Water Scarcity[edit | edit source]
Water makes up 75% of the Earth’s surface. Ninety-seven percent of this waster is in oceans, which is saltwater. This leaves only 3% of fresh water that is fit for human consumption, which are found in groundwater, rivers, and lakes. Less than 1% is actually within human reach. This means that available freshwater resources are limited and being increasingly depleted at fast rates. The Earth does have freshwater reserves under its surface, but it is too deep to access in an economic efficient manner. Water scarcity is a worldwide problem. In 2005, 2.8 billion people lived in areas under severe water stress. By 2030, the OECD Environmental Outlook estimates that this number will increase by about 1 billion, which means about 3.9 billion people will be struggling to get water. That would be 47% of the population (Khawaji, 2008).
Many semi-arid and arid regions suffer from water shortages. Another problem is that damage is caused if water abstraction rates exceed natural renewal rates, leading to depletion of salinization of water and land desertification.
Increasing amounts of freshwater will be needed in the future with population rise and increase living standards. That is why technologies, like desalination are becoming important to many countries, like the United Arab Emirates. Looking at the Jebel Ali Plant in Dubai, which just opened their M station, seeing how sustainable desalination is important.
History of Dubai[edit | edit source]
Unlike western cities, Dubai went from pre-industrial to industrial to post-industrial in only 50 years, rather than over a century. It progressed from a fishing settlement on the Arabian Gulf to a dominant 21st century city. It is seen as one of the most successful cities of the 1990s measured by economic growth and real estate activity. Current unemployment is low at about 5%. GDP per capita is more than five times that of its largest neighbor. GDP per capita is well in excess of other states in the region. It has a high of about five million annual visitors, which is more than Egypt or India. The pearl industry was the economic base in most of the 19th century (Pacione, 2005).
The city had an economic boost in 1902 when Persia imposed a high custom duties on merchants operating from their ports. This created a transfer of the Indian trade along with merchants, craftsmen, and their families, to the ports of Dubai. Early decades of the 20th century being the key distribution center for trade with the interior, also became main port where goods from India where re-exported to Persia and neighboring countries.
Following the discovery of petroleum offshore in 1966, the development of the ore industry revolutionized the economy and society of Dubai. Oil revenues enabled government to undertake major infrastructure and industrial projects, like the construction of Port Rashid, the dry dock, an aluminum smelter, and the Jebel Ali port and industrial area. In addition, the local merchant community was very important because many had connections to international contacts (Pacione, 2005).
Urban development had four major phases in Dubai: 1900-1955, 1956-1970, 1971-1980, 1980-Present. Rapid population growth: 1833: 1,500 1900: 10,000 1968: 59,000 1985: 370,788 1995: 689,420 2000: 862,387 53% born abroad 2002: 961,000 Source: Pacione, 2005
Dubai had two major reasons for such rapid growth. First is immigration. The economic expansion based on oil industry created demand for labor and expertise that could only be satisfied from abroad. The second was a natural increase. The city began to have higher fertility rates and a decrease in infant mortality rates, and in addition, an increase in life expectancy due to modern health care. Currently, it is facing the challenge of providing adequate infrastructure and services to rapidly growing city. (Pacione, 2005)
Desalination[edit | edit source]
Global water consumption levels have increased dramatically over the past century. Many places, like the Middle East and North Africa are having challenges of exceeding the limits of renewable water resources. Fortunately, costs of desalination and its energy intensity have been reduced over past decades. Desalinated water is the main source of potable water in the Middle East.
Currently, the global capacity is about 32 million m3, with more than 15,000 desalination plants. This is sufficient to supply about 160 million people (Schiffler, 2004). A hot spot of intense desalination has been the Arabian Gulf, but has spread to the Mediterranean Sea, Red Sea, California, China, and Australia. Seventy-seven percent of desalination plants are in the Middle East and North Africa. Followed by Europe with 10%, the Americas with 7%, and the Asia-Pacific with 6% of the plants. The Arabian Gulf has capacity of 11 million m3/day. The main producers in the Gulf are United Arab Emirates, Saudi Arabia, and Kuwait. In the Mediterranean, Spain is largest in the region with 7% of worldwide capacity. The Red Sea makes 14% of worldwide capacity which is 3.4 million m3/day. Looking in the future, worldwide desalination is increasing at a rapid pace (Lattemann, 2008).
