ASSESSMENT OF FUTURE WATER RESOURCES
SUSTAINABILITY BASED ON 4 NATIONAL TAPS OF
SINGAPORE
FOO CHIOU LOOI
DEPARTMENT OF CIVIL & ENVIRONMENTAL ENGINEERING
NATIONAL UNIVERSITY OF SINGAPORE
2014/2015
ASSESSMENT OF FUTURE WATER RESOURCES
SUSTAINABILITY BASED ON 4 NATIONAL TAPS OF
SINGAPORE
FOO CHIOU LOOI
A THESIS SUBMITTED
FOR THE DEGREE OF BACHELOR OF ENGINEERING
DEPARTMENT OF CIVIL & ENVIRONMENTAL ENGINEERING
NATIONAL UNIVERSITY OF SINGAPORE
Acknowledgement
I would like to thank my supervisor, Dr Pat Yeh for the guidance in this project. He taught me what is independent research and learning. Also, Dr Vladan Babovic, who provided valuable feedback and encouragement as my examiner.
I would also like to mention the following people:
Ying Jie: I am glad to have known you and I wish you all the best in your studies. I will remember that I made a friend during my last year of study in the university.
Jeslyn: Thank you for listening to me. You are the only one who understands those.
You might not remember, but I appreciate the help you provided over the three years.
I hope that you can attain your academic goal and all the best to your future.
Li Ying, Yveline, Iao Tim, Guijin, Jie Ying, Yi Ru: You people add colours to my otherwise mundane life. You know how I always say that it is difficult to achieve my goals but you give me encouragement and believe I can do it (at least you said so). To
Iao Tim, suddenly we had a lot more to talk after I know that we have a similar project topic. I treated those as encouragements for us. Now I wish good results for both of us.
Last but not least, my parents who tolerated my occasional unreasonableness but still stand by me and care for me and also, myself for not giving up.
i
Table of Contents Acknowledgement ...... i
Summary ...... iv
List of Acronyms ...... v
List of Figures ...... vi
List of Tables ...... vii
1. Introduction ...... 1
1.1 Water resource situation around the world ...... 1
1.2 Research motivation ...... 2
1.3 Methodology ...... 3
2. Water resources in Singapore ...... 4
2.1 Water supply ...... 4
2.1.1 The first tap: local catchment water ...... 4
2.1.2 The second tap: imported water ...... 5
2.1.3 The third tap: NEWater ...... 5
2.1.4 The fourth tap: desalinated water ...... 7
2.1.5 Estimated production cost of each tap ...... 7
2.1.6 Alternate sources of water ...... 8
2.1.7 Potential future water supply ...... 9
2.2 Water demand ...... 10
2.3 Water sustainability ...... 10
3. Estimated future water supply and demand ...... 12
ii
3.1 Estimated future water demand ...... 12
3.1.1 Domestic ...... 12
3.1.2 Non-domestic ...... 15
3.1.3 Estimated future daily demand ...... 17
3.2 Estimated future supply ...... 17
4. Sustainability index ...... 18
5. Discussion ...... 19
5.1 Future demand ...... 19
5.2 Future supply ...... 19
5.2.1 Desalination ...... 20
5.2.2 NEWater ...... 22
6. Conclusion ...... 24
References ...... 26
Appendices ...... 29
A. Articles read ...... 29
B. List of figures ...... 30
C. List of data ...... 33
iii
Summary
Per capita availability of fresh water is the lowest in Asia as compared to the rest of the world, with Central Asia and parts of Southeast Asia under the condition of “high water stress”.
Singapore is a “water-stressed” country with per capita water availability of
110.9m3/year. Its mean annual rainfall of 2400mm is high as compared to the global average of 1050mm. The challenge is in collecting those rainfall with a limited land space and in the absence of natural aquifers and lakes. To overcome this challenge, the
PUB has developed a diversity of water supply for Singapore over the years, which are known as the Four National Taps.
Even though the water demand is met by the four taps now, the future contains uncertainty. Climate change will affect the water use and the catchment volume available. As for the second tap, it is not very stable due to the complexity of the relationship between Singapore and Malaysia. Also, discussions on new water agreement beyond 2061 had not been successful. Both desalination and NEWater processes are energy-intensive and more expensive.
