• 
• Japanese
• 
• IETC's Focal Area
• Waste Management
• Publications & Tools
• Meetings & Workshops
• Global Partnership on Waste Management
• Water and Sanitation
• Publications & Tools
• Meetings & Workshops
• Resources
• Publications & Tools
• About IETC
• Background and History
• Director
• Activity Reports
• Supporting Foundations
• Contact Us

2. Water Quality Improvement Technology

The limited freshwater resources in most of the Arab countries of West Asia was the impetus to search for sources to help satisfy the increasing water demands, especially for drinking and domestic purposes. This is a primary rationale for all the Gulf countries to expand their construction of seawater desalination plants, as well as to expand their activities in desalinization of highly-saline groundwater. There is no doubt that the availability of energy at a reasonable cost, as well as the expansion of many residential concentrations near coastal areas, has facilitated the expansion of seawater desalination plants in these countries. Further, the countries have concluded that transporting natural water over long distances to supply such residential communities is very costly, compared to desalination of saline water.

Tin a reasonable cost, in addition to the spread of most of the residential concentrations near the coast, has helped these countries to expand in establishing seawater desalination plants. These countries have also realized that transporting natural water for long distances to supply these residential communities is costly, compared to the desalination of saline water.

Water desalination technologies have been used in the Gulf countries for a half century, with their use expected to multiply in the next 20-25 years, increasing at the rate of about 7%, based on data from International Atomic Energy Agency (IAEA, 1999). The production of the desalinated water in the Gulf countries currently comprises about 60% of the total volume of desalinated water in the world. For the rest of the West Asia region countries, the use of desalination technology is still limited, primarily because of the high costs. The estimated volumes of desalinated water in Jordan is 3.08 million m³/year, Syria - 2.00 million m³/year, Iraq - 121.00 million m³/year, Lebanon - 1.70 million m³/year, and Yemen - 5.00 million m³/year.

At the same time, the use of wastewater, including drainage water of all types, is also starting to attract the attention of the Arab countries of West Asia, as a means of augmenting freshwater resources. The construction of sanitary drainage water treatment plants (and agricultural drainage on a smaller scale) has increased, and the water is being used to irrigate some agricultural crops and green fields, and to artificially recharge groundwater. Use of this water source for domestic purposes is still limited because of health and social considerations. The quantity of treated wastewater in the West Asia region is estimated to be about 362.2 million m³/year (ACSAD, 1997). Expansion of the reuse of treated sanitary drainage water will doubtless become an essential strategic choice, especially in view of the large quantities of water needed for domestic purposes.

It also is noted that artificial groundwater recharge technologies, using treated sanitary drainage water or floodwater, will help improve its water quality, due primarily to infiltration of the water through the permeable soil separating the aquifer from the ground surface. Injection of freshwater into brackish groundwater aquifers also improves its quality. The injected freshwater is typically from conventional sources or from the excess water production of desalination plants.

2.1 Water Desalination Technologies

Water desalination technologies can be categorized on the basis of the energy used to run them, usually thermal or electric. The technologies utilizing thermal energy are known as the multi-stage flash (MSF), multiple-effect distillation (MED) and vapor compression (VC). The desalination technologies that use electric energy rely on a membrane system, such as reverse osmosis (RO) and electro dialysis (ED). There also are other technologies that rely on solar energy or combined electric and thermal energy. Each of these technologies has advantages and disadvantages, based on the quantity and quality of the required water and the location. The distributon of the different technologies among the countries of the West Asia region is outlined in Table 9. The multi-stage flash technology (Figure 42) is the most-used technology for the Arabian Peninsula. Table 9 also illustrates the types, capacities and numbers of desalination plants in a number of Arab countries, as well as the technologies being used (Tayseer Dabagh and Ahmed Belhag, 1997).

Table 9. Types, capacities and number of desalination plants in some countries of the West Asia region

2.1.1 Distillation Desalination (DD)

Distillation desalination is considered one of the oldest technologies used in desalination of seawater and saline water. It was developed over several decades, and several different technologies have evolved from it, including multi-stage flash (MSF), multiple-effect distillation (MED) and vapor compression (VC). This has facilitated the widespread use of the seawater distillation desalination technology.

Figure 42. Annual capacity of desalination plants in the Gulf countries

Multi-Stage Flash Desalination (MSF)

Technology Description

This technology is based on passing the water to be desalinated into a container and heating it to high temperatures, causing it to boil and the pressure in the container to decrease. A part of the water flashes to a vapor stage, while the rest of the hot water continues flowing through a series of chambers or stages. These chambers exhibit gradually-decreasing temperatures and pressures, leading to the transformation of the water into vapor (the pressure in each chamber is maintained at values less than the level of saturated vapor pressure). With this procedure, the water loses some of its salt in each stage, and the salt remains with the residuals. The vapor is then condensed, transforming it into liquid freshwater. This technology requires the water to pass through at least 20-25 chambers, and the desalination efficiency improves with increasing numbers of chambers (Figure 43). The cost of the initial construction works, as well as the economic return, increases with the number of chambers. The first system to employ this technology was established in Kuwait in 1977. Since then, its use has increased to about 70% of the total desalination plants. Despite introduction of a new technology in the early-1990’s, 50% of the plants still use the MSF method. It has a high recovery rate in producing freshwater (less than 30 particles/million). The required temperatures ranges between 90-110 degrees.

Figure 43. Multi-stage flash desalination process

The MSF technology is one of most popular systems in the Gulf countries, with the existing installed capacity of the systems being about 8.28 million m³/day. This is approximately 72% of the desalination capacity of these countries. Having first been used in the 1950’s, this technology represents the oldest water desalination system used in the region. The technology has proven its effectiveness and spread to the other countries in the region. A feature of the technology is that it can utilize excess thermal energy. Thus, it is possible to combine the production of large amounts of power and water in one station, thereby satisfying the demand for both of them. More attention is given to the distillation system, especially because of its high durability under various conditions and its ease in treating raw water (usually seawater), compared to the reverse osmosis method used in the rest of the world.

Multiple-Effect Distillation Desalination (MED)

This method was widely used before the MSF method. The water is pumped through a series of heated horizontal tubes to evaporate it. The water usually passes outside the horizontal evaporation tube (Figure 44), where water is sprinkled. In some small units with small capacities, the water is evaporated inside vertical evaporation tubes (Figure 45). The vapor resulting from each stage is condensed in the following stage, where it can be used as a thermal source for evaporation. Thus, the process proceeds in a chain reaction form, with each evaporator also serving as a condenser for the vapor resulting from the previous stage. The vapor resulting from the last stage is condensed and released into the cooling system. Energy consumption is reduced if the vapor pressure is captures again (thermally or mechanically) in the last stage. The required heating temperature is 65^o C. This method has a recovery rate between 40-65%. However, its operational and maintenance difficulties have resulted in its declining use.

Figure 44. Conceptual diagram of horizontal-tube multi-effect distillation process

Figure 45. Conceptual diagram of horizontal multi-effect with vertical stacked effects

Based on the nature of the vapor production, there are few types of this technology. Examples include Thermo-Vapor Compression (TVC) and the Mechanical Vapor Compression (MVC). These systems can produce desalinated water in small amounts, and they operate independently of power generation plants.

Table of Contents

• Brochure
• 
• 



• International Year of Forests
• 
• 



• World Environment Day
• 
• 



• UNEP Campaign
• 
•