Desal on the Rise

Most of the water we use comes from rivers, lakes, and aquifers, but as extraction reaches historic maximum levels, available supply diminishes to minimum levels. The dwindling water supply has tripled water rates and increased water rationing along the California coastline and in other parts of the world.

“We must develop a management plan,” insists Lisa Henthorne, chief technology officer for Water Standard and International Desalination Association (IDA) director.

To do so requires a matrix consisting of demand scenarios in all seasons, supply options, environmental impact, and cost. “We encourage conservation,” says Henthorne. “Water conservation is critical, but if we can’t meet demand, we have to turn to desalination and reuse.”

Desalination: The Case for…and Against
Desalination can be more expensive than reuse, but Henthorne points out that neither option is widely accepted in the US—although some communities rely 100% on desalination for water. She estimates that there are roughly 15,000 desalination plants worldwide, the largest of which produces 900,000 cubic meters per day (CMD). The total capacity of all the desalination plants in the world is 59.9 million CMD, up from 53.3 million CMD at the end of 2008. Despite the increasing reliance on desalination and the growing number of plants worldwide, there are still only a few in the US. “We haven’t crossed that bridge to a big extent yet,” she says. But we need to.

In reality, we already have. Despite the American psychological block against reuse, we are reusing water. As Jorge Aguinaldo, vice president of business development for Doosan Hydro Technology, the US-based subsidiary of Doosan Heavy Industries & Construction, points out, there is a lot of water recycling already taking place. For example, he says, “Every city along the Mississippi River takes water from and discharges back into it.”

In Singapore, they treat wastewater and put it in the lake where they get their drinking water, Aguinaldo relates. Known as indirect potable reuse, there are few restrictions on the use of highly treated reclaimed water if it has been blended with a larger body of water first, such as a reservoir or aquifer.

“It’s the same concept in Australia, and in California, they treat wastewater and put it into the aquifer, where they pump drinking water,” he says. “It’s a form of indirect water recycling.”

And yet, he acknowledges, there’s a prevalent fear of “toilet to tap” in this country. What is needed is education on water use and recycling, says Aguinaldo, who belongs to the American Water Works Association’s committee on water use and desalination.

Water and Sand
When supplies are low, the only answer is to restrict use. “Water use has been down 40% because of allocation,” speculates G. G. Pique, president and chief executive officer of Energy Recovery Inc. (ERI). Conversely, prices have been up.

He compares water rates: Where many parts of the US charge one dollar per cubic meter and the cost is about three dollars in Norway, it’s seven dollars in Monterey, CA. “What’s our alternative?” he asks. “We pay more for this water, or we have no water.”

To ease some of the water restrictions and the financial pain in Sand City, CA, ERI has been working on a brackish water desalination facility capable of producing up to 300,000 gallons of potable water a day. “The water is very brackish,” emphasizes Pique. “It’s too salty for watering or consumption.”

ERI is a global company with an 80% share of the market, Pique boasts, adding that they have set precedents in environmental issues. The Sand City project is the first full-scale municipal desalination plant in California to receive the California Department of Public Health approval under the new drinking water regulations.

The $7 million plant addressed several typical environmental concerns: impingement—if water from the ocean is taken in too quickly, it can drown the marine life; inframement—if the screen is too big, it can catch marine life; and carbon footprint—it takes energy to desalinate.

Many existing methods of desalinating seawater consume significant amounts of energy, making desalination unaffordable for some areas. New innovative technology designed and developed by ERI reduces the energy required for seawater desalination as much as 80% in typical applications. ERI’s Pressure Exchanger recycles much of the energy used in seawater desalination by continually reclaiming the otherwise lost pressure energy from the reject or brine water with up to 98% efficiency. This improves the energy efficiency of seawater reverse osmosis (RO) by up to 60%.

Because the water is brackish and requires less processing, Pique says they were able to cut 90% of the energy requirement for this application. In addition, in Sand City, they’re mitigating issues of impingement and inframement by incorporating shallow beach wells to catch seawater and rain water, which further lowers the energy requirement to desalinate from 800 psi to 400 psi, and reduces the risk of endangering sea life. For that reason, he says, ecologists like this plant, but it also has a practical side. “If you catch water from an open pipe, plankton and fish foul the membrane. This way is more sustainable. It requires [fewer] chemicals to clean and you get cleaner water.”

With valuable coastal real estate at stake, the beachwells can be vertical or slanted to save space. Thanks to 15–20 miles of permeable sand dunes, Pique says they can “capture a lot of water with not a lot of wells.” They are virtually invisible: drilled and covered up, and connected to the plant across Highway 101.

The device itself is simple—and small, Pique notes, estimating its size as approximately 20 feet by 30 feet. It is a free-wheeling pump constructed from a unique ceramic material made from aluminum oxide, which is sintered at high temperatures to make it three times tougher than steel and non-corrosive. Pressure-driven (by water), it has no shaft or motor and only one moving part. Through the direct transfer of energy, it achieves a 98% efficiency rate, saving approximately 900 MWh of energy and reducing carbon dioxide (CO₂) emissions by more than 4.6 million tons per year. “It saves the equivalent [in energy] of a nuclear plant.”

Every percent of improvement in efficiency means millions of dollars in energy savings over the life of the plant. Able to process 1 million gallons per day (gpd), it will benefit a community that has dealt with water rationing and allocations for 15–20 years.

Waste Not, Want Not
Faced with high costs and usage restrictions, Pique insists that recycling is the way of the future. “We need to recycle,” he says. “We need to build plants now because we need water.”

Growing populations, more stringent regulations, dwindling traditional water supplies, and aging infrastructure are putting financial demands on governments and municipalities faced with meeting daily needs in their communities. As they struggle to provide quality water in the required quantities, they are turning to new techniques and options once shunned in the US.

An alternative—particularly for inland communities far from sources of seawater—is to reuse wastewater. “We must consider municipal and industrial wastewater as a resource,” insists Henthorne. Most wastewater can be effectively purified for reuse, often more economically than processing seawater. Faced with the scarcity of quality water sources, she considers the reuse and recycling of wastewater a viable alternative.

Desalination is not only for seawater, declares Aguinaldo. It’s also for wastewater. Around 5% of the desalination market treats pure water largely for industrial applications, and 5.1% of global desalination capacity is used to treat wastewater streams, typically for water reuse.

“We treat sewage any way and discharge it,” continues Aguinaldo. “If we can recover it and pass it through the process, we can use it for non-potable purposes such as irrigation and industrial use. We need water to have sewage.”

He points out that because the level of salinity is not as high as in seawater, the required operating pressure is lower, thereby reducing the cost. “The only problem is you need a separate distribution system,” he says.

Despite Americans’ aversion to the idea, Henthorne says wastewater can be cleaned to standards exceeding drinking water using a lot of the same technology that’s used for desalination, although each method requires a different operating pressure. That, however, can be to the benefit of reused water. “Seawater is very corrosive,” she says. You need metallic material sophisticated to withstand high pressure and corrosion, which adds to the cost. Plus, higher pressure means higher operating costs.”

Even rain water is not clean, Pique states. But when filtered through a RO membrane, treated with ultraviolet (UV) light and chlorine, water from any source can become “purer than mountain spring water.” While UV treatment is mandatory, he considers membrane barrier technology critical for recycling in particular because there are “a lot of things, such as parasites, chlorine doesn’t kill.”

High-Pressure Operation
Doosan Hydro Technology’s 85 water and wastewater treatment engineers are busily engaged in full-time research on several technologies, some of which Aguinaldo expects will be commercialized in 1–2 years. But it’s a long, drawn-out process. “The US developed the technology years ago, but it takes time to implement a project,” he explains. “Singapore implements in two years, but here, it’s around 10 years, because there are so many environmental issues and political opposition. We do extensive pilot testing.”

One of the challenges in using the membrane is operating pressure, he says. “You need pressure to operate the process, and operating pressure is high.”