The future supply of each tap will be estimated by taking into account of plans of having new desalination or NEWater plants. The focus will be on the sustainability of the processes of NEWater and desalination since they will be the major sources of water in the future. The demand will be estimated based on equations presented in the literature. The uncertainties in the results of the estimated future demand, the most possible future sources of water supply and future work will also be discussed.
iv
List of Acronyms
Forward Osmosis: FO
Liquefied Natural Gas: LNG
Meter: m
Millimeters: mm
Million gallons of water per day: mgd
Public Utilities Board: PUB
Reverse Osmosis: RO
Sanitary Appliance Fee: SAF
Seawater Reverse Osmosis: SWRO
Unaccounted-for-water: UFW
Variable Salinity Plant: VSP
Waterborne Fee: WBF
Water Conservation Tax: WCT
World Health Organization: WHO
v
List of Figures
Figure 3-1: Past and estimated future population ...... 12
Figure 3-2: Past per capita demand ...... 14
Figure 3-3: Past and estimated future GDP per capita ...... 16
Figure B- 1: Access and efficiency standards, adapted from (Ministry of the
Environment & Water Resources, 2014) ...... 30
Figure B- 2: Key figures of water supply and demand data, adapted from (Ministry of the Environment & Water Resources, 2014) ...... 30
Figure B- 3: Typical operation cost in RO, adapted from (Ghalavand et al., 2014) ..... 31
Figure B- 4: General process of FO, adapted from (Ghalavand et al., 2014) ...... 31
Figure B- 5: Comparison of flux between FO and RO, adapted from (Ghalavand et al.,
2014) ...... 31
Figure B- 6: Comparison of energy consumption between FO and other processes, adapted from (Ghalavand et al., 2014) ...... 32
vi
List of Tables
Table 1-1: Classification based on W/Q ...... 1
Table 1-2: Classification based on Q/c ...... 1
Table 2-1: Capacities of NEWater plants ...... 6
Table 2-2: Capacities of desalination plants ...... 7
Table 2-3: Estimated production cost of each tap ...... 8
Table 3-1: Current demand situation ...... 12
Table 3-2: Past and estimated future population ...... 13
Table 3-3: Population estimates based on data from
(http://populationpyramid.net/singapore/2030/) ...... 13
Table 3-4: Estimated future per capita demand ...... 14
Table 3-5: Estimated future total domestic demand ...... 15
Table 3-6: Estimated future total industrial demand ...... 16
Table 3-7: Estimated future daily demand ...... 17
Table C- 1: Population data ...... 33
Table C- 2: Per capita domestic demand ...... 34
Table C- 3: GDP per capita ...... 35
vii
1. Introduction
1.1 Water resource situation around the world
70% of the Earth’s surface is covered by water. However, only 3% is fresh water. Of those, 2.5% is locked in the polar ice caps and only 0.5% is available for human use, in the form of aquifers, rainfall, natural lakes, reservoirs and rivers (Fry, 2006). Per capita availability of fresh water is the lowest in Asia as compared to the rest of the world. The Central Asia and parts of Southeast Asia are above the threshold of “high water stress” condition as the ratio of water use to availability exceeds 0.4 (Kog, Lim,
Long, Kwa, & Nanyang Technological University. Institute of Defence andStrategic,
2002). Tables 1-1 and 1-2 summarizes the classifications of water stress indices.
Table 1-1: Classification based on W/Q
Withdrawal-to-availability ratio, W/Q Classification < 0.1 No-stress 0.1 < W/Q < 0.2 Low stress 0.2 < W/Q < 0.4 Moderate stress W/Q > 0.4 High stress
Table 1-2: Classification based on Q/c Per capita water availability, Q/c Classification (m3 c-1 y-1) > 1700 No-stress 1000 < Q/c < 1700 Moderate stress Q/c < 1000 High stress < 500 Extreme stress
Singapore is a “water-stressed” country as the amount of water available for each person is 110.9m3/year (AQUASTAT, 2014), less than 1000m3/year. The mean annual rainfall in Singapore is 2400 millimeters (mm). This amount is high as compared to the global average of 1050mm, as cited in p.109 of (Kog et al., 2002).
Introduction | 1
The challenge is in collecting those rainfall for use as Singapore is a small island with limited land space and no natural aquifers and lakes to collect rainwater (PUB, 2015a).
To overcome this challenge, the Public Utilities Board (PUB), which is Singapore’s national water agency, has developed a diversity of water supply for Singapore over the years. Known as the Four National Taps, they are the local catchment water, imported water from Malaysia, NEWater, and desalinated water.
1.2 Research motivation
The definition of sustainability is “development that meets the needs of the present without compromising the ability of future generations to meet their own needs”
(United Nations, 1987). It can be translated into providing enough quality water for the country’s use for now and in the future. For the case of Singapore, even though the demand is met by the four taps now, the future contains uncertainty.
Water demand increased by 5% per day on average when Singapore experienced the driest period in March 2014 (Ee, 2014). Prolonged dry weather will also affect the catchment volume available. As for the second tap, it is not very stable due to the complexity of the relationship between Singapore and Malaysia. Also, discussions on new water agreement beyond 2061 had not been successful (Kog et al., 2002). Even though the cost of desalination process has decreased over the years, as cited in p.64 of
(Kog et al., 2002), it is still higher than the first two sources. Besides, both desalination and NEWater processes are energy-intensive (PUB, 2013b).
Therefore, there is a need evaluate the sustainability of the water resources in
Singapore.