Desalination is not only for seawater. Current trends show that for the process of desalination, the source water is usually seawater with 58% of production. Brackish water makes up 22% of desalination source water and 5% is wastewater. Desalinated water is an excellent water source for industrial processes needing high quality water. Desalinated water for irrigation is less common but may increase significantly. Currently, it is only feasible if high value crops are grown (Schiffler, 2004).
The cost of desalinated water is one of the most important factors. Eighty percent of the costs of desalination comes from energy consumption and investment costs. Energy consumption is dependent on process design, type of membrane, energy recovery system, quality of desalinated water, wastewater disposal systems, and pumping systems for pumping (Lapuente, 2012). About 0.7 kWh/m3 is theoretically the minimum energy required to obtain freshwater from seawater. In reality, it ranges from 3-15 kWh/m3. Many countries using desalination have significant domestic fossil energy sources, so energy sources are not a problem (Schiffler, 2004).
Investment costs are the start-up costs, including land, construction, and infrastructure costs needed to have the plant operational. The average financial cost of desalination is US $0.45 – 0.70/m3. In arid countries, water cost from distant conventional water sources, like dams, is often close or higher than desalination. Another cost improvement for desalination is plant life. Plant lifetimes have increased. Previously, plant lifetime was less than 15 years. Now it is about 20-25 years (Schiffler, 2004).
Many desalination technologies developed in last several decades to help supply freshwater. Seawater desalination process separates saline seawater into 2 streams: a freshwater stream containing a low concentration of dissolved salts, and a concentrated brine stream. Seawater is unsuitable for human consumption and for industrial and agricultural uses. By removing salts from the unlimited supply of seawater, desalination is important source of freshwater. Some countries depend on desalination technologies for the purpose of meeting their freshwater requirements. In the Middle East, seawater desalination is a vital and dependable freshwater water resource in countries such as Saudi Arabia, UAE, and Kuwait (Khawaji, 2008).
Desalination processes are thermal, distillation, and membrane processes. Some of the most important technologies are multi-stage flash, reverse osmosis, and multiple-effect distillation. Most new plants use membrane technologies, especially reverse osmosis.
Desalination helps reduce the pressure on conventional water resources and relieves pressure on overexploited water bodies. In addition, desalinated water is free from pathogens, which may be helpful for some developing countries. The water actually needs to be re-mineralized before drinking (Schiffler, 2004).
Controversy
Desalination is a controversial technology. It has had environmental and health problems. These problems have been reduced through technological progress. Many Impacts still remain, especially during operating phase of plants. One of the biggest environmental problems is the discharge of brine, which is a by-product of desalination. The brine is a concentrated salt solution that is hot and contain chemicals. This is usually released back into the sea, which can impact the coastal or marine ecosystems. The warm brine can actually change the temperature of the water making the habitat unlivable for some species. This can change the makeup of the biodiversity (Schiffler, 2004).
The other key impact to the environment is the greenhouse gas emission in the production of electricity and steam needed to power plant. It is a very energy intensive process, which can pollutant the air.
Another problem is the source water intake. Basically, large pipes are put in the ocean to take in seawater. Some loss of aquatic organisms who collide with intake screens or are drawn into plant with water have been a problem (Lattemann, 2008). In addition, noise, visual disturbance, interference with public access and recreation, and the potential accidental oil spills are concerning (Schiffler, 2004).
Heavy metals are another problem. Copper-nickel alloys commonly used as heat exchanger materials in distillation plants. Copper concentrations in reject stream of 15-100 ug/L. USA EPA recommends copper concentrates of 4.8 ug/L for brief exposure and 3.1 ug/L for long term. Anti-scalants prevent scale formation. This in the reject stream can cause a problem of eutrophication. Coagulants for coagulation and media filtration. Intense coloration of reject streams, red, which may increase turbidity and reduce light penetration. Also in reject streams: antifoaming agents, cleaning chemicals (Lattemann, 2008).
Desalination plants should take steps to mitigate impacts on environment. Source water intakes use combination of different meshed screens and low intake velocity, so that prevents any animals from being sucked in. Energy use has the potential for renewable energy use. Site selection is also important. Ecosystems and habitats should be avoided, if unique, protected, endangered, important for feeding or reproduction in area. The site should be close to sea, to water distribution networks and consumers to avoid construction and land use pipe lines and pumping efforts for water distribution. Allow energy connection to other infrastructure, like roads and power grid (Lattemann, 2008).
