The project has been ten years in the planning stages, five years in obtaining the appropriate California permits, and two and a half years in construction. It is designed to meet all regulatory standards for drinking water, and has obtained full approval from the California Coastal Commission, the State Lands Commission, and the Regional Water Quality Control Board. The locally controlled high-quality water source is expected to be fully functional by the end of 2010 and will have created at least 2,100 new jobs in its making and in its on-going service. Servicing the cities of Carlsbad, San Diego, Encinitas, Oceanside, San Marcos, Solana Beach, Rancho Santa Fe. Escondido, Chula Vista, and National City, as well as the unincorporated cities of Rainbow, Bonsall, and Fallbrook, the Carlsbad Desalination Project stands to ensure residents that they will have an unlimited supply of potable water for personal and agricultural purposes.
What is Desalination?
Desalination is a process whereby saline water is separated into two streams, one in which salt and pollutants have been removed to create fresh water, and the other containing the remaining dissolved salts, non volatile organics, and other waste products, known in the industry as "brine."
How is Desalination Achieved?
There are several processes that achieve desalination. One is Multi Stage Flash Distillation, where salt water is heated in order to produce vapor that is then condensed to form fresh water. This process functions with a series of spaces that contain heat exchangers and condensate collectors. Each stage incorporates a different pressure that relates to the boiling point of water at different stage temperatures. Containing a cold and hot inlet, feed water is pumped in and warmed until it reaches almost maximum temperature. Once it reaches the brine heater, a greater amount of heat is added, whereby the water is then directed back to lower pressure and temperature stages. The water is now considered brine, or waste water, and is heated so that a portion of the brine water boils or "flashes," creating steam. As the steam cools and condenses, the brine is pumped out and discharged, leaving purified water behind.
Another method for desalinating water is Thermal Desalination, where seawater is converted to wet steam by vaporization due to vacuum pressure. The dry component of the steam is then heated by a vapor heater, which condenses and purifies it for potable use. This method uses a turbine exhaust system that helps to minimize the normal heat requirement in order to save energy consumption.
Vacuum Desalination is a method similar to the thermal method and is beginning to be combined with solar power, which helps reduce CO2 emissions during processing. Here a vacuum is created using barometric pressure. The vacuum pressure is created in a vertical tube, operating on the premise that atmospheric pressure supports water in a column up to 9 meters high, and by using a taller tube, liquid then will drop back to create a vacuum. This method allows for a fast rate of evaporation, which in turn uses less energy than conventional desalination processes. Included is an evaporator for circulating heated water, which forces seawater to evaporate. The steam that is then created enters a condenser where fresh water is then extracted and collected.
A third process is Reverse Osmosis or RO technology. Here pressure is applied to water whereby ions, salts, non-volatile organics, and other dissolved solids are separated out, leaving potable water behind. In this modality, the unit draws saline water through small pipes filled with RO membranes, which catch and then discharge the debris. The final product is then piped to a local distribution system where it is available for the population as drinking water. In Reverse Osmosis technology, no heating is necessary to create desalination.
Advantages of Desalination
Because of the increasing scarcity of fresh water resources, desalination is becoming a viable option for use in the global arena. As natural resources such as rivers, lakes, and other bodies of water become more polluted and brackish, finding ways to purify otherwise non-usable water is essential.
Delivering potable water to communities all over the world is key to maintaining health and stability in an environment where we can no longer take this resource's continuing availability for granted. Desalination is becoming crucial for people living in arid areas where water is already scarce, such as in the deserts of the Middle East as well as arid areas in countries like Africa, India and the like. Because desalinated water can also be used to irrigate land, it also becomes essential for making food more available in areas where farming would otherwise be difficult. The ability to provide desalinated water to hospitals, manufacturing plants, resorts, and a myriad of other applications, makes this process key as water purification becomes tantamount to survival. Because the trend points to a continued decrease of potable water supplies in the future, the ability to desalinate seawater is one of the great advantages in helping to maintain a viable natural balance throughout the world.