Introduction | 2
1.3 Methodology
This thesis aims to assess the sustainability of the water resources in Singapore. The future supply of each tap will be estimated, since the capacity of local catchment is confidential. Plans of having new desalination or NEWater plants will also be taken into account. The focus will be on the processes of NEWater and desalination since they will be the major sources of water in the future. The demand will be estimated based on equations presented in the literature.
Introduction | 3
2. Water resources in Singapore
2.1 Water supply
2.1.1 The first tap: local catchment water
The first reservoir in Singapore, the Thomson Road Reservoir (known as MacRitchie
Reservoir now), was the result of a donation of $13000 from philanthropist Tan Kim
Seng for waterworks in 1857. It was formed by impounding the water with an earth dam. In 1867, after the embankment was completed, municipal water supply was available (Kog et al., 2002).
The catchment area currently covers two-thirds of Singapore’s land surface.
Rainwater and used water are collected in different systems. Rainwater is collected in the storm water collection system which consists of drains, canals, rivers, storm water collection ponds, pumping stations and connecting pipelines before it is stored in the
17 reservoirs (PUB, 2015a). The reservoirs were built either by damming the river estuaries or from ground up. The Reservoir Integration Scheme connects the various reservoirs through a system of pumps and pipelines. This allows excess water collected in one reservoir to be pumped into another reservoir for storage to reduce wastage (Onn, 2010).
According to (Kog et al., 2002), the storage capacity of the 14 reservoirs in 2002 was
140 million m3 (30800 million gallons). However, no data on the storage capacity is available after the opening of Marina Reservoir, Punggol Reservoir and Serangoon
Reservoir. Dr Vladan Babovic suggested that it is reasonable to assume the capacity of the local catchment to be around 250 million m3 (55000 million gallons). The production cost of water from the local catchment is also not available. Water resources in Singapore | 4
2.1.2 The second tap: imported water
The causeway between Singapore and Malaysia was completed in 1924.
Subsequently, water agreements were signed between both countries in 1927 and
1961. The 1961 agreement replaced the one in 1927 and had expired in 2011.
The only agreement in force now is the 1962 Agreement, which is known as the “Johor
River Water Agreement”. It allows Singapore to draw up to 250 million gallons of water per day (mgd) from the Johor River until 2061 (Onn, 2010). Singapore is to pay
Johor 3 Malaysia sen per 1000 gallons of raw water while Johor pays Singapore 50
Malaysia sen per 1000 gallons of treated water it buys back from Singapore. Based on the above, the production cost from this tap is S$0.20/m3 (including 2.40 Malaysian
Ringgit to treat 1000 gallons of raw water). The 1990 agreement allowed Singapore to dam Sungei Linggiu for additional water to be drawn on top of the 250mgd (Kog et al.,
2002).
The cost of the additional water is the maximum of these two formulas: (1) half the difference between the price of water sold in Singapore and the price paid, less operating, distribution and management costs; (2) 115% of the price the Johor State
charges its population for water. The contract will expire in 2061, as cited in p.15 of
(Segal, 2004).
2.1.3 The third tap: NEWater
When Singapore began treating its sewage instead of releasing it into the sea in 1974, it also experimented with water recycling. However, the first test recycling plant was closed in 1975 as it was expensive and unreliable. In 1998, the idea of NEWater was
Water resources in Singapore | 5
generated from a collaboration between the PUB and the then Ministry of the
Environment (now known as the Ministry of the Environment and Water Resources).
In May 2000, the NEWater prototype plant at the Bedok water reclamation plant began operations. Since then, studies were carried out to evaluate the quality of NEWater for potable use. The Bedok and Kranji NEWater plants, with a capacity of 6mgd and
5mgd respectively, were opened in February 2003, after validating its quality and reliability. The Seletar NEWater plant with a capacity of 9mgd was opened in June
2004 (Onn, 2010). However, it was decommissioned in 2011, together with the closure of Seletar Water Reclamation Plant (PUB, 2011). The Ulu Pandan NEWater plant, which will supply 32mgd of NEWater for a period of 20 years, was opened in
March 2007. The Changi NEWater plant was opened in May 2010 with a capacity of
50mgd (PUB, 2013b). The production cost of NEWater is around 50% of desalinated water (Kog et al., 2002).
NEWater currently meets up to 30% of Singapore’s water demand and is mainly for non-potable use. The plan of PUB is to increase the capacity of the NEWater plants so that it can meet up to 55% of the future water demand by 2060 (PUB, 2015a).
Table 2-1: Capacities of NEWater plants Plant Year of commissioning Capacity (mgd) Bedok 2002 19 Kranji 2002 17 Ulu Pandan 2007 32 Changi 2010 50 Total 118
Water resources in Singapore | 6
2.1.4 The fourth tap: desalinated water
Singapore determined that desalination was technically feasible and financially viable in 1995 after conducting study trips to the plants in other countries when it has been evaluating desalination technologies since the 1970s. In 1998, a test desalination plant was built through a collaboration between Singapore Power, AquaGen, and Singapore
Technologies (Onn, 2010).