Jebel Ali Desalination Plant[edit | edit source]
The Jebel Ali M station was officially opened on April 8, 2013. It is the UAE’s largest power and desalination plant. The Dh10 billion gas-fired M-station joins the other plants operated by Dubai Electricity and Water Authority (Dewa) at Jebel Ali. It has increased efficiency which means less fuel is needed to produce a given amount of power. A surcharge on power and water bills is linked to the price Dewa pays for the fuel it uses at plants. The efficiency of plants are 82%, while in Europe the efficiency is only 45%.
The plant capacity of 2,060 Mega Watts and 140 million gallons of water a day. It has six gas turbines that generated power and hot exhaust gases are fed through boilers that heat seawater to produce steam. Steam is either used to drive steam turbines, producing more power, or fed through the eight desalination units to produce drinkable water. The plant’s flexible design means the amount used for each purpose can be adjusted to meet their demands. Desalination units are the largest individual ones of their kind in the world. Using the waste heat in order to produce water or power. Advanced technologies have reduced greenhouse gas emissions and generate power and water with a minimal carbon footprint. The plant was opened by Sheikh Hamdan bin Rashid, the Deputy Ruler of Dubai, Minister of Finance, and the president of Dewa.
The M station cost US $2.72 billion. It consists of six 234 megawatt gas turbines and eight multi-stage flash desalination units, each producing 80,000 m3 per day of water. Gas turbines are able to burn diesel, if principle natural gas lines fail, there is enough diesel stored at plant to keep working for ten days. The desalination plant contracted was Italy’s FISIA
The M station goal is to increase electricity and water production capacity to meet the economic growth. Huge pipes draw in up to a billion gallons of water from the Arabian Gulf per day. Pipes that feed the other Jebel Ali stations stretch one kilometer out to sea, but M station ones are just offshore. This is a precaution to prevent operations being affected by spills from oil tankers out in the Arabian Gulf. In the event of a spill, booms would be placed around intakes to shield them from floating oil and enable the M station to continue to operate, while other plants would have to be shutdown. (Jebel Ali M Station officially opened, 2013; Dubai Water and Electricity Authority).
Comparison to Other Desalination Methods[edit | edit source]
Multi-Stage Flash (MSF)
The Jebel Ali Plant uses Multi-Stage Flash (MSF) desalination technology. It is the most widely used thermal desalination technology. It accounts for 90% of all thermal desalination production. It is also the most robust of all desalination technologies and is able to process water at a very high rate with little maintenance. It is capable of producing large yields of desalted water. It operates using four to forty chambers, or stages, each with successively lower temperature and pressure, to rapidly vaporize water, which is condensed afterwards to form freshwater. It operates at top brine temperatures of 90-120 degrees Celsius. The capital and energy costs are the highest of all desalination technologies. It also requires larger land area and materials, making it also have the largest footprint (Thye, 2010).
Forced outage of larger plants, even for short periods, creates serious problems due to the limited storage capacity of desalted water. MSF system is preferred because of its high availability. MSF known for high energy consumption compared to other systems, more MSF units are still ordered and contracted in the Middle East especially for large capacity units (Darwish, 2002).
Reverse Osmosis (RO)
Another type of desalination technology is reverse osmosis (RO). RO is a membrane desalination technology. Globally, it is the most used desalination technology. This is the most dominant membrane technology at 88% of all membrane desalination. During RO, salt water is pumped with high pressure through semi-permeable membranes made of synthetic materials that only allow water to pass, leaving salts and contaminants behind in a brine. It is made up of four subsystems: pretreatment, high pressure pump, membrane modules, and post treatment. There are two different types of membranes that can be used, spiral wound or hollow fiber. RO is available in a wide range of capacities, the largest plant currently has a capacity of 320,000 m3/day. RO has a low capital cost but significant maintenance costs due to the high cost of membrane replacement. The membrane life expectancy can be as little as five to seven years. The majority of the energy is required to drive the high pressure feed water pump system. RO systems are vulnerable to feed water quality changes. There is also an issue of mechanical failures due to high pressure operation (Darwish, 2002).
Reverse osmosis (RO) is the main competitor of MSF systems. It has reductions in costs and energy intensity and is reliable. RO became more attractive by continuous improvements in membrane materials. Main advantages of RO over MSF are: consumes less energy, no need to combine power plant or interfere with its operation, has simple on and off operation, delivered in modules, no need to shut off the whole plant for emergency or routine maintenance (Darwish, 2002).