In a 1988 report, the Congressional Office of Technology Assessment made the suggestion that desalinated water could be used to treat contaminated groundwater from processes such as mine runoff, agricultural abuses, landfill, storage tank leakage, and the like. Here again, the advantages of water purification processes are obvious. Creating desalination plants worldwide will also create new jobs within populations as construction and operational needs increase.
Energy Used to Operate Desalination Plants
Desalination plants require powerful energy sources for operation. It takes an enormous amount of energy to separated salts and other wastes from sea or brackish water. Many plants are still using oil-burning methods to run their desalination processes. The Middle East, which has the financial resources and the oil reserves to invest in oil-based equipment, is relying on this more conventional modality, which is not the most viable in terms of environmental responsibility. In an estimate by Cyprian expert on water heating systems,Soteris Kalogirou, PhD, estimated that 10,000 tons of oil per year are needed to create 1,000 cubic meters per day of fresh water.
Using fossil fuel as an electrical source for desalination processes contributes to climate change by creating air pollution and other detrimental side effects. The high cost of fossil fuels is also prohibitive to many communities in need of pure water. The irony of burning oil to provide citizens with fresh water is too great for this paradigm to continue. Without the ability to maintain healthy carbon dioxide levels in the atmosphere, water desalination becomes less viable. According to an article in the Encyclopedia of Desalination and Water Resources, the estimate on the amount of energy necessary for desalination around the world is equivalent to the total energy requirement of Sweden.
A more environmentally sound method of providing energy for desalination is via thermal energy. This can be achieved through using flat plate collectors in order to harness solar power. Solar ponds and tube collectors can also be used to reach the required temperatures of 80 to 130C temperatures necessary for the desalination process. Using photovoltaic panels is another viable way to concentrate the temperature needed for the collectors used in thermodynamic cycles such as vapor compression or reverse osmosis.
Desalination processes are also costly, where creating drinkable seawater can be as expensive as $1,300 to $2,200 per acre-foot, (the volume of water that covers one acre to the depth of one foot). Costs vary according to the water's salinity, as well as what specific treatment is used for desalination. Where non-seawater resources are used, the cost is less: for example the Los Angeles metropolitan water district purifying process costs $27 to $195 per acre-foot due to its use of alternative water sources.
Desalination Waste and its Effect on the Environment
The general statistic on the amount of feed water discharged as waste ranges from 20-70% of the general feed flow, depending on how high the salt content is in the feed water and what type of desalination technology is used for purification. According to the California Coastal Commission's report in 1993, for every 100 gallons of seawater, 15 to 50 gallons of potable water is produced, with the rest consisting of brine and solid waste. This wastewater is usually funneled into underground wells or back into the sea. Because the waste, or brine, consists of hot, salty, chemical laden water it can easily harm living creatures. The responsibility of desalination plants is to provide adequate control of brine before it is injected back into the environment. This means diluting it, lowering its temperature, and making sure that it is placed far from fresh water as well as from natural habitats of local marine, fowl, and animal life. Improper dumping of brine can mean indelible harm to our oceans, their marine populations, and surrounding areas.
When the Tampa Bay Seawater Desalination Plant was constructed in April 2007 and touted as the largest seawater desalination plant in the U.S., it met with serious problems due to bad planning. As the plant dumped its waste in a less than responsible manner, problems ensued with pollution as well as the proliferation of various invasive species such as Asian Green Mussels, causing costly setbacks to the project.
Desalination Plants Around the World
Desalination plants are being constructed around the world as demand increases for reliable water sources. Because of our changing climate, diminishing rainfall, and growing populations, naturally sustainable water supplies are rapidly becoming fewer and smaller where they do exist.
According to an article in Reuters, there are now close to 12,500 desalination plants worldwide, with approximately 60% of this number located in the Middle East where they are a must for desert-based communities. Israel is home to one of the largest reverse osmosis plants in the world, which is the third of a planned group of five that will be completed over the next few years. Other countries using desalination methods include North Africa, India, Algeria, Australia, Southern Europe, China, Singapore, and the United States.