In 2005, the first desalination plant, SingSpring Desalination Plant, was built with a capacity of 30mgd. Together with the second desalination plant, the Tuaspring
Desalination Plant with a capacity of 70mgd, desalinated water currently meets up to
25% of Singapore’s water demand. The plan of PUB is to increase the capacity of desalination plants so that it can meet up to 25% of the future water demand by 2060
(PUB, 2013a). Desalinated water is the domestic and industrial supplies for the western part of Singapore.
Table 2-2: Capacities of desalination plants Plant Year of commissioning Capacity (mgd) SingSpring 2005 30 Tuaspring 2013 70 Total 100
2.1.5 Estimated production cost of each tap
It was reported that the selling price of desalinated water from Tuaspring Desalination
Plant for the first year was $0.45/m3 while the selling price of desalinated water from
SingSpring Desalination Plant for the first year was S$0.78/m3 (TODAY Online,
2013).
Water resources in Singapore | 7
Table 2-3 summarizes the estimated production costs of water from each tap. The production cost of water from the local catchment is assumed to be S$0.30/m3.
Imported water from Malaysia is the cheapest source while desalinated water cost the most. Note: all costs are relative; they may not reflect the actual costs at the present as they are not accessible.
Table 2-3: Estimated production cost of each tap
Tap Production Cost (S$/m3) Local catchment 0.30 Imported water from Malaysia 0.20 NEWater 0.23 Desalinated water 0.45
2.1.6 Alternate sources of water
Alternate sources of water are also available for private use. These include rainwater harvesting, greywater recycling and use of seawater (PUB, 2014). Developers who satisfy the conditions imposed by PUB are allowed to build rainwater collection systems to collect rainwater for non-potable use within their own premises.
“Greywater” is untreated used water which has not come into contact with toilet waste.
This includes used water from washings, such as showers, and laundry and excludes used water from the toilets and kitchen sinks. Greywater recycling is to reuse treated greywater after it has gone through treatment such as membrane filtration and disinfection to ensure the quality of the treated greywater for non-potable use. The treated greywater may be used for toilet flushing and general washing. It is not allowed for use in high pressure jet washing, irrigation sprinklers and general washing at markets and food establishments due to public health concerns.
Water resources in Singapore | 8
The use of seawater is encouraged for cooling and process use for industries located on offshore islands or near the sea.
2.1.7 Potential future water supply
2.1.7.1 Variable Salinity Plant
As all the major rivers are dammed to create reservoirs, the Variable Salinity Plant
(VSP) can tap water from the smaller streams near the shoreline as damming these small catchments is not cost effective. It can produce clean water from canal water during rainy season. When the weather is dry, it can perform seawater desalination.
The demonstration plant at Sungei Tampines since 2007 proves that the technology is viable. The aim of PUB is to increase the overall catchment area of Singapore to 90% with VSP so that more rainwater can be harvested to increase the domestic water supply at a lower cost (PUB, 2013b).
2.1.7.2 Groundwater
A study is currently being carried out on the possibility of groundwater in the Western and Southern parts of Singapore and Jurong Island underlying Jurong Formation as it may contain aquifers (Eco-Business, 2013). The groundwater will only be extracted if the groundwater models developed indicate that there will be no impact on the existing buildings and infrastructure. Even if substantial amount of groundwater cannot be extracted regularly, it can serve as "water banks" for drought periods.
2.1.7.3 Water from Indonesia
An agreement between Singapore and Indonesia was signed in 1991 for the supply of water (1000mgd) at S$0.01/m3 from Riau in Indonesia via undersea pipelines. A joint venture was created in 1992 to develop supply of water from Bintan but the project was not continued due to political uncertainty in Indonesia (Kog et al., 2002).
Water resources in Singapore | 9
2.2 Water demand
The current water demand in Singapore is around 400mgd with 45% belonging to the domestic at 151 liters/capita/day and 55% belonging to the non-domestic (PUB,
2015b). The demand is managed through a range of water conservation plans which encourage the people not to waste water. The per capita domestic water demand had decreased from 165 litres/day in 2003 to the current 150.4/day. PUB aims to lower this figure to 147 litres by 2020 and 140 litres by 2030. The total projected demand could be doubled by 2060, where 70% would be non-domestic demand, according to
PUB.
2.3 Water sustainability
PUB tracks some standards on water sustainability under the Environment and Water
Regulations and Standards (SEWERAGE AND DRAINAGE ACT) which are listed in appendices.
Figure B-1 lists the percentage of access to drinking water sources and improved sanitation, the quality of our drinking water and the percentage of unaccounted for water over the years. Singaporeans have 100% access to drinking water sources and improved sanitation, and our quality of drinking water is assured since it passed all the tests on drinking water quality, meeting the standards set by World Health
Organization (WHO).
