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Wednesday, May 25, 2022

Thirsty City Explores Viability of Saltwater, Wastewater

Thirsty City Explores Viability of Saltwater, Wastewater

Squeeze: Using ‘reverse osmosis,’ workers at the West Basin Municipal Water District plant in El Segundo remove plankton, dirt and salt from seawater. Recycled or ‘graywater’ is used for watering some of the area’s golf courses.


Staff Reporter

In order to survive in a desert, Los Angeles has always needed to be creative in managing its water needs.

Most of its efforts have focused on finding and developing traditional sources of water in the state’s rivers, lakes and natural snowpack. But in recent years, more attention has been paid to alternative technologies to better use or re-use resources. Some technologies sound futuristic, such as desalination of seawater, but others are more manageable and built upon conservation principles.

Desalination has been the most obvious alternative considering L.A.’s coastal location. Up to now, its high cost had kept state and local officials from giving it serious thought, although new desalination processes have made it more feasible financially.

The Metropolitan Water District of Southern California is studying five proposals for seawater desalination plants, and a facility in El Segundo is already experimenting with the process.

New desalination process

The older desalination process involved boiling the water to a temperature high enough to eliminate harmful contaminants, but this became too expensive due to the high power costs needed for the process.

Newer plants are using a cheaper reverse osmosis process, which was developed at UCLA in the late 1960s as the main component of desalination.

Reverse osmosis, or “RO,” works best in conjunction with a filtration and disinfectant process. Working in three stages, the seawater is brought into the plant and first goes through filters. Thin, straw-like filaments remove matter like plankton, protozoa and dirt but leaves the salt, said Paul Shoenberger, chief of engineering and operations at the West Basin Municipal Water District, which operates the El Segundo plant.

Next, the water is forced through membranes with high water pressure, leaving the salt behind.

Based on the water pressure and the size of openings in the membranes, the degree of salinity can be controlled. “Going in, the ocean water has 35,000 parts per million of salinity, and after reverse osmosis, has 350 parts per million,” said Shoenberger. Typical drinking water has between 250 and 500 parts per million.

Lastly, the water is disinfected using chlorine or ultra violet light, and then can be consumed. A more immediate use is to inject it into the ground to protect ground water supplies from salt intrusion, said Tom West, an environmental engineer at water management consultant Camp Dresser & McKee.

Water recycling

A similar technology can be used in conjunction with wastewater treatment plants and is part of the more general concept of water recycling. Much of the water treated in this process is used for non-drinking purposes, such as industrial or agricultural uses. “It doesn’t make sense to bring water in from miles away and throw it away after only one use,” said Jerry Gewe, assistant general manager for water at the Los Angeles Department of Water and Power.

In some cases, the water is only given tertiary treatment, such as a filtration process to remove contaminants. Sometimes a biological process is applied, where water sits in ponds and natural bacteria naturally eliminate contaminants.

“Recycling works best when there is a close proximity between entities,” said Gewe. For example, the Los Angeles/Glendale water treatment plant gets its water from the L.A. River, which is used to water golf courses that are right across the street.

Twenty years ago, the cost of treating water was in the range of $4,000 per acre foot. Evolving technology has made the process easier and cheaper, and recent projects have cost $800-900 per acre-foot, as compared to water from a utility company that averages $550 per acre-foot, said West. An acre-foot is enough to meet the water needs of two families for a year.

While water technologies continue to evolve, conservation efforts throughout Los Angeles have also progressed. “We’re using the same amount of water we did 20 years ago even though the population has increased,” said Shoenberger.

Tiered rate structures have been in place since 1992, where a higher cost is charged for a customer who uses more water. “This works to discourage excess water use,” said Gewe.

Also in place are rebate programs where people are given $100-$150 to replace their washing machines and toilets with water saving ones.

The use of “graywater” in homes is also being promoted by water officials. Such household systems collect water from showers or sinks, which is then used for non-drinking purposes like watering lawns.

Conservation efforts are even targeting the types of lawns and gardens Angelenos grow. “The goal is to develop gardens that require less water but still give us the lifestyle we want,” Gewe said.

Will all that be enough?

Kevin Starr, the state librarian and professor in the School of Policy, Planning and Development at USC is skeptical. “Our state population in 2040 will be 60 million people, and the formula that is in place now is not going to work for that many people,” he said. “We’re going to have to grow in a more clustered and dense style, with more communal use of water and more use of graywater.”

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