The Growing Use of Composite Materials in the Desalination Process

The vast majority of the Earth’s surface is covered by saltwater and people living on the remaining land need fresh water to sustain life. But, as our readers are well aware, more than 1 billion people lack reliable access to fresh water and that count is only expected to grow. Remarkably, almost 60 percent of the world’s population lives less than 60 km from a seacoast. Desalinated seawater may be poised to become one of the main alternative freshwater resources in those regions. Composite materials are being used widely to enable these desalination projects.
Desalting has actually been around for more than 2,000 years; historically, it has been used aboard ships and was especially important in 19th Century colonial expansion, which required fresh water for ships and colonies. In the 20th Century, the corrosive effects of seawater on desalination equipment spurred the use of plastics. When engineers demand material properties that plastics alone cannot meet, composite materials are used. In fact, composites have been used for more than 30 years in desalination plants around the world, primarily in piping and other components that come into direct contact with seawater.
Desalination plants around the world use miles and miles of corrosion-resistant fiberglass reinforced polymer (FRP) low-pressure piping as a distribution network, primarily over land, to carry seawater from the sea to the plant, to distribute the potable water that is produced, to carry the brine back to the ocean, and for internal plant treatment piping and energy recovery devices.
Older, smaller plants typically used high-density polyethylene (HDPE), but FRP is more cost-effective than HDPE in the larger-diameter pipes generally used in the biggest plants. FRP materials and processes can also be tailored to meet specific mechanical property requirements and have the additional advantages of corrosion and chemical resistance, flexibility and the capacity to withstand mild shock. FRP also is commonly used to construct storage tanks and piping used in desalination plants for sodium hypochlorite (NaOCl), often used in chlorination of desalination process water, and for sulfuric acid, which can be very difficult to store in metal but can be handled in FRP tanks and piping at ambient temperatures and concentrations below 50 percent.