Mobile desalination units are also becoming more prevalent. During the Persian Gulf War, the U.S. Army was able to produce up to 3,000 gallons of potable water a day through the use of on-site systems that are able to test water and execute desalination quickly and efficiently.
Two Leading Edge Users of Desalination
Israel is fast becoming one of the leaders in desalination processing. With the Sorek Desalination Plant, capacity is designed for 150 million cubic meters per year by using reverse osmosis technology. This makes it one of the largest RO facilities in the world so far.
The design and development of a desalination plant in Tenes, Algeria in conjunction with the San Francisco basedEnergy Recovery, Inc. allows for 1.6 million cubic meters of water to be produced per day where it is then distributed throughout the country. Algeria is fast becoming a global leader through its liaison with Energy Recovery, Inc, where it is employing PX devices to help reduce its CO2 emissions created by desalination, while saving more than 750 megawatts of energy per year.
The Future of Desalination and the Control of Waste
As desalination technology advances, processes are becoming not only economically viable, but environmentally feasible. In reverse osmosis systems, membranes are being created with longer lasting filtration, making them more effective while helping to lower long-term plant operating costs. Renewable energy production processes are now at the forefront for providing desalination plants with power in order to ensure that modalities become environmentally responsible as desalination becomes the norm. Solar desalination technology, which is a replica of how nature produces rain, is one of the most viable methods, with wind energy and photovotaics fast becoming options.
Based in San Francisco, California, with offices in Madrid, Shanghai, the United Arab Emirates, and Florida, Energy Recovery, Inc. is responsible for introducing new technology in the form of thePX pressure device, which creaties greater efficiency and helps reduce the carbon footprint in the desalination process. The PX pressure device is a rotary positive displacement pump that, according to Energy Recovery, Inc. is an "aluminum oxide rotor, floating in an almost frictionless hydrodynamic bearing." Created for reverse osmosis processes, the device requires less energy use at lower recoveries, making desalination super efficient, more affordable, and sustainable. The freewheeling pump incorporated into the design is made from a ceramic material created from aluminum oxide that is three times stronger than steel and completely non-corrosive. As such, it is low maintenance and reliable. PX devices can also be adjusted to correspond with variations in operating conditions, such as changes in temperature, salinity, and performance, making them ideal for all working conditions. There are currently over 7,000 PX devices currently in use or under contract for use at desalination plants worldwide.
A fully transportable desalination unit, otherwise known as what is known the M3, or mini mobile modular system, is currently being employed as a "smart" water desalination and filtration system. According to an article in Water Online, researchers at UCLA's Henry Samueli School of Engineering and Applied Science have designed and created these all-in-one plants where every type of water source can be tested and evaluated on-site. The M3 is designed to measure water pH, temperature, salinity, and turbidity, among other variables. It is made with computer-operated valves that adjust automatically and can be configured to run with minimum energy consumption.
Because the M3 is fully mobile, it can be moved from site to site, providing all necessary information and in doing so, saving time and cutting costs. The M3 unit has already proved itself effective in a field study in the San Joaquin Valley where agricultural water was saturated with calcium sulfate salts. Here one reverse osmosis stage was used where 65% of the water fed into the system was easily converted into potable water. Hand in hand with an advanced accelerated chemical demineralization technology developed at UCLA, the M3 unit has the potential for recovering 95% water during the desalination process. Because it is compact enough to be placed on the back of a small truck or van, the M3 can easily be deployed to areas where fresh water is necessary during emergency situations. With a capacity of generating up to 6,000 gallons of drinking water per day from seawater, or 8 to 9,000 gallons of water per day from brackish groundwater, the M3 can supply enough water to sustain up to 12,000 people on a daily basis. It has proven itself by adapting to a myriad of variations in source water and is fully operational where most conventional reverse osmosis systems falter.
As researchers investigate how to preserve the environment while providing potable water to the world, innovations will keep coming. In a pilot program at the Tularosa Basin Natural Desalination Research Facility in Alamogordo, New Mexico, experts are studying more innovative alternatives for using renewable energy in order to reduce operational costs as well as the carbon footprint created by desalination plants.
