers that divert used water flows from the existing sewers into the deep tunnels. Used water is conveyed through the deep tunnels entirely by gravity to three WRPs located in Kranji, Changi and Tuas at the northern, eastern and western ends of Singapore respectively. The Kranji WRP was an existing facility, while the Changi and Tuas WRPs are new ones built under the DTSS project. After being treated at the WRPs, the reclaimed water is channelled to NEWater factories and further purified into NEWater. Any excess treated water is discharged into the sea through the outfall pipes.5

Phase 1
Work on Phase 1 of the DTSS project commenced in 2000 and was completed in 2008 at a cost of S$3.4 billion.6

This phase comprised a new WRP at Changi, two 5 km-long deep-sea outfall pipes, 60 km of link sewers, as well as 48 km of deep tunnel sewers made up of two sections, namely, the North Tunnel running between the Kranji and Changi WRPs, and the Spur Tunnel extending westward from the North Tunnel. The Changi WRP has the capacity to treat 900,000 cu m of used water per day. In 2010, a NEWater factory was built atop the WRP. Treated used water from the WRP is directed to the NEWater factory and further purified for reuse, with any excess discharged into the sea.7

Phase 2
Construction for Phase 2 began in 2017 and is scheduled to be completed by 2025.8 Estimated to cost S$6.5 billion, Phase 2 encompasses a new WRP at Tuas along with its corresponding outfall pipe, 40 km of deep tunnel sewers and 60 km of link sewers.9

While Phase 1 serves the eastern part of Singapore, Phase 2 covers the western and southern parts of the island. In this phase, domestic used water and industrial used water will be conveyed separately through the South Tunnel and Industrial Tunnel respectively. The South Tunnel will be connected via a short Spur Tunnel to the existing deep tunnels built in Phase 1.10 The South and Industrial tunnels both lead to the Tuas WRP, which will have the capacity to treat 800,000 cu m of used water per day. A NEWater factory integrated with the WRP will facilitate the recycling of used water into NEWater.11

The Tuas WRP will also be co-located with the National Environment Agency’s Integrated Waste Management Facility (IWMF). Collectively called Tuas Nexus, both facilities will allow Singapore to harness potential synergies in the water-energy-waste nexus. For example, food waste from the IWMF will be co-digested with sewage sludge at the WRP to produce a higher yield of biogas (a form of biofuel produced through the decomposition of organic matter). The biogas is then conveyed to the IWMF to improve the thermal efficiency of the incineration plant, thereby boosting electricity production. The electricity generated at the IWMF will fully power both facilities at Tuas Nexus, with excess electricity fed to the grid.12

Impact
Singapore’s sewerage system previously consisted of six water reclamation plants, one sludge treatment works and 139 pumping stations located islandwide.13

After the completion of DTSS Phase 1 in 2008, the Kim Chuan, Seletar and Bedok WRPs, as well as the Serangoon Sludge Treatment Works, were closed progressively.14 Once Phase 2 commences operations, the Ulu Pandan and Jurong WRPs will also be phased out.15 The numerous pumping stations used in the conventional conveyance system will be phased out too, since gravity is used in DTSS to transport used water to the WRPs.16

The implementation of DTSS will eventually halve the land area occupied by used water infrastructure, which was 300 ha in the 1990s. The completion of Phase 1 has already reduced this to 190 ha. By freeing up land for other developments, DTSS has allowed Singapore to optimise the use of this scarce resource.17 For instance, the land once used by the Seletar WRP is now occupied by Seletar Aerospace Park.18

Two other advantages of DTSS are: It does not need to be continuously upgraded and expanded;19 and it has eliminated the risk of used water contaminating water catchments due to failures at the pumping stations or breakages in the mains since intermediate pumping systems are no longer needed.20

Awards
Recognised as an outstanding engineering innovation, the DTSS project received the Institution of Engineers Singapore Prestigious Engineering Achievement Award and the ASEAN Outstanding Engineering Achievement Award in 2005, as well as the International Water Association’s Project Innovation Award in 2008.21