Multiple-Effect Distillation (MED)
Multiple-Effect Distillation (MED) is a thermal desalination technology like MSF. It uses vapors produced by eight to sixteen chambers subsequently condenses into distillate in the following chamber group by reducing ambient pressure. Maximum temperature of 70 degrees Celsius. This technology was actually developed by the chemical industry. Units are generally built at capacities of 600 to 30,000 m3/day. Similar to the MSF, the MED technology has significant energy costs (Thye, 2010).
Comparison
In order to compare the three desalination technologies, the cost, energy consumption, and renewable energy potential was looked at. As the following two charts show, the distribution of technologies globally and within the UAE are different. Globally, RO is used primarily, while in the UAE, the MSF technology is used most often.
Looking at another comparison shows a similar result (Thye, 2010). The cost of RO is between $0.92-3.56 per m3, MED is between $0.90-3.06, and MSF is between $1.36-4.30. The MSF is the most expensive total cost without investment and investment costs allow are larger than the other two.
Energy is also a factor when deciding which technology is best. Energy uses a significant of thermal and/or electrical energy. For one cubic meter of water, 55-220 kWh of thermal energy and 4-6 kWh of electrical energy is needed in a MSF plant. MSF Plants operates at an average of 112 degrees Celsius. MED operates at lower temps of <70 degrees Celsius. One cubic meter of water takes about 40-220 kWh of thermal energy and 1.5-2.5 kWh of electrical energy. RO does not need thermal energy and just uses electricity of about 2.8-12 kWh. It also operates at lower temperature of under 40 degrees Celsius (Lattemann, 2008).
Renewable energy is becoming more and more prominent in the world’s energy. Looking for technologies that work with renewable energy is important because our fossil fuels are in limited supply. Many countries do not want to rely on foreign oil to supply their country with energy. One researcher looked into the potential for renewable energy use in desalination technologies. RO has the most potential for renewable energy source. It can work with both wind and solar energy. MSF and MED technologies need thermal energy and solar thermal energy is the only way to get the heat needed from a renewable energy source.
Conclusions[edit | edit source]
After comparing the costs, energy use, and renewable energy potential, the most sustainable option would be to use reverse osmosis desalination technology rather than the multi-stage flash technology. Also, it is noticed that MSF technology dominates the UAE, which is most likely because of their source of energy is from domestic fossil fuels. Unlike many countries who are trying to not be dependent on foreign fuels, the UAE continues to use fossil fuel technologies because it has its own large stock. This is probably why they continue to use MSF technologies in addition to its large production capacity.
The most sustainable option would be to conserve water rather than desalination of new sources. This would be the best, economically and environmentally.
References[edit | edit source]
Darwish, M.A., Al Asfour, F., Al-Najem, N. “Energy consumption in equivalent work by different desalting methods: case study for Kuwait.” Desalination 152 (2002): 83-92.
Dubai Water and Electricity Authority (DEWA). “Electricity. Power and Desalination Plants Installed Capacity for the Year 2012.” Government of Dubai. http://www.dewa.gov.ae/aboutus/electStats2012.aspx
“Jebel Ali M Station officially opened in Dubai.” Desalination and Water Reuse. (April 9, 2013). http://www.desalination.biz/news/news_story.asp?id=7018&title=Jebel+Ali+M+Station+officially+opened+in+Dubai
Khawaji, Akili, Kutubkhanah, Ibrahim,Wie, Jong-Mihn. “Advances in seawater desalination technologies.” Desalination 221 (2008) 47-69.
Lapuente, Enrique. “Full cost in desalination. A case study of the Segura River Basin.” Desalination 300 (2012): 40-45
Lattemann, Sabine, and Thomas Höpner. "Environmental impact and impact assessment of seawater desalination." Desalination 220.1 (2008): 1-15.
Mezher, Toufic, Fath, Hassan, Abbas, Zeina, Khaled, Arslan. “Techno-economic assessment and environmental impacts of desalination technologies.” Desalination 266 (2011): 263-273.
Pacione, Michael. "Dubai." Cities 22.3 (2005): 255-265.
Schiffler, Manuel. “Perspectives and challenges for desalination in the 21st century.” Desalination 165 (2004): 1-9.
Simpson, Colin. “UAE’s largest power and desalination plant opens at Jebel Ali.” The National. (April 9, 2013). http://www.thenational.ae/news/uae-news/uae-s-largest-power-and-desalination-plant-opens-at-jebel-ali
Thye, John. “Desalination: Can it be Greenhouse Gas Free and Cost Competitive?” Yale School of Forestry and Environmental Studies. May 9, 2010.