Unaccounted-for-water (UFW) refers to the water lost in the network of pipelines between the drinking water treatment plants and the consumers due to leakage or other reasons. This is often due to the lack of maintenance which results in the deterioration of the network over time. The percentage of UFW has been reduced to about 5% over
Water resources in Singapore | 10
the years due to the comprehensive maintenance regime. UFW in other countries can range from 10% to 30% (PUB, 2015a).
Figure B-2 lists some data on water supply and demand over the years. In short, these are the data that is available.
Water resources in Singapore | 11
3. Estimated future water supply and demand
Data on population and GDP per capita was obtained from Singstat
(www.singstat.gov.sg). Data on per capita water demand was obtained from the PUB website. Only data from the years 1995 to 2014 was taken into consideration for consistency.
Table 3-1: Current demand situation
Current per Current total Current total Current Current total capita Current domestic non- domestic total demand demand population demand demand demand (litres/day) (litres/day) (litres/day) (litres/day) (mgd) 150.4 5,469,724 822,646,490 1,005,456,821 1,828,103,310 402.1
3.1 Estimated future water demand
3.1.1 Domestic
3.1.1.1 Estimated future population
The future population was estimated based on the past trend. A polynomial trend line of order 2 was selected as it fits the data the most.
8,000,000 y = 2628.2x2 - 1E+07x + 1E+10 7,000,000 R² = 0.9773 6,000,000 5,000,000 Population 4,000,000 Past population 3,000,000 Poly. (Past population) 2,000,000 1,000,000 0 1990 2000 2010 2020 2030 Years
Figure 3-1: Past and estimated future population
Estimated future water supply and demand | 12
Table 3-2: Past and estimated future population Estimated Year Actual population Error (%) population 2014 5,469,724 5,560,272 1.7 2020 6,560,326 2030 8,647,599 2040 11,260,519 2050 14,399,084 2060 18,063,296 2070 22,253,153
However, the estimates after the year 2020 seem to be unrealistic. So, the projections from (http://populationpyramid.net/singapore/2030/) were adopted.
Table 3-3: Population estimates based on data from (http://populationpyramid.net/singapore/2030/) Year Estimated population 2020 6,057,000 2030 6,577,000 2040 6,904,000 2050 7,064,000 2060 7,096,000 2070 6,988,000
Estimated future water supply and demand | 13
3.1.1.2 Estimated future per capita demand
175
170
165 Per capita demand 160 (litres/day) Past per capita demand 155
150
145 1990 1995 2000 2005 2010 2015 Year
Figure 3-2: Past per capita demand
The future per capita demand was estimated using the least square method with the latest two data points (in the year 2013 and 2014) in a linear trend.
Table 3-4: Estimated future per capita demand Year Estimated per capita demand (litres/day) 2020 146.8 2030 140.8 2040 134.8 2050 128.8 2060 122.8 2070 116.8
3.1.1.3 Estimated future total domestic demand
The total domestic demand is calculated based on the equation,
푝표푝푢푙푎푡푖표푛 × 푑푎푖푙푦 푝푒푟 푐푎푝푖푡푎 푑푒푚푎푛푑 ( 3-1)
Estimated future water supply and demand | 14
Table 3-5: Estimated future total domestic demand Estimated future Estimated future Estimated Estimated future per capita total domestic Year future total domestic demand demand population demand (mgd) (litres/day) (litres/day) 2020 6,057,000 146.8 889,167,600 195.6 2030 6,577,000 140.8 926,041,600 203.7 2040 6,904,000 134.8 930,659,200 204.7 2050 7,064,000 128.8 909,843,200 200.1 2060 7,096,000 122.8 871,388,800 191.7 2070 6,988,000 116.8 816,198,400 179.5
3.1.2 Non-domestic
In this project, the non-domestic demand will be assumed as industrial demand only.
As there is a relationship between GDP per capita and industrial demand, data on GDP and current industrial demand will be needed. The future GDP per capita was estimated by extending the past trend and the present industrial demand was scaled to the current GDP per capita, such that a relationship was obtained between the amounts of water used per $1000. The equation used was:
푠푐푎푙푒 × 퐺퐷푃 푝푒푟 푐푎푝푖푡푎 (3-2)
Estimated future water supply and demand | 15
3.1.2.1 Estimated future GDP per capita
140,000 y = 76.491x2 - 304575x + 3E+08 120,000 R² = 0.963 100,000 80,000 Past GDP per GDP per capita capita (S$) 60,000 Poly. (Past GDP 40,000 per capita) 20,000 0 1990 2000 2010 2020 2030 Year
Figure 3-3: Past and estimated future GDP per capita
The future GDP per capita was estimated based on the past trend. A polynomial trend line of order 2 was selected as it fits the data the most.