Author
Centre for Liveable Cities



References
1. Tan, Y. S., Lee, T. J., & Tan, K. (2009). Clean, green and blue: Singapore’s journey towards environmental and water sustainability. Singapore: ISEAS Publishing, pp. 182–183. (Call no.: RSING 363.70095957 TAN); Tan, G. P. (2016). Water. Singapore: Institute of Policy Studies; Straits Times Press Pte Ltd, p. 29. (Call no.: RSING 363.61095957 TAN)
2. Tan, Y. S., Lee, T. J., & Tan, K. (2009). Clean, green and blue: Singapore’s journey towards environmental and water sustainability. Singapore: ISEAS Publishing, pp. 187–188. (Call no.: RSING 363.70095957 TAN); Tan, G. P. (2016). Water. Singapore: Institute of Policy Studies; Straits Times Press Pte Ltd, pp. 29–30. (Call no.: RSING 363.61095957 TAN)
3. Ministry of the Environment. (1997, March 25). Speech by Mr Yeo Cheow Tong, Minister for Health and Minister for the Environment, at the ground-breaking ceremony of the Ulu Pandan Sewage Treatment Works compact and covered extension on Tuesday, 25 March 1997, at 10.30 am [Press release]. Retrieved from National Archives Singapore website: http://www.nas.gov.sg/archivesonline/
4. Ministry of Information and The Arts. (1998, August 23).
Prime Minister’s National Day Rally speech, 1998 [Press release]. Retrieved from National Archives Singapore website: http://www.nas.gov.sg/archivesonline/
5. Ministry of the Environment and Water Resources. (2001, January 20).
Deep Tunnel Sewerage System (DTSS) [Press release]. Retrieved from National Archives of Singapore website: http://www.nas.gov.sg/archivesonline/; PUB, Singapore's National Water Agency. (2017, November 20). Factsheet: About the Deep Tunnel Sewerage System (DTSS) [Press release]. Retrieved from National Archives of Singapore website: http://www.nas.gov.sg/archivesonline/; PUB, Singapore's National Water Agency. (n.d.). About Deep Tunnel Sewerage System. Retrieved 2019, October 23 from PUB website: https://www.pub.gov.sg/dtss/about
6. Ministry of the Environment. (2000, July 8). Speech by Mr Lee Yock Suan, Minister for the Environment and Minister for Information & The Arts at the ground-breaking ceremony for the Deep Tunnel Sewerage System Contract T-05 Kranji Tunnel at Mandai Road on Sat 8th July 2000 at 10.00 am [Press release]. Retrieved from National Archives Singapore website: http://www.nas.gov.sg/archivesonline/; PUB, Singapore's National Water Agency. (n.d.). Phase 1. Retrieved 2019, October 23 from PUB website: https://www.pub.gov.sg/dtss/phase1
7. PUB, Singapore's National Water Agency. (n.d.). About Deep Tunnel Sewerage System. Retrieved 2019, October 23 from PUB website: https://www.pub.gov.sg/dtss/about; PUB, Singapore's National Water Agency. (2017, November 20). Factsheet: About the Deep Tunnel Sewerage System (DTSS) [Press release]. Retrieved from National Archives of Singapore website: http://www.nas.gov.sg/archivesonline/; PUB, Singapore's National Water Agency. (n.d.). Phase 1. Retrieved 2019, October 23 from PUB website: https://www.pub.gov.sg/dtss/phase1
8. Sregantan, N. (2017, November 20). PUB starts second phase of DTSS with S$2.3b of work contracted out. The Business Times. Retrieved 2019, October 23 from The Business Times website: https://www.businesstimes.com.sg/government-economy/pub-starts-second-phase-of-dtss-with-s23b-of-work-contracted-out
9. PUB, Singapore's National Water Agency. (2016, February 2). Deep Tunnel Sewerage System (DTSS) Phase 2. Retrieved 2019, October 23 from PUB website: https://www.pub.gov.sg/dtss/Documents/DTSS_Ph2_18Feb2016.pdf
10. PUB, Singapore's National Water Agency. (2017, November 20). PUB breaks ground for conveyance system of Deep Tunnel Sewerage System Phase 2 [Press release]. Retrieved from National Archives of Singapore website: http://www.nas.gov.sg/archivesonline/; PUB, Singapore's National Water Agency. (2017, November 20). Factsheet: About the Deep Tunnel Sewerage System (DTSS) [Press release]. Retrieved from National Archives of Singapore website: http://www.nas.gov.sg/archivesonline/