Over the last 20 years, there has been considerable improvement. Necessary operating pressure used to be 1,000 psi, but the membrane reduced it to 800. Aguinaldo credits, in part, new materials like the nano tubes that reduce pressure and save energy.

Another consideration is how to recover waste energy. Saline wash water has high pressure. Energy consumption can be reduced if it’s recovered. One way to improve efficiency and reduce energy usage is with pre-treatment of the membrane desalination, Aguinaldo says. If the water feeding into the membrane has been treated, the result yielded will be of better quality—and will be achieved with lower operating pressure. “It requires less maintenance and is more efficient.”

There’s new technology for pre-treatment, he continues. An additional membrane is used, providing ultra microfiltration. The water passes through the plastic membrane prior to the osmosis membrane. “There’s a cost, but what choice is there?” acknowledges Aguinaldo.

Minera Esperanza Seawater Desalination Project
There is no choice in Chile. The Minera Esperanza copper and gold mine in Antofagasta, Chile, needs potable and process water, but there are no fresh water sources in the area. “It’s a desert in the mountains,” concludes Karim Nesicolaci, commercial manager with Severn Trent Services, which has been awarded the contract to provide a seawater desalination plant. “It’s an arid area in the middle of nowhere,” says Nesicolaci. “The closest city is 800 miles away.”

Chile is the number one source of copper in the world, and Nesicolaci says mining is a common application for desalting plants, where potable-quality water is used in a wash tank. This project has the additional challenge of being at an elevation of 8,000 feet. From the Pacific Ocean, 400 kilometers of 36-inch-diameter pipe will deliver seawater to the ultrafiltration (UF) and RO system, and other process lines for other uses. Nesicolaci says it’s “intense work.”

Once at the mine site, 5% of the seawater will be processed to obtain the product water. Construction of the 634,000-gpd (2,400-cubic meters per day) plant—owned by Antofagasta PLC of London and Marubeni Corporation of Tokyo—is currently in execution, Nesicolaci indicates. He expects this fast-track project to be up-and-running in July or August, barring any unforeseen obstacles. As of May, 50% of the components were in shipping containers, while some were still being assembled. The equipment will be installed and commissioned by Proequipos Ltda of Santiago, Chile.

The real innovation on the project is the membrane. Two Severn Trent Services UAT 705,000-gpd (2,671 CMD) UF trains using Dow UF membranes and two Severn Trent Services UAT 634,000-gpd (2,400 CMD) RO trains using Dow FilmTec 16-inch membranes will be installed at the plant. Nesicolaci explains that the two modules are capable of processing 317,000 gpd (1,200 CMD times two). The UF pretreatment system will not require a coagulant and will operate at 90% recovery, while the single-pass RO system will operate at 45% recovery, producing water quality below 400-parts-per-million total dissolved solids.

Although it’s not a pilot, it is one of the first projects to incorporate 16-inch membranes; industry standard is 8-inch. “This is a new innovation,” proclaims Nesicolaci. “There are very few in the market.”

It’s so new, he says, that Dow Chemical is sending people to see its performance for startup runs. He explains that a group of manufacturers “got together and agreed on the new size” because of the advantages, including: fewer membranes needed, leading to fewer pipe connections, shorter pipe runs, and a smaller building to house the desalting system. The larger membranes are wider in diameter, leaving a smaller environmental footprint. “With eight-inch membranes, we’d use 70, but with the larger ones, we only use 15,” he says. They are identical in performance, but “less bulky,” he adds. And the “cost is a wash.”

Confirming that the large membranes are “the most efficient application for the project,” he notes that they are more efficient than evaporative technology, and that the “project would be bigger if we used steam, capital investment higher.”

Water management is all about efficiency. “We need to think about how to use water more efficiently,” emphasizes Henthorne. “We don’t appreciate the value of water.” To meet our future water supply needs in an affordable way, IDA is participating in social education to promote the importance of conservation and endorse the use of desalination and reuse process.