Table 3-6: Estimated future total industrial demand Estimated Estimated Current total Amount of future future total non- domestic water used total Year GDP per capita (S$) industrial demand per $1000 industrial demand (litres/day) (litres) demand (litres/day) (mgd) 2014 71,318.00 1,005,456,821 14,098,220 2020 98,332.75 1,386,316,730 304.9 2030 150,471.07 2,121,374,200 466.6 2040 217,907.61 3,072,109,374 675.8 2050 300,642.38 4,238,522,252 932.3 2060 398,675.37 5,620,612,834 1236.4 2070 512,006.58 7,218,381,120 1587.8
Estimated future water supply and demand | 16
3.1.3 Estimated future daily demand
Table 3-7: Estimated future daily demand Percentage of Percentage of Daily demand Year domestic demand industrial demand (mgd) (%) (%) 2020 500.5 39.1 60.9 2030 670.3 30.4 69.6 2040 880.5 23.3 76.7 2050 1132.5 17.7 82.3 2060 1428.0 13.4 86.6 2070 1767.4 10.2 89.8
3.2 Estimated future supply
According to PUB, plans are made to ensure that NEWater and desalination can meet
80% of our water demand by 2060. With the expansion of the Changi and Kranji
NEWater factories and the implementation of Tuas NEWater factory, by year 2030 the capacity of NEWater plants will increase by more than 160mgd. There will be plans to increase capacity of Changi NEWater plant by more than 50mgd over the next 5–10 years and a new Tuas NEWater factory with an initial plant treatment capacity of
25mgd. The Kranji NEWater plant will be expanded by 22,710 m3/d (5mgd).
A third desalination plant, Tuas 3 seawater desalination plant, will be in operation by the end of 2016 (Global Water Intelligence, 2014). It will have an initial capacity of
136,260 m3/day (30mgd). The remaining 20% will be met by our local catchment and
VSP.
Estimated future water supply and demand | 17
4. Sustainability index
The water resource sustainability index (SI) is used to define sustainability of the water resource. If the water supply is greater than the water demand, then
푤푎푡푒푟 푠푢푝푝푙푦 − 푤푎푡푒푟 푑푒푚푎푛푑 (4-1) 푆퐼 = 푤푎푡푒푟 푠푢푝푝푙푦
If the water supply is less than or equal to the water demand, then
(4-2) 푆퐼 = 0
Therefore, the water supply should at least be greater than the water demand in order to be sustainable. The SI was not calculated as the supply for the years of calculated demand was not known.
Sustainability index | 18
5. Discussion
5.1 Future demand
There are uncertainties in the results of estimated future demand. The future population presented in Table 3-2 was estimated based on polynomial trend. However, actual population is dependent on factors such as birth/death rates, immigration/emigration rates. Table 3-3 presents a more realistic estimate of the future population. The future per capita demand was estimated using the least square method in a linear trend. However, future per capita demand may not follow a linear trend and is affected by weather and conservation measures implemented. The future
GDP per capita was estimated based on polynomial trend. However, GDP is an economic product and there is an economic way of forecasting annual growth rate.
Since the results were based on extrapolation, the further the estimated year, the more uncertainty it carries.
5.2 Future supply
The most possible future sources of water supply are local catchment, NEWater and desalination. The chance of Singapore renewing the water agreement with Malaysia is not high given the past unsuccessful negotiations and the complex relationship between the two countries. The chance of importing water from Indonesia is very low, as the construction cost of the submarine pipeline is around half of the construction cost. Besides, the project has been delayed for a long time with no update. Whichever is the case, the supply needs to be greater than the estimated future demand to ensure sufficiency and sustainability.
Discussion | 19
5.2.1 Desalination
Desalination methods can be divided into four categories (Ghalavand, Hatamipour, &
Rahimi, 2014). They are thermal, crystallization, membrane, others. Under the membrane category there are four methods: Reverse Osmosis (RO), Forward Osmosis
(FO), Electro Dialysis (ED) and microbial cell. The technology adopted in Singapore is Seawater Reverse Osmosis (SWRO).
5.2.1.1 Reverse Osmosis (RO)
RO is the most commonly used technology in membrane desalination where the process is based on separation. In this process, water flows opposite to the natural flow across the membrane as an external pressure higher than the osmotic pressure is applied on the sea water to overcome the osmotic pressure. This leaves the dissolved salts behind the membrane. Since no heating or phase separation change is required, it is the most energy efficient desalination process in practice (Baten & Stummeyer,
2013). Most of the energy required for desalting is for the pressurizing of the sea water feed as much energy is used for pumping, due to the high pressure gradient.
Figure B-3 shows the typical operation cost in a RO process.
A typical large SWRO plant consists of feed water pre-treatment, high pressure pumping, membrane separation, and permeate post-treatment. The major design considerations for sea water RO plants are the conversion or recovery ratio, flux, membrane life, permeate salinity, power consumption, and feed water temperature.
The power consumption is about 2–5 kWh/m3 of water processed.
