Desalination: Unlocking Fresh Water
Desalination: Unlocking Fresh Water
Water is the most valuable resource on Earth for sustaining life. Humans require fresh water for many things including drinking and irrigation. According to the U.S. Geological Survey website, about 97% of all water on the planet is saline water (1). This means that the majority of water has too many total dissolved solids (TDS) to be usable. As the human population grows, demands for fresh water supplies increase. One technology being developed to meet this growing demand is desalination.
Desalination allows us to utilize seawater and brackish groundwater that was previously considered unsafe for use. Water is classified as fresh if it contains less than 1,000 milligrams per liter (mg/L) of TDS (2). The goal of desalination is to bring water into this safe range. There are many methods of desalination but the most common method is reverse osmosis (RO). Reverse osmosis is popular due to the relatively low cost compared to other methods (3).
RO desalination incorporates the use of membrane technology to remove TDS from seawater or brackish ground water to create useable fresh water. There are four major components to the RO desalination process (4). First, the water is pretreated to remove suspended solids and control scaling on the membrane. Secondly, a pump raises pressure in order to …show more content…
push the water through the membrane. Next, the membrane prevents the passage of TDS and minerals from the feed to the fresh water chamber. Finally, the water that has passed through the membrane is stabilized and treated to balance the pH level and make it suitable for drinking.
The San Antonio Water System (SAWS) states that every ten gallons of brackish groundwater processed at the H2Oaks Center in Bexar County produces nine gallons of fresh water (5). That leaves one gallon of salts and minerals that need to be disposed of. SAWS utilizes an injection well to dispose of this material 5,000 feet below the surface. This is safely below the brackish water zone which is accessed at about 1,600 feet.
The higher percentage of TDS in seawater makes it more expensive to process than brackish groundwater using current technology (6). In places like Texas the lower cost and high availability makes RO desalination of brackish groundwater much more attractive than seawater. The average cost to produce 1 acre-foot of fresh water from brackish groundwater is estimated between $357 and $782 (6). This is preferable to the estimated $800 to $1400 to produce the same amount from seawater.
The vast amount of easily accessible saline water makes desalination very attractive. However, according to the Scientific American, most environmental advocates view desalination as a last resort. “Sourcing fresh water from streams, rivers, lakes and underground aquifers and adhering to strict water conservation measures are much more viable for both economic and environmental reasons in most situations” (7).
Although cost and environmental impact are major concerns, the need for fresh water is too great a driving factor to dissuade us from the development of desalination.
As research in this area increases, the cost is being driven down. Alternative energy sources will reduce the need for use of fossil fuels, and will lower the cost and reduce waste as a result. Some desalination plants use energy reclamation devices such as turbines in order to further lower the cost of production. There is also the possibility that valuable minerals can be processed from the resulting waste water and sold for consumer and industrial
applications.
Life on Earth depends on water. The progress of human civilization can be tracked across the planet in direct relation to supplies of this most valuable resource. As we reach the limit of our fresh water supply we also reach the limit of our progress. Research and technology will allow us to surpass current challenges. With 97% of the planet’s water locked up in oceans and brackish groundwater, desalination may be the key to unlocking our future.
Water is the most valuable resource on Earth for sustaining life. Humans require fresh water for many things including drinking and irrigation. According to the U.S. Geological Survey website, about 97% of all water on the planet is saline water (1). This means that the majority of water has too many total dissolved solids (TDS) to be usable. As the human population grows, demands for fresh water supplies increase. One technology being developed to meet this growing demand is desalination.
Desalination allows us to utilize seawater and brackish groundwater that was previously considered unsafe for use. Water is classified as fresh if it contains less than 1,000 milligrams per liter (mg/L) of TDS (2). The goal of desalination is to bring water into this safe range. There are many methods of desalination but the most common method is reverse osmosis (RO). Reverse osmosis is popular due to the relatively low cost compared to other methods (3).
RO desalination incorporates the use of membrane technology to remove TDS from seawater or brackish ground water to create useable fresh water. There are four major components to the RO desalination process (4). First, the water is pretreated to remove suspended solids and control scaling on the membrane. Secondly, a pump raises pressure in order to …show more content…
push the water through the membrane. Next, the membrane prevents the passage of TDS and minerals from the feed to the fresh water chamber. Finally, the water that has passed through the membrane is stabilized and treated to balance the pH level and make it suitable for drinking.
The San Antonio Water System (SAWS) states that every ten gallons of brackish groundwater processed at the H2Oaks Center in Bexar County produces nine gallons of fresh water (5). That leaves one gallon of salts and minerals that need to be disposed of. SAWS utilizes an injection well to dispose of this material 5,000 feet below the surface. This is safely below the brackish water zone which is accessed at about 1,600 feet.
The higher percentage of TDS in seawater makes it more expensive to process than brackish groundwater using current technology (6). In places like Texas the lower cost and high availability makes RO desalination of brackish groundwater much more attractive than seawater. The average cost to produce 1 acre-foot of fresh water from brackish groundwater is estimated between $357 and $782 (6). This is preferable to the estimated $800 to $1400 to produce the same amount from seawater.
The vast amount of easily accessible saline water makes desalination very attractive. However, according to the Scientific American, most environmental advocates view desalination as a last resort. “Sourcing fresh water from streams, rivers, lakes and underground aquifers and adhering to strict water conservation measures are much more viable for both economic and environmental reasons in most situations” (7).
Although cost and environmental impact are major concerns, the need for fresh water is too great a driving factor to dissuade us from the development of desalination.
As research in this area increases, the cost is being driven down. Alternative energy sources will reduce the need for use of fossil fuels, and will lower the cost and reduce waste as a result. Some desalination plants use energy reclamation devices such as turbines in order to further lower the cost of production. There is also the possibility that valuable minerals can be processed from the resulting waste water and sold for consumer and industrial
applications.
Life on Earth depends on water. The progress of human civilization can be tracked across the planet in direct relation to supplies of this most valuable resource. As we reach the limit of our fresh water supply we also reach the limit of our progress. Research and technology will allow us to surpass current challenges. With 97% of the planet’s water locked up in oceans and brackish groundwater, desalination may be the key to unlocking our future.