11. Sewage superhighway. (2017, November 21).
The Straits Times. Retrieved 2019, October 23 from The Straits Times website: https://www.straitstimes.com/singapore/sewage-superhighway; PUB, Singapore's National Water Agency. (2018, November 28). Tuas WRP DTSS 2 Industry briefing. Retrieved 2019, October 23 from PUB website: https://www.pub.gov.sg/dtss/Documents/Tuas-Water-Reclamation-Plant-Industry-Briefing-2.0-28Nov2018.pdf
12. PUB, Singapore's National Water Agency, & National Environment Agency. (2018, July 9). PUB and NEA to call over S$5 billion in tenders for Tuas Nexus [Press release]. Retrieved 2019, October 23 from National Environment Agency website: https://www.nea.gov.sg/media/news/news/index/pub-and-nea-to-call-over-s5-billion-in-tenders-for-tuas-nexus
13. Ministry of the Environment and Water Resources. (2001, January 20). Deep Tunnel Sewerage System (DTSS) [Press release]. Retrieved from National Archives of Singapore website: http://www.nas.gov.sg/archivesonline/
14. Kog, Y. C. Transboundary urban water: The case study of Singapore and Malaysia. In
Q. Grafton, K. A. Daniell, C. Nauges, J-D. Rinaudo, & N. W. W. Chan (Eds.). Understanding and managing urban water in transition. (2015). Springer: Dordrecht; Heidelberg; New York; London. p. 586. (Not in NLB holdings)
15. PUB, Singapore's National Water Agency. (2017, November 20). Factsheet: About the Deep Tunnel Sewerage System (DTSS) [Press release]. Retrieved from National Archives of Singapore website: http://www.nas.gov.sg/archivesonline/
16. Tan, Y. S., Lee, T. J., & Tan, K. (2009).
Clean, green and blue: Singapore’s journey towards environmental and water sustainability. Singapore: ISEAS Publishing, p. 189. (Call no.: RSING 363.70095957 TAN)
17. PUB, Singapore's National Water Agency. (n.d.). Benefits. Retrieved 2019, October 23 from PUB website: https://www.pub.gov.sg/dtss/benefits
18. Siau, M. E. (2017, November 20). Construction begins for S$6.5 billion, 100km superhighway for used water. TODAY. Retrieved 2019, October 23 from TODAY website: https://www.todayonline.com/singapore/construction-begins-s65-bn-superhighway-used-water
19. Tan, Y. S., Lee, T. J., & Tan, K. (2009). Clean, green and blue: Singapore’s journey towards environmental and water sustainability. Singapore: ISEAS Publishing, p. 189. (Call no.: RSING 363.70095957 TAN)
20. Tan, Y. S., Lee, T. J., & Tan, K. (2009). Clean, green and blue: Singapore’s journey towards environmental and water sustainability. Singapore: ISEAS Publishing, p. 189. (Call no.: RSING 363.70095957 TAN); Tan, G. P. (c2016). Water. Singapore: Institute of Policy Studies; Straits Times Press Pte Ltd, pp. 29–31. (Call no.: RSING 363.61095957 TAN)
21. Tan, Y. S., Lee, T. J., & Tan, K. (2009). Clean, green and blue: Singapore’s journey towards environmental and water sustainability. Singapore: ISEAS Publishing, p. 188. (Call no.: RSING 363.70095957 TAN)


Further resources
Centre for Liveable Cities, & Public Utilities Board. (2012). Water: From scarce resource to national asset. Singapore: Cengage Learning Asia.
(Call no.: RSING 333.91095957 WAT)

Paulo, D. A., & D’Souza, A. (2018, February 17). The long road to ensuring that Singapore’s waste doesn’t go to waste. Channel NewsAsia. Retrieved 2019, October 23 from Channel NewsAsia website: https://www.channelnewsasia.com/news/cnainsider/singapore-tuas-waste-management-electricity-food-recycling-9961788

PUB, Singapore's National Water Agency. (n.d.). Tuas Nexus. Retrieved 2019, October 23 from PUB website: https://www.pub.gov.sg/sites/assets/PressReleaseDocuments/Tuas%20Nexus%20-%20Factsheet.pdf

 

The information in this article is valid as at November 2019 and correct as far as we are able to ascertain from our sources. It is not intended to be an exhaustive or complete history of the subject. Please contact the Library for further reading materials on the topic.

 

 

 

 

Subject
Domestic policy (Water Resource Management)
Sewerage--Singapore
Environmental technology
Politics and Government>>Public Utilities