5.2.1.2 Forward Osmosis (FO)
Unlike RO, FO requires osmotic pressure instead of hydraulic pressure. A concentrated solution of high osmotic pressure called draw solution is used so that
Discussion | 20
water can be induced to flow from saline water across the membrane, leaving behind the salt. The draw solution is now diluted and needs to be re-concentrated before the system can yield potable water, and the process repeats. Figure B-4 illustrates the general process of FO.
As compared to RO, FO has more desalination flux and uses less pumping energy.
Figures B-5 and B-6 show the comparison of flux between FO and RO and energy consumption between FO and other processes respectively. Researchers at Yale
University and in Singapore are looking into FO technology (Likhachev & Li, 2013).
5.2.1.3 Towards sustainability
Over the years, the market share of SWRO has increased steadily in countries of
Cooperation Council for the Arab States of the Gulf (GCC) and non-GCC countries.
On top of this, substantial efficiency improvements have been achieved through energy recovery, improved membrane characteristics, improved pump efficiencies and the use of variable frequency drives for controlling the pump heads. As compared to plants being built in the 1980s with specific power demand as high as 10kWh/m3, the SWRO plants now require approximately 3–5kWh/m3, depending on specific conditions and constraints such as temperature and salinity of seawater, and the detailed process configuration (Baten & Stummeyer, 2013).
There does not seem to have any technology now with the potential to bring the energy efficiency of SWRO lower. However, renewable energy may have a potential to improve the sustainability of desalination since almost all desalination plants today are powered by fossil energy.
Discussion | 21
Singapore receives modest amounts of insolation and is often interrupted by clouds on most days. It is calculated that 40km2 of photovoltaic (PV) solar panels would be required to power Singapore, so solar energy does not seem feasible as it is expensive.
Singapore has low wind speeds and large wind farms cannot be built with limited land and sea areas. Tapping on wave or tidal energy is not feasible as waves which are more 1 meter (m) in height are rare in the Singapore Straits (Friess & Oliver, 2015).
It has been reported that hot springs are found in Singapore (Michelle, Palmer, Oliver,
& Tjiawi, 2013). A study was carried out by (Michelle et al., 2013) on the feasibility of having geothermal desalination in Singapore. It was found that even though it is possible to have geothermal desalination in Singapore and the cost of operation may be less than that of a SWRO plant, it does not seem economically feasible to invest in geothermal desalination in Singapore with the current knowledge of the geothermal resource. Further research would need to be done to know more about the geothermal resource and to determine if geothermal desalination is feasible in Singapore.
Otherwise, the cold energy released from the cooling of Liquefied Natural Gas (LNG) can be used for desalination by freezing (Efrat, 2011) since Singapore handles the distribution of LNG (Friess & Oliver, 2015).
5.2.2 NEWater
NEWater is produced from a three-stage production process known as Microfiltration
(MF), Reverse Osmosis (RO) and Ultraviolet (UV) disinfection (PUB, 2015a).
In the process of MF, the treated used water is passed through membranes so that suspended solids, colloidal particles, disease-causing bacteria, some viruses and
Discussion | 22
protozoan cysts are filtered and retained on the surface of the membrane. The filtered water therefore contains only dissolved salts and organic molecules. In RO, a semi- permeable membrane with very small pores is used. It allows only very small molecules like water molecules to pass through, excluding contaminants such as bacteria, viruses, heavy metals, nitrate, chloride, sulphate, by-products of disinfection, aromatic hydrocarbons, pesticides which are undesirable. The water is then free from bacteria, viruses and the amount of salts and organic matters it has is negligible.
After going through RO, the water is already of high quality. As a safety precaution,
UV disinfection is used to ensure the inactiveness of all organisms and the purity of the product water. The NEWater is then ready for use after some alkaline chemicals are added to restore the pH balance.
Similar to desalination, the use of geothermal as a replacement of the existing source of energy for RO in the process of NEWater or the adoption of FO instead can be considered to improve the sustainability of NEWater.
Discussion | 23
6. Conclusion
The fact that Singapore is enjoying a reliable and diversified water supply, credit has to be given to PUB and the government of Singapore. Since imported water from
Malaysia is one of the cheapest sources of water supply, effort has been made to engage in negotiations on the renewal of the water agreement. On top of that, PUB is always looking into new ways to augment our water supply. This can be seen from the researches in VSP and groundwater, and also attempts to diversify our water import from Malaysia and Indonesia. Researches are also conducted for the processes of desalination and NEWater to decrease the energy use.
The sustainability of our water resources is managed from the supply and demand sides. It is ensured that the people have access to drinking water sources of good quality and improved sanitation. The UFW has also decreased over the years with comprehensive maintenance regime to reduce wastage. The water tariffs also reflect the scarcity value of our water with the Water Conservation Tax (WCT) and Sanitary
Appliance Fee (SAF) and Waterborne Fee (WBF). This is logical as higher water prices encourage conservation and the result is seen from the decreasing per capita demand over the years.
Sustainability of the water supply is achieved when it is sufficient and affordable in terms of resources used to meet the current and future demand. The sustainability of the local catchment depends on the weather. It might not be that sustainable if
Singapore experiences more frequent droughts in the future as the volume collected would be affected. In addition, higher temperature could increase the concentration of water pollutants and make the local catchment more prone to pollution. VSP would be
Conclusion | 24
more sustainable since it can produce clean water from the rain water collected or perform seawater desalination otherwise. The same goes for imported water from
Malaysia as climate change affects not only Singapore. It seems to affect Malaysia more, as seen from the occasions of water rationing due to dry spells. Desalination and NEWater can be more sustainable if the researches on decreased energy use are successful.
The work done in this thesis could be better. Besides the extrapolation of data which might lead to greater uncertainties for results in the further years, equation 3-1 is also not comprehensive. Per capita demand is also affected by the weather, for example drier weather will see an increase in per capita demand. However, it is not taken into account. On top of that, climate change may result in unreliable supply from the local catchment due to droughts and floods.
An integration of the above using system dynamics may be possible if the governing equations are known. System dynamics has been widely used in water resources planning and management. It enables the understanding of the behaviour of complex systems over time and captures the internal feedback loops and time delays that are affecting the behaviour of the entire system (Xi & Poh, 2014).
It might also be useful to compare the current demand among different countries to have a better idea of the water demand situation of Singapore.
Conclusion | 25
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Appendices
A. Articles read
Brown, Thomas C., Foti, Romano, & Ramirez, Jorge A. (2013). Projected freshwater
withdrawals in the United States under a changing climate. Water Resources Research,
49(3), 1259-1276. doi: 10.1002/wrcr.20076
Kiguchi, Masashi, Shen, Yanjun, Kanae, Shinjiro, & Oki, Taikan. (2014). Re-evaluation of
future water stress due to socio-economic and climate factors under a warming
climate. Hydrological Sciences Journal, 60(1), 14-29. doi:
10.1080/02626667.2014.888067
Onn, Lee Poh. (2003). The Water Issue Between Singapore and Malaysia: No Solution In
Sight? - The Water Issue Between Singapore and Malaysia: No Solution In Sight?1.
ISEAS Working Papers.Economics and Finance, 1.
Shen, Yanjun, Oki, Taikan, Kanae, Shinjiro, Hanasaki, Naota, Utsumi, Nobuyuki, & Kiguchi,
Masashi. (2014). Projection of future world water resources under SRES scenarios: an
integrated assessment. Hydrological Sciences Journal, 59(10), 1775-1793. doi:
10.1080/02626667.2013.862338
Appendices | 29
B. List of figures
Figure B- 1: Access and efficiency standards, adapted from (Ministry of the Environment & Water Resources, 2014)
Figure B- 2: Key figures of water supply and demand data, adapted from (Ministry of the Environment & Water Resources, 2014)
Appendices | 30
Figure B- 3: Typical operation cost in RO, adapted from (Ghalavand et al., 2014)
Figure B- 4: General process of FO, adapted from (Ghalavand et al., 2014)
Figure B- 5: Comparison of flux between FO and RO, adapted from (Ghalavand et al., 2014)
Appendices | 31
Figure B- 6: Comparison of energy consumption between FO and other processes, adapted from (Ghalavand et al., 2014)
Appendices | 32
C. List of data
Table C- 1: Population data
Year Total Population 1995 3,524,506 1996 3,670,704 1997 3,796,038 1998 3,927,213 1999 3,958,723 2000 4,027,887 (Census) 2001 4,138,012 2002 4,175,950 2003 4,114,826 2004 4,166,664 2005 4,265,762 2006 4,401,365 2007 4,588,599 2008 4,839,396 2009 4,987,573 2010 5,076,732 (Census) 2011 5,183,688 2012 5,312,437 2013 5,399,162 2014 5,469,724
Appendices | 33
Table C- 2: Per capita domestic demand Per capita domestic demand Year (litres per capita per day) 1995 172.0 1996 170.0 1997 170.0 1998 166.0 1999 165.0 2000 165.0 2001 165.0 2002 165.0 2003 165.0 2004 162.0 2005 160.0 2006 158.0 2007 157.0 2008 156.0 2009 155.0 2010 154.0 2011 153.0 2012 152.0 2013 151.0 2014 150.4
Appendices | 34
Table C- 3: GDP per capita
Year S$ 1995 35,346 1996 37,031 1997 39,179 1998 36,525 1999 36,944 2000 41,018 2001 38,660 2002 39,423 2003 41,070 2004 46,320 2005 49,715 2006 53,355 2007 59,114 2008 56,201 2009 56,111 2010 63,498 2011 66,816 2012 68,205 2013 70,047 2014 71,318
Appendices | 35