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From Toilet to Tap

Filtered sewage water may be the key water source of the 21st century.

By Jennifer Barone
May 23, 2008 5:00 AMNov 12, 2019 6:37 AM


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In January, public officials and residents of Orange County, California, toasted the culmination of a water supply project more than a decade in the making. But at these festivities champagne took a backseat to the beverage of choice as celebrants lifted glasses of recycled sewage water.

More than a billion people worldwide lack clean drinking water. While demand for freshwater access continues to increase—after tripling in the last 50 years—global supplies are becoming scarcer. Major rivers vital to surrounding populations are in danger of drying out. Groundwater reserves face a similar fate. The situation threatens to grow worse in the future as extreme droughts occur more often, according to the Intergovernmental Panel on Climate Change.

In the United States more than 2.1 trillion gallons of water are flushed down toilets every year. What most people think of as sewage is a freshwater reserve that, with a few steps of treatment, could provide drinking water for millions. Recognizing this, Orange County’s water and sanitation districts have begun recycling sewage into drinking water at the world’s largest plant of its kind, the $487 million Groundwater Replenishment System. The treated water, which exceeds state and federal heath standards, is being used to recharge the underground aquifer that feeds the taps of more than 2.3 million residents of the region. Other municipalities in California, Texas, Florida, Singapore, and Australia are exploring similar projects.

“We are, in essence, creating a new source of water,” says civil engineer Michael Markus, general manager of the Orange County Water District. “Right now we have severe challenges here,” he says, “where our imports have been reduced by about a third, and we’re sitting on an eight-year drought on the Colorado River.”

The treatment system, which began operation in January, purifies wastewater that would otherwise be dumped into the Pacific, creating 70 million gallons a day of clean water. “It’s a way to utilize an available resource instead of discarding it into the ocean, where it’s instantly no longer of use as freshwater,” says environmental health scientist Kellogg Schwab, who directs the Center for Water and Health at Johns Hopkins University.

Recycling starts with sewage treatment by the Orange County Sanitation District, which removes solid waste and uses micro­organisms to break down organic materials. The water then heads to the recycling facility for purification. It passes at low pressure through an ultrafine filter that strains out particulate matter, bacteria, and the single-celled organisms known as protozoans (amoebas and their kin). Next comes reverse osmosis, in which the water is forced through a plastic membrane at high pressure to remove even tinier pollutants including viruses, salts, and pesticides. Treatment with hydrogen peroxide and ultraviolet light completes the process.

Half of the near-distilled-quality reclaimed water is injected into a saltwater barrier—an underground supply of freshwater that prevents brine from creeping inland from the sea and contaminating fresh reserves. The rest is pumped 13 miles north to a recharge basin in Anaheim, where it slowly percolates down into the ground to supplement the aquifer that provides drinking water to the community. Though all indications suggest that the water is safe the minute it emerges from filtration, direct recycling is not yet publicly accepted in the United States, according to the Environmental Protection Agency (EPA). A 2004 report from the agency found that people view recycled water that has passed through an aquifer or reservoir as being cleaner, though in some cases the recycled water is actually of higher quality than the natural sources it joins. Only one plant in the world, in Namibia, supplies recycled water directly to users without first mixing it with water from natural sources.

The biggest challenge in any water reuse program is not the technology. Rather, it is gaining public acceptance and overcoming what recycling experts have aptly named the “yuck factor.” In past years, proposals that met all technical requirements have been killed by opponents who were simply repulsed by the idea, despite abundant evidence that reclaimed water is safe and clean. For example, in 1999 citizens of San Diego rejected a recycling program for drinking water. While most agreed that such water would be fine for landscaping and irrigation, 63 percent opposed using it for drinking. Opponents said they did not trust the recycling process, had health concerns, or did not have enough information about recycled water. The option is under exploration once again in the face of continuing shortages.

To get the word out about the process and the high quality of the filtered water, the Orange County Groundwater Replenishment System’s developers made more than 2,000 community presentations. They also took the proposal and the results of water quality tests to local and state officials, members of the medical and public-health communities, environmental advocacy groups, and scientists, earning endorsements across a broad base. “They are to be commended for bringing a lot of people to the table to get involved in this,” Schwab says. Visitors were invited to tour the plant and sample filtered water. (Water district officials note that first-timers were often pleasantly surprised by the pure, clean taste.)

Robert Bastian, a senior environmental scientist with the EPA who has followed the project throughout its development, calls it “very well designed” and notes that “you’re getting even better tracking of the quality of the recharge water than you would if it were coming from more ‘natural’ sources. You know more about the water that’s recharging the area now because you have control of it all the way.” Environmental scientist Michael Aitken of the University of North Carolina at Chapel Hill School of Public Health predicts that recycling will become increasingly important as a supplement to water supplies around the country. Orange County’s treatment process is “the gold standard for how to do it right,” he says.

According to Orange County Water District officials, recycling trumps many other options for supplementing the local water supply. They estimate that reusing water consumes 50 percent less energy than importing it—that is, bringing it in from outside Southern California. Annual operating costs for the recycling facility are estimated at about $27 million, currently comparable to the cost of importing it, but import prices are predicted to rise because of growing populations throughout the Southwest. Moreover, unlike recycled water, imports are not always available during a drought. Desalinating seawater, another option that had been under consideration, would be considerably more expensive than recycling—from 50 percent to 400 percent more so. Schwab and Bastian hope that the Groundwater Replenishment System will serve as a model for other places struggling to meet their water supply needs, helping to boost prosperity and even save lives around the